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# Communication Systems/Time-Division Multiplexing Consider a situation where there are multiple signals which would all like to use the same wire (or medium). For instance, a telephone company wants multiple signals on the same wire at the same time. It certainly would save a great deal of space and money by doing this, not to mention time by not having to install new wires. How would they be able to do this? One simple answer is known as **Time-Division Multiplexing**. ## Time Division Multiplexing **Time-Division Multiplexing** (TDM) is a convenient method for combining various digital signals onto a single transmission media such as wires, fiber optics or even radio. These signals may be interleaved at the bit, byte, or some other level. The resulting pattern may be transmitted directly, as in digital carrier systems, or passed through a modem to allow the data to pass over an analog network. Digital data is generally organized into frames for transmission and individual users assigned a time slot, during which frames may be sent. If a user requires a higher data rate than that provided by a single channel, multiple time slots can be assigned. Digital transmission schemes in North America and Europe have developed along two slightly different paths, leading to considerable incompatibility between the networks found on the two continents. BRA (basic rate access) is a single digitized voice channel, the basic unit of digital multiplexing. : :  ```{=html} <!-- --> ``` : :  ### North American TDM The various transmission rates are not integral numbers of the basic rate. This is because additional framing and synchronization bits are required at every multiplexing level. : :  In North America, the basic digital channel format is known as DS-0. These are grouped into frames of 24 channels each. A concatenation of 24 channels and a start bit is called a frame. Groups of 12 frames are called multiframes or superframes. These vary the start bit to aid in synchronizing the link and add signaling bits to pass control messages. : :  #### S Bit Synchronization The S bit is used to identify the start of a DS-1 frame. There are 8 thousand S bits per second. They have an encoded pattern, to aid in locating channel position within the frame. : :  This forms a regular pattern of 1 0 1 0 1 0 for the odd frames and 0 0 1 1 1 0 for the even frames. Additional synchronization information is encoded in the DS-1 frame when it is used for digital data applications, so lock is more readily acquired and maintained. For data customers, channel 24 is reserved as a special sync byte, and bit 8 of the other channels is used to indicate if the remaining 7 bits are user data or system control information. Under such conditions, the customer has an effective channel capacity of 56 Kbps. To meet the needs of low speed customers, an additional bit is robbed to support sub-rate multiplexer synchronization, leaving 6 x 8 Kbps = 48 Kbps available. Each DS-0 can be utilized as: : : • 5 x 9.6 Kbps channels or : • 10 x 4.8 Kbps channels or : • 20 x 2.48 Kbps channels. In the DS-2 format, 4 DS-1 links are interleaved, 12 bits at a time. An additional 136 Kbps is added for framing and control functions resulting in a total bit rate of 6.312 Mbps. #### Signaling Signaling provides control and routing information. Two bits, called the A and B bits, are taken from each channel in frames 6 and 12 in the multiframe. The A bit is the least significant bit in each channel in frame 6, and the B bit is the least significant bit in each channel in frame 12. This provides a signaling rate of 666 2/3 bps per channel. The quality of voice transmission is not noticeably affected when 2% of the signal is robbed for signaling. For data, it may be a different story. If the data is encoded in an analog format such as FSK or PSK, then robbing bits is of no consequence, but if the data is already in digital form, then robbing bits results in unacceptable error rates. It is for this reason that in North America, a 64 Kbps clear channel cannot readily be switched through the PSTN. This means that data customers are limited to 56 Kbps clear channels. This simple condition has a profound effect on the development of new services such as ISDN. In most facilities, the A and B bits represent the status of the telephone hook switch, and correspond to the M lead on the E&M interface of the calling party. #### ESF CCITT has modified the North American digital hierarchy for the deployment of ISDN, by means of recommendation G.704. ESF consists of 24 DS-0 channels in a frame, but groups them into a 24-frame multiframe instead of the usual 12-frame multiframe. The S bit is renamed the F bit, but only 1/4 of them are used for synchronization. This is possible because of improvements in frame search techniques and allows more signaling states to be defined. Bit robbing is still used for signaling over an ESF link, but with the advent of ISDN, it will not be permitted. Instead, channel 24 is used to support a D channel. : :  #### Typical T1 CPE Application The large telecom carriers are not the only ones who deploy high-speed TDM facilities. In many cases, heavy users of voice or data services can reduce their transmission costs by concentrating their numerous low speed lines on to a high speed facility. There are many types of T1 multiplexers available today. Some are relatively simple devices, while others allow for channel concatenation, thus supporting a wide range of data rates. The ability to support multiple DS-0s allows for easy facilitation of such protocols as the video teleconferencing standard, Px64. : :  #### Multiplexers Multiplexing units are often designated by the generic term M~*ab*~ where*a* is input DS level and *b* is the output DS level. Thus, an M13 multiplexer combines 28 DS--1s into a single DS--3 and an M23 multiplexer combines 7 DS--2s into a single DS--3. : :  #### ZBTSI ZBTSI (zero byte time slot interchange) is used on DS--4 links. Four DS-1 frames are loaded into a register, and renumbered 1--96. If there are any empty slots \[all zeros\], the first framing bit is inverted and all blank slots are relocated to the front of the frame. Channel 1 is then loaded with a 7-bit number corresponding to the original position of the first empty slot. Bit 8 used to indicate whether the following channel contains user information or another address for an empty slot. If there is a second vacancy, bit 8 in the previous channel is set, and the empty slot address is placed in channel 2. This process continues until all empty positions are filled. The decoding process at the receiver is done in reverse. Borrowing 1 in 4 framing bits for this system is not enough to cause loss of synchronization and provides a 64 Kbps clear channel to the end-user. ### European TDM Carriers European systems were developed along slightly different principles. The 64 Kbps channel is still the basic unit, but signaling is not included in each channel. Instead, common channel signaling is used. In a level 1 carrier, channels 0 and 16 are reserved for signaling and control. This subtle difference means that European systems did not experience the toll fraud and 56 k bottlenecks common to North American systems, and they experience a much larger penetration of ISDN services. : :  ```{=html} <!-- --> ``` : :  ## Zero Substitutions In order to prevent transmission systems from loosing lock on the data stream, it is necessary to avoid long strings of zeros. One of the most effective ways of doing this is to replace the zeros with a predetermined code. This substitution must be done in such a way that the receiver can identify it and strip it off before passing the data stream to the client. AMI provides a simple means of detecting substitutions. In the normal course of events, alternate marks are inverted. Therefor, deliberately inducing a bipolarvariation at the transmitter can alert the receiver of a substitution. However, a single violation is indistinguishable from a transmission error. Consequently, some additional condition must also occur. There are two common methods to create a second condition: : · Create a second bipolar violation in the opposite direction, within a specified time. This has the effect of keeping the average signal level at zero. : · Count the number of marks from the last substitution to predict the next type of violation ### B6ZS B6ZS (binary six zero substitution) is used on T2 AMI transmission links. Synchronization can be maintained by replacing strings of zeros with bipolar violations. Since alternate marks have alternate polarity, two consecutive pulses of the same polarity constitute a violation. Therefore, violations can be substituted for strings of zeros, and the receiver can determine where substitutions were made. Since the last mark may have been either positive (+) or negative (-), there are two types of substitutions: : :  These substitutions force two consecutive violations. A single bit error does not create this condition. : :  ### B8ZS This scheme uses the same substitution as B6ZS. : :  ### B3ZS B3ZS is more involved than B6ZS, and is used on DS--3 carrier systems. The substitution is not only dependent on the polarity of the last mark, but also on the number of marks since the last substitution. : :  ```{=html} <!-- --> ``` : :  ### HDB3 HDB3 (high density binary 3) introduces bipolar violations when four consecutive zeros occur. It can therefore also be called B4ZS. The second and thirds zeros are left unchanged, but the fourth zero is given the same polarity as the last mark. The first zero may be modified to a one to make sure that successive violations are of alternate polarity. : :  HDB3 is used in Europe. Violation, or V pulses are injected after three consecutive zeros. The fourth zero is given the same polarity as the last mark. In the event of long strings of zeros occurring, a succession of single polarity pulses would occur, and a dc offset would build-up. To prevent this, the first zero in a group of 4, may be modified to a 1. This B or balancing pulse assures that successive violations are of alternate polarity. : :  ### Block Code Substitution These schemes operate on bytes rather than a bit at a time. Some transmit the signal as binary levels, but most use multi-level pulses. Some authors categorize these as line codes. A binary block code has the designation *n*B*m*B, where *n* input bits are encoded into *m* output bits. The most common of these is the 3B4B code. : :  In Europe 4B3T, which encodes 4 binary bits into 3 ternary levels, has been selected as the BRA for ISDN. In North America, 2B1Q which encodes 2 binary bits into 1 quaternary level has been selected for BRA. : :  Some block codes do not generate multilevel pulses. For example, 24B1P or 24B25B simply adds a P or parity bit to a 24 bit block. ## Benefits of TDM TDM is all about cost: fewer wires and simpler receivers are used to transmit data from multiple sources to multiple destinations. TDM also uses less bandwidth than Frequency-Division Multiplexing (FDM) signals, unless the bitrate is increased, which will subsequently increase the necessary bandwidth of the transmission. ## Synchronous TDM Synchronous TDM is a system where the transmitter and the receiver both know exactly which signal is being sent. Consider the following diagram: `Signal A ---> |---| |A|B|C|A|B|C|   |------| ---> Signal A`\ `Signal B ---> |TDM| --------------> |De-TDM| ---> Signal B`\ `Signal C ---> |---|                 |------| ---> Signal C` In this system, starting at time-slice 0, every third time-slice is reserved for Signal A; starting at time-slice 1, every third time-slice is reserved for Signal B; and starting at time-slice 2, every third time-slice is reserved for Signal C. In this situation, the receiver (De-TDM) needs only to switch after the signal on each time-slice is received. ------------------------------------------------------------------------ The data flow of each input connection is divided into units where each input occupies one input time slot. Each input connection has a time slot alloted in the output irrespective of the fact whether it is sending data or not. `      A -----|A3|A2|A1|---> |---| .............|C3|B3|A3|C2|B2|A2|C1|B1|A1|   |------| --->  A`\ `             |  |  |  |                        |        |        |`\ `      B -----|B3|B2|B1|---> |MUX| -------------|--------|--------|----------> |De-MUX| --->  B`\ `             |  |  |  |                        |        |        |`\ `      C -----|C3|C2|C1|---> |---|              |        |        |            |------| --->  C`\ `                   <-->                                 <-------->`\ `                  Bit Interval                       Frame (x seconds)` Sync TDM is inefficient when one or more input lines have no data to send. Thus, it is used with lines with high data traffic. ------------------------------------------------------------------------ Sampling rate is same for all signals. Maximum sampling rate = twice the maximum frequency all the signals. ## Statistical TDM Synchronous TDM is beneficial because the receiver and transmitter can both cost very little. However, consider the most well-known network: the Internet. In the Internet, a given computer might have a data rate of 1kbps when hardly anything is happening, but might have a data rate of 100kbps when downloading a large file from a fast server. How are the time-slices divided in this instance? If every time slice is made big enough to hold 100Kbps, when the computer isn\'t downloading any data, all of that time and electricity will be wasted. If every time-slice is only big enough for the minimum case, the time required to download bigger files will be greatly increased. The solution to this problem is called **Statistical TDM**, and is the solution that the Internet currently uses. In Statistical TDM, each data item, known as the payload (we used time-slices to describe these earlier), is appended with a certain amount of information about who sent it, and who is supposed to receive it (the header). The combination of a payload and a header is called a **packet**. Packets are like envelopes in the traditional \"snail mail\" system: Each packet contains a destination address and a return address as well as some enclosed data. Because of this, we know where each packet was sent from and where it is going. The downside to statistical TDM is that the sender needs to be smart enough to write a header, and the receiver needs to be smart enough to read the header and (if the packet is to be forwarded,) send the packet toward its destination. ### Link Utilization Statistical multiplexing attempts to maximize the use of a communication path. The study of this is often called *queuing theory*. A queue is simply a line of customers or packets waiting to be served. Under most circumstances, the arrival rate is unpredictable and therefor follows a random or Poisson distribution pattern, whereas the service time is constant. The utilization or fraction of time actually used by a packet multiplexing system to process packets is given by: : :  The queue length or average number of items waiting to be served is given by: $$q = \frac{{\rho ^2 }}{{2\left( {1 - \rho } \right)}} + \rho$$ : :  ```{=html} <!-- --> ``` : : **Example** ```{=html} <!-- --> ``` : : A T1 link has been divided into a number of 9.6 Kbps channels and has a combined user data rate of 1.152 Mbps. Access to this channel is offered to 100 customers, each requiring 9.6 Kbps data 20% of the time. If the user arrival time is strictly random find the T1 link utilization. ```{=html} <!-- --> ``` : : **Solution** ```{=html} <!-- --> ``` : : The utilization or fraction of time used by the system to process packets is given by: $$\rho = \frac{{\alpha NR}}{M} = \frac{{0.2 \times 100 \times 9.6 \times 10^3 }}{{1.152 \times 10^6 }} = 0.167$$ : : A 24 channel system dedicated to DATA, can place five 9.6 Kbps customers in each of 23 channels, for a total of 115 customers. In the above statistical link, 100 customers created an *average* utilization of 0.167 and were easily fitted, with room to spare if they transmit on the average 20% of the time. If however, the customer usage were not randomly distributed, then the above analysis would have to be modified. This example shows the potential for statistical multiplexing. If channels were assigned on a demand basis (only when the customer had something to send), a single T1 may be able to support hundreds of low volume users. A utilization above 0.8 is undesirable in a statistical system, since the slightest variation in customer requests for service would lead to buffer overflow. Service providers carefully monitor delay and utilization and assign customers to maximize utilization and minimize cost. ## Packets Packets will be discussed in greater detail once we start talking about digital networks (specifically the Internet). Packet headers not only contain address information, but may also include a number of different fields that will display information about the packet. Many headers contain error-checking information (checksum, Cyclic Redundancy Check) that enables the receiver to check if the packet has had any errors due to interference, such as electrical noise. ## Duty Cycles Duty cycle is defined as \" the time that is effectively used to send or receive the data, expressed as a percentage of total period of time.\" The more the duty cycle , the more effective transmission or reception. We can define the pulse width, τ, as being the time that a bit occupies from within its total alloted bit-time *T~b~*. If we have a duty cycle of *D*, we can define the pulse width as: $$\tau = DT_b$$ Where: $$0 < \tau \le T_b$$ The pulse width is equal to the bit time if we are using a 100% duty cycle.

# Communication Systems/Frequency-Division Multiplexing ## Introduction It turns out that many wires have a much higher bandwidth than is needed for the signals that they are currently carrying. Analog Telephone transmissions, for instance, require only 3 000 Hz of bandwidth to transmit human voice signals. Over short distances, however, twisted-pair telephone wire has an available bandwidth of nearly 100000 Hz! There are several terrestrial radio based communications systems deployed today. They include: - Cellular radio - Mobile radio - Digital microwave radio Mobile radio service was first introduced in the St. Louis in 1946. This system was essentially a radio dispatching system with an operator who was able to patch the caller to the PSTN via a switchboard. Later, an improved mobile telephone system, IMTS, allowed customers to dial their own calls without the need for an operator. This in turn developed into the cellular radio networks we see today. The long haul PSTNs and packet data networks use a wide variety of transmission media including - Terrestrial microwave - Satellite microwave - Fiber optics - Coaxial cable In this section, we will be concerned with terrestrial microwave systems. Originally, microwave links used FDM exclusively as the access technique, but recent developments are changing analog systems to digital where TDM is more appropriate. ### Fixed Access Assignment Three basic methods can be used to combine customers on to fixed channel radio links: - FDMA - (Frequency division multiple access) analog or digital - TDMA - (Time division multiple access) three conversation paths are time division multiplexed in 6.7 mSec time slots on a single carrier. - CDMA - (Code division multiple access) this uses spread spectrum techniques to increase the subscriber density. The transmitter hops through a pseudo-random sequence of frequencies. The receiver is given the sequence list and is able to follow the transmitter. As more customers are added to the system, the signal to noise will gradually degrade. This is in contrast to AMPS where customers are denied access once all of the frequencies are assigned code division multiple access \[digital only\] : :  ## What is FDM? **Frequency Division Multiplexing** (FDM) allows engineers to utilize the extra space in each wire to carry more than one signal. By frequency-shifting some signals by a certain amount, engineers can shift the spectrum of that signal up into the unused band on that wire. In this way, multiple signals can be carried on the same wire, without having to divy up time-slices as in Time-Division Multiplexing schemes.In analog transmission, signals are commonly multiplexed using frequency-division multiplexing (FDM), in which the carrier bandwidth is divided into subchannels of different frequency widths, each carrying a signal at the same time in parallel Traditional terrestrial microwave and satellite links employ FDM. Although FDM in telecommunications is being reduced, several systems will continue to use this technique, namely: broadcast & cable TV, and commercial & cellular radio. ### Analog Carrier Systems The standard telephony voice band \[300 -- 3400 Hz\] is heterodyned and stacked on high frequency carriers by single sideband amplitude modulation. This is the most bandwidth efficient scheme possible. : :  The analog voice channels are pre-grouped into threes and heterodyned on carriers at 12, 16, and 20 kHz. The resulting upper sidebands of four such pregroups are then heterodyned on carriers at 84, 96, 108, and 120 kHz to form a 12-channel group. Since the lower sideband is selected in the second mixing stage, the channel sequence is reversed and a frequency inversion occurs within each channel. : :  This process can continue until the available bandwidth on the coaxial cable or microwave link is exhausted. : :  In the North American system, there are: - 12 channels per group - 5 groups per supergroup - 10 super groups per mastergroup - 6 master groups per jumbogroup In the European CCITT system, there are: - 12 channels per group - 5 groups per supergroup - 5 super groups per mastergroup - 3 master groups per supermastergroup There are other FDM schemes including: - L600 - 600 voice channels 60--2788 kHz - U600 - 600 voice channels 564--3084 kHz - L3 - 1860 voice channels 312--8284 kHz, comprised of 3 mastergroups and a supergroup - L4 - 3600 voice channels, comprised of six U600s ## Benefits of FDM FDM allows engineers to transmit multiple data streams simultaneously over the same channel, at the expense of bandwidth. To that extent, FDM provides a trade-off: faster data for less bandwidth. Also, to demultiplex an FDM signal requires a series of bandpass filters to isolate each individual signal. Bandpass filters are relatively complicated and expensive, therefore the receivers in an FDM system are generally expensive. ## Examples of FDM As an example of an FDM system, Commercial broadcast radio (AM and FM radio) simultaneously transmits multiple signals or \"stations\" over the airwaves. These stations each get their own frequency band to use, and a radio can be tuned to receive each different station. Another good example is cable television, which simultaneously transmits every channel, and the TV \"tunes in\" to which channel it wants to watch. ## Orthogonal FDM Orthogonal Frequency Division Multiplexing (OFDM) is a more modern variant of FDM that uses orthogonal sub-carriers to transmit data that does not overlap in the frequency spectrum and is able to be separated out using frequency methods. OFDM has a similar data rate to traditional FDM systems, but has a higher resilience to disruptive channel conditions such as noise and channel fading.

# Communication Systems/What is Modulation? Modulation is a term that is going to be used very frequently in this book. So much in fact, that we could almost have renamed this book \"Principles of Modulation\", without having to delete too many chapters. So, the logical question arises: What exactly is modulation? ## Definition **Modulation** is a process of mixing a signal with a sinusoid to produce a new signal. This new signal, conceivably, will have certain benefits over an un-modulated signal. Mixing of low frequency signal with high frequency carrier signal is called modulation. $$f(t) = A \sin(\omega t + \phi)$$ we can see that this sinusoid has 3 parameters that can be altered, to affect the shape of the graph. The first term, A, is called the magnitude, or amplitude of the sinusoid. The next term, $\omega$ is known as the frequency, and the last term, $\phi$ is known as the phase angle. All 3 parameters can be altered to transmit data. The sinusoidal signal that is used in the modulation is known as the **carrier signal**, or simply \"the carrier\". The signal that is used in modulating the carrier signal(or sinusoidal signal) is known as the \"data signal\" or the \"message signal\". It is important to notice that a simple sinusoidal carrier contains no information of its own. In other words we can say that modulation is used because some data signals are not always suitable for direct transmission, but the modulated signal may be more suitable. ## Types of Modulation There are 3 basic types of modulation: Amplitude modulation, Frequency modulation, and Phase modulation. amplitude modulation : a type of modulation where the amplitude of the carrier signal is modulated (changed) in proportion to the message signal while the frequency and phase are kept constant. frequency modulation : a type of modulation where the frequency of the carrier signal is modulated (changed) in proportion to the message signal while the amplitude and phase are kept constant. phase modulation : a type of modulation where the phase of the carrier signal is varied accordance to the low frequency of the message signal is known as phase modulation. ## Why Use Modulation? Why use modulation at all? To answer this question, let\'s consider a channel that essentially acts like a bandpass filter: both the lowest frequency components and the highest frequency components are attenuated or unusable in some way, with transmission only being practical over some intermediate frequency range. If we can\'t send low-frequency signals, then we need to shift our signal up the frequency ladder. Modulation allows us to send a signal over a bandpass frequency range. If every signal gets its own frequency range, then we can transmit multiple signals *simultaneously* over a single channel, all using different frequency ranges. Another reason to modulate a signal is to allow the use of a smaller antenna. A baseband (low frequency) signal would need a huge antenna because in order to be efficient, the antenna needs to be about 1/10th the length of the wavelength. Modulation shifts the baseband signal up to a much higher frequency, which has much smaller wavelengths and allows the use of a much smaller antenna. ## Examples Think about your car radio. There are more than a dozen (or so) channels on the radio at any time, each with a given frequency: 100.1 MHz, 102.5 MHz etc\... Each channel gets a certain range (usually about 0.22 MHz), and the entire bayot gets transmitted over that range. Modulation makes it all possible, because it allows us to send voice and music (which are essential baseband signals) over a bandpass (or \"Broadband\") channel. ## Non-sinusoidal modulation A sine wave at one frequency can be separated from a sine wave at another frequency (or a cosine wave at the same frequency) because the two signals are \"orthogonal\". There are other sets of signals, such that every signal in the set is orthogonal to every other signal in the set. A simple orthogonal set is time multiplexed division (TDM) \-- only one transmitter is active at any one time. Other more complicated sets of orthogonal waveforms---Walsh codes and various pseudo-noise codes such as Gold codes and maximum length sequences---are also used in some communication systems. The process of combining these waveforms with data signals is sometimes called \"modulation\", because it is so very similar to the way modulation combines sine waves with data signals. ## Further reading - Data Coding Theory/Spectrum Spreading - Wikipedia:Walsh code - Wikipedia:Gold code - Wikipedia:pseudonoise code - Wikipedia:maximum length sequence

# Communication Systems/Analog vs. Digital There is lots of talk nowadays about buzzwords such as \"Analog\" and \"Digital\". Certainly, engineers who are interested in creating a new communication system should understand the difference. Which is better, analog or digital? What is the difference? What are the pros and cons of each? This chapter will look at the answers to some of these questions. ## What are They? What exactly is an analog signal, and what is a digital signal? Analog : Analog signals are continuous in both time and value. Analog signals are used in many systems, although the use of analog signals has declined with the advent of cheap digital signals. All natural signals are Analog in nature or analog signal is that signal which amplitude on Y axis change with time on X axis\... ```{=html} <!-- --> ``` Digital : Digital signals are discrete in time and value. Digital signals are signals that are represented by binary numbers, \"1\" or \"0\". The 1 and 0 values can correspond to different discrete voltage values, and any signal that *doesn\'t quite fit* into the scheme just gets rounded off. or digital signal is that signal which have certain or fixed value on Y axis change with time on X axis\... Digital signals are sampled, quantized & encoded version of continuous time signals which they represent. In addition, some techniques also make the signal undergo encryption to make the system more tolerant to the channel. ## What are the Pros and Cons? Each paradigm has its own benefits and problems Analog : Analog systems are less tolerant to noise, make good use of bandwidth, and are easy to manipulate mathematically. However, analog signals require hardware receivers and transmitters that are designed to perfectly fit the particular transmission.\ Digital : Digital signals are more tolerant to noise, but digital signals can be completely corrupted in the presence of excess noise. In digital signals, noise could cause a 1 to be interpreted as a 0 and vice versa, which makes the received data different than the original data. Imagine if the army transmitted a position coordinate to a missile digitally, and a single bit was received in error. This single bit error could cause a missile to miss its target by miles. Luckily, there are systems in place to prevent this sort of scenario, such as checksums and CRCs, which tell the receiver when a bit has been corrupted and ask the transmitter to resend the data. The primary benefit of digital signals is that they can be handled by simple, standardized receivers and transmitters, and the signal can be then dealt with in software (which is comparatively cheap to change). ```{=html} <!-- --> ``` Discrete Digital and Analogue: Discrete data has a fixed set of possible values.\ Digital data is a type of Discrete data where the fixed value can either be 1 or 0.\ Analogue data can take on any real value. ## Sampling and Reconstruction The process of converting from analog data to digital data is called \"sampling\". The process of recreating an analog signal from a digital one is called \"reconstruction\". This book will not talk about either of these subjects in much depth beyond this, although other books on the topic of EE might, such as A-level Physics (Advancing Physics)/Digitisation/Digitisation "wikilink"). ## Further reading - Electronics/Digital to Analog & Analog to Digital Converters

# Communication Systems/Communication Mediums Signals need a channel to follow, so that they can move from place to place. These **Communication Mediums**, or \"channels\" are things like wires and antennae that transmit the signal from one location to another. Some of the most common channels are listed below: ## Twisted Pair Wire **Twisted Pair** is a transmission medium that uses two conductors that are twisted together to form a pair. The concept for the twist of the conductors is to prevent interference. Ideally, each conductor of the pair basically receives the same amount of interference, positive and negative, effectively cancelling the effect of the interference. Typically, most inside cabling has four pairs with each pair having a different twist rate. The different twist rates help to further reduce the chance of crosstalk by making the pairs appear electrically different in reference to each other. If the pairs all had the same twist rate, they would be electrically identical in reference to each other causing crosstalk, which is also referred to as capacitive coupling. Twisted pair wire is commonly used in telephone and data cables with variations of categories and twist rates. Other variants of Twisted Pair are the **Shielded Twisted Pair** cables. The shielded types operate very similar to the non-shielded variety, except that Shielded Twisted Pair also has a layer of metal foil or mesh shielding around all the pairs or each individual pair to further shield the pairs from electromagnetic interference. Shielded twisted pair is typically deployed in situations where the cabling is subjected to higher than normal levels of interference. ## Coaxial Cable Another common type of wire is **Coaxial Cable**. Coaxial cable (or simply, \"coax\") is a type of cable with a single data line, surrounded by various layers of padding and shielding. The most common coax cable, common television cable, has a layer of wire mesh surrounding the padded core, that absorbs a large amount of EM interference, and helps to ensure a relatively clean signal is transmitted and received. Coax cable has a much higher bandwidth than a twisted pair, but coax is also significantly more expensive than an equal length of twisted pair wire. Coax cable frequently has an available bandwidth in excess of hundreds of megahertz (in comparison with the hundreds of kilohertz available on twisted pair wires). Originally, Coax cable was used as the backbone of the telephone network because a single coaxial cable could hold hundreds of simultaneous phone calls by a method known as \"Frequency Division Multiplexing\" (discussed in a later chapter). Recently however, Fiber Optic cables have replaced Coaxial Cable as the backbone of the telephone network because Fiber Optic channels can hold many more simultaneous phone conversations (thousands at a time), and are less susceptible to interference, crosstalk, and noise then Coaxial Cable. ## Fiber Optics **Fiber Optic** cables are thin strands of glass that carry pulses of light (frequently infrared light) across long distances. Fiber Optic channels are usually immune to common RF interference, and can transmit incredibly high amounts of data very quickly. There are 2 general types of fiber optic cable: single frequency cable, and multi-frequency cable. single frequency cable carries only a single frequency of laser light, and because of this there is no self-interference on the line. Single-frequency fiber optic cables can attain incredible bandwidths of many gigahertz. Multi-Frequency fiber optics cables allow a Frequency-Division Multiplexed series of signals to each inhabit a given frequency range. However, interference between the different signals can decrease the range over which reliable data can be transmitted. ## Wireless Transmission In **wireless transmission systems**, signals are propagated as Electro-Magnetic waves through free space. Wireless signals are transmitted by a transmitter, and received by a receiver. Wireless systems are inexpensive because no wires need to be installed to transmit the signal, but wireless transmissions are susceptible not only to EM interference, but also to physical interference. A large building in a city, for instance can interfere with cell-phone reception, and a large mountain could block AM radio transmissions. Also, WiFi internet users may have noticed that their wireless internet signals don\'t travel through walls very well. There are 2 types of antennas that are used in wireless communications, **isotropic**, and **directional**. ### Isotropic People should be familiar with isotropic antennas because they are everywhere: in your car, on your radio, etc\... Isotropic antennas are omni-directional in the sense that they transmit data out equally (or nearly equally) in all directions. These antennas are excellent for systems (such as FM radio transmission) that need to transmit data to multiple receivers in multiple directions. Also, Isotropic antennas are good for systems in which the direction of the receiver, relative to the transmitter is not known (such as cellular phone systems). ### Directional Directional antennas focus their transmission power in a single narrow direction range. Some examples of directional antennas are satellite dishes, and wave-guides. The downfall of the directional antennas is that they need to be pointed directly at the receiver all the time to maintain transmission power. This is useful when the receiver and the transmitter are not moving (such as in communicating with a geo-synchronous satellite).

# Communication Systems/Coherent Receivers ## Receiver Design It turns out that if we know what kind of signal to expect, we can better receive those signals. This should be intuitive, because it is hard to find something if we don\'t know what precisely we are looking for. How is a receiver supposed to know what is data and what is noise, if it doesnt know what data looks like? Coherent transmissions are transmissions where the receiver knows what type of data is being sent. Coherency implies a strict timing mechanism, because even a data signal may look like noise if you look at the wrong part of it. In contrast, noncoherent receivers don\'t know exactly what they are looking for, and therefore noncoherent communication systems need to be far more complex (both in terms of hardware and mathematical models) to operate properly. This section will talk about coherent receivers, first discussing the \"Simple Receiver\" case, and then going into theory about what the optimal case is. Once we know mathematically what an optimal receiver should be, we then discuss two actual implementations of the optimal receiver. It should be noted that the remainder of this book will discuss optimal receivers. After all, why would a communication\'s engineer use anything that is less than the best? ## The Simple Receiver A simple receiver is just that: simple. A general simple receiver will consist of a low-pass filter (to remove excess high-frequency noise), and then a sampler, that will select values at certain points in the wave, and interpolate those values to form a smooth output curve. In place of a sampler (for purely analog systems), a general envelope filter can also be used, especially in AM systems. In other systems, different tricks can be used to demodulate an input signal, and acquire the data. However simple receivers, while cheap, are not the best choice for a receiver. Occasionally they are employed because of their price, but where performance is an issue, a better alternative receiver should be used. ## The Optimal Receiver Engineers are able to mathematically predict the structure of the optimal receiver. Read that sentence again: Engineers are able to design, analyze, and build the best possible receiver, for any given signal. This is an important development for several reasons. First, it means that no more research should go into finding a better receiver. The best receiver has already been found, after all. Second, it means any communications system will not be hampered (much) by the receiver. ### Derivation here we will attempt to show how the coherent receiver is derived. ### Matched Receiver The matched receiver is the logical conclusion of the optimal receiver calculation. The matched receiver convolves the signal with itself, and then tests the output. Here is a diagram: `s(t)----->(Convolve with r(t))----->` This looks simple enough, except that convolution modules are often expensive. An alternative to this approach is to use a correlation receiver. ### Correlation Receiver The correlation receiver is similar to the matched receiver, instead with a simple switch: The multiplication happens first, and the integration happens second. Here is a general diagram: `           r(t)`\ `            |`\ `            v`\ `s(t) ----->(X)----->(Integrator)--->` In a digital system, the integrator would then be followed by a threshold detector, while in an analog receiver, it might be followed by another detector, like an envelope detector. ## Conclusion To do the best job of receiving a signal we need to know the form of the signal that we are sending. After all we can\'t design a receiver until after we\'ve decided how the signal will be sent. This method poses some problems in that the receiver must be able to line up the received signal with the given reference signal to work the magic: if the received signal and the reference signal are out of sync with each other, either as a function of an error in phase or an error in frequency, then the optimal receiver will not work. ## Further reading

# Communication Systems/Analog Modulation Introduction ## Analog Modulation Overview Let\'s take a look at a generalized sinewave: $$x\left( t \right) = A\sin \left( {\omega t + \theta } \right)$$ It consists of three components namely; amplitude, frequency and phase. Each of which can be decomposed to provide finer detail: $$x(t) = A s(t) \sin ( 2 \pi [f_c + kf_m(t)] t + \alpha \phi(t) )$$ ## Types of Analog Modulation We can see 3 parameters that can be changed in this sine wave to send information: - $A s(t)$. This term is called the \"Amplitude\", and changing it is called \"Amplitude Modulation\" (AM) - $kf_m(t)$ This term is called the \"Frequency Shift\", and changing it is called \"Frequency Modulation\" - $\alpha \phi (t)$. this term is called the \"Phase angle\", and changing it is called \"Phase Modulation\". - The terms frequency and phase modulation are often combined into a more general group called \"Angle Modulation\". ## The Breakdown Each term consists of a coefficient (called a \"scaling factor\"), and a function of time that corresponds to the information that we want to send. The scaling factor out front, A, is also used as the transmission power coefficient. When a radio station wants their signal to be stronger (regardless of whether it is AM, FM, or PM), they \"crank-up\" the power of A, and send more power out onto the airwaves. ## How we Will Cover the Material We are going to go into separate chapters for each different type of modulation. This book will attempt to discuss some of the mathematical models and techniques used with different modulation techniques. It will also discuss some practical information about how to construct a transmitter/receiver, and how to use each modulation technique effectively.

# Communication Systems/FM and PM Generalization ## Concept We can see from our initial overviews that FM and PM modulation schemes have a lot in common. Both of them are altering the angle of the carrier sinusoid according to some function. It turns out that we can go so far as to generalize the two together into a single modulation scheme known as **angle modulation**. Note that we will never abbreviate \"angle modulation\" with the letters \"AM\", because Amplitude modulation is completely different from angle modulation. ## Instantaneous Phase Let us now look at some things that FM and PM have of common: $$s_{FM} = A\cos (2 \pi [f_c + ks(t)]t + \phi)$$ $$s_{PM} = A\cos (2 \pi f_c t + \alpha s(t))$$ What we want to analyze is the *argument of the sinusoid*, and we will call it Psi. Let us show the Psi for the bare carrier, the FM case, and the PM case: $$\Psi_{carrier}(t) = 2 \pi f_c t + \phi$$ $$\Psi_{FM}(t) = 2 \pi[f_c + ks(t)] t + \phi$$ $$\Psi_{PM}(t) = 2 \pi f_c t + \alpha s(t)$$ $$s(t) = A\cos(\Psi(t))$$ This Psi value is called the *Instantaneous phase* of the sinusoid. ## Instantaneous Frequency Using the Instantaneous phase value, we can find the *Instantaneous frequency* of the wave with the following formula: $$f(t) = \frac{d\Psi(t)}{dt}$$ We can also express the instantaneous phase in terms of the instantaneous frequency: $$\Psi(t) = \int_{-\infty}^t f(\lambda)d\lambda$$ Where the Greek letter \"lambda\" is simply a dummy variable used for integration. Using these relationships, we can begin to study FM and PM signals further. ## Determining FM or PM If we are given the equation for the instantaneous phase of a particular angle modulated transmission, is it possible to determine if the transmission is using FM or PM? it turns out that it is possible to determine which is which, by following 2 simple rules: 1. In PM, instantaneous phase is a linear function. 2. In FM, instantaneous frequency minus carrier frequency is a linear function. For a refresher course on Linearity, there is a chapter on the subject in the Signals and Systems book worth re-reading. ## Bandwidth In a PM system, we know that the value $\alpha s(t)$ can never go outside the bounds of $(-\pi, \pi]$. Since sinusoidal functions oscillate between \[-1, 1\], we can use them as a general PM generating function. Now, we can combine FM and PM signals into a general equation, called *angle modulation*: $$v(t) = A \sin ( 2 \pi f_c t + \beta \sin (2 \pi f_m t))$$ If we want to analyze the spectral components of this equation, we will need to take the Fourier transform of this. But, we can\'t integrate a sinusoid of a sinusoid, much less find the transform of it. So, what do we do? It turns out (and the derivation will be omitted here, for now) that we can express this equation as an infinite sum, as such: $$v(t) = A \sum_{n = -\infty}^{\infty}J_n(\beta) \sin [2 \pi(nf_m + f_c)t]$$ But, what is the term $J_n(\beta)$? J is the *Bessel function*, which is a function that exists only as an open integral (it is impossible to write it in closed form). Fortunately for us, there are extensive tables tabulating Bessle function values. ## The Bessel Function The definition of the Bessel function is the following equation: $$J_n(\beta) = \frac{1}{2\pi} \int_{-\pi}^\pi e^{j[\beta sin\theta - n\theta]} d\theta$$ The bessel function is a function of 2 variables, N and $\beta$. Bessel Functions have the following properties: - If n is even: $$J_{-n}(\beta) = J_n(\beta)$$ - If n is odd: $$J_{-n}(\beta) = -J_n(\beta)$$ - $J_{n-1} + J_{n+1} = \frac{2n}{\beta}J_n(\beta)$. The bessel function is a relatively advanced mathematical tool, and we will not analyze it further in this book. ## Carson\'s Rule If we have our generalized function: $$v(t) = A\sin ( 2 \pi f_c t + \beta \sin (2 \pi f_m t))$$ We can find the bandwidth BW of the signal using the following formula: $$BW=2(\beta + 1)f_m = 2(\Delta f + f_m)$$ where $\Delta f$ is the maximum frequency deviation, of the transmitted signal, from the carrier frequency. It is important to note that Carson\'s rule is only an approximation (albeit one that is used in industry frequently). ## Demodulation: First Step Now, it is important to note that FM and PM signals both do the same first 2 steps during demodulation: 1. Pass the signal through a **limiter**, to remove amplitude peaks 2. Pass the signal through a bandpass filter to remove low and high frequency noise (as much as possible, without filtering out the signal). Once we perform these two steps, we no longer have white noise, because we\'ve passed the noise through a filter. Now, we say the noise is **colored**. here is a basic diagram of our demodulator, so far: `      channel`\ `s(t) ---------> r(t) --->|Limiter|--->|Bandpass Filter|---->z(t)` Where z(t) is the output of the bandpass filter. ## Filtered Noise To denote the new, filtered noise, and new filtered signal, we have the following equation: $$z(t) = \gamma A \cos (\Psi(t)) + n_0(t)$$ Where we call the additive noise $n_0(t)$ because it has been filtered, and is not white noise anymore. $n_0(t)$ is known as **narrow band noise**, and can be denoted as such: $$n_0(t) = \mathbf{W}(t) \cos(2 \pi f_c t) + \mathbf{Z}(t) \sin(2 \pi f_c t)$$ Now, once we have it in this form, we can use a trigonometric identity to make this equation more simple: $$n_0(t) = \mathbf{R}(t) \cos(2 \pi f_c t + \mathbf{\Theta}(t))$$ Where $$\mathbf{R}(t) = \sqrt{\mathbf{W}(t)^2 + \mathbf{Z}(t)^2}$$ $$\mathbf{\Theta}(t) = tan^{-1} (\mathbf{Z}(t)/\mathbf{W(t)})$$ Here, the new noise parameter R(t) is a **rayleigh** random variable, and is discussed in the next chapter. ## Noise Analysis R(t) is a noise function that affects the amplitude of our received signal. However, our receiver passes the signal through a limiter, which will remove amplitude fluctuations from our signal. For this reason, R(t) doesnt affect our signal, and can be safely ignored for now. This means that the only random variable that is affecting our signal is the variable $\mathbf{\Theta}(t)$, \"Theta\". Theta is a uniform random variable, with values between pi and -pi. Values outside this range \"Wrap around\" because phase is circular.

# Communication Systems/AM Receivers ## AM Receivers The most common receivers in use today are the super heterodyne type. They consist of: ::\*Antenna ::\*RF amplifier ::\*Local Oscillator and Mixer ::\*IF Section ::\*Detector and Amplifier The need for these subsystems can be seen when one considers the much simpler and inadequate TRF or tuned radio frequency amplifier. ### TRF Amplifier It is possible to design an RF amplifier to accept only a narrow range of frequencies, such as one radio station on the AM band. : :  By adjusting the center frequency of the tuned circuit, all other input signals can be excluded. : :  The AM band ranges from about 500 kHz to 1600 kHz. Each station requires 10 kHz of this spectrum, although the baseband signal is only 5 kHz. Recall that for a tuned circuit: $Q = \frac{{f_c }}{B}$. The center or resonant frequency in an RLC network is most often adjusted by varying the capacitor value. However, the Q remains approximately constant as the center frequency is adjusted. This suggests that as the bandwidth varies as the circuit is tuned. : : For example, the Q required at the lower end of the AM band to select only one radio station would be approximately: $$Q = \frac{{f_c }}{B} = \frac{{500\;kHz}}{{10\;kHz}} = 50$$ : : As the tuned circuit is adjusted to the higher end of the AM band, the resulting bandwidth is: $$B = \frac{{f_c }}{Q} = \frac{{1600\;kHz}}{{50}} = 30\;kHz$$ A bandwidth this high could conceivably pass three adjacent stations, thus making meaningful reception impossible. To prevent this, the incoming RF signal is heterodyned to a fixed IF or intermediate frequency and passed through a constant bandwidth circuit. ### Superheterodyne Receiver : :  The RF amplifier boosts the RF signal into the mixer. It has broad tuning and amplifies not just one RF station, but many of them simultaneously. It also amplifies any input noise and even contributes some of its own. The other mixer input is a high frequency sine wave created by a local oscillator. In AM receivers, it is always 455 kHz above the desired station carrier frequency. An ideal mixer will combine the incoming carrier with the local oscillator to create sum and difference frequencies. . A real mixer combines two signals and creates a host of new frequencies: : : • A dc level : • The original two frequencies : • The sum and difference of the two input frequencies : • Harmonics of the two input frequencies : • Sums and differences of all of the harmonics Since the RF amplifier passes several radio stations at once, the mixer output can be very complex. However, the only signal of real interest is the difference between the desired station carrier frequency and the local oscillator frequency. This difference frequency, also called the IF (intermediate frequency) will alway be 455 kHz. By passing this through a 10 kHz BPF (band pass filter) centered at 455 kHz, the bulk of the unwanted signals can be eliminated. #### Local Oscillator Frequency Since the mixer generates sum and difference frequencies, it is possible to generate the 455 kHz IF signal if the local oscillator is either above or below the IF. The inevitable question is which is preferable. : : **Case I The local Oscillator is above the IF.** This would require that the oscillator tune from (500 + 455) kHz to (1600 + 455) kHz or approximately 1 to 2 MHz. It is normally the capacitor in a tuned RLC circuit, which is varied to adjust the center frequency while the inductor is left fixed. ```{=html} <!-- --> ``` : : Since $f_c = \frac{1}{{2\pi \sqrt {LC} }}$ ```{=html} <!-- --> ``` : : solving for *C* we obtain $C = \frac{1}{{L\left( {2\pi f_c } \right)^2 }}$ ```{=html} <!-- --> ``` : : When the tuning frequency is a maximum, the tuning capacitor is a minimum and vice versa. Since we know the range of frequencies to be created, we can deduce the range of capacitance required. $$\frac{{C_{\max } }}{{C_{\min } }} = \frac{{L\left( {2\pi f_{\max } } \right)^2 }}{{L\left( {2\pi f_{\min } } \right)^2 }} = \left( {\frac{{2\;MHz}}{{1\;MHz}}} \right)^2 = 4$$ Making a capacitor with a 4:1 value change is well within the realm of possibility. : : **Case II The local Oscillator is below the IF**. This would require that the oscillator tune from (500 - 455) kHz to (1600 - 455) kHz or approximately 45 kHz to 1145 kHz, in which case: $$\frac{{C_{\max } }}{{C_{\min } }} = \left( {\frac{{1145\;kHz}}{{45\;kHz}}} \right)^2 \approx 648$$ It is not practical to make a tunable capacitor with this type of range. Therefore the local oscillator in a standard AM receiver is above the radio band. #### Image Frequency Just as there are two oscillator frequencies, which can create the same IF, two different station frequencies can create the IF. The undesired station frequency is known as the image frequency. ;;; If any circuit in the radio front end exhibits non-linearities, there is a possibility that other combinations may create the intermediate frequency. Once the image frequency is in the mixer, there is no way to remove it since it is now heterodyned into the same IF band as the desired station. ### AM Detection There are two basic types of AM detection, coherent and non-coherent. Of these two, the non-coherent is the simpler method. ::\*Non-coherent detection does not rely on regenerating the carrier signal. The information or modulation envelope can be removed or detected by a diode followed by an audio filter. ::\*Coherent detection relies on regenerating the carrier and mixing it with the AM signal. This creates sum and difference frequencies. The difference frequency corresponds to the original modulation signal. Both of these detection techniques have certain drawbacks. Consequently, most radio receivers use a combination of both. #### Envelope Detector : :  An envelope detector is simply a half wave rectifier followed by a low pass filter. In the case of commercial AM radio receivers, the detector is placed after the IF section. The carrier at this point is 455 kHz while the maximum envelope frequency is only 5 kHz. Since the ripple component is nearly 100 times the frequency of the highest baseband signal and does not pass through any subsequent audio amplifiers. : : An AM signal where the carrier frequency is only 10 times the envelope frequency would have considerable ripple: ```{=html} <!-- --> ``` : : {width="300"} #### Synchronous Detector In a synchronous or coherent detector, the incoming AM signal is mixed with the original carrier frequency. : :  If you think this looks suspiciously like a mixer, you are absolutely right! A synchronous detector is one where the difference frequency between the two inputs is zero Hz. Of in other words, the two input frequencies are the same. Let\'s check the math. Recall that the AM input is mathematically defined by: $$e_{am} = \underbrace {\sin \omega _c t}_{{\rm{Carrier}}} + \underbrace {\frac{m}{2}\sin \left( {\omega _c - \omega _m } \right)t}_{{\rm{Lower}}\;{\rm{Sideband}}} - \underbrace {\frac{m}{2}\sin \left( {\omega _c + \omega _m } \right)t}_{{\rm{Upper}}\;{\rm{Sideband}}}$$ : : At the multiplier output, we obtain: $${\rm{mixer}}\;{\rm{out = }}e_{am} \times \sin \omega _c t = \underbrace { - \frac{m}{2}\sin \omega _m t}_{{\rm{Original}}\;{\rm{Modulation}}\;{\rm{Signal}}}\underbrace { - \frac{1}{2}\sin 2\omega _c t - \frac{m}{4}\sin \left( {2\omega _c - \omega _m } \right)t + \frac{m}{4}\sin \left( {2\omega _c + \omega _m } \right)t}_{{\rm{AM}}\;{\rm{signal}}\;{\rm{centered}}\;{\rm{at}}\;{\rm{2}}\;{\rm{times}}\;{\rm{the}}\;{\rm{carrier}}\;{\rm{frequency}}}$$ : : The high frequency component can be filtered off leaving only the original modulation signal. ```{=html} <!-- --> ``` : : This technique has one serious drawback. The problem is how to create the exact carrier frequency. If the frequency is not exact, the entire baseband signal will be shifted by the difference. A shift of only 50 Hz will make the human voice unrecognizable. It is possible to use a PLL (phase locked loop), but making one tunable for the entire AM band is not trivial. As a result, most radio receivers use an oscillator to create a fixed intermediate frequency. This is then followed by an envelope detector or a fixed frequency PLL. #### Squaring Detector The squaring detector is also a synchronous or coherent detector. It avoids the problem of having to recreate the carrier by simply squaring the input signal. It essentially uses the AM signal itself as a sort of wideband carrier. : :  ```{=html} <!-- --> ``` : : The output of the multiplier is the square of the input AM signal: $$\left( {e_{am} } \right)^2 = \left( {\sin \omega _c t + \frac{m}{2}\sin \left( {\omega _c - \omega _m } \right)t - \frac{m}{2}\sin \left( {\omega _c + \omega _m } \right)t} \right)^2$$ Since the input is being multiplied by the ${\sin \omega _c t}$ component, one of the resulting difference terms is the original modulation signal. The principle difficulty with this approach is trying to create a linear, high frequency multiplier.

# Communication Systems/Binary Modulation Schemes This page discusses the binary modulation schemes and \"keying\". ## What is \"Keying?\" Square waves, sinc waves, and raised-cosine rolloff waves are all well and good, but all of them have drawbacks. If we use an optimal, matched filter, we can eliminate the effect of jitter, so frankly, why would we consider square waves at all? Without jitter as a concern, it makes no sense to correct for jitter, or even take it into consideration. However, since the matched filter needs to look at individual symbols, the transmitted signal can\'t suffer from any intersymbol interference either. Therefore, we aren\'t using the sinc pulse. Since the raised-cosine roll-off wave suffers from both these problems (in smaller amounts, however), we don\'t want to use that pulse either. So the question is, what other types of pulses can we send? It turns out that if we use some of the techniques we have developed using analog signal modulation, and implement a sinusoidal carrier wave, we can create a signal with no inter-symbol interference, very low bandwidth, and no worries about jitter. Just like analog modulation, there are 3 aspects of the carrier wave that we can change: the amplitude, the frequency, and the phase angle. Instead of \"modulation\", we call these techniques **keying** techniques, because they are operating on a binary-number basis. There is one important point to note before continuing with this discussion: Binary signals **are not** periodic signals. Therefore, we cannot expect that a binary signal is going to have a discrete spectra like a periodic squarewave will have. For this reason, the spectral components of binary data are continuous spectra. ## Amplitude Shift Keying In an ASK system, we are changing the amplitude of the sine wave to transmit digitial data. We have the following cases: - Binary 1: $A_1 \sin(f_c t)$ - Binary 0: $A_0 \sin(f_c t)$ The simplest modulation scheme sets A0 = 0V (turning the transmitter off), and setting A1 = +5V (any random non-zero number turns the transmitter on). This special case of ASK is called OOK (On-Off keying). Morse code uses OOK. Another common special case of ASK sets A1 to some positive number, and A0 to the corresponding negative number A0 = -A1. We will mention this case again later. In ASK, we have the following equation: $$a(t) \sin(\omega t)$$ by the principal of duality, multiplication in the time domain becomes convolution in the frequency domain, and vice-versa. Therefore, our frequency spectrum will have the following equation: $$A(j\omega) * \delta(t - \omega)$$ where the impulse function is the fourier-transform of the sinusoid, centered at the frequency of the wave. the value for A is going to be a sinc wave, with a width dependent on the bitrate. We remember from the Signals and Systems book that convolution of a signal with an impulse is that signal centered where the impulse was centered. Therefore, we know now that the frequency domain shape of this curve is a sinc wave centered at the carrier frequency. ## Frequency Shift Keying In **Frequency Shift Keying** (FSK), we can logically assume that the parameter that we will be changing is the frequency of the sine wave. FSK is unique among the different keying methods in that data is never transmitted *at* the carrier frequency, but is instead transmitted at a certain offset from the carrier frequency. If we have a carrier frequency of $f_c$, and a frequency offset of $\Delta f$, we can transmit binary values as such: - Binary 1: $A \sin ((f_c + \Delta f)t)$ - Binary 0: $A \sin ((f_c - \Delta f)t)$ Similar to ASK, we have FSK, which uses 2 different frequencies to transmit data. For now we will call them $\omega1, \omega2$. Using the same logic that we used above, the fourier representations of these waves will be (respectively): $$A_1(j\omega) * \delta(t - \omega1)$$ $$A_0(j\omega) * \delta(t - \omega2)$$ With one sinc wave centered at the first frequency, and one sinc wave centered at the second frequency. Notice that A1 and A0 are the half-square waves associated with the 1s and the 0s, respectively. These will be described later. ### Error Rate The BER of coherent QPSK in the presence of gaussian and Rayleigh noise is as follows: : {\| border=1 \|- \| Gaussian Noise \|\| Rayleigh Fading \|- \| $\frac{1}{2}\operatorname{erfc} \left( \sqrt{\frac{E_b}{N_0}} \right)$ \| $\frac{1}{2}\left( 1 - \sqrt{\frac{\gamma_0}{2 + \gamma_0}} \right)$ \|} ## Phase Shift Keying PSK systems are slightly different then ASK and FSK systems, and because of this difference, we can exploit an interesting little trick of trigonometry. PSK is when we vary the phase angle of the wave to transmit different bits. For instance: - Binary 1: $A \sin(f_c t + \phi_1)$ - Binary 0: $A \sin(f_c t + \phi_0)$ If we evenly space them out around the unit-circle, we can give ourselves the following nice values: - Binary 1: $A \sin(f_c t + 0)$ - Binary 0: $A \sin(f_c t + \pi)$ Now, according to trigonometry, we have the following identity: $\sin(f_c t + \pi) = -\sin(f_c t)$ So in general, our equations for each signal (s) is given by: - $s_1(t) = A\sin(f_c t)$ - $s_0(t) = -A\sin(f_c t)$ Which looks awfully like an ASK signal. Therefore, we can show that the spectrum of a PSK signal is the same as the spectrum of an ASK signal. There are two commonally used forms of Phase Shift keying Modulation: Binary Phase Shift Keying (BPSK) Quadrature Phase Shift Keying (QPSK) Binary Phase Shift keying is set out above. ### QPSK Quadrature Phase Shift Keying utilises the fact that a cosine wave is in quadrature to a sine wave, allowing 2 bits to be simultaneously represented. - Binary 11: $A \sin(f_c t + 0) + \cos(f_c+\pi/2)$ - Binary 10: $A \sin(f_c t + 0) + \cos(f_c -\pi/2)$ - Binary 01: $A \sin(f_c t + \pi) + + \cos(f_c+\pi/2)$ - Binary 00: $A \sin(f_c t + \pi) + + \cos(f_c - \pi/2)$ QPSK has the advantage over BPSK of requiring half the transmission band width for the same data rate, and error probability. ### Error Rate The BER of coherent BPSK in the presence of gaussian and Rayleigh noise is as follows: : {\| border=1 \|- \| Gaussian Noise \|\| Rayleigh Fading \|- \| $\frac{1}{2}\operatorname{erfc} \left( \sqrt{\frac{E_b}{N_0}} \right)$ \| $\frac{1}{2}\left( 1 - \sqrt{\frac{\gamma_0}{1 + \gamma_0}} \right)$ \|} ## Binary Transmitters ## Binary Receivers

# Communication Systems/M-ary Modulation Schemes Now what if try to cram more information into a single bittime? If we take 2 bits at a time, and arrange them together, we can assign each set of 2 bits to a different symbol, and then we can transmit the different symbols. ## Pronunciation `"M-ary" is pronounced like "em airy".` ## Example: Q-ASK Let us use the following scheme: - \"00\" = +5V - \"01\" = +1.66V - \"10\" = -1.66V - \"11\" = -5V we can see now that we can transmit data *twice as fast* using this scheme, although we need to have a more complicated receiver, that can decide between 4 different pulses (instead of 2 different pulses, like we have been using). ## Bits Per Symbol All popular communication systems transmit an integer number of bits per symbol. We can relate the number of bits (\"k\") and the number of different symbols (\"m\") with the following equation: $$m = 2^k$$ This causes the number of symbols to be a power of two. With M-ary modulation techniques, the \"symbols per second\" rate can be much slower than the \"bits per second\" data rate. ## QPSK Quadrature phase shift keying (aka 4-PSK) is PSK modulation that has four points in the constellation. !QPSK Modulator !QPSK Demodulator There are several variations on this technique: - simple QPSK - DQPSK (differential QPSK) - OQPSK (offset QPSK) - SOPSK (shaped offset QPSK) - π/4 QPSK (shifted constellation QPSK) ## CPFSK (MSK) \[MSK\]minimum shift keying ## DPSK ## For further reading - Wikipedia:Constellation diagram - Wikipedia:Quadrature amplitude modulation

# Communication Systems/Wave Propagation This page will discuss some of the fundamental basics of EM wave propagation. ## Electromagnetic Spectrum : :  ## Radio Waves Maxwell first predicted the existence of electromagnetic waves in the 19th century. He came to this conclusion by careful examination of the equations describing electric and magnetic phenomenon. It was left up to Hertz to create these waves, and Marconi to exploit them. In spite of one hundred years of study, exactly what radio waves are and why they exist, remain somewhat of a mystery. Electromagnetic waves in free space, or TEM waves, consist of electric and magnetic fields, each at right angles to each other and the direction of propagation. : :  The relationship between wavelength and frequency is given by: $$c = \lambda f$$ : : where c is the speed of light (approximately 300,000 m/s in vacuum), f is the frequency of the wave, and λ is the wavelength of the wave. Radio waves can be reflected and refracted in a manner similar to light. They are affected by the ground terrain, atmosphere and other objects. Maxwell's equations state that a time varying magnetic field produces an electric field and a time varying electric field produces a magnetic field. This is kind of a chicken and egg situation. Radio waves propagate outward from an antenna, at the speed of light. The exact nature of these waves is determined by the transmission medium. In free space, they travel in straight lines, whereas in the atmosphere, they generally travel in a curved path. In a confined or guided medium, radio waves do not propagate in the TEM mode, but rather in a TE or TM mode. Radio waves interact with objects in three principle ways: : : Reflection -- A radio wave bounces off an object larger than its wavelength. : Diffraction -- Waves bend around objects. : Scattering -- A radiowave bounces off an object smaller than its wavelength. Because of these complex interactions, radio wave propagation is often examined in three distinct regions in order to simplify the analysis: : : Surface (or ground) waves are located very near the earth's surface. : Space waves occur in the lower atmosphere (troposphere). : Sky waves occur in the upper atmosphere (ionosphere). The boundaries between these regions are somewhat fuzzy. In many cases, it is not possible to examine surface waves without considering space waves. : :  ### Common RF Band Designations Frequency band name Frequency Wavelength ----------------------------------- ----------------- -------------------- ELF - Extremely Low Frequency 3 -- 30 Hz 100000 -- 10000 km SLF - Super Low Frequency 30 -- 300 Hz 10000 -- 1000 km ULF - Ultra Low Frequency 300 -- 3000 Hz 1000 -- 100 km VLF - Very Low Frequency 3 -- 30 kHz 100 -- 10 km LF - Low Frequency 30 -- 300 kHz 10 -- 1 km MF - Medium Frequency 300 -- 3000 kHz 1000 -- 100 m HF - High Frequency 3 -- 30 MHz 100 -- 10 m VHF - Very High Frequency 30 -- 300 MHz 10 -- 1 m UHF - Ultra High Frequency 300 -- 3000 MHz 1000 -- 100 mm SHF - Super High Frequency 3 -- 30 GHz 100 -- 10 mm EHF - Extremely High Frequency 30 -- 300 GHz 10 -- 1 mm THF - Tremendously High Frequency 300 -- 3000 GHz 1 -- 0.1 mm ### Surface Waves These are the principle waves used in AM, FM and TV broadcast. Objects such as buildings, hills, ground conductivity, etc. have a significant impact on their strength. Surface waves are usually vertically polarized with the electric field lines in contact with the earth. : :  #### Refraction Because of refraction, the radio horizon is larger than the optical horizon by about 4/3. The typical maximum direct wave transmission distance (in km) is dependent on the height of the transmitting and receiving antennas (in meters): $$d_{\max } \approx \sqrt {17h_t } + \sqrt {17h_r } \quad {\rm{km}}$$ However, the atmospheric conditions can have a dramatic effect on the amount of refraction. : :  ##### Super Refraction In super refraction, the rays bend more than normal thus shortening the radio horizon. This phenomenon occurs when temperature increases but moisture decreases with height. Paradoxically, in some cases, the radio wave can travel over enormous distances. It can be reflected by the earth, rebroadcast and super refracted again. ##### Sub refraction In sub refraction, the rays bend less than normal. This phenomenon occurs when temperature decreases but moisture increases with height. In extreme cases, the radio signal may be refracted out into space. ### Space Waves These waves occur within the lower 20 km of the atmosphere, and are comprised of a direct and reflected wave. The radio waves having high frequencies are basically called as space waves. These waves have the ability to propagate through atmosphere, from transmitter antenna to receiver antenna. These waves can travel directly or can travel after reflecting from earth's surface to the troposphere surface of earth. So, it is also called as Tropospherical Propagation. In the diagram of medium wave propagation, c shows the space wave propagation. Basically the technique of space wave propagation is used in bands having very high frequencies. E.g. V.H.F. band, U.H.F band etc. At such higher frequencies the other wave propagation techniques like sky wave propagation, ground wave propagation can't work. Only space wave propagation is left which can handle frequency waves of higher frequencies. The other name of space wave propagation is line of sight propagation. There are some limitations of space wave propagation. 1. These waves are limited to the curvature of the earth. 2. These waves have line of sight propagation, means their propagation is along the line of sight distance. The line of sight distance is that exact distance at which both the sender and receiver antenna are in sight of each other. So, from the above line it is clear that if we want to increase the transmission distance then this can be done by simply extending the heights of both the sender as well as the receiver antenna. This type of propagation is used basically in radar and television communication. The frequency range for television signals is nearly 80 to 200 MHz. These waves are not reflected by the ionosphere of the earth. The property of following the earth's curvature is also missing in these waves. So, for the propagation of television signal, geostationary satellites are used. The satellites complete the task of reflecting television signals towards earth. If we need greater transmission then we have to build extremely tall antennas. #### Direct Wave This is generally a line of sight transmission, however, because of atmospheric refraction the range extends slightly beyond the horizon. #### Ground Reflected Wave Radio waves may strike the earth, and bounce off. The strength of the reflection depends on local conditions. The received radio signal can cancel out if the direct and reflected waves arrive with the same relative strength and 180^o^ out of phase with each other. Horizontally polarized waves are reflected with almost the same intensity but with a 180^o^ phase reversal. Vertically polarized waves generally reflect less than half of the incident energy. If the angle of incidence is greater than 10^o^ there is very little change in phase angle. ### Sky Waves These waves head out to space but are reflected or refracted back by the ionosphere. The height of the ionosphere ranges from 50 to 1,000 km.[^1] Radio waves are refracted by the ionized gas created by solar radiation. The amount of ionization depends on the time of day, season and the position in the 11-year sun spot cycle. The specific radio frequency refracted is a function of electron density and launch angle. A communication channel thousands of kilometers long can be established by successive reflections at the earth's surface and in the upper atmosphere. This ionospheric propagation takes place mainly in the HF band. The ionosphere is composed of several layers, which vary according to the time of day. Each layer has different propagation characteristics: : : D layer -- This layer occurs only during the day at altitudes of 60 to 90 km. High absorption takes place at frequencies up to 7 MHz. : E layer -- This layer occurs at altitudes of 100 to 125 km. In the summer, dense ionization clouds can form for short periods. These clouds called *sporadic E* can refract radio signals in the VHF spectrum. This phenomenon allows amateur radio operators to communicate over enormous distances. : F layer - This single nighttime layer splits into two layers (F1 and F2) during the day. The F1 layer forms at about 200 km and F2 at about 400 km. The F2 layer propagates most HF short-wave transmissions. Because radio signals can take many paths to the receiver, multipath fading can occur. If the signals arrive in phase, the result is a stronger signal. If they arrive out of phase with each other, they tend to cancel. Deep fading, lasting from minutes to hours over a wide frequency range, can occur when solar flares increase the ionization in the D layer. The useful transmission band ranges between the LUF (lowest usable frequency) and MUF (maximum usable frequency). Frequencies above the MUF are refracted into space. Below the LUF, radio frequencies suffer severe absorption. If a signal is near either of these two extremes, it may be subject to fading. Meteors create ionization trails that reflect radio waves. Although these trails exist for only a few seconds, they have been successfully used in communications systems spanning 1500 km. The Aurora Borealis or Northern Lights cause random reflection in the 3 - 5 MHz region. Aurora causes signal flutter at 100 Hz to 2000 Hz thus making voice transmission impossible. ## Fading and Interference Radio signals may vary in intensity for many reasons. ### Flat Earth Reflections (Horizontal Polarization) There are at least two possible paths for radio waves to travel when the antennas are near the earth: direct path and reflected path. These two signals interact in a very complex manner. However, ignoring polarization and assuming a flat earth can produce some interesting mathematical descriptions. : :  ```{=html} <!-- --> ``` : : *p~1~* = direct wave path length ```{=html} <!-- --> ``` : : *p~2~* = reflected wave path length $$\Delta$$*p* = *p~2~ - p~1~* difference in path lengths : : *d* = distance From the geometry we can observe: $$p_1^2 = \left( {h_r - h_t } \right)^2 + d^2$$ $$p_2^2 = \left( {h_r + h_t } \right)^2 + d^2$$ $$p_2^2 - p_1^2 = \left( {h_r - h_t } \right)^2 + d^2 - \left( {h_r + h_t } \right)^2 - d^2 = 4h_r h_t$$ $$\left( {p_2 - p_1 } \right)\left( {p_2 + p_1 } \right) = 4h_r h_t$$ But$\Delta p = \left( {p_2 - p_1 } \right)$ and $d \approx p_1 \approx p_2$ $$\Delta p2d \approx 4h_r h_t$$ therefore $\Delta p \approx \frac{{2h_r h_t }}{d}$ If the difference in the two paths $\Delta$*p*, is 1/2 $\lambda$ long, the two signals tend to cancel. If $\Delta$*p* is equal to $\lambda$, the two signals tend to reinforce. The path difference $\Delta$*p* therefore corresponds to a phase angle change of: $$\varphi _p = \frac{{2\pi }}{\lambda }\Delta p = \frac{{4\pi h_r h_t }}{{\lambda d}}$$ The resultant received signal is the sum of the two components. The situation is unfortunately made more complex by the fact that the phase integrity of the reflected wave is not maintained at the point of reflection. If we limit the examination of reflected waves to the horizontally polarized situation, we obtain the following geometry: : :  Applying the cosine rule to this diagram, we obtain a resultant signal of: $$E_r = E_1 \sqrt {2\left( {1 - \cos \varphi _p } \right)} = 2E_1 \sin \left( {\frac{{\varphi _p }}{2}} \right)$$ The signal strength of the direct wave is the unit distance value divided by the distance: $E_r = \frac{{E_0 }}{d}$ Therefore, the received signal can be written as: $$E_r = \frac{{2E_0 }}{d}\sin \left( {\frac{{2\pi h_r h_t }}{{\lambda d}}} \right)$$ For small angles this can be approximated by: $$E_r \approx \frac{{2E_0 }}{d}\frac{{2\pi h_r h_t }}{{\lambda d}} = E_0 \frac{{4\pi h_r h_t }}{{\lambda d^2 }}$$ ### Multipath Fading The received signal is generally a combination of many signals, each coming over a different path. The phase and amplitude of each component are related to the nature of the path. These signals combine in a very complex manner. Some multipath fading effects are characterized by delay spread, Rayleigh and Ricean fading, doppler shifting, etc. Fading is the most significant phenomenon causing signal degradation. There are several different categories of fading: ::\* Flat fading: the entire pass band of interest is affected equally (also known as narrow or amplitude varying channels). ::\*Frequency selective fading: certain frequency components are affected more than others (also known as wideband channels). This phenomenon tends to introduce inter-symbol interference. ::\*Slow fading: the channel characteristics vary at less than the baud rate. ::\*Fast fading: the channel characteristics vary faster than the baud rate. #### Time Dispersion Time dispersion occurs when signals arrive at different times. Signals traveling at the speed of light move about 1 foot in 1 nanosecond. This spreading tends to limit the bit rate over RF links. #### Rayleigh Fading The Rayleigh distribution can be used to describe the statistical variations of a flat fading channel. Generally, the strength of the received signal falls off as the inverse square of the distance between the transmitter and receiver. However, in cellular systems, the antennas are pointed slightly down and the signal falls of more quickly. : : {width="300"} #### Ricean Fading The Ricean distribution is used to describe the statistical variations of signals with a strong direct or line-of-sight component and numerous weaker reflected ones. This can happen in any multipath environment such as inside buildings or in an urban center. A received signal is generally comprised of several signals, each taking a slightly different path. Since some may add constructively in-phase and others out of phase, the overall signal strength may vary by 40 dB or more if the receiver is moved even a very short distance. #### Doppler Shift A frequency shift is caused by the relative motion of the transmitter and receiver, or any object that reflects/refracts signal. This movement creates random frequency modulation. Doppler frequency shift is either positive or negative depending on whether the transmitter is moving towards or away from the receiver. This Doppler frequency shift is given by: $$f_d = \frac{{v_m }}{c}f_c$$ *v~m~* is the relative motion of the transmitter with respect to the receiver, *c* is the speed of light and *f~c~* is the transmitted frequency. In the multipath environment, the relative movement of each path is generally different. Thus, the signal is spread over a band of frequencies. This is known as the Doppler spread. ### Atmospheric Diffraction Radio waves cannot penetrate very far into most objects. Consequently, there is often a shadow zone behind objects such as buildings,hills, etc. The radio shadow zone does not have a very sharp cutoff due to spherical spreading, also called Huygens' principle. Each point on a wavefront acts as it were a point source radiating along the propagation path. The overall wavefront is the vector sum of all the point sources or wavelets. The wavelet magnitude is proportional to $1 + \cos \theta$ where $\theta$ is measured from the direction of propagation. The amplitude is maximum in the direction of propagation and zero in the reverse direction. ## Reflection Reflection normally occurs due to the surface of earth or building & hills which have large dimension relative to the wavelength of the propagation waves. The reflected wave changes the incident angle. There is similarity b/w the reflection of light by a conducting medium. In both cases, angle of reflection is equal to angle of incidence. The equality of the angles of reflection & incidence follows the second law of reflection for light. ## Diffraction Diffraction occurs in beams of light or waves when they become spread out as a result of passing through a narrow slit. Maximum diffraction occurs when the slit through which the wave passes through is equal to the wavelength of the wave. Diffraction will result in constructive and destructive interference. ## Path Loss ## References [^1]: <http://www.hq.nasa.gov/iwgsdi/Ionosphere.html>

# Communication Systems/Antennas ## Antennas The purpose of an antenna is to collect and convert electromagnetic waves to electronic signals. Transmission lines then guide these to the receiver front end. The relevant electric fields associated with an antenna are extremely complex and have the general form: $$E = j30\beta ^2 Idz\left( {\frac{j}{{\beta r}} + \frac{1}{{\left( {\beta r} \right)^2 }} + \frac{1}{{\left( {\beta r} \right)^3 }}} \right)\sin \theta e^{ - j\beta r}$$ where *Idz* = moment of differential current element in rms amp meters $$\beta = \frac{{2\pi }}{\lambda }$$ : : *r* = distance in meters The near field or Fresnel region consists of three fields. The electrostatic (*1/r^3^*) and inductive (*1/r^2^*) fields fall off in intensity quite quickly. The far field or Fraunhoffer region consists entirely of the (*j/r*) radiated field. This article will only consider this radiated field. Although most antennas are simply a piece of bent wire, their interaction with electromagnetic fields is quite complex, and a whole array of terms is needed to characterize them: ::\**Beamwidth*: the angle defines by the radiation pattern where the signal strength drops 3 dB of its maximum value in a given plane. ::\**Polarization*: the plane of electric field polarization with respect to the earth. ::\**Gain*: a figure of merit used to quantify the signal capturing ability of the antenna. It is closely related to directivity and beamwidth. ::\**Effective area*: a measure of the antenna's ability to collect energy. It is related to gain by the expression: $A = \frac{{G\lambda ^2 }}{{4\pi }}$. ::\**Input impedance*: The impedance, which is necessary in the receiver for maximum power transfer to occur. ::\**Radiation resistance*: the ratio of the power driving the antenna to the square of the current driving its terminals. ::\**Bandwidth*: the usable frequency band associated with the antenna. Before any antenna can be selected, the center frequency and operating bandwidth must be known. In general, the higher the operating frequency, the smaller the antenna. Antenna gain is always measured against a known reference such as an isotropic source (*dBi*) or a half wave dipole (*dBd*). Antenna Type Typical Gain \[*dBd*\] ------------------ ------------------------ Dipole 0 Omni 0 Gain Omni 3 --- 12 Mobile Whip -0.6 to +5.5 Corner Reflector 4 --- 10 Log Periodic 3 --- 8 Horn 5 --- 12 Helix 5 --- 12 Microstrip Patch 3 --- 15 Yagi 3 --- 20 Panel 5 --- 20 Increasing antenna gain by 3 dB generally requires increasing the size by a factor of 2-3 or by reducing the beamwidth. Vertical omni directional antennas and collinear arrays are used for line-of-sight communications with ground-based mobile units. Sectoring can be accomplished by panel antennas. Fixed point-to-point links generally use a yagi or parabolic dish. Antennas exhibit reciprocity, which means they have the same gain whether used for transmitting or receiving. ### Isotropic Radiators An isotropic source radiates energy equally well in all directions. Stars are isotropic radiators. Our sun is an extremely powerful radiator, broadcasting 64 Megawatts per square meter of surface. Although it is not possible to construct isotropic radio antennas, the concept provides useful analytical tools. The power density as a function of distance from an isotropic source is easily calculated. It is simply the total energy broadcast, divided by the area it passes through, in this case, a sphere. $$P_{DI} = \frac{{P_t }}{{4\pi r^2 }}$$ watts/m^2^ Isotropic gain is also called absolute gain. Antennas gains with respect to isotropic gain are specified in units of dBi. Antenna gains can also be specified with respect to a half wave dipole or a short vertical antenna. The gain of a half-wave dipole is 1.64 dBi, and that of a dipole is 2.15 dBi. ### Non Isotropic Radiators Virtually all types of antennas are non-isotropic sources. That is that they tend to radiate more energy in a particular direction. : :  Because of this non-uniform energy distribution, the antenna appears to have a gain (*G~t~*) (if broadcasting the same power) relative to an isotropic radiator along its principal axis and a loss in other most directions. The power density along the antenna axis is given by: $$P_D = \frac{{P_t G_t }}{{4\pi r^2 }}$$ watts/m^2^ The receiving antenna attempts to collect this radiated energy through an effective area (*A~eff~*). The received power is therefore: $$P_r = \frac{{P_t G_t }}{{4\pi r^2 }}A_{eff}$$ watts It would seem reasonable to conclude that the effective area is simply the physical size of the antenna. Fortunately, this is not the case, and very small antennas are possible. It has been determined that there is a relationship between effective area, transmitted wavelength and antenna gain: $$\frac{{A_{eff} }}{{G_r }} = \frac{{\lambda ^2 }}{{4\pi }}$$ Therefore, the received power can be expressed as: : : $P_r = P_t G_t G_r \left( {\frac{\lambda }{{4\pi r}}} \right)^2$ watts Recall that: $\lambda = \frac{c}{f}$ If *f* is expressed in MHz, *c* in meters per second, and *r* in km, then the received power in dB can be expressed as: $$P_r = P_t + G_t + G_r - \left( {32.45 + 20\log r + 20\log f} \right)$$ dB ### Electric Field Strength If the power density of an electromagnetic wave is known, the field strength can be obtained from: $$E = \sqrt {Z_0 P_D }$$ where: $$Z_0 = \sqrt {\frac{\mu }{\varepsilon }} = \sqrt {\frac{{4\pi \times 10^{ - 7} }}{{8.854 \times 10^{ - 12} }}} = 120\pi$$ (for free space) Therefore the field strength at one meter is: $$E_o = \sqrt {120\pi \frac{{P_t G_t }}{{4\pi r^2 }}} = \sqrt {30P_t G_t }$$ volts/m ## Antenna Types Antennas come in a bewildering array of shapes and sizes however, they can be divided into two broad categories : Marconi and Hertzian. Marconi antennas are electrically unbalanced and a require a ground plane. Hertzian antennas are electrically balanced and do not require a ground plane. Depending on one\'s point of view, it is possible to consider one type the subset of the other. This will become clearer later on. ## Marconi Antenna Marconi antennas are usually 1/4 wavelength long and require a path to ground. The ground plane itself acts as a reflector of energy, and combines with the directly radiated wave to create the overall radiation pattern. If the ground is dry or otherwise a poor conductor, a copper grid is generally laid out on the ground. The impedance of a 1/4 $\lambda$ Marconi antenna is 36.6 $\Omega$. : :  !100 px Notice that a Marconi antenna could be considered as a dipole antenna with one of the poles buried in the ground. The ground acts as a reflector to create the appearance of an buried antenna in the same way that a mirror creates the appearance of someone behind the glass. Increasing the antenna length has a significant impact on the radiation pattern: : :  ### Helical Antenna Most Marconi antennas operate in the broadside mode, which means that the bulk of the signal radiates off the side of the wire. However it is possible to modify the antenna to operate in the end fire mode: : :  ## Hertzian Antenna Hertzian antennas do not require a path to either ground or a ground plane. The simplest antenna of this type is the elementary doublet. It is a hypothetical antenna where the instantaneous current magnitude is constant along its length. : :  The radiation pattern for this antenna is donut shaped, with the antenna rod running through the hole. The bulk of the energy is radiated at right angles to the rod and nothing off the ends. : :  This antenna is often used as a reference instead of an isotropic radiator, since close approximations of it can be constructed. Other antennas can be considered as being composed of a series of doublets. The field strength at any distance and angle can be calculated from: $$E = \frac{{60\pi LI}}{{\lambda r}}$$ Where : : *L* = doublet length in meters : $\lambda$= wavelength in meters : *I* = current in amps (rms) : *r* = distance in meters ### Dipole Antenna A dipole is sometimes referred to as a Hertzian dipole. Since it has a relatively simple construction and its radiation characteristics are well defined, it is often used as the standard to which all other antennas are compared. The dipole radiation pattern is shaped like a slightly flattened donut. : :  The simplest antenna is the dipole. The relationship between antenna current and electric field is given by: $$E_\theta = j\eta \frac{{e^{ - j\beta r} }}{{2\pi r}}I\frac{{\cos \left( {\frac{{\beta L\cos \theta }}{2}} \right) - \cos \left( {\frac{{\beta L}}{2}} \right)}}{{\sin \theta }}$$ where: : : *E* = electric field strength : $\theta$ = angle from antenna axis (in radians) : *I* = antenna current (rms) : $\eta$ = intrinsic impedance (377 $\Omega$) : *L* = antenna length : *r* = distance A ½ $\lambda$ dipole has an impedance of about 70 $\Omega$. To increase this impedance and more closely match the characteristics of a twin lead cable, the dipole may be folded. A ½ $\lambda$ folded dipole has an input impedance of about 280 $\Omega$, and is used as the driving element in many other types of antennas. Most TV receivers are equipped with two indoor antennas, one to cover the VHF band and the other the UHF band. The most common VHF antennas are the extendible monopole and vee dipole colloquially known as the rabbit ears. These are available with either a 75 $\Omega$ or 300 $\Omega$ impedance and have a typical gain of -4 dB with respect to a ½ $\lambda$ dipole. The vee dipole has a lower input impedance than a straight dipole of the same length, but under some conditions, it can exhibit a higher directivity due to the reduction of sidelobes. The common UHF antennas are the circular loop and triangular dipole. They typically have a 300 $\Omega$ impedance. The dipole version sometimes has a reflecting screen to improve the gain and directivity. ### Halfwave Dipole The radiation pattern of the half wave dipole is very much like a donut. : :  The distribution of voltage, current, and impedance resemble: : :  By increasing the length of the dipole, the donut tends to flatten out and then explodes into complex multi lobed shapes. ### Folded Dipole : :  folded dipole antenna has high input impedance as compared to ordinary dipole. ### Loop Antenna The entire UHF band can be received on a single 20.3 cm diameter loop. The circumference varies from one wavelength at 470 MHz to 1.7 wavelengths at 806 MHz. The directivity is about 3.5 dB. The mid band gain is 3 dB higher than a ½ $\lambda$ dipole, but falls off to about 1 dB at either end. : :  Loop antennas that are much smaller than wavelength they are attempting to catch, exhibit a null in the direction of the loop axis. This makes it suitable for radio direction finding equipment. If the loop size is increased, it begins to generate a lobe across the axis and in line with the feed. ### Triangular Dipole (Bowtie) : :  The bowtie antenna is formed of two triangular sheets connected to a transmission line and provides a 3 dB gain over a simple dipole. It can also be constructed of a wire mesh if the spacing is less than 1/10 wavelength. The input impedance is a function of length and flare angle. For television applications, the flare angle a is between 60^o^ and 80^o^. If the antenna is mounted ¼ $\lambda$ in front of a reflecting surface, the gain increases to approximately 9 dB. Stacking two of them vertically one wavelength apart, increases the overall gain to about 12 dB. If the receiver is located at a great distance from the broadcast tower, it is often necessary to use an outdoor antenna. These often have a gain of 15 dB. Placing the antenna on a tall mast also increases the received signal strength by as much as an additional 14 dB. A further improvement occurs because these antennas have a greater immunity to interference, due to their complex structure. Most outdoor antennas are a combination of two antennas \[UHF and VHF\] in a single structure. The VHF antenna is generally a log-periodic dipole array. The UHF antenna may be an LPDA, Yagi-Uda, corner reflector, parabolic reflector, or triangular dipole array with reflecting screen. ### Log Periodic Dipole Array \[LPDA\] This antenna is called a log periodic array because the impedance variations across the usable band are periodic functions of frequency. The high impedance version is mounted on an insulated boom and feed by a balanced cable. The average domestic antenna of this type has a gain of about 4.5 dB in the low VHF band, rising to 7 dB in the high VHF band. : :  $$\tau = \frac{{X_n }}{{X_{n + 1} }} = \frac{{L_n }}{{L_{n + 1} }} = \frac{{s_n }}{{s_{_{n + 1} } }} = \frac{{d_n }}{{d_{n + 1} }}$$ \-- Typically $0.7 \le \tau \le 0.95$ $$\alpha = \tan ^{ - 1} \left( {\frac{{1 - \tau }}{{4\sigma }}} \right)$$ \-- Typically $10^0 \le \alpha \le 45^0$ $$\sigma = \frac{{d_n }}{{2L_n }}$$ : : Bandwidth: $B = \frac{{f_{high} }}{{f_{low} }}\left( {1 + 7.7\left( {1 - \tau } \right)^2 \cot \alpha } \right)$ ```{=html} <!-- --> ``` : : Number of dipoles: $N = 1 + \frac{{\ln B}}{{\ln \frac{1}{\tau }}}$ Most CATV applications use a 75 $\Omega$ unbalanced configuration, because it is more compatible with their cable feeds and equipment. : :  Two parallel conducting booms form a low impedance transmission line. Phase reversal between dipoles is obtained by alternate attachment to the booms. An UHF LPDA can be constructed from V-shaped dipoles. The dipoles are used in their ½ $\lambda$ and 3/2 $\lambda$ modes and eliminate the need for higher frequency dipoles. ### Yagi Uda Antenna : :  The dipole is typically 0.40 to 0.50 wavelengths long. The reflector is normally 0.55 wavelengths long and placed anywhere from 0.1 to 0.25 wavelengths behind the dipole. The reflector spacing has no effect on the forward gain, but does influence the front to back ratio and input impedance. The directors are normally 0.4 to 0.45 wavelengths long and are spaced at 0.3 to 0.4 wavelengths in front of the dipole. An antenna will usually have 6 to 12 directors. ### Parabolic Reflector : : ## Antenna Arrays By combining several radiating elements together, the overall radiation pattern can be modified to suit a particular application. In some cases the antennas must be manually steered, but in other cases they can be electronically steered using phase shifting between elements. : : !200 px {width="200"} The array factor is the increase in field strength in an array when compared to a single element radiating the same power: : :  $$AF = \left| {\frac{{\sin \left( {\frac{{n\varphi }}{2}} \right)}}{{\sqrt n \sin \left( {\frac{\varphi }{2}} \right)}}} \right| \vdots \quad \quad \quad AF_{\max } = \sqrt n$$ : : Where: $$\varphi = \frac{{2\pi }}{\lambda }s\cos \left( \theta \right) + \alpha$$ : : = phase difference between radiated fields from adjacent elements : : *n* = number of radiating elements : *s* = element spacing in wavelengths : $\alpha$ = current phase shift between elements : $\theta$ = angle from array axis ### Broadside Array If all of the elements are fed in-phase, there will always be a broadside radiation pattern. However, depending on the relative spacing, an end fire pattern can also be created. : :  The radiating elements in the above illustration can be placed such that they reinforce one another along the array axis, or not. An end fire pattern is recreated when they reinforce. By varying the space or phase shift between the elements, the size and direction of the side lobes can be adjusted between these two extremes. Increasing the number of radiating elements increases the overall array gain. : :  Determining the array factor is sometimes relatively straightforward. By definition, the signal strength for a broadside array is a maximum when $\theta$ = 90^o^ and a minimum when $\theta$ = 0^o^ Since the array factor is a maximum when $\varphi$ = 0^o^ we can determine the current phase shift $\alpha$, required to create a broadside radiation pattern for a given frequency or element spacing: $$\varphi = \frac{{2\pi }}{\lambda }s\cos \left( \theta \right) + \alpha$$ $$0 = \frac{{2\pi }}{\lambda }s\cos \left( \theta \right) + \alpha$$ $$\alpha = 0$$ : : Therefore the array factor for a broadside array is: $$AF = \left| {\frac{{\sin \left( {\frac{{n\varphi }}{2}} \right)}}{{\sqrt n \sin \left( {\frac{\varphi }{2}} \right)}}} \right|\quad {\rm{where}}\quad \varphi = \frac{{2\pi }}{\lambda }s\cos \left( \theta \right)$$ $${\rm{generally}}\quad s = \frac{\lambda }{2}\quad \quad \quad {\rm{therefore}}\quad \quad \quad \varphi = 2cos\left( \theta \right)$$ Each element may have its own feed or there may be a single feed: : :  This form of antenna is often deployed in vertical stacks, with a reflector spaced 1/4 wavelength behind the curtain. This broadband dipole curtain array is the standard antenna for 100 to 500 kW short-wave broadcasting stations. : :  CBC Radio International operates eight curtain arrays at Sackville NB. Three have an output power of 100 kW and five have an output of 250 kW. They are tunable over the range of 4.9 to 21.7 MHz. Signals are beamed to Africa, Europe, Latin America, The Caribbean, the USA, and Mexico. ### Endfire Array If all of the elements are positioned in such a way that the combined wave fronts reinforce along the array axis. : :  Calculate the array factor is relatively straightforward. The signal strength is a maximum when $\theta$ = 0^o^ and a minimum when $\theta$ = 90^o^ Since the array factor is a maximum when $\varphi$ = 0^o^ we can determine the value of $\alpha$: $$\varphi = \frac{{2\pi }}{\lambda }s\cos \left( \theta \right) + \alpha$$ $$0 = \frac{{2\pi }}{\lambda }s\cos \left( 0 \right) + \alpha$$ $$\alpha = - \frac{{2\pi }}{\lambda }s$$ : : The array factor for an end fire array is: $$AF = \left| {\frac{{\sin \left( {\frac{{n\varphi }}{2}} \right)}}{{\sqrt n \sin \left( {\frac{\varphi }{2}} \right)}}} \right|\quad {\rm{where}}\quad \varphi = \frac{{2\pi }}{\lambda }s\left( {\cos \left( \theta \right) - 1} \right)$$ $${\rm{generally}}\quad s = \frac{\lambda }{4}\quad \quad \quad {\rm{therefore}}\quad \quad \quad \varphi = \frac{\pi }{2}\left( {cos\left( \theta \right) - 1} \right)$$ Varying the spacing for a 6-element array produced the following patterns: : :  ### Phased Array By varying the phase shift between elements, a beam or multiple beams can be pointed towards a given direction. This forms the basis of the large electronically steered radar system currently being deployed. Collectively theses systems are known as phased arrays. : : !300 px The PAVE PAWS early warning radar for example has 1792 active crossed dipole antennas on a 102-foot face. Each face can scan 120^o^ in azimuth and 80^o^ in elevation. The array has a range of 300 miles and can produce multiple beams, which can be redirected in milliseconds. ## Further reading - Wifi/Building an antenna

# Communication Systems/Noise Figure This page is going to talk about the effect of noise on transmission systems. ## Types of Noise Most man made electro-magnetic noise occurs at frequencies below 500 MHz. The most significant of these include: : : • Hydro lines : • Ignition systems : • Fluorescent lights : • Electric motors Therefore deep space networks are placed out in the desert, far from these sources of interference. There are also a wide range of natural noise sources which cannot be so easily avoided, namely: : : •*Atmospheric noise* - lighting \< 20 MHz : •*Solar noise* - sun - 11 year sunspot cycle : •*Cosmic noise* - 8 MHz to 1.5 GHz : •*Thermal or Johnson noise*. Due to free electrons striking vibrating ions. : •*White noise* - white noise has a constant spectral density over a specified range of frequencies. Johnson noise is an example of white noise. : •*Gaussian noise* - Gaussian noise is completely random in nature however, the probability of any particular amplitude value follows the normal distribution curve. Johnson noise is Gaussian in nature. : •*Shot noise* - bipolar transistors $$i_n = \sqrt {2qI_{dc} \Delta f}$$ : : where *q* = electron charge 1.6 x 10^-19^ coulombs : •*Excess noise, flicker, 1/f, and pink noise* \< 1 KHz are Inversely proportional to frequency and directly proportional to temperature and dc current : •*Transit time noise* - occurs when the electron transit time across a junction is the same period as the signal. Of these, only Johnson noise can be readily analysed and compensated for. The noise power is given by: $$P_n = kTB$$ Where: : : *k* = Boltzmann\'s constant (1.38 x 10^-23^ J/K) : T = temperature in degrees Kelvin : B = bandwidth in Hz This equation applies to copper wire wound resistors, but is close enough to be used for all resistors. Maximum power transfer occurs when the source and load impedance are equal. ### Combining Noise Voltages The instantaneous value of two noise voltages is simply the sum of their individual values at the same instant. $$v_{total\;inst} = v_{1\;inst} + v_{2\;inst}$$ This result is readily observable on an oscilloscope. However, it is not particularly helpful, since it does not result in a single stable numerical value such as one measured by a voltmeter. If the two voltages are coherent \[K = 1\], then the total rms voltage value is the sum of the individual rms voltage values. $$v_{total\;rms} = v_{1\;rms} + v_{2\;rms}$$ If the two signals are completely random with respect to each other \[K = 0\], such as Johnson noise sources, the total power is the sum of all of the individual powers: $$P_{total\;random\;noise} = P_{n1\;random} + P_{n2\;random}$$ A Johnson noise of power *P = kTB*, can be thought of as a noise voltage applied through a resistor, Thevenin equivalent. : :  An example of such a noise source may be a cable or transmission line. The amount of noise power transferred from the source to a load, such as an amplifier input, is a function of the source and load impedances. : :  If the load impedance is 0 $\Omega$, no power is transferred to it since the voltage is zero. If the load has infinite input impedance, again no power is transferred to it since there is no current. Maximum power transfer occurs when the source and load impedances are equal. $$P_{L\;\max } = \frac{{e_s^2 }}{{4R_s }}$$ The rms noise voltage at maximum power transfer is: $$e_n = \sqrt {4RP} = \sqrt {4RkTB}$$ : :  Observe what happens if the noise resistance is resolved into two components: $$e_n^2 = 4RkTB = 4\left( {R_1 + R_2 } \right)kTB = e_{n1}^2 + e_{n2}^2$$ From this we observe that random noise resistance can be added directly, but random noise voltages add vectorially: : :  If the noise sources are not quite random, and there is some correlation between them \[0 \< K \< 1\], the combined result is not so easy to calculate: $$P_{Total\;\left( {{\rm{not }}\;{\rm{quite}}\;{\rm{ random}}} \right)} = \frac{{E_1^2 + E_2^2 + 2KE_1 E_2 }}{{R_0 }} = P_1 + P_2 = 2K\sqrt {P_1 + P_2 }$$ : : where ```{=html} <!-- --> ``` : : *K* = correlation \[0 _\<_ *K* _\<_ 1\] : *R~0~* = reference impedance ## Noise Temperature The amount of noise in a given transmission medium can be equated to thermal noise. Thermal noise is well-studied, so it makes good sense to reuse the same equations when possible. To this end, we can say that any amount of radiated noise can be approximated by thermal noise with a given **effective temperature**. Effective temperature is measured in Kelvin. Effective temperature is frequently compared to the **standard temperature**, $T_o$, which is 290 Kelvin. In microwave applications, it is difficult to speak in terms of currents and voltages since the signals are more aptly described by field equations. Therefore, temperature is used to characterize noise. The total noise temperature is equal to the sum of all the individual noise temperatures. ## Noise Figure The terms used to quantify noise can be somewhat confusing but the key definitions are: : : **Signal to noise ratio**: It is either unitless or specified in dB. The S/N ratio may be specified anywhere within a system. $$\frac{S}{N} = \frac{{{\rm{signal}}\;{\rm{power}}}}{{{\rm{noise}}\;{\rm{power}}}} = \frac{{P_s }}{{P_n }}$$ $$\left( {\frac{S}{N}} \right)_{dB} = 10\log \frac{{P_s }}{{P_n }}$$ : : **Noise Factor (or Noise Ratio)**: $F = \frac{{\left( {\frac{S}{N}} \right)_{in} }}{{\left( {\frac{S}{N}} \right)_{out} }}$ (unit less) ```{=html} <!-- --> ``` : : **Noise Figure**: $NF = 10\log F = SNR_{in} - SNR_{out}$ dB This parameter is specified in all high performance amplifiers and is measure of how much noise the amplifier itself contributes to the total noise. In a perfect amplifier or system, *NF* = 0 dB. This discussion does not take into account any noise reduction techniques such as filtering or dynamic emphasis. : :  ### Friiss\' Formula & Amplifier Cascades It is interesting to examine an amplifier cascade to see how noise builds up in a large communication system. $$F = \frac{{\left( {\frac{S}{N}} \right)_{in} }}{{\left( {\frac{S}{N}} \right)_{out} }} = \frac{{S_{in} }}{{N_{in} }} \times \frac{{N_{out} }}{{S_{out} }}$$ Amplifier gain can be defined as: $G = \frac{{S_{out} }}{{S_{in} }}$ : :  ```{=html} <!-- --> ``` : : Therefore the output signal power is: $S_{out} = GS_{in}$ ```{=html} <!-- --> ``` : : and the noise factor (ratio) can be rewritten as: $F = \frac{{S_{in} }}{{N_{in} }} \times \frac{{N_{out} }}{{GS_{in} }} = \frac{{N_{out} }}{{GN_{in} }}$ ```{=html} <!-- --> ``` : : The output noise power can now be written: $N_{out} = FGN_{in}$ From this we observe that the input noise is increased by the noise ratio and amplifier gain as it passes through the amplifier. A noiseless amplifier would have a noise ratio (factor) of 1 or noise figure of 0 dB. In this case, the input noise would only be amplified by the gain since the amplifier would not contribute noise. : : The minimum noise that can enter any system is the Johnson Noise: $$N_{in\left( {{\rm{minimum}}} \right)} = kTB$$ : : Therefore the minimum noise that can appear at the output of any amplifier is: $$N_{out\left( {{\rm{minimum}}} \right)} = FGkTB$$ : : The output noise of a perfect amplifier would be (*F* = 1): $$N_{out\left( {{\rm{perfect}}} \right)} = GkTB$$ : : The difference between these two values is the noised created (added) by the amplifier itself: $$N_{out\left( {{\rm{added}}} \right)} = N_{out\left( {{\rm{minimum}}} \right)} - N_{out\left( {{\rm{perfect}}} \right)} = FGkTB - GkTB = \left( {F - 1} \right)GkTB$$ : : This is the additional (created) noise, appearing at the output. **The total noise out of the amplifier is then given by:** $$N_{total} = N_{out\left( {{\rm{perfect}}} \right)} + N_{out\left( {{\rm{added}}} \right)} = GkTB + \left( {F - 1} \right)GkTB$$ If a second amplifier were added in series, the total output noise would consist the first stage noise amplified by the second stage gain, plus the additional noise of the second amplifier: $$N_{total} = G_1 G_2 kTB + \left( {F_1 - 1} \right)G_1 G_2 kTB + \left( {F_2 - 1} \right)G_2 kTB$$ : : If we divide both sides of this expression by the common term: $G_1 G_2 kTB$ ```{=html} <!-- --> ``` : : we obtain: $$\frac{{N_{total} }}{{G_1 G_2 kTB}} = \frac{{G_1 G_2 kTB + \left( {F_1 - 1} \right)G_1 G_2 kTB + \left( {F_2 - 1} \right)G_2 kTB}}{{G_1 G_2 kTB}}$$ : : Recall: $F = \frac{{N_{out} }}{{GN_{in} }} = \frac{{N_{total} }}{{G_1 G_2 kTB}}$ ```{=html} <!-- --> ``` : : Then: $F_{overall} = F_1 + \frac{{F_2 - 1}}{{G_1 }}$ This process can be extended to include more amplifiers in cascade to arrive at: : **Friiss\' Formula** $$F = F_1 + \frac{{F_2 - 1}}{{G_1 }} + \frac{{F_3 - 1}}{{G_1 G_2 }} +$$ This equation shows that the overall system noise figure is largely determined by the noise figure of the first stage in a cascade since the noise contribution of any stage is divided by the gains of the preceding stages. This is why the 1st stage in any communication system should be an LNA (low noise amplifier). ## Receiver Sensitivity In a given bandwidth, W, we can show that the noise power N equals: $$N = F(kT_0)W$$ From N, we can show that the sensitivity of the receiver is equal to $$SNR \times N$$ ## Cascaded Systems

# Communication Systems/Wired Transmission This page will discuss the topic of signal propagation through physical mediums, such as wires. ## Transmission Line Equation Many kinds of communication systems require signals at some point to be conveyed over copper wires. The following analysis requires two assumptions: : : • A transmission line can be decomposed into small, distributed passive electrical elements : • These elements are independent of frequency (i.e. although *reactance* is a function of frequency, resistance, capacitance and inductance are not) These two assumptions limit the following analysis to frequencies up to the low MHz region. The second assumption is particularly difficult to defend since it is well known that the resistance of a wire increases with frequency because the conduction cross-section decreases. This phenomenon is known as the skin effect and is not easy to evaluate. : :  The purpose behind the following mathematical manipulation is to obtain an expression that defines the voltage (or current) at any time (*t*) along any portion (*x*) of the transmission line. Later, this analysis will be extended to include the frequency domain. Recall the characteristic equations for inductors and capacitors: $$v = L\frac{{\partial i}}{{\partial t}}$$ and $i = C\frac{{\partial v}}{{\partial t}}$ ### Kirchoff\'s Voltage Law Kirchoff\'s voltage law (KVL) simply states that the sum of all voltage potentials around a closed loop equal zero. Or in other words, if you walked up a hill and back down, the net altitude change would be zero. : : Applying KVL in the above circuit, we obtain: $$v\left( {x,t} \right) = R\Delta xi\left( {x,t} \right) + L\Delta x\frac{{\partial i}}{{\partial t}}\left( {x,t} \right) + v\left( {x + \Delta x,t} \right)$$ : : Rearranging: $$v\left( {x,t} \right) - v\left( {x + \Delta x,t} \right) = R\Delta xi\left( {x,t} \right) + L\Delta x\frac{{\partial i}}{{\partial t}}\left( {x,t} \right)$$ : : But the LHS (left hand side) of the above equation, represents the voltage drop across the cable element $\Delta v$, therefor: $$\Delta v = R\Delta xi\left( {x,t} \right) + L\Delta x\frac{{\partial i}}{{\partial t}}\left( {x,t} \right)$$ : : Dividing through by $\Delta x$, we obtain: $$\frac{{\Delta v}}{{\Delta x}} = Ri\left( {x,t} \right) + L\frac{{\partial i}}{{\partial t}}\left( {x,t} \right)$$ : : The LHS is easily recognized as a derivative. Simplifying the notation: $$\frac{{\partial v}}{{\partial x}} = Ri + L\frac{{\partial i}}{{\partial t}}$$ This expression has both current and voltage in it. It would be convenient to write the equation in terms of current or voltage as a function of distance or time. ### Simplifying the Equation (trust me) The first step in separating voltage and current is to take the derivative with respect to the position *x* (**Equation 1**): $$\frac{{\partial ^2 v}}{{\partial x^2 }} = R\frac{{\partial i}}{{\partial x}} + L\frac{{\partial ^2 i}}{{\partial x\partial t}}$$ : : The next step is to eliminate the current terms, leaving an expression with voltage only. The change in current along the line is equal to the current being shunted across the line through the capacitance *C* and conductance *G*. By applying KCL in the circuit, we obtain the necessary information (**Equation 2**): $$\frac{{\partial i}}{{\partial x}} = Gv + C\frac{{\partial v}}{{\partial t}}$$ : : Taking the derivative with respect to time, we obtain (**Equation 3**): $$\frac{{\partial ^2 i}}{{\partial x\partial t}} = G\frac{{\partial v}}{{\partial t}} + C\frac{{\partial ^2 v}}{{\partial t^2 }}$$ : : Substituting (**Equation 2**) and (**Equation 3**) into (**Equation 1**), we obtain the desired simplification: $$\frac{{\partial ^2 v}}{{\partial x^2 }} = R\left[ {Gv + C\frac{{\partial v}}{{\partial t}}} \right] + L\left[ {G\frac{{\partial v}}{{\partial t}} + C\frac{{\partial ^2 v}}{{\partial t^2 }}} \right]$$ : : Collecting the terms, we obtain: ```{=html} <!-- --> ``` : : **The Transmission Line Equation for Voltage** $$\frac{{\partial ^2 v}}{{\partial x^2 }} = RGv + \left( {RC + LG} \right)\frac{{\partial v}}{{\partial t}} + LC\frac{{\partial ^2 v}}{{\partial t^2 }}$$ This equation is known as the transmission line equation. Note that it has voltage at any particular location *x* as a function of time *t*. : : Similarly for current, we obtain: ```{=html} <!-- --> ``` : : **The Transmission Line Equation for Current** $$\frac{{\partial ^2 i}}{{\partial x^2 }} = RGi + \left( {RC + LG} \right)\frac{{\partial i}}{{\partial t}} + LC\frac{{\partial ^2 i}}{{\partial t^2 }}$$ But we\'re not quite done yet. ### Solving the Transmission Line Equation Historically, a mathematician would solve the transmission line equation for *v* by assuming a solution for *v*, substituting it into the equation, and observing whether the result made any sense. An engineer would follow a similar procedure by making an "educated guess" based on some laboratory experiments, as to what the solution might be. Today there are more sophisticated techniques used to find solutions. In this respect, the engineer may lag behind the mathematician by several centuries in finding applications for mathematical tools. To solve the transmission line equation, we shall guess that the solution for the voltage function is of the form: $$v\left( t \right) = e^{j\omega t} e^{ - \gamma x}$$ The first term represents a unity vector rotating at an angular velocity of $\omega$ radians per second, in other words, a sine wave of some frequency. The second term denotes the sinusoid being modified by the transmission line, namely its amplitude decaying exponentially with distance. If we let $\gamma$ be a complex quantity, we can also include any phase changes which occur as the signal travels down the line. : The sine wave is used as a signal source because it is easy to generate, and manipulate mathematically. Euler's Identity shows the relationship between exponential notation and trigonometric functions: ```{=html} <!-- --> ``` : : **Euler\'s Identity** $$e^{j\omega t} = \cos \left( {\omega t} \right) + j\sin \left( {\omega t} \right)$$ : : Going back to our educated guess, we will let $\gamma = \alpha + j\beta$, therefore: $$v\left( t \right) = e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} = e^{ - \alpha x} e^{\left( {\omega t - \beta x} \right)j}$$ : : The term $e^{ - \alpha x}$ represents the exponential amplitude decay as this signal travels down the line. $\alpha$ is known as the attenuation coefficient and is expressed in Nepers per meter. ```{=html} <!-- --> ``` : : The term $e^{\left( {\omega t - \beta x} \right)j}$ represents the frequency of the signal at any point along the line. $\beta$ component is known as the phase shift coefficient, and is expressed in radians per meter. ```{=html} <!-- --> ``` : : Substituting our *educated guess* $$v\left( t \right) = e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x}$$ : : into the transmission line equation for voltage, we obtain: $$\frac{{\partial ^2 }}{{\partial x^2 }}\left[ {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] = RG\left[ {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] + \left( {RC + LG} \right)\frac{\partial }{{\partial t}}\left[ {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] + LC\frac{{\partial ^2 }}{{\partial t^2 }}\left[ {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right]$$ This looks pretty intimidating, but if you can do basic differentials and algebra, you can do this! #### Simplifying the Equation (trust me) The idea now is to work through the math to see if we come up with a reasonable solution. If we arrive at a contradiction or an unreasonable result, it means that our educated guess was wrong and we have to do more experimenting and come up with a better guess as to how voltage and current travel down a transmission line. Let\'s look at this equation one term at a time: : : LHS = RHS Term 1 + RHS Term 2 + RHS Term 3 ```{=html} <!-- --> ``` : : Starting with the left hand side (LHS) we get the following simplification: $$\frac{{\partial ^2 }}{{\partial x^2 }}\left[ {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] = \frac{\partial }{{\partial x}}\left[ { - \left( {\alpha + j\beta } \right)e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] = \left( {\alpha + j\beta } \right)^2 e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x}$$ : : Believe it or not, the RHS Term 1 does not need simplifying. ```{=html} <!-- --> ``` : : Simplifying the RHS Term 2, we obtain: $$\left( {RC + LG} \right)\frac{\partial }{{\partial t}}\left[ {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] = \left( {RC + LG} \right)j\omega \left( {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right)$$ : : Simplifying the RHS Term 3, we obtain: $$LC\frac{{\partial ^2 }}{{\partial t^2 }}\left[ {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] = LC\frac{\partial }{{\partial t}}\left[ {j\omega e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right] = - LC\omega ^2 e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x}$$ : : Let\'s put it all back together: $$\left( {\alpha + j\beta } \right)^2 e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} = RG\left( {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right) + \left( {RC + LG} \right)j\omega \left( {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right) - LC\omega ^2 \left( {e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} } \right)$$ : : Note that each of the four terms contain the expression $e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x}$. ```{=html} <!-- --> ``` : : Therefore we end up with: $$\left( {\alpha + j\beta } \right)^2 = RG + \left( {RC + LG} \right)j\omega - LC\omega ^2$$ : : And this can be further simplified to: ```{=html} <!-- --> ``` : : **Attenuation and Phase Shift Coefficients** $$\alpha + j\beta = \gamma = \sqrt {\left( {R + j\omega L} \right)\left( {G + j\omega C} \right)}$$ This result is not self contradictory or unreasonable. Therefore we conclude that our educated guess was right and we have successfully found an expression for attenuation and phase shift on a transmission line as a function of its distributed electrical components and frequency. ### Lossless Transmission Line Signal loss occurs by two basic mechanisms: signal power can be dissipated in a resistor \[or conductance\] or signal currents may be shunted to an AC ground via a reactance. In transmission line theory, a lossless transmission line does not dissipate power. Signals, will still gradually diminish however, as shunt reactances return the current to the source via the ground path. For the power loss to equal zero, R = G = 0. This condition occurs when the transmission line is very short. An oscilloscope probe is an example of a very short transmission line. The transmission line equation reduces to the voltage equation: $$\frac{{\partial ^2 v}}{{\partial x^2 }} = LC\frac{{\partial ^2 v}}{{\partial t^2 }}$$ : : and the current equation: $$\frac{{\partial ^2 i}}{{\partial x^2 }} = LC\frac{{\partial ^2 i}}{{\partial t^2 }}$$ To determine how sinusoidal signals are affected by this type of line, we simply substitute a sinusoidal voltage or current into the above expressions and solve as before, or we could take a much simpler approach. We could start with the solution for the general case: $$\alpha + j\beta = \gamma = \sqrt {\left( {R + j\omega L} \right)\left( {G + j\omega C} \right)}$$ : : Let *R* = *G* = 0, and simplify: $$\alpha + j\beta = \sqrt {\left( {j\omega L} \right)\left( {j\omega C} \right)} = \omega \left( {LC} \right)^2 j$$ : : Equating the real and imaginary parts: $$\alpha = 0$$ $$\beta = \omega \sqrt {LC}$$ This expression tells us that **a signal travelling down a lossless transmission line, experiences a phase shift directly proportional to its frequency.** #### Phase Velocity A new parameter, known as phase velocity, can be extracted from these variables: $$V_p = \frac{1}{{\sqrt {LC} }} = \frac{\omega }{\beta }$$ meters per second Phase velocity is the speed at which a fixed point on a wavefront, appears to move. In the case of wire transmission lines, it is also the velocity of propagation., typically: 0.24c \< Vp \< 0.9c . The distance between two identical points on a wavefront is its wavelength ($\lambda$) and since one cycle is defined as 2$\pi$ radians: $$\lambda = \frac{{2\pi }}{\beta }$$ and $\omega = 2\pi f$ : : therefore: $$V_p = \lambda f$$ In free space, the phase velocity is 3 x 10^8^ meters/sec, the speed of light. In a cable, the phase velocity is somewhat lower because the signal is carried by electrons. In a waveguide transmission line, the phase velocity exceeds the speed of light. ### Distortionless Transmission Line A distortionless line does not distort the signal phase, but does introduce a signal loss. Since common transmission lines are not super conductors, the signal will decrease in amplitude but retain the same shape as the input. This characteristic is essential for long cable systems. Phase distortion does not occur if the phase velocity *V~p~* is constant at all frequencies. By definition, a phase shift of 2$\pi$ radians occurs over one wavelength $\lambda$. : : Since $$V_p = \lambda f\quad \quad \lambda = \frac{{2\pi }}{\beta }\quad \quad f = \frac{\omega }{{2\pi }}$$ : : Then: $$V_p = \frac{{2\pi }}{\beta } \times \frac{\omega }{{2\pi }} = \frac{\omega }{\beta }$$ This tells us that in order for phase velocity *V~p~* to be constant, the phase shift coefficient $\beta$, must vary directly with frequency $\omega$. : : Recall $$\gamma = \sqrt {\left( {R + j\omega L} \right)\left( {G + j\omega C} \right)} = \alpha + j\beta$$ The problem now is to find $\beta$. This can be done as follows: $$\gamma = \sqrt {\left( {\frac{{R + j\omega L}}{{j\omega L}}} \right)\left( {j\omega L} \right)\left( {\frac{{G + j\omega C}}{{j\omega C}}} \right)\left( {j\omega C} \right)} = j\omega \sqrt {LC} \sqrt {1 + \frac{R}{{j\omega L}}} \sqrt {1 + \frac{G}{{j\omega C}}}$$ It may seem that we have lost $\beta$, but do not give up. The 2nd and 3rd roots can be expanded by means of the Binomial Expansion. : : Recall: $$\left( {1 + x} \right)^n = 1 + nx + \frac{{n\left( {n - 1} \right)}}{{2!}}x^2 + \frac{{n\left( {n - 1} \right)\left( {n - 2} \right)}}{{3!}}x^3 + \cdots$$ : : In this instance *n* = 1/2. Since the contribution of successive terms diminishes rapidly, $\gamma$ is expanded to only 3 terms: $$\gamma \approx j\omega \sqrt {LC} \left( {1 + \frac{1}{2}\frac{R}{{j\omega L}} - \frac{1}{8}\left( {\frac{R}{{j\omega L}}} \right)^2 } \right)\left( {1 + \frac{1}{2}\frac{G}{{j\omega C}} - \frac{1}{8}\left( {\frac{G}{{j\omega C}}} \right)^2 } \right)$$ This may seem complex, but remember it is only algebra and it will reduce down to simple elegance. Expanding the terms we obtain: $$\gamma \approx j\omega \sqrt {LC} \left\{ \begin{array}{l} 1 + \frac{1}{2}\frac{G}{{j\omega C}} - \frac{1}{8}\left( {\frac{G}{{j\omega C}}} \right)^2 + \frac{1}{2}\frac{R}{{j\omega L}} - \frac{1}{4}\frac{{RG}}{{\omega ^2 LC}} \\ - \frac{1}{{16}}\frac{R}{{j\omega L}}\left( {\frac{G}{{j\omega C}}} \right)^2 - \frac{1}{8}\left( {\frac{R}{{j\omega L}}} \right)^2 \\ - \frac{1}{{16}}\left( {\frac{R}{{j\omega L}}} \right)^2 \frac{G}{{j\omega C}} + \frac{1}{{64}}\left( {\frac{R}{{j\omega L}}} \right)^2 \left( {\frac{G}{{j\omega C}}} \right)^2 \\ \end{array} \right\}$$ : : Since $\gamma = \alpha + j\beta$, we merely have to equate the real and imaginary terms to find $\beta$. $$\beta \approx \omega \sqrt {LC} \left\{ {1 + \underbrace {\frac{1}{8}\left( {\frac{G}{{\omega C}}} \right)^2 - \frac{1}{4}\frac{{RG}}{{\omega ^2 LC}} + \frac{1}{8}\left( {\frac{R}{{\omega L}}} \right)^2 }_{{\rm{Difference}}\;{\rm{of}}\;{\rm{squares}}} + \underbrace {\frac{1}{{64}}\left( {\frac{R}{{\omega L}}} \right)^2 \left( {\frac{G}{{\omega C}}} \right)^2 }_{{\rm{Very}}\;{\rm{small}}}} \right\}$$ : : Or $$\beta \approx \omega \sqrt {LC} \left\{ {1 + \frac{1}{8}\left( {\frac{R}{{\omega L}} - \frac{G}{{\omega C}}} \right)^2 } \right\}$$ : : Note that if $\frac{R}{{\omega L}} = \frac{G}{{\omega C}}$ then $\beta \approx \omega \sqrt {LC}$ From this we observe that $\beta$ is directly proportional to $\omega$. : : Therefore the **requirement for distortionless transmission is:** ```{=html} <!-- --> ``` : : *RC = LG* : : This is one of the essential design characteristics for a broadband coax cable network. If we equate the real terms, we obtain: $$\alpha \approx \sqrt {RG}$$ So there is a reason to study algebra after all! ## The Frequency Domain Signal analysis is often performed in the frequency domain. This tells us how the transmission line affects the spectral content of the signals they are carrying. To determine this, it is necessary to find the Fourier Transform of the transmission line equation. Recall: $$\frac{{\partial ^2 v}}{{\partial x^2 }} = RGv + \left( {RC + LG} \right)\frac{{\partial v}}{{\partial t}} + LC\frac{{\partial ^2 v}}{{\partial t^2 }}$$ and recall (hopefully) the Fourier Transform (which converts the time domain to the frequency domain): $$\mathbb{F}\left\{ {f\left( t \right)} \right\} = F\left( \omega \right) = \int\limits_{ - \infty }^\infty {e^{ - j\omega t} f\left( t \right)dt}$$ To prevent this analysis from 'blowing up', we must put a stipulation on the voltage function namely, that it vanishes to zero at an infinite distance down the line. This comprises a basic boundary condition. $${\text{let}}\quad v \to 0\quad {\text{as}}\quad x \to \infty$$ This stipulation is in agreement with actual laboratory experiments. It is well known that the signal magnitude diminishes as the path lengthens. Likewise, a time boundary condition, that the signal was zero at some time in the distant past and will be zero at some time in the distant future, must be imposed. $${\text{let}}\quad v \to 0\quad {\text{as}}\quad t \to \infty$$ Although engineers have no difficulty imposing these restrictions, mathematical purists, are somewhat offended. For this and other reasons, other less restrictive transforms have been developed. The most notable in this context, is the Laplace transform, which does not have the same boundary conditions. Having made the necessary concessions in order to continue our analysis, we must find the Fourier Transform corresponding to the following terms: $$\mathbb{F}\left\{ v \right\}\quad \quad \quad \mathbb{F}\left\{ {\frac{{\partial v}} {{\partial t}}} \right\}\quad \quad \quad \mathbb{F}\left\{ {\frac{{\partial ^2 v}} {{\partial t^2 }}} \right\}$$ $${\text{Let:}}\quad \quad \quad \mathbb{F}\left\{ v \right\} = V$$ : : Then applying the transform on the derivative, we obtain: $$\mathbb{F}\left\{ {\frac{{\partial v}} {{\partial t}}} \right\} = \int\limits_{ - \infty }^\infty {e^{ - j\omega t} \frac{{\partial v}} {{\partial t}}dt}$$ This equation can be solved by using integration by parts: $$\int {u\,dv} = uv - \int {v\,du}$$ $${\text{let}}\quad u = e^{ - j\omega t} \quad \quad \quad \therefore du = - j\omega e^{ - j\omega t}$$ $${\text{and}}\quad dv = \frac{{\partial v}}{{\partial t}}\quad \quad \quad \therefore v = v$$ $$\therefore \mathbb{F}\left\{ {\frac{{\partial v}} {{\partial t}}} \right\} = e^{ - j\omega t} \left. v \right|_{ - \infty }^\infty - \int\limits_{ - \infty }^\infty {v\left( { - j\omega e^{ - j\omega t} } \right)dt}$$ Applying the boundary conditions when t goes to infinity makes the 1st term disappear. $$\therefore \mathbb{F}\left\{ {\frac{{\partial v}} {{\partial t}}} \right\} = j\omega \int\limits_{ - \infty }^\infty {e^{ - j\omega t} v\,dt}$$ Note that the resulting integral is simply the Fourier Transform. In other words: $$\mathbb{F}\left\{ {\frac{{\partial v}} {{\partial t}}} \right\} = j\omega \mathbb{F}\left\{ v \right\} = j\omega V$$ : : similarly: $$\mathbb{F}\left\{ {\frac{{\partial ^2 v}} {{\partial t^2 }}} \right\} = \left( {j\omega } \right)^2 \mathbb{F}\left\{ v \right\} = \left( {j\omega } \right)^2 V$$ We can now write the transmission line equation in the frequency domain: $$\frac{{\partial ^2 V}} {{\partial x^2 }} = RGV + \left( {RC + LG} \right)j\omega V + LC\left( {j\omega } \right)^2 V$$ : : where: $$V = V\left( \omega \right) = \mathbb{F}\left\{ {v\left( t \right)} \right\}$$ : : Rearranging the terms, we obtain: $$\frac{{\partial ^2 V}} {{\partial x^2 }} = \left[ {RG + \left( {RC + LG} \right)j\omega + \left( {j\omega L} \right)\left( {j\omega C} \right)} \right]V$$ : : or $$\frac{{\partial ^2 V}} {{\partial x^2 }} = \left[ {\left( {R + j\omega L} \right)\left( {G + j\omega C} \right)} \right]V$$ : : since: $$\sqrt {\left( {R + j\omega L} \right)\left( {G + j\omega C} \right)} = \alpha + j\beta = \gamma$$ : : then $$\frac{{\partial ^2 V}}{{\partial x^2 }} = \gamma ^2 V$$ : : or $$\frac{{\partial ^2 V}}{{\partial x^2 }} - \gamma ^2 V = 0$$ This represents the most general form of the transmission line equation in the frequency domain. This equation must now be solved for V to observe how voltage (or current) varies with distance and frequency. This can be done by assuming a solution of the form: $$V = \underbrace {Ae^{ - \gamma x} }_{{\text{forward}}\;{\text{wave}}} + \underbrace {Be^{\gamma x} }_{{\text{reverse}}\;{\text{wave}}}$$ These terms represent an exponential decay as the signal travels down the transmission line. If we ignore any reflections, assuming that the cable is infinitely long or properly terminated, this simplifies to: $$V = V_0 e^{ - \gamma x}$$ To verify whether this assumption is correct, substitute it into the equation, and see if a contradiction occurs. If there is no contradiction, then our assumption constitutes a valid solution. $$\frac{{\partial ^2 }}{{\partial x^2 }}V_0 e^{ - \gamma x} - \gamma ^2 V_0 e^{ - \gamma x} = 0$$ $$\frac{\partial }{{\partial x}}\left( { - \gamma ^2 V_0 e^{ - \gamma x} } \right) - \gamma ^2 V_0 e^{ - \gamma x} = 0$$ $$\gamma ^2 V_0 e^{ - \gamma x} - \gamma ^2 V_0 e^{ - \gamma x} = 0$$ $$0 = 0$$ Thus we validate the assumed solution. This tells us that in the frequency domain, the voltage or current on a transmission line decays exponentially: $$V = V_0 e^{ - \gamma x}$$ : : where: $$\gamma = \sqrt {\left( {R + j\omega } \right)\left( {G + j\omega } \right)} = \left| \gamma \right|\angle \varphi = \alpha + j\beta$$ $$\gamma = {\text{ propagation}}\;{\text{constant}}$$ $$\alpha = {\text{ attenuation}}\;{\text{coeficient}}$$ $$\beta = {\text{phase}}\;{\text{coefficient}}$$ In exponential notation, a sinusoid may be represented by a rotating unity vector, of some frequency: $$e^{j\omega t} = \cos \omega t + j\sin \omega t$$ Note that the magnitude of this function is 1, but the phase angle is changing as a function of *t*. : : If we let: $V_0 = e^{j\omega t}$ ```{=html} <!-- --> ``` : : Then: $V_0 = e^{j\omega t} e^{ - \gamma x} = e^{j\omega t} e^{ - \left( {\alpha + j\beta } \right)x} = \underbrace {e^{ - \alpha x} }_{{\text{attenuation}}\;vs.\;x}\overbrace {e^{j\left( {\omega t - \beta x} \right)} }^{{\text{phase}}\;vs{\text{.}}\;t\;{\text{and}}\;x}$ This result is quite interesting because it is the same solution for the transmission line equation in the time domain. The term ${e^{ - \alpha x} }$ represents an exponential decay. The signal is attenuated as length *x* increases. The amount of attenuation is defined as: : : Attenuation in Nepers: $N = \left| {\ln e^{ - \alpha x} } \right| = \alpha x$ ```{=html} <!-- --> ``` : : Attenuation in dB: $= 20\log e^{ - \alpha x} \approx 8.68589\alpha x$ This allows us to determine the attenuation at any frequency at any point in a transmission line, if we are given the basic line parameters of*R, L, G, & C*. The term ${e^{j\left( {\omega t - \beta x} \right)} }$ represents a rotating unity vector since: $$e^{j\left( {\omega t - \beta x} \right)} = \cos \left( {\omega t - \beta x} \right) + j\sin \left( {\omega t - \beta x} \right)$$ The phase angle of this vector is ${\beta x}$ radians. ## Characteristic Impedance The characteristic impedance of a transmission line is also known as its surge impedance, and should not be confused with its resistance. If a line is infinitely long, electrical signals will still propagate down it, even though the resistance approaches infinity. The characteristic impedance is determined from its AC attributes, not its DC ones. Recall from our earlier analysis:

# Communication Systems/Wireless Transmission This page will discuss Wireless EM wave propagation, and some basics about antennas. ## Isotropic Antennas An isotropic antenna radiates it\'s transmitted power equally in all directions. This is an ideal model; all real antennas have at least some directionality associated with them. However, it is mathematically convenient, and good enough for most purposes. ### Power Flux Density If the transmitted power is spread evenly across a sphere of radius R from the antenna, we can find the power per unit area of that sphere, called the **Power Flux Density** using the Greek letter Φ (capital phi) and the following formula: $$\Phi = \frac{P_T}{4 \pi R^2}$$ Where $P_T$ is the total transmitted power of the signal. ### Effective Area The **effective area** of an antenna is the equivalent amount of area of transmission power, from a non-ideal isotropic antenna that appears to be the area from an ideal antenna. For instance, if our antenna is non-ideal, and 1 meter squared of area can effectively be modeled as .5 meters squared from an ideal antenna, then we can use the ideal number in our antenna. We can relate the actual area and the effective area of our antenna using the *antenna efficiency* number, as follows: $$\eta = \frac{A_e}{A}$$ The area of an ideal isotropic antenna can be calculated using the wavelength of the transmitted signal as follows: $$A = \frac{\lambda^2}{4 \pi}$$ ### Received Power The amount of power that is actually received by a receiver placed at distance R from the isotropic antenna is denoted $P_R$, and can be found with the following equation: $$P_R = \Phi_R A_e$$ Where $\Phi_R$ is the power flux density at the distance R. If we plug in the formula for the effective area of an ideal isotropic antenna into this equation, we get the following result: $$P_R = \frac{P_T}{(4 \pi R / \lambda)^2} = \frac{P_T}{L_P}$$ Where $L_P$ is the path-loss, and is defined as: $$L_P = \left( \frac{4 \pi R}{\lambda} \right)^2$$ The amount of power lost across freespace between two isotropic antenna (a transmitter and a receiver) depends on the wavelength of the transmitted signal. ## Directional Antennas A directional antenna, such as a parabolic antenna, attempts to radiate most of its power in the direction of a known receiver. Here are some definitions that we need to know before we proceed: Azimuth Angle:The Azimuth angle, often denoted with a θ (Greek lower-case Theta), is the angle that the direct transmission makes with respect to a given reference angle (often the angle of the target receiver) when looking down on the antenna from above.\ Elevation Angle:The elevation angle is the angle that the transmission direction makes with the ground. Elevation angle is denoted with a φ (Greek lower-case phi) ### Directivity Given the above definitions, we can define the transmission gain of a directional antenna as a function of θ and φ, assuming the same transmission power: $$G_T(\theta, \phi) = \frac{\Phi_{\theta,\ \phi}}{\Phi_{isotropic}}$$ ### Effective Area The effective area of a parabolic antenna is given as such: $$A_e = \eta \frac{\pi D^2}{4}$$ ### Transmit Gain $$G_{max} = \frac{4 \pi A_e}{\lambda^2}$$ If we are at the transmit antenna, and looking at the receiver, the angle that the transmission differs from the direction that we are looking is known as Ψ (Greek upper-case Psi), and we can find the transmission gain as a function of this angle as follows: $$G(\Psi) = \left( \frac{2J_1((\pi D / \lambda) sin(\Psi))}{sin(\Psi)} \right)^2 \left( \frac{\lambda}{\pi D} \right)^2$$ Where $J_1(\ )$ denotes the first-order bessel function. ### Friis Equation The **Friis Equation** is used to relate several values together when using directional antennas: $$P_R = \frac{P_T G_T G_R}{L_P}$$ The Friis Equation is the fundamental basis for **link-budget analysis**. ## Link-Budget Analysis If we express all quantities from the Friis Equation in decibels, and divide both sides by the noise-density of the transmission medium, N0, we get the following equation: $$C/N_0 = EIRP - L_P + (G_R/T_e) - k$$ Where C/N0 is the received carrier-to-noise ratio, and we can decompose N0 as follows: $$N_0 = kTe$$ k is Boltzmann\'s constant, (-228.6dBW) and Te is the effective temperature of the noise signal (in degrees Kelvin). EIRP is the \"Equivalent Isotropic Radiated Power\", and is defined as: $$EIRP = G_T P_T$$ To perform a link-budget analysis, we add all the transmission gain terms from the transmitter, we add the receive gain divided by the effective temperature, and we subtract Boltzmann\'s constant and all the path losses of the transmission. ## Further reading - Jean-Claude Wippler. \"What if you're out of wireless range?\". 2013.

# Communication Systems/Space-Division Multiplexing This page is all about **Space-Division Multiplexing** (SDM). - What is SDM: When we want to transmit multiple messages, the goal is maximum reuse of the given resources: time and frequency. Time-Division Multiplexing (TDM), operates by dividing the time up into time slices, so that the available time can be reused. Frequency-Division Multiplexing (FDM), operates by dividing up the frequency into transmission bands, so that the frequency spectrum can be reused. However, if we remember our work with directional antennas, we can actually reuse both time and frequency, by transmitting our information along parallel channels. This is known as **Space-Division Multiplexing**. ## Technical categorisations ### Spatial Coding ## Multipathing ## Application systems ### MIMO Systems ### Smart antenna

# Communication Systems/Fading Channels Over large distances, signal quality degrades even without the presence of large quantities of AWGN. This degradation is known as **fading**, and channels that exhibit these properties are known as **fading channels**. ## What Causes Fading Fading can be caused due to natural weather disturbances, such as rainfall, snow, fog, hail and extremely cold air over a warm earth. Fading can also be created by man made disturbances, such as irrigation, or from multiple transmission paths, irregular earth surfaces, and varying terrains. ## Fading Channel Models ### Rician fading ### Rayleigh Fading ### nakagami fading ## Scales of Fading ### *Large-Scale Fading* Fading generally is a signal loss either in amplitude or phase due to sudden changes in Channel response. Large scale fading \" Shadowing\" concerns about large distances effect so, its affect appears clearly in case of the a moving vehicle where the signal is influenced by Multipath phenomena where the transmitted signal is received from more than one path. ### Small-Scale Fading Small scale fading is concerned about very small changes in the position of Transmitter or receiver in order of the wavelength as this affect greatly the received frequency due to doppler effect so as the speed of the vehicle increases as the frequency is more rapidly changing and it can be described as fast or slow fading AND flat or slow fading. ## Small-Scale Fading Types ### Frequency-Selective Fading ### Flat Fading In flat fading, the coherence bandwidth of the channel is larger than the bandwidth of the signal. Therefore, all frequency components of the signal will experience the same magnitude of fading. a signal undergoes flat fading if: `                                 Bs << Bc` ### Fast Fading Fast fading occurs when coherant time of the channel is small relative to the delay constraint of the channel. Amplitude and phase changes imposed by the channel varies considerably over period of use.

# Bourne Shell Scripting/Appendix D: Cookbook ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ !Wikimedia Commons logo{width="20"} **\[`{{localurl:{{NAMESPACE}}:{{PAGENAME}}|action=edit&section=new}}`{=mediawiki} Post a new Cookbook entry\]** If you use the title box, then you do not need to put a title in the body. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ ## Branch on extensions When writing a bash script which should do different things based on the extension of a file, the following pattern is helpful. ``` shell #filepath should be set to the name(with optional path) of the file in question ext=${filepath##*.} if [[ "$ext" == txt ]] ; then #do something with text files fi ``` (Source: slike.com Bash FAQ). ## Rename several files This recipe shows how to rename several files following a pattern. In this example, the user has huge collection of screenshots. This user wants to rename the files using a Bourne-compatible shell. Here is an \"ls\" at the shell prompt to show you the filenames. The goal is to rename images like \"snapshot1.png\" to \"nethack-kernigh-22oct2005-01.png\". ``` console $ ls snapshot1.png snapshot25.png snapshot40.png snapshot56.png snapshot71.png snapshot10.png snapshot26.png snapshot41.png snapshot57.png snapshot72.png snapshot11.png snapshot27.png snapshot42.png snapshot58.png snapshot73.png snapshot12.png snapshot28.png snapshot43.png snapshot59.png snapshot74.png snapshot13.png snapshot29.png snapshot44.png snapshot6.png snapshot75.png snapshot14.png snapshot3.png snapshot45.png snapshot60.png snapshot76.png snapshot15.png snapshot30.png snapshot46.png snapshot61.png snapshot77.png snapshot16.png snapshot31.png snapshot47.png snapshot62.png snapshot78.png snapshot17.png snapshot32.png snapshot48.png snapshot63.png snapshot79.png snapshot18.png snapshot33.png snapshot49.png snapshot64.png snapshot8.png snapshot19.png snapshot34.png snapshot5.png snapshot65.png snapshot80.png snapshot2.png snapshot35.png snapshot50.png snapshot66.png snapshot81.png snapshot20.png snapshot36.png snapshot51.png snapshot67.png snapshot82.png snapshot21.png snapshot37.png snapshot52.png snapshot68.png snapshot83.png snapshot22.png snapshot38.png snapshot53.png snapshot69.png snapshot9.png snapshot23.png snapshot39.png snapshot54.png snapshot7.png snapshot24.png snapshot4.png snapshot55.png snapshot70.png ``` First, to add a \"0\" (zero) before snapshots 1 through 9, write a for loop (in effect, a short shell script). - Use `?` which is a filename pattern for a single character. Using it, I can match snapshots 1 through 9 but miss 10 through 83 by saying `snapshot?.png`. - Use `${`*parameter*`#`*pattern*`}` to substitute the value of *parameter* with the *pattern* removed from the beginning. This is to get rid of \"snapshot\" so I can put in \"snapshot0\". - Before actually running the loop, insert an \"echo\" to test that the commands will be correct. ``` console $ for i in snapshot?.png; do echo mv "$i" "snapshot0${i#snapshot}"; done mv snapshot1.png snapshot01.png mv snapshot2.png snapshot02.png mv snapshot3.png snapshot03.png mv snapshot4.png snapshot04.png mv snapshot5.png snapshot05.png mv snapshot6.png snapshot06.png mv snapshot7.png snapshot07.png mv snapshot8.png snapshot08.png mv snapshot9.png snapshot09.png ``` That seems good, so run it by removing the \"echo\". ``` console $ for i in snapshot?.png; do mv "$i" "snapshot0${i#snapshot}"; done ``` An ls confirms that this was effective. Now change prefix \"snapshot\" to \"nethack-kernigh-22oct2005-\". Run a loop similar to the previous one: ``` console $ for i in snapshot*.png; do \ > mv "$i" "nethack-kernigh-22oct2005-${i#snapshot}" \ > done ``` This saves the user from typing 83 \"mv\" commands. ## Long command line options The builtin `getopts` does not support long options so the external `getopt` is required. (On some systems, `getopt` *also* does not support long options, so the next example will not work.) ``` shell eval set -- $(getopt -l install-opts: "" "$@") while true; do case "$1" in --install-opts) INSTALL_OPTS=$2 shift 2 ;; --) shift break ;; esac done echo $INSTALL_OPTS ``` The call to `getopt` quotes and reorders the command line arguments found in `$@`. `set` then makes replaces `$@` with the output from `getopt` Another example of getopt use can also be found in the Advanced Bash Script Guide ## Process certain files through xargs In this recipe, we want to process a large list of files, but we must run one command for each file. In this example, we want to convert the sampling rates of some sound files to 44100 hertz. The command is **`sox file.ogg -r 44100 conv/file.ogg`**, which converts `file.ogg` to a new file `conv/file.ogg`. We also want to skip files that are already 44100 hertz. First, we need the sampling rates of our files. One way is to use the **`file`** command: ``` console $ file *.ogg audio_on.ogg: Ogg data, Vorbis audio, mono, 44100 Hz, ~80000 bps beep_1.ogg: Ogg data, Vorbis audio, stereo, 44100 Hz, ~193603 bps cannon_1.ogg: Ogg data, Vorbis audio, mono, 48000 Hz, ~96000 bps ... ``` (The files in this example are from Secret Maryo Chronicles.) We can use **`grep -v`** to filter out all lines that contain \'44100 Hz\': ``` console $ file *.ogg | grep -v '44100 Hz' cannon_1.ogg: Ogg data, Vorbis audio, mono, 48000 Hz, ~96000 bps ... jump_small.ogg: Ogg data, Vorbis audio, mono, 8000 Hz, ~22400 bps live_up.ogg: Ogg data, Vorbis audio, mono, 22050 Hz, ~40222 bps ... ``` We finished with \"grep\" and \"file\", so now we want to remove the other info and leave only the filenames to pass to \"sox\". We use the text utility **`cut`**. The option **`-d:`** divides each line into fields at the colon; **`-f1`** selects the first field. ``` console $ file *.ogg | grep -v '44100 Hz' | cut -d: -f1 cannon_1.ogg ... jump_small.ogg live_up.ogg ... ``` We can use another pipe to supply the filenames on the standard input, but \"sox\" expects them as arguments. We use **`xargs`**, which will run a command repeatedly using arguments from the standard input. The **`-n1`** option specifies one argument per command. For example, we can run **`echo sox`** repeatedly: ``` console $ file *.ogg | grep -v '44100 Hz' | cut -d: -f1 | xargs -n1 echo sox sox cannon_1.ogg ... sox itembox_set.ogg sox jump_small.ogg ... ``` However, these commands are wrong. The full command for cannon_1.ogg, for example, is **`sox cannon_1.ogg -r 44100 conv/cannon_1.ogg`**. \"xargs\" will insert incoming data into placeholders indicated by \"{}\". We use this strategy in our pipeline. If we have doubt, then first we can build a test pipeline with \"echo\": ``` console $ file *.ogg | grep -v '44100 Hz' | cut -d: -f1 | \ > xargs -i 'echo sox {} -r 44100 conv/{}' sox cannon_1.ogg -r 44100 conv/cannon_1.ogg ... sox itembox_set.ogg -r 44100 conv/itembox_set.ogg sox jump_small.ogg -r 44100 conv/jump_small.ogg ... ``` It worked, so let us remove the \"echo\" and run the \"sox\" commands: ``` console $ mkdir conv $ file *.ogg | grep -v '44100 Hz' | cut -d: -f1 | \ > xargs -i 'sox {} -r 44100 conv/{}' ``` After a wait, the converted files appear in the `conv` subdirectory. The above three lines alone did the entire conversion. ## Simple playlist frontend for GStreamer If you have GStreamer, the command `gst-launch filesrc location=`*`filename`*` ! decodebin ! audioconvert ! esdsink` will play a sound or music file of any format for which you have a GStreamer plugin. This script will play through a list of files, optionally looping through them. (Replace \"esdsink\" with your favorite sink.) ``` {.shell .numberLines} #!/bin/sh loop=false if test x"$1" == x-l; then loop=true shift fi while true; do for i in "$@"; do if test -f "$i"; then echo "${0##*/}: playing $i" > /dev/stderr gst-launch filesrc location="$i" ! decodebin ! audioconvert ! esdsink else echo "${0##*/}: not a file: $i" > /dev/stderr fi done if $loop; then true; else break; fi done ``` This script demonstrates some common Bourne shell tactics: - \"loop\" is a boolean variable. It works because its values \"true\" and \"false\" are both Unix commands (and sometimes shell builtins), thus you can use them as conditions in `if` and `while` statements. - The shell builtin \"shift\" removes \$1 from the argument list, thus shifting \$2 to \$1, \$3 to \$2, and so forward. This script uses it to process an \"-l\" option. - The substitution `${0##*/}` gives everything in \$0 after the last slash, thus \"playlist\", not \"/home/musicfan/bin/playlist\".

# Introduction to Numerical Methods/Introduction Mathematical models are a central piece of science and engineering. Some models have closed-form solutions, therefore they can be solved analytically. Many models can not be solved analytically or the analytic solution is too costly to be practical. All models can be solved computationally and the result may not be the exact answer but it can be useful. George E. P. Box was right by saying All models are wrong, but some are useful. Since errors are inevitable a more practical question we ought to ask is how close the answer needs to be for it to be useful. In lots of engineering situations the only way to get the \"right answer\" is to use the following formula: right answer = wrong answer + corrections Missile Knows Where It Is is an audio click explaining how a missile guidance system can possibly work by repeatedly correcting it errors. Before we discuss how to manage errors lets explore the sources of errors.

# Introduction to Numerical Methods/Rounding Off Errors # Rounding Off Errors Learning objectives: - recognize the sources of overflow and underflow errors - convert between decimal representation and floating point representation - understand the IEEE 754 standard of a floating point representation on computers - calculate the machine epsilon of a representation. ## Integer Overflow (Error) How are integers represented on a computer? Most computers use the 2\'s complement representation. Assume we have 4 bits to store and operate on an integer we may end up with the following situation: ` 0111 (7)`\ `+0001 (1)`\ `-----`\ ` 1000 (-8)` The numbers in parentheses are the decimal value represented by the 2\'s complement binary integers. The result is obviously wrong because adding positive numbers should never result in a negative number. The reason for the error is that result exceeds the range of values the 4-bit can store with the 2\'s complement notation. The following example gives the wrong answer for the same reason. The leading 1 can not be stored. ` 1000 (-8)`\ `+1111 (-1)`\ `-----`\ `10111 (7)` ## Floating-point Underflow (Error) In math numbers have infinite precision, but numerals (representations of number) have finite precision. One third (1/3) can not be represented precisely in decimal or it would require a infinite number of digits, which is impossible. Similarly 0.2 can not be represented precisely in binary, which means its binary representation is not precise (an approximation). When numbers are computed/calculated on a computer, the representations of the numbers are being manipulated and the result will very likely be imprecise. This is an important limitation of computing. Essentially the computer must be considered a part of our model when we solve problems computationally. We must factor the computer in because it is a binary computer approximating base ten numbers. An floating-point underflow or underflow happens when the result of a calculation is too small to be stored. A underflow can be caused by the (negative) overflow of the exponent. : What is the binary representation of $11.1875_{10}$? ### Fixed-point Representation Any real number can be represented in binary as a fixed-point number. To convert the number from its decimal (base 10) representation to its binary representation we need to convert the integer part and the fractional part to binary separately, because different methods are required. Please check out the following resource on how to do that 1. With a fixed number of digits and a fixed decimal point the range of representable values is fixed. Given five digits as follows $nnn.nn_{10}$, we can represent positive values from $0.01_{10}$ to $999.99_{10}$. Using the following scientific notation $nnn \times 10^{nn}$ we can represent positive values ranging from $0.01_{10}$ to $99900_{10}$, which is much larger than that of the fixed-point representation. ### Floating-point Representation Given a fixed number of digits we can represent a larger range of values using the floating-point format. The IEEE 754 format is a international standard on floating-point representation of numbers in computers. A 32-bit floating point number (single precision) is represented using three parts as shown in the figure: : a sign bit, a (biased) exponent, and a fraction. !The number 0.15625 represented as a single-precision IEEE 754-1985 floating-point number. See text for explanation. The value represented by an IEEE 754 single precision floating point number can be calculated using the following formula: $$(-1)^{sign} \times 1.fraction \times 2^{exponent - 127}$$ For example to store in IEEE single precision floating point format $0.15625_{10}=0.00101_{2}=1.01_2 \times 2^{-3}$, we need to store a sign bit of $0$ (0 means positive and 1 means negative), a fraction of $.01$, and a biased exponent of $-3_{10}+127_{10}=124_{10}=1111100_2$. Because all numbers, except 0, will have a leading one in the binary \"scientific\" representation that one is not stored in IEEE 754 format to save one bit. We will say how the value 0 is represented in a moment. The biased exponent is just a clever way to use the available bits to represent more values and make number comparison faster. We will use 8-bit exponent as an example. In the figure above, we have 8-bit which can represent $2^8=256_{10}$ different things. The bit patterns have no intrinsic meaning, so we can use them to represent anything we want. The green part shows the values those bit patterns represent when they are treated as binary representations of unsigned integers. The problem is that we want to represent negative values as well. One easy solution is to treat the left most bit as the sign bit: 0 means positive and 1 means negative, which result in two zeros $+0$ and $-0$. The blue part shows what happens when we use the 2\'s complement scheme to represent both positive and negative values using the same set of bit patterns. Recall that the 2\'s complement scheme is often used to simply hardware design so that we can use addition to do subtraction: a - b is the same as a + (the 2\'s complement of -b). To get the 2\'s complement of a positive integer is to invert all the bits and add 1 to it. Now any subtraction can be done with a inversion and two additions. The problem with 2\'s complement representation is that a \"larger\" looking pattern does not necessarily represent a larger value. !This figure shows how the biased exponent for IEEE 754 works. The red part shows the biased exponent represented by the same set of bit patterns. As you can see a \"larger\" looking pattern always represent a larger value except for the all one patterns, which is used to represent a special value. The advantage of the biased exponent representation is that each value is represented by a unique pattern (no two zeros) and comparing floating point numbers is easier. The exponent is put before the fraction in IEEE 754 standard so that floating point numbers can be compared by treating their bit patterns as unsigned integers (much faster). The following table shows some special values represented by special bit patterns. biased expoent fraction numbers ---------------- ---------- -------------------- 00\...00 0 0 00\...00 nonzero denormalized 11\...11 0 +/- infinity 11\...11 nonzero NaN (Not a Number) Because the implicit/hidden 1 is always added to the fraction to get the represented value a special pattern is needed to represent the zero value. Now the result of a division by zero can be represented as +/- infinity (division by zero in integer operation will crash your program). $\sqrt{-4}$, $$ and $0/0$ can be represented as NaN, which helps debugging your programs. : What is the IEEE 754 floating-point representation of this number: $-2.340625 \times 10^1$ : What is the decimal equivalent of this IEEE 754 floating-point number: 1100 0000 1111 0000 0000 0000 0000 0000? : What is the largest IEEE 754 single precision floating-point number? What are the downsides of floating-point or scientific representation? With five digits we can represent $999.99_{10}$ precisely using fixed point notation. However, when we use the following scientific/floating-point notation $n.nn \times 10^{nn}$ the closest value we can represent is $9.99 \times 10^{02}$ and the error is $999.99-999=0.99$ - a loss of precision. ### Real v.s. Floating-point Number Lines This figure illustrates the different the number line for real numbers and that for floating point numbers. The following observations can be made: - The real number line is continuous, dense, and infinite. - The floating-point number (representation) line is discrete, sparse, and finite. - A group of real numbers are represented by the same floating-point number (an approximation). - The sizes of groups get larger and larger as the floating-point numbers get larger. Lets study a concrete example. With four decimal digits and a fixed point representation ($nnn.n$) we can represent 0, 0.1, 0.2, 0.3, \..., 999.8, 999.9 with equal distance between the consecutive numbers. With a floating-point representation ($+n.nn \times 10^{\pm n}$) , the smallest value we can represent is $1.00 \times 10^{-9}=0.\underbrace{0...0}_8 1$ and the largest representable value is $1.11 \times 10^{+9}=1110000000$. Now lets look at representable values by this floating-point number format around some points on the number line: - Next to 0: $1.00 \times 10^{-9}=0.\underbrace{0...0}_8 1, 1.01 \times 10^{-9}=0.\underbrace{0...0}_8 101, 1.02 \times 10^{-9}=0.\underbrace{0...0}_8 102, ...$ (the distance between consecutive numbers is 0.00000000001) - Next to 1: $1.00 \times 10^{0}=1, 1.01 \times 10^{0}=1.01, 1.02 \times 10^{0}=1.02, ...$ (the distance between consecutive numbers is 0.01) - Next to 10: $1.00 \times 10^{1}=10, 1.01 \times 10^{1}=10.1, 1.02 \times 10^{1}=10.2, ...$ (the distance between consecutive numbers is 0.1) - Next to 100: $1.00 \times 10^{2}=100, 1.01 \times 10^{2}=101, 1.02 \times 10^{2}=102, ...$ (the distance between consecutive numbers is 1) - Next to 1000: $1.00 \times 10^{3}=1000, 1.01 \times 10^{3}=1010, 1.02 \times 10^{3}=1020, ...$ (the distance between consecutive numbers is 10) As you can see not every real number can be represented using the floating-point format. The distribution of the representable values is not uniform: it is denser around smaller values and more sparse (spread out) around larger values, which means the larger a value we want to represent the less precise we can do it. What is the smallest IEEE 754 single precision number greater than 1? ### Machine Epsilon Machine epsilon is defined to be the smallest positive number which, when added to 1, gives a number different from 1. The machine epsilon for floating-point format is $b^{-(p-1)}$, where $b$ is the base (radix) and $p$ (precision) is the number of digits for the fraction plus one. What is the machine epsilon of IEEE 754 floating-point numbers?

# Introduction to Numerical Methods/Measuring Errors # Measuring Errors In this lesson we will learn how to quantify errors. Learning objectives - identify true and relative true errors - identify approximate and relative approximate errors - explain the relationship between the absolute relative approximate error and the number of significant digits - identify significant digits Reference : Chapter 1 of Holistic Numerical Methods ## True and Relative True Errors A true error ($E_t$) is defined as the difference between the true (exact) value and an approximate value. This type of error is only measurable when the true value is available. You might wonder why we would use an approximate value instead of the true value. One example would be when the true value cannot be represented precisely due to the notational system or the limit of the physical storage we use. `true error (`$E_t$`) = true value - approximate value` A true error doesn\'t signify how important an error is. For instance, a 0.1 pound error is a very small error when measuring a person\'s weight, but the same error can be disastrous when measuring the dosage of a medicine. Relative true error ($\epsilon_t$) is defined as the ratio between the true error and the true value. `relative true error (`$\epsilon_t$`)   = true error / true value` ## Approximate and Relative Approximate Errors Oftentimes the true value is unknown to us, especially in numerical computing. In this case we will have to quantify errors using approximate values only. When an iterative method is used, we get an approximate value at the end of each iteration. The approximate error ($E_a$) is defined as the difference between the present approximate value and the previous approximation (i.e. the change between the iterations). `approximate error (`$E_a$`) = present approximation – previous approximation` Similarly we can calculate the relative approximate error ($\epsilon_a$) by dividing the approximate error by the present approximate value. `relative approximate error (`$\epsilon_a$`)  = approximate error / present approximation` ## Relative Approximate Error and Significant Digits Assume our iterative method yield a better approximation as the iteration goes on. Oftentimes we can set an acceptable tolerance to stop the iteration at when the relative approximate error is small enough. We often set the tolerance in terms of the number of significant digits - the number of digits that carry meaning contributing to its precision. It corresponds to the number of digits in the scientific notation to represent a number\'s significand or mantissa. An approximate rule for minimizing the error is as follows: if the absolute relative approximate error is less than or equal to a predefined tolerance (usually in terms of the number of significant digits), then the acceptable error has been reached and no more iterations would be required. Given the absolute relative approximate error, we can derive the least number of digits that are significant using the same equation. $|\epsilon_a| \le 0.5 \times 10^{2-m}%$

# Introduction to Numerical Methods/Python Programming # Python Programming Objectives: - familiarize with the Python programming language and command-line interface - use correct control structures - write simple Python programs with correct syntax - import and use libraries Resources: - Introduction to Python for Computational Science and Engineering (A beginner's guide) - Google\'s Python class for developers - The Beginner\'s Python Tutorial - The Official Python Tutorial - The Official Python for Beginners - Introduction to Python - IPython Python is a scripting language. You can use the interactive Python console to write and execute code. After you log into a Unix/Linux system you can type the type the word \"python\" (with the quotes) to start the console and hit \^D (ctrl+D) will exit the console. This kind of interactivity makes it ideal for exploratory discovery - finding a solution by exploring and experimentation. ## REPL The Python console executes a Read-Eval-Print Loop (REPL), which means it prompts you for a expression/command and once you hit enter it will read your expression, evaluate it, print the value of the expression, and prompt you for the next expression. This makes it very easy to test a Python statement. You can use it as a calculator: ``` Python >>>1+2 3 >>>2**3 8 >>> # this is a comment ... >>> 2**0.5 1.4142135623730951 ``` ## Import Libraries Many useful functions have been implemented in libraries. To use the functions you need to import them so that their names are recognized. The dir() function prints a directory of objects (functions) available in a module: ``` python >>>import math >>>dir(math) ['__doc__', '__name__', '__package__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'hypot', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'modf', 'pi', 'pow', 'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'trunc'] >>> help(math.exp) Help on built-in function exp in module math: exp(...) exp(x) Return e raised to the power of x. >>> # this is similar to 2 ** 0.5 >>> math.sqrt(2) 1.4142135623730951 ``` The help() function can be used to find the meaning and the usage of an object from a library as shown in the previous code example. Note that you need to hit the letter Q to quit the help session to return to the Python console. ## Data Types Python is not a strongly typed language, which means you do not need to declare a specific data type for a variable. But data items associated with variables have types, which are implied - derived from the expression or the operation on the data items. Therefore the data type of a variable can change over time. The type() function will tell you the type of data stored in a variable. ``` Python >>> type(a) <type 'int'> >>> type(1) <type 'int'> >>> a = 1.0 >>> type(a) <type 'float'> >>> a = "one" >>> type(a) <type 'str'> >>> a = False >>> print a False >>> type(a) <type ’bool’> >>> a = 1 + 2j >>> type(a) <type 'complex'> >>> a = [1, 2, 3] >>> type(a) <type 'list'> ``` There are functions that convert between data types, e.g. int(), float(), str(), and list(). ``` Python >>> a = int("123") >>> a 123 >>> type(a) <type 'int'> >>> a = float("123.4") >>> a 123.4 >>> type(a) <type 'float'> >>> a = str(123.4) >>> a '123.4' >>> type(a) <type 'str'> >>> a = list("one two three") >>> a ['o', 'n', 'e', ' ', 't', 'w', 'o', ' ', 't', 'h', 'r', 'e', 'e'] >>> type(a) <type 'list'> ``` Data types get promoted automatically as necessary. ``` Python >>> import sys >>> sys.maxint 9223372036854775807 >>> type(sys.maxint) <type 'int'> >>> type(sys.maxint+1) <type 'long'> ``` In Python strings, lists and tuples are sequences. They can be indexed and sliced in the same way. A list in Python can contain data items of different type. ``` Python >>> range(10) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> for i in range(10): ... print i ** 2 ... 0 1 4 9 16 25 36 49 64 81 ``` ## Source Files In addition to write and running Python code directly in the console you can save your commands/statements in a file and run the whole file as a script using the Python interpreter. For example, in a shell command-line you can type the following to run your program/script called hello.py: ``` bash python hello.py ``` Indentation matters in Python because it is used for defining scopes, which eliminates the use of braces {}. Please make sure the code at the same level are indented the same amount represented by tab or space characters. ## Formatted Printing You can print numbers using a format string similar to the printf function in C. ``` Python >>>a = 0.1 >>> a 0.1 >>>print "%20.19f" % a 0.1000000000000000056 ``` This example show the limit of the floating point number representation. 1/10 can not be represented precisely because it is not a power of two. Even though the console prints a as 0.1 the underlying representation is almost 0.1. ## Numerical Computation ``` Python >>> import math >>> a = math.sqrt(2) >>> a 1.4142135623730951 >>> a ** 2 2.0000000000000004 ``` The following example will run forever till the result overflows the registers because x will never become exactly 1.0 because the representation of 0.1 is an approximation (with an error). ``` Python >>> x = 0.0 >>> while not x == 1.0: ... x = x + 0.1 ... print("x=%19.17g" % (x)) ... x=0.10000000000000001 x=0.20000000000000001 x=0.30000000000000004 x=0.40000000000000002 x= 0.5 x=0.59999999999999998 x=0.69999999999999996 ``` The moral of the lesson is: do not compare floating point numbers for strict equality. Alternatively we can calculate the distance between the two numbers and stop when the distance is short enough (less than a threshold). ``` Python >>> x = 0.0 >>> while abs(x - 1.0) > 1e-8: ... x = x + 0.1 ... print("x=%19.17g" % (x)) ... x=0.10000000000000001 x=0.20000000000000001 x=0.30000000000000004 x=0.40000000000000002 x= 0.5 x=0.59999999999999998 x=0.69999999999999996 x=0.79999999999999993 x=0.89999999999999991 x=0.99999999999999989 ``` If we know exactly how many iterations to perform we can use a for loop as shown below. Note that range(1, 11) =\> \[1, 2, 3, 4, 5, 6, 7, 8, 9, 10\]. ``` Python >>> for i in range(1, 11): ... x = i * 0.1 ... print("x=%19.17g" % (x)) ... x=0.10000000000000001 x=0.20000000000000001 x=0.30000000000000004 x=0.40000000000000002 x= 0.5 x=0.60000000000000009 x=0.70000000000000007 x=0.80000000000000004 x=0.90000000000000002 x= 1 ``` What does the following piece of code compute? Will the loop ever finish? Why? ``` Python >>> eps = 1.0 >>> while 1.0 + eps > 1.0: ... eps = eps / 2.0 ... >>> print eps 1.11022302463e-16 ``` The value eps has will always be a power of 2, therefore there will not be any rounding off errors. However, as the while loop continues eps gets smaller and smaller. Eventually eps become so small it becomes nothing comparing to 1.0, which means adding it to 1.0 will result in 1.0. Recall that the machine epsilon is the smallest value when added to 1.0 will result in value different than 1.0. If a number is less than the machine epsilon and it will cause no effect when it is added to 1.0. `sys.float_info` tells us that the machine epsilon is 2.220446049250313e-16, which is slightly less than 2x1.11022302463e-16=2.22044604926e-16. This is why when the loop ends eps equals 1.11022302463e-16. ## Symbolic Computation The SymPy library for Python allows us to manipulate variables symbolically (as symbols). The following code snippets demonstrates some basic functionality of SymPy. ``` python >>> from sympy import Symbol >>> x = Symbol('x'); >>> x+2*x+3*x 6*x >>> y=x+2*x+3*x >>> y 6*x >>> y.subs(x, 2) 12 >>> from sympy import diff >>> diff(y, x) 6 >>> from sympy import sin, cos >>> diff(sin(x), x) cos(x) >>> diff(cos(x), x) -sin(x) >>> y = 4 - 1/x >>> y.diff() x**(-2) >>> y.diff().subs(x, 0.5) 4.00000000000000 >>> from sympy import series >>> sin(x).series(x, 0) x - x**3/6 + x**5/120 + O(x**6) >>> sin(x).series(x, 0, 10) x - x**3/6 + x**5/120 - x**7/5040 + x**9/362880 + O(x**10) ``` ## Numpy Array and Linear Algebra Sources: - Numpy Tutorial - Scipy Tutorial A array in numpy is multidimensional table of elements of the same type. The elements are indexed by a tuple of positive integers. The name of the class for numpy arrays is ndarray, a.k.a array. Each array object has a number of attributes: - mdim: number of dimensions - shape: a tuple of integers indicating the size of the array in each dimension. A matrix with m rows and n columns will have (m, n) as its shape. - size: the total number elements in an array. - dtype: the type of elements in an array. You can install numpy and scipy on Ubuntu as follows: ``` shell sudo apt-get install python-numpy python-scipy python-matplotlib python-sympy ``` The elements in an array can be referenced using different syntax as shown in the examples below. ``` python >>> from numpy import * >>> a = arange(15).reshape(3, 5) >>> a array([[ 0, 1, 2, 3, 4], [ 5, 6, 7, 8, 9], [10, 11, 12, 13, 14]]) >>> type(a) <type 'numpy.ndarray'> >>> a.shape (3, 5) >>> (rows, cols) = a.shape >>> rows 3 >>> cols 5 >>> a.ndim 2 >>> a.size 15 >>> a[2, 3] 13 >>> a[2][3] 13 >>> a[-1] array([10, 11, 12, 13, 14]) >>> a[-2] array([5, 6, 7, 8, 9]) >>> a[-2:] array([[ 5, 6, 7, 8, 9], [10, 11, 12, 13, 14]]) >>> a[2:] array([[10, 11, 12, 13, 14]]) >>> a[:-3] array([], shape=(0, 5), dtype=int64) >>> a[:] array([[ 0, 1, 2, 3, 4], [ 5, 6, 7, 8, 9], [10, 11, 12, 13, 14]]) >>> a[1, ...] array([5, 6, 7, 8, 9]) >>> a[:, 0] array([ 0, 5, 10]) ``` A numpy array can be created from a regular Python list or tuple using the array function. The type of the array elements depends on that of the elements in the sequences. ``` python >>> a = array([[1, 2], [2, 3]]) >>> a array([[1, 2], [2, 3]]) >>> a = array(((4, 5), (6, 7))) >>> a array([[4, 5], [6, 7]]) >>> a.dtype dtype('int64') >>>>>> b = array([(1.2, 1.3), (1.4, 1.5)]) >>> b array([[ 1.2, 1.3], [ 1.4, 1.5]]) >>> b.dtype dtype('float64') ``` Numpy includes functions that create arrays with default values. The eye() function creates a identity matrix and the identity() performs a similar function. The copy function clones an array object includes the data it contains. ``` python >>> zeros((2, 3)) array([[ 0., 0., 0.], [ 0., 0., 0.]]) >>> ones((3, 4)) array([[ 1., 1., 1., 1.], [ 1., 1., 1., 1.], [ 1., 1., 1., 1.]]) >>> empty((2, 3)) array([[ 2.68156159e+154, 2.68156159e+154, 2.68156242e+154], [ 2.68156159e+154, 2.68156159e+154, 2.68156159e+154]]) >>> eye(3, 3) array([[ 1., 0., 0.], [ 0., 1., 0.], [ 0., 0., 1.]]) >>> identity(3, float) array([[ 1., 0., 0.], [ 0., 1., 0.], [ 0., 0., 1.]]) ``` Arithmetic operations on numpy arrays are element-wise operations. The product \* operator does a element-wise multiplication. The dot function performs matrix multiplications. ``` python >>> a array([[1, 2], [3, 4]]) >>> b = a.copy() >>> b array([[1, 2], [3, 4]]) >>> a*b array([[ 1, 4], [ 9, 16]]) >>> dot(a, b) array([[ 7, 10], [15, 22]]) ``` Numpy also includes a number of basic linear algebra functions. ``` python >>> from numpy.linalg import * >>> a = array([[1.0, 2.0], [3.0, 4.0]]) >>> a array([[ 1., 2.], [ 3., 4.]]) >>> a.transpose() array([[ 1., 3.], [ 2., 4.]]) >>> inv(a) array([[-2. , 1. ], [ 1.5, -0.5]]) >>> y = array([[5.], [7.]]) >>> solve(a, y) array([[-3.], [ 4.]]) ``` ## IPython Notebook The IPython Notebook is an interactive environment that allows coding, executing, documentation of your Python commands. Resources: - How to share an IPython notebook - A gallery of IPython notebooks - A matplotlib tutorial - Exploratory computing with Python

# Introduction to Numerical Methods/Numerical Differentiation # Numerical Differentiation Objectives: - explain the definitions of forward, backward, and center divided methods for numerical differentiation - find approximate values of the first derivative of continuous functions - reason about the accuracy of the numbers - find approximate values of the first derivative of discrete functions (given at discrete data points) Resources - numpy - Numerical Differentiation ## Forward Divided Difference Method $f^{'}(x) = \frac{f(x+h)-f(x)}{h} + O(h)$ The following code implements this method: ``` python from math import exp def forward_diff(f, x, h=0.0001): df = (f(x+h) - f(x))/h return df x = 0.5 df = forward_diff(exp, x) print 'first derivative = ', df print 'exp(', x, ') = ', exp(x) ``` ## Backward Divided Difference Method $f^{'}(x) = \frac{f(x)-f(x-h)}{h} + O(h)$ The following code implements this method: ``` python from math import exp def backward_diff(f, x, h=0.0001): df = (f(x) - f(x-h))/h return df x = 0.5 df = backward_diff(exp, x) print 'first derivative = ', df print 'exp(', x, ') = ', exp(x) ``` ## Center Divided Difference Method $f^{'}(x) = \frac{f(x+h)-f(x-h)}{2h} + O(h^{2})$ The following code implements this method: ``` python from math import exp def center_diff(f, x, h=0.0002): df = (f(x+h) - f(x-h))/(2.0*h) return df x = 0.5 df = center_diff(exp, x) print 'first derivative = ', df print 'exp(', x, ') = ', exp(x) ``` ## Second Derivative $f^{''}(x) = \frac{f(x+h) - 2 f(x) + f(x-h)}{h^2} + O(h^2)$ ## Taylor Series Taylor series allows us to taylor expand a function into an infinite series. If the function is infinitely differentiable at number h, we can use the Taylor series to approximate the function. We can derive the backward, the forward, and the center divided difference methods using Taylor series, which also give the quantitative estimate of the error in the approximation. $f(x+h) = f(x) + f^{'}(x)h + \frac{f^{(2)}(x)}{2!}h^{2}+\frac{f^{(3)}(x)}{3!}h^{3}+ \cdots \quad$ For instance the $sin(x)$ function can be approximated by the truncated Taylor series: $\sin\left( x \right) \approx x - \frac{x^3}{3!} + \frac{x^5}{5!} - \frac{x^7}{7!}\!$ !The sine function (blue) is closely approximated by its Taylor polynomial of degree 7 (pink) for a full period centered at the origin. is closely approximated by its Taylor polynomial of degree 7 (pink) for a full period centered at the origin."){width="400"} ## Effect of Step Size The following is a program that calculates the first derivative of $e^x$ at x=0.5 from the center divided difference formula using different values of h. The result shows that the approximation becomes more accurate (more significant digits) as step size becomes smaller but the when the step size becomes too small the rounding off error become significant. ``` python from math import exp def center_diff(f, x, h=0.0001): df = (f(x+h) - f(x-h))/(2.0*h) return df x = 0.5 df = center_diff(exp, x) print 'first derivative = ', df print 'exp(', x, ') = ', exp(x) h=0.125 for i in range(50): df = center_diff(exp, x, h) print "h=", h, "df=", df h = h/2.0 ```

# Introduction to Numerical Methods/Roots of Equations # Root Finding Objectives: - find solutions of quadratic and cubic equations - derive the formula and follow the algorithms for the solutions of non-linear equations using the following methods: - Bisection - Newton-Raphson - Secant - False-Position Resources - book chapters on various methods - Root Finding Algorithms - Bisection Method - Newton\'s Method - Secant Method - False-Position Method Roots (or Zeros) of a function f(x) are values of x that produces an output of 0. Roots can be real or complex numbers. Finding the root of $f(x)-g(x)$ is the same as solving the equation $f(x) = g(x)$. Solving an equation is finding the values that satisfy the condition specified by the equation. Lower degree (quadratic, cubic, and quartic) polynomials have closed-form solutions, but numerical methods may be easier to use. To solve a quadratic equation we can use the quadratic formula: $$ax^2+bx+c=0$$ $$x=\frac{-b\pm\sqrt{b^2-4ac\ }}{2a}$$ There are many root-find algorithms for solving equations numerically. ## Bisection Method The bisection method starts with two guesses and uses a binary search algorithm to improve the answers. If a function is continuous between the two initial guesses, the bisection method is guaranteed to converge. Here is a picture that illustrates the idea: ![A few steps of the bisection method applied over the starting range \[a1;b1\]. The bigger red dot is the root of the function.](Bisection_method.svg "A few steps of the bisection method applied over the starting range [a1;b1]. The bigger red dot is the root of the function."){width="400"} The advantages of bisection method include guaranteed convergence on continuous functions and the error is bounded. The disadvantages of bisection method include relatively slow convergence and non convergence on certain functions. ## Newton-Raphson Method Newton\'s Method (a.k.a Newton-Raphson Method) is an open method for solving non-linear equations. Contrary to a bracketing-method (e.g. bisection method) Newton\'s method needs one initial guess but it doesn\'t guarantee to converge. The basic idea of Newton\'s method is as follows: : Given a function *f* of \"x\" and a initial guess $x_{0}$ for the root of this function, a better guess $x_{1}$ is : $x_{1} = x_0 - \frac{f(x_0)}{f'(x_0)}$ : This is the Newton-Raphson formula. The following animation illustrates the method: !The function ƒ is shown in blue and the tangent line is in red. We see that xn+1 is a better approximation than xn for the root x of the function f.{width="400"} Lets solve the following equations using Newton\'s method: $$f(x)=x^{2}+2$$ $$f(x)=sin(x)=0$$ $$f(x)=a-\frac{1}{x}=0$$ ``` python from sympy import Symbol, diff, sin x = Symbol('x') y = sin(x) derivative = diff(y, x) ''' Solve f with initial guess g using Newton's method. Stop when the absolute relative approximate error is smaller than the tolerance or the max # iterations is reached. ''' def newton(f, derivative, g, tolerance, max_iteration): x_previous = g for i in range(max_iteration): x_current = x_previous - \ y.subs(x, x_previous).evalf()/derivative.subs(x, x_previous).evalf() error = abs((x_current-x_previous)/x_current) print "current x:", x_current, " error:", error x_previous = x_current if error < tolerance: break; newton(y, derivative, 5, 0.005, 15) ``` ``` bash $ python newton.py current x: 8.38051500624659 error: 0.403377955140806 current x: 10.1008867567293 error: 0.170318883075941 current x: 9.29864101772707 error: 0.0862755898924158 current x: 9.42545121429349 error: 0.0134540186653470 current x: 9.42477796066766 error: 7.14344283379346e-5 ``` ### Limitations of Newton\'s Method #### Division by Zero Because a division is involved in Newton\'s formula when the denominator becomes zero the method won\'t continue correctly. The following program demonstrates this issue. ``` python from sympy import Symbol, diff x = Symbol('x') y = 4 - 1.0/x derivative = diff(y, x) ''' Solve f with initial guess g using Newton's method. Stop when the absolute relative approximate error is smaller than the tolerance or the max # iterations is reached. ''' def newton(f, derivative, g, tolerance, max_iteration): x_previous = g for i in range(max_iteration): x_current = x_previous - \ y.subs(x, x_previous)/derivative.subs(x, x_previous) error = abs((x_current-x_previous)/x_current) print "current x:", x_current, " error:", error x_previous = x_current if error < tolerance: break; newton(y, derivative, 0.5, 0.005, 15) ``` Output: ``` bash $ python newton.py current x: 0 error: oo current x: nan error: nan current x: nan error: nan current x: nan error: nan current x: nan error: nan current x: nan error: nan ... ``` #### Divergence at Inflection Points When the initial guess is near a inflection point the method may diverge from the desired root. The following code using the same implementation of Newton\'s method (assume the newton function is imported) demonstrates divergence at an inflection point (x=0). ``` bash from sympy import Symbol, diff x = Symbol('x') y = (x-1)**3 + 0.5 derivative = diff(y, x) newton(y, derivative, 5, 0.005, 15) ``` ``` bash $ python newton.py current x: 3.65625000000000 error: 0.367521367521368 current x: 2.74721164936563 error: 0.330894909696631 current x: 2.11021215705302 error: 0.301865141940137 current x: 1.60492272680972 error: 0.314837232847788 current x: 0.947823175470885 error: 0.693272298403532 current x: -60.2548036313237 error: 1.01573025084058 current x: -39.8365801731819 error: 0.512549605648313 current x: -26.2244867245776 error: 0.519060433539279 current x: -17.1498826852607 error: 0.529135050417335 current x: -11.1004277326071 error: 0.544974941360464 current x: -7.06809009701998 error: 0.570498901434099 current x: -4.38128712811798 error: 0.613245124168828 current x: -2.59328016409484 error: 0.689476975445585 current x: -1.40842833626215 error: 0.841258157995587 current x: -0.634351912031382 error: 1.22026340513730 ``` ## Secant Method Secant method is similar to Newton\'s method in that it is an open method and use a intersection to get the improved estimate of the root. Secant method avoids calculating the first derivatives by estimating the derivative values using the slope of a secant line. The following figure illustrates the secant method with two initial guesses and two successive improved estimates: !The first two iterations of the secant method. The red curve shows the function f and the blue lines are the secants. For this particular case, the secant method will not converge.{width="400"} The formula for secant method is as follows: $$x_{i+1} =x_{i}-\frac{f(x_{i})(x_{i}-x_{i-1})}{f(x_{i})-f(x_{i-1})}$$ ## False-Position Method The false-position method is similar to the bisection method in that it requires two initial guesses (bracketing method). Instead of using the midpoint as the improved guess, the false-position method use the root of secant line that passes both end points. The following figure illustrates the idea. !The first two iterations of the false position method. The red curve shows the function f and the blue lines are the secants.{width="400"} The formula for false-position method is as follows: $$x_{r}=\frac{x_uf(x_l) - x_lf(x_u)}{f(x_l) - f(x_u)}$$

# Introduction to Numerical Methods/System of Linear Equations Objectives - define vector and matrix - add, subtract, and multiply matrices - find the transpose of a square matrix - define the inverse of a matrix - setup simultaneous linear equations in matrix form Resources - book chapter - Python programming # Vectors and Matrices A matrix) is a rectangular array of things, such as numbers, symbols, or expressions. Matrices are commonly used to express linear transformations and system of linear equations. A triangular matrix is a special type of square matrices. If all entries of A below the main diagonal are zero, A is called an upper triangular matrix#Diagonal_and_triangular_matrices). : $a_{ij}=0$ for all $i>j$ Similarly if all entries of A above the main diagonal are zero, A is called a lower triangular matrix. : $a_{ij}=0$ for all $i<j$ If all entries outside the main diagonal are zero, A is called a diagonal matrix. : $a_{ij}=0$ for all $i \ne j$ This matrix $$\begin{bmatrix} 1 & 4 & 2 \\ 0 & 3 & 4 \\ 0 & 0 & 1 \\ \end{bmatrix}$$ is upper triangular and this matrix $$\begin{bmatrix} 1 & 0 & 0 \\ 2 & 8 & 0 \\ 4 & 9 & 7 \\ \end{bmatrix}$$ is lower triangular. The identity matrix#Identity_matrix) of size n is the n-by-n matrix in which all the elements on the main diagonal are equal to 1 and all other elements are equal to 0. ## Matrix Multiplication  Matrix multiplication takes two matrices and produces another matrix. The rule for the operation is illustrated as follows: $$\overset{4\times 2 \text{ matrix}}{\begin{bmatrix} {\color{Brown}{a_{11}}} & {\color{Brown}{a_{12}}} \\ \cdot & \cdot \\ {\color{Orange}{a_{31}}} & {\color{Orange}{a_{32}}} \\ \cdot & \cdot \\ \end{bmatrix}} \overset{2\times 3\text{ matrix}}{\begin{bmatrix} \cdot & {\color{Plum}{b_{12}}} & {\color{Violet}{b_{13}}} \\ \cdot & {\color{Plum}{b_{22}}} & {\color{Violet}{b_{23}}} \\ \end{bmatrix}} = \overset{4\times 3\text{ matrix}}{\begin{bmatrix} \cdot & x_{12} & x_{13} \\ \cdot & \cdot & \cdot \\ \cdot & x_{32} & x_{33} \\ \cdot & \cdot & \cdot \\ \end{bmatrix}}$$ The values at the intersections marked with circles are: $$\begin{align} x_{12} & = {\color{Brown}{a_{11}}}{\color{Plum}{b_{12}}} + {\color{Brown}{a_{12}}}{\color{Plum}{b_{22}}} \\ x_{13} & = {\color{Brown}{a_{11}}}{\color{Violet}{b_{13}}} + {\color{Brown}{a_{12}}}{\color{Violet}{b_{23}}} \\ x_{32} & = {\color{Orange}{a_{31}}}{\color{Plum}{b_{12}}} + {\color{Orange}{a_{32}}}{\color{Plum}{b_{22}}} \\ x_{33} & = {\color{Orange}{a_{31}}}{\color{Violet}{b_{13}}} + {\color{Orange}{a_{32}}}{\color{Violet}{b_{23}}} \end{align}$$ ## Transpose of a Matrix The transpose of a matrix is defined as follows: The **transpose** of a matrix **A** is another matrix **A**^T^ created by any one of the following equivalent actions: - reflect **A** over its main diagonal (which runs from top-left to bottom-right) to obtain **A**^T^ - write the rows of **A** as the columns of **A**^T^ - write the columns of **A** as the rows of **A**^T^: The following figure illustrates the idea: !The transpose AT of a matrix A can be obtained by reflecting the elements along its main diagonal. Repeating the process on the transposed matrix returns the elements to their original position.{width="200"} ## Inverse of a Matrix An *n*-by-*n* square matrix **A** is called **invertible** if there exists an *n*-by-*n* square matrix **B** such that $$\mathbf{AB} = \mathbf{BA} = \mathbf{I}_n \$$ where **I**~*n*~ denotes the *n*-by-*n* identity matrix and the multiplication used is ordinary matrix multiplication. **B** is called the **\'\'inverse**\'\' of **A**, denoted by **A**^−1^. ## Represent System of Linear Equations in Matrix Form $$\begin{alignat}{7} 2x &&\; + \;&& y &&\; - \;&& z &&\; = \;&& 8 & \qquad (L_1) \\ -3x &&\; - \;&& y &&\; + \;&& 2z &&\; = \;&& -11 & \qquad (L_2) \\ -2x &&\; + \;&& y &&\; +\;&& 2z &&\; = \;&& -3 & \qquad (L_3) \end{alignat}$$ We can represent this system of linear equations in matrix form as shown below: $$\begin{bmatrix} 2x & + & y & - & z \\ -3x & - & y & + & 2z \\ -2x & + & y & + & 2z \end{bmatrix} = \begin{bmatrix} 8 \\ -11 \\ -3 \end{bmatrix}$$ Then we can use matrix multiplication to separate the variables. $$\begin{bmatrix} 2 & 1 & -1 \\ -3 & -1 & 2 \\ -2 & 1 & 2 \end{bmatrix} \begin{bmatrix} x \\ y \\ z \end{bmatrix} = \begin{bmatrix} 8 \\ -11 \\ -3 \end{bmatrix}$$ $$\begin{bmatrix} 25 & 5 & 1 \\ 64 & 8 & 1 \\ 144 & 12 & 1 \end{bmatrix} \begin{bmatrix} a_1 \\ a_2 \\ a_3 \end{bmatrix} = \begin{bmatrix} 106.8 \\ 177.2 \\ 279.2 \end{bmatrix}$$ The general matrix form for system of linear equations is as follows: $$A_{n \times n}X_{n \times 1} = C_{n \times 1}$$ Matrix A is the coefficient matrix. X is the solution vector (matrix) and C is the right hand side vector. If we multiply the inverse of A on bother sides we can see the solution is closely related to the inverse of A. $$\begin{alignat}{3} A^{-1}AX &&\; = \;&& A^{-1}C \\ IX &&\; = \;&& A^{-1}C \\ X &&\; = \;&& A^{-1}C \end{alignat}$$ # Gaussian Elimination Sources: - book chapter - Gaussian elimination is an algorithm for solving a system of linear equations, which is similar to finding the inverse of an invertible square matrix. The algorithm consists of a sequence of row reduction operations performed on the associated matrix of coefficients. There are three types of elementary row operations: - swapping two rows - multiplying a row by a non-zero constant - adding a multiple of one row to another row. For example, the first linear equation (L~1~, pivot equation) can be used to eliminate $x$ from the next two equations: : $$\begin{alignat}{7} 2x &&\; + \;&& y &&\; - \;&& z &&\; = \;&& 8 & \qquad (L_1) \\ -3x &&\; - \;&& y &&\; + \;&& 2z &&\; = \;&& -11 & \qquad (L_2) \\ -2x &&\; + \;&& y &&\; +\;&& 2z &&\; = \;&& -3 & \qquad (L_3) \end{alignat}$$ Then L~2~ (pivot equation) can be used to eliminate $y$ from L~3~. This process is called forward elimination. Now L~3~ can be solved with one unknown $z$, which can be used to substitute the $z$ in L~2~ to solve $y$. This process is called backward substitution. The algorithm for the Gaussian Elimination method can be implemented as follows: ``` python ''' x = gauss_elimin(a, b) Solves [a][x] = [b] by Gauss elimination. ''' from numpy import dot, array def gauss_elimin(a, b): (rows, cols) = a.shape # elimination phase for row in range(0, rows-1): # pivot equation/row for i in range(row+1, rows): if a[i, row] != 0.0: factor = a[i, row]/a[row, row] a[i, row+1:rows] = a[i, row+1:rows] - factor*a[row, row+1:rows] b[i] = b[i] - factor*b[row] # back substitution for k in range(rows-1,-1,-1): b[k] = (b[k] - dot(a[k, k+1:rows],b[k+1:rows]))/a[k, k] return b a = array([[3, 2.0], [-6, 6]]) b = array([7, 6]) print gauss_elimin(a, b) ``` # Gaussian Elimination with Partial Pivoting Gaussian elimination method is prone to round-off errors especially when a large number equations allows the error to accumulate. Another problem is the division by zero error. For example, the following matrix will break the method because the second pivot element is zero and the method requires the pivot elements to be non-zero. $$\left[ \begin{array}{ccc|c} 1 & -1 & 2 & 8 \\ 0 & 0 & -1 & -11 \\ 0 & 2 & -1 & -3 \end{array} \right]$$ Gaussian elimination with partial pivoting is similar to the Gaussian elimination except that in the $i$th forward elimination step the maximum of $|a_{i,i}|, |a_{i+1, i}|, ..., |a_{n, i}|$ is found and the row that contains the maximum will be swapped with the pivot row. The previous coefficient matrix would look as follows after the swaps. $$\left[ \begin{array}{ccc|c} 1 & -1 & 2 & 8 \\ 0 & 2 & -1 & -3 \\ 0 & 0 & -1 & -11 \end{array} \right]$$ # Gauss-Seidel Method Gaussian elimination is a direct (straightforward) method that transforms the original equations to equivalent ones that are easier to solve. Some systems of equations have no solution because for example the number of equations is less than the number of unknowns or one equation contradicts another equation. Gauss-Seidel method is an iterative (or indirect) method that starts with a guess at the solution and repeatedly refine the guess till it converges (the convergence criterion is met). This method is advantageous because it is more computationally efficient when the coefficient matrix is large and sparse and the round-off errors can be control by adjusting the error tolerance. The algorithm consists the following steps: 1. rewrite each equation for the corresponding unknowns, for example, the first equation is written with $x_1$ on the left-hand side and the second equation with $x_2$ on the left-hand side: $$x_i = \frac{c_{i}-\sum_{j=1, j \ne i}^{n}a_{ij}x_{j}}{a_{ii}}, i=1,2,3, ..., n.$$ 1. find initial guess for the $x_i$\'s. 2. use the rewritten equations to calculate the new estimates - always using the most recent estimates. 3. repeat the previous step till the largest absolute relative approximate error among all $x_i$\'s is less than the specified tolerance. The drawback of most iterative method is that it may not converge when the system of equations has a coefficient matrix that is not diagonally dominant. A system of equations where the coefficient matrix is diagonally dominant does always converge. The matrix A is diagonally dominant if $$|a_{ii}| \geq \sum_{j\neq i} |a_{ij}| \quad\text{for all } i,$$ and $$|a_{ii}| > \sum_{j\neq i} |a_{ij}| \quad\text{for at least one } i.$$ An implementation in Python using numpy simply iterates to produce the solution vector. # LU Decomposition LU decomposition factors the coefficient matrix A to the product of a lower triangular matrix and an upper triangular matrix: A = LU. The process of deriving L and U from A is called LU decomposition or LU factorization, which is similar to Gaussian elimination method. Once LU decomposition is done, we can use the system of linear equations represented by A using forward and back substitutions: $$\begin{alignat}{3} AX &&\; = \;&& C \\ LUX &&\; = \;&& C \\ L^{-1}LUX &&\; = \;&& L^{-1}C \\ UX &&\; = \;&& L^{-1}C\\ \end{alignat}$$ Let $L^{-1}C=Z$, which means $LZ=C$ and $Z$ can be solved by forward elimination. From $UX=Z$ we can solve X using backward elimination. One method of LU decomposition is similar to Gaussian elimination. For a $3 \times 3$: $$A= \begin{bmatrix} a_{11} & a_{12} & a_{13} \\ a_{21} & a_{22} & a_{23} \\ a_{31} & a_{32} & a_{33} \\ \end{bmatrix} = \begin{bmatrix} 1 & 0 & 0 \\ l_{21} & 1 & 0 \\ l_{31} & l_{32} & 1 \\ \end{bmatrix} \begin{bmatrix} u_{11} & u_{12} & u_{13} \\ 0 & u_{22} & u_{23} \\ 0 & 0 & u_{33} \\ \end{bmatrix}.$$ $$A= \begin{bmatrix} u_{11} & u_{12} & u_{13} \\ u_{11}l_{21} & u_{12}l_{21}+u_{22} & u_{13}l_{21}+u_{23} \\ u_{11}l_{31} & u_{12}l_{31}+u_{22}l_{32} & u_{13}l_{31}+u_{23}l_{32}+u_{33} \\ \end{bmatrix}$$ From the last matrix we can see to eliminate $a_{21}$ we need to multiple the first row of A by $l_{21}$ and similarly to eliminate $a_{31}$ by multiplying the first row by $l_{31}$. To calculate L we can simply record the multipliers used in the forward elimination steps and the matrix U is the same as the resultant upper triangular matrix from forward elimination. Sample code in Python ## Find the Inverse of a Matrix Finding the inverse of a matrix is a process related to solving the system of linear equations. If the inverse of a coefficient matrix is found then the system of equations represented by the coefficient matrix is solved. $$\begin{alignat}{3} AX &&\; = \;&& C \\ A^{-1}AX &&\; = \;&& A^{-1}C \\ X &&\; = \;&& A^{-1}C \\ \end{alignat}$$ One way to find the inverse of a matrix is to find each column of the inverse matrix separately by solving a system of linear equations. If $AB=I$ and $$A = \begin{bmatrix} a_{11} & a_{12} & a_{13} \\ a_{21} & a_{22} & a_{23} \\ a_{31} & a_{32} & a_{33} \end{bmatrix} \ B= \begin{bmatrix} b_{11} & b_{12} & b_{13} \\ b_{21} & b_{22} & b_{23} \\ b_{31} & b_{32} & b_{33} \end{bmatrix}$$ then $$A \begin{bmatrix} b_{11} \\ b_{21} \\ b_{31} \end{bmatrix} = LU \begin{bmatrix} b_{11} \\ b_{21} \\ b_{31} \end{bmatrix} = \begin{bmatrix} 1 \\ 0 \\ 0 \end{bmatrix}$$. We can calculate the first column of $B$ by solving a system of equations using the LU decomposition method. The rest of the columns can be calculated in a similar fashion. As you can see the LU decomposition method is advantageous the LU decomposition is performed once and the result is used many times, which lowers the computational complexity of the whole solution.

# Introduction to Numerical Methods/Interpolation Objectives - understand interpolation - derive Newton's divided difference method of interpolation - derive Lagrangian method of interpolation - apply the interpolation methods to solve problems - find derivatives and integrals of discrete functions using interpolation Resources - Direct method chapter - Newton\'s method chapter - Lagrange method chapter - Spline method chapter - A Chronology of Interpolation - NIST Digital Library of Mathematical Functions # Interpolation Interpolation is the process of deriving a simple function from a set of discrete data points so that the function passes through all the given data points (i.e. reproduces the data points exactly) and can be used to estimate data points in-between the given ones. It is necessary because in science and engineering we often need to deal with discrete experimental data. Interpolation is also used to simplify complicated functions by sampling data points and interpolating them using a simpler function. Polynomials are commonly used for interpolation because they are easier to evaluate, differentiate, and integrate - known as polynomial interpolation. It can be proven that given n+1 data points it is always possible to find a polynomial of order/degree n to pass through/reproduce the n+1 points. # Direct Method Given n+1 data points the direct method assumes the following polynomial: $$y=f(x)=a_0+a_{1}x+a_{2}x^{2} + ... + a_{n}x^{n}$$ With n+1 values for $x$ and the n+1 corresponding values for $y$ we can solve for $a_{0}, a_{1}, ..., a_{n}$ by solving the n+1 simultaneous linear equations, which is known as the direct method. For example, given two data points $(x_{0}, y_{0})$ and $(x_{1}, y_{1})$ we can use a linear function $y=f(x)=a_{0}+a_{1}x$ to pass through the two data points: $$y_{0}=a_{0}+a_{1}x_{0}$$ $$y_{1}=a_{0}+a_{1}x_{1}$$ Once we solve for $a_{0}$and $a_{1}$ (the coefficients of $f(x)$) we can use the function as the basis for interpolation - estimating the missing data points in-between. # Newton\'s Method In Newton\'s method the interpolating function is written in Newton polynomial(a.k.a Newton form). For example, given one data point $(x_{0}, y_{0})$ we can only derive a polynomial of order zero: $y=f(x)=a_{0}$. Because $f(x_{0})=y_{0}$ the newton polynomial of order zero is $y=f(x)=y_{0}$. Given two data points we can write Newton\'s polynomial in the form of $y=f(x)=a_{0}+a_{1}(x-x_{0})$. Plugging in the two data points gives us $$a_{0}=y_{0}$$ $$a_{1}=\frac{y_{1}-y_{0}}{x_{1}-x_{0}}$$ Obviously this function passes through both data points (i.e. accurately reproduces the two data points). The first derivative of the function at $x=x_{0}$ is $f'(x_{0})=a_{1}=\frac{y_{1}-y_{0}}{x_{1}-x_{0}}$, which matches the result from the forward divided difference method. Given three data points we can write Newton\'s polynomial in the form of $$y=f(x)=a_{0}+a_{1}(x-x_{0})+a_{2}(x-x_{1})(x-x_{0})$$ Plugging in the three data points gives us : As $y_{0}=a_{0}$ we get $a_{0}=y_{0}$ : As $y_{1}=a_{0}+a_{1}(x_{1}-x_{0})$ we get $a_{1}=\frac{y_{1}-y_{0}}{x_{1}-x_{0}}$ : As $y_{2}=a_{0}+a_{1}(x_{2}-x_{0})+a_{2}(x_{2}-x_{1})(x_{2}-x_{0})$ : we get : `<math>`{=html} \\begin{align} a\_{2}&=\\frac{y\_{2}-a\_{0}-a\_{1}(x\_{2}-x\_{0})}{(x\_{2}-x\_{1})(x\_{2}-x\_{0})}\\\\ `      &=\frac{y_{2}-y_{0}-\frac{y_{1}-y_{0}}{x_{1}-x_{0}}(x_{2}-x_{0})}{(x_{2}-x_{1})(x_{2}-x_{0})}\\`\ `      &=\frac{y_{2}-y_{0}-\frac{y_{1}-y_{0}}{x_{1}-x_{0}}((x_{2}-x_{1})+(x_{1}-x_{0}))}{(x_{2}-x_{1})(x_{2}-x_{0})}\\`\ `      &=\frac{y_{2}-y_{0}-\frac{y_{1}-y_{0}}{x_{1}-x_{0}}(x_{2}-x_{1}) - (y_{1}-y_{0})}{(x_{2}-x_{1})(x_{2}-x_{0})}\\`\ `      &=\frac{y_{2}-y_{1}-\frac{y_{1}-y_{0}}{x_{1}-x_{0}}(x_{2}-x_{1})}{(x_{2}-x_{1})(x_{2}-x_{0})}\\`\ `      &=\frac{\frac{y_{2}-y_{1}}{x_{2}-x_{1}}-\frac{y_{1}-y_{0}}{x_{1}-x_{0}}}{x_{2}-x_{0}}\\` \\end{align} `</math>`{=html} This third degree polynomial function passes all three data points (the second derivative and the third derivative at $x_{0}$ and $x_{1}$match that from the divided difference method). From the two examples we can see the coefficients of a Newton polynomial follow a pattern known as divided difference. For example$a_{1}=\frac{y_{1}-y_{0}}{x_{1}-x_{0}}$ is called divided difference of order 1 (denoted as $f[x_{0}, x_{1}]$) because it depends on $x_{0}$ and $x_{1}$. The divided difference notation can be used to write the general order (form) Newton polynomial: $$f(x)=f[x_{0}]+fx_{0}, x_{1}+fx_{0}, x_{1}, x_{2}(x-x_{1})+...$$ $$+fx_{0}, x_{1}, x_{2}, ...,x_{n}(x-x_{1})(x-x_{2})...(x-x_{n-1})$$ Where $$a_{0}=f[x_{0}]=y_{0}$$ because $f[x_{i}]=y_{i}$ by definition $$a_{1}=f[x_{0}, x_{1}]=\frac{f[x_{1}]-f[x_{0}]}{x_{1}-x_{0}}$$ $$a_{2}=f[x_{0}, x_{1}, x_{2}]=\frac{f[x_{1}, x_{2}]-f[x_{0}, x_{1}]}{x_{2}-x_{0}}$$ $$\dots$$ $$a_{k}=f[x_{0}, x_{1}, x_{2}, \dots, x_{k-1}, x_{k}]=\frac{f[x_{1}, x_{2}, \dots, x_{k-1}, x_{k}]-f[x_{0}, x_{1}, x_{2}, \dots, x_{k-1}]}{x_{k}-x_{0}}$$ We can calculate the coefficients of Newton polynomial using the following table $$\begin{matrix} x_0 & y_0 = f[x_0] & & & \\ & & f[x_0,x_1] & & \\ x_1 & y_1 = f[x_1] & & f[x_0,x_1,x_2] & \\ & & f[x_1,x_2] & & f[x_0,x_1,x_2,x_3]\\ x_2 & y_2 = f[x_2] & & f[x_1,x_2,x_3] & \\ & & f[x_2,x_3] & & \\ x_3 & y_3 = f[x_3] & & & \\ \end{matrix}$$ because $$f[x_{i}]=y_{i}$$ $$f[x_{i}, x_{i+1}]=\frac{f[x_{i+1}]-f[x_{i}]}{x_{i+1}-x_{i}}$$ The following figures shows the dependency between the divided differences: !A table for solving the coefficients of a Newton\'s polynomial.{width="800"} For example, given data points $(1, 6)$, $(2, 11)$, $(3, 18)$, and $(4, 27)$ we can draw the following table: $$\begin{array}{|c||c|c|c|c|c|} i & x_{i} & y_{i} & f[x_i,x_{i+1}] & f[x_i, x_{i+1}, x_{i+2}] & f[x_i, x_{i+1}, x_{i+2}, x_{i+3}]\\ \hline 0 & x_{0}=1 & \begin{align}y_0&=f[x_0]\\ &=6\end{align} & \begin{align}f[x_{0}, x_{1}] &=\frac{f[x_{1}]-f[x_{0}]}{x_{1}-x_{0}}\\ &=\frac{11-6}{2-1}\\ &=5 \end{align}& \begin{align} f[x_{0},x_{1}, x_{2}]&=\frac{f[x_{1}, x_{2}]-f[x_{0},x_{1}]}{x_{2}-x_{0}}\\ &=\frac{7-5}{3-1} \\ &=1 \end{align}& \begin{align}&f[x_{0},x_{1},x_{2},x_{3}]\\ &=\frac{f[x_{1},x_{2},x_{3}]-f[x_{0},x_{1},x_{2}]}{x_{3}-x_{0}}\\ &=\frac{1-1}{4-1}\\ &=0\end{align}\\ \hline 1 & x_{1}=2 & \begin{align}y_1&=f[x_1]\\ &=11\end{align} & \begin{align}f[x_{1}, x_{2}] &=\frac{f[x_{2}]-f[x_1]}{x_{2}-x_{1}}\\ &=\frac{18-11}{3-2}\\ &=7 \end{align} & \begin{align} f[x_{1},x_{2}, x_{3}]&=\frac{f[x_{2}, x_{3}]-f[x_{1},x_{2}]}{x_{3}-x_{1}}\\ &=\frac{9-7}{4-2} \\ &=1 \end{align}& \\ \hline 2 & x_{2}=3 & \begin{align}y_2&=f[x_2]\\ &=18\end{align} & \begin{align}f[x_{2}, x_{3}] &=\frac{f[x_{3}]-f[x_2]}{x_{3}-x_{2}}\\ &=\frac{27-18}{4-3}\\ &=9 \end{align} & & \\ \hline 3 & x_{3}=4 & \begin{align}y_3&=f[x_3]\\ &=27\end{align} & & & \\ \end{array}$$ The four data points lie on a polynomial of order 2, which is why the coefficient $a_{3}$($f[x_{0},x_{1},x_{2},x_{3}]$) is zero. Given $[a_{0}, a_{1}, a_{2}] = [6, 5, 1]$ the result polynomial is: $$\begin{align}y&=a_{0}+a_{1}(x-x_{0})+a_{2}(x-x_{1})(x-x_{0})\\ &=6+5\times(x-1)+1\times(x-2)(x-1)\\ &=x^{2}+2x+3\end{align}$$ Once the coefficients of a Newton\'s polynomial are solved, we can evaluate the polynomial function for any $x$. A Newton polynomial is often rewritten in a nested form: $$f(x)=a_{0}+(x-x_{0})(a_{1}+(x-x_{1})(a_{2}+(x-x_{2})(a_{3}+...+a_{n}(x-x_{n-1}))...)$$, because this nested form of interpolating polynomial is easier to evaluate because x only appears in the function n times. For example, the nested form of a third order interpolating polynomial is: $$f(x)=a_{0}+(x-x_{0})(a_{1}+(x-x_{1})(a_{2} +(x-x_{2})a_{3}))$$ The algorithm of Newton\'s method and its implementation can be found in this Jupyter notebook. # Lagrange Form Lagrange polynomial is another form used for polynomial interpolation. It is called a form because with a given set of distinct points the interpolating polynomial is unique. We can arrive at the same polynomial through different methods. The Lagrange form specifies the interpolation polynomial as: $$f_{n}(x) := \sum_{i=0}^{n}L_i(x)f(x_{i})$$ $$L_i(x) := \prod_{\begin{smallmatrix}0\le m\le n\\ m\neq i\end{smallmatrix}} \frac{x-x_m}{x_i-x_m} = \frac{(x-x_0)}{(x_i-x_0)} \cdots \frac{(x-x_{i-1})}{(x_i-x_{i-1})} \frac{(x-x_{i+1})}{(x_i-x_{i+1})} \cdots \frac{(x-x_n)}{(x_i-x_n)},$$ where $n$ is the order of the polynomial. For example, given two data points we get $n=1$ and $$\begin{align} f(x)&=L_{0}f(x_{0})+L_{1}f(x_{1})\\ &=\frac{x-x_{1}}{x_{0}-x_{1}}f(x_{0})+\frac{x-x_{0}}{x_{1}-x_{0}}f(x_{1})\\ \end{align}$$ Obviously the function curve passes both data points. The first derivative also matches that of the divided difference method: $$\begin{align} f'(x)&=\frac{f(x_{0})}{x_{0}-x_{1}}+\frac{f(x_{1})}{x_{1}-x_{0}}\\ &=\frac{f(x_{1})-f(x_{0})}{x_{1}-x_{0}}\\ \end{align}$$ # Spline Interpolation Spline interpolation uses a number of polynomial functions to interpolate a set of data points with each polynomial for two adjacent data points. The Spline method is necessary because often times when the order of the polynomial become large polynomial interpolation shows oscillatory behavior (instability known as Runge\'s phenomenon). The following iPython notebook shows an example that suffers this issue: 1 Spline method is not another method for finding polynomial interpolation of a discrete function, but instead it results in a piecewise polynomial (splines) in order to avoid the oscillatory behavior. The most common spline interpolations are linear, quadratic, and cubic splines. Linear interpolation uses lines to connect each pair of consecutive data points resulting in a piecewise interpolation. !Interpolation example linear{width="400"} A quadratic spline#Examples) uses a quadratic polynomial to connect consecutive data points. !Quadratic spline six segments{width="400"} A function f(x) is a quadratic spline if the following conditions are true: 1. The domain of $f(x)$ is an interval \[a, b\]. 2. $f(x)$ and $f'(x)$ are continuous on \[a, b\]. 3. The data points $x_{i}$ such that $a=x_{0} <x_{1} <\dots<x_{n} =b$ and $f(x)$ is a polynomial of order at most 2 on each subinterval $[x_{i} , x_{i +1}]$.

# Introduction to Numerical Methods/Regression Objectives - define linear and non-linear regression models. - reason about goodness of fit criteria. - derive coefficients of linear regression models. - derive coefficients of non-linear regression models Resources - textbook chapter on linear regression - non-linear regression \_\_TOC\_\_ Regression is different from interpolation in that it allows us to approximate overdetermined system, which has more equations than unknowns. This is useful when the exact solution is too expensive or unnecessary due to errors in the data, such as measurement errors or random noise. # Linear Regression Linear regression finds a linear function that most nearly passes through the given data points - the regression (function) line best fits the data. We must define our metric for measuring the goodness of fit. If all data points lie on the function it is a perfect fit, otherwise there are errors in the function representation of the data. We can measure the deviations of the data points from the function. As shown in the following example (source) neither the sum of errors nor the sum of the absolute errors is a good metric. The data include four points (2, 4), (3, 6), (2, 6), and (3, 8). We use a straight line to fit the data. Two possible solutions are shown in iPython notebook (Example 1). ## Straight Line (one variable) Lets look at the example of fitting a straight line to data, i.e. find a linear regression model with one variable that represents the data. The function is $f(x)=a_{0}+a_{1}x$ and the (cost) sum of squares of errors function to be minimized is $$S(a_0,a_1)=\sum_{i=1}^{n}{(y_i-f(x_i))}^2=\sum_{i=1}^{n}{[y_i-a_{0}-a_{1}x_{i}]}^2$$ We can minimize the $S(a,b)$ function by setting the gradient to zero. Because the function has two parameters (variables) there are two gradient equations: $$\frac{\partial S}{\partial a_{0}}=2\sum_{i=1}^{n}(y_{i}-a_{0}-a_{1}x_{i})(-1)=0$$ $$\frac{\partial S}{\partial a_{1}}=2\sum_{i=1}^{n}(y_{i}-a_{0}-a_{1}x_{i})(-x_{i})=0$$ The partial derivative represents the rate of change of the function value with respect to an independent variable while all other variables being held fixed. When a partial derivative becomes zero it means the change has stopped. This implies that we have reach a minimum or a maximum, which can be determined by checking the sign of the 2nd derivative. Let\'s consider: $$\begin{align} -\sum_{i=1}^{n}y_{i}+\sum_{i=1}^{n}a_{0}+\sum_{i=1}^{n}a_{1}x_{i}&=0\\ -\sum_{i=1}^{n}y_{i}+na_0+\sum_{i=1}^{n}a_{1}x_{i}&=0\\ \end{align}$$ and $$\begin{align} -\sum_{i=1}^{n}y_{i}x_{i}+\sum_{i=1}^{n}a_{0}x_{i}+\sum_{i=1}^{n}a_{1}x_{i}^{2}&=0\\ \end{align}$$, we can derive $$\begin{align} na_{0}+a_{1}\sum_{i=1}^{n}x_{i}&=\sum_{i=1}^{n}y_{i}\\ a_{0}\sum_{i=1}^{n}x_{i}+a_{1}\sum_{i=1}^{n}x_{i}^2&=\sum_{i=1}^{n}x_{i}y_{i} \end{align}$$. Therefore, we can calculate $a_{0}$ and $a_{1}$ as follows: $$a_{1}=\frac{n\sum_{i=1}^{n}x_{i}y_{i}-\sum_{i=1}^{n}x_{i}\sum_{i=1}^{n}y_{i}}{n\sum_{i=1}^{n}x_{i}^{2} - (\sum_{i=1}^{n}x_{i})^{2}}$$ $$a_{0}=\frac{\sum_{i=1}^{n}x_{i}^{2}\sum_{i=1}^{n}y_{i}-\sum_{i=1}^{n}x_{i}\sum_{i=1}^{n}x_{i}y_{i}}{n\sum_{i=1}^{n}x_{i}^2-(\sum_{i=1}^{n}x_{i})^2}$$. Given the following definitions: $$\begin{align} \bar{x}&=\frac{\sum_{i=1}^{n}x_{i}}{n}\\ \bar{y}&=\frac{\sum_{i=1}^{n}y_{i}}{n}\\ S_{1}&=\sum_{i=1}^{n}x_{i}y_{i}-n\bar{x}\bar{y}\\ S_{2}&=\sum_{i=1}^{n}x_{i}^{2}-n\bar{x}^2 \end{align}$$ we get $$a_{1}=\frac{S1}{S2}$$ $$a_{0}=\bar{y}-a_{1}\bar{x}$$. # Multi-linear Regression A linear regression line models the relationship between independent variables (predictors) and a response variable. Once the model is built it can be used for prediction. In almost all real-world regression models multiple predictors (independent variables) are involved to model multiple factors that affect the response (dependent variable) from the system. Such models are known as multi-linear models. ## Normal Equation Another way to find the parameters of a regression model that minimize the sum of squares of errors is to solve the corresponding normal equation. Given a matrix equation $Ax=b$, the normal equation is that which minimizes the sum of the square differences between the left and right sides: $$A^{T}Ax=A^{T}b$$. Given a hypothesized regression model and a dataset we can construct the left side to express the values our model would predict using the data. A should be a $m \times n$ matrix where each row represents one of the $m$ data points (samples) and each column of each row represents a multiplier for each of the $n$ parameters. $x$ is a $1 \times n$ column vector for the unknown parameters. The right side $b$ should be a $1 \times m$ column vector that stores the corresponding $y$ values for the data points. Recall the example that fits a straight line (model) $y=a_{0}+a_{1}x$ to the following data points. --- --- x y 2 4 2 6 3 6 3 8 --- --- : data points We can construct the left side of the matrix equation $Ax=b$ as: $$Ax=\underbrace{ \begin{bmatrix} 1 & 2 \\ 1 & 2 \\ 1 & 3 \\ 1 & 3 \end{bmatrix}}_{A} \underbrace{ \begin{bmatrix} a_{0} \\ a_{1} \end{bmatrix}}_{x}$$, which should result in a column vector of the values our model would predict: $$\begin{bmatrix} a_{0}+2a_{1}\\ a_{0}+2a_{1}\\ a_{0}+3a_{1}\\ a_{0}+3a_{1} \end{bmatrix}$$. The right side should be a vector of corresponding values from the data points: : `<math>`{=html} b= \\begin{bmatrix} 4 \\\\ 6 \\\\ 6 \\\\ 8 \\end{bmatrix}. `</math>`{=html} To minimize the sum of square differences between the left and the right sides is equivalent to solving the following normal equation: $$A^{T}Ax=A^{T}b$$. The normal equation for our example is: $$\underbrace{ \begin{bmatrix} 1 & 1 & 1 & 1 \\ 2 & 2 & 3 & 3 \end{bmatrix}}_{A^{T}} \underbrace{ \begin{bmatrix} 1 & 2 \\ 1 & 2 \\ 1 & 3 \\ 1 & 3 \end{bmatrix}}_{A} \underbrace{ \begin{bmatrix} a_{0} \\ a_{1} \end{bmatrix}}_{x} = \underbrace{ \begin{bmatrix} 1 & 1 & 1 & 1 \\ 2 & 2 & 3 & 3 \end{bmatrix}}_{A^T} \underbrace{ \begin{bmatrix} 4 \\ 6 \\ 6 \\ 8 \end{bmatrix}}_{b}$$ If $A^{T}A$ is invertible, the solution vector should be unique and give us the values for the parameters $a_{0}$ and $a_{1}$ that minimizes the difference between the model and the data, i.e. the model best fits the data. When we determine a regression line of the form $y=a_{0}+a_{1}x$ that fits four data points, we have four equations that can be written as $Ax=y$ or $$\begin{bmatrix} 1 & x^{(1)} \\ 1 & x^{(2)} \\ 1 & x^{(3)} \\ 1 & x^{(4)} \end{bmatrix} \begin{bmatrix} a_{0} \\ a_{1} \end{bmatrix} = \begin{bmatrix} y^{(0)} \\ y^{(1)} \\ y^{(2)} \\ y^{(3)} \end{bmatrix}$$ To solve the model we are effectively minimizing $||Ax-b||$. $y=a_{0}+a_{1}x+a_{2}x^2$ $y=a_{0}+a_{1}sin(x)$ $y=a_{0}e^{-a_{1}x}$ The method introduced in the previous section boils down to solving a system of linear equations with two unknowns in the following form: $$\begin{bmatrix} p & q \\ r & s \end{bmatrix} \begin{bmatrix} a_{0} \\ a_{1} \end{bmatrix} = \begin{bmatrix} u \\ v \end{bmatrix}$$ It is not hard to imagine that with $n$ independent variables and $m$ data points we can derive a similar system of linear equations with $n$ unknowns. Then numerical methods, such as Gaussian elimination can be used to solve for the parameters. We could also use normal equations and matrix operations to solve for the parameters. ## Gradient Descent Gradient descent is a method for finding local minimum of a function. The method is based on the concept of Gradient, which is a generalization of the derivative of a function in one dimension (slope or tangent) to a function in multiple dimensions. For a function with $n$ variables the gradient at a particular point is a vector whose components are the $n$ partial derivatives of the function. The following figure shows the gradient of a function. !The gradient of the function −(cos^2^*x* + cos^2^*y*)^2^}} depicted as a projected vector field on the bottom plane.2}} depicted as a projected vector field on the bottom plane."){width="400"} Because the gradient points in the direction of the greatest rate of increase of the function and its magnitude is the slope of the graph in that direction, we can start at a random point and take steps proportional to the negative of the gradient of the current point to find the local minimum - gradient decent or steepest descent. Recall that gradients in multiple dimensions are partial derivatives of the cost function with respect to the parameters for the dimensions: $$S(a_0,a_1, \cdots, a_n)=\sum_{i=1}^{n}{(y^{(i)}-f(x_1^{(i)},x_2^{(i)},\cdots, x_n^{(i)}))}^2=\sum_{i=1}^{n}{(y^{(i)}-a_{0}-a_{1}x_{1}^{(i)}-\cdots-a_{n}x_{n}^{(i)})}^2$$ $$\frac{\partial S}{\partial a_{0}}=2\sum_{i=1}^{n}(y^{(i)}-a_{0}-a_{1}x_{1}^{(i)}-a_{2}x_{2}^{(i)}-\dots-a_{n}x_{n}^{(i)})(-1)$$ $$\frac{\partial S}{\partial a_{1}}=2\sum_{i=1}^{n}(y^{(i)}-a_{0}-a_{1}x_{1}^{(i)}-a_{2}x_{2}^{(i)}-\dots-a_{n}x_{n}^{(i)})(-x_{1}^{(i)})$$ $$\cdots$$ $$\frac{\partial S}{\partial a_{n}}=2\sum_{i=1}^{n}(y^{(i)}-a_{0}-a_{1}x_{1}^{(i)}-a_{2}x_{2}^{(i)}-\dots-a_{n}x_{n}^{(i)})(-x_{n}^{(i)})$$ Gradient descent can be used to solve non-linear regression models. # Non-linear Regression Non-linear regression models the relationship in observational data by a function which is a nonlinear combination of the model parameters and depends on one or more independent variables. Some nonlinear regression problems can be transformed to a linear domain. For example, solving $y=a_{0}+a_{1}x+a_{2}x^{2}$ is equivalent to solving $y=a_{0}+a_{1}x+a_{2}z$ where $z=x^{2}$. Here is an example of a gradient descent solution to a non-linear regression model.

# Introduction to Numerical Methods/Integration Resources: - notes on Trapezoidal Rule - notes on Simpson's 1/3 Rule - notes on Romberg Rule - notes on integrating discrete functions \_\_TOC\_\_ The fundamental theorem of calculus states that differentiation and integration are inverse operations: when a continuous function is first integrated and then differentiated or vice versa, the original function will be obtained. However the integrand $f(x)$ may be known only at certain points, such as data measured from an experiment or from sampling, which is common in computer applications. Sometimes even though the formula for an integrand is known, it is difficult or impossible to find the antiderivative in an elementary function form, e.g the antiderivative of $f(x)=exp(-x^2)$, cannot be written in elementary form. Computing a numerical integration (approximation) can be easier than solving the integral symbolically. <http://mathworld.wolfram.com/NumericalIntegration.html> # Trapezoidal Rule The trapezoidal rule approximates the area under the curve of the function $f(x)$ as a trapezoid: $$\int_{a}^{b} f(x)\, dx \approx (b-a) \left[\frac{f(a) + f(b)}{2} \right].$$ Effectively we are estimating the average function value using two samples. The trapezoidal rule belongs to a class of formulas called Newton--Cotes formulas (evaluating the integrand at equally spaced points). Another way to look at it is that trapezoidal rule approximates the integrand by a first order polynomial and then integrating the polynomial over interval of integration as illustrated in the figure. !The function *f*(*x*) (in blue) is approximated by a linear function (in red). (in blue) is approximated by a linear function (in red).") The multiple segment Trapezoidal Rule can be used to improve the accuracy of the approximation by using a sequence of samples: !Illustration of trapezoidal rule used on a sequence of samples (in this case, a non-uniform grid)..") Lets look at an example that approximate the area of a swimming pool. # Simpson\'s 1/3 Rule Simpson\'s rule is a numerical integration method that uses the following approximation formula: $$\int_{a}^{b} f(x) \, dx \approx \tfrac{b-a}{6}\left[f(a) + 4f\left(\tfrac{a+b}{2}\right)+f(b)\right].$$ The Simpson\'s rule can be derived by approximating the integrand as a second order polynomial (quadratic) function as shown in the figure: !Simpson\'s rule can be derived by approximating the integrand *f*(*x*) (in blue) by the quadratic interpolant *P*(*x*) (in red). (in blue) by the quadratic interpolant P(x) (in red).") $$P(x) = f(a) \tfrac{(x-m)(x-b)}{(a-m)(a-b)} + f(m) \tfrac{(x-a)(x-b)}{(m-a)(m-b)} + f(b) \tfrac{(x-a)(x-x2-x3....-m)}{(b-a)(b-m)}.$$ Another way to look at it is that Simpson's rule is an extension of Trapezoidal rule where the integrand is approximated by a second order polynomial. A sample implementation of Simpson\'s rule is available. # Romberg\'s Rule The true errors result from the trapezoidal rule is negatively proportional to the number of segments cubed. Richardson extrapolation is a sequence acceleration method for getting a better estimate by refining such errors. A practical application of Richardson extrapolation is Romberg integration. A geometric example is available. <http://www.oscer.ou.edu/AreaUnderCurveExample.pdf> # Integration of Discrete Functions The trapezoidal rule with unequal segments can be used to integrate discrete functions, which are defined by a set of data points. Interpolation methods, such as polynomial interpolation and spline interpolation, can be applied to find the function profile, which can be integrated as a continuous function. In addition linear regression can also be used for the same purpose. # Multi-dimensional Integration Monte Carlo method is class of computational methods that uses repeated random sampling to obtain numerical results. To estimate multi-dimensional integrals Monte Carlo method may yield greater accuracy for the same number of function evaluations than repeated integrations using one-dimensional methods. For example we can estimate the value of $\pi$ as shown in the example. !Monte Carlo method applied to approximating the value of . After placing 30000 random points, the estimate for is within 0.07% of the actual value. This happens with an approximate probability of 20%. The path tracing algorithm in computer graphics applies the Monte Carlo method to render 3D scenes. It uses repeated random sampling to achieve more accurate estimation making it one of the most physically accurate 3D graphics rendering methods in existence source.

# Introduction to Numerical Methods/Ordinary Differential Equations Resources: - notes on Ordinary Differential Equations - notes on Euler\'s Method - notes on Runge-Kutta 2nd Order Method - notes on Runge-Kutta 4th Order Method \_\_TOC\_\_ A differential equation is a equation that relates some function with its derivatives. Such relationship is commonly found in dynamic system modeling where the rate of change of a quantity is affect by another quantity, which can be a function of other quantities. Therefore differential equations are often used to mathematically represent such relations in many disciplines including engineering, physics, economics, and biology. We will focus on ordinary differential equations, which involves no partial derivative. The solution to a differential equation is the function or a set of functions that satisfies the equation. Some simple differential equations with explicit formulas are solvable analytically, but we can always use numerical methods to estimate the answer using computers to a certain degree of accuracy. <http://martinfowler.com/bliki/TwoHardThings.html> \"Two hard things in computer science: cache invalidation, naming things, and off-by-one errors.\" # Initial Value Problem The general form of first order differential equation: $y'=f(x, y)$ or $y'=f(x, y(x))$. The solution contains an arbitrary constant (the constant of integration) because $z(x)=y(x)+c$ satisfies all differential equations $y(x)$ satisfies. With an auxiliary condition, e.g. y(a)=b, we can solve y\'=F(x, y). This is known as the initial value problem. An indefinite integral of a function $f(x)$ is a class of functions $F(x)$ so that $F'(x)=f(x)$. The indefinite integral is also known as the antiderivative. The definite integral of a function over a fixed interval is a number. # Connection with Integration To calculate the integral $F(x)=\int_{a}^{x}f(t)dt$ is to find a $F(x)$ that satisfies the condition $\frac{dF(x)}{dx}=f(x)$, $F(a)=0$. In other words, integration can be used to solve differential equations with a initial condition. # Euler\'s Method !Illustration of the Euler method. The unknown curve is in blue, and its polygonal approximation is in red. Euler\'s method uses a step-wise approach to solve ordinary differential equations with an initial condition. Given $\frac{dy}{dx} = f(x,y)$ and $y(x_{0})=y_{0}$ ($x$ is an independent variable and $y$ is a dependent variable) Euler\'s methods solves for $y_{i}$ for $x=x_i$. Euler\'s method can be derived in a number of ways. Lets look at a geographical description. Given that $\frac{dy}{dx} = f(x,y)$ at a particular point $(x_{i}, y_{i})$ we can approximate $f(x_{i}, y_{i})$ with $\frac{y_{i+1}-y_{i}}{x_{i+1}-x_{i}}$. The derivative represents the instantaneous (happening continuously) change in $y$ at $x$: $$\lim_{\Delta x \to 0}\frac{\Delta y}{\Delta x}=\frac{dy}{dx}=y'(x)$$ The average change in $y$ over $x$ is : $\frac{y_{i+1}-y_{i}}{x_{i+1}-x_{i}}=\frac{\Delta y}{\Delta x}$, which represents a discrete version of the change (changes over \"steps\" of time). If the change in $x$ is small enough, either of the two can be used to approximate the other. Assume that we know the derivative function of an unknown curve and wants to find the shape of the curve (a function that satisfies a differential equation). We can start from a known point, use the differential equation as as a formula to get the slope of the tangent line to the curve at any point on the curve, and take a small step along that tangent line up to the next point. If the step is small enough, we can expect the next point to be close to the curve. If we pretend that point is still on the curve, the same process can be used to find the next point and so on. Graphically we are using a polynomial to approximate the unknown curve. The gap between the two curves represents the error of the approximation, which can be reduced by shortening the step sizes. We just derived the formula for Euler\'s method: $$y_{i+1} = y_{i} + f(x_{i},y_{i})(x_{i+1}-x_{i})$$ ## Example Given $\frac{dy}{dx} = y$, and $y(0)=1$, solve it for $x$ at 1, i.e. y(1). The Euler\'s method formula is a recursively defined function, which can be calculated iteratively. $(x_{i+1}-x_{i})$ is called the step size. If we pick a step size of 1 the solution is as follows: !Illustration of numerical integration for the equation $y'=y, y(0)=1.$ Blue is the Euler method; green, the midpoint method; red, the exact solution, $y=e^t.$ The step size is *h* = 1.0.=1. Blue is the Euler method; green, the midpoint method; red, the exact solution, y=e^t. The step size is h = 1.0."){width="200"} : {\| class=\"wikitable\" \|- ! $i$ !! $x_{i}$ !! $y_i$ !!$dy/dx$ \|- \| 0 \|\| 0 \|\| 1 \|\| 1 \|- \| 1 \|\| 1 \|\| 2 \|\| 2 \|- \| 2 \|\| 2 \|\| 4 \|\| 4 \|- \| 3 \|\| 3 \|\| 8 \|\| 8 \|} Another way to derive Euler\'s method is to use taylor expansion around $x_{i}$: $$y(x_0 + h) = y(x_0) + h y'(x_0) + \frac{1}{2}h^2 y''(x_0) + O(h^3).$$ If we ignore higher order derivative terms we get the Euler\'s method formula: $$y(x_0 + h) = y(x_0) + h y'(x_0)$$ # Runge-Kutta 2nd Order Method One of the Runge-Kutta 2nd order method is the midpoint method, which is a modified Euler\'s method (one-step method) for numerically solving ordinary differential equations: $$y'(x) = f(x, y(x)), \quad y(x_0) = y_0$$. The midpoint method is given by the formula $$y_{i+1} = y_i + hf\left(x_i+\frac{h}{2},y_i+\frac{h}{2}f(x_i, y_i)\right)$$. Note that $y_{i}$ is the approximation of $y(x_{i})$ using this method. !Illustration of the midpoint method assuming that $y_n$ equals the exact value $y(t_n).$ The midpoint method computes $y_{n+1}$ so that the red chord is approximately parallel to the tangent line at the midpoint (the green line).. The midpoint method computes y_{n+1} so that the red chord is approximately parallel to the tangent line at the midpoint (the green line).") # Runga-Kutta 4th Order Method The Runga-Kutta 4th order method is often called \"RK4\", \"classical Runge--Kutta method\" or simply as \"the Runge--Kutta method\". $$\begin{align} y_{i+1} &= y_i + \tfrac{h}{6}\left(k_1 + 2k_2 + 2k_3 + k_4 \right)\\ x_{i+1} &= x_i + h \\ \end{align}$$ for *i* = 0, 1, 2, 3, . . . , using $$\begin{align} k_1 &= f(x_i, y_i), \\ k_2 &= f(x_i + \tfrac{h}{2}, y_i + \tfrac{1}{2} k_1 h), \\ k_3 &= f(x_i + \tfrac{h}{2}, y_i + \tfrac{1}{2} k_2 h), \\ k_4 &= f(x_i + h, y_i + k_3 h). \end{align}$$ This method calculate $y_{i+1}$ by adding to $y_i$) a weighted average of four increments, each of which is the step size $h$ multiplied by an estimated slope: - $k_1$ is the increment based on the estimated slope at the beginning of the interval (Euler\'s method) ; - $k_2$ is the increment based on the slope at the midpoint of the interval; - $k_3$ is again the increment based on the slope at the midpoint, but now using $k_2$; - $k_4$ is the increment based on the slope at the end of the interval, using $k_3$. In averaging the four increments, greater weight is given to the increments at the midpoint. The weights are chosen such that if $f$ is independent of $y$, so that the differential equation is equivalent to a simple integral. # Case Study source solution in a iPython notebook

# Consciousness Studies/Introduction Everyone has their own view of the nature of consciousness based on their education and background. The intention of this book is to expand this view by providing an insight into the various ideas and beliefs on the subject as well as a review of current work in neuroscience. The neuroscientist should find the philosophical discussion interesting because this provides first-person insights into the nature of consciousness and also provides some subtle arguments about why consciousness is not a simple problem. The student of philosophy will find a useful introduction to the subject and information about neuroscience and physics that is difficult to acquire elsewhere. It is often said that consciousness cannot be defined. This is not true; philosophers have indeed defined it in its own terms. It can be described in terms of two principal components: firstly **phenomenal consciousness** which consists of our experience with things laid out in space and time, sensations, emotions, thoughts, etc., and secondly **access consciousness** which is the processes that act on the things in experience. Phenomenal consciousness is much like the "perceptual space" of psychological and physiological research. It is the many simultaneous events that become the space of experience in general and it is now a legitimate target of scientific research. As will be seen in the following pages, the issue for the scientist and philosopher is to determine the location and form of the things in phenomenal consciousness and even to consider whether such a thing could exist. Is phenomenal consciousness directly things in the world beyond the body, is it brain activity based on things in the world and internal processes --- a sort of virtual reality --- or is it some spiritual or other phenomenon? ## A note on Naive Realism The study of consciousness may seem to be esoteric or outside of the main stream but it includes some very real problems in science and philosophy. The most obvious problem is how we can see anything at all. Many people with a smattering of geometry tend to believe that they have a \'point eye\' that sees the world, and this idea is known as perceptual \"Naive Realism\". Physical considerations show that this idea is highly contentious; we have two eyes with different images in each, normally the only images in the world are created by optical instruments such as the eye, and the photons that carry light to the observer cannot and do not all converge at a single point. Some of the discrepancies between the physical reality and our experience are shown in the illustrations.   The naive realist idea of perception involves a point eye looking at a geometrical form. But the physics is different; there are two eyes with sometimes very different images in each. Light is refracted over the entire area of the cornea and directed over the entire area of the retina - there is no \'point eye\'. The cloud of photons that compose light must get in the way of the view but naive realism neglects this, regarding the photons as somehow transparent yet gathering as an impossible group of millions of photons in a viewing point. Light rays go everywhere, it is only after light has passed through an optical instrument such as the eye that an image is formed. Hold up a sheet of paper - there are no images on it. The illustrations show the nature of one of the most difficult problems studied by neuroscience: how can the images on the two retinas become experience? How can we imagine things or experience dreams and hallucinations? Studies on the neural basis of binocular rivalry and MRI studies of imagination are leading the way in our comprehension of these problems but there is still **no physical theory that is congruent with sensory experience**. The problem of *binding* also takes us further from Naive Realism; we experience speech at the mouth of the speaker even though we might be listening through headphones, how is sound, touch etc. bound to vision? The objective of the scientific study of consciousness is to discover how we convert data from the world into our experience. A degree of Naive Realism is a sensible idea for coping with the everyday problems of working and living. Most physical scientists and people in general are, to some extent, Naive Realists until they study the biology of sensation and the problems of perception and consciousness. There is often a suspicion, or even fear, amongst Naive Realists that any analysis of conscious experience is a suggestion that the world does not exist or everything is imaginary. These fears are unfounded: Neuroscience is a study of the part of the physical world represented by brain activity and is part of medicine. ## Intended audience and how to read this book This book is intended as a complementary text for neuroscience and philosophy degree courses. The book is divided into four parts. If you are not interested in some part, skip to the next. The first part is a detailed historical review of the philosophy of phenomenal consciousness. The second part is a discussion of philosophical theories, it is intended to be challenging and even irritating. Philosophy undergraduates are encouraged to criticise and react to this part. The third part is a review of the neuroscience of consciousness and is suitable for undergraduate studies in the field. The end of the book is a discussion of theories of consciousness. Being freely available to all students the book can serve as a source for seminars even if you disagree with the content i.e.: "Why is (a given section) an oversimplification/biased/out of date etc.?" The text covers a difficult area that straddles the humanities and science faculties. It is probably more oriented towards the scientist who needs a scientific insight into philosophical theory rather than vice versa. It is suitable as a **supplementary text** for the following **undergraduate** modules, units and courses: - Neurophysiology/Neurobiology modules (physiology of perception, physiology of consciousness, neuronal basis of consciousness) - Neuropsychology modules - Neuroanatomy modules - Cognitive psychology/Cognitive science - Psychology of consciousness - Psychology - behaviourism vs cognitivism debate - Philosophy of mind and metaphysics - Computing - Artificial intelligence and consciousness - Consciousness studies courses This is a "Wikibook" and, in this edition, has more breadth than depth. In some areas, particularly in the huge field of the philosophy of consciousness, topics are introduced and the obvious flaws or successes pointed out but a fully referenced, in-depth treatment is sometimes absent at this stage. We need your help and contributions from scholars in the field are invited. Please contribute but please, at the very least, scan the book first to ensure that your prospective contribution has not been included already! In particular contributors who wish to write "all self respecting scientists think that the brain is a digital computer" should read the section on information theory and add their contribution to the section on the possibility of conscious digital computers.

# Consciousness Studies/Introduction#A note on Naive Realism Everyone has their own view of the nature of consciousness based on their education and background. The intention of this book is to expand this view by providing an insight into the various ideas and beliefs on the subject as well as a review of current work in neuroscience. The neuroscientist should find the philosophical discussion interesting because this provides first-person insights into the nature of consciousness and also provides some subtle arguments about why consciousness is not a simple problem. The student of philosophy will find a useful introduction to the subject and information about neuroscience and physics that is difficult to acquire elsewhere. It is often said that consciousness cannot be defined. This is not true; philosophers have indeed defined it in its own terms. It can be described in terms of two principal components: firstly **phenomenal consciousness** which consists of our experience with things laid out in space and time, sensations, emotions, thoughts, etc., and secondly **access consciousness** which is the processes that act on the things in experience. Phenomenal consciousness is much like the "perceptual space" of psychological and physiological research. It is the many simultaneous events that become the space of experience in general and it is now a legitimate target of scientific research. As will be seen in the following pages, the issue for the scientist and philosopher is to determine the location and form of the things in phenomenal consciousness and even to consider whether such a thing could exist. Is phenomenal consciousness directly things in the world beyond the body, is it brain activity based on things in the world and internal processes --- a sort of virtual reality --- or is it some spiritual or other phenomenon? ## A note on Naive Realism The study of consciousness may seem to be esoteric or outside of the main stream but it includes some very real problems in science and philosophy. The most obvious problem is how we can see anything at all. Many people with a smattering of geometry tend to believe that they have a \'point eye\' that sees the world, and this idea is known as perceptual \"Naive Realism\". Physical considerations show that this idea is highly contentious; we have two eyes with different images in each, normally the only images in the world are created by optical instruments such as the eye, and the photons that carry light to the observer cannot and do not all converge at a single point. Some of the discrepancies between the physical reality and our experience are shown in the illustrations.   The naive realist idea of perception involves a point eye looking at a geometrical form. But the physics is different; there are two eyes with sometimes very different images in each. Light is refracted over the entire area of the cornea and directed over the entire area of the retina - there is no \'point eye\'. The cloud of photons that compose light must get in the way of the view but naive realism neglects this, regarding the photons as somehow transparent yet gathering as an impossible group of millions of photons in a viewing point. Light rays go everywhere, it is only after light has passed through an optical instrument such as the eye that an image is formed. Hold up a sheet of paper - there are no images on it. The illustrations show the nature of one of the most difficult problems studied by neuroscience: how can the images on the two retinas become experience? How can we imagine things or experience dreams and hallucinations? Studies on the neural basis of binocular rivalry and MRI studies of imagination are leading the way in our comprehension of these problems but there is still **no physical theory that is congruent with sensory experience**. The problem of *binding* also takes us further from Naive Realism; we experience speech at the mouth of the speaker even though we might be listening through headphones, how is sound, touch etc. bound to vision? The objective of the scientific study of consciousness is to discover how we convert data from the world into our experience. A degree of Naive Realism is a sensible idea for coping with the everyday problems of working and living. Most physical scientists and people in general are, to some extent, Naive Realists until they study the biology of sensation and the problems of perception and consciousness. There is often a suspicion, or even fear, amongst Naive Realists that any analysis of conscious experience is a suggestion that the world does not exist or everything is imaginary. These fears are unfounded: Neuroscience is a study of the part of the physical world represented by brain activity and is part of medicine. ## Intended audience and how to read this book This book is intended as a complementary text for neuroscience and philosophy degree courses. The book is divided into four parts. If you are not interested in some part, skip to the next. The first part is a detailed historical review of the philosophy of phenomenal consciousness. The second part is a discussion of philosophical theories, it is intended to be challenging and even irritating. Philosophy undergraduates are encouraged to criticise and react to this part. The third part is a review of the neuroscience of consciousness and is suitable for undergraduate studies in the field. The end of the book is a discussion of theories of consciousness. Being freely available to all students the book can serve as a source for seminars even if you disagree with the content i.e.: "Why is (a given section) an oversimplification/biased/out of date etc.?" The text covers a difficult area that straddles the humanities and science faculties. It is probably more oriented towards the scientist who needs a scientific insight into philosophical theory rather than vice versa. It is suitable as a **supplementary text** for the following **undergraduate** modules, units and courses: - Neurophysiology/Neurobiology modules (physiology of perception, physiology of consciousness, neuronal basis of consciousness) - Neuropsychology modules - Neuroanatomy modules - Cognitive psychology/Cognitive science - Psychology of consciousness - Psychology - behaviourism vs cognitivism debate - Philosophy of mind and metaphysics - Computing - Artificial intelligence and consciousness - Consciousness studies courses This is a "Wikibook" and, in this edition, has more breadth than depth. In some areas, particularly in the huge field of the philosophy of consciousness, topics are introduced and the obvious flaws or successes pointed out but a fully referenced, in-depth treatment is sometimes absent at this stage. We need your help and contributions from scholars in the field are invited. Please contribute but please, at the very least, scan the book first to ensure that your prospective contribution has not been included already! In particular contributors who wish to write "all self respecting scientists think that the brain is a digital computer" should read the section on information theory and add their contribution to the section on the possibility of conscious digital computers.

# Consciousness Studies/Introduction#Intended audience and how to read this book Everyone has their own view of the nature of consciousness based on their education and background. The intention of this book is to expand this view by providing an insight into the various ideas and beliefs on the subject as well as a review of current work in neuroscience. The neuroscientist should find the philosophical discussion interesting because this provides first-person insights into the nature of consciousness and also provides some subtle arguments about why consciousness is not a simple problem. The student of philosophy will find a useful introduction to the subject and information about neuroscience and physics that is difficult to acquire elsewhere. It is often said that consciousness cannot be defined. This is not true; philosophers have indeed defined it in its own terms. It can be described in terms of two principal components: firstly **phenomenal consciousness** which consists of our experience with things laid out in space and time, sensations, emotions, thoughts, etc., and secondly **access consciousness** which is the processes that act on the things in experience. Phenomenal consciousness is much like the "perceptual space" of psychological and physiological research. It is the many simultaneous events that become the space of experience in general and it is now a legitimate target of scientific research. As will be seen in the following pages, the issue for the scientist and philosopher is to determine the location and form of the things in phenomenal consciousness and even to consider whether such a thing could exist. Is phenomenal consciousness directly things in the world beyond the body, is it brain activity based on things in the world and internal processes --- a sort of virtual reality --- or is it some spiritual or other phenomenon? ## A note on Naive Realism The study of consciousness may seem to be esoteric or outside of the main stream but it includes some very real problems in science and philosophy. The most obvious problem is how we can see anything at all. Many people with a smattering of geometry tend to believe that they have a \'point eye\' that sees the world, and this idea is known as perceptual \"Naive Realism\". Physical considerations show that this idea is highly contentious; we have two eyes with different images in each, normally the only images in the world are created by optical instruments such as the eye, and the photons that carry light to the observer cannot and do not all converge at a single point. Some of the discrepancies between the physical reality and our experience are shown in the illustrations.   The naive realist idea of perception involves a point eye looking at a geometrical form. But the physics is different; there are two eyes with sometimes very different images in each. Light is refracted over the entire area of the cornea and directed over the entire area of the retina - there is no \'point eye\'. The cloud of photons that compose light must get in the way of the view but naive realism neglects this, regarding the photons as somehow transparent yet gathering as an impossible group of millions of photons in a viewing point. Light rays go everywhere, it is only after light has passed through an optical instrument such as the eye that an image is formed. Hold up a sheet of paper - there are no images on it. The illustrations show the nature of one of the most difficult problems studied by neuroscience: how can the images on the two retinas become experience? How can we imagine things or experience dreams and hallucinations? Studies on the neural basis of binocular rivalry and MRI studies of imagination are leading the way in our comprehension of these problems but there is still **no physical theory that is congruent with sensory experience**. The problem of *binding* also takes us further from Naive Realism; we experience speech at the mouth of the speaker even though we might be listening through headphones, how is sound, touch etc. bound to vision? The objective of the scientific study of consciousness is to discover how we convert data from the world into our experience. A degree of Naive Realism is a sensible idea for coping with the everyday problems of working and living. Most physical scientists and people in general are, to some extent, Naive Realists until they study the biology of sensation and the problems of perception and consciousness. There is often a suspicion, or even fear, amongst Naive Realists that any analysis of conscious experience is a suggestion that the world does not exist or everything is imaginary. These fears are unfounded: Neuroscience is a study of the part of the physical world represented by brain activity and is part of medicine. ## Intended audience and how to read this book This book is intended as a complementary text for neuroscience and philosophy degree courses. The book is divided into four parts. If you are not interested in some part, skip to the next. The first part is a detailed historical review of the philosophy of phenomenal consciousness. The second part is a discussion of philosophical theories, it is intended to be challenging and even irritating. Philosophy undergraduates are encouraged to criticise and react to this part. The third part is a review of the neuroscience of consciousness and is suitable for undergraduate studies in the field. The end of the book is a discussion of theories of consciousness. Being freely available to all students the book can serve as a source for seminars even if you disagree with the content i.e.: "Why is (a given section) an oversimplification/biased/out of date etc.?" The text covers a difficult area that straddles the humanities and science faculties. It is probably more oriented towards the scientist who needs a scientific insight into philosophical theory rather than vice versa. It is suitable as a **supplementary text** for the following **undergraduate** modules, units and courses: - Neurophysiology/Neurobiology modules (physiology of perception, physiology of consciousness, neuronal basis of consciousness) - Neuropsychology modules - Neuroanatomy modules - Cognitive psychology/Cognitive science - Psychology of consciousness - Psychology - behaviourism vs cognitivism debate - Philosophy of mind and metaphysics - Computing - Artificial intelligence and consciousness - Consciousness studies courses This is a "Wikibook" and, in this edition, has more breadth than depth. In some areas, particularly in the huge field of the philosophy of consciousness, topics are introduced and the obvious flaws or successes pointed out but a fully referenced, in-depth treatment is sometimes absent at this stage. We need your help and contributions from scholars in the field are invited. Please contribute but please, at the very least, scan the book first to ensure that your prospective contribution has not been included already! In particular contributors who wish to write "all self respecting scientists think that the brain is a digital computer" should read the section on information theory and add their contribution to the section on the possibility of conscious digital computers.

# Consciousness Studies/Early Ideas *This section is an academic review of major contributions to consciousness studies. Readers who are interested in the current philosophy of consciousness will find this in Part II and readers interested in the neuroscience of consciousness should refer to Part III.* Vedic Sciences are present the first known ideas related to consciousness, dating back to at least 1500 years ago according to The British Library. The ten books of Rig Veda, which are attributed to the end of the Bronze period, which are on of the ten oldest living texts of the world, illuminates us on ultimate or supreme consciousness. In the Rig Veda (R.V. IV. XL. 5) Nrishad is the dweller amongst humans; Nrishad is explained as Chaitanya or \'Consciousness\' or Prana or \'vitality\' because both dwell in humans. In his commentary on the Isha Upanishad,\[5\] Sri Aurobindo explains that the Atman, the Self manifests through a seven-fold movement of Prakrti. These seven folds of consciousness, along with their dominant principles are:\[6\] annamaya puruṣa - physical prāṇamaya puruṣa - nervous / vital manomaya puruṣa - mental / mind vijñānamaya puruṣa - knowledge and truth ānandamaya puruṣa - Aurobindo\'s concept of Delight, otherwise known as Bliss caitanya puruṣa - infinite divine self-awareness\[7\] sat puruṣa - state of pure divine existence The first five of these are arranged according to the specification of the panchakosha from the second chapter of the Taittiriya Upanishad. The final three elements make up satcitananda, with cit being referred to as chaitanya. The essential nature of Brahman as revealed in deep sleep and Yoga is Chaitanya (pure consciousness).\[8\] The earliest use of the word soul or Ātman in Indian texts is also found in the Rig Veda (c. 1500 BC)(RV X.97.11).\[20\] Yāska, the ancient Indian grammarian, commenting on this Rigvedic verse, accepts the following meanings of Ātman: the pervading principle, the organism in which other elements are united and the ultimate sentient principle.\[21\] Other hymns of Rig Veda where the word Ātman appears include I.115.1, VII.87.2, VII.101.6, VIII.3.24, IX.2.10, IX.6.8, and X.168.4.\[22\] The Rig Veda takes one from before creation, through creation of the world, to creation of self, and ends with the creation of creation itself, after which creation of the universe came. Upon close reading, one can trace the various stages of consciousness to the material world, from absolute truth or Sat to absolute material or Asat, two recurring concepts that run through the entire Rig Veda. The Greeks had no exact equivalent for the term \'consciousness\', which has a wide range of meanings in modern usage, but in the thinkers below we find an analysis of phenomenal consciousness and the source of many ideas developed by later Socratics, especially the Stoics, and by Christian thinkers like Augustine. ## Aristotle (c. 350 BC) *On the Soul* (De Anima) <http://psychclassics.yorku.ca/Aristotle/De-anima/> !AristotleAristotle, perhaps more than any other ancient Greek philosopher, set the terms of reference for the future discussion of the problem of consciousness. His idea of the mind is summarised in the illustration below. Aristotle was a physicalist, believing that things are embodied in the material universe: `<font face="times new roman">`{=html}\"\... That is precisely why the study of the soul \[psyche\] must fall within the science of Nature, at least so far as in its affections it manifests this double character. Hence a physicist would define an affection of soul differently from a dialectician; the latter would define e.g. anger as the appetite for returning pain for pain, or something like that, while the former would define it as a boiling of the blood or warm substance surround the heart. The latter assigns the material conditions, the former the form or formulable essence; for what he states is the formulable essence of the fact, though for its actual existence there must be embodiment of it in a material such as is described by the other.\"(Book I, 403a)`</font>`{=html} The works of Aristotle provide our first clear account of the concept of signals and information. He was aware that an event can change the state of matter and this change of state can be transmitted to other locations where it can further change a state of matter: `<font face="times new roman">`{=html}\"If what has colour is placed in immediate contact with the eye, it cannot be seen. Colour sets in movement not the sense organ but what is transparent, e.g. the air, and that, extending continuously from the object to the organ, sets the latter in movement. Democritus misrepresents the facts when he expresses the opinion that if the interspace were empty one could distinctly see an ant on the vault of the sky; that is an impossibility. Seeing is due to an affection or change of what has the perceptive faculty, and it cannot be affected by the seen colour itself; it remains that it must be affected by what comes between. Hence it is indispensable that there be something in between-if there were nothing, so far from seeing with greater distinctness, we should see nothing at all.\" (Book II, 419a\])`</font>`{=html} He was also clear about the relationship of information to \'state\': `<font face="times new roman">`{=html}\"By a \'sense\' is meant what has the power of receiving into itself the sensible forms of things without the matter. This must be conceived of as taking place in the way in which a piece of wax takes on the impress of a signet-ring without the iron or gold; we say that what produces the impression is a signet of bronze or gold, but its particular metallic constitution makes no difference: in a similar way the sense is affected by what is coloured or flavoured or sounding, but it is indifferent what in each case the substance is; what alone matters is what quality it has, i.e. in what ratio its constituents are combined\"(Book II, 424a)`</font>`{=html} Aristotle also mentioned the problem of the simultaneity of experience. The explanation predates Galilean and modern physics so lacks our modern language to explain how many things could be at a point and an instant: `<font face="times new roman">`{=html}\"\... just as what is called a \'point\' is, as being at once one and two, properly said to be divisible, so here, that which discriminates is qua undivided one, and active in a single moment of time, while so far forth as it is divisible it twice over uses the same dot at one and the same time. So far forth then as it takes the limit as two\' it discriminates two separate objects with what in a sense is divided: while so far as it takes it as one, it does so with what is one and occupies in its activity a single moment of time. (Book III, 427a)`</font>`{=html} He described the problem of recursion that would occur if the mind were due to the flow of material things in space: `<font face="times new roman">`{=html}\"\...mind is either without parts or is continuous in some other way than that which characterizes a spatial magnitude. How, indeed, if it were a spatial magnitude, could mind possibly think? Will it think with any one indifferently of its parts? In this case, the \'part\' must be understood either in the sense of a spatial magnitude or in the sense of a point (if a point can be called a part of a spatial magnitude). If we accept the latter alternative, the points being infinite in number, obviously the mind can never exhaustively traverse them; if the former, the mind must think the same thing over and over again, indeed an infinite number of times (whereas it is manifestly possible to think a thing once only).\"(Book I, 407a)`</font>`{=html} Aristotle explicitly mentions the regress: `<font face="times new roman">`{=html}\"..we must fall into an infinite regress or we must assume a sense which is aware of itself.\" (Book III,425b)`</font>`{=html} However, this regress was not as problematic for Aristotle as it is for philosophers who are steeped in nineteenth century ideas. Aristotle was a physicalist who was not burdened with materialism and so was able to escape from the idea that the only possibility for the mind is a flow of material from place to place over a succession of disconnected instants. He was able to propose that subjects and objects are part of the same thing, he notes that thought is both temporally and spatially extended: `<font face="times new roman">`{=html}\"But that which mind thinks and the time in which it thinks are in this case divisible only incidentally and not as such. For in them too there is something indivisible (though, it may be, not isolable) which gives unity to the time and the whole of length; and this is found equally in every continuum whether temporal or spatial.\" (Book III,430b)`</font>`{=html} This idea of time allowed him to identify thinking with the object of thought, there being no need to cycle thoughts from instant to instant because mental time is extended: `<font face="times new roman">`{=html}\"In every case the mind which is actively thinking is the objects which it thinks.\"`</font>`{=html} He considered imagination to be a disturbance of the sense organs: `<font face="times new roman">`{=html}\"And because imaginations remain in the organs of sense and resemble sensations, animals in their actions are largely guided by them, some (i.e. the brutes) because of the non-existence in them of mind, others (i.e. men) because of the temporary eclipse in them of mind by feeling or disease or sleep.(Book III, 429a)\"`</font>`{=html} And considered that all thought occurs as images: `<font face="times new roman">`{=html}\"To the thinking soul images serve as if they were contents of perception (and when it asserts or denies them to be good or bad it avoids or pursues them). That is why the soul never thinks without an image.\"(Book III, ).`</font>`{=html} Aristotle also described the debate between the cognitive and behaviourist approaches with their overtones of the conflict between modern physicalism and pre twentieth century materialism: `<font face="times new roman">`{=html}\"Some thinkers, accepting both premisses, viz. that the soul is both originative of movement and cognitive, have compounded it of both and declared the soul to be a self-moving number.\"(Book I, 404b)`</font>`{=html} The idea of a \'self-moving number\' is not as absurd as it seems, like much of Ancient Greek philosophy. Aristotle was also clear about there being two forms involved in perception. He proposed that the form and properties of the things that are directly in the mind are incontrovertible but that our inferences about the form and properties of the things in the world that give rise to the things in the mind can be false: `<font face="times new roman">`{=html}\"Perception (1) of the special objects of sense is never in error or admits the least possible amount of falsehood. (2) That of the concomitance of the objects concomitant with the sensible qualities comes next: in this case certainly we may be deceived; for while the perception that there is white before us cannot be false, the perception that what is white is this or that may be false. (3) Third comes the perception of the universal attributes which accompany the concomitant objects to which the special sensibles attach (I mean e.g. of movement and magnitude); it is in respect of these that the greatest amount of sense-illusion is possible.\"(Book III, 428b)`</font>`{=html} Imagination, according to this model, lays out things in the senses. ## Galen The \'physicians\' (most especially Galen) incorporated ideas from the Hippocractics and from Plato into a view in which 3 (or more) inner senses---most basically memory, estimation, and imagination---were associated with 3 ventricles in the brain. *This is a **stub** that needs further expansion*. ## Homer (c. 800-900 BC) The *Iliad* and *Odyssey* Odyssey !HomerPanpsychism and panexperientialism can be traced to, at least, Homer\'s Iliad. Just reading the book allows us to experience what a different focus of consciousness feels like. It is a way of being, being a Homeric Greek, thus distinct from being a modern man. Both states of consciousness result in different ways of experiencing the world. As we read the Iliad, we are drawn into the book through the images it creates in us and the feelings it evokes in us through the meter and the language. The reader becomes the book. \"The reader became the book, and the summer night was like the conscious being of the book\" (Wallace Stevens). That experience of becoming the book, of losing yourself in the book, is the experience of a different aspect of consciousness, being a Homeric Greek. Homer frequently ascribes even our emotions to the world around us. The ancients do not just fear but fear grips them, for example: \"So spake Athene, and pale fear gat hold of them all. The arms flew from their hands in their terror and fell all upon the ground, as the goddess uttered her voice\" (Odyssey book XXIV). The German classicist Bruno Snell, in *The Discovery of the Mind* provides us with \"a convincing account of the enormous change in \... human personality which took place during the centuries covered by Homer (to) Socrates.\"(The London Times Literary Supplement). Snell\'s book establishes two distinct aspects of consciousness. He says, \"The experience of Homer differs from our own\" (p.v); \"For Homer, psyche is the force which keeps the human being alive\...\"(p. 8). When the psyche leaves, the owner loses consciousness. The Homeric *psyche* is where pan-psychism originates. It begins in a conception of consciousness as a force that is separate from the body. Snell compares Homer to the tragedy of Orestes, which focuses on the individual. \"Homer concentrates on the action (process) and the situation in preference to the agent\...\"(p. 211) Orestes is in a different state of consciousness, \"a new state of consciousness\"(p. 211). ## Plato (427-347 BC) The Republic <http://www.constitution.org/pla/repub_00.htm> Especially book VI <http://www.constitution.org/pla/repub_06.htm> and book VII (the Cave) <http://www.constitution.org/pla/repub_07.htm> !PlatoPlato\'s most interesting contributions to consciousness studies are in book VI of *The Republic*. His idea of the mind is illustrated below.  He believes that light activates pre-existing capabilities in the eyes: `<font face="times new roman">`{=html}\"Sight being, as I conceive, in the eyes, and he who has eyes wanting to see; color being also present in them, still unless there be a third nature specially adapted to the purpose, the owner of the eyes will see nothing and the colors will be invisible.\"`</font>`{=html} However, it is in the metaphor of **the divided line** that Plato introduces a fascinating account of the relationships and properties of things. He points out that analysis deals in terms of the relationships of pure forms: `<font face="times new roman">`{=html}\"And do you not know also that although they make use of the visible forms and reason about them, they are thinking not of these, but of the ideals which they resemble; not of the figures which they draw, but of the absolute square and the absolute diameter, and so on \-- the forms which they draw or make, and which have shadows and reflections in water of their own, are converted by them into images, but they are really seeking to behold the things themselves, which can only be seen with the eye of the mind?\"`</font>`{=html} Notice how he introduces the notion of a mind\'s eye observing mental content arranged as geometrical forms. He proposes that through this mode of ideas we gain understanding: `<font face="times new roman">`{=html}\"And the habit which is concerned with geometry and the cognate sciences I suppose that you would term understanding, and not reason, as being intermediate between opinion and reason.\"`</font>`{=html} However, the understanding can also contemplate knowledge: `<font face="times new roman">`{=html}\"..I understand you to say that knowledge and being, which the science of dialectic contemplates, are clearer than the notions of the arts, as they are termed, which proceed from hypotheses only: these are also contemplated by the understanding, and not by the senses: yet, because they start from hypotheses and do not ascend to a principle, those who contemplate them appear to you not to exercise the higher reason upon them, although when a first principle is added to them they are cognizable by the higher reason. \"`</font>`{=html} Plato\'s work is not usually discussed in this way but is extended to universals such as the idea of the colour red as a universal that can be applied to many specific instances of things. In \"Plato\'s Cave\" (Book VII) Plato describes how experience could be some transfer from or copy of real things rather than the things themselves: !Plato\'s Cave`<font face="times new roman">`{=html}\"And now, I said, let me show in a figure how far our nature is enlightened or unenlightened: --- Behold! human beings living in a underground den, which has a mouth open towards the light and reaching all along the den; here they have been from their childhood, and have their legs and necks chained so that they cannot move, and can only see before them, being prevented by the chains from turning round their heads. Above and behind them a fire is blazing at a distance, and between the fire and the prisoners there is a raised way; and you will see, if you look, a low wall built along the way, like the screen which marionette players have in front of them, over which they show the puppets.`</font>`{=html} `<font face="times new roman">`{=html}I see.`</font>`{=html} `<font face="times new roman">`{=html}And do you see, I said, men passing along the wall carrying all sorts of vessels, and statues and figures of animals made of wood and stone and various materials, which appear over the wall? Some of them are talking, others silent.`</font>`{=html} `<font face="times new roman">`{=html}You have shown me a strange image, and they are strange prisoners.`</font>`{=html} `<font face="times new roman">`{=html}Like ourselves, I replied; and they see only their own shadows, or the shadows of one another, which the fire throws on the opposite wall of the cave?`</font>`{=html} `<font face="times new roman">`{=html}True, he said; how could they see anything but the shadows if they were never allowed to move their heads?`</font>`{=html} `<font face="times new roman">`{=html}And of the objects which are being carried in like manner they would only see the shadows?`</font>`{=html} `<font face="times new roman">`{=html}Yes, he said.`</font>`{=html} `<font face="times new roman">`{=html}And if they were able to converse with one another, would they not suppose that they were naming what was actually before them?`</font>`{=html} `<font face="times new roman">`{=html}Very true.`</font>`{=html} `<font face="times new roman">`{=html}And suppose further that the prison had an echo which came from the other side, would they not be sure to fancy when one of the passers-by spoke that the voice which they heard came from the passing shadow?`</font>`{=html} `<font face="times new roman">`{=html}No question, he replied.`</font>`{=html} `<font face="times new roman">`{=html}To them, I said, the truth would be literally nothing but the shadows of the images.`</font>`{=html} `<font face="times new roman">`{=html}That is certain.`</font>`{=html} `<font face="times new roman">`{=html}And now look again, and see what will naturally follow it, the prisoners are released and disabused of their error. At first, when any of them is liberated and compelled suddenly to stand up and turn his neck round and walk and look towards the light, he will suffer sharp pains; the glare will distress him, and he will be unable to see the realities of which in his former state he had seen the shadows; and then conceive some one saying to him, that what he saw before was an illusion, but that now, when he is approaching nearer to being and his eye is turned towards more real existence, he has a clearer vision, --- what will be his reply? And you may further imagine that his instructor is pointing to the objects as they pass and requiring him to name them, --- will he not be perplexed? Will he not fancy that the shadows which he formerly saw are truer than the objects which are now shown to him?\"`</font>`{=html} This early intuition of information theory predates Aristotle\'s concept of the transfer of states from one place to another. ## Parmenides (c. 480 BC) *On Nature* ## Siddhartha Gautama (c. 500 BC) Buddhist Texts !BuddhaSiddhartha Gautama was born about 563BC. He became known as \'Buddha\' (\'the awakened one\') from the age of about thirty five. Buddha handed down a way of life that might lead, eventually, to an enlightened state called Nirvana. In the three centuries after his death Buddhism split into two factions, the Mahayana (greater raft or vehicle) and the Theravada (the way of the elders). The Mahayana use the slightly derogatory term Hinayana (lesser raft or vehicle) for Theravada Buddhism. Mahayana Buddhism gave rise to other sects such as Zen Buddhism in Japan and Vajrayana Buddhism in Tibet. Mahayana Buddhism is more like a religion, complete with god like entities whereas Theravada Buddhism is more like a philosophy. Theravada Buddhist meditation is described in books called the Pali Canon which contains the \'Vinayas\' that describe monastic life, the \'Suttas\' which are the central teachings of Theravada Buddhism and the \'Abhidhamma\' which is an analysis of the other two parts or \'pitakas\'. Two meditational systems are described: the development of serenity (samathabhavana) and the development of insight (vipassanabhavana). The two systems are complementary, serenity meditation providing a steady foundation for the development of insight. As meditation proceeds the practitioner passes through a series of stages called \'jhanas\'. There are four of these stages of meditation and then a final stage known as the stage of the \'immaterial jhanas\'. **The Jhanas** The first jhana is a stage of preparation where the meditator rids themselves of the hindrances (sensual desire, ill will, sloth and torpor, restlessness and worry, and doubt). This is best achieved by seclusion. During the process of getting rid of the hindrances the meditator develops the five factors: applied thought, sustained thought, rapture, happiness and one-pointedness of mind. This is done by concentrating on a practice object until it can be easily visualised. Eventually the meditator experiences a luminous replica of the object called the counterpart sign (patibhaganimitta). Applied thought involves examining, visualising and thinking about the object. Sustained thought involves always returning to the object, not drifting away from it. Rapture involves a oneness with the object and is an ecstacy that helps absorption with and in the object. Happiness is the feeling of happiness that everyone has when something good happens (unlike rapture, which is a oneness with the object of contemplation). One-pointedness of mind is the ability to focus on a single thing without being distracted. The second jhana involves attaining the first without effort, there is no need for applied or sustained thought, only rapture, happiness and one-pointedness of mind remain. The second jhana is achieved by contemplating the first jhana. The second jhana is a stage of effortless concentration. The third jhana involves mindfulness and discernment. The mindfulness allows an object of meditation to be held effortlessly in the mind. The discernment consists of discerning the nature of the object without delusion and hence avoiding rapture. In the fourth jhana mindfulness is maintained but the delusion of happiness is contemplated. Eventually mindfulness remains without pleasure or pain. In the fourth jhana the meditator achieves \"purity of mindfulness due to equanimity\" (upekkhasatiparisuddhi). **The Immaterial Jhanas** The first four jhanas will be familiar from earlier, Hindu meditational techniques. Once the fourth jhana has been achieved the meditator can embark on the immaterial jhanas. There are four immaterial jhanas: the base of boundless space, the base of boundless consciousness, the base of nothingness, and the base of neither-perception-nor-non-perception. The base of boundless space is achieved by meditating on the absence of the meditation object. It is realised that the space occupied by the object is boundless and that the mind too is boundless space. The base of boundless consciousness involves a realisation that the boundless space is boundless consciousness. The base of nothingness is a realisation that the present does not exist, the meditator should \"give attention to the present non-existence, voidness, secluded aspect of that same past consciousness belonging to the base consisting of boundless space\" (Gunaratana 1988). The base of neither-perception-nor-non-perception is a realisation that nothing is perceived in the void. In Theravada Buddhism the attainment of the fourth jhana and its immaterial jhanas represents a mastery of serenity meditation. This is a foundation for insight meditation. Buddhism is very practical and eschews delusions. It is realised that serenity meditation is a state of mind, a steady foundation that might, nowadays be called a physiological state. It is through insight meditation where the practitioner becomes a philosopher that enlightenment is obtained. **Further reading** The Buddhist Publication Society. Especially: The Jhanas In Theravada Buddhist Meditation by Henepola Gunaratana. The Wheel Publication No. 351/353 . 1988 Buddhist Publication Society. <http://www.accesstoinsight.org/lib/bps/index.html>

# Consciousness Studies/Medieval Concepts It is sometimes said that before the 17th century, there was no distinction between conscience and consciousness (both being referenced by the same Latin word \'conscius---from \'conscientia\'). One feature of the soul being its ability to know itself, and the soul being witnessed also by God, there was a sense in which conscience was a knowledge of the inner life shared with God. In fact, Boris Hennig [^1] proposes that Descartes did not invent an entirely new sense of conscience, but if anything adapted this Augustinian sense of the term. The Augustinians themselves can be said to have adapted this use of conscius from the Latin Stoics like Seneca. On the other hand the Ancient Greek philosophers were clear that there was a problem of mind and the work of Descartes can be seen as more directly connected with Aristotle rather than with medieval philosophy. ## References [^1]: \"Cartesian Conscientia\", *British Journal for the History of Philosophy* 15(3) 2007: 455 -- 484.

# Consciousness Studies/Seventeenth And Eighteenth Century Philosophy ## Rene Descartes (1596-1650) Descartes was also known as Cartesius. He had an empirical approach to consciousness and the mind, describing in his *Meditations on First Philosophy* (1641) what it is like to be human. His idea of perception is summarised in the diagram below.  ### Dubitability Descartes is probably most famous for his statement: `<font face="times new roman">`{=html}\"But immediately upon this I observed that, whilst I thus wished to think that all was false, it was absolutely necessary that I, who thus thought, should be somewhat; and as I observed that this truth, I think, therefore I am (COGITO ERGO SUM), was so certain and of such evidence that no ground of doubt, however extravagant, could be alleged by the sceptics capable of shaking it, I concluded that I might, without scruple, accept it as the first principle of the philosophy of which I was in search.\"`</font>`{=html} Descartes is clear that what he means by *thought* is all the things that occur in experience, whether dreams, sensations, symbols etc.: `<font face="times new roman">`{=html}\"5. Of my thoughts some are, as it were, images of things, and to these alone properly belongs the name IDEA; as when I think \[ represent to my mind \] a man, a chimera, the sky, an angel or God. Others, again, have certain other forms; as when I will, fear, affirm, or deny, I always, indeed, apprehend something as the object of my thought, but I also embrace in thought something more than the representation of the object; and of this class of thoughts some are called volitions or affections, and others judgments.\" (Meditation III).`</font>`{=html} He repeats this general description of thought in many places in the Meditations and elsewhere. What Descartes is saying is that his meditator has thoughts; that there are thoughts and this cannot be doubted when and where they occur (Russell (1945) makes this clear). Needless to say the basic *cogito* put forward by Descartes has provoked endless debate, much of it based on the false premise that Descartes was presenting an inference or argument rather than just saying that thought certainly exists. However, the extent to which the philosopher can go beyond this certainty to concepts such as God, science or the soul is highly problematical. ### The description of thoughts and mind !DescartesDescartes uses the words \"ideas\" and \"imagination\" in a rather unusual fashion. The word \"idea\" he defines as follows: `<font face="times new roman">`{=html}\"5. Of my thoughts some are, as it were, images of things, and to these alone properly belongs the name IDEA; as when I think \[ represent to my mind \] a man, a chimera, the sky, an angel or God.\" (Meditation III).`</font>`{=html} As will be seen later, Descartes regards his mind as an unextended thing (a point) so \"images of things\" or \"IDEAS\" require some way of being extended. In the *Treatise on Man* (see below) he is explicit that ideas are extended things in the brain, on the surface of the \"common sense\". In *Rules for the Direction of the Mind* he notes that we \"receive ideas from the common sensibility\", an extended part of the brain. This usage of the term \"ideas\" is very strange to the modern reader and the source of many mistaken interpretations. It should be noted that occasionally Descartes uses the term \'idea\' according to its usual meaning where it is almost interchangeable with \'thought\' in general but usually he means a representation laid out in the brain. Descartes considers the imagination to be the way that the mind \"turns towards the body\" (by which Descartes means the part of the brain in the body called the senses communis): `<font face="times new roman">`{=html}\"3. I remark, besides, that this power of imagination which I possess, in as far as it differs from the power of conceiving, is in no way necessary to my \[nature or\] essence, that is, to the essence of my mind; for although I did not possess it, I should still remain the same that I now am, from which it seems we may conclude that it depends on something different from the mind. And I easily understand that, if some body exists, with which my mind is so conjoined and united as to be able, as it were, to consider it when it chooses, it may thus imagine corporeal objects; so that this mode of thinking differs from pure intellection only in this respect, that the mind in conceiving turns in some way upon itself, and considers some one of the ideas it possesses within itself; but in imagining it turns toward the body, and contemplates in it some object conformed to the idea which it either of itself conceived or apprehended by sense.\" Meditations VI `</font>`{=html} So ideas, where they become imagined images of things were thought by Descartes to involve a phase of creating a form in the brain. Descartes gives a clear description of his experience as a container that allows length, breadth, depth, continuity and time with contents arranged within it: `<font face="times new roman">`{=html}\"2. But before considering whether such objects as I conceive exist without me, I must examine their ideas in so far as these are to be found in my consciousness, and discover which of them are distinct and which confused.`</font>`{=html} `<font face="times new roman">`{=html}3. In the first place, I distinctly imagine that quantity which the philosophers commonly call continuous, or the extension in length, breadth, and depth that is in this quantity, or rather in the object to which it is attributed. Further, I can enumerate in it many diverse parts, and attribute to each of these all sorts of sizes, figures, situations, and local motions; and, in fine, I can assign to each of these motions all degrees of duration.\"(Meditation V).`</font>`{=html} He points out that sensation occurs by way of the brain, conceptualising the brain as the place in the body where the extended experiences are found : Meditations VI: `<font face="times new roman">`{=html}\"20. I remark, in the next place, that the mind does not immediately receive the impression from all the parts of the body, but only from the brain, or perhaps even from one small part of it, viz., that in which the common sense (senses communis) is said to be, which as often as it is affected in the same way gives rise to the same perception in the mind, although meanwhile the other parts of the body may be diversely disposed, as is proved by innumerable experiments, which it is unnecessary here to enumerate.\" `</font>`{=html} He finds that both imaginings and perceptions are extended things and hence in the (brain part) of the body. The area of extended things is called the *res extensa*, it includes the brain, body and world beyond. He also considers the origin of intuitions, suggesting that they can enter the mind without being consciously created: Meditations VI, 10 : `<font face="times new roman">`{=html}\"10. Moreover, I find in myself diverse faculties of thinking that have each their special mode: for example, I find I possess the faculties of imagining and perceiving, without which I can indeed clearly and distinctly conceive myself as entire, but I cannot reciprocally conceive them without conceiving myself, that is to say, without an intelligent substance in which they reside, for \[in the notion we have of them, or to use the terms of the schools\] in their formal concept, they comprise some sort of intellection; whence I perceive that they are distinct from myself as modes are from things. I remark likewise certain other faculties, as the power of changing place, of assuming diverse figures, and the like, that cannot be conceived and cannot therefore exist, any more than the preceding, apart from a substance in which they inhere. It is very evident, however, that these faculties, if they really exist, must belong to some corporeal or extended substance, since in their clear and distinct concept there is contained some sort of extension, but no intellection at all. Further, I cannot doubt but that there is in me a certain passive faculty of perception, that is, of receiving and taking knowledge of the ideas of sensible things; but this would be useless to me, if there did not also exist in me, or in some other thing, another active faculty capable of forming and producing those ideas. But this active faculty cannot be in me \[in as far as I am but a thinking thing\], seeing that it does not presuppose thought, and also that those ideas are frequently produced in my mind without my contributing to it in any way, and even frequently contrary to my will. This faculty must therefore exist in some substance different from me, in which all the objective reality of the ideas that are produced by this faculty is contained formally or eminently, as I before remarked; and this substance is either a body, that is to say, a corporeal nature in which is contained formally \[and in effect\] all that is objectively \[and by representation\] in those ideas; or it is God himself, or some other creature, of a rank superior to body, in which the same is contained eminently. But as God is no deceiver, it is manifest that he does not of himself and immediately communicate those ideas to me, nor even by the intervention of any creature in which their objective reality is not formally, but only eminently, contained. For as he has given me no faculty whereby I can discover this to be the case, but, on the contrary, a very strong inclination to believe that those ideas arise from corporeal objects, I do not see how he could be vindicated from the charge of deceit, if in truth they proceeded from any other source, or were produced by other causes than corporeal things: and accordingly it must be concluded, that corporeal objects exist. Nevertheless, they are not perhaps exactly such as we perceive by the senses, for their comprehension by the senses is, in many instances, very obscure and confused; but it is at least necessary to admit that all which I clearly and distinctly conceive as in them, that is, generally speaking all that is comprehended in the object of speculative geometry, really exists external to me. \"`</font>`{=html} He considers that the mind itself is the thing that generates thoughts and is not extended (occupies no space). This \'mind\' is known as the *res cogitans*. The mind works on the imaginings and perceptions that exist in that part of the body called the brain. This is Descartes\' dualism: it is the proposition that there is an unextended place called the mind that acts upon the extended things in the brain. Meditations VI, 9: `<font face="times new roman">`{=html}\"\... And although I may, or rather, as I will shortly say, although I certainly do possess a body with which I am very closely conjoined; nevertheless, because, on the one hand, I have a clear and distinct idea of myself, in as far as I am only a thinking and unextended thing, and as, on the other hand, I possess a distinct idea of body, in as far as it is only an extended and unthinking thing, it is certain that I, \[that is, my mind, by which I am what I am\], is entirely and truly distinct from my body, and may exist without it.\"`</font>`{=html} Notice that the intellection associated with ideas is part of an \"active faculty capable of forming and producing those ideas\" that has a \"corporeal nature\" (it is in the brain). This suggests that the \"thinking\" in the passage above applies only to those thoughts that are unextended, however, it is difficult to find a definition of these particular thoughts. \"Rules for the Direction of the Mind\" demonstrates Descartes\' dualism. He describes the brain as the part of the body that contains images or phantasies of the world but believes that there is a further, spiritual mind that processes the images in the brain: `<font face="times new roman">`{=html}\"My fourth supposition is that the power of movement, in fact the nerves, originate in the brain, where the phantasy is seated; and that the phantasy moves them in various ways, as the external sense `<organ>`{=html} moves the `<organ of>`{=html} common sensibility, or as the whole pen is moved by its tip. This illustration also shows how it is that the phantasy can cause various movements in the nerves, although it has not images of these formed in itself, but certain other images, of which these movements are possible effects. For the pen as a whole does not move in the same way as its tip; indeed, the greater part of the pen seems to go along with an altogether different, contrary motion. This enables us to understand how the movements of all other animals are accomplished, although we suppose them to have no consciousness (rerum cognitio) but only a bodily `<organ of>`{=html} phantasy; and furthermore, how it is that in ourselves those operations are performed which occur without any aid of reason.`</font>`{=html} `<font face="times new roman">`{=html}My fifth and last supposition is that the power of cognition properly so called is purely spiritual, and is just as distinct from the body as a whole as blood is from bone or a hand from an eye; and that it is a single power. Sometimes it receives images from the common sensibility at the same time as the phantasy does; sometimes it applies itself to the images preserved in memory; sometimes it forms new images, and these so occupy the imagination that often it is not able at the same time to receive ideas from the common sensibility, or to pass them on to the locomotive power in the way that the body left to itself -would. \"`</font>`{=html} Descartes sums up his concept of a point soul seeing forms in the world via forms in the sensus communis in *Passions of the Soul*, 35: \"By this means the two images which are in the brain form but one upon the gland, which, acting immediately upon the soul, causes it to see the form in the mind\". ### Anatomical and physiological ideas In his *Treatise on Man* Descartes summarises his ideas on how we perceive and react to things as well as how consciousness is achieved anatomically and physiologically. The \'Treatise\' was written at a time when even galvanic electricity was unknown. The excerpt given below covers Descartes\' analysis of perception and stimulus-response processing.  `<font face="times new roman">`{=html} \"Thus for example \[in Fig 1\], if fire A is close to foot B, the tiny parts of this fire (which, as you know, move about very rapidly) have the power also to move the area of skin which they touch. In this way they pull the tiny fibre *cc* which you see attached to it, and simultaneously open the entrance to the pore *de*, located opposite the point where this fiber terminates - just as when you pull one end of a string, you cause a bell hanging at the other end to ring at the same time.`</font>`{=html} `<font face="times new roman">`{=html}When the entrance to the pore or small tube *de* is opened in this way, the animal spirits from cavity F enter and are carried through it - some to muscles which serve to pull the foot away from the fire, some to muscles which turn the eyes and head to look at it, and some to muscles which make the hands move and the whole body turn in order to protect it.`</font>`{=html} `<font face="times new roman">`{=html}Now I maintain that when God unites a rational soul to this machine (in a way that I intend to explain later) he will place its principle seat in the brain, and will make its nature such that the soul will have different sensations corresponding to the different ways in which the entrances to the pores in the internal surface of the brain are opened by means of nerves.`</font>`{=html}  `<font face="times new roman">`{=html}In order to see clearly how ideas are formed of the objects which strike the senses, observe in this diagram \[fig 2\] the tiny fibres 12, 34, 56, and the like, which make up the optic nerve and stretch from the back of the eye at 1, 3, 5 to the internal surface of the brain at 2, 4, 6. Now assume that these fibres are so arranged that if the rays coming, for example, from point A of the object happen to press upon the back of the eye at point 1, they pull the whole of fibre 12 and enlarge the opening of the tiny tube marked 2. In the same way, the rays which come from point B enlarge the opening of the tiny tube 4, and likewise for the others. We have already described how, depending on the different ways in which the points 1, 3, 5 are pressed by these rays, a figure is traced on the back of the eye corresponding to that of the object ABC. Similarly it is obvious that, depending on the different ways in which the tiny tubes 2, 4, 6 are opened by the fibres 12, 34, 56 etc., a corresponding figure must also be traced on the internal surface of the brain.`</font>`{=html} \..... `<font face="times new roman">`{=html}And note that by \'figures\' I mean not only things which somehow represent the position of the edges and surfaces of objects, but also anything which, as I said above, can give the soul occasion to perceive movement, size, distance, colours, sounds, smells and other such qualities. And I also include anything that can make the soul feel pleasure, pain, hunger, thirst, joy, sadness and other such passions.`</font>`{=html} \... `<font face="times new roman">`{=html}Now among these figures, it is not those imprinted on the external sense organs, or on the internal surface of the brain, which should be taken to be ideas - but only those which are traced in the spirits on the surface of gland H (*where the seat of the imagination and the \'common sense\' is located*). That is to say, it is only the latter figures which should be taken to be the forms or images which the rational soul united to this machine will consider directly when it imagines some object or perceives it by the senses.`</font>`{=html} `<font face="times new roman">`{=html}And note that I say \'imagines or perceives by the senses\'. For I wish to apply the term \'idea\' generally to all impressions which the spirits can receive as they leave gland H. These are to be attributed to the \'common\' sense when they depend on the presence of objects; but they may also proceed from many other causes (as I shall explain later), and they should then be attributed to the imagination. \"`</font>`{=html} The *common sense* is referred to by philosophers as the *senses communis*. Descartes considered this to be the place where all the sensations were bound together and proposed the pineal gland for this role. This was in the days before the concept of \'dominance\' of parts of the brain had been developed so Descartes reasoned that only a single organ could host a bound representation. Notice how Descartes is explicit about ideas being **traced in the spirits on the surface of the gland**. Notice also how the rational soul will consider forms on the common sense **directly**. Descartes believed that animals are not conscious because, although he thought they possessed the stimulus-response loop in the same way as humans he believed that they do not possess a soul. ## John Locke (1632-1704) Locke\'s most important philosophical work on the human mind was \"An Essay Concerning Human Understanding\" written in 1689. His idea of perception is summarised in the diagram below:  Locke is an Indirect Realist, admitting of external objects but describing these as represented within the mind. The objects themselves are thought to have a form and properties that are the *archetype* of the object and these give rise in the brain and mind to derived copies called *ektypa*. Like Descartes, he believes that people have souls that produce thoughts. Locke considers that sensations make their way from the senses to the brain where they are laid out for understanding as a \'view\': `<font face="times new roman">`{=html}\"And if these organs, or the nerves which are the conduits to convey them from without to their audience in the brain,- the mind\'s presence-room (as I may so call it)- are any of them so disordered as not to perform their functions, they have no postern to be admitted by; no other way to bring themselves into view, and be perceived by the understanding.\" (Chapter III, 1).`</font>`{=html} He considers that what is sensed becomes a mental thing: Chapter IX: Of Perception paragraph 1: `<font face="times new roman">`{=html}\"This is certain, that whatever alterations are made in the body, if they reach not the mind; whatever impressions are made on the outward parts, if they are not taken notice of within, there is no perception. Fire may burn our bodies with no other effect than it does a billet, unless the motion be continued to the brain, and there the sense of heat, or idea of pain, be produced in the mind; wherein consists actual perception. \"`</font>`{=html} !LockeLocke calls the contents of consciousness \"ideas\" (cf: Descartes, Malebranche) and regards sensation, imagination etc. as being similar or even alike. Chapter I: Of Ideas in general, and their Original: `<font face="times new roman">`{=html}\"1. Idea is the object of thinking. Every man being conscious to himself that he thinks; and that which his mind is applied about whilst thinking being the ideas that are there, it is past doubt that men have in their minds several ideas,- such as are those expressed by the words whiteness, hardness, sweetness, thinking, motion, man, elephant, army, drunkenness, and others: it is in the first place then to be inquired, How he comes by them? `</font>`{=html} `<font face="times new roman">`{=html}I know it is a received doctrine, that men have native ideas, and original characters, stamped upon their minds in their very first being. This opinion I have at large examined already; and, I suppose what I have said in the foregoing Book will be much more easily admitted, when I have shown whence the understanding may get all the ideas it has; and by what ways and degrees they may come into the mind;- for which I shall appeal to every one\'s own observation and experience. `</font>`{=html} `<font face="times new roman">`{=html}2. All ideas come from sensation or reflection. Let us then suppose the mind to be, as we say, white paper, void of all characters, without any ideas:- How comes it to be furnished? Whence comes it by that vast store which the busy and boundless fancy of man has painted on it with an almost endless variety? Whence has it all the materials of reason and knowledge? To this I answer, in one word, from EXPERIENCE. In that all our knowledge is founded; and from that it ultimately derives itself. Our observation employed either, about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understandings with all the materials of thinking. These two are the fountains of knowledge, from whence all the ideas we have, or can naturally have, do spring. `</font>`{=html} `<font face="times new roman">`{=html}3. The objects of sensation one source of ideas. First, our Senses, conversant about particular sensible objects, do convey into the mind several distinct perceptions of things, according to those various ways wherein those objects do affect them. And thus we come by those ideas we have of yellow, white, heat, cold, soft, hard, bitter, sweet, and all those which we call sensible qualities; which when I say the senses convey into the mind, I mean, they from external objects convey into the mind what produces there those perceptions. This great source of most of the ideas we have, depending wholly upon our senses, and derived by them to the understanding, I call SENSATION.`</font>`{=html} `<font face="times new roman">`{=html}4. The operations of our minds, the other source of them. Secondly, the other fountain from which experience furnisheth the understanding with ideas is,- the perception of the operations of our own mind within us, as it is employed about the ideas it has got;- which operations, when the soul comes to reflect on and consider, do furnish the understanding with another set of ideas, which could not be had from things without. And such are perception, thinking, doubting, believing, reasoning, knowing, willing, and all the different actings of our own minds;- which we being conscious of, and observing in ourselves, do from these receive into our understandings as distinct ideas as we do from bodies affecting our senses. This source of ideas every man has wholly in himself; and though it be not sense, as having nothing to do with external objects, yet it is very like it, and might properly enough be called internal sense. But as I call the other SENSATION, so I Call this REFLECTION, the ideas it affords being such only as the mind gets by reflecting on its own operations within itself. By reflection then, in the following part of this discourse, I would be understood to mean, that notice which the mind takes of its own operations, and the manner of them, by reason whereof there come to be ideas of these operations in the understanding. These two, I say, viz. external material things, as the objects of SENSATION, and the operations of our own minds within, as the objects of REFLECTION, are to me the only originals from whence all our ideas take their beginnings. The term operations here I use in a large sense, as comprehending not barely the actions of the mind about its ideas, but some sort of passions arising sometimes from them, such as is the satisfaction or uneasiness arising from any thought.`</font>`{=html} `<font face="times new roman">`{=html}5. All our ideas are of the one or the other of these. The understanding seems to me not to have the least glimmering of any ideas which it doth not receive from one of these two. External objects furnish the mind with the ideas of sensible qualities, which are all those different perceptions they produce in us; and the mind furnishes the understanding with ideas of its own operations. \"`</font>`{=html} He calls ideas that come directly from the senses *primary qualities* and those that come from reflection upon these he calls *secondary qualities*: `<font face="times new roman">`{=html}\"9. Primary qualities of bodies. Qualities thus considered in bodies are, First, such as are utterly inseparable from the body, in what state soever it be; and such as in all the alterations and changes it suffers, all the force can be used upon it, it constantly keeps; and such as sense constantly finds in every particle of matter which has bulk enough to be perceived; and the mind finds inseparable from every particle of matter, though less than to make itself singly be perceived by our senses: \...\...\.... These I call original or primary qualities of body, which I think we may observe to produce simple ideas in us, viz. solidity, extension, figure, motion or rest, and number. 10. Secondary qualities of bodies. Secondly, such qualities which in truth are nothing in the objects themselves but power to produce various sensations in us by their primary qualities\.....\" (Chapter VIII).`</font>`{=html} He gives examples of secondary qualities: `<font face="times new roman">`{=html}\"13. How secondary qualities produce their ideas. After the same manner, that the ideas of these original qualities are produced in us, we may conceive that the ideas of secondary qualities are also produced, viz. by the operation of insensible particles on our senses. \.....v.g. that a violet, by the impulse of such insensible particles of matter, of peculiar figures and bulks, and in different degrees and modifications of their motions, causes the ideas of the blue colour, and sweet scent of that flower to be produced in our minds. It being no more impossible to conceive that God should annex such ideas to such motions, with which they have no similitude, than that he should annex the idea of pain to the motion of a piece of steel dividing our flesh, with which that idea hath no resemblance.\" (Chapter VIII).`</font>`{=html} He argues against all conscious experience being in mental space (does not consider that taste might be on the tongue or a smell come from a cheese): Chapter XIII: Complex Ideas of Simple Modes:- and First, of the Simple Modes of the Idea of Space - paragraph 25: `<font face="times new roman">`{=html}\"I shall not now argue with those men, who take the measure and possibility of all being only from their narrow and gross imaginations: but having here to do only with those who conclude the essence of body to be extension, because they say they cannot imagine any sensible quality of any body without extension,- I shall desire them to consider, that, had they reflected on their ideas of tastes and smells as much as on those of sight and touch; nay, had they examined their ideas of hunger and thirst, and several other pains, they would have found that they included in them no idea of extension at all, which is but an affection of body, as well as the rest, discoverable by our senses, which are scarce acute enough to look into the pure essences of things.\"`</font>`{=html} Locke understood the \"specious\" or extended present but conflates this with longer periods of time: Chapter XIV. Idea of Duration and its Simple Modes - paragraph 1: `<font face="times new roman">`{=html}\"Duration is fleeting extension. There is another sort of distance, or length, the idea whereof we get not from the permanent parts of space, but from the fleeting and perpetually perishing parts of succession. This we call duration; the simple modes whereof are any different lengths of it whereof we have distinct ideas, as hours, days, years, &c., time and eternity.\" `</font>`{=html} Locke is uncertain about whether extended ideas are viewed from an unextended soul. `<font face="times new roman">`{=html}\"He that considers how hardly sensation is, in our thoughts, reconcilable to extended matter; or existence to anything that has no extension at all, will confess that he is very far from certainly knowing what his soul is. It is a point which seems to me to be put out of the reach of our knowledge: and he who will give himself leave to consider freely, and look into the dark and intricate part of each hypothesis, will scarce find his reason able to determine him fixedly for or against the soul\'s materiality. Since, on which side soever he views it, either as an unextended substance, or as a thinking extended matter, the difficulty to conceive either will, whilst either alone is in his thoughts, still drive him to the contrary side.\"(Chapter III, 6).`</font>`{=html} ## David Hume (1711-1776) **Hume (1739--40). A Treatise of Human Nature: Being An Attempt to Introduce the Experimental Method of Reasoning Into Moral Subjects.** !HumeHume represents a type of pure empiricism where certainty is only assigned to present experience. As we can only directly know the mind he works within this constraint. He admits that there can be consistent bodies of knowledge within experience and would probably regard himself as an Indirect Realist but with the caveat that the things that are inferred to be outside the mind, in the physical world, could be no more than inferences within the mind. Hume has a clear concept of mental space and time that is informed by the senses: `<font face="times new roman">`{=html}\"The idea of space is convey\'d to the mind by two senses, the sight and touch; nor does anything ever appear extended, that is not either visible or tangible. That compound impression, which represents extension, consists of several lesser impressions, that are indivisible to the eye or feeling, and may be call\'d impressions of atoms or corpuscles endow\'d with colour and solidity. But this is not all. \'Tis not only requisite, that these atoms shou\'d be colour\'d or tangible, in order to discover themselves to our senses; \'tis also necessary we shou\'d preserve the idea of their colour or tangibility in order to comprehend them by our imagination. There is nothing but the idea of their colour or tangibility, which can render them conceivable by the mind. Upon the removal of the ideas of these sensible qualities, they are utterly annihilated to the thought or imagination.\'`</font>`{=html} `<font face="times new roman">`{=html}Now such as the parts are, such is the whole. If a point be not consider\'d as colour\'d or tangible, it can convey to us no idea; and consequently the idea of extension, which is compos\'d of the ideas of these points, can never possibly exist. But if the idea of extension really can exist, as we are conscious it does, its parts must also exist; and in order to that, must be consider\'d as colour\'d or tangible. We have therefore no idea of space or extension, but when we regard it as an object either of our sight or feeling.`</font>`{=html} `<font face="times new roman">`{=html}The same reasoning will prove, that the indivisible moments of time must be fill\'d with some real object or existence, whose succession forms the duration, and makes it be conceivable by the mind.\"`</font>`{=html} In common with Locke and Eastern Philosophy, Hume considers reflection and sensation to be similar, perhaps identical: `<font face="times new roman">`{=html}\"Thus it appears, that the belief or assent, which always attends the memory and senses, is nothing but the vivacity of those perceptions they present; and that this alone distinguishes them from the imagination. To believe is in this case to feel an immediate impression of the senses, or a repetition of that impression in the memory. \'Tis merely the force and liveliness of the perception, which constitutes the first act of the judgment, and lays the foundation of that reasoning, which we build upon it, when we trace the relation of cause and effect.\"`</font>`{=html} Hume considers that the origin of sensation can never be known, believing that the canvass of the mind contains our view of the world whatever the ultimate source of the images within the view and that we can construct consistent bodies of knowledge within these constraints: `<font face="times new roman">`{=html}\"As to those impressions, which arise from the senses, their ultimate cause is, in my opinion, perfectly inexplicable by human reason, and \'twill always be impossible to decide with certainty, whether they arise immediately from the object, or are produc\'d by the creative power of the mind, or are deriv\'d from the author of our being. Nor is such a question any way material to our present purpose. We may draw inferences from the coherence of our perceptions, whether they be true or false; whether they represent nature justly, or be mere illusions of the senses.\"`</font>`{=html} It may be possible to trace the origins of Jackson\'s Knowledge Argument in Hume\'s work: `<font face="times new roman">`{=html}\" Suppose therefore a person to have enjoyed his sight for thirty years, and to have become perfectly well acquainted with colours of all kinds, excepting one particular shade of blue, for instance, which it never has been his fortune to meet with. Let all the different shades of that colour, except that single one, be plac\'d before him, descending gradually from the deepest to the lightest; \'tis plain, that he will perceive a blank, where that shade is wanting, said will be sensible, that there is a greater distance in that place betwixt the contiguous colours, than in any other. Now I ask, whether \'tis possible for him, from his own imagination, to supply this deficiency, and raise up to himself the idea of that particular shade, tho\' it had never been conveyed to him by his senses? I believe i here are few but will be of opinion that he can; and this may serve as a proof, that the simple ideas are not always derived from the correspondent impressions; tho\' the instance is so particular and singular, that \'tis scarce worth our observing, and does not merit that for it alone we should alter our general maxim.\"`</font>`{=html} **David Hume (1748) An Enquiry Concerning Human Understanding** Hume\'s view of Locke and Malebranche: `<font face="times new roman">`{=html}\"The fame of Cicero flourishes at present; but that of Aristotle is utterly decayed. La Bruyere passes the seas, and still maintains his reputation: But the glory of Malebranche is confined to his own nation, and to his own age. And Addison, perhaps, will be read with pleasure, when Locke shall be entirely forgotten.\"`</font>`{=html} He is clear about relational knowledge in space and time: `<font face="times new roman">`{=html}\"13. .. But though our thought seems to possess this unbounded liberty, we shall find, upon a nearer examination, that it is really confined within very narrow limits, and that all this creative power of the mind amounts to no more than the faculty of compounding, transposing, augmenting, or diminishing the materials afforded us by the senses and experience. When we think of a golden mountain, we only join two consistent ideas, gold, and mountain, with which we were formerly acquainted.\"`</font>`{=html} \... `<font face="times new roman">`{=html}19. Though it be too obvious to escape observation, that different ideas are connected together; I do not find that any philosopher has attempted to enumerate or class all the principles of association; a subject, however, that seems worthy of curiosity. To me, there appear to be only three principles of connexion among ideas, namely, Resemblance, Contiguity in time or place, and Cause or Effect.\"`</font>`{=html} He is also clear that, although we experience the output of processes, we do not experience the processes themselves: `<font face="times new roman">`{=html}\"29. It must certainly be allowed, that nature has kept us at a great distance from all her secrets, and has afforded us only the knowledge of a few superficial qualities of objects; while she conceals from us those powers and principles on which the influence of those objects entirely depends. Our senses inform us of the colour, weight, and consistence of bread; but neither sense nor reason can ever inform us of those qualities which fit it for the nourishment and support of a human body. Sight or feeling conveys an idea of the actual motion of bodies; but as to that wonderful force or power, which would carry on a moving body for ever in a continued change of place, and which bodies never lose but by communicating it to others; of this we cannot form the most distant conception. ..`</font>`{=html} `<font face="times new roman">`{=html}58. \... All events seem entirely loose and separate. One event follows another; but we never can observe any tie between them. They seem conjoined, but never connected. And as we can have no idea of any thing which never appeared to our outward sense or inward sentiment, the necessary conclusion seems to be that we have no idea of connexion or power at all, and that these words are absolutely without any meaning, when employed either in philosophical reasonings or common life. \"`</font>`{=html} Our idea of process is not a direct experience but seems to originate from remembering the repetition of events: `<font face="times new roman">`{=html}\"59 ..It appears, then, that this idea of a necessary connexion among events arises from a number of similar instances which occur of the constant conjunction of these events; nor can that idea ever be suggested by any one of these instances, surveyed in all possible lights and positions. But there is nothing in a number of instances, different from every single instance, which is supposed to be exactly similar; except only, that after a repetition of similar instances, the mind is carried by habit, upon the appearance of one event, to expect its usual attendant, and to believe that it will exist.\"`</font>`{=html} ## Emmanuel Kant (1724-1804) !kantKant\'s greatest work on the subject of consciousness and the mind is Critique of Pure Reason (1781). Kant describes his objective in this work as discovering the axioms (\"a priori concepts\") and then the processes of \'understanding\'. `<font face="times new roman">`{=html}P12 \"This enquiry, which is somewhat deeply grounded, has two sides. The one refers to the objects of pure understanding, and is intended to expound and render intelligible the objective validity of its a priori concepts. It is therefore essential to my purposes. The other seeks to investigate the pure understanding itself, its possibility and the cognitive faculties upon which it rests; and so deals with it in its subjective aspect. Although this latter exposition is of great importance for my chief purpose, it does not form an essential part of it. For the chief question is always simply this: - what and how much can the understanding and reason know apart from all experience?\"`</font>`{=html} Kant\'s idea of perception and mind is summarised in the illustration below:  \'Experience\' is simply accepted. Kant believes that the physical world exists but is not known directly: `<font face="times new roman">`{=html}P 24 \"For we are brought to the conclusion that we can never transcend the limits of possible experience, though that is precisely what this science is concerned, above all else, to achieve. This situation yields, however, just the very experiment by which, indirectly, we are enabled to prove the truth of this first estimate of our a priori knowledge of reason, namely, that such knowledge has to do only with appearances, and must leave the thing in itself as indeed real per se, but as not known by us. \"`</font>`{=html} Kant is clear about the form and content of conscious experience. He notes that we can only experience things that have appearance and \'form\' - content and geometrical arrangement. `<font face="times new roman">`{=html}P65-66 \"IN whatever manner and by whatever means a mode of knowledge may relate to objects, intuition is that through which it is in immediate relation to them, and to which all thought as a means is directed. But intuition takes place only in so far as the object is given to us. This again is only possible, to man at least, in so far as the mind is affected in a certain way. The capacity (receptivity) for receiving representations through the mode in which we are affected by objects, is entitled sensibility. Objects are given to us by means of sensibility, and it alone yields us intuitions; they are thought through the understanding, and from the understanding arise concepts. But all thought must, directly or indirectly, by way of certain characters relate ultimately to intuitions, and therefore, with us, to sensibility, because in no other way can an object be given to us. The effect of an object upon the faculty of representation, so far as we are affected by it, is sensation. That intuition which is in relation to the object through sensation, is entitled empirical. The undetermined object of an empirical intuition is entitled appearance. That in the appearance which corresponds to sensation I term its matter; but that which so determines the manifold of appearance that it allows of being ordered in certain relations, I term the form of appearance. That in which alone the sensations can be posited and ordered in a certain form, cannot itself be sensation; and therefore, while the matter of all appearance is given to us a posteriori only, its form must lie ready for the sensations a priori in the mind, and so must allow of being considered apart from all sensation. \"`</font>`{=html} Furthermore he realises that experience exists without much content. That consciousness depends on form: `<font face="times new roman">`{=html}P66 \"The pure form of sensible intuitions in general, in which all the manifold of intuition is intuited in certain relations, must be found in the mind a priori. This pure form of sensibility may also itself be called pure intuition. Thus, if I take away from the representation of a body that which the understanding thinks in regard to it, substance, force, divisibility, etc. , and likewise what belongs to sensation, impenetrability, hardness, colour, etc. , something still remains over from this empirical intuition, namely, extension and figure. These belong to pure intuition, which, even without any actual object of the senses or of sensation, exists in the mind a priori as a mere form of sensibility. The science of all principles of a priori sensibility I call transcendental aesthetic.\"`</font>`{=html} Kant proposes that space exists in our experience and that experience could not exist without it (apodeictic means \'incontrovertible): `<font face="times new roman">`{=html}P 68 \"1. Space is not an empirical concept which has been derived from outer experiences. For in order that certain sensations be referred to something outside me (that is, to something in another region of space from that in which I find myself), and similarly in order that I may be able to represent them as outside and alongside one another, and accordingly as not only different but as in different places, the representation of space must be presupposed. The representation of space cannot, therefore, be empirically obtained from the relations of outer appearance. On the contrary, this outer experience is itself possible at all only through that representation. 2. Space is a necessary a priori representation, which underlies all outer intuitions. We can never represent to ourselves the absence of space, though we can quite well think it as empty of objects. It must therefore be regarded as the condition of the possibility of appearances, and not as a determina- tion dependent upon them. It is an a priori representation, which necessarily underlies outer appearances. \* 3. The apodeictic certainty of all geometrical propositions and the possibility of their a priori construction is grounded in this a priori necessity of space. \...\...\...\"`</font>`{=html} He is equally clear about the necessity of time as part of experience but he has no clear exposition of the (specious present) extended present: `<font face="times new roman">`{=html}P 74 \"1. Time is not an empirical concept that has been derived from any experience. For neither coexistence nor succession would ever come within our perception, if the representation of time were not presupposed as underlying them a priori. Only on the presupposition of time can we represent to ourselves a number of things as existing at one and the same time (simultaneously) or at different times (successively). They are connected with the appearances only as effects accidentally added by the particular constitution of the sense organs. Accordingly, they are not a priori representations, but are grounded in sensation, and, indeed, in the case of taste, even upon feeling (pleasure and pain), as an effect of sensation. Further, no one can have a priori a representation of a colour or of any taste; whereas, since space concerns only the pure form of intuition, and therefore involves no sensation whatsoever, and nothing empirical, all kinds and determinations of space can and must be represented a priori, if concepts of figures and of their relations are to arise. Through space alone is it possible that things should be outer objects to us. ..2. 3.. 4.. 5\...\"`</font>`{=html} Kant has a model of experience as a succession of 3D instants, based on conventional 18th century thinking, allowing his reason to overcome his observation. He says of time that: `<font face="times new roman">`{=html}P 79 \" It is nothing but the form of our inner intuition. If we take away from our inner intuition the peculiar condition of our sensibility, the concept of time likewise vanishes; it does not inhere in the objects, but merely in the subject which intuits them. I can indeed say that my representations follow one another; but this is only to say that we are conscious of them as in a time sequence, that is, in conformity with the form of inner sense. Time is not, therefore, something in itself, nor is it an objective determination inherent in things.\"`</font>`{=html} This analysis is strange because if uses the geometric term \"form\" but then uses the processing term \"succession\". ## Gottfried Wilhelm Leibniz (1646-1716) !LeibnizLeibniz is one of the first to notice that there is a problem with the proposition that computational machines could be conscious: `<font face="times new roman">`{=html}\"One is obliged to admit that perception and what depends upon it is inexplicable on mechanical principles, that is, by figures and motions. In imagining that there is a machine whose construction would enable it to think, to sense, and to have perception, one could conceive it enlarged while retaining the same proportions, so that one could enter into it, just like into a windmill. Supposing this, one should, when visiting within it, find only parts pushing one another, and never anything by which to explain a perception. Thus it is in the simple substance, and not in the composite or in the machine, that one must look for perception.\" Monadology, 17.`</font>`{=html} Leibniz considered that the world was composed of \"monads\": `<font face="times new roman">`{=html}\"1. The Monad, of which we shall here speak, is nothing but a simple substance, which enters into compounds. By \'simple\' is meant \'without parts.\' (Theod. 10.) `</font>`{=html} `<font face="times new roman">`{=html}2. And there must be simple substances, since there are compounds; for a compound is nothing but a collection or aggregatum of simple things.`</font>`{=html} `<font face="times new roman">`{=html}3. Now where there are no parts, there can be neither extension nor form \[figure\] nor divisibility. These Monads are the real atoms of nature and, in a word, the elements of things. \" (Monadology 1714).`</font>`{=html} These monads are considered to be capable of perception through the meeting of things at a point: `<font face="times new roman">`{=html}\"They cannot have shapes, because then they would have parts; and therefore one monad in itself, and at a moment, cannot be distinguished from another except by its internal qualities and actions; which can only be its *perceptions* (that is, the representations of the composite, or of what is external, in the simple), or its *appetitions* (its tending to move from one perception to another, that is), which are the principles of change. For the simplicity of a substance does not in any way rule out a multiplicity in the modifications which must exist together in one simple substance; and those modifications must consist in the variety of its relationships to things outside it - like the way in which in a *centre*, or a *point*, although it is completely simple, there are an infinity of angles formed which meet in it.\" (Principles of Nature and Grace 1714).`</font>`{=html} Leibniz also describes this in his \"New System\": `<font face="times new roman">`{=html}\"It is only atoms of substance, that is to say real unities absolutely devoid of parts, that can be the sources of actions, and the absolute first principles of the composition of things, and as it were the ultimate elements in the analysis of substances `<substantial things>`{=html}. They might be called *metaphysical points*; they have *something of the nature of life* and a kind of *perception*, and *mathematical points* are their *point of view* for expressing the universe.\"(New System (11) 1695).`</font>`{=html} Having identified perception with metaphysical points Leibniz realises that there is a problem connecting the points with the world (cf: epiphenomenalism): `<font face="times new roman">`{=html}\"Having decided these things, I thought I had reached port, but when I set myself to think about the union of the soul with the body I was as it were carried back into the open sea. For I could find no way of explaining how the body can make something pass over into the soul or vice versa, or how one created substance can communicate with another.\"(New System (12) 1695).`</font>`{=html} Leibniz devises a theory of \"pre-established harmony\" to overcome this epiphenomenalism. He discusses how two separate clocks could come to tell the same time and proposes that this could be due to mutual influence of one clock on the other (\"the way of influence\"), continual adjustment by a workman (\"the way of assistance\") or by making the clocks so well that they are always in agreement (\"the way of pre-established agreement\" or harmony). He considers each of these alternatives for harmonising the perceptions with the world and concludes that only the third is viable: `<font face="times new roman">`{=html}\"Thus there remains only my theory, *the way of pre-established harmony*, set up by a contrivance of divine foreknowledge, which formed each of these substances from the outset in so perfect, so regular, and so exact a manner, that merely by following out its own laws, which were given to it when it was brought into being, each substance is nevertheless in harmony with the other, just as if there were a mutual influence between them, or as if in addition to his general concurrence God were continually operating upon them. (Third Explanation of the New System (5), 1696).\"`</font>`{=html} This means that he must explain how perceptions involving the world take place: `<font face="times new roman">`{=html}\"Because of the plenitude of the world everything is linked, and every body acts to a greater or lesser extent on every other body in proportion to distance, and is affected by it in return. It therefore follows that every monad is a living mirror, or a mirror endowed with internal activity, representing the universe in accordance with its own point of view, and as orderly as the universe itself. The perceptions of monads arise one out of another by the laws of appetite, or of the *final causes of good and evil* (which are prominent perceptions, orderly or disorderly), just as changes in bodies or in external phenomena arise one from another by the laws of *efficient causes*, of motion that is. Thus there is perfect *harmony* between the perceptions of the monad and the motions of bodies, pre-established from the outset, between the system of efficient causes and that of final causes. And it is that harmony that the agreement or physical union between the soul and body consists, without either of them being able to change the laws of the other.\" (Principles of Nature and Grace (3) 1714).`</font>`{=html} The \"laws of appetite\" are defined as: `<font face="times new roman">`{=html}\"The action of the internal principle which brings about change, or the passage from one perception to another, can be called *appetition*. In fact appetite cannot always attain in its entirety the whole of the perception towards which it tends, but it always obtains some part of it, and attains new perceptions. Monadology 15.`</font>`{=html} Leibniz thought animals had souls but not minds: `<font face="times new roman">`{=html}\"But *true* reasoning depends on necessary or eternal truths like those of logic, numbers, and geometry, which make indubitable connections between ideas, and conclusions which are inevitable. Animals in which such conclusions are never perceived are called *brutes*; but those which recognise such necessary truths are what are rightly called *rational animals* and their souls are called *minds*. (Principles of Nature and Grace (5) 1714).`</font>`{=html} Minds allow reflection and awareness: `<font face="times new roman">`{=html}\"And it is by the knowledge of necessary truths, and by the abstractions they involve, that we are raised to *acts of reflection*, which make us aware of what we call *myself*, and make us think of this or that thing as in *ourselves*. And in this way, by thinking of ourselves, we think of being, of substance, of simples and composites, of the immaterial - and, by realising that what is limited in us is limitless in him, of God himself. And so these *acts of reflection* provide the principle objects of our reasonings.\" Monadology, 30.`</font>`{=html} ## George Berkeley (1685 - 1753) A Treatise on the Principles of Human Knowledge. 1710 !BerkeleyBerkeley introduces the Principles of Human Knowledge with a diatribe against abstract ideas. He uses the abstract ideas of animals as an example: `<font face="times new roman">`{=html}\"Introduction. 9\...\.....The constituent parts of the abstract idea of animal are body, life, sense, and spontaneous motion. By body is meant body without any particular shape or figure, there being no one shape or figure common to all animals, without covering, either of hair, or feathers, or scales, &c., nor yet naked: hair, feathers, scales, and nakedness being the distinguishing properties of particular animals, and for that reason left out of the abstract idea. Upon the same account the spontaneous motion must be neither walking, nor flying, nor creeping; it is nevertheless a motion, but what that motion is it is not easy to conceive. `</font>`{=html} He then declares that such abstractions cannot be imagined. He emphasises that ideas are \"represented to myself\" and have shape and colour: `<font face="times new roman">`{=html}\"Introduction. 10. Whether others have this wonderful faculty of abstracting their ideas, they best can tell: for myself, I find indeed I have a faculty of imagining, or representing to myself, the ideas of those particular things I have perceived, and of variously compounding and dividing them. I can imagine a man with two heads, or the upper parts of a man joined to the body of a horse. I can consider the hand, the eye, the nose, each by itself abstracted or separated from the rest of the body. But then whatever hand or eye I imagine, it must have some particular shape and colour. Likewise the idea of man that I frame to myself must be either of a white, or a black, or a tawny, a straight, or a crooked, a tall, or a low, or a middle-sized man. I cannot by any effort of thought conceive the abstract idea above described. And it is equally impossible for me to form the abstract idea of motion distinct from the body moving, and which is neither swift nor slow, curvilinear nor rectilinear; and the like may be said of all other abstract general ideas whatsoever.\"`</font>`{=html} This concept of ideas as extended things, or representations, is typical of the usage amongst philosophers in the 17th and 18th century and can cause confusion in modern readers. Berkeley considers that words that are used to describe classes of things in the abstract can only be conceived as particular cases: `<font face="times new roman">`{=html}\"Introduction. 15\... Thus, when I demonstrate any proposition concerning triangles, it is to be supposed that I have in view the universal idea of a triangle; which ought not to be understood as if I could frame an idea of a triangle which was neither equilateral, nor scalenon, nor equicrural; but only that the particular triangle I consider, whether of this or that sort it matters not, doth equally stand for and represent all rectilinear triangles whatsoever, and is in that sense universal. All which seems very plain and not to include any difficulty in it.`</font>`{=html} Intriguingly, he considers that language is used to directly excite emotions as well as to communicate ideas: `<font face="times new roman">`{=html}\"Introduction. 20. \... I entreat the reader to reflect with himself, and see if it doth not often happen, either in hearing or reading a discourse, that the passions of fear, love, hatred, admiration, disdain, and the like, arise immediately in his mind upon the perception of certain words, without any ideas coming between.`</font>`{=html} Berkeley considers that extension is a quality of mind: `<font face="times new roman">`{=html}\"11. Again, great and small, swift and slow, are allowed to exist nowhere without the mind, being entirely relative, and changing as the frame or position of the organs of sense varies. The extension therefore which exists without the mind is neither great nor small, the motion neither swift nor slow, that is, they are nothing at all. But, say you, they are extension in general, and motion in general: thus we see how much the tenet of extended movable substances existing without the mind depends on the strange doctrine of abstract ideas.\" `</font>`{=html} He notes that the rate at which things pass may be related to the mind: `<font face="times new roman">`{=html}\"14\..... Is it not as reasonable to say that motion is not without the mind, since if the succession of ideas in the mind become swifter, the motion, it is acknowledged, shall appear slower without any alteration in any external object? `</font>`{=html} Berkeley raises the issue of whether objects exist without being perceived. He bases his argument on the concept of perception being the perceiving of \"our own ideas or sensations\": `<font face="times new roman">`{=html}\"4. It is indeed an opinion strangely prevailing amongst men, that houses, mountains, rivers, and in a word all sensible objects, have an existence, natural or real, distinct from their being perceived by the understanding. But, with how great an assurance and acquiescence soever this principle may be entertained in the world, yet whoever shall find in his heart to call it in question may, if I mistake not, perceive it to involve a manifest contradiction. For, what are the fore-mentioned objects but the things we perceive by sense? and what do we perceive besides our own ideas or sensations? and is it not plainly repugnant that any one of these, or any combination of them, should exist unperceived?\"`</font>`{=html} He further explains this concept in terms of some Eternal Spirit allowing continued existence. Berkeley is clear that the contents of the mind have \"colour, figure, motion, smell, taste etc.\": `<font face="times new roman">`{=html}\"7. From what has been said it follows there is not any other Substance than Spirit, or that which perceives. But, for the fuller proof of this point, let it be considered the sensible qualities are colour, figure, motion, smell, taste, etc., i.e. the ideas perceived by sense. Now, for an idea to exist in an unperceiving thing is a manifest contradiction, for to have an idea is all one as to perceive; that therefore wherein colour, figure, and the like qualities exist must perceive them; hence it is clear there can be no unthinking substance or substratum of those ideas.\"`</font>`{=html} He elaborates the concept that there is no unthinking substance or substratum for ideas and all is mind: `<font face="times new roman">`{=html}\"18. But, though it were possible that solid, figured, movable substances may exist without the mind, corresponding to the ideas we have of bodies, yet how is it possible for us to know this? Either we must know it by sense or by reason. As for our senses, by them we have the knowledge only of our sensations, ideas, or those things that are immediately perceived by sense, call them what you will: but they do not inform us that things exist without the mind, or unperceived, like to those which are perceived. This the materialists themselves acknowledge. It remains therefore that if we have any knowledge at all of external things, it must be by reason, inferring their existence from what is immediately perceived by sense. But what reason can induce us to believe the existence of bodies without the mind, from what we perceive, since the very patrons of Matter themselves do not pretend there is any necessary connexion betwixt them and our ideas? I say it is granted on all hands (and what happens in dreams, phrensies, and the like, puts it beyond dispute) that it is possible we might be affected with all the ideas we have now, though there were no bodies existing without resembling them. Hence, it is evident the supposition of external bodies is not necessary for the producing our ideas; since it is granted they are produced sometimes, and might possibly be produced always in the same order, we see them in at present, without their concurrence. \"`</font>`{=html} and stresses that there is no apparent connection between mind and the proposed material substrate of ideas: `<font face="times new roman">`{=html}\"19. But, though we might possibly have all our sensations without them, yet perhaps it may be thought easier to conceive and explain the manner of their production, by supposing external bodies in their likeness rather than otherwise; and so it might be at least probable there are such things as bodies that excite their ideas in our minds. But neither can this be said; for, though we give the materialists their external bodies, they by their own confession are never the nearer knowing how our ideas are produced; since they own themselves unable to comprehend in what manner body can act upon spirit, or how it is possible it should imprint any idea in the mind. \..... `</font>`{=html} Berkeley makes a crucial observation, that had also been noticed by Descartes, that ideas are passive: `<font face="times new roman">`{=html}\"25. All our ideas, sensations, notions, or the things which we perceive, by whatsoever names they may be distinguished, are visibly inactive- there is nothing of power or agency included in them. So that one idea or object of thought cannot produce or make any alteration in another. To be satisfied of the truth of this, there is nothing else requisite but a bare observation of our ideas. For, since they and every part of them exist only in the mind, it follows that there is nothing in them but what is perceived: but whoever shall attend to his ideas, whether of sense or reflexion, will not perceive in them any power or activity; there is, therefore, no such thing contained in them. A little attention will discover to us that the very being of an idea implies passiveness and inertness in it, insomuch that it is impossible for an idea to do anything, or, strictly speaking, to be the cause of anything: neither can it be the resemblance or pattern of any active being, as is evident from sect. 8. Whence it plainly follows that extension, figure, and motion cannot be the cause of our sensations. To say, therefore, that these are the effects of powers resulting from the configuration, number, motion, and size of corpuscles, must certainly be false. `</font>`{=html} He considers that \"the cause of ideas is an incorporeal active substance or Spirit (26)\". He summarises the concept of an Eternal Spirit that governs real things and a representational mind that copies the form of the world as follows: `<font face="times new roman">`{=html}\"33. The ideas imprinted on the Senses by the Author of nature are called real things; and those excited in the imagination being less regular, vivid, and constant, are more properly termed ideas, or images of things, which they copy and represent. But then our sensations, be they never so vivid and distinct, are nevertheless ideas, that is, they exist in the mind, or are perceived by it, as truly as the ideas of its own framing. The ideas of Sense are allowed to have more reality in them, that is, to be more strong, orderly, and coherent than the creatures of the mind; but this is no argument that they exist without the mind. They are also less dependent on the spirit, or thinking substance which perceives them, in that they are excited by the will of another and more powerful spirit; yet still they are ideas, and certainly no idea, whether faint or strong, can exist otherwise than in a mind perceiving it. `</font>`{=html} Berkeley considers that the concept of distance is a concept in the mind and also that dreams can be compared directly with sensations: `<font face="times new roman">`{=html}\"42. Thirdly, it will be objected that we see things actually without or at distance from us, and which consequently do not exist in the mind; it being absurd that those things which are seen at the distance of several miles should be as near to us as our own thoughts. In answer to this, I desire it may be considered that in a dream we do oft perceive things as existing at a great distance off, and yet for all that, those things are acknowledged to have their existence only in the mind.\"`</font>`{=html} He considers that ideas can be extended without the mind being extended: `<font face="times new roman">`{=html}\"49. Fifthly, it may perhaps be objected that if extension and figure exist only in the mind, it follows that the mind is extended and figured; since extension is a mode or attribute which (to speak with the schools) is predicated of the subject in which it exists. I answer, those qualities are in the mind only as they are perceived by it- that is, not by way of mode or attribute, but only by way of idea; and it no more follows the soul or mind is extended, because extension exists in it alone, than it does that it is red or blue, because those colours are on all hands acknowledged to exist in it, and nowhere else. As to what philosophers say of subject and mode, that seems very groundless and unintelligible. For instance, in this proposition \"a die is hard, extended, and square,\" they will have it that the word die denotes a subject or substance, distinct from the hardness, extension, and figure which are predicated of it, and in which they exist. This I cannot comprehend: to me a die seems to be nothing distinct from those things which are termed its modes or accidents. And, to say a die is hard, extended, and square is not to attribute those qualities to a subject distinct from and supporting them, but only an explication of the meaning of the word die. `</font>`{=html} Berkeley proposes that time is related to the succession of ideas: `<font face="times new roman">`{=html}\"98. For my own part, whenever I attempt to frame a simple idea of time, abstracted from the succession of ideas in my mind, which flows uniformly and is participated by all beings, I am lost and embrangled in inextricable difficulties. I have no notion of it at all, only I hear others say it is infinitely divisible, and speak of it in such a manner as leads me to entertain odd thoughts of my existence; since that doctrine lays one under an absolute necessity of thinking, either that he passes away innumerable ages without a thought, or else that he is annihilated every moment of his life, both which seem equally absurd. Time therefore being nothing, abstracted from the succession of ideas in our minds, it follows that the duration of any finite spirit must be estimated by the number of ideas or actions succeeding each other in that same spirit or mind. Hence, it is a plain consequence that the soul always thinks; and in truth whoever shall go about to divide in his thoughts, or abstract the existence of a spirit from its cogitation, will, I believe, find it no easy task. `</font>`{=html} `<font face="times new roman">`{=html}\"99. So likewise when we attempt to abstract extension and motion from all other qualities, and consider them by themselves, we presently lose sight of them, and run into great extravagances. All which depend on a twofold abstraction; first, it is supposed that extension, for example, may be abstracted from all other sensible qualities; and secondly, that the entity of extension may be abstracted from its being perceived. But, whoever shall reflect, and take care to understand what he says, will, if I mistake not, acknowledge that all sensible qualities are alike sensations and alike real; that where the extension is, there is the colour, too, i.e., in his mind, and that their archetypes can exist only in some other mind; and that the objects of sense are nothing but those sensations combined, blended, or (if one may so speak) concreted together; none of all which can be supposed to exist unperceived.\" `</font>`{=html} He regards \"spirit\" as something separate from ideas and attempts to answer the charge that as spirit is not an idea it cannot be known: `<font face="times new roman">`{=html}\"139. But it will be objected that, if there is no idea signified by the terms soul, spirit, and substance, they are wholly insignificant, or have no meaning in them. I answer, those words do mean or signify a real thing, which is neither an idea nor like an idea, but that which perceives ideas, and wills, and reasons about them. \....`</font>`{=html} ## Thomas Reid (1710-1796) !ReidThomas Reid is generally regarded as the founder of Direct Realism. Reid was a Presbyterian minister for the living of Newmachar near Aberdeen from 1737. He is explicit about the \'directness\' of his realism: `<font face="times new roman">`{=html}\"It is therefore acknowledged by this philosopher to be a natural instinct or prepossession, a universal and primary opinion of all men, a primary instinct of nature, that the objects which we immediately perceive by our senses are not images in our minds, but external objects, and that their existence is independent of us and our perception. (Thomas Reid Essays, 14)\"`</font>`{=html} In common with Descartes and Malebranche, Reid considers that the mind itself is an unextended thing: `<font face="times new roman">`{=html}\".. I take it for granted, upon the testimony of common sense, that my mind is a substance-that is, a permanent subject of thought; and my reason convinces me that it is an unextended and invisible substance; and hence I infer that there cannot be in it anything that resembles extension (Inquiry)\".`</font>`{=html} Reid is also anxious to equate the unextended mind with the soul: `<font face="times new roman">`{=html}\"The soul, without being present to the images of the things perceived, could not possibly perceive them. A living substance can only there perceive, where it is present, either to the things themselves, (as the omnipresent God is to the whole universe,) or to the images of things, as the soul is in its proper sensorium.\"`</font>`{=html} Reid\'s Direct Realism is therefore the idea that the physical objects in the world are in some way presented directly to a soul. This approach is known as \"Natural Dualism\". Reid\'s views show his knowledge of Aristotle\'s ideas: `<font face="times new roman">`{=html}\"When we perceive an object by our senses, there is, first, some impression made by the object upon the organ of sense, either immediately, or by means of some medium. By this, an impression is made upon the brain, in consequence of which we feel some sensation. \" (Reid 1785)`</font>`{=html} He differs from Aristotle because he believes that the content of phenomenal consciousness is things in themselves, not signals derived from things in the brain. However, he has no idea how such a phenomenon could occur: `<font face="times new roman">`{=html}\"How a sensation should instantly make us conceive and believe the existence of an external thing altogether unlike it, I do not pretend to know; and when I say that the one suggests the other, I mean not to explain the manner of their connection, but to express a fact, which everyone may be conscious of namely, that, by a law of our nature, such a conception and belief constantly and immediately follow the sensation.\" (Reid 1764).`</font>`{=html} Reid\'s idea of mind is almost impossible to illustrate because it lacks sufficient physical definition. It is like naive realism but without any communication by light between object and observer. Reid was largely ignored until the rise of modern Direct Realism.  Reading between the lines, it seems that Reid is voicing the ancient intuition that the observer and the content of an observation are directly connected in some way. As will be seen later, this intuition cannot distinguish between a direct connection with the world itself and a direct connection with signals from the world beyond the body that are formed into a virtual reality in the brain. ## References - Descartes, R. (1628). Rules For The Direction of The Mind. - Descartes, R. (1637). DISCOURSE ON THE METHOD OF RIGHTLY CONDUCTING THE REASON, AND SEEKING TRUTH IN THE SCIENCES. - Descartes, R. (1641). Meditations on First Philosophy. - Descartes, R. (1664) \"Treatise on Man\". Translated by John Cottingham, et al. The Philosophical Writings of Descartes, Vol. 1 (Cambridge: Cambridge University Press, 1985) 99-108. - Kant, I. (1781) Critique of Pure Reason. Trans. Norman Kemp Smith with preface by Howard Caygill. Pub: Palgrave Macmillan. - Locke, J. (1689). An Essay Concerning Human Understanding - Reid, T. (1785). Essays on the Intellectual Powers of Man. Edited by Brookes, Derek. Edinburgh: Edinburgh University Press, 2002. - Reid, T. (1764). An Inquiry into the Human Mind on the Principles of Common Sense. Edited by Brookes, Derek. Edinburgh: Edinburgh University Press, 1997. - Russell, B. (1945). A History of Western Philosophy. New York: Simon and Schuster. **Further Reading** See: \"Thomas Reid\" at Wikisource - Cartesian Conscientia by Robert Hennig

# Consciousness Studies/The Description Of Consciousness *This section presents the empirical idea of consciousness. What consciousness is like before theories are applied to explain it. It is based on descriptions from the Historical Review.* ## The definition and description of phenomenal consciousness What is it like to be conscious? Before embarking on the analysis of phenomenal consciousness it is important to have a definition of what it is that we are attempting to explain. The article below considers empirical descriptions of phenomenal consciousness. It shows that phenomenal consciousness is the space, time and content of our minds (where the content contains intuitions and feelings). As will be seen in later parts of the book not all philosophers and scientists accept that this \"phenomenal consciousness\" actually exists. ### Introduction Empirical descriptions of phenomenal consciousness have been available in Western literature for centuries and in Eastern literature for millennia. It is often maintained that no-one can define consciousness but there is a large body of literature that gives a clear empirical description of it. Perhaps the claim that no-one can define consciousness is frustration at the fact that no-one can explain consciousness. Weiskrantz (1988) asserted that \"Each of us will have his or her own idea of what, if anything, is meant by consciousness\...\" and that insisting upon a precise definition would be a mistake. Koch and Crick (1999) stated that \"Consciousness is a vague term with many usages and will, in the fullness of time, be replaced by a vocabulary that more accurately reflects the contribution of different brain processes.\" But is consciousness really a \"vague term\" and should we each have our own idea of what it means? The empirical descriptions of Descartes, Kant and others are summarised below under the headings of space, time, qualia and awareness. These descriptions show that consciousness is not a vague term at all. ### Space and Time Kant (1781) argued that our minds must be capable of representing objects in space and time. Experiences presuppose space and time as pure concepts of reason. Without space, objects could not be differentiated and would have no properties. Without representation in time, the concepts of succession of events and simultaneity would be unknown to us. James(1904) also describes experience as extended in space and says that the idea that \"inner experience is absolutely inextensive seems to me little short of absurd\". Descartes (1641, Meditation V, 3) was also clear that imaginings and perceptions are experiences where things are arranged in space and time: \"In the first place, I distinctly imagine that quantity which the philosophers commonly call continuous, or the extension in length, breadth, and depth that is in this quantity, or rather in the object to which it is attributed. Further, I can enumerate in it many diverse parts, and attribute to each of these all sorts of sizes, figures, situations, and local motions; and, in time, I can assign to each of these motions all degrees of duration.\" Descartes was, as was so often the case, well ahead of his time by describing continuity and dimensionality, the factors that define his view of space as an actual vector space accessible to mathematical and physical analysis (See section on Descartes for a full discussion.) Gregory (1966) also pointed out that we see things as if they are projected into space around us. The idea of projection was implicit in Kant's and Descartes' descriptions, which are from the viewpoint of an observer looking out at contents of experience, but Gregory is explicit (although he believes that explanations based on the projection are absurd). Kant and Descartes describe consciousness as something extended in time but it is Clay and James who draw this fully to our attention. James (1890) quotes E.R. Clay who coined the term \"specious present\" to describe how we exist for more than a durationless instant and then goes on to say: \"In short, the practically cognized present is no knife-edge, but a saddle-back, with a certain breadth of its own on which we sit perched, and from which we look in two directions into time. The unit of composition of our perception of time is a duration, with a bow and a stern, as it were\--a rearward\--and a forward-looking end. It is only \[p. 610\] as parts of this duration-block that the relation of succession of one end to the other is perceived. We do not first feel one end and then feel the other after it, and from the perception of the succession infer an interval of time between, but we seem to feel the interval of time as a whole, with its two ends embedded in it.\" Notice how James' observer is at an instant but the mind is stretched over time. James' mental time is probably not the same as physical time. Hermann Weyl, the Nobel prize-winning physicist, wrote that reality is a \"four-dimensional continuum which is neither \'time\' nor \'space.\' Only the consciousness that passes on in one portion of this world experiences the detached piece which comes to meet it and passes behind it, as history, that is, as a process that is going forward in time and takes place in space\" (Weyl 1918). In other words consciousness has a way of containing events in the same order as they occur in the world but seems to use a mental time that is different from physical time. ### Qualia Qualia are types of things that occur in conscious experience. The colour purple is a good example of a quale (Tye, 1997). Hume (1739) pointed out of things in the mind that \"\[t\]here is nothing but the idea of their colour or tangibility, which can render them conceivable by the mind;\" in other words, qualia might be things in the mind rather than attributes. Qualia appear to be exceptional and inexplicable: Churchland (1988) writes \"How on earth can a feeling of pain result from ions passing across a membrane?\" Descartes (Meditations VI, 6, 1641) clearly describes qualia. ### Awareness Descartes, Locke, Hume, Reid and Kant describe conscious phenomena as if there is an observer in their mind looking out at qualia or feeling qualia in the space and time around about. Descartes and Kant thought that the mind must also contain a conceptualisation or intuition of the meaning of its space, time and content so that the qualia become grouped into objects, the objects into events and the events into meaning and expectation. As Kant put it, we have \"intuitions\" about the relations between things. In modern parlance our conscious experience appears to contain the output from an unconscious processor; although Kant\'s term, \"intuition,\" is a more scientific approach because it is an observation without assumptions about causes. If the present is extended in time, or a \"specious\" present as Clay put it, then many moments are available through which it is possible to apprehend both a question and its answer: the processor can frame the question and provide the answer. The observation that our minds extend through time means that this processor does not need to be recursive to provide the outputs we experience as intuitions (one moment can contain an intuition about another whilst both are in the mind). Descartes (Meditations VI, 10, 1641) considered the origin of intuitions: \"Further, I cannot doubt but that there is in me a certain passive faculty of perception, that is, of receiving and taking knowledge of the ideas of sensible things; but this would be useless to me, if there did not also exist in me, or in some other thing, another active faculty capable of forming and producing those ideas. But this active faculty cannot be in me \[in as far as I am but a thinking thing\], seeing that it does not presuppose thought, and also that those ideas are frequently produced in my mind without my contributing to it in any way, and even frequently contrary to my will.\" Descartes suspected that the ideas were formed unconsciously, probably in the brain. ### Types of Consciousness It is sometimes held that there are many types of consciousness, Antony (2001) lists: phenomenal consciousness, access consciousness, state consciousness, creature consciousness, introspective consciousness and self-consciousness. Antony takes the view that these are all \'modulations\' of the term consciousness and do not mean that there are in fact different types of consciousness. In other words these \'types of consciousness\' are modulations of the intuition of content arranged in space and time that is the singular consciousness described by Kant and Descartes. According to this explanation access consciousness is the time extended form of processes in phenomenal consciousness, self-consciousness is the time extended form of bodily processes and inner speech etc.. As an example, if we say a word then think it soundlessly it is evident that inner speech is whole, time extended words coming from the vague direction of the vocal chords (or both ears), when we move a limb much of the whole movement is present in our experience as a set of displacements at the position of the limb and extended through time. The nature of consciousness as described above, i.e. phenomenal or subjective consciousness, must be distinguished from the type of consciousness used in Medical clinical states. Clinical consciousness is determined partly by the ascending reticular activating system (ARAS) in the brain stem extending into higher anatomic levels of the brain including the cortex. Alerting or arousal is the function of the ARAS and is the doorway to awareness. Failure of this system or its components results in clinical states ranging from a temporary loss of consciousness as noted in head injuries (concussion) all the way to complete coma. The comatose state includes failure of eye opening to stimulation, a motor response more than just simple reflex withdrawal movements and lack of verbalization. Coma can be produced by structural lesions of the brain, metabolic and nutritional disorders, exogenous toxins, central nervous system infections, seizures, temperature-related extremes (e.g. hypothermia or hyperthermia) and most commonly trauma. Included in this extreme are such entities as persistent vegetative state and the minimally conscious state. The gamut ranges through stupor, prolonged concussion, and transient concussion. This use of the term 'consciousness' is not the nature of 'consciousness' as used in this article and must be distinguished as such. ### Observations and Denials There can be little doubt that most descriptions of conscious phenomenology have described the same things although some have used terms such as \'continuity\' for time and \'representation\' for space. Our conscious experiences are the experience of being an observer that has qualia distributed in space and time around a point. This experience is imbued with intuitions. Contrary to the views of Weiskrantz and of Koch and Crick there seems to be no need to await a definition of consciousness. It has been described for centuries. So why did these authors feel a need to suspend any definition? The answer is that over the years there has been no widely accepted theory of how this empirical consciousness could occur. This led certain philosophers such as Ryle (1949) to question whether the description of consciousness was credible. In most cases this sceptical analysis begins with an explanatory discussion of consciousness such as: if information travels from the observation to the observer then the observer contains the information so there must be another observer within to observe this second set of information. In this case the conclusion is that this implies an impossible homunculus or Ryle's \"ghost in the machine\" so observation and observer's cannot occur in the mind. This is an interesting argument but it can also be framed to give exactly the opposite result. The scientific form of the argument would be: the observed form of conscious experience cannot occur if it relies on information transfer, therefore the hypothesis that information transfer is all that is required to explain consciousness is wrong and some other explanation is needed. (This means that although the content of consciousness is derived from the senses via signals in neurones, conscious experience is not these signals flowing into a nexus). In science the observation is paramount and cannot be discarded because it conflicts with theory. The process of discounting an observation when an explanation fails also applies to other aspects of consciousness studies. As Gregory (1988) put it: \" \'If you can't explain it -- deny it\' is one strategy for dealing with embarrassing questions such as \'what is consciousness?\' \". If we discount these denials then the empirical observations of Kant and Descartes and the other empiricists are the bedrock of consciousness studies and consciousness can indeed be described as an observation containing the space, time and content of our minds (where the content contains intuitions and feelings). This simple definition of the experience we call consciousness is internally consistent and can be expressed in mathematical language. Phenomenal consciousness is a multidimensional manifold with vectors pointing towards the centre (the apparent observation point). The content can be both the input and output of processors that are external to the manifold. *Adapted from the article The description and definition of consciousness by Alex Green in Science and Consciousness Review (with permission of the author).* A non-mathematical description of consciousness is: a collection of events arranged in time and space that form directed elements that all point at the same place and instant. ### The viewing point and the observer Green\'s summary of phenomenal consciousness deserves further elaboration and description. Science begins with empirical descriptions. To experience phenomenal consciousness simply lean back with your eyes open and listen. Phenomenal consciousness is the observational space and time that is occurring and the simultaneous things within it that point at the apparent viewing point. It includes bodily sensations, inner speech and the smell on and around things etc. Phenomenal consciousness is experience itself. If the experience is a lucid dream it may contain a fantastical image, if it is a perception it may contain information about something in the world beyond the body. Experience is not usually an experience **of** the content of experience, experience is already there, arranged in space and time (see note below).  The illustrations show the difference between an actual 3D part of the world, 2D representations of that part of the world, conscious experience itself and naive realism. It is well known that a 3D object cannot be shown on a 2D surface. Its form is specified as sets of coordinates. Most visual experiences are arranged as views. Views are represented on paper using perspective drawings. Pictures that use perspective are scaled images of the world as it would appear on the retina of one eye. In experience itself things are arranged as things directed at a point (vectors). Nothing flows into the point. Experience is a manifold of events that are loosely based on data from the retinas and other sense organs. It has contents like the drawing on paper but instead of being a collection of ink particles confined to 2D it is a set of vectors directed at a point. Experience also involves things arranged in time. Things can be simultaneous and there is continuity. Arrangements in time are independent of arrangements in space. The phonemes of a word do not overlap each other and the stages of a movement do not create a smear. These independent arrangements in time are akin to the way that things that are arranged left and right do not overlap things that are arranged up and down. Left and right are independent of up and down. In a similar way, time seems to be an independent direction for arranging things. Our experience differs from naive realism. In naive realism experience is believed to be an impossible physical meeting of light rays at a single point in the eye that through some unspecified mechanism project back to their source. **Naive realism is a primitive dynamical interpretation of experience**, an attempt to explain an empirical geometrical form in terms of flows of matter. In contrast, in experience there seems to be a set of vectors directed at a point.  An intriguing feature of the empirical form of experience is that things seem to be separated by angular separations. This allows objects of any size to be represented and explains how a page of text on our laps and the dome of a planetarium can be encompassed in the same form. The apparent viewing point has caused considerable difficulty for many empiricist philosophers (although the British Empiricists tended to avoid it). When philosophers have stopped describing conscious experience and tried to explain the viewing point they have often resorted to the supernatural: Descartes, Malebranche and Reid all explained the viewing point in terms of a supernatural soul at a point that does the seeing or experiencing. But none of the empiricists describe anything flowing into the viewing point; indeed nothing does flow or could flow into and through a point. The empirical truth is that the viewing point is a geometrical phenomenon, not the recipient of some simultaneous flow of everything in experience. Just look, your viewing point is where everything in experience is directed but things are not pouring into it and it, itself, is a point, it cannot and does not contain anything. This seems to be Aristotle\'s insight when he wrote \"In every case the mind which is actively thinking is the objects which it thinks.\" The field of vectors that are the content of consciousness are also difficult to interpret; some philosophers believe that they are in the brain and form a representation of the world whilst others believe that they are directly attached to things in the world beyond the body. The empirical description of consciousness allows us to make a sharp distinction between the scientific activities of measurement and observation. Measurement is the change in state of a measuring instrument in response to an event in the environment. Observation is the occurrence of events in the geometrical manifold that we call our conscious experience. This section has used the descriptions provided by generations of philosophers to characterise the **phenomenon** of consciousness. Many modern philosophers assume that readers are familiar with these empirical descriptions and use \"what it is like to be conscious\" as a shorthand for these empirical reports. From the seventeenth century onwards it was realised that these descriptions are difficult to explain using Newtonian physics or elementary information theory. `<font size=1>`{=html}\* Note: the term \"experience of\" should be reserved for things that act as a source of the content of experience, such as the QM fields that constitute the things that are sensed. We have an \"experience of\" a flower when signals from the flower are composed into the form of a flower in our experience. Sometimes there is an \"experience of\" the content of consciousness, for instance when intuitions about the content occur. See later modules for a discussion.`</font>`{=html} ### References - Antony,M.V. Is \'Consciousness\' Ambiguous? Journal of Consciousness Studies 8(2), 2001, 19-44. <http://research.haifa.ac.il/~antony/papers/Ambiguous.htm> - Block, N. 1995. On a Confusion about a Function of Consciousness, The Behavioral and Brain Sciences, 18, 2 (June 1995): 227-247. <http://cogprints.ecs.soton.ac.uk/archive/00000231/00/199712004.html> - Churchland, P.S. 1988. Reduction and the neurobiological basis of consciousness. Chapter 14 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. - Descartes, R. 1641. Meditations on First Philosophy <http://www.orst.edu/instruct/phl302/texts/descartes/meditations/meditations.html> - James, W. 1890. The Principles of Psychology <http://psychclassics.yorku.ca/James/Principles/prin15.htm> - James, W. 1904. Does consciousness exist? Journal of Philosophy, Psychology, and Scientific Methods, 1, 477-491. <http://psychclassics.yorku.ca/James/consciousness.htm> - Gregory, R.L. 1966. Eye and Brain. London: Weidenfield and Nicolson. - Gregory, R.L. 1988. Consciousness in science and philosophy: conscience and con-science. Chapter 12 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. - Kant, I. 1781. The Transcendental Aesthetic. Critique of Pure Reason. Tr. Norman Kemp-Smith. Macmillan Press Ltd. <http://www.arts.cuhk.edu.hk/Philosophy/Kant/cpr/cpr-open.html> See also this link <http://www.utm.edu/research/iep/k/kantmeta.htm> - Koch, C and Crick, F. 1999. 116, Consciousness, neural basis of. <http://www.klab.caltech.edu/~koch/Elsevier-NCC.html> - McGinn, C. 1995. Consciousness and Space. In: Conscious Experience, Thomas Metzinger (Ed). 1995, Imprint Academic. <http://www.nyu.edu/gsas/dept/philo/courses/consciousness97/papers/ConsciousnessSpace.html> - Ryle, G. 1949. The Concept of Mind. Hutchinson & Co. London. - Tye, M. 1997. Qualia, Stanford Encyclopedia of Philosophy <http://plato.stanford.edu/entries/qualia> - Weiskrantz, L. 1988. Some contributions of neuropsychology of vision and memory to the problem of consciousness. Chapter 8 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. - Weyl, H. 1918. Space Time Matter. Dover Edition 1952, p. 217.

# Consciousness Studies/The Conflict *This section is about how regression and recursion seem to undermine the idea of conscious experience being anywhere in the universe.*. ## The conflict - supervenience and the location of the contents of phenomenal consciousness When we touch something or look at a view what we are probably touching or seeing is a thing in the world, out there, beyond our bodies. Many philosophers and almost all scientists would agree with this surmise. But is our conscious experience itself directly the things we touch or more like a picture of those things on television or something else entirely? Furthermore, can we really be certain that what we believe we experience truly occurs? Suppose for the moment that our experience truly does occur and consists of things laid out in time and space. Conscious experience appears to be a simultaneous set of things (i.e.: things arranged in space) but where are these things and what is this space? The things that occur in conscious experience could be a virtual reality in the brain based on the world beyond the body, or they could be the things themselves, viewed directly through some unknown phenomenon or it has even been suggested that they could be something non-physical. The problem of where the contents of conscious experience are located has provoked some of the fiercest battles in the philosophy of consciousness. There are three broad positions, the first is Direct Realism in which it is held that the contents of conscious experience are directly things in the world, the second is Indirect Realism where it is proposed that the contents of conscious experience are representations, usually in the physical brain, based on things \'out there\' in the world and the third is idealism where it is held that there is no physical world, only non-physical conscious experience. These three classifications overlap considerably, for instance some Natural Dualists believe that the contents of sensory experience are directly the world beyond the body but some thoughts are based in a non-physical soul and some philosophers introduce the dualist notion of a \"logical space\" containing disembodied information. Philosophers often use the concept of \'supervenience\' to examine the location of the contents of consciousness. Supervenience is the relation between two sets of properties. Supervenience can be simple; for example a golden ring supervenes on a piece of the metal gold. Supervenience can also be quite complex such as the idea that life supervenes on the biological processes in a cell. The most difficult cases of supervenience are where a high level description is related to simpler physical properties such as form and content. There are formal statements of supervenience: `The properties of A supervene on the properties of B if no two possible`\ `situations are identical with respect to the properties of A while`\ `differing with respect to the properties of B (after Chalmers 1996).` Lewis gives a simpler, if less technical, definition of supervenience: `A dot-matrix picture has global properties -- it is symmetrical, `\ `it is cluttered, and whatnot -- and yet all there is to the picture `\ `is dots and non-dots at each point of the matrix. The global `\ `properties are nothing but patterns in the dots. They supervene: no `\ `two pictures could differ in their global properties without `\ `differing, somewhere, in whether there is or there isn't a dot". `\ `Lewis, D., 1986, On the Plurality of Worlds, Oxford: Blackwell` One set of properties is said to supervene *locally* on another set of properties if the second set is determined by the first. Shape is an example of local supervenience; for instance a gold wire forged in a circle determines a gold ring. A set of properties is said to supervene *globally* on another if the entire context of the properties must be included; for instance, two organisms could be physically identical but demonstrate different behaviours in different environments. In this case the physical form of an organism does not totally determine the behaviour. Philosophers also divide supervenience into logical supervenience and natural supervenience. Logical supervenience deals with possible relations in possible worlds while natural supervenience deals with relations that occur in the natural world. See elementary information theory for a discussion of supervenience in information systems. A particular problem posed by consciousness studies is whether conscious phenomenal experience supervenes on the physical world and, if so, where. To answer these questions philosophers and neuroscientists must have a good understanding of physics. They should be aware of elementary physical ontology such as kinetic energy being the relativistic mass increase of a particle in a four dimensional universe and Newton\'s laws being due to the exploration of all paths in space-time. Without a good knowledge of physics there is the danger that we will be asking whether phenomenal consciousness supervenes on an abstract model of the world which does not supervene on the world itself (i.e.: *we may be asking if conscious phenomenal experience supervenes on Newtonian physics or supervenes on information systems theory rather than asking how phenomenal consciousness might supervene on the natural world*). The possibility that conscious experience does not really occur, at least in the form that we believe it occurs, is known as the problem of the \"Incorrigibility of the cogito\" (Harrison 1984). If Descartes\' idea that \"I think therefore I am\" is not beyond question (incorrigible) then the idea of phenomenal consciousness may be incorrect. (See for instance: Special relativity for beginners Special relativity for beginners Quantum physics explains Newton's laws of motion <http://www.eftaylor.com/pub/OgbornTaylor.pdf> ) ## The problem of regression The philosopher Gilbert Ryle was concerned with what he called the intellectualist legend which requires intelligent acts to be the product of the conscious application of mental rules. The intellectualist legend is also known as the \"Dogma of the Ghost in the Machine,\" the \"Two-Lives Legend,\" the \"Two-Worlds Story,\" or the \"Double-Life Legend\". Ralph Waldo Emerson summarised the intellectualist legend in the statement that \"The ancestor of every action is a thought.\" Ryle argued against the idea that every action requires a conscious thought and showed that this \'intellectualist legend\' results in an infinite regress of thought: `"According to the legend, whenever an agent does anything `\ `intelligently, his act is preceded and steered by another internal `\ `act of considering a regulative proposition appropriate to his `\ `practical problem. [...] Must we then say that for the hero's `\ `reflections how to act to be intelligent he must first reflect how `\ `best to reflect how to act? The endlessness of this implied regress `\ `shows that the application of the criterion of appropriateness does `\ `not entail the occurrence of a process of considering this criterion."`\ `(The Concept of Mind (1949)) ` image:constudregress.gif `"The crucial objection to the intellectualist legend is this. The `\ `consideration of propositions is itself an operation the execution `\ `of which can be more or less intelligent, less or more stupid. But if, `\ `for any operation to be intelligently executed, a prior theoretical `\ `operation had first to be performed and performed intelligently, it `\ `would be a logical impossibility for anyone ever to break into the `\ `circle." ` Variants of Ryle\'s regress are commonly aimed at cognitivist theories. For instance, in order to explain the behavior of rats, Edward Tolman suggested that the rats were constructing a \"cognitive map\" that helped them locate reinforcers, and he used intentional terms (e.g., expectancies, purposes, meanings) to describe their behavior. This led to a famous attack on Tolman\'s work by Guthrie who pointed out that if one was implying that every action must be preceded by a cognitive \'action\' (a \'thought\' or \'schema\' or \'script\' or whatever), then what \'causes\' this act? Clearly it must be preceded by another cognitive action, which must in turn must be preceded by another and so on, in an infinite regress unless an external input occurs at some stage. As a further example, we may take note of the following statement from The Concept of Mind (1949): \"The main object of this chapter is to show that there are many activities which directly display qualities of mind, yet are neither themselves intellectual operations nor yet effects of intellectual operations. Intelligent practice is not a step-child of theory. On the contrary theorizing is one practice amongst others and is itself intelligently or stupidly conducted.\" Ryle noted that \"theorizing is one practice amongst others.\" and hence would translate the statement by Emerson into, \"The ancestor of every action is an action.\" or \"The ancestor of every behavior is a behavior,\". Each behaviour would require yet another behavior to preface it as its ancestor, and an infinite regress would occur. It should be noted that Ryle's regress is a critique of cognitivism which arises from the Behaviorist tradition. Near the end of The Concept of Mind, Ryle states, \"The Behaviorists' methodological program has been of revolutionary importance to the program of psychology. But more, it has been one of the main sources of the philosophical suspicion that the two-worlds story is a myth.\" But Ryle's brand of logical behaviorism is not to be confused with the radical behaviorism of B. F. Skinner or the methodological behaviorism of John B. Watson. For as Alex Byrne noted, \"Ryle was indeed, as he reportedly said, 'only one arm and one leg a behaviorist'.\" Arguments that involve regress are well known in philosophy. In fact any reflexive, or self referencing process or argument will involve a regress if there is no external input. This applies whether the agent that engages in the process is a digital computer or intelligent agent (cf: Smith (1986), Yates (1991)). Ryle\'s regress suggests that intelligent acts are not created within phenomenal consciousness. They may have non-conscious components or even be entirely non-conscious. Ryle argued that this might mean that consciousness is just a \"ghost in the machine\" of the brain because consciousness would be epiphenomenal if it is not the creator of intelligent acts. However, as will be seen below, this conclusion may be premature and certainly cannot be used to dismiss phenomenal consciousness as non-existent or not present in the brain. ## The Subject-Object paradox This paradox was clearly enunciated by William James in 1904: \"Throughout the history of philosophy the subject and its object have been treated as absolutely discontinuous entities; and thereupon the presence of the latter to the former, or the \'apprehension\' by the former of the latter, has assumed a paradoxical character which all sorts of theories had to be invented to overcome.\" James (1904). The Subject-Object paradox points out that a conscious subject appears to observe itself as an object. But if it observes itself as an object then, as an object it cannot be a subject. As Bermudez(1998) puts it: \"Any theory that tries to elucidate the capacity to think first-person thoughts through linguistic mastery of the first-person pronoun will be circular, because the explanandum is part of the explanans..\" Thomas Reid uses this paradox to suggest that everything that is observed must be external to the soul and hence proposed that experience was the world itself. Wittgenstein (1949) offers a way out of the paradox by denying the existence of the subject: `<span style="font-family:times new roman;">`{=html}\"5.63 1. The thinking, presenting subject; there is no such thing. If I wrote a book The World as I Found It, I should also have therein to report on my body and say which members obey my will and which do not, etc. This then would be a method of isolating the subject or rather of showing that in an important sense there is no subject: that is to say, of it alone in this book mention could not be made. 5.632. The subject does not belong to the world but it is a limit of the world. 5.633. Where in the world is a metaphysical subject to be noted? You say that this case is altogether like that of the eye and the field of sight. But you do not really see the eye. And from nothing in the field of sight can it be concluded that it is seen from an eye\... 5.64 1. \...The philosophical I is not the man, not the human body or the human soul of which psychology treats, but the metaphysical subject, the limit --- not a part of the world.\"`</span>`{=html}(Wittgenstein 1949). Wittgenstein\'s view is similar to that voiced by Green (2002) in which there is nothing at the point centre of the manifold of events (there is no point eye). James (1904), Lektorsky (1980) and many others have also attempted to resolve the paradox by proposing that there is really no observer, only the observation or \'reflexive act\' of perception. This idea reaches its zenith in Brentano\'s concept of \"intentionality\" in which the subject and object are fused into a form of \"aboutness\": `<span style="font-family:times new roman;">`{=html}\"Every psychical phenomenon is characterized by what the Scholastics of the Middle Ages called the intentional (or sometimes the mental) inexistence of an object, and what we should like to call, although not quite unambiguously, the reference (Beziehung) to a content, the directedness (Richtung) toward an object (which in this context is not to be understood as something real) or the immanent-object quality (immanente Gegenständlichkeit). Each contains something as its object, though not each in the same manner. In the representation (Vorstellung) something is represented, in the judgment something is acknowledged or rejected, in desiring it is desired, etc. This intentional inexistence is peculiar alone to psychical phenomena. No physical phenomenon shows anything like it. And thus we can define psychical phenomena by saying that they are such phenomena as contain objects in themselves by way of intention (intentional).\"`</span>`{=html} Brentano, F. (1874). These authors have all identified the content of perception with either the world itself, the manifold of events or a synthetic \'about\' the world itself in an attempt at avoiding the paradox, however, as will be seen later, there are other solutions to the paradox. Bermúdez, J. (1998), The Paradox of Self-Consciousness, Bradford/MIT Press. Brentano, F. (1874). Psychology from an empirical standpoint. Vol1. <http://www.marxists.org/reference/subject/philosophy/works/ge/brentano.htm> William James (1904). A World of Pure Experience. First published in Journal of Philosophy, Psychology, and Scientific Methods, 1, 533-543, 561-570. <http://psychclassics.yorku.ca/James/experience.htm> ## The homunculus fallacy in philosophy of mind A Homunculus argument accounts for a phenomenon in terms of the very phenomenon that it is supposed to explain (Richard Gregory (1987)). Homunculus arguments are always fallacious. In the psychology and philosophy of mind \'homunculus arguments\' are extremely useful for detecting where theories of mind fail or are incomplete. Homunculus arguments are common in the theory of vision. Imagine a person watching a movie. He sees the images as something separate from himself, projected on the screen. How is this done? A simple theory might propose that the light from the screen forms an image on the retinas in the eyes and something in the brain looks at these as if they are the screen. The Homunculus Argument shows this is not a full explanation because all that has been done is to place an entire person, or homunculus, behind the eye who gazes at the retinas. A more sophisticated argument might propose that the images on the retinas are transferred to the visual cortex where it is scanned. Again this cannot be a full explanation because all that has been done is to place a little person in the brain behind the cortex. In the theory of vision the Homunculus Argument invalidates theories that do not explain \'projection\', the experience that the viewing point is separate from the things that are seen. (Adapted from Gregory (1987), (1990)). In the case of vision it is sometimes suggested that each homunculus would need a homunculus inside it ad infinitum. This is the **recursion** form of the homunculus concept. Notice that, unlike the case of regress, the recursion would occur after the event. An homunculus argument should be phrased in such a way that the conclusion is always that if a homunculus is required then the theory is wrong. After all, homunculi do not exist. Very few people would propose that there actually is a little man in the brain looking at brain activity. However, this proposal has been used as a \'straw man\' in theories of mind. Gilbert Ryle (1949) proposed that the human mind is known by its intelligent acts. (see Ryle\'s Regress). He argued that if there is an inner being inside the brain that could steer its own thoughts then this would lead to an absurd repetitive cycle or \'regress\' before a thought could occur: \"According to the legend, whenever an agent does anything intelligently, his act is preceded and steered by another internal act of considering a regulative proposition appropriate to his practical problem.\" \"\.... Must we then say that for the ..\[agent\'s\].. reflections how to act to be intelligent he must first reflect how best to reflect how to act? The endlessness of this implied regress shows that the application of the appropriateness does not entail the occurrence of a process of considering this criterion.\" The homunculus argument and the regress argument are often considered to be the same but this is not the case. The homunculus argument says that if there is a need for a \'little man\' to complete a theory then the theory is wrong. The regress argument says that an intelligent agent would need to think before it could have a thought. Ryle\'s theory is that intelligent acts cannot be a property of an inner being or mind, if such a thing were to exist. The idea that conscious experience is a flow of information into an unextended place (a point eye) leaves itself open to the charge of inserting an homunculus beyond the point eye. On careful reading few, if any, real theories actually propose a flow through the point eye but suggest some sort of nebulous direct relation with the information in front of the eye. For instance, Descartes has a point soul directly considering the contents of the common sense and Reid has a point eye directly considering the world itself. `<span style="font-size:x-small;">`{=html}Questions: It might be said that the homunculus fallacy means that either the materialist interpretation of conscious experience is wrong or conscious experience does not exist: discuss. Physicalism is not materialism, discuss. Could physical phenomena such as entanglement or space-time theories of observation, where the observed vectors are constrained to the manifold, avoid the homunculus fallacy?`</span>`{=html} ## Berkeley\'s \"passive ideas\" Ryle\'s regress, when applied to consciousness, is based on an analysis of conscious intellectual activity as a succession of states. At any moment the conscious intellect contains one state such as \'I will think of a word\'. This means that either the state has just popped into mind or there was a previous state that gave rise to it such as \'I will think of thinking of a word\'. Descartes and other empiricists have noted that thoughts do indeed just pop into mind. So if we transfer Ryle\'s analysis to the real world we discover that the regress is avoided by removing the starting point of a series of thoughts from conscious phenomenal experience. A train of thought just begins, it has no conscious origin and Descartes\' implication is that it has probably been synthesised non-consciously. Suppose Descartes and our own experience are correct, suppose thoughts do just pop into mind, if this happens can there still be a conscious intellectual agent or are intellectual agents largely non-conscious? One of the simplest intellectual processes is a test for equality i.e.: \'does A equal B?\' and a routing of flow as a result of the test i.e.: \'if A = B then goto\'. Can an intellectual agent perform an equality test in conscious phenomenal experience? Consider the test of whether \'A = A\', you attend to the left \'A\' then the right \'A\' and declare them equal. What have you actually done? The feeling that the symbols are equal just pops into mind. Psychologists and philosophers use the word \'intuition\' for this popping of answers into mind (Kant 1781). It is usually accompanied by emotional experience (Damasio 1994, Bierman 2004). If intellectual activity is actually a succession of things that just pop into phenomenal consciousness then Ryle\'s conclusion that phenomenal consciousness is like a \"ghost in the machine\" of the brain would to some extent justified. Phenomenal consciousness would not be intellectual activity. Phenomenal consciousness would contain the stages, or succession of states, of intellectual activity but would not contain the processes that connect these stages. This observation that conscious experience is a succession of **passive ideas** is well known in philosophy (cf: George Berkeley, Principles of Human Knowledge, 25). ## More on the conflict Click above for more on Phenomenal consciousness, access consciousness, Direct Realism, Indirect Realism, Dualism, Idealism and Panpsychism. ## References - Harrison, J. (1984). The incorrigibility of the cogito. Mind: New Series, Vol. 93, No. XCIII, 1984. The problem of regression - Ryle, G. (1949) The Concept of Mind. The University of Chicago Press, 1949. ```{=html} <!-- --> ``` - Smith, Q. (1986). The infinite regress of temporal attributions. The Southern Journal of Philosophy (1986) Vol. XXIV, No. 3, 383 (Section 3). <http://web.archive.org/web/20060507144913/http://www.qsmithwmu.com/the_infinite_regress.htm> ```{=html} <!-- --> ``` - Yates, S. (1991). Self referential arguments in philosophy. Reason Papers 16. (Fall 1991) 133-164. <http://www.mises.org/reasonpapers/pdf/16/rp_16_7.pdf> The homunculus argument - Gregory, R.L. (1990) Eye and Brain: The Psychology of Seeing, Oxford University Press Inc. New York. ```{=html} <!-- --> ``` - Gregory, T.L. (1987). The Oxford Companion to Mind. Oxford University Press. Subject-object paradox - James, W. (1904)Does \'Consciousness\' Exist? Journal of Philosophy, Psychology, and Scientific Methods, 1, 477-491. - Hegel, G.W.F. PHILOSOPHY OF MIND: SECTION I. MIND SUBJECTIVE B. PHENOMENOLOGY OF MIND CONSCIOUSNESS Part Three of the Encyclopaedia of the Philosophical Sciences ```{=html} <!-- --> ``` - Velmans, M. (1996) Consciousness and the \"Casual Paradox\". Behavioral and Brain Sciences, 19 (3): 538-542. - \[Bermudez, J.L. (1999) The Paradox of Self-Consciousness (representation and Mind) Psycoloquy: 10,#35 Ontological status - Bierman, D.J. (2004) Non Conscious Processes Preceding Intuitive decisions <http://m0134.fmg.uva.nl/~djb/publications/2004/Intuition_bialsymp2004.pdf> ```{=html} <!-- --> ``` - Damasio, A.R. (1994). Descartes\' error: Emotion, reason and the human brain. New York: Grosset/Putnam Book. ```{=html} <!-- --> ``` - Kant, I. Critique of Pure Reason <http://www.arts.cuhk.edu.hk/Philosophy/Kant/cpr/> Direct Realism - Aydede, M. (2001) Naturalism, introspection, and direct realism about pain. Consciousness and Emotion, Vol. 2, No. 1, 2001, pp. 29-73. <http://web.clas.ufl.edu/users/maydede/pain.pdf> - Chapman, C.R., and Y. Nakamura (1999). A Passion of the Soul: An Introduction to Pain for Consciousness Researchers. Consciousness and Cognition, 8: 391-422. ```{=html} <!-- --> ``` - Dennett, D. (1991). Consciousness Explained. Boston: Little, Brown ```{=html} <!-- --> ``` - Fowler C A (1986): "An event approach to the study of speech perception from a direct-realist perspective", J of Phonetics 14(1):3-28. ```{=html} <!-- --> ``` - Gibson, J. J. (1966) The Senses Considered as Perceptual Systems. Houghton Mifflin Company,Boston. ```{=html} <!-- --> ``` - Gibson, J. J. (1979) Ecological Approach to Visual Perception.: Lawrence Erlbaum Associates Publishers, Hillsdate. ```{=html} <!-- --> ``` - Gregory, R.L. 1988. Consciousness in science and philosophy: conscience and con-science. Chapter 12 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. ```{=html} <!-- --> ``` - Le Morvan, Pierre (2004). Arguments against direct realism and how to counter them. *The American Philosophical Quarterly*, *41*(3), 221-234.\] (pdf) <http://www.tcnj.edu/~lemorvan/DR_web.pdf> ```{=html} <!-- --> ``` - Oliveira, André L. G. and Oliveira, Luis F. (2002) Toward an ecological conception of timbre. In Proceedings Auditory Perception Cognition and Action Meeting 2002, Kansas City. <http://cogprints.org/2713/> ```{=html} <!-- --> ``` - Skinner, B. F. Science and Human Behavior . New York: Macmillan, 1953. ```{=html} <!-- --> ``` - Skinner, B. F. 1971. Beyond Freedom and Dignity. New York: Knopf. ```{=html} <!-- --> ``` - Skinner, B. F. 1948. Walden Two. New York: Macmillan. ```{=html} <!-- --> ``` - Tye, M. (2004). ANOTHER LOOK AT REPRESENTATIONALISM ABOUT PAIN. Consciousness and Emotion 2004, special issue on pain, edited by Murat Aydede (with replies by M. Aydede, N. Block, B. Maund, and P. Noordhof <http://sun.soci.niu.edu/~phildept/MT/RepresentationalismAndPain.pdf> ```{=html} <!-- --> ``` - Vygotsky, L.S.(1925) Consciousness as a problem in the psychology of behavior. Undiscovered Vygotsky: Etudes on the pre-history of cultural-historical psychology (European Studies in the History of Science and Ideas. Vol. 8), pp. 251-281. Peter Lang Publishing. <http://www.marxists.org/archive/vygotsky/works/1925/consciousness.htm> ```{=html} <!-- --> ``` - Ziff, Paul. \"About Behaviourism.\" Analysis 18 (1958): 132-136. Quoted by Larry Hauser in the Internet Encyclopedia of Philosophy. <http://www.utm.edu/research/iep/b/behavior.htm#B>. F. Skinner: Radical Behaviorism

# Consciousness Studies/The Conflict#The regression argument *This section is about how regression and recursion seem to undermine the idea of conscious experience being anywhere in the universe.*. ## The conflict - supervenience and the location of the contents of phenomenal consciousness When we touch something or look at a view what we are probably touching or seeing is a thing in the world, out there, beyond our bodies. Many philosophers and almost all scientists would agree with this surmise. But is our conscious experience itself directly the things we touch or more like a picture of those things on television or something else entirely? Furthermore, can we really be certain that what we believe we experience truly occurs? Suppose for the moment that our experience truly does occur and consists of things laid out in time and space. Conscious experience appears to be a simultaneous set of things (i.e.: things arranged in space) but where are these things and what is this space? The things that occur in conscious experience could be a virtual reality in the brain based on the world beyond the body, or they could be the things themselves, viewed directly through some unknown phenomenon or it has even been suggested that they could be something non-physical. The problem of where the contents of conscious experience are located has provoked some of the fiercest battles in the philosophy of consciousness. There are three broad positions, the first is Direct Realism in which it is held that the contents of conscious experience are directly things in the world, the second is Indirect Realism where it is proposed that the contents of conscious experience are representations, usually in the physical brain, based on things \'out there\' in the world and the third is idealism where it is held that there is no physical world, only non-physical conscious experience. These three classifications overlap considerably, for instance some Natural Dualists believe that the contents of sensory experience are directly the world beyond the body but some thoughts are based in a non-physical soul and some philosophers introduce the dualist notion of a \"logical space\" containing disembodied information. Philosophers often use the concept of \'supervenience\' to examine the location of the contents of consciousness. Supervenience is the relation between two sets of properties. Supervenience can be simple; for example a golden ring supervenes on a piece of the metal gold. Supervenience can also be quite complex such as the idea that life supervenes on the biological processes in a cell. The most difficult cases of supervenience are where a high level description is related to simpler physical properties such as form and content. There are formal statements of supervenience: `The properties of A supervene on the properties of B if no two possible`\ `situations are identical with respect to the properties of A while`\ `differing with respect to the properties of B (after Chalmers 1996).` Lewis gives a simpler, if less technical, definition of supervenience: `A dot-matrix picture has global properties -- it is symmetrical, `\ `it is cluttered, and whatnot -- and yet all there is to the picture `\ `is dots and non-dots at each point of the matrix. The global `\ `properties are nothing but patterns in the dots. They supervene: no `\ `two pictures could differ in their global properties without `\ `differing, somewhere, in whether there is or there isn't a dot". `\ `Lewis, D., 1986, On the Plurality of Worlds, Oxford: Blackwell` One set of properties is said to supervene *locally* on another set of properties if the second set is determined by the first. Shape is an example of local supervenience; for instance a gold wire forged in a circle determines a gold ring. A set of properties is said to supervene *globally* on another if the entire context of the properties must be included; for instance, two organisms could be physically identical but demonstrate different behaviours in different environments. In this case the physical form of an organism does not totally determine the behaviour. Philosophers also divide supervenience into logical supervenience and natural supervenience. Logical supervenience deals with possible relations in possible worlds while natural supervenience deals with relations that occur in the natural world. See elementary information theory for a discussion of supervenience in information systems. A particular problem posed by consciousness studies is whether conscious phenomenal experience supervenes on the physical world and, if so, where. To answer these questions philosophers and neuroscientists must have a good understanding of physics. They should be aware of elementary physical ontology such as kinetic energy being the relativistic mass increase of a particle in a four dimensional universe and Newton\'s laws being due to the exploration of all paths in space-time. Without a good knowledge of physics there is the danger that we will be asking whether phenomenal consciousness supervenes on an abstract model of the world which does not supervene on the world itself (i.e.: *we may be asking if conscious phenomenal experience supervenes on Newtonian physics or supervenes on information systems theory rather than asking how phenomenal consciousness might supervene on the natural world*). The possibility that conscious experience does not really occur, at least in the form that we believe it occurs, is known as the problem of the \"Incorrigibility of the cogito\" (Harrison 1984). If Descartes\' idea that \"I think therefore I am\" is not beyond question (incorrigible) then the idea of phenomenal consciousness may be incorrect. (See for instance: Special relativity for beginners Special relativity for beginners Quantum physics explains Newton's laws of motion <http://www.eftaylor.com/pub/OgbornTaylor.pdf> ) ## The problem of regression The philosopher Gilbert Ryle was concerned with what he called the intellectualist legend which requires intelligent acts to be the product of the conscious application of mental rules. The intellectualist legend is also known as the \"Dogma of the Ghost in the Machine,\" the \"Two-Lives Legend,\" the \"Two-Worlds Story,\" or the \"Double-Life Legend\". Ralph Waldo Emerson summarised the intellectualist legend in the statement that \"The ancestor of every action is a thought.\" Ryle argued against the idea that every action requires a conscious thought and showed that this \'intellectualist legend\' results in an infinite regress of thought: `"According to the legend, whenever an agent does anything `\ `intelligently, his act is preceded and steered by another internal `\ `act of considering a regulative proposition appropriate to his `\ `practical problem. [...] Must we then say that for the hero's `\ `reflections how to act to be intelligent he must first reflect how `\ `best to reflect how to act? The endlessness of this implied regress `\ `shows that the application of the criterion of appropriateness does `\ `not entail the occurrence of a process of considering this criterion."`\ `(The Concept of Mind (1949)) ` image:constudregress.gif `"The crucial objection to the intellectualist legend is this. The `\ `consideration of propositions is itself an operation the execution `\ `of which can be more or less intelligent, less or more stupid. But if, `\ `for any operation to be intelligently executed, a prior theoretical `\ `operation had first to be performed and performed intelligently, it `\ `would be a logical impossibility for anyone ever to break into the `\ `circle." ` Variants of Ryle\'s regress are commonly aimed at cognitivist theories. For instance, in order to explain the behavior of rats, Edward Tolman suggested that the rats were constructing a \"cognitive map\" that helped them locate reinforcers, and he used intentional terms (e.g., expectancies, purposes, meanings) to describe their behavior. This led to a famous attack on Tolman\'s work by Guthrie who pointed out that if one was implying that every action must be preceded by a cognitive \'action\' (a \'thought\' or \'schema\' or \'script\' or whatever), then what \'causes\' this act? Clearly it must be preceded by another cognitive action, which must in turn must be preceded by another and so on, in an infinite regress unless an external input occurs at some stage. As a further example, we may take note of the following statement from The Concept of Mind (1949): \"The main object of this chapter is to show that there are many activities which directly display qualities of mind, yet are neither themselves intellectual operations nor yet effects of intellectual operations. Intelligent practice is not a step-child of theory. On the contrary theorizing is one practice amongst others and is itself intelligently or stupidly conducted.\" Ryle noted that \"theorizing is one practice amongst others.\" and hence would translate the statement by Emerson into, \"The ancestor of every action is an action.\" or \"The ancestor of every behavior is a behavior,\". Each behaviour would require yet another behavior to preface it as its ancestor, and an infinite regress would occur. It should be noted that Ryle's regress is a critique of cognitivism which arises from the Behaviorist tradition. Near the end of The Concept of Mind, Ryle states, \"The Behaviorists' methodological program has been of revolutionary importance to the program of psychology. But more, it has been one of the main sources of the philosophical suspicion that the two-worlds story is a myth.\" But Ryle's brand of logical behaviorism is not to be confused with the radical behaviorism of B. F. Skinner or the methodological behaviorism of John B. Watson. For as Alex Byrne noted, \"Ryle was indeed, as he reportedly said, 'only one arm and one leg a behaviorist'.\" Arguments that involve regress are well known in philosophy. In fact any reflexive, or self referencing process or argument will involve a regress if there is no external input. This applies whether the agent that engages in the process is a digital computer or intelligent agent (cf: Smith (1986), Yates (1991)). Ryle\'s regress suggests that intelligent acts are not created within phenomenal consciousness. They may have non-conscious components or even be entirely non-conscious. Ryle argued that this might mean that consciousness is just a \"ghost in the machine\" of the brain because consciousness would be epiphenomenal if it is not the creator of intelligent acts. However, as will be seen below, this conclusion may be premature and certainly cannot be used to dismiss phenomenal consciousness as non-existent or not present in the brain. ## The Subject-Object paradox This paradox was clearly enunciated by William James in 1904: \"Throughout the history of philosophy the subject and its object have been treated as absolutely discontinuous entities; and thereupon the presence of the latter to the former, or the \'apprehension\' by the former of the latter, has assumed a paradoxical character which all sorts of theories had to be invented to overcome.\" James (1904). The Subject-Object paradox points out that a conscious subject appears to observe itself as an object. But if it observes itself as an object then, as an object it cannot be a subject. As Bermudez(1998) puts it: \"Any theory that tries to elucidate the capacity to think first-person thoughts through linguistic mastery of the first-person pronoun will be circular, because the explanandum is part of the explanans..\" Thomas Reid uses this paradox to suggest that everything that is observed must be external to the soul and hence proposed that experience was the world itself. Wittgenstein (1949) offers a way out of the paradox by denying the existence of the subject: `<span style="font-family:times new roman;">`{=html}\"5.63 1. The thinking, presenting subject; there is no such thing. If I wrote a book The World as I Found It, I should also have therein to report on my body and say which members obey my will and which do not, etc. This then would be a method of isolating the subject or rather of showing that in an important sense there is no subject: that is to say, of it alone in this book mention could not be made. 5.632. The subject does not belong to the world but it is a limit of the world. 5.633. Where in the world is a metaphysical subject to be noted? You say that this case is altogether like that of the eye and the field of sight. But you do not really see the eye. And from nothing in the field of sight can it be concluded that it is seen from an eye\... 5.64 1. \...The philosophical I is not the man, not the human body or the human soul of which psychology treats, but the metaphysical subject, the limit --- not a part of the world.\"`</span>`{=html}(Wittgenstein 1949). Wittgenstein\'s view is similar to that voiced by Green (2002) in which there is nothing at the point centre of the manifold of events (there is no point eye). James (1904), Lektorsky (1980) and many others have also attempted to resolve the paradox by proposing that there is really no observer, only the observation or \'reflexive act\' of perception. This idea reaches its zenith in Brentano\'s concept of \"intentionality\" in which the subject and object are fused into a form of \"aboutness\": `<span style="font-family:times new roman;">`{=html}\"Every psychical phenomenon is characterized by what the Scholastics of the Middle Ages called the intentional (or sometimes the mental) inexistence of an object, and what we should like to call, although not quite unambiguously, the reference (Beziehung) to a content, the directedness (Richtung) toward an object (which in this context is not to be understood as something real) or the immanent-object quality (immanente Gegenständlichkeit). Each contains something as its object, though not each in the same manner. In the representation (Vorstellung) something is represented, in the judgment something is acknowledged or rejected, in desiring it is desired, etc. This intentional inexistence is peculiar alone to psychical phenomena. No physical phenomenon shows anything like it. And thus we can define psychical phenomena by saying that they are such phenomena as contain objects in themselves by way of intention (intentional).\"`</span>`{=html} Brentano, F. (1874). These authors have all identified the content of perception with either the world itself, the manifold of events or a synthetic \'about\' the world itself in an attempt at avoiding the paradox, however, as will be seen later, there are other solutions to the paradox. Bermúdez, J. (1998), The Paradox of Self-Consciousness, Bradford/MIT Press. Brentano, F. (1874). Psychology from an empirical standpoint. Vol1. <http://www.marxists.org/reference/subject/philosophy/works/ge/brentano.htm> William James (1904). A World of Pure Experience. First published in Journal of Philosophy, Psychology, and Scientific Methods, 1, 533-543, 561-570. <http://psychclassics.yorku.ca/James/experience.htm> ## The homunculus fallacy in philosophy of mind A Homunculus argument accounts for a phenomenon in terms of the very phenomenon that it is supposed to explain (Richard Gregory (1987)). Homunculus arguments are always fallacious. In the psychology and philosophy of mind \'homunculus arguments\' are extremely useful for detecting where theories of mind fail or are incomplete. Homunculus arguments are common in the theory of vision. Imagine a person watching a movie. He sees the images as something separate from himself, projected on the screen. How is this done? A simple theory might propose that the light from the screen forms an image on the retinas in the eyes and something in the brain looks at these as if they are the screen. The Homunculus Argument shows this is not a full explanation because all that has been done is to place an entire person, or homunculus, behind the eye who gazes at the retinas. A more sophisticated argument might propose that the images on the retinas are transferred to the visual cortex where it is scanned. Again this cannot be a full explanation because all that has been done is to place a little person in the brain behind the cortex. In the theory of vision the Homunculus Argument invalidates theories that do not explain \'projection\', the experience that the viewing point is separate from the things that are seen. (Adapted from Gregory (1987), (1990)). In the case of vision it is sometimes suggested that each homunculus would need a homunculus inside it ad infinitum. This is the **recursion** form of the homunculus concept. Notice that, unlike the case of regress, the recursion would occur after the event. An homunculus argument should be phrased in such a way that the conclusion is always that if a homunculus is required then the theory is wrong. After all, homunculi do not exist. Very few people would propose that there actually is a little man in the brain looking at brain activity. However, this proposal has been used as a \'straw man\' in theories of mind. Gilbert Ryle (1949) proposed that the human mind is known by its intelligent acts. (see Ryle\'s Regress). He argued that if there is an inner being inside the brain that could steer its own thoughts then this would lead to an absurd repetitive cycle or \'regress\' before a thought could occur: \"According to the legend, whenever an agent does anything intelligently, his act is preceded and steered by another internal act of considering a regulative proposition appropriate to his practical problem.\" \"\.... Must we then say that for the ..\[agent\'s\].. reflections how to act to be intelligent he must first reflect how best to reflect how to act? The endlessness of this implied regress shows that the application of the appropriateness does not entail the occurrence of a process of considering this criterion.\" The homunculus argument and the regress argument are often considered to be the same but this is not the case. The homunculus argument says that if there is a need for a \'little man\' to complete a theory then the theory is wrong. The regress argument says that an intelligent agent would need to think before it could have a thought. Ryle\'s theory is that intelligent acts cannot be a property of an inner being or mind, if such a thing were to exist. The idea that conscious experience is a flow of information into an unextended place (a point eye) leaves itself open to the charge of inserting an homunculus beyond the point eye. On careful reading few, if any, real theories actually propose a flow through the point eye but suggest some sort of nebulous direct relation with the information in front of the eye. For instance, Descartes has a point soul directly considering the contents of the common sense and Reid has a point eye directly considering the world itself. `<span style="font-size:x-small;">`{=html}Questions: It might be said that the homunculus fallacy means that either the materialist interpretation of conscious experience is wrong or conscious experience does not exist: discuss. Physicalism is not materialism, discuss. Could physical phenomena such as entanglement or space-time theories of observation, where the observed vectors are constrained to the manifold, avoid the homunculus fallacy?`</span>`{=html} ## Berkeley\'s \"passive ideas\" Ryle\'s regress, when applied to consciousness, is based on an analysis of conscious intellectual activity as a succession of states. At any moment the conscious intellect contains one state such as \'I will think of a word\'. This means that either the state has just popped into mind or there was a previous state that gave rise to it such as \'I will think of thinking of a word\'. Descartes and other empiricists have noted that thoughts do indeed just pop into mind. So if we transfer Ryle\'s analysis to the real world we discover that the regress is avoided by removing the starting point of a series of thoughts from conscious phenomenal experience. A train of thought just begins, it has no conscious origin and Descartes\' implication is that it has probably been synthesised non-consciously. Suppose Descartes and our own experience are correct, suppose thoughts do just pop into mind, if this happens can there still be a conscious intellectual agent or are intellectual agents largely non-conscious? One of the simplest intellectual processes is a test for equality i.e.: \'does A equal B?\' and a routing of flow as a result of the test i.e.: \'if A = B then goto\'. Can an intellectual agent perform an equality test in conscious phenomenal experience? Consider the test of whether \'A = A\', you attend to the left \'A\' then the right \'A\' and declare them equal. What have you actually done? The feeling that the symbols are equal just pops into mind. Psychologists and philosophers use the word \'intuition\' for this popping of answers into mind (Kant 1781). It is usually accompanied by emotional experience (Damasio 1994, Bierman 2004). If intellectual activity is actually a succession of things that just pop into phenomenal consciousness then Ryle\'s conclusion that phenomenal consciousness is like a \"ghost in the machine\" of the brain would to some extent justified. Phenomenal consciousness would not be intellectual activity. Phenomenal consciousness would contain the stages, or succession of states, of intellectual activity but would not contain the processes that connect these stages. This observation that conscious experience is a succession of **passive ideas** is well known in philosophy (cf: George Berkeley, Principles of Human Knowledge, 25). ## More on the conflict Click above for more on Phenomenal consciousness, access consciousness, Direct Realism, Indirect Realism, Dualism, Idealism and Panpsychism. ## References - Harrison, J. (1984). The incorrigibility of the cogito. Mind: New Series, Vol. 93, No. XCIII, 1984. The problem of regression - Ryle, G. (1949) The Concept of Mind. The University of Chicago Press, 1949. ```{=html} <!-- --> ``` - Smith, Q. (1986). The infinite regress of temporal attributions. The Southern Journal of Philosophy (1986) Vol. XXIV, No. 3, 383 (Section 3). <http://web.archive.org/web/20060507144913/http://www.qsmithwmu.com/the_infinite_regress.htm> ```{=html} <!-- --> ``` - Yates, S. (1991). Self referential arguments in philosophy. Reason Papers 16. (Fall 1991) 133-164. <http://www.mises.org/reasonpapers/pdf/16/rp_16_7.pdf> The homunculus argument - Gregory, R.L. (1990) Eye and Brain: The Psychology of Seeing, Oxford University Press Inc. New York. ```{=html} <!-- --> ``` - Gregory, T.L. (1987). The Oxford Companion to Mind. Oxford University Press. Subject-object paradox - James, W. (1904)Does \'Consciousness\' Exist? Journal of Philosophy, Psychology, and Scientific Methods, 1, 477-491. - Hegel, G.W.F. PHILOSOPHY OF MIND: SECTION I. MIND SUBJECTIVE B. PHENOMENOLOGY OF MIND CONSCIOUSNESS Part Three of the Encyclopaedia of the Philosophical Sciences ```{=html} <!-- --> ``` - Velmans, M. (1996) Consciousness and the \"Casual Paradox\". Behavioral and Brain Sciences, 19 (3): 538-542. - \[Bermudez, J.L. (1999) The Paradox of Self-Consciousness (representation and Mind) Psycoloquy: 10,#35 Ontological status - Bierman, D.J. (2004) Non Conscious Processes Preceding Intuitive decisions <http://m0134.fmg.uva.nl/~djb/publications/2004/Intuition_bialsymp2004.pdf> ```{=html} <!-- --> ``` - Damasio, A.R. (1994). Descartes\' error: Emotion, reason and the human brain. New York: Grosset/Putnam Book. ```{=html} <!-- --> ``` - Kant, I. Critique of Pure Reason <http://www.arts.cuhk.edu.hk/Philosophy/Kant/cpr/> Direct Realism - Aydede, M. (2001) Naturalism, introspection, and direct realism about pain. Consciousness and Emotion, Vol. 2, No. 1, 2001, pp. 29-73. <http://web.clas.ufl.edu/users/maydede/pain.pdf> - Chapman, C.R., and Y. Nakamura (1999). A Passion of the Soul: An Introduction to Pain for Consciousness Researchers. Consciousness and Cognition, 8: 391-422. ```{=html} <!-- --> ``` - Dennett, D. (1991). Consciousness Explained. Boston: Little, Brown ```{=html} <!-- --> ``` - Fowler C A (1986): "An event approach to the study of speech perception from a direct-realist perspective", J of Phonetics 14(1):3-28. ```{=html} <!-- --> ``` - Gibson, J. J. (1966) The Senses Considered as Perceptual Systems. Houghton Mifflin Company,Boston. ```{=html} <!-- --> ``` - Gibson, J. J. (1979) Ecological Approach to Visual Perception.: Lawrence Erlbaum Associates Publishers, Hillsdate. ```{=html} <!-- --> ``` - Gregory, R.L. 1988. Consciousness in science and philosophy: conscience and con-science. Chapter 12 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. ```{=html} <!-- --> ``` - Le Morvan, Pierre (2004). Arguments against direct realism and how to counter them. *The American Philosophical Quarterly*, *41*(3), 221-234.\] (pdf) <http://www.tcnj.edu/~lemorvan/DR_web.pdf> ```{=html} <!-- --> ``` - Oliveira, André L. G. and Oliveira, Luis F. (2002) Toward an ecological conception of timbre. In Proceedings Auditory Perception Cognition and Action Meeting 2002, Kansas City. <http://cogprints.org/2713/> ```{=html} <!-- --> ``` - Skinner, B. F. Science and Human Behavior . New York: Macmillan, 1953. ```{=html} <!-- --> ``` - Skinner, B. F. 1971. Beyond Freedom and Dignity. New York: Knopf. ```{=html} <!-- --> ``` - Skinner, B. F. 1948. Walden Two. New York: Macmillan. ```{=html} <!-- --> ``` - Tye, M. (2004). ANOTHER LOOK AT REPRESENTATIONALISM ABOUT PAIN. Consciousness and Emotion 2004, special issue on pain, edited by Murat Aydede (with replies by M. Aydede, N. Block, B. Maund, and P. Noordhof <http://sun.soci.niu.edu/~phildept/MT/RepresentationalismAndPain.pdf> ```{=html} <!-- --> ``` - Vygotsky, L.S.(1925) Consciousness as a problem in the psychology of behavior. Undiscovered Vygotsky: Etudes on the pre-history of cultural-historical psychology (European Studies in the History of Science and Ideas. Vol. 8), pp. 251-281. Peter Lang Publishing. <http://www.marxists.org/archive/vygotsky/works/1925/consciousness.htm> ```{=html} <!-- --> ``` - Ziff, Paul. \"About Behaviourism.\" Analysis 18 (1958): 132-136. Quoted by Larry Hauser in the Internet Encyclopedia of Philosophy. <http://www.utm.edu/research/iep/b/behavior.htm#B>. F. Skinner: Radical Behaviorism

# Consciousness Studies/The Conflict#The subject-object paradox *This section is about how regression and recursion seem to undermine the idea of conscious experience being anywhere in the universe.*. ## The conflict - supervenience and the location of the contents of phenomenal consciousness When we touch something or look at a view what we are probably touching or seeing is a thing in the world, out there, beyond our bodies. Many philosophers and almost all scientists would agree with this surmise. But is our conscious experience itself directly the things we touch or more like a picture of those things on television or something else entirely? Furthermore, can we really be certain that what we believe we experience truly occurs? Suppose for the moment that our experience truly does occur and consists of things laid out in time and space. Conscious experience appears to be a simultaneous set of things (i.e.: things arranged in space) but where are these things and what is this space? The things that occur in conscious experience could be a virtual reality in the brain based on the world beyond the body, or they could be the things themselves, viewed directly through some unknown phenomenon or it has even been suggested that they could be something non-physical. The problem of where the contents of conscious experience are located has provoked some of the fiercest battles in the philosophy of consciousness. There are three broad positions, the first is Direct Realism in which it is held that the contents of conscious experience are directly things in the world, the second is Indirect Realism where it is proposed that the contents of conscious experience are representations, usually in the physical brain, based on things \'out there\' in the world and the third is idealism where it is held that there is no physical world, only non-physical conscious experience. These three classifications overlap considerably, for instance some Natural Dualists believe that the contents of sensory experience are directly the world beyond the body but some thoughts are based in a non-physical soul and some philosophers introduce the dualist notion of a \"logical space\" containing disembodied information. Philosophers often use the concept of \'supervenience\' to examine the location of the contents of consciousness. Supervenience is the relation between two sets of properties. Supervenience can be simple; for example a golden ring supervenes on a piece of the metal gold. Supervenience can also be quite complex such as the idea that life supervenes on the biological processes in a cell. The most difficult cases of supervenience are where a high level description is related to simpler physical properties such as form and content. There are formal statements of supervenience: `The properties of A supervene on the properties of B if no two possible`\ `situations are identical with respect to the properties of A while`\ `differing with respect to the properties of B (after Chalmers 1996).` Lewis gives a simpler, if less technical, definition of supervenience: `A dot-matrix picture has global properties -- it is symmetrical, `\ `it is cluttered, and whatnot -- and yet all there is to the picture `\ `is dots and non-dots at each point of the matrix. The global `\ `properties are nothing but patterns in the dots. They supervene: no `\ `two pictures could differ in their global properties without `\ `differing, somewhere, in whether there is or there isn't a dot". `\ `Lewis, D., 1986, On the Plurality of Worlds, Oxford: Blackwell` One set of properties is said to supervene *locally* on another set of properties if the second set is determined by the first. Shape is an example of local supervenience; for instance a gold wire forged in a circle determines a gold ring. A set of properties is said to supervene *globally* on another if the entire context of the properties must be included; for instance, two organisms could be physically identical but demonstrate different behaviours in different environments. In this case the physical form of an organism does not totally determine the behaviour. Philosophers also divide supervenience into logical supervenience and natural supervenience. Logical supervenience deals with possible relations in possible worlds while natural supervenience deals with relations that occur in the natural world. See elementary information theory for a discussion of supervenience in information systems. A particular problem posed by consciousness studies is whether conscious phenomenal experience supervenes on the physical world and, if so, where. To answer these questions philosophers and neuroscientists must have a good understanding of physics. They should be aware of elementary physical ontology such as kinetic energy being the relativistic mass increase of a particle in a four dimensional universe and Newton\'s laws being due to the exploration of all paths in space-time. Without a good knowledge of physics there is the danger that we will be asking whether phenomenal consciousness supervenes on an abstract model of the world which does not supervene on the world itself (i.e.: *we may be asking if conscious phenomenal experience supervenes on Newtonian physics or supervenes on information systems theory rather than asking how phenomenal consciousness might supervene on the natural world*). The possibility that conscious experience does not really occur, at least in the form that we believe it occurs, is known as the problem of the \"Incorrigibility of the cogito\" (Harrison 1984). If Descartes\' idea that \"I think therefore I am\" is not beyond question (incorrigible) then the idea of phenomenal consciousness may be incorrect. (See for instance: Special relativity for beginners Special relativity for beginners Quantum physics explains Newton's laws of motion <http://www.eftaylor.com/pub/OgbornTaylor.pdf> ) ## The problem of regression The philosopher Gilbert Ryle was concerned with what he called the intellectualist legend which requires intelligent acts to be the product of the conscious application of mental rules. The intellectualist legend is also known as the \"Dogma of the Ghost in the Machine,\" the \"Two-Lives Legend,\" the \"Two-Worlds Story,\" or the \"Double-Life Legend\". Ralph Waldo Emerson summarised the intellectualist legend in the statement that \"The ancestor of every action is a thought.\" Ryle argued against the idea that every action requires a conscious thought and showed that this \'intellectualist legend\' results in an infinite regress of thought: `"According to the legend, whenever an agent does anything `\ `intelligently, his act is preceded and steered by another internal `\ `act of considering a regulative proposition appropriate to his `\ `practical problem. [...] Must we then say that for the hero's `\ `reflections how to act to be intelligent he must first reflect how `\ `best to reflect how to act? The endlessness of this implied regress `\ `shows that the application of the criterion of appropriateness does `\ `not entail the occurrence of a process of considering this criterion."`\ `(The Concept of Mind (1949)) ` image:constudregress.gif `"The crucial objection to the intellectualist legend is this. The `\ `consideration of propositions is itself an operation the execution `\ `of which can be more or less intelligent, less or more stupid. But if, `\ `for any operation to be intelligently executed, a prior theoretical `\ `operation had first to be performed and performed intelligently, it `\ `would be a logical impossibility for anyone ever to break into the `\ `circle." ` Variants of Ryle\'s regress are commonly aimed at cognitivist theories. For instance, in order to explain the behavior of rats, Edward Tolman suggested that the rats were constructing a \"cognitive map\" that helped them locate reinforcers, and he used intentional terms (e.g., expectancies, purposes, meanings) to describe their behavior. This led to a famous attack on Tolman\'s work by Guthrie who pointed out that if one was implying that every action must be preceded by a cognitive \'action\' (a \'thought\' or \'schema\' or \'script\' or whatever), then what \'causes\' this act? Clearly it must be preceded by another cognitive action, which must in turn must be preceded by another and so on, in an infinite regress unless an external input occurs at some stage. As a further example, we may take note of the following statement from The Concept of Mind (1949): \"The main object of this chapter is to show that there are many activities which directly display qualities of mind, yet are neither themselves intellectual operations nor yet effects of intellectual operations. Intelligent practice is not a step-child of theory. On the contrary theorizing is one practice amongst others and is itself intelligently or stupidly conducted.\" Ryle noted that \"theorizing is one practice amongst others.\" and hence would translate the statement by Emerson into, \"The ancestor of every action is an action.\" or \"The ancestor of every behavior is a behavior,\". Each behaviour would require yet another behavior to preface it as its ancestor, and an infinite regress would occur. It should be noted that Ryle's regress is a critique of cognitivism which arises from the Behaviorist tradition. Near the end of The Concept of Mind, Ryle states, \"The Behaviorists' methodological program has been of revolutionary importance to the program of psychology. But more, it has been one of the main sources of the philosophical suspicion that the two-worlds story is a myth.\" But Ryle's brand of logical behaviorism is not to be confused with the radical behaviorism of B. F. Skinner or the methodological behaviorism of John B. Watson. For as Alex Byrne noted, \"Ryle was indeed, as he reportedly said, 'only one arm and one leg a behaviorist'.\" Arguments that involve regress are well known in philosophy. In fact any reflexive, or self referencing process or argument will involve a regress if there is no external input. This applies whether the agent that engages in the process is a digital computer or intelligent agent (cf: Smith (1986), Yates (1991)). Ryle\'s regress suggests that intelligent acts are not created within phenomenal consciousness. They may have non-conscious components or even be entirely non-conscious. Ryle argued that this might mean that consciousness is just a \"ghost in the machine\" of the brain because consciousness would be epiphenomenal if it is not the creator of intelligent acts. However, as will be seen below, this conclusion may be premature and certainly cannot be used to dismiss phenomenal consciousness as non-existent or not present in the brain. ## The Subject-Object paradox This paradox was clearly enunciated by William James in 1904: \"Throughout the history of philosophy the subject and its object have been treated as absolutely discontinuous entities; and thereupon the presence of the latter to the former, or the \'apprehension\' by the former of the latter, has assumed a paradoxical character which all sorts of theories had to be invented to overcome.\" James (1904). The Subject-Object paradox points out that a conscious subject appears to observe itself as an object. But if it observes itself as an object then, as an object it cannot be a subject. As Bermudez(1998) puts it: \"Any theory that tries to elucidate the capacity to think first-person thoughts through linguistic mastery of the first-person pronoun will be circular, because the explanandum is part of the explanans..\" Thomas Reid uses this paradox to suggest that everything that is observed must be external to the soul and hence proposed that experience was the world itself. Wittgenstein (1949) offers a way out of the paradox by denying the existence of the subject: `<span style="font-family:times new roman;">`{=html}\"5.63 1. The thinking, presenting subject; there is no such thing. If I wrote a book The World as I Found It, I should also have therein to report on my body and say which members obey my will and which do not, etc. This then would be a method of isolating the subject or rather of showing that in an important sense there is no subject: that is to say, of it alone in this book mention could not be made. 5.632. The subject does not belong to the world but it is a limit of the world. 5.633. Where in the world is a metaphysical subject to be noted? You say that this case is altogether like that of the eye and the field of sight. But you do not really see the eye. And from nothing in the field of sight can it be concluded that it is seen from an eye\... 5.64 1. \...The philosophical I is not the man, not the human body or the human soul of which psychology treats, but the metaphysical subject, the limit --- not a part of the world.\"`</span>`{=html}(Wittgenstein 1949). Wittgenstein\'s view is similar to that voiced by Green (2002) in which there is nothing at the point centre of the manifold of events (there is no point eye). James (1904), Lektorsky (1980) and many others have also attempted to resolve the paradox by proposing that there is really no observer, only the observation or \'reflexive act\' of perception. This idea reaches its zenith in Brentano\'s concept of \"intentionality\" in which the subject and object are fused into a form of \"aboutness\": `<span style="font-family:times new roman;">`{=html}\"Every psychical phenomenon is characterized by what the Scholastics of the Middle Ages called the intentional (or sometimes the mental) inexistence of an object, and what we should like to call, although not quite unambiguously, the reference (Beziehung) to a content, the directedness (Richtung) toward an object (which in this context is not to be understood as something real) or the immanent-object quality (immanente Gegenständlichkeit). Each contains something as its object, though not each in the same manner. In the representation (Vorstellung) something is represented, in the judgment something is acknowledged or rejected, in desiring it is desired, etc. This intentional inexistence is peculiar alone to psychical phenomena. No physical phenomenon shows anything like it. And thus we can define psychical phenomena by saying that they are such phenomena as contain objects in themselves by way of intention (intentional).\"`</span>`{=html} Brentano, F. (1874). These authors have all identified the content of perception with either the world itself, the manifold of events or a synthetic \'about\' the world itself in an attempt at avoiding the paradox, however, as will be seen later, there are other solutions to the paradox. Bermúdez, J. (1998), The Paradox of Self-Consciousness, Bradford/MIT Press. Brentano, F. (1874). Psychology from an empirical standpoint. Vol1. <http://www.marxists.org/reference/subject/philosophy/works/ge/brentano.htm> William James (1904). A World of Pure Experience. First published in Journal of Philosophy, Psychology, and Scientific Methods, 1, 533-543, 561-570. <http://psychclassics.yorku.ca/James/experience.htm> ## The homunculus fallacy in philosophy of mind A Homunculus argument accounts for a phenomenon in terms of the very phenomenon that it is supposed to explain (Richard Gregory (1987)). Homunculus arguments are always fallacious. In the psychology and philosophy of mind \'homunculus arguments\' are extremely useful for detecting where theories of mind fail or are incomplete. Homunculus arguments are common in the theory of vision. Imagine a person watching a movie. He sees the images as something separate from himself, projected on the screen. How is this done? A simple theory might propose that the light from the screen forms an image on the retinas in the eyes and something in the brain looks at these as if they are the screen. The Homunculus Argument shows this is not a full explanation because all that has been done is to place an entire person, or homunculus, behind the eye who gazes at the retinas. A more sophisticated argument might propose that the images on the retinas are transferred to the visual cortex where it is scanned. Again this cannot be a full explanation because all that has been done is to place a little person in the brain behind the cortex. In the theory of vision the Homunculus Argument invalidates theories that do not explain \'projection\', the experience that the viewing point is separate from the things that are seen. (Adapted from Gregory (1987), (1990)). In the case of vision it is sometimes suggested that each homunculus would need a homunculus inside it ad infinitum. This is the **recursion** form of the homunculus concept. Notice that, unlike the case of regress, the recursion would occur after the event. An homunculus argument should be phrased in such a way that the conclusion is always that if a homunculus is required then the theory is wrong. After all, homunculi do not exist. Very few people would propose that there actually is a little man in the brain looking at brain activity. However, this proposal has been used as a \'straw man\' in theories of mind. Gilbert Ryle (1949) proposed that the human mind is known by its intelligent acts. (see Ryle\'s Regress). He argued that if there is an inner being inside the brain that could steer its own thoughts then this would lead to an absurd repetitive cycle or \'regress\' before a thought could occur: \"According to the legend, whenever an agent does anything intelligently, his act is preceded and steered by another internal act of considering a regulative proposition appropriate to his practical problem.\" \"\.... Must we then say that for the ..\[agent\'s\].. reflections how to act to be intelligent he must first reflect how best to reflect how to act? The endlessness of this implied regress shows that the application of the appropriateness does not entail the occurrence of a process of considering this criterion.\" The homunculus argument and the regress argument are often considered to be the same but this is not the case. The homunculus argument says that if there is a need for a \'little man\' to complete a theory then the theory is wrong. The regress argument says that an intelligent agent would need to think before it could have a thought. Ryle\'s theory is that intelligent acts cannot be a property of an inner being or mind, if such a thing were to exist. The idea that conscious experience is a flow of information into an unextended place (a point eye) leaves itself open to the charge of inserting an homunculus beyond the point eye. On careful reading few, if any, real theories actually propose a flow through the point eye but suggest some sort of nebulous direct relation with the information in front of the eye. For instance, Descartes has a point soul directly considering the contents of the common sense and Reid has a point eye directly considering the world itself. `<span style="font-size:x-small;">`{=html}Questions: It might be said that the homunculus fallacy means that either the materialist interpretation of conscious experience is wrong or conscious experience does not exist: discuss. Physicalism is not materialism, discuss. Could physical phenomena such as entanglement or space-time theories of observation, where the observed vectors are constrained to the manifold, avoid the homunculus fallacy?`</span>`{=html} ## Berkeley\'s \"passive ideas\" Ryle\'s regress, when applied to consciousness, is based on an analysis of conscious intellectual activity as a succession of states. At any moment the conscious intellect contains one state such as \'I will think of a word\'. This means that either the state has just popped into mind or there was a previous state that gave rise to it such as \'I will think of thinking of a word\'. Descartes and other empiricists have noted that thoughts do indeed just pop into mind. So if we transfer Ryle\'s analysis to the real world we discover that the regress is avoided by removing the starting point of a series of thoughts from conscious phenomenal experience. A train of thought just begins, it has no conscious origin and Descartes\' implication is that it has probably been synthesised non-consciously. Suppose Descartes and our own experience are correct, suppose thoughts do just pop into mind, if this happens can there still be a conscious intellectual agent or are intellectual agents largely non-conscious? One of the simplest intellectual processes is a test for equality i.e.: \'does A equal B?\' and a routing of flow as a result of the test i.e.: \'if A = B then goto\'. Can an intellectual agent perform an equality test in conscious phenomenal experience? Consider the test of whether \'A = A\', you attend to the left \'A\' then the right \'A\' and declare them equal. What have you actually done? The feeling that the symbols are equal just pops into mind. Psychologists and philosophers use the word \'intuition\' for this popping of answers into mind (Kant 1781). It is usually accompanied by emotional experience (Damasio 1994, Bierman 2004). If intellectual activity is actually a succession of things that just pop into phenomenal consciousness then Ryle\'s conclusion that phenomenal consciousness is like a \"ghost in the machine\" of the brain would to some extent justified. Phenomenal consciousness would not be intellectual activity. Phenomenal consciousness would contain the stages, or succession of states, of intellectual activity but would not contain the processes that connect these stages. This observation that conscious experience is a succession of **passive ideas** is well known in philosophy (cf: George Berkeley, Principles of Human Knowledge, 25). ## More on the conflict Click above for more on Phenomenal consciousness, access consciousness, Direct Realism, Indirect Realism, Dualism, Idealism and Panpsychism. ## References - Harrison, J. (1984). The incorrigibility of the cogito. Mind: New Series, Vol. 93, No. XCIII, 1984. The problem of regression - Ryle, G. (1949) The Concept of Mind. The University of Chicago Press, 1949. ```{=html} <!-- --> ``` - Smith, Q. (1986). The infinite regress of temporal attributions. The Southern Journal of Philosophy (1986) Vol. XXIV, No. 3, 383 (Section 3). <http://web.archive.org/web/20060507144913/http://www.qsmithwmu.com/the_infinite_regress.htm> ```{=html} <!-- --> ``` - Yates, S. (1991). Self referential arguments in philosophy. Reason Papers 16. (Fall 1991) 133-164. <http://www.mises.org/reasonpapers/pdf/16/rp_16_7.pdf> The homunculus argument - Gregory, R.L. (1990) Eye and Brain: The Psychology of Seeing, Oxford University Press Inc. New York. ```{=html} <!-- --> ``` - Gregory, T.L. (1987). The Oxford Companion to Mind. Oxford University Press. Subject-object paradox - James, W. (1904)Does \'Consciousness\' Exist? Journal of Philosophy, Psychology, and Scientific Methods, 1, 477-491. - Hegel, G.W.F. PHILOSOPHY OF MIND: SECTION I. MIND SUBJECTIVE B. PHENOMENOLOGY OF MIND CONSCIOUSNESS Part Three of the Encyclopaedia of the Philosophical Sciences ```{=html} <!-- --> ``` - Velmans, M. (1996) Consciousness and the \"Casual Paradox\". Behavioral and Brain Sciences, 19 (3): 538-542. - \[Bermudez, J.L. (1999) The Paradox of Self-Consciousness (representation and Mind) Psycoloquy: 10,#35 Ontological status - Bierman, D.J. (2004) Non Conscious Processes Preceding Intuitive decisions <http://m0134.fmg.uva.nl/~djb/publications/2004/Intuition_bialsymp2004.pdf> ```{=html} <!-- --> ``` - Damasio, A.R. (1994). Descartes\' error: Emotion, reason and the human brain. New York: Grosset/Putnam Book. ```{=html} <!-- --> ``` - Kant, I. Critique of Pure Reason <http://www.arts.cuhk.edu.hk/Philosophy/Kant/cpr/> Direct Realism - Aydede, M. (2001) Naturalism, introspection, and direct realism about pain. Consciousness and Emotion, Vol. 2, No. 1, 2001, pp. 29-73. <http://web.clas.ufl.edu/users/maydede/pain.pdf> - Chapman, C.R., and Y. Nakamura (1999). A Passion of the Soul: An Introduction to Pain for Consciousness Researchers. Consciousness and Cognition, 8: 391-422. ```{=html} <!-- --> ``` - Dennett, D. (1991). Consciousness Explained. Boston: Little, Brown ```{=html} <!-- --> ``` - Fowler C A (1986): "An event approach to the study of speech perception from a direct-realist perspective", J of Phonetics 14(1):3-28. ```{=html} <!-- --> ``` - Gibson, J. J. (1966) The Senses Considered as Perceptual Systems. Houghton Mifflin Company,Boston. ```{=html} <!-- --> ``` - Gibson, J. J. (1979) Ecological Approach to Visual Perception.: Lawrence Erlbaum Associates Publishers, Hillsdate. ```{=html} <!-- --> ``` - Gregory, R.L. 1988. Consciousness in science and philosophy: conscience and con-science. Chapter 12 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. ```{=html} <!-- --> ``` - Le Morvan, Pierre (2004). Arguments against direct realism and how to counter them. *The American Philosophical Quarterly*, *41*(3), 221-234.\] (pdf) <http://www.tcnj.edu/~lemorvan/DR_web.pdf> ```{=html} <!-- --> ``` - Oliveira, André L. G. and Oliveira, Luis F. (2002) Toward an ecological conception of timbre. In Proceedings Auditory Perception Cognition and Action Meeting 2002, Kansas City. <http://cogprints.org/2713/> ```{=html} <!-- --> ``` - Skinner, B. F. Science and Human Behavior . New York: Macmillan, 1953. ```{=html} <!-- --> ``` - Skinner, B. F. 1971. Beyond Freedom and Dignity. New York: Knopf. ```{=html} <!-- --> ``` - Skinner, B. F. 1948. Walden Two. New York: Macmillan. ```{=html} <!-- --> ``` - Tye, M. (2004). ANOTHER LOOK AT REPRESENTATIONALISM ABOUT PAIN. Consciousness and Emotion 2004, special issue on pain, edited by Murat Aydede (with replies by M. Aydede, N. Block, B. Maund, and P. Noordhof <http://sun.soci.niu.edu/~phildept/MT/RepresentationalismAndPain.pdf> ```{=html} <!-- --> ``` - Vygotsky, L.S.(1925) Consciousness as a problem in the psychology of behavior. Undiscovered Vygotsky: Etudes on the pre-history of cultural-historical psychology (European Studies in the History of Science and Ideas. Vol. 8), pp. 251-281. Peter Lang Publishing. <http://www.marxists.org/archive/vygotsky/works/1925/consciousness.htm> ```{=html} <!-- --> ``` - Ziff, Paul. \"About Behaviourism.\" Analysis 18 (1958): 132-136. Quoted by Larry Hauser in the Internet Encyclopedia of Philosophy. <http://www.utm.edu/research/iep/b/behavior.htm#B>. F. Skinner: Radical Behaviorism

# Consciousness Studies/The Conflict#The homunculus argument *This section is about how regression and recursion seem to undermine the idea of conscious experience being anywhere in the universe.*. ## The conflict - supervenience and the location of the contents of phenomenal consciousness When we touch something or look at a view what we are probably touching or seeing is a thing in the world, out there, beyond our bodies. Many philosophers and almost all scientists would agree with this surmise. But is our conscious experience itself directly the things we touch or more like a picture of those things on television or something else entirely? Furthermore, can we really be certain that what we believe we experience truly occurs? Suppose for the moment that our experience truly does occur and consists of things laid out in time and space. Conscious experience appears to be a simultaneous set of things (i.e.: things arranged in space) but where are these things and what is this space? The things that occur in conscious experience could be a virtual reality in the brain based on the world beyond the body, or they could be the things themselves, viewed directly through some unknown phenomenon or it has even been suggested that they could be something non-physical. The problem of where the contents of conscious experience are located has provoked some of the fiercest battles in the philosophy of consciousness. There are three broad positions, the first is Direct Realism in which it is held that the contents of conscious experience are directly things in the world, the second is Indirect Realism where it is proposed that the contents of conscious experience are representations, usually in the physical brain, based on things \'out there\' in the world and the third is idealism where it is held that there is no physical world, only non-physical conscious experience. These three classifications overlap considerably, for instance some Natural Dualists believe that the contents of sensory experience are directly the world beyond the body but some thoughts are based in a non-physical soul and some philosophers introduce the dualist notion of a \"logical space\" containing disembodied information. Philosophers often use the concept of \'supervenience\' to examine the location of the contents of consciousness. Supervenience is the relation between two sets of properties. Supervenience can be simple; for example a golden ring supervenes on a piece of the metal gold. Supervenience can also be quite complex such as the idea that life supervenes on the biological processes in a cell. The most difficult cases of supervenience are where a high level description is related to simpler physical properties such as form and content. There are formal statements of supervenience: `The properties of A supervene on the properties of B if no two possible`\ `situations are identical with respect to the properties of A while`\ `differing with respect to the properties of B (after Chalmers 1996).` Lewis gives a simpler, if less technical, definition of supervenience: `A dot-matrix picture has global properties -- it is symmetrical, `\ `it is cluttered, and whatnot -- and yet all there is to the picture `\ `is dots and non-dots at each point of the matrix. The global `\ `properties are nothing but patterns in the dots. They supervene: no `\ `two pictures could differ in their global properties without `\ `differing, somewhere, in whether there is or there isn't a dot". `\ `Lewis, D., 1986, On the Plurality of Worlds, Oxford: Blackwell` One set of properties is said to supervene *locally* on another set of properties if the second set is determined by the first. Shape is an example of local supervenience; for instance a gold wire forged in a circle determines a gold ring. A set of properties is said to supervene *globally* on another if the entire context of the properties must be included; for instance, two organisms could be physically identical but demonstrate different behaviours in different environments. In this case the physical form of an organism does not totally determine the behaviour. Philosophers also divide supervenience into logical supervenience and natural supervenience. Logical supervenience deals with possible relations in possible worlds while natural supervenience deals with relations that occur in the natural world. See elementary information theory for a discussion of supervenience in information systems. A particular problem posed by consciousness studies is whether conscious phenomenal experience supervenes on the physical world and, if so, where. To answer these questions philosophers and neuroscientists must have a good understanding of physics. They should be aware of elementary physical ontology such as kinetic energy being the relativistic mass increase of a particle in a four dimensional universe and Newton\'s laws being due to the exploration of all paths in space-time. Without a good knowledge of physics there is the danger that we will be asking whether phenomenal consciousness supervenes on an abstract model of the world which does not supervene on the world itself (i.e.: *we may be asking if conscious phenomenal experience supervenes on Newtonian physics or supervenes on information systems theory rather than asking how phenomenal consciousness might supervene on the natural world*). The possibility that conscious experience does not really occur, at least in the form that we believe it occurs, is known as the problem of the \"Incorrigibility of the cogito\" (Harrison 1984). If Descartes\' idea that \"I think therefore I am\" is not beyond question (incorrigible) then the idea of phenomenal consciousness may be incorrect. (See for instance: Special relativity for beginners Special relativity for beginners Quantum physics explains Newton's laws of motion <http://www.eftaylor.com/pub/OgbornTaylor.pdf> ) ## The problem of regression The philosopher Gilbert Ryle was concerned with what he called the intellectualist legend which requires intelligent acts to be the product of the conscious application of mental rules. The intellectualist legend is also known as the \"Dogma of the Ghost in the Machine,\" the \"Two-Lives Legend,\" the \"Two-Worlds Story,\" or the \"Double-Life Legend\". Ralph Waldo Emerson summarised the intellectualist legend in the statement that \"The ancestor of every action is a thought.\" Ryle argued against the idea that every action requires a conscious thought and showed that this \'intellectualist legend\' results in an infinite regress of thought: `"According to the legend, whenever an agent does anything `\ `intelligently, his act is preceded and steered by another internal `\ `act of considering a regulative proposition appropriate to his `\ `practical problem. [...] Must we then say that for the hero's `\ `reflections how to act to be intelligent he must first reflect how `\ `best to reflect how to act? The endlessness of this implied regress `\ `shows that the application of the criterion of appropriateness does `\ `not entail the occurrence of a process of considering this criterion."`\ `(The Concept of Mind (1949)) ` image:constudregress.gif `"The crucial objection to the intellectualist legend is this. The `\ `consideration of propositions is itself an operation the execution `\ `of which can be more or less intelligent, less or more stupid. But if, `\ `for any operation to be intelligently executed, a prior theoretical `\ `operation had first to be performed and performed intelligently, it `\ `would be a logical impossibility for anyone ever to break into the `\ `circle." ` Variants of Ryle\'s regress are commonly aimed at cognitivist theories. For instance, in order to explain the behavior of rats, Edward Tolman suggested that the rats were constructing a \"cognitive map\" that helped them locate reinforcers, and he used intentional terms (e.g., expectancies, purposes, meanings) to describe their behavior. This led to a famous attack on Tolman\'s work by Guthrie who pointed out that if one was implying that every action must be preceded by a cognitive \'action\' (a \'thought\' or \'schema\' or \'script\' or whatever), then what \'causes\' this act? Clearly it must be preceded by another cognitive action, which must in turn must be preceded by another and so on, in an infinite regress unless an external input occurs at some stage. As a further example, we may take note of the following statement from The Concept of Mind (1949): \"The main object of this chapter is to show that there are many activities which directly display qualities of mind, yet are neither themselves intellectual operations nor yet effects of intellectual operations. Intelligent practice is not a step-child of theory. On the contrary theorizing is one practice amongst others and is itself intelligently or stupidly conducted.\" Ryle noted that \"theorizing is one practice amongst others.\" and hence would translate the statement by Emerson into, \"The ancestor of every action is an action.\" or \"The ancestor of every behavior is a behavior,\". Each behaviour would require yet another behavior to preface it as its ancestor, and an infinite regress would occur. It should be noted that Ryle's regress is a critique of cognitivism which arises from the Behaviorist tradition. Near the end of The Concept of Mind, Ryle states, \"The Behaviorists' methodological program has been of revolutionary importance to the program of psychology. But more, it has been one of the main sources of the philosophical suspicion that the two-worlds story is a myth.\" But Ryle's brand of logical behaviorism is not to be confused with the radical behaviorism of B. F. Skinner or the methodological behaviorism of John B. Watson. For as Alex Byrne noted, \"Ryle was indeed, as he reportedly said, 'only one arm and one leg a behaviorist'.\" Arguments that involve regress are well known in philosophy. In fact any reflexive, or self referencing process or argument will involve a regress if there is no external input. This applies whether the agent that engages in the process is a digital computer or intelligent agent (cf: Smith (1986), Yates (1991)). Ryle\'s regress suggests that intelligent acts are not created within phenomenal consciousness. They may have non-conscious components or even be entirely non-conscious. Ryle argued that this might mean that consciousness is just a \"ghost in the machine\" of the brain because consciousness would be epiphenomenal if it is not the creator of intelligent acts. However, as will be seen below, this conclusion may be premature and certainly cannot be used to dismiss phenomenal consciousness as non-existent or not present in the brain. ## The Subject-Object paradox This paradox was clearly enunciated by William James in 1904: \"Throughout the history of philosophy the subject and its object have been treated as absolutely discontinuous entities; and thereupon the presence of the latter to the former, or the \'apprehension\' by the former of the latter, has assumed a paradoxical character which all sorts of theories had to be invented to overcome.\" James (1904). The Subject-Object paradox points out that a conscious subject appears to observe itself as an object. But if it observes itself as an object then, as an object it cannot be a subject. As Bermudez(1998) puts it: \"Any theory that tries to elucidate the capacity to think first-person thoughts through linguistic mastery of the first-person pronoun will be circular, because the explanandum is part of the explanans..\" Thomas Reid uses this paradox to suggest that everything that is observed must be external to the soul and hence proposed that experience was the world itself. Wittgenstein (1949) offers a way out of the paradox by denying the existence of the subject: `<span style="font-family:times new roman;">`{=html}\"5.63 1. The thinking, presenting subject; there is no such thing. If I wrote a book The World as I Found It, I should also have therein to report on my body and say which members obey my will and which do not, etc. This then would be a method of isolating the subject or rather of showing that in an important sense there is no subject: that is to say, of it alone in this book mention could not be made. 5.632. The subject does not belong to the world but it is a limit of the world. 5.633. Where in the world is a metaphysical subject to be noted? You say that this case is altogether like that of the eye and the field of sight. But you do not really see the eye. And from nothing in the field of sight can it be concluded that it is seen from an eye\... 5.64 1. \...The philosophical I is not the man, not the human body or the human soul of which psychology treats, but the metaphysical subject, the limit --- not a part of the world.\"`</span>`{=html}(Wittgenstein 1949). Wittgenstein\'s view is similar to that voiced by Green (2002) in which there is nothing at the point centre of the manifold of events (there is no point eye). James (1904), Lektorsky (1980) and many others have also attempted to resolve the paradox by proposing that there is really no observer, only the observation or \'reflexive act\' of perception. This idea reaches its zenith in Brentano\'s concept of \"intentionality\" in which the subject and object are fused into a form of \"aboutness\": `<span style="font-family:times new roman;">`{=html}\"Every psychical phenomenon is characterized by what the Scholastics of the Middle Ages called the intentional (or sometimes the mental) inexistence of an object, and what we should like to call, although not quite unambiguously, the reference (Beziehung) to a content, the directedness (Richtung) toward an object (which in this context is not to be understood as something real) or the immanent-object quality (immanente Gegenständlichkeit). Each contains something as its object, though not each in the same manner. In the representation (Vorstellung) something is represented, in the judgment something is acknowledged or rejected, in desiring it is desired, etc. This intentional inexistence is peculiar alone to psychical phenomena. No physical phenomenon shows anything like it. And thus we can define psychical phenomena by saying that they are such phenomena as contain objects in themselves by way of intention (intentional).\"`</span>`{=html} Brentano, F. (1874). These authors have all identified the content of perception with either the world itself, the manifold of events or a synthetic \'about\' the world itself in an attempt at avoiding the paradox, however, as will be seen later, there are other solutions to the paradox. Bermúdez, J. (1998), The Paradox of Self-Consciousness, Bradford/MIT Press. Brentano, F. (1874). Psychology from an empirical standpoint. Vol1. <http://www.marxists.org/reference/subject/philosophy/works/ge/brentano.htm> William James (1904). A World of Pure Experience. First published in Journal of Philosophy, Psychology, and Scientific Methods, 1, 533-543, 561-570. <http://psychclassics.yorku.ca/James/experience.htm> ## The homunculus fallacy in philosophy of mind A Homunculus argument accounts for a phenomenon in terms of the very phenomenon that it is supposed to explain (Richard Gregory (1987)). Homunculus arguments are always fallacious. In the psychology and philosophy of mind \'homunculus arguments\' are extremely useful for detecting where theories of mind fail or are incomplete. Homunculus arguments are common in the theory of vision. Imagine a person watching a movie. He sees the images as something separate from himself, projected on the screen. How is this done? A simple theory might propose that the light from the screen forms an image on the retinas in the eyes and something in the brain looks at these as if they are the screen. The Homunculus Argument shows this is not a full explanation because all that has been done is to place an entire person, or homunculus, behind the eye who gazes at the retinas. A more sophisticated argument might propose that the images on the retinas are transferred to the visual cortex where it is scanned. Again this cannot be a full explanation because all that has been done is to place a little person in the brain behind the cortex. In the theory of vision the Homunculus Argument invalidates theories that do not explain \'projection\', the experience that the viewing point is separate from the things that are seen. (Adapted from Gregory (1987), (1990)). In the case of vision it is sometimes suggested that each homunculus would need a homunculus inside it ad infinitum. This is the **recursion** form of the homunculus concept. Notice that, unlike the case of regress, the recursion would occur after the event. An homunculus argument should be phrased in such a way that the conclusion is always that if a homunculus is required then the theory is wrong. After all, homunculi do not exist. Very few people would propose that there actually is a little man in the brain looking at brain activity. However, this proposal has been used as a \'straw man\' in theories of mind. Gilbert Ryle (1949) proposed that the human mind is known by its intelligent acts. (see Ryle\'s Regress). He argued that if there is an inner being inside the brain that could steer its own thoughts then this would lead to an absurd repetitive cycle or \'regress\' before a thought could occur: \"According to the legend, whenever an agent does anything intelligently, his act is preceded and steered by another internal act of considering a regulative proposition appropriate to his practical problem.\" \"\.... Must we then say that for the ..\[agent\'s\].. reflections how to act to be intelligent he must first reflect how best to reflect how to act? The endlessness of this implied regress shows that the application of the appropriateness does not entail the occurrence of a process of considering this criterion.\" The homunculus argument and the regress argument are often considered to be the same but this is not the case. The homunculus argument says that if there is a need for a \'little man\' to complete a theory then the theory is wrong. The regress argument says that an intelligent agent would need to think before it could have a thought. Ryle\'s theory is that intelligent acts cannot be a property of an inner being or mind, if such a thing were to exist. The idea that conscious experience is a flow of information into an unextended place (a point eye) leaves itself open to the charge of inserting an homunculus beyond the point eye. On careful reading few, if any, real theories actually propose a flow through the point eye but suggest some sort of nebulous direct relation with the information in front of the eye. For instance, Descartes has a point soul directly considering the contents of the common sense and Reid has a point eye directly considering the world itself. `<span style="font-size:x-small;">`{=html}Questions: It might be said that the homunculus fallacy means that either the materialist interpretation of conscious experience is wrong or conscious experience does not exist: discuss. Physicalism is not materialism, discuss. Could physical phenomena such as entanglement or space-time theories of observation, where the observed vectors are constrained to the manifold, avoid the homunculus fallacy?`</span>`{=html} ## Berkeley\'s \"passive ideas\" Ryle\'s regress, when applied to consciousness, is based on an analysis of conscious intellectual activity as a succession of states. At any moment the conscious intellect contains one state such as \'I will think of a word\'. This means that either the state has just popped into mind or there was a previous state that gave rise to it such as \'I will think of thinking of a word\'. Descartes and other empiricists have noted that thoughts do indeed just pop into mind. So if we transfer Ryle\'s analysis to the real world we discover that the regress is avoided by removing the starting point of a series of thoughts from conscious phenomenal experience. A train of thought just begins, it has no conscious origin and Descartes\' implication is that it has probably been synthesised non-consciously. Suppose Descartes and our own experience are correct, suppose thoughts do just pop into mind, if this happens can there still be a conscious intellectual agent or are intellectual agents largely non-conscious? One of the simplest intellectual processes is a test for equality i.e.: \'does A equal B?\' and a routing of flow as a result of the test i.e.: \'if A = B then goto\'. Can an intellectual agent perform an equality test in conscious phenomenal experience? Consider the test of whether \'A = A\', you attend to the left \'A\' then the right \'A\' and declare them equal. What have you actually done? The feeling that the symbols are equal just pops into mind. Psychologists and philosophers use the word \'intuition\' for this popping of answers into mind (Kant 1781). It is usually accompanied by emotional experience (Damasio 1994, Bierman 2004). If intellectual activity is actually a succession of things that just pop into phenomenal consciousness then Ryle\'s conclusion that phenomenal consciousness is like a \"ghost in the machine\" of the brain would to some extent justified. Phenomenal consciousness would not be intellectual activity. Phenomenal consciousness would contain the stages, or succession of states, of intellectual activity but would not contain the processes that connect these stages. This observation that conscious experience is a succession of **passive ideas** is well known in philosophy (cf: George Berkeley, Principles of Human Knowledge, 25). ## More on the conflict Click above for more on Phenomenal consciousness, access consciousness, Direct Realism, Indirect Realism, Dualism, Idealism and Panpsychism. ## References - Harrison, J. (1984). The incorrigibility of the cogito. Mind: New Series, Vol. 93, No. XCIII, 1984. The problem of regression - Ryle, G. (1949) The Concept of Mind. The University of Chicago Press, 1949. ```{=html} <!-- --> ``` - Smith, Q. (1986). The infinite regress of temporal attributions. The Southern Journal of Philosophy (1986) Vol. XXIV, No. 3, 383 (Section 3). <http://web.archive.org/web/20060507144913/http://www.qsmithwmu.com/the_infinite_regress.htm> ```{=html} <!-- --> ``` - Yates, S. (1991). Self referential arguments in philosophy. Reason Papers 16. (Fall 1991) 133-164. <http://www.mises.org/reasonpapers/pdf/16/rp_16_7.pdf> The homunculus argument - Gregory, R.L. (1990) Eye and Brain: The Psychology of Seeing, Oxford University Press Inc. New York. ```{=html} <!-- --> ``` - Gregory, T.L. (1987). The Oxford Companion to Mind. Oxford University Press. Subject-object paradox - James, W. (1904)Does \'Consciousness\' Exist? Journal of Philosophy, Psychology, and Scientific Methods, 1, 477-491. - Hegel, G.W.F. PHILOSOPHY OF MIND: SECTION I. MIND SUBJECTIVE B. PHENOMENOLOGY OF MIND CONSCIOUSNESS Part Three of the Encyclopaedia of the Philosophical Sciences ```{=html} <!-- --> ``` - Velmans, M. (1996) Consciousness and the \"Casual Paradox\". Behavioral and Brain Sciences, 19 (3): 538-542. - \[Bermudez, J.L. (1999) The Paradox of Self-Consciousness (representation and Mind) Psycoloquy: 10,#35 Ontological status - Bierman, D.J. (2004) Non Conscious Processes Preceding Intuitive decisions <http://m0134.fmg.uva.nl/~djb/publications/2004/Intuition_bialsymp2004.pdf> ```{=html} <!-- --> ``` - Damasio, A.R. (1994). Descartes\' error: Emotion, reason and the human brain. New York: Grosset/Putnam Book. ```{=html} <!-- --> ``` - Kant, I. Critique of Pure Reason <http://www.arts.cuhk.edu.hk/Philosophy/Kant/cpr/> Direct Realism - Aydede, M. (2001) Naturalism, introspection, and direct realism about pain. Consciousness and Emotion, Vol. 2, No. 1, 2001, pp. 29-73. <http://web.clas.ufl.edu/users/maydede/pain.pdf> - Chapman, C.R., and Y. Nakamura (1999). A Passion of the Soul: An Introduction to Pain for Consciousness Researchers. Consciousness and Cognition, 8: 391-422. ```{=html} <!-- --> ``` - Dennett, D. (1991). Consciousness Explained. Boston: Little, Brown ```{=html} <!-- --> ``` - Fowler C A (1986): "An event approach to the study of speech perception from a direct-realist perspective", J of Phonetics 14(1):3-28. ```{=html} <!-- --> ``` - Gibson, J. J. (1966) The Senses Considered as Perceptual Systems. Houghton Mifflin Company,Boston. ```{=html} <!-- --> ``` - Gibson, J. J. (1979) Ecological Approach to Visual Perception.: Lawrence Erlbaum Associates Publishers, Hillsdate. ```{=html} <!-- --> ``` - Gregory, R.L. 1988. Consciousness in science and philosophy: conscience and con-science. Chapter 12 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. ```{=html} <!-- --> ``` - Le Morvan, Pierre (2004). Arguments against direct realism and how to counter them. *The American Philosophical Quarterly*, *41*(3), 221-234.\] (pdf) <http://www.tcnj.edu/~lemorvan/DR_web.pdf> ```{=html} <!-- --> ``` - Oliveira, André L. G. and Oliveira, Luis F. (2002) Toward an ecological conception of timbre. In Proceedings Auditory Perception Cognition and Action Meeting 2002, Kansas City. <http://cogprints.org/2713/> ```{=html} <!-- --> ``` - Skinner, B. F. Science and Human Behavior . New York: Macmillan, 1953. ```{=html} <!-- --> ``` - Skinner, B. F. 1971. Beyond Freedom and Dignity. New York: Knopf. ```{=html} <!-- --> ``` - Skinner, B. F. 1948. Walden Two. New York: Macmillan. ```{=html} <!-- --> ``` - Tye, M. (2004). ANOTHER LOOK AT REPRESENTATIONALISM ABOUT PAIN. Consciousness and Emotion 2004, special issue on pain, edited by Murat Aydede (with replies by M. Aydede, N. Block, B. Maund, and P. Noordhof <http://sun.soci.niu.edu/~phildept/MT/RepresentationalismAndPain.pdf> ```{=html} <!-- --> ``` - Vygotsky, L.S.(1925) Consciousness as a problem in the psychology of behavior. Undiscovered Vygotsky: Etudes on the pre-history of cultural-historical psychology (European Studies in the History of Science and Ideas. Vol. 8), pp. 251-281. Peter Lang Publishing. <http://www.marxists.org/archive/vygotsky/works/1925/consciousness.htm> ```{=html} <!-- --> ``` - Ziff, Paul. \"About Behaviourism.\" Analysis 18 (1958): 132-136. Quoted by Larry Hauser in the Internet Encyclopedia of Philosophy. <http://www.utm.edu/research/iep/b/behavior.htm#B>. F. Skinner: Radical Behaviorism

# Consciousness Studies/The Conflict2#Phenomenal consciousness and access consciousness *This part of this section is about the where and when of the experience called consciousness. Is it in the world, in the brain or are the world and brain within it?* ## Phenomenal consciousness and access consciousness Block(1995) drew attention to the way that there appear to be two types of consciousness: *phenomenal* consciousness and *access* consciousness: `Phenomenal consciousness is experience; the phenomenally`\ `conscious  aspect of a state is what it is like to be in that`\ `state. The mark of access-consciousness, by contrast, is `\ `availability for use in reasoning and rationally guiding speech `\ `and action. (Block 1995).` *See the section on Ned Block\'s ideas for a deeper coverage of his approach to access and phenomenal consciousness.* Block uses Nagel\'s famous (1974) paper, \"What is it like to be a bat?\" as an exemplary description of phenomenal consciousness. Excellent descriptions have also been proffered by the empiricist philosophers who gave lengthy descriptions of consciousness as partly experience itself. Although Block has formalised the idea of phenomenal and access consciousness similar ideas have also been put forward by many philosophers including Kant and Whitehead. Access consciousness has two interpretations, in the first, used by Block, it applies to the functions that appear to operate on phenomenal consciousness. In the second, used by the behaviourists and eliminativists, it is some property of the functions of the brain that can be called \'consciousness\'. This division between phenomenal and functional aspects of consciousness is useful because it emphasises the idea of phenomenal consciousness as observation rather than action. Some philosophers such as Huxley in 1874, have taken the view that because phenomenal consciousness appears to have no function it is of no importance or cannot exist. James (1879) introduced the term \"epiphenomenalism\" to summarise the idea that consciousness has no function. The idea that phenomenal consciousness cannot exist is a type of *Eliminativism* (also known as Eliminative Materialism). Eliminativism owes much to the work of Sellars(1956) and Feyerbend (1963). Dennett (1978) applied Eliminativism to phenomenal consciousness and denies that pain is real. Others such as Rey(1997) have also applied eliminativism to phenomenal consciousness. Dennett (1988) redefines consciousness in terms of access consciousness alone, he argues that \"Everything real has properties, and since I don\'t deny the reality of conscious experience, I grant that conscious experience has properties\". Having related all consciousness to properties he then declares that these properties are actually judgements of properties. He considers judgements of the properties of consciousness to be identical to the properties themselves. He writes: `<font face="times">`{=html}\"The infallibilist line on qualia treats them as properties of one\'s experience one cannot in principle misdiscover, and this is a mysterious doctrine (at least as mysterious as papal infallibility) unless we shift the emphasis a little and treat qualia as logical constructs out of subjects\' qualia-judgments: a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F. \"`</font>`{=html} Having identified \"properties\" with \"judgement of properties\" he can then show that the judgements are insubstantial, hence the properties are insubstantial and hence the qualia are insubstantial or even non-existent. Dennett concludes that qualia can be rejected as non-existent: `<font face="times">`{=html}\"So when we look one last time at our original characterization of qualia, as ineffable, intrinsic, private, directly apprehensible properties of experience, we find that there is nothing to fill the bill. In their place are relatively or practically ineffable public properties we can refer to indirectly via reference to our private property-detectors\-- private only in the sense of idiosyncratic. And insofar as we wish to cling to our subjective authority about the occurrence within us of states of certain types or with certain properties, we can have some authority\--not infallibility or incorrigibility, but something better than sheer guessing\--but only if we restrict ourselves to relational, extrinsic properties like the power of certain internal states of ours to provoke acts of apparent re- identification. So contrary to what seems obvious at first blush, there simply are no qualia at all. \" (Dennett 1988)`</font>`{=html} Dennett\'s asserts that \"a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F\". This is a statement of the belief that qualia are the same as processes such as judgements. Processes such as judgements are flows of data where one state examines a previous state in a succession over time and embody what Whitehead called the \"materialist\" concept of time. Dennett does not consider how a scientific concept of time might affect his argument. Dennett\'s argument has been persuasive and there are now many philosophers and neuroscientists who believe that the problem of phenomenal consciousness does not exist. This means that, to them, what we call \'consciousness\' can only be a property of the functions performed by the brain and body. According to these philosophers only access consciousness exists. Those who support the idea of phenomenal consciousness also tend to frame it in terms of nineteenth century theory where one state examines a previous state in a succession over time, for instance Edelman(1993) places the past in memories at an instant and time within experience is explained as continuing modelling processes: `<font face="times">`{=html}\"Primary consciousness is the state of being mentally aware of things in the world\--of having mental images in the present. But it is not accompanied by any sense of a person with a past and a future\.... In contrast, higher-order consciousness involves the recognition by a thinking subject of his or her own acts or affections. It embodies a model of the personal, and of the past and the future as well as the present. It exhibits direct awareness\--the noninferential or immediate awareness of mental episodes without the involvement of sense organs or receptors. It is what we humans have in addition to primary consciousness. We are conscious of being conscious.\" `</font>`{=html} Block(2004) also suggests this flow from state to state in his idea of \"Reflexivity\" where our idea of familiarity with an object is due to one state being analysed by another: `<font face="times">`{=html}\"Thus in the "conscious" case, the subject must have a state that is about the subject's own perceptual experience (looking familiar) and thus conscious in what might be termed a "reflexive" sense. An experience is conscious in this sense just in case it is the object of another of the subject's states; for example, one has a thought to the effect that one has that experience. The reflexive sense of \'consciousness\' contrasts with phenomenality, which perhaps attaches to some states which are not the objects of other mental states. Reflexive consciousness might better be called 'awareness' than 'consciousness'. Reflexivity is phenomenality plus something else (reflection) and that opens up the possibility in principle for phenomenality without reflection. For example, it is at least conceptually possible for there to be two people in pain, one of whom is introspecting the pain the other not. (Perhaps infants or animals can have pain but don't introspect it.) The first is reflexively conscious of the pain, but both have phenomenally conscious states, since pain is by its very nature a phenomenally conscious state. \"`</font>`{=html} Both Block and Edelman allow phenomenal consciousness, our experience, as an unexplained phenomenon. Block, Edelman and also Dennett\'s ideas of consciousness are shown in the illustration below:  This model differs from the empirical reports of phenomenal consciousness that were considered earlier. According to the empirical reports the present moment in our experience is extended so the succession of outputs or stages of access consciousness could constitute the contents of phenomenal consciousness. In other words phenomenal consciousness is composed of periods of access consciousness. This is how it seems to the empiricist and in our own experience but how such a state could be explained in terms of brain activity is highly problematical. Given that nineteenth century ideas cannot explain such a state a scientific explanation will be required. The idea that phenomenal consciousness misrepresents or \"misdiscovers\" itself (Dennett 1988) deserves further discussion. According to materialism the present instant has no duration so can only be known in succeeding instants as a report or memory and this could be wrong. Whitehead considered that this viewpoint originates in an archaic view of science, particularly the concept of time in science: \"The eighteenth and nineteenth centuries accepted as their natural philosophy a certain circle of concepts which were as rigid and definite as those of the philosophy of the middle ages, and were accepted with as little critical research. I will call this natural philosophy \'materialism.\' Not only were men of science materialists, but also adherents of all schools of philosophy. The idealists only differed from the philosophic materialists on question of the alignment of nature in reference to mind. But no one had any doubt that the philosophy of nature considered in itself was of the type which I have called materialism. It is the philosophy which I have already examined in my two lectures of this course preceding the present one. It can be summarised as the belief that nature is an aggregate of material and that this material exists in some sense at each successive member of a one-dimensional series of extensionless instants of time. Furthermore the mutual relations of the material entities at each instant formed these entities into a spatial configuration in an unbounded space. It would seem that space\-\--on this theory-would be as instantaneous as the instants, and that some explanation is required of the relations between the successive instantaneous spaces. The materialistic theory is however silent on this point; and the succession of instantaneous spaces is tacitly combined into one persistent space. This theory is a purely intellectual rendering of experience which has had the luck to get itself formulated at the dawn of scientific thought. It has dominated the language and the imagination of science since science flourished in Alexandria, with the result that it is now hardly possible to speak without appearing to assume its immediate obviousness.\" (Whitehead 1920). ## Direct Realism and Direct Perception Direct Realism proposes that phenomenal experience is directly objects in the world without any intervening representation. It is motivated by the belief that the Problem of Regression, the Subject-Object Paradox and the recursion form of the Homunculus arguments show that phenomenal consciousness cannot occur in the brain alone. Direct Realists reason that if phenomenal consciousness cannot be things in the brain then it must be something outside the brain. There are two principle types of Direct Realism: Natural Dualism and Behaviourism (both Radical and Analytical). Some behaviourists use the term "Direct Perception" rather than Direct Realism and consider that only the invariant parts of perception are direct (see for instance Michaels and Carello 1981). Thomas Reid is generally regarded as the founder of Direct Realism. In his Natural Dualism he proposed that the soul is in direct contact with the contents of experience and these contents are things in the world beyond the body. The Direct Realism of Reid is summarised in the statement of his famous disciple Sir William Hamilton: \"In the simplest act of perception I am conscious of myself as the perceiving subject and of an external reality as the object perceived\". Reid\'s Natural Dualism has now been largely replaced by radical and analytical behaviourism which eschew the idea of a soul and propose that phenomenal consciousness, if it exists at all, is a behavioural reflex. The modern justification of Direct Realism mainly consists of arguments against Indirect Realism or Representationalism. Philosophers such as Austin (1962) and Le Morvan (2004) have summarised the Direct Realism debate and have identified the following arguments in favour of Indirect Realism and given rebuttals to each of them: 1\. The Causal Argument: perception involves a succession of causal events such as the reflection of photons, bleaching of retinal pigments etc. so perception must involve the end of this causal chain. The Direct Realist response is that, although there may be a causal chain in sensation this does not inevitably imply that the end of the chain is the content of phenomenal experience. 2\. The Time Lag Argument: it takes time for light to travel from an object to the senses, time for chemical changes in the retina etc\... The Direct Realist response is that direct perception may be referred back in time. 3\. The Partial Character of Perception Argument: we only perceive the surface of objects, and then only a part of the surface. As the whole object would be perceived directly perception must be indirect. The Direct Realist response is that direct perception could occur even if only parts of an object were perceived. 4\. The Perceptual Relativity Argument: things appear to be different shapes depending upon the point of view. The Direct Realist response is that if perception can occur backwards in time it should have no problem occurring back down a line of sight. However, Le Morvan\'s argument does not seem to encompass the geometrical nature of phenomenal experience, seeking to explain geometry in terms of movement. 5\. The Argument from Perceptual Illusion: A stick may appear bent when projecting from the surface of water. Direct Realists apply the argument used in (4) to this problem. The bent stick illusion is a physical event in the world beyond the eye rather than a normal optical illusion such as the Muller-Lyer illusion etc., see (6) for a discussion of optical illusions. 6\. The Argument from Hallucination: Hallucinations are not in the world beyond the body. This is highly problematical for Direct Realists especially when phenomena such as lucid dreams, dreams and visual imaginations are included along with hallucinations. Direct Realists classify these phenomena as not being perceptions or deny that they actually exist as phenomena. Indirect Realists would maintain that all of perception is a reconstruction and use optical illusions such as the Muller-Lyer, Ames Room etc. to justify this contention so the Direct Realist approach to hallucination, dreams etc. might seem like an unwillingness to accept Indirect Realism rather than an argument. 7\. The Dubitability Argument (cf: Indubitability argument): we cannot doubt current phenomenal experience but we can doubt the world beyond the body therefore phenomenal experience is not the world beyond the body. Direct Realists fall back on Presentism or functional Presentism to defeat this argument. If phenomenal experience is instantaneous and made anew at each instant then anything can be doubted. The points above have summarised the Direct Realist stance on visual perception. Other sensory modalities have also been considered in the Direct Realism debate. Fowler (1986) considered that sounds were attached to objects in the world. This idea is strange because sounds only seem to be closely attached to objects in the world when these objects are seen as well as heard. For example, when a subject is blindfolded it is found that there can be a large error in locating the position of a sound in the world, this is especially true for low frequency sounds. The Direct Realist approach has difficulty explaining the transition from sounds with an indefinite location when a subject is blindfolded to sounds that are bound to visual events when the blindfold is removed. It also runs into problems explaining how the sound of speech from a single loudspeaker can become bound to lip movements on a cinema screen. If the binding does not occur in the brain then where does it occur? Pain is particularly problematic for Direct Realism because, unlike colour vision where \'red\' is inferred to be a property of electrons or light, pain is an inner experience that is not a property of tissue damage. Tissue damage has properties such as bleeding, wheal formation etc. but pain seems to be phenomenal experience in the brain and \'phantom pain\' can occur without tissue damage (see Aydede (2001), Tye (2004) and Chapman, and Nakamura (1999) for further analysis). On closer inspection other sensations also appear to be inner experiences rather than direct sensations. For instance, the red crosses of different hues in the illustration below are all due to the same physical wavelengths of light. In this case the range of hues in experience is unrelated to the actual physical red on the page or screen. Another problem for Direct Realism is that it does not overcome the problems that it is supposed to solve. The argument for Direct Realism begins with the idea that there are severe problems with representationalism (the idea that phenomenal experience is in the brain) and that direct perception is an alternative that does not have these problems. However on closer inspection Direct Realism suffers from almost same problems as representationalism. If phenomenal experience is the world itself then Ryle\'s regress applies to the world itself and this can only be avoided by assuming that phenomenal experience is a subset of the world (i.e.: a representation) that receives input from other parts of the world that are not part of phenomenal experience. It is also commonly assumed that Direct Realism avoids the recursion argument because it is believed that the separation of the observer from the things that are observed is simply due to the geometry of the world. If such simple geometry is possible between the eye and the world then it should also be possible in the brain and a similar geometrical explanation could be invoked to avoid recursion in representations. These points are shown in the illustration below: image:Constuddir1.gif Scientists have a further problem with Direct Realism. The illustration below demonstrates that our scientific knowledge of the world differs markedly from our phenomenal experience. image:constuddirect.gif It is difficult to see how the form and content of phenomenal experience could supervene directly on the world beyond the body. The world inferred from measurements beyond the body seems to be a nebulous set of quantum phenomena that are arranged as probability fields in three dimensions at any instant. The objects in this real world are mostly space. The world of phenomenal experience on the other hand contains objects that are one-sided, and are like a 2 dimensional field of vectors directed simultaneously at an observation point which is apparently separate from them. Phenomenal experience is not three dimensional, the rear of objects is not available within it at any instant. Visual phenomenal experience seems to be a geometrical relationship between an abstract observation point and the reflection properties of the part of the world external to the body. It is a form that crudely overlies the angular separations in inferred reality, providing approximate directional data. It is not like things in themselves beyond the body, not even in type, being a set of directional vectors. (See the module on the neuroscience of perception for a discussion of depth perception). If the form and content of visual phenomenal experience are abstractions separated according to the angular positions of things in the world beyond the body then theories which propose that phenomenal experience is the world itself are problematical. It should be noted that things arranged according to angular positions can appear to overlie any group of similar things along a radius from the centre point.  If Direct Realists admit that things are as they appear to be, observed according to angular positions at a \'point eye\', then any representation of things on the inside of a sphere of any radius would appear similar. The geometry of the \'point eye\' is problematical whether the view contains the world itself or a representation of the world; it cannot be the movements of lumps of matter or energy and the point observation cannot be due to lumps all landing at a point. In other words the \'view\' is inconsistent with nineteenth century materialism and will require a scientific explanation. Radical and Analytical Behaviourism tackle the problem of the difference between the world inferred from measurements beyond the body and the phenomenal world by denying phenomenal consciousness and maintaining that access and reflex consciousness are all that exists or is necessary. Radical Behaviourism is an offshoot of psychological behaviourism and was established as a philosophical adjunct to Marxism by Vygotsky and popularised by Burrhus Frederic Skinner (see Skinner 1953). There is another movement in psychological behaviourism which is similar to Radical Behaviourism called Ecological Psychology (see Gibson 1966, 1979 and also Michaels and Carello 1981). Analytical Behaviourism is a philosophical movement established by Gilbert Ryle (see Ryle 1949). The core of Analytical and Radical Behaviourism is the assumption that consciousness exists for a durationless instant so that the Dubitability Argument and the Regression and Recursion Arguments can be applied (Ryle 1949, Skinner 1971 and see the sections on Ryle\'s Regress and the Subject-Object Paradox above). As a result the Direct Realist is able to insinuate that subjects only think that they have had a particular experience (cf: Dennett 1991a). It is intriguing that Eliminativists also maintain that experience is the world itself, for instance an insight into Dennett\'s idea of the mind is to be found on pages 407-408 of Consciousness Explained: \"It seemed to him, according to the text, as if his mind - his visual field - were filled with intricate details of gold-green buds an wiggling branches, but although this is how it seemed this was an illusion. No such \"plenum\" ever came into his mind; the plenum remained out in the world where it is didn\'t have to be represented, but could just be. When we marvel, in those moments of heightened self-consciousness, at the glorious richness of our conscious experience, the richness we marvel at is actually the richness of the world outside, in all its ravishing detail. It does not \"enter\" our conscious minds, but is simply available\" This is a clear description of Direct Realism (although Dennett does not describe himself as a direct realist). Radical Behaviourism is sometimes described as the dictum that the only psychological events that are of importance are those that occur outside the head. The absurdity of this has led to jokes: Q: What does one behaviorist say to another when they meet on the street? A: You\'re fine. How am I? Q: What does one behaviorist say to another after sex? A: That was great for you. How was it for me? (Ziff 1958) However Vygotsky, Skinner and other Radical Behaviourists hold that inner behaviour is possible so that events within the brain can result in reward or punishment. Vygotsky (1925) describes this approach: \"Consciousness is wholly reduced to the transmitting mechanisms of reflexes operating according to general laws, i.e., no processes other than reactions can be admitted into the organism. The way is also paved for the solution of the problem of self-awareness and self-observation. Inner perception and introspection are possible only thanks to the existence of a proprioceptive field and secondary reflexes, which are connected with it. This is always the echo of a reaction.\" Hence Radical Behaviourists are able to make the claim that what are believed to be representations with phenomenal content are processes. Even events such as pain can then be explained as reflexes involving organs within the skin. However, by opening the possibility that such reflexes could occur at any sense organ, including the eye, this makes Radical Behaviourism a mixed Direct Realist/Indirect Realist philosophy with consciousness as a process, not a separate thing such as phenomenal consciousness (see the section on representationalism and intentionality below). But this raises a serious issue for science: can the phenomenal consciousness that seems to contain our observations really be argued out of existence on the basis of a theory? As Gregory (1988) put it: " 'If you can't explain it -- deny it' is one strategy for dealing with embarrassing questions such as 'what is consciousness?' ". But is this the right strategy? Direct Realism fails to overcome the problems of regression and recursion inherent in representations. It proposes that phenomenal consciousness is identical to the physical world beyond the body but must then use a plethora of arguments to explain why this is evidently not so. When confronted with these problems its proponents resort to the argument that everything can be doubted and can misrepresent itself. Yet it is still widely believed. It should be noted that Direct Realism is espoused in Religious Natural Dualism, some forms of Augustinian theology, nineteenth century materialism and its offspring such as Marxism, post-modernism, post-Marxism, and various sociological movements. It is also necessary for some forms of Strong AI to occur. Perhaps this explains why few ideas have attracted as much attention and defence as Direct Realism. It is interesting to compare the Direct Realist and Indirect Realist interpretations of something as simple as a cartoon on television (such as the image below). According to Indirect Realism the cartoon would be a moving representation constructed in the brain using data from the senses. This leads to the prediction of brain mechanisms for modelling motions, combining colours, binding sound and vision etc., many of which have been verified. Can you demonstrate how the theory of Direct Realism could explain the phenomenal experience that contains the cartoon and produce a list of the predictions made by the theory?  In science a theory should be of predictive value, for instance, information theory describes how the state of a thing can be impressed on a carrier so that a signal can be transmitted from one place to another. This theory predicts what will happen when the signal arrives at its destination and how the state of the source can be inferred from the events at the destination, the total amount of information that can be transmitted etc. At the destination it is the form of the signal that is directly known by interaction and measurement, the form of the source is inferred. Direct Realism is a direct challenge to this information theory but does it deliver a more powerful predictive description of phenomenal consciousness or is experience always dependent on what happens to the information flow between things in the world and somewhere in the brain? Does direct realism have a physical theory? Ultimately it appears as if Direct Realism is about various understandings of Information Theory. For example, Austin (1962) discusses what we see when we see a church camouflaged as a barn and comments that: \"We see, of course, a church that now looks like a barn.\". Do we see a church or a barn? Scientific information theory is clear about this, the church is an entity composed of selected information from the quantum state of its constituents, the optical image of a camouflaged church is an arrangement of photons emanating from a screen on which it is projected, the retina has an arrangement of chemical and electrical events based on an optical image and conscious visual experience correlates with the arrangement of things on the retina. The fact that conscious experience also correlates with classifications of the retinal image as a barn or a church suggests that conscious experience is an arrangement of things in the brain based on both the retinal arrangement and the contents of a relational database. Austin\'s arguments have been mythologised as a final demonstration that \"sense data\" theories are false. However, as will be seen below, sense data theories merely claim that there is a succession of information states between an information state outside the body and that reported as conscious experience i.e.: subjects report that a church is camouflaged when it is camouflaged. ## Indirect Realism Indirect realism proposes that phenomenal consciousness exists and is a set of signals or **sense data**, usually in the brain. This was proposed by philosophers from Aristotle to Locke and was probably the most widespread idea of conscious experience until the eighteenth century. The idea of sense data is discussed in depth by Russell (1912). Russell\'s original definition is given below: `<font face="times new roman">`{=html}\"Let us give the name of \'sense-data\' to the things that are immediately known in sensation: such things as colours, sounds, smells, hardnesses, roughnesses, and so on. We shall give the name \'sensation\' to the experience of being immediately aware of these things. Thus, whenever we see a colour, we have a sensation of the colour, but the colour itself is a sense-datum, not a sensation. The colour is that of which we are immediately aware, and the awareness itself is the sensation. It is plain that if we are to know anything about the table, it must be by means of the sense-data \-- brown colour, oblong shape, smoothness, etc. \-- which we associate with the table; but, for the reasons which have been given, we cannot say that the table is the sense-data, or even that the sense-data are directly properties of the table.\"`</font>`{=html} Russell\'s definition is a materialist concept in which experience is always **of** something because the durationless instant of the present has always gone. As such it differs from some empiricist ideas where experience is not confined to the durationless instant. Science is Indirect Realist because it holds that the scientist can only make **measurements** of events in the world. These measurements give rise to signals as a result of interaction with the event. According to **decoherence theory** the signals are a state that is a mixture of the state of the measuring instrument and the state of the thing being measured. For example, the eyes are measuring instruments that are sensitive to photons, photons are signals containing a state that is based on the state of electrons in a surface and the state of electrons is based on the state of the surface etc. Scientific inference allows some aspects of the state of the surface to be inferred from the state of the photons. In modern Indirect Realism there is an attempt to distinguish the phenomenal content of conscious experience from the processing involved in accessing this phenomenal content. According to these theories phenomenal experience is an arrangement of signals that are the content of the experience. This arrangement forms a *representation* of things in the world so this form of indirect realism is known as **Representationalism**. Tye (2003) describes types of representationalist theory: `<font face="times new roman">`{=html}\"Representationalism, as I have presented it so far, is an identity thesis with respect to qualia: qualia are supposedly one and the same as certain representational contents.\"`</font>`{=html} Tye also describes variants of this idea of representationalism: `<font face="times new roman">`{=html}\"Sometimes it is held instead that qualia are one and the same as certain representational properties of experiences; and sometimes it is is argued that these representational properties are themselves irreducible (Siewert 1998). There is also a weaker version of representationalism, according to which it is metaphysically necessary that experiences exactly alike with respect to their representational contents are exactly alike with respect to their qualia. Obviously, this supervenience thesis leaves open the further question as to the essential nature of qualia.\"`</font>`{=html} (Tye 2003). In a scientific sense Direct Realists believe that phenomenal experience is the signals that occur next to things in the world beyond the body (which they call \"things in themselves\") and Indirect Realists usually believe that phenomenal experience is signals in the brain. It can be seen from the pattern of signal flow that the signals travelling into the brain preserve the spatial relationships of the original signals and encode the properties in the original signals. This means that the original signals next to the QM sources and the signals in the brain are equivalent provided the latter are oriented appropriately relative to signals from the body. Either set of signals could transmit or contain the same information. Both Direct and Indirect Realism cannot, at present, explain the physics of how a viewing point occurs in experience i.e.: how we seem to see through an apparent space to the signals that are the contents of experience. So the choice between Direct Realism and Indirect Realism reduces to whether there is only one set of signals or a chain of signals between the world and phenomenal experience. The philosophical arguments for Indirect Realism are listed below: 1\. Variable perspective: when we see things the view changes so what we see must be a different set of signals depending on the view rather than a constant object. 2\. Illusions: we can see through fingers and see a variety of colours where measurements tell us one exists. Direct Realists quote the \"bent stick illusion\", which is not really an illusion at all, being a physical event. 3\. Hallucinations: two people can have phenomenal experience containing a table. The first may be viewing a real table whereas the second may be hallucinating a table. If the tables are the same (phenomenally) then experience is indirect. 4\. Double vision: press the side of one eye, two images appear (cf Hume 1739) yet there are not two things in the world. 5\. Time gap arguments: according to materialism the past has gone. The things being seen no longer exist in the state that relates to the state in experience. In the extreme case, some stars in the night sky no longer exist but are still in experience so experience must be a derived signal. 6\. Secondary qualities such as pain, colour and smell do not exist as physical things in the source of signals and are likely to be properties of signals in the brain.  Indirect Realism has received strong support from recent discoveries in neuroscience, for example, it is now clear that both the colour and motion in phenomenal experience are added by cortical processes. In Cerebral **Achromatopsia** patients have suffered trauma to area V4 of the cerebral cortex and report seeing the world in greyscale with no colour vision and in Congenital Achromatopsia people do not even understand the meaning of \'colour\'. In an astonishing ailment called **Akinetopsia** patients perceive movement as a succession of stationary images (Rizzo *et al.* 1995). Akinetopsia is usually associated with damage to cortical area V5. Moutoussis and Zeki (1997) have demonstrated that the addition of colour occurs more rapidly than the addition of motion. The section on the Neuroscience of Consciousness describes these discoveries and many other aspects of the creation of phenomenal experience in the brain. Unfortunately knowledge of the whereabouts of the signals that are the content of conscious experience does not resolve the problem of phenomenal consciousness. Whether these signals are next to objects in the world or at the end of a chain of signals in the brain there still remains the problem of how they become arranged in the form of experience. If such a thing occurs at all. ### Intentionality and representation There is a materialist interpretation of representationalism in which representations are redefined as intentional states: `<font face="times new roman">`{=html}\"One way of explaining what is meant by 'intentionality' in the (more obscure) philosophical sense is this: it is that aspect of mental states or events that consists in their being of or about things (as pertains to the questions, 'What are you thinking of?' and 'What are you thinking about?'). Intentionality is the aboutness or directedness of mind (or states of mind) to things, objects, states of affairs, events. So if you are thinking about San Francisco, or about the increased cost of living there, or about your meeting someone there at Union Square---your mind, your thinking, is directed toward San Francisco, or the increased cost of living, or the meeting in Union Square. To think at all is to think of or about something in this sense. This 'directedness' conception of intentionality plays a prominent role in the influential philosophical writings of Franz Brentano and those whose views developed in response to his (to be discussed further in Section 3).\"(Siewert 2003)`</font>`{=html} This definition allows \"representation\" to be redefined as a data stream rather than a set of things arranged in some mental or neural state that represents things in space. Husserl thought this approach would allow a description of consciousness that \"carefully abstains from affirming the existence of anything in spatio-temporal reality\" (Siewert 2003) although it could be argued that a data stream such as any description can never escape the constraints of representation in time at some place. Unfortunately the concept of \"intentionality\" has become so diverse that it could be applied to almost any aspect of the description of consciousness. An interesting example of this is given by Loar (2001) where \"intentionality\" is considered to overlap \"representing\" and \"conceiving\": `<font face="times new roman">`{=html}\"A person\'s thoughts represent things to her \-- conceive things \-- in many ways: perceptually, memory-wise, descriptively, by naming, by analogy, by intuitive sorting, theoretically, abstractly, implicitly and explicitly. These various manners of conceiving have something in common: they have intentional properties, and they have them essentially. `</font>`{=html} The usage of the term \"intentional state\" has become so broad that it now means little more than a state that is about another state. References Siewert, C. (2003). Consciousness and Intentionality. The Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/consciousness-intentionality/> Also see Loar, B. (2001) "Phenomenal Intentionality as the Basis of Mental Content", in Reflections and Replies, ed. M. Hahn and B. Ramsberg, MIT. <http://www.nyu.edu/gsas/dept/philo/courses/concepts/loar.html> Williford, K. (2002) The intentionality of consciousness and the consciousness of intentionality. Intentionality: Past and Future, edited by Gábor Forrai and George Kampis, Amsterdam/New York: Rodopi. <http://web.stcloudstate.edu/kwwilliford/Intentionality%20of%20Consciousness.pdf> Byrne, A. (2001). Intentionalism Defended. Philosophical Review 110 (April 2001):199-240. <http://stripe.colorado.edu/~leeds/byrne.pdf> ### Cartesian materialism The term \"Cartesian materialism\" once meant the idea that the mind is in the brain (see for instance Block 1995). The term had largely fallen out of use in philosophy until revived by Daniel Dennett (1991) in the book *Consciousness Explained*. Dennett uses a very particular definition of the term in his discussions and also uses a particular definition of the word \"mind\". See the section on Daniel Dennett for Dennett\'s critique. Philosophers who adhere to the idea that the mind is in the brain tend to call themselves \"indirect realists\" or \"representationalists\" where the substrate of conscious experience is in the brain and would deny that Dennett\'s critique applies to their proposals. Dennett\'s critique makes the materialist assumption that if there is a representation in the brain then a further flow of material out of this representation would be required for the representation to become part of mind. ### Identity theories of mind The idea that mental states are brain states is known as the **identity theory of mind**. There are two sorts of identity theory, in **type** identity theory it is held that mental states are identical to brain states whereas in **token** identity theory it is held that mental states correlate with brain states. Type identity theory was attacked by Putnam in \"The Nature of Mental States\" where he pointed out that if mental states are functions then type identity theory would presuppose that animals that had the same mental states would need to have identical brain structures. He suggested that this is unlikely, it being more probable that animals have functional systems that perform similar overall functions but which are not identical. In other words, if it is assumed that conscious experience is a set of functions then token identity theory is more probable than type identity theory. Putnam\'s critique does not preclude identity theories of mind that involve \"passive ideas\" (i.e.: states that are not classical functions). Most identity theories of mind would be representational, the physical states representing the world in some way. All identity theories of mind involve Cartesian materialism in the sense of the mental states being brain states. According to identity theories the mind is in the brain. Putnam, H. (1967) The nature of mental states. In The Nature of Mind, edited by Rosenthal, pp. 197--203. Originally published as \"Psychological predicates in Art, Mind, and Religion\", edited by Capitan and Merill, pp. 37--48. ## Dualism Prior to considering the arguments surrounding dualism it is important to have a clear idea of \"information\" because many of these arguments have parallels with the difference between information as a set of states that can be transmitted and the substrate on which this information is expressed or from which the information is derived. See Elementary information and information systems theory. ### Cartesian dualism Descartes, a philosopher, analysed his experience and developed an empirical description of how it is arranged. He described mental images and perceptions as extended in space and with a duration. He called these extended things **ideas** (Cartesian ideas) and proposed that they are patterns in the brain. Descartes thought the pineal gland was the most likely location for these ideas because it is one of the few single organs in the brain. He also proposed that there is a rational soul that directly contacts these ideas: `<font face="times new roman">`{=html}\"Now among these figures, it is not those imprinted on the external sense organs, or on the internal surface of the brain, which should be taken to be ideas - but only those which are traced in the spirits on the surface of gland H *(where the seat of the imagination and the \'common sense\' is located)*. That is to say, it is only the latter figures which should be taken to be the forms or images which the rational soul united to this machine will consider directly when it imagines some object or perceives it by the senses.\" Descartes (1664)`</font>`{=html} See section on Descartes for more information and references. Descartes considered that the soul was a physical point, an unextended entity that acts like a mind\'s eye. He called this unextended place the *res cogitans* and concluded that it was a substance that differed from that of material things: `<font face="times new roman">`{=html}\".. I thence concluded that I was a substance whose whole essence or nature consists only in thinking, and which, that it may exist, has need of no place, nor is dependent on any material thing; so that \" I,\" that is to say, the mind by which I am what I am, is wholly distinct from the body, and is even more easily known than the latter, and is such, that although the latter were not, it would still continue to be all that it is.\"Descartes (1637)`</font>`{=html} This unextended substance that is not material gives the word \"substance\" a new meaning. It has been attacked as a concept by Locke, Hume, Berkely and many other philosophers. The concept of there being two substances, that which composes the physical world and that which composes the soul, is the origin of the word **Dualism** but dualism, as a concept, has been extended beyond this original meaning. Cartesian dualism is a type of **substance dualism**. Cartesian dualism is an attempt to explain our experience. According to Descartes something supernatural would be needed for an unextended viewing point to exist. Reid\'s **Natural Dualism** also has a point soul looking at things but proposes that the things in question are forms in the world rather than in the brain. ### Property dualism Another sort of dualism has arisen out of a particular interpretation of the regress and homunculus arguments. These arguments show that phenomenal experience is not due entirely to flows from place to place (i.e.: it is not due to classical processes and functions). Property dualism asserts that when matter is organized in the appropriate way (i.e. in the way that living human bodies are organized), mental properties emerge. As Goldman (1993) pointed out, qualitative experience does not seem to be needed in a functional description of a system: `<font face="times new roman">`{=html}\"For any functional description of a system that is in pain (or has an itch), it seems as if we can imagine another system with the same functional description but lacking the qualitative property of painfulness (or itchiness).\" `</font>`{=html} Certainly a functional system that merely reports the words \"I am in pain\" when it is dropped on the floor does not require any qualitative property of painfulness. The *absent qualia* arguments suggest that even in a large system there would be no need for qualitative properties for the performance of any classical function. Chalmers (1993) commenting on Goldman\'s point, said that this implies that **zombies** might exist, functional replicas of humans but without qualia. He then denied that a complete functional replica of a human could exist without also including qualia: `<font face="times new roman">`{=html}\"It seems to me that the only way to avoid this conclusion is to deny that Zombie Dave is a conceptual possibility; and the only principled way to deny that Zombie Dave is a conceptual possibility is to allow that functional organization is conceptually constitutive of qualitative content.\" Chalmers (1993).`</font>`{=html} In other words he identifies qualia with function. According to Chalmers (1996) qualia are a particular type of function: `<font face="times new roman">`{=html}\"I claim that conscious experience arises from fine-grained functional organization. More specifically, I will argue for a principle of organizational invariance, holding that given any system that has conscious experiences, then any system that has the same fine-grained functional organization will have qualitatively identical experiences. According to this principle, consciousness is an organizational invariant: a property that remains constant over all functional isomorphs of a given system. Whether the organization is realized in silicon chips, in the population of China, or in beer cans and ping-pong balls does not matter. As long as the functional organisation is right, conscious experience will be determined.\" p249`</font>`{=html} Chalmers\' idea of functional organisation has within it a sometimes vague implication that the functional units must have a particular form; for instance, in the development of his argument, he refers to "fine grained" replacement of organic functional units with inorganic units. Chalmers is actually making two major points, firstly that qualia occur during the motion of things (functions), secondly that qualia are independent of any particular substrate.\*\* For the first point to be consistent with materialism the qualia must have no effect on the function, they must be **epiphenomenal**. Epiphenomenal qualia would not be forbidden by the regress and homunculus arguments and would be akin to Berkeley\'s \"passive ideas\". Whether or not epiphenomenal qualia are physical depends upon the definition of the word \"physical\". If physical functions cause qualia but qualia cannot affect functions then the qualia are \"physical\" in the sense of being caused by physical events but might be regarded as non-physical in the sense of being isolated from further physical events. In philosophical terms they violate the principle of **Causal Closure**. However, there are other definitions of physicalism based on arguments such as **Methodological Naturalism** which hold that anything that can be investigated using the methods of natural science is a physical thing (see Stoljar 2001). Thus, although epiphenomenal qualia may not conform to materialism they may be encompassed by physicalism; as events that are related to material events they are awaiting a physical theory of how they emerge from a given function. The reader might consider whether phenomenal consciousness is indeed epiphenomenal. Empirical reports describe it as something that is different from the world beyond the body (see direct realism) - could we generate empirical reports of an epiphenomenon? The term **property dualism** describes how physical events might give rise to a set of properties that cannot be predicted from the fine structure of the physical system. The \"dualism\" is present because one set of events is related to two sets of properties, one of which is not related by materialism to the set of events. In the case of the proposal about consciousness outlined above an extra assumption, beyond materialism, would be needed to explain qualia. Property dualism might be defined as a theory that there could be a theory of consciousness but that this requires some new assumption. As far as the \"when and where\" of consciousness are concerned, property dualism states that it is somewhere in the processes performed by the organism and the parts of the organism. `<font size=1>`{=html} \*\* In terms of information processing, Chalmers is proposing that qualia are the enactment of a particular information processing structure.`</font>`{=html} - Block, N. (2006). Max Black\'s objection to mind-body identity. Oxford Review of Metaphysics No.3. <http://philrsss.anu.edu.au/BlockFest/MaxBlack.rtf> - Chalmers, D.J. (1993) Commentary on \"The Psychology of Folk Psychology\". Behavioral and Brain Sciences 16:35-36, 1993 - Chalmers, D.J. (1996) \"The Conscious Mind: In Search of a Fundamental Theory\". Oxford University Press. 1996. - Goldman, A.I., (1993). The Psychology of Folk Psychology. Behavioral and Brain Sciences 16: 15-28 (1993). <http://www.ecs.soton.ac.uk/~harnad/Papers/Py104/goldman.psyc.html> ### Predicate dualism Predicate dualism is the view espoused by most non-reductive physicalists, such as Donald Davidson(1980) and Jerry Fodor(1968), who maintain that while there is only one ontological category of substances and properties of substances (usually physical), the predicates that we use to describe mental events cannot be redescribed in terms of (or reduced to) physical predicates of natural languages. If we characterize predicate monism as the view subscribed to by eliminative materialists, who maintain that such intentional predicates as believe, desire, think, feel, etc., will eventually be eliminated from both the language of science and from ordinary language because the entities to which they refer do not exist, then predicate dualism is most easily defined as the negation of this position. Predicate dualists believe that so-called \"folk psychology\", with all of its propositional attitude ascriptions, is an ineliminable part of the enterprise of describing, explaining and understanding human mental states and behavior. Davidson, for example, subscribes to Anomalous Monism, according to which there can be no strict psycho-physical laws which connect mental and physical events under their descriptions as mental and physical events. However, all mental events also have physical descriptions. It is in terms of the latter that such events can be connected in law-like relations with other physical events. Mental predicates are irreducibly different in character (rational, holistic and necessary) from physical predicates (contingent, atomic and causal). (Section based on Wikipedia article) - Davidson, D (1980). Essays on Actions and Events. Oxford University Press. - Fodor,J. (1968) *Psychological Explanation*, Random House. . ### The interaction between mind and brain in dualism #### Interactionism Interactionism is the view that mental states, such as beliefs and desires, causally interact with physical states. This is a position which is very appealing to common-sense intuitions, notwithstanding the fact that it is very difficult to establish its validity or correctness by way of logical argumentation or empirical proof. It is appealing to common-sense because we are surrounded by such everyday occurrences as a child\'s touching a hot stove (physical event) which causes him to feel pain (mental event) and then yell and scream (physical event) which causes his parents to experience a sensation of fear and protectiveness (mental event) and so on. #### Epiphenomalism According to epiphenomenalism, all mental events are caused by a physical event and have no physical consequences. So, a mental event of deciding to pick up a rock (call it \"M\") is caused by the firing of specific neurons in the brain (call it \"P\"), however when the arm and hand move to pick up a rock (call it \"E\") this is only caused by P. The physical causes are in principle reducible to fundamental physics, and therefore mental causes are eliminated using this reductionist explanation. If P causes M and E, there is no overdetermination in the explanation for E. #### Parallelism Psycho-physical parallelism is a very unusual view about the interaction between mental and physical events which was most prominently, and perhaps only truly, advocated by Gottfried Wilhelm von Leibniz. Like Malebranche and others before him, Leibniz recognized the weaknesses of Descartes\' account of causal interaction taking place in a physical location in the brain. Malebranche decided that such a material basis of interaction between material and immaterial was impossible and therefore formulated his doctrine of occasionalism, stating that the interactions were really caused by the intervention of God on each individual occasion. Leibniz idea is that God has created a pre-established harmony such that it only seems as if physical and mental events cause, and are caused by, one another. In reality, mental causes only have mental effects and physical causes only have physical effects. Hence the term parallelism is used to describe this view. #### Occasionalism Occasionalism argues that bodily events are the occasion of an act by the Creator causing a corresponding mental event, and vice versa. Any such view requires a theological structure as a premise. #### Further reading - Robinson, Howard, \"Dualism\", The Stanford Encyclopedia of Philosophy (Fall 2003 Edition), Edward N. Zalta (ed.), <http://plato.stanford.edu/archives/fall2003/entries/dualism/> - Robinson, H. (2003) \"Dualism\", in S. Stich and T. Warfield (eds) The Blackwell Guide to Philosophy of Mind, Blackwell, Oxford, 85-101. - Amoroso, R.L. (2010) \"The complementarity of Mind and Body: Realizing the Dream of Descartes, Einstein and Eccles\", New York: Nova Science Publishers, `, ``https://www.novapublishers.com/catalog/product_info.php?products_id=12759` ## Idealism According to Idealism only the mental truly exists. The form and content of personal conscious experience might be related to the structure of the world and brain in several ways. It could be a **solipsism** or be the mind of God. *This is a **stub** and needs expansion*. ## Panpsychism ### Etymology Ancient Greek *pan* (πᾶν : \"all, everything, whole\") and *psyche* (ψυχή : \"soul, mind\").[^1] Psyche is the from ψύχω (*psukhō*, \"I blow\") and means mind or \'life-breath\'. Philip Goff, a proponent of panpsychism, carves out a distinction between panexperientialism and pancognitivism. Panexperientialism is the belief that *experience* is ubiquitous, while pancognitivism is the belief that *cognition* is ubiquitous. Most modern purponents of panpsychism, such as Annaka Harris and David Chalmers, are careful to distance themselves from pancognitivism. In some interpretations, such as monadism, Panpsychism and Idealism can overlap because the universe is conceived as being composed of an infinity of point consciousnesses that each contain information about the whole universe. The form and content of personal conscious experience might be related to the structure of the world and brain in many ways. *This is a **stub** and needs expansion*. ## References Seager W. & Allen-Hermanson (2001). 'Panpsychism.' Online document: Stanford Encyclopedia of Philosophy, \[online\], <http://plato.stanford.edu/entries/panpsychism/>, \[accessed 10/2005\] **Supervenience** - Chalmers, D.J. (1996). The Conscious Mind. Oxford University Press. **The problem of regression** - Ryle, G. (1949) The Concept of Mind. The University of Chicago Press, 1949. **The homunculus argument** - Gregory, R.L. (1990) Eye and Brain: The Psychology of Seeing, Oxford University Press Inc. New York. - Gregory, T.L. (1987). The Oxford Companion to Mind. Oxford University Press. **Subject-object paradox** - James, W. (1904)Does \'Consciousness\' Exist? Journal of Philosophy, Psychology, and Scientific Methods, 1, 477-491. - Hegel, G.W.F. PHILOSOPHY OF MIND: SECTION I. MIND SUBJECTIVE B. PHENOMENOLOGY OF MIND CONSCIOUSNESS Part Three of the Encyclopaedia of the Philosophical Sciences - Velmans, M. (1996) Consciousness and the \"Casual Paradox\". Behavioral and Brain Sciences, 19 (3): 538-542. - Bermudez, J.L. (1999) The Paradox of Self-Consciousness (representation and Mind) Psycoloquy: 10,#35 **Ontological status** - Bierman, D.J. (2004) Non Conscious Processes Preceding Intuitive decisions <http://m0134.fmg.uva.nl/~djb/publications/2004/Intuition_bialsymp2004.pdf> - Damasio, A.R. (1994). Descartes\' error: Emotion, reason and the human brain. New York: Grosset/Putnam Book. - Kant, I. Critique of Pure Reason <http://www.arts.cuhk.edu.hk/Philosophy/Kant/cpr/> **Phenomenal consciousness and access consciousness** Block, N. (1995) On a confusion about a function of consciousness. Behavioral and Brain Sciences 18 (2): 227-287. <http://www.bbsonline.org/documents/a/00/00/04/31/bbs00000431-00/bbs.block.html> Block, N. (2004). *The Encyclopedia of Cognitive Science*. <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/ecs.pdf> Dennett, D. (1978). Why You Can\'t Make a Computer that Feels Pain, in: Brainstorms. Cambridge, MA: MIT Press: 190-229. Dennett, D. (1988). Quining Qualia. in A. Marcel and E. Bisiach, eds, Consciousness in Modern Science, Oxford University Press 1988. Reprinted in W. Lycan, ed., Mind and Cognition: A Reader, MIT Press, 1990, A. Goldman, ed. Readings in Philosophy and Cognitive Science, MIT Press, 1993. <http://ase.tufts.edu/cogstud/papers/quinqual.htm> Edelman, G.M. (1993). Bright Air, Brilliant Fire: On the Matter of the Mind. New York: Feyerabend, P. (1963). Mental Events and the Brain, Journal of Philosophy 40:295-6. Huxley, T. H. (1874). On the Hypothesis that Animals are Automata, and its History, The Fortnightly Review, n.s.16:555-580. Reprinted in Method and Results: Essays by Thomas H. Huxley (New York: D. Appleton and Company, 1898). Nagel, T. (1974). What is it like to be a bat? The Philosophical Review LXXXIII, 4 (October 1974): 435-50. <http://web.archive.org/19990218140703/members.aol.com/NeoNoetics/Nagel_Bat.html> Rey, Georges, (1997). Contemporary Philosophy of Mind.Blackwell: Oxford Sellars W. (1956). Empiricism and the Philosophy of Mind, In: Feigl H and Scriven M (eds) The Foundations of Science and the Concepts of Psychology and Psychoanalysis: Minnesota Studies in the Philosophy of Science, Vol. 1. Minneapolis: University of Minnesota Press: 253-329 Whitehead, A.N. (1920). The Concept of Nature. Chapter 3: Time. <http://spartan.ac.brocku.ca/~lward/Whitehead/Whitehead_1920/White1_03.html> **Direct Realism** - Austin, J.L. (1962) Sense and Sensibilia, ed. by Geoffrey J. Warnock (Oxford, 1962) - Aydede, M. (2001) Naturalism, introspection, and direct realism about pain. Consciousness and Emotion, Vol. 2, No. 1, 2001, pp. 29--73. <http://web.clas.ufl.edu/users/maydede/pain.pdf> - Chapman, C.R., and Y. Nakamura (1999). A Passion of the Soul: An Introduction to Pain for Consciousness Researchers. Consciousness and Cognition, 8: 391-422. - Dennett, D. (1991a). Consciousness Explained. Boston: Little, Brown - Dennett, D. (1991b). Lovely and suspect qualities. Commentary on David Rosenthal, \"The Independence of Consciousness and Sensory Quality\" in E. Villanueva, ed., Consciousness, (SOFIA Conference, Buenos Aires), Atascadero, CA: Ridgeview 1991. <http://ase.tufts.edu/cogstud/papers/lovely&s.htm> - Fowler C A (1986): "An event approach to the study of speech perception from a direct-realist perspective", J of Phonetics 14(1):3-28. - Gibson, J. J. (1966) The Senses Considered as Perceptual Systems. Houghton Mifflin Company,Boston. - Gibson, J. J. (1979) Ecological Approach to Visual Perception.: Lawrence Erlbaum Associates Publishers, Hillsdate. - Gregory, R.L. 1988. Consciousness in science and philosophy: conscience and con-science. Chapter 12 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. - Le Morvan, Pierre (2004). Arguments against direct realism and how to counter them. *The American Philosophical Quarterly*, *41*(3), 221-234.\] (pdf) <http://www.tcnj.edu/~lemorvan/DR_web.pdf> - Michaels, C. F. and Carello, C. (1981). Direct Perception. Century Psychology Series. Prentice-Hall. . 1981. Download this book at <http://ione.psy.uconn.edu/~psy254/MC.pdf> - Oliveira, André L. G. and Oliveira, Luis F. (2002) Toward an ecological conception of timbre. In Proceedings Auditory Perception Cognition and Action Meeting 2002, Kansas City. <http://cogprints.org/2713/> - Skinner, B. F. Science and Human Behavior . New York: Macmillan, 1953. - Skinner, B. F. 1971. Beyond Freedom and Dignity. New York: Knopf. - Skinner, B. F. 1948. Walden Two. New York: Macmillan. - Tye, M. (2004). ANOTHER LOOK AT REPRESENTATIONALISM ABOUT PAIN. Consciousness and Emotion 2004, special issue on pain, edited by Murat Aydede (with replies by M. Aydede, N. Block, B. Maund, and P. Noordhof <http://sun.soci.niu.edu/~phildept/MT/RepresentationalismAndPain.pdf> - Vygotsky, L.S.(1925) Consciousness as a problem in the psychology of behavior. Undiscovered Vygotsky: Etudes on the pre-history of cultural-historical psychology (European Studies in the History of Science and Ideas. Vol. 8), pp. 251--281. Peter Lang Publishing. <http://www.marxists.org/archive/vygotsky/works/1925/consciousness.htm> - Ziff, Paul. \"About Behaviourism.\" Analysis 18 (1958): 132-136. Quoted by Larry Hauser in the Internet Encyclopedia of Philosophy. <http://www.utm.edu/research/iep/b/behavior.htm#B>. F. Skinner: Radical Behaviorism **Indirect Realism** - Moutoussis, K. and Zeki, S. (1997). A direct demonstration of perceptual asynchrony in vision. Proceedings of the Royal Society of London, Series B: Biological Sciences, 264, 393 - 399. - Rizzo, M., Nawrot, M. & Zihl, J. (1995). Motion and shape perception in cerebral akinetopsia.Brain, 118. 1105-1127. <http://nawrot.psych.ndsu.nodak.edu/Publications/Nawrot.pdf/RizzoNawrotZihl.1995.pdf> - Russell, B. (1912). Problems of Philosophy. Home University Library. <http://www.ditext.com/russell/rus1.html> - Tye, M. (2003) Qualia. Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/qualia/#Repqualia> Further reading: - Hume, D. (1739). A Treatise of Human Nature. <http://www.class.uidaho.edu/mickelsen/ToC/hume%20treatise%20ToC.htm> - Firth, R. (1949) Sense Data and the Percept Theory, Mind, 58 (1949); 59 (1950). (Describes early reasons for rejecting Indirect Realism) <http://www.ditext.com/firth/spt.html> - Grush, R. (2000). Self, world and space: The meaning and mechanisms of ego- and allocentric spatial representation. Brain and Mind 1(1):59-92. <http://mind.ucsd.edu/papers/sws/sws.html> [^1]: Clarke, D.S. *Panpsychism: Past and Recent Selected Readings*. State University of New York Press, 2004. p.1

# Consciousness Studies/The Conflict2#Direct realism *This part of this section is about the where and when of the experience called consciousness. Is it in the world, in the brain or are the world and brain within it?* ## Phenomenal consciousness and access consciousness Block(1995) drew attention to the way that there appear to be two types of consciousness: *phenomenal* consciousness and *access* consciousness: `Phenomenal consciousness is experience; the phenomenally`\ `conscious  aspect of a state is what it is like to be in that`\ `state. The mark of access-consciousness, by contrast, is `\ `availability for use in reasoning and rationally guiding speech `\ `and action. (Block 1995).` *See the section on Ned Block\'s ideas for a deeper coverage of his approach to access and phenomenal consciousness.* Block uses Nagel\'s famous (1974) paper, \"What is it like to be a bat?\" as an exemplary description of phenomenal consciousness. Excellent descriptions have also been proffered by the empiricist philosophers who gave lengthy descriptions of consciousness as partly experience itself. Although Block has formalised the idea of phenomenal and access consciousness similar ideas have also been put forward by many philosophers including Kant and Whitehead. Access consciousness has two interpretations, in the first, used by Block, it applies to the functions that appear to operate on phenomenal consciousness. In the second, used by the behaviourists and eliminativists, it is some property of the functions of the brain that can be called \'consciousness\'. This division between phenomenal and functional aspects of consciousness is useful because it emphasises the idea of phenomenal consciousness as observation rather than action. Some philosophers such as Huxley in 1874, have taken the view that because phenomenal consciousness appears to have no function it is of no importance or cannot exist. James (1879) introduced the term \"epiphenomenalism\" to summarise the idea that consciousness has no function. The idea that phenomenal consciousness cannot exist is a type of *Eliminativism* (also known as Eliminative Materialism). Eliminativism owes much to the work of Sellars(1956) and Feyerbend (1963). Dennett (1978) applied Eliminativism to phenomenal consciousness and denies that pain is real. Others such as Rey(1997) have also applied eliminativism to phenomenal consciousness. Dennett (1988) redefines consciousness in terms of access consciousness alone, he argues that \"Everything real has properties, and since I don\'t deny the reality of conscious experience, I grant that conscious experience has properties\". Having related all consciousness to properties he then declares that these properties are actually judgements of properties. He considers judgements of the properties of consciousness to be identical to the properties themselves. He writes: `<font face="times">`{=html}\"The infallibilist line on qualia treats them as properties of one\'s experience one cannot in principle misdiscover, and this is a mysterious doctrine (at least as mysterious as papal infallibility) unless we shift the emphasis a little and treat qualia as logical constructs out of subjects\' qualia-judgments: a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F. \"`</font>`{=html} Having identified \"properties\" with \"judgement of properties\" he can then show that the judgements are insubstantial, hence the properties are insubstantial and hence the qualia are insubstantial or even non-existent. Dennett concludes that qualia can be rejected as non-existent: `<font face="times">`{=html}\"So when we look one last time at our original characterization of qualia, as ineffable, intrinsic, private, directly apprehensible properties of experience, we find that there is nothing to fill the bill. In their place are relatively or practically ineffable public properties we can refer to indirectly via reference to our private property-detectors\-- private only in the sense of idiosyncratic. And insofar as we wish to cling to our subjective authority about the occurrence within us of states of certain types or with certain properties, we can have some authority\--not infallibility or incorrigibility, but something better than sheer guessing\--but only if we restrict ourselves to relational, extrinsic properties like the power of certain internal states of ours to provoke acts of apparent re- identification. So contrary to what seems obvious at first blush, there simply are no qualia at all. \" (Dennett 1988)`</font>`{=html} Dennett\'s asserts that \"a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F\". This is a statement of the belief that qualia are the same as processes such as judgements. Processes such as judgements are flows of data where one state examines a previous state in a succession over time and embody what Whitehead called the \"materialist\" concept of time. Dennett does not consider how a scientific concept of time might affect his argument. Dennett\'s argument has been persuasive and there are now many philosophers and neuroscientists who believe that the problem of phenomenal consciousness does not exist. This means that, to them, what we call \'consciousness\' can only be a property of the functions performed by the brain and body. According to these philosophers only access consciousness exists. Those who support the idea of phenomenal consciousness also tend to frame it in terms of nineteenth century theory where one state examines a previous state in a succession over time, for instance Edelman(1993) places the past in memories at an instant and time within experience is explained as continuing modelling processes: `<font face="times">`{=html}\"Primary consciousness is the state of being mentally aware of things in the world\--of having mental images in the present. But it is not accompanied by any sense of a person with a past and a future\.... In contrast, higher-order consciousness involves the recognition by a thinking subject of his or her own acts or affections. It embodies a model of the personal, and of the past and the future as well as the present. It exhibits direct awareness\--the noninferential or immediate awareness of mental episodes without the involvement of sense organs or receptors. It is what we humans have in addition to primary consciousness. We are conscious of being conscious.\" `</font>`{=html} Block(2004) also suggests this flow from state to state in his idea of \"Reflexivity\" where our idea of familiarity with an object is due to one state being analysed by another: `<font face="times">`{=html}\"Thus in the "conscious" case, the subject must have a state that is about the subject's own perceptual experience (looking familiar) and thus conscious in what might be termed a "reflexive" sense. An experience is conscious in this sense just in case it is the object of another of the subject's states; for example, one has a thought to the effect that one has that experience. The reflexive sense of \'consciousness\' contrasts with phenomenality, which perhaps attaches to some states which are not the objects of other mental states. Reflexive consciousness might better be called 'awareness' than 'consciousness'. Reflexivity is phenomenality plus something else (reflection) and that opens up the possibility in principle for phenomenality without reflection. For example, it is at least conceptually possible for there to be two people in pain, one of whom is introspecting the pain the other not. (Perhaps infants or animals can have pain but don't introspect it.) The first is reflexively conscious of the pain, but both have phenomenally conscious states, since pain is by its very nature a phenomenally conscious state. \"`</font>`{=html} Both Block and Edelman allow phenomenal consciousness, our experience, as an unexplained phenomenon. Block, Edelman and also Dennett\'s ideas of consciousness are shown in the illustration below:  This model differs from the empirical reports of phenomenal consciousness that were considered earlier. According to the empirical reports the present moment in our experience is extended so the succession of outputs or stages of access consciousness could constitute the contents of phenomenal consciousness. In other words phenomenal consciousness is composed of periods of access consciousness. This is how it seems to the empiricist and in our own experience but how such a state could be explained in terms of brain activity is highly problematical. Given that nineteenth century ideas cannot explain such a state a scientific explanation will be required. The idea that phenomenal consciousness misrepresents or \"misdiscovers\" itself (Dennett 1988) deserves further discussion. According to materialism the present instant has no duration so can only be known in succeeding instants as a report or memory and this could be wrong. Whitehead considered that this viewpoint originates in an archaic view of science, particularly the concept of time in science: \"The eighteenth and nineteenth centuries accepted as their natural philosophy a certain circle of concepts which were as rigid and definite as those of the philosophy of the middle ages, and were accepted with as little critical research. I will call this natural philosophy \'materialism.\' Not only were men of science materialists, but also adherents of all schools of philosophy. The idealists only differed from the philosophic materialists on question of the alignment of nature in reference to mind. But no one had any doubt that the philosophy of nature considered in itself was of the type which I have called materialism. It is the philosophy which I have already examined in my two lectures of this course preceding the present one. It can be summarised as the belief that nature is an aggregate of material and that this material exists in some sense at each successive member of a one-dimensional series of extensionless instants of time. Furthermore the mutual relations of the material entities at each instant formed these entities into a spatial configuration in an unbounded space. It would seem that space\-\--on this theory-would be as instantaneous as the instants, and that some explanation is required of the relations between the successive instantaneous spaces. The materialistic theory is however silent on this point; and the succession of instantaneous spaces is tacitly combined into one persistent space. This theory is a purely intellectual rendering of experience which has had the luck to get itself formulated at the dawn of scientific thought. It has dominated the language and the imagination of science since science flourished in Alexandria, with the result that it is now hardly possible to speak without appearing to assume its immediate obviousness.\" (Whitehead 1920). ## Direct Realism and Direct Perception Direct Realism proposes that phenomenal experience is directly objects in the world without any intervening representation. It is motivated by the belief that the Problem of Regression, the Subject-Object Paradox and the recursion form of the Homunculus arguments show that phenomenal consciousness cannot occur in the brain alone. Direct Realists reason that if phenomenal consciousness cannot be things in the brain then it must be something outside the brain. There are two principle types of Direct Realism: Natural Dualism and Behaviourism (both Radical and Analytical). Some behaviourists use the term "Direct Perception" rather than Direct Realism and consider that only the invariant parts of perception are direct (see for instance Michaels and Carello 1981). Thomas Reid is generally regarded as the founder of Direct Realism. In his Natural Dualism he proposed that the soul is in direct contact with the contents of experience and these contents are things in the world beyond the body. The Direct Realism of Reid is summarised in the statement of his famous disciple Sir William Hamilton: \"In the simplest act of perception I am conscious of myself as the perceiving subject and of an external reality as the object perceived\". Reid\'s Natural Dualism has now been largely replaced by radical and analytical behaviourism which eschew the idea of a soul and propose that phenomenal consciousness, if it exists at all, is a behavioural reflex. The modern justification of Direct Realism mainly consists of arguments against Indirect Realism or Representationalism. Philosophers such as Austin (1962) and Le Morvan (2004) have summarised the Direct Realism debate and have identified the following arguments in favour of Indirect Realism and given rebuttals to each of them: 1\. The Causal Argument: perception involves a succession of causal events such as the reflection of photons, bleaching of retinal pigments etc. so perception must involve the end of this causal chain. The Direct Realist response is that, although there may be a causal chain in sensation this does not inevitably imply that the end of the chain is the content of phenomenal experience. 2\. The Time Lag Argument: it takes time for light to travel from an object to the senses, time for chemical changes in the retina etc\... The Direct Realist response is that direct perception may be referred back in time. 3\. The Partial Character of Perception Argument: we only perceive the surface of objects, and then only a part of the surface. As the whole object would be perceived directly perception must be indirect. The Direct Realist response is that direct perception could occur even if only parts of an object were perceived. 4\. The Perceptual Relativity Argument: things appear to be different shapes depending upon the point of view. The Direct Realist response is that if perception can occur backwards in time it should have no problem occurring back down a line of sight. However, Le Morvan\'s argument does not seem to encompass the geometrical nature of phenomenal experience, seeking to explain geometry in terms of movement. 5\. The Argument from Perceptual Illusion: A stick may appear bent when projecting from the surface of water. Direct Realists apply the argument used in (4) to this problem. The bent stick illusion is a physical event in the world beyond the eye rather than a normal optical illusion such as the Muller-Lyer illusion etc., see (6) for a discussion of optical illusions. 6\. The Argument from Hallucination: Hallucinations are not in the world beyond the body. This is highly problematical for Direct Realists especially when phenomena such as lucid dreams, dreams and visual imaginations are included along with hallucinations. Direct Realists classify these phenomena as not being perceptions or deny that they actually exist as phenomena. Indirect Realists would maintain that all of perception is a reconstruction and use optical illusions such as the Muller-Lyer, Ames Room etc. to justify this contention so the Direct Realist approach to hallucination, dreams etc. might seem like an unwillingness to accept Indirect Realism rather than an argument. 7\. The Dubitability Argument (cf: Indubitability argument): we cannot doubt current phenomenal experience but we can doubt the world beyond the body therefore phenomenal experience is not the world beyond the body. Direct Realists fall back on Presentism or functional Presentism to defeat this argument. If phenomenal experience is instantaneous and made anew at each instant then anything can be doubted. The points above have summarised the Direct Realist stance on visual perception. Other sensory modalities have also been considered in the Direct Realism debate. Fowler (1986) considered that sounds were attached to objects in the world. This idea is strange because sounds only seem to be closely attached to objects in the world when these objects are seen as well as heard. For example, when a subject is blindfolded it is found that there can be a large error in locating the position of a sound in the world, this is especially true for low frequency sounds. The Direct Realist approach has difficulty explaining the transition from sounds with an indefinite location when a subject is blindfolded to sounds that are bound to visual events when the blindfold is removed. It also runs into problems explaining how the sound of speech from a single loudspeaker can become bound to lip movements on a cinema screen. If the binding does not occur in the brain then where does it occur? Pain is particularly problematic for Direct Realism because, unlike colour vision where \'red\' is inferred to be a property of electrons or light, pain is an inner experience that is not a property of tissue damage. Tissue damage has properties such as bleeding, wheal formation etc. but pain seems to be phenomenal experience in the brain and \'phantom pain\' can occur without tissue damage (see Aydede (2001), Tye (2004) and Chapman, and Nakamura (1999) for further analysis). On closer inspection other sensations also appear to be inner experiences rather than direct sensations. For instance, the red crosses of different hues in the illustration below are all due to the same physical wavelengths of light. In this case the range of hues in experience is unrelated to the actual physical red on the page or screen. Another problem for Direct Realism is that it does not overcome the problems that it is supposed to solve. The argument for Direct Realism begins with the idea that there are severe problems with representationalism (the idea that phenomenal experience is in the brain) and that direct perception is an alternative that does not have these problems. However on closer inspection Direct Realism suffers from almost same problems as representationalism. If phenomenal experience is the world itself then Ryle\'s regress applies to the world itself and this can only be avoided by assuming that phenomenal experience is a subset of the world (i.e.: a representation) that receives input from other parts of the world that are not part of phenomenal experience. It is also commonly assumed that Direct Realism avoids the recursion argument because it is believed that the separation of the observer from the things that are observed is simply due to the geometry of the world. If such simple geometry is possible between the eye and the world then it should also be possible in the brain and a similar geometrical explanation could be invoked to avoid recursion in representations. These points are shown in the illustration below: image:Constuddir1.gif Scientists have a further problem with Direct Realism. The illustration below demonstrates that our scientific knowledge of the world differs markedly from our phenomenal experience. image:constuddirect.gif It is difficult to see how the form and content of phenomenal experience could supervene directly on the world beyond the body. The world inferred from measurements beyond the body seems to be a nebulous set of quantum phenomena that are arranged as probability fields in three dimensions at any instant. The objects in this real world are mostly space. The world of phenomenal experience on the other hand contains objects that are one-sided, and are like a 2 dimensional field of vectors directed simultaneously at an observation point which is apparently separate from them. Phenomenal experience is not three dimensional, the rear of objects is not available within it at any instant. Visual phenomenal experience seems to be a geometrical relationship between an abstract observation point and the reflection properties of the part of the world external to the body. It is a form that crudely overlies the angular separations in inferred reality, providing approximate directional data. It is not like things in themselves beyond the body, not even in type, being a set of directional vectors. (See the module on the neuroscience of perception for a discussion of depth perception). If the form and content of visual phenomenal experience are abstractions separated according to the angular positions of things in the world beyond the body then theories which propose that phenomenal experience is the world itself are problematical. It should be noted that things arranged according to angular positions can appear to overlie any group of similar things along a radius from the centre point.  If Direct Realists admit that things are as they appear to be, observed according to angular positions at a \'point eye\', then any representation of things on the inside of a sphere of any radius would appear similar. The geometry of the \'point eye\' is problematical whether the view contains the world itself or a representation of the world; it cannot be the movements of lumps of matter or energy and the point observation cannot be due to lumps all landing at a point. In other words the \'view\' is inconsistent with nineteenth century materialism and will require a scientific explanation. Radical and Analytical Behaviourism tackle the problem of the difference between the world inferred from measurements beyond the body and the phenomenal world by denying phenomenal consciousness and maintaining that access and reflex consciousness are all that exists or is necessary. Radical Behaviourism is an offshoot of psychological behaviourism and was established as a philosophical adjunct to Marxism by Vygotsky and popularised by Burrhus Frederic Skinner (see Skinner 1953). There is another movement in psychological behaviourism which is similar to Radical Behaviourism called Ecological Psychology (see Gibson 1966, 1979 and also Michaels and Carello 1981). Analytical Behaviourism is a philosophical movement established by Gilbert Ryle (see Ryle 1949). The core of Analytical and Radical Behaviourism is the assumption that consciousness exists for a durationless instant so that the Dubitability Argument and the Regression and Recursion Arguments can be applied (Ryle 1949, Skinner 1971 and see the sections on Ryle\'s Regress and the Subject-Object Paradox above). As a result the Direct Realist is able to insinuate that subjects only think that they have had a particular experience (cf: Dennett 1991a). It is intriguing that Eliminativists also maintain that experience is the world itself, for instance an insight into Dennett\'s idea of the mind is to be found on pages 407-408 of Consciousness Explained: \"It seemed to him, according to the text, as if his mind - his visual field - were filled with intricate details of gold-green buds an wiggling branches, but although this is how it seemed this was an illusion. No such \"plenum\" ever came into his mind; the plenum remained out in the world where it is didn\'t have to be represented, but could just be. When we marvel, in those moments of heightened self-consciousness, at the glorious richness of our conscious experience, the richness we marvel at is actually the richness of the world outside, in all its ravishing detail. It does not \"enter\" our conscious minds, but is simply available\" This is a clear description of Direct Realism (although Dennett does not describe himself as a direct realist). Radical Behaviourism is sometimes described as the dictum that the only psychological events that are of importance are those that occur outside the head. The absurdity of this has led to jokes: Q: What does one behaviorist say to another when they meet on the street? A: You\'re fine. How am I? Q: What does one behaviorist say to another after sex? A: That was great for you. How was it for me? (Ziff 1958) However Vygotsky, Skinner and other Radical Behaviourists hold that inner behaviour is possible so that events within the brain can result in reward or punishment. Vygotsky (1925) describes this approach: \"Consciousness is wholly reduced to the transmitting mechanisms of reflexes operating according to general laws, i.e., no processes other than reactions can be admitted into the organism. The way is also paved for the solution of the problem of self-awareness and self-observation. Inner perception and introspection are possible only thanks to the existence of a proprioceptive field and secondary reflexes, which are connected with it. This is always the echo of a reaction.\" Hence Radical Behaviourists are able to make the claim that what are believed to be representations with phenomenal content are processes. Even events such as pain can then be explained as reflexes involving organs within the skin. However, by opening the possibility that such reflexes could occur at any sense organ, including the eye, this makes Radical Behaviourism a mixed Direct Realist/Indirect Realist philosophy with consciousness as a process, not a separate thing such as phenomenal consciousness (see the section on representationalism and intentionality below). But this raises a serious issue for science: can the phenomenal consciousness that seems to contain our observations really be argued out of existence on the basis of a theory? As Gregory (1988) put it: " 'If you can't explain it -- deny it' is one strategy for dealing with embarrassing questions such as 'what is consciousness?' ". But is this the right strategy? Direct Realism fails to overcome the problems of regression and recursion inherent in representations. It proposes that phenomenal consciousness is identical to the physical world beyond the body but must then use a plethora of arguments to explain why this is evidently not so. When confronted with these problems its proponents resort to the argument that everything can be doubted and can misrepresent itself. Yet it is still widely believed. It should be noted that Direct Realism is espoused in Religious Natural Dualism, some forms of Augustinian theology, nineteenth century materialism and its offspring such as Marxism, post-modernism, post-Marxism, and various sociological movements. It is also necessary for some forms of Strong AI to occur. Perhaps this explains why few ideas have attracted as much attention and defence as Direct Realism. It is interesting to compare the Direct Realist and Indirect Realist interpretations of something as simple as a cartoon on television (such as the image below). According to Indirect Realism the cartoon would be a moving representation constructed in the brain using data from the senses. This leads to the prediction of brain mechanisms for modelling motions, combining colours, binding sound and vision etc., many of which have been verified. Can you demonstrate how the theory of Direct Realism could explain the phenomenal experience that contains the cartoon and produce a list of the predictions made by the theory?  In science a theory should be of predictive value, for instance, information theory describes how the state of a thing can be impressed on a carrier so that a signal can be transmitted from one place to another. This theory predicts what will happen when the signal arrives at its destination and how the state of the source can be inferred from the events at the destination, the total amount of information that can be transmitted etc. At the destination it is the form of the signal that is directly known by interaction and measurement, the form of the source is inferred. Direct Realism is a direct challenge to this information theory but does it deliver a more powerful predictive description of phenomenal consciousness or is experience always dependent on what happens to the information flow between things in the world and somewhere in the brain? Does direct realism have a physical theory? Ultimately it appears as if Direct Realism is about various understandings of Information Theory. For example, Austin (1962) discusses what we see when we see a church camouflaged as a barn and comments that: \"We see, of course, a church that now looks like a barn.\". Do we see a church or a barn? Scientific information theory is clear about this, the church is an entity composed of selected information from the quantum state of its constituents, the optical image of a camouflaged church is an arrangement of photons emanating from a screen on which it is projected, the retina has an arrangement of chemical and electrical events based on an optical image and conscious visual experience correlates with the arrangement of things on the retina. The fact that conscious experience also correlates with classifications of the retinal image as a barn or a church suggests that conscious experience is an arrangement of things in the brain based on both the retinal arrangement and the contents of a relational database. Austin\'s arguments have been mythologised as a final demonstration that \"sense data\" theories are false. However, as will be seen below, sense data theories merely claim that there is a succession of information states between an information state outside the body and that reported as conscious experience i.e.: subjects report that a church is camouflaged when it is camouflaged. ## Indirect Realism Indirect realism proposes that phenomenal consciousness exists and is a set of signals or **sense data**, usually in the brain. This was proposed by philosophers from Aristotle to Locke and was probably the most widespread idea of conscious experience until the eighteenth century. The idea of sense data is discussed in depth by Russell (1912). Russell\'s original definition is given below: `<font face="times new roman">`{=html}\"Let us give the name of \'sense-data\' to the things that are immediately known in sensation: such things as colours, sounds, smells, hardnesses, roughnesses, and so on. We shall give the name \'sensation\' to the experience of being immediately aware of these things. Thus, whenever we see a colour, we have a sensation of the colour, but the colour itself is a sense-datum, not a sensation. The colour is that of which we are immediately aware, and the awareness itself is the sensation. It is plain that if we are to know anything about the table, it must be by means of the sense-data \-- brown colour, oblong shape, smoothness, etc. \-- which we associate with the table; but, for the reasons which have been given, we cannot say that the table is the sense-data, or even that the sense-data are directly properties of the table.\"`</font>`{=html} Russell\'s definition is a materialist concept in which experience is always **of** something because the durationless instant of the present has always gone. As such it differs from some empiricist ideas where experience is not confined to the durationless instant. Science is Indirect Realist because it holds that the scientist can only make **measurements** of events in the world. These measurements give rise to signals as a result of interaction with the event. According to **decoherence theory** the signals are a state that is a mixture of the state of the measuring instrument and the state of the thing being measured. For example, the eyes are measuring instruments that are sensitive to photons, photons are signals containing a state that is based on the state of electrons in a surface and the state of electrons is based on the state of the surface etc. Scientific inference allows some aspects of the state of the surface to be inferred from the state of the photons. In modern Indirect Realism there is an attempt to distinguish the phenomenal content of conscious experience from the processing involved in accessing this phenomenal content. According to these theories phenomenal experience is an arrangement of signals that are the content of the experience. This arrangement forms a *representation* of things in the world so this form of indirect realism is known as **Representationalism**. Tye (2003) describes types of representationalist theory: `<font face="times new roman">`{=html}\"Representationalism, as I have presented it so far, is an identity thesis with respect to qualia: qualia are supposedly one and the same as certain representational contents.\"`</font>`{=html} Tye also describes variants of this idea of representationalism: `<font face="times new roman">`{=html}\"Sometimes it is held instead that qualia are one and the same as certain representational properties of experiences; and sometimes it is is argued that these representational properties are themselves irreducible (Siewert 1998). There is also a weaker version of representationalism, according to which it is metaphysically necessary that experiences exactly alike with respect to their representational contents are exactly alike with respect to their qualia. Obviously, this supervenience thesis leaves open the further question as to the essential nature of qualia.\"`</font>`{=html} (Tye 2003). In a scientific sense Direct Realists believe that phenomenal experience is the signals that occur next to things in the world beyond the body (which they call \"things in themselves\") and Indirect Realists usually believe that phenomenal experience is signals in the brain. It can be seen from the pattern of signal flow that the signals travelling into the brain preserve the spatial relationships of the original signals and encode the properties in the original signals. This means that the original signals next to the QM sources and the signals in the brain are equivalent provided the latter are oriented appropriately relative to signals from the body. Either set of signals could transmit or contain the same information. Both Direct and Indirect Realism cannot, at present, explain the physics of how a viewing point occurs in experience i.e.: how we seem to see through an apparent space to the signals that are the contents of experience. So the choice between Direct Realism and Indirect Realism reduces to whether there is only one set of signals or a chain of signals between the world and phenomenal experience. The philosophical arguments for Indirect Realism are listed below: 1\. Variable perspective: when we see things the view changes so what we see must be a different set of signals depending on the view rather than a constant object. 2\. Illusions: we can see through fingers and see a variety of colours where measurements tell us one exists. Direct Realists quote the \"bent stick illusion\", which is not really an illusion at all, being a physical event. 3\. Hallucinations: two people can have phenomenal experience containing a table. The first may be viewing a real table whereas the second may be hallucinating a table. If the tables are the same (phenomenally) then experience is indirect. 4\. Double vision: press the side of one eye, two images appear (cf Hume 1739) yet there are not two things in the world. 5\. Time gap arguments: according to materialism the past has gone. The things being seen no longer exist in the state that relates to the state in experience. In the extreme case, some stars in the night sky no longer exist but are still in experience so experience must be a derived signal. 6\. Secondary qualities such as pain, colour and smell do not exist as physical things in the source of signals and are likely to be properties of signals in the brain.  Indirect Realism has received strong support from recent discoveries in neuroscience, for example, it is now clear that both the colour and motion in phenomenal experience are added by cortical processes. In Cerebral **Achromatopsia** patients have suffered trauma to area V4 of the cerebral cortex and report seeing the world in greyscale with no colour vision and in Congenital Achromatopsia people do not even understand the meaning of \'colour\'. In an astonishing ailment called **Akinetopsia** patients perceive movement as a succession of stationary images (Rizzo *et al.* 1995). Akinetopsia is usually associated with damage to cortical area V5. Moutoussis and Zeki (1997) have demonstrated that the addition of colour occurs more rapidly than the addition of motion. The section on the Neuroscience of Consciousness describes these discoveries and many other aspects of the creation of phenomenal experience in the brain. Unfortunately knowledge of the whereabouts of the signals that are the content of conscious experience does not resolve the problem of phenomenal consciousness. Whether these signals are next to objects in the world or at the end of a chain of signals in the brain there still remains the problem of how they become arranged in the form of experience. If such a thing occurs at all. ### Intentionality and representation There is a materialist interpretation of representationalism in which representations are redefined as intentional states: `<font face="times new roman">`{=html}\"One way of explaining what is meant by 'intentionality' in the (more obscure) philosophical sense is this: it is that aspect of mental states or events that consists in their being of or about things (as pertains to the questions, 'What are you thinking of?' and 'What are you thinking about?'). Intentionality is the aboutness or directedness of mind (or states of mind) to things, objects, states of affairs, events. So if you are thinking about San Francisco, or about the increased cost of living there, or about your meeting someone there at Union Square---your mind, your thinking, is directed toward San Francisco, or the increased cost of living, or the meeting in Union Square. To think at all is to think of or about something in this sense. This 'directedness' conception of intentionality plays a prominent role in the influential philosophical writings of Franz Brentano and those whose views developed in response to his (to be discussed further in Section 3).\"(Siewert 2003)`</font>`{=html} This definition allows \"representation\" to be redefined as a data stream rather than a set of things arranged in some mental or neural state that represents things in space. Husserl thought this approach would allow a description of consciousness that \"carefully abstains from affirming the existence of anything in spatio-temporal reality\" (Siewert 2003) although it could be argued that a data stream such as any description can never escape the constraints of representation in time at some place. Unfortunately the concept of \"intentionality\" has become so diverse that it could be applied to almost any aspect of the description of consciousness. An interesting example of this is given by Loar (2001) where \"intentionality\" is considered to overlap \"representing\" and \"conceiving\": `<font face="times new roman">`{=html}\"A person\'s thoughts represent things to her \-- conceive things \-- in many ways: perceptually, memory-wise, descriptively, by naming, by analogy, by intuitive sorting, theoretically, abstractly, implicitly and explicitly. These various manners of conceiving have something in common: they have intentional properties, and they have them essentially. `</font>`{=html} The usage of the term \"intentional state\" has become so broad that it now means little more than a state that is about another state. References Siewert, C. (2003). Consciousness and Intentionality. The Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/consciousness-intentionality/> Also see Loar, B. (2001) "Phenomenal Intentionality as the Basis of Mental Content", in Reflections and Replies, ed. M. Hahn and B. Ramsberg, MIT. <http://www.nyu.edu/gsas/dept/philo/courses/concepts/loar.html> Williford, K. (2002) The intentionality of consciousness and the consciousness of intentionality. Intentionality: Past and Future, edited by Gábor Forrai and George Kampis, Amsterdam/New York: Rodopi. <http://web.stcloudstate.edu/kwwilliford/Intentionality%20of%20Consciousness.pdf> Byrne, A. (2001). Intentionalism Defended. Philosophical Review 110 (April 2001):199-240. <http://stripe.colorado.edu/~leeds/byrne.pdf> ### Cartesian materialism The term \"Cartesian materialism\" once meant the idea that the mind is in the brain (see for instance Block 1995). The term had largely fallen out of use in philosophy until revived by Daniel Dennett (1991) in the book *Consciousness Explained*. Dennett uses a very particular definition of the term in his discussions and also uses a particular definition of the word \"mind\". See the section on Daniel Dennett for Dennett\'s critique. Philosophers who adhere to the idea that the mind is in the brain tend to call themselves \"indirect realists\" or \"representationalists\" where the substrate of conscious experience is in the brain and would deny that Dennett\'s critique applies to their proposals. Dennett\'s critique makes the materialist assumption that if there is a representation in the brain then a further flow of material out of this representation would be required for the representation to become part of mind. ### Identity theories of mind The idea that mental states are brain states is known as the **identity theory of mind**. There are two sorts of identity theory, in **type** identity theory it is held that mental states are identical to brain states whereas in **token** identity theory it is held that mental states correlate with brain states. Type identity theory was attacked by Putnam in \"The Nature of Mental States\" where he pointed out that if mental states are functions then type identity theory would presuppose that animals that had the same mental states would need to have identical brain structures. He suggested that this is unlikely, it being more probable that animals have functional systems that perform similar overall functions but which are not identical. In other words, if it is assumed that conscious experience is a set of functions then token identity theory is more probable than type identity theory. Putnam\'s critique does not preclude identity theories of mind that involve \"passive ideas\" (i.e.: states that are not classical functions). Most identity theories of mind would be representational, the physical states representing the world in some way. All identity theories of mind involve Cartesian materialism in the sense of the mental states being brain states. According to identity theories the mind is in the brain. Putnam, H. (1967) The nature of mental states. In The Nature of Mind, edited by Rosenthal, pp. 197--203. Originally published as \"Psychological predicates in Art, Mind, and Religion\", edited by Capitan and Merill, pp. 37--48. ## Dualism Prior to considering the arguments surrounding dualism it is important to have a clear idea of \"information\" because many of these arguments have parallels with the difference between information as a set of states that can be transmitted and the substrate on which this information is expressed or from which the information is derived. See Elementary information and information systems theory. ### Cartesian dualism Descartes, a philosopher, analysed his experience and developed an empirical description of how it is arranged. He described mental images and perceptions as extended in space and with a duration. He called these extended things **ideas** (Cartesian ideas) and proposed that they are patterns in the brain. Descartes thought the pineal gland was the most likely location for these ideas because it is one of the few single organs in the brain. He also proposed that there is a rational soul that directly contacts these ideas: `<font face="times new roman">`{=html}\"Now among these figures, it is not those imprinted on the external sense organs, or on the internal surface of the brain, which should be taken to be ideas - but only those which are traced in the spirits on the surface of gland H *(where the seat of the imagination and the \'common sense\' is located)*. That is to say, it is only the latter figures which should be taken to be the forms or images which the rational soul united to this machine will consider directly when it imagines some object or perceives it by the senses.\" Descartes (1664)`</font>`{=html} See section on Descartes for more information and references. Descartes considered that the soul was a physical point, an unextended entity that acts like a mind\'s eye. He called this unextended place the *res cogitans* and concluded that it was a substance that differed from that of material things: `<font face="times new roman">`{=html}\".. I thence concluded that I was a substance whose whole essence or nature consists only in thinking, and which, that it may exist, has need of no place, nor is dependent on any material thing; so that \" I,\" that is to say, the mind by which I am what I am, is wholly distinct from the body, and is even more easily known than the latter, and is such, that although the latter were not, it would still continue to be all that it is.\"Descartes (1637)`</font>`{=html} This unextended substance that is not material gives the word \"substance\" a new meaning. It has been attacked as a concept by Locke, Hume, Berkely and many other philosophers. The concept of there being two substances, that which composes the physical world and that which composes the soul, is the origin of the word **Dualism** but dualism, as a concept, has been extended beyond this original meaning. Cartesian dualism is a type of **substance dualism**. Cartesian dualism is an attempt to explain our experience. According to Descartes something supernatural would be needed for an unextended viewing point to exist. Reid\'s **Natural Dualism** also has a point soul looking at things but proposes that the things in question are forms in the world rather than in the brain. ### Property dualism Another sort of dualism has arisen out of a particular interpretation of the regress and homunculus arguments. These arguments show that phenomenal experience is not due entirely to flows from place to place (i.e.: it is not due to classical processes and functions). Property dualism asserts that when matter is organized in the appropriate way (i.e. in the way that living human bodies are organized), mental properties emerge. As Goldman (1993) pointed out, qualitative experience does not seem to be needed in a functional description of a system: `<font face="times new roman">`{=html}\"For any functional description of a system that is in pain (or has an itch), it seems as if we can imagine another system with the same functional description but lacking the qualitative property of painfulness (or itchiness).\" `</font>`{=html} Certainly a functional system that merely reports the words \"I am in pain\" when it is dropped on the floor does not require any qualitative property of painfulness. The *absent qualia* arguments suggest that even in a large system there would be no need for qualitative properties for the performance of any classical function. Chalmers (1993) commenting on Goldman\'s point, said that this implies that **zombies** might exist, functional replicas of humans but without qualia. He then denied that a complete functional replica of a human could exist without also including qualia: `<font face="times new roman">`{=html}\"It seems to me that the only way to avoid this conclusion is to deny that Zombie Dave is a conceptual possibility; and the only principled way to deny that Zombie Dave is a conceptual possibility is to allow that functional organization is conceptually constitutive of qualitative content.\" Chalmers (1993).`</font>`{=html} In other words he identifies qualia with function. According to Chalmers (1996) qualia are a particular type of function: `<font face="times new roman">`{=html}\"I claim that conscious experience arises from fine-grained functional organization. More specifically, I will argue for a principle of organizational invariance, holding that given any system that has conscious experiences, then any system that has the same fine-grained functional organization will have qualitatively identical experiences. According to this principle, consciousness is an organizational invariant: a property that remains constant over all functional isomorphs of a given system. Whether the organization is realized in silicon chips, in the population of China, or in beer cans and ping-pong balls does not matter. As long as the functional organisation is right, conscious experience will be determined.\" p249`</font>`{=html} Chalmers\' idea of functional organisation has within it a sometimes vague implication that the functional units must have a particular form; for instance, in the development of his argument, he refers to "fine grained" replacement of organic functional units with inorganic units. Chalmers is actually making two major points, firstly that qualia occur during the motion of things (functions), secondly that qualia are independent of any particular substrate.\*\* For the first point to be consistent with materialism the qualia must have no effect on the function, they must be **epiphenomenal**. Epiphenomenal qualia would not be forbidden by the regress and homunculus arguments and would be akin to Berkeley\'s \"passive ideas\". Whether or not epiphenomenal qualia are physical depends upon the definition of the word \"physical\". If physical functions cause qualia but qualia cannot affect functions then the qualia are \"physical\" in the sense of being caused by physical events but might be regarded as non-physical in the sense of being isolated from further physical events. In philosophical terms they violate the principle of **Causal Closure**. However, there are other definitions of physicalism based on arguments such as **Methodological Naturalism** which hold that anything that can be investigated using the methods of natural science is a physical thing (see Stoljar 2001). Thus, although epiphenomenal qualia may not conform to materialism they may be encompassed by physicalism; as events that are related to material events they are awaiting a physical theory of how they emerge from a given function. The reader might consider whether phenomenal consciousness is indeed epiphenomenal. Empirical reports describe it as something that is different from the world beyond the body (see direct realism) - could we generate empirical reports of an epiphenomenon? The term **property dualism** describes how physical events might give rise to a set of properties that cannot be predicted from the fine structure of the physical system. The \"dualism\" is present because one set of events is related to two sets of properties, one of which is not related by materialism to the set of events. In the case of the proposal about consciousness outlined above an extra assumption, beyond materialism, would be needed to explain qualia. Property dualism might be defined as a theory that there could be a theory of consciousness but that this requires some new assumption. As far as the \"when and where\" of consciousness are concerned, property dualism states that it is somewhere in the processes performed by the organism and the parts of the organism. `<font size=1>`{=html} \*\* In terms of information processing, Chalmers is proposing that qualia are the enactment of a particular information processing structure.`</font>`{=html} - Block, N. (2006). Max Black\'s objection to mind-body identity. Oxford Review of Metaphysics No.3. <http://philrsss.anu.edu.au/BlockFest/MaxBlack.rtf> - Chalmers, D.J. (1993) Commentary on \"The Psychology of Folk Psychology\". Behavioral and Brain Sciences 16:35-36, 1993 - Chalmers, D.J. (1996) \"The Conscious Mind: In Search of a Fundamental Theory\". Oxford University Press. 1996. - Goldman, A.I., (1993). The Psychology of Folk Psychology. Behavioral and Brain Sciences 16: 15-28 (1993). <http://www.ecs.soton.ac.uk/~harnad/Papers/Py104/goldman.psyc.html> ### Predicate dualism Predicate dualism is the view espoused by most non-reductive physicalists, such as Donald Davidson(1980) and Jerry Fodor(1968), who maintain that while there is only one ontological category of substances and properties of substances (usually physical), the predicates that we use to describe mental events cannot be redescribed in terms of (or reduced to) physical predicates of natural languages. If we characterize predicate monism as the view subscribed to by eliminative materialists, who maintain that such intentional predicates as believe, desire, think, feel, etc., will eventually be eliminated from both the language of science and from ordinary language because the entities to which they refer do not exist, then predicate dualism is most easily defined as the negation of this position. Predicate dualists believe that so-called \"folk psychology\", with all of its propositional attitude ascriptions, is an ineliminable part of the enterprise of describing, explaining and understanding human mental states and behavior. Davidson, for example, subscribes to Anomalous Monism, according to which there can be no strict psycho-physical laws which connect mental and physical events under their descriptions as mental and physical events. However, all mental events also have physical descriptions. It is in terms of the latter that such events can be connected in law-like relations with other physical events. Mental predicates are irreducibly different in character (rational, holistic and necessary) from physical predicates (contingent, atomic and causal). (Section based on Wikipedia article) - Davidson, D (1980). Essays on Actions and Events. Oxford University Press. - Fodor,J. (1968) *Psychological Explanation*, Random House. . ### The interaction between mind and brain in dualism #### Interactionism Interactionism is the view that mental states, such as beliefs and desires, causally interact with physical states. This is a position which is very appealing to common-sense intuitions, notwithstanding the fact that it is very difficult to establish its validity or correctness by way of logical argumentation or empirical proof. It is appealing to common-sense because we are surrounded by such everyday occurrences as a child\'s touching a hot stove (physical event) which causes him to feel pain (mental event) and then yell and scream (physical event) which causes his parents to experience a sensation of fear and protectiveness (mental event) and so on. #### Epiphenomalism According to epiphenomenalism, all mental events are caused by a physical event and have no physical consequences. So, a mental event of deciding to pick up a rock (call it \"M\") is caused by the firing of specific neurons in the brain (call it \"P\"), however when the arm and hand move to pick up a rock (call it \"E\") this is only caused by P. The physical causes are in principle reducible to fundamental physics, and therefore mental causes are eliminated using this reductionist explanation. If P causes M and E, there is no overdetermination in the explanation for E. #### Parallelism Psycho-physical parallelism is a very unusual view about the interaction between mental and physical events which was most prominently, and perhaps only truly, advocated by Gottfried Wilhelm von Leibniz. Like Malebranche and others before him, Leibniz recognized the weaknesses of Descartes\' account of causal interaction taking place in a physical location in the brain. Malebranche decided that such a material basis of interaction between material and immaterial was impossible and therefore formulated his doctrine of occasionalism, stating that the interactions were really caused by the intervention of God on each individual occasion. Leibniz idea is that God has created a pre-established harmony such that it only seems as if physical and mental events cause, and are caused by, one another. In reality, mental causes only have mental effects and physical causes only have physical effects. Hence the term parallelism is used to describe this view. #### Occasionalism Occasionalism argues that bodily events are the occasion of an act by the Creator causing a corresponding mental event, and vice versa. Any such view requires a theological structure as a premise. #### Further reading - Robinson, Howard, \"Dualism\", The Stanford Encyclopedia of Philosophy (Fall 2003 Edition), Edward N. Zalta (ed.), <http://plato.stanford.edu/archives/fall2003/entries/dualism/> - Robinson, H. (2003) \"Dualism\", in S. Stich and T. Warfield (eds) The Blackwell Guide to Philosophy of Mind, Blackwell, Oxford, 85-101. - Amoroso, R.L. (2010) \"The complementarity of Mind and Body: Realizing the Dream of Descartes, Einstein and Eccles\", New York: Nova Science Publishers, `, ``https://www.novapublishers.com/catalog/product_info.php?products_id=12759` ## Idealism According to Idealism only the mental truly exists. The form and content of personal conscious experience might be related to the structure of the world and brain in several ways. It could be a **solipsism** or be the mind of God. *This is a **stub** and needs expansion*. ## Panpsychism ### Etymology Ancient Greek *pan* (πᾶν : \"all, everything, whole\") and *psyche* (ψυχή : \"soul, mind\").[^1] Psyche is the from ψύχω (*psukhō*, \"I blow\") and means mind or \'life-breath\'. Philip Goff, a proponent of panpsychism, carves out a distinction between panexperientialism and pancognitivism. Panexperientialism is the belief that *experience* is ubiquitous, while pancognitivism is the belief that *cognition* is ubiquitous. Most modern purponents of panpsychism, such as Annaka Harris and David Chalmers, are careful to distance themselves from pancognitivism. In some interpretations, such as monadism, Panpsychism and Idealism can overlap because the universe is conceived as being composed of an infinity of point consciousnesses that each contain information about the whole universe. The form and content of personal conscious experience might be related to the structure of the world and brain in many ways. *This is a **stub** and needs expansion*. ## References Seager W. & Allen-Hermanson (2001). 'Panpsychism.' Online document: Stanford Encyclopedia of Philosophy, \[online\], <http://plato.stanford.edu/entries/panpsychism/>, \[accessed 10/2005\] **Supervenience** - Chalmers, D.J. (1996). The Conscious Mind. Oxford University Press. **The problem of regression** - Ryle, G. (1949) The Concept of Mind. The University of Chicago Press, 1949. **The homunculus argument** - Gregory, R.L. (1990) Eye and Brain: The Psychology of Seeing, Oxford University Press Inc. New York. - Gregory, T.L. (1987). The Oxford Companion to Mind. Oxford University Press. **Subject-object paradox** - James, W. (1904)Does \'Consciousness\' Exist? Journal of Philosophy, Psychology, and Scientific Methods, 1, 477-491. - Hegel, G.W.F. PHILOSOPHY OF MIND: SECTION I. MIND SUBJECTIVE B. PHENOMENOLOGY OF MIND CONSCIOUSNESS Part Three of the Encyclopaedia of the Philosophical Sciences - Velmans, M. (1996) Consciousness and the \"Casual Paradox\". Behavioral and Brain Sciences, 19 (3): 538-542. - Bermudez, J.L. (1999) The Paradox of Self-Consciousness (representation and Mind) Psycoloquy: 10,#35 **Ontological status** - Bierman, D.J. (2004) Non Conscious Processes Preceding Intuitive decisions <http://m0134.fmg.uva.nl/~djb/publications/2004/Intuition_bialsymp2004.pdf> - Damasio, A.R. (1994). Descartes\' error: Emotion, reason and the human brain. New York: Grosset/Putnam Book. - Kant, I. Critique of Pure Reason <http://www.arts.cuhk.edu.hk/Philosophy/Kant/cpr/> **Phenomenal consciousness and access consciousness** Block, N. (1995) On a confusion about a function of consciousness. Behavioral and Brain Sciences 18 (2): 227-287. <http://www.bbsonline.org/documents/a/00/00/04/31/bbs00000431-00/bbs.block.html> Block, N. (2004). *The Encyclopedia of Cognitive Science*. <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/ecs.pdf> Dennett, D. (1978). Why You Can\'t Make a Computer that Feels Pain, in: Brainstorms. Cambridge, MA: MIT Press: 190-229. Dennett, D. (1988). Quining Qualia. in A. Marcel and E. Bisiach, eds, Consciousness in Modern Science, Oxford University Press 1988. Reprinted in W. Lycan, ed., Mind and Cognition: A Reader, MIT Press, 1990, A. Goldman, ed. Readings in Philosophy and Cognitive Science, MIT Press, 1993. <http://ase.tufts.edu/cogstud/papers/quinqual.htm> Edelman, G.M. (1993). Bright Air, Brilliant Fire: On the Matter of the Mind. New York: Feyerabend, P. (1963). Mental Events and the Brain, Journal of Philosophy 40:295-6. Huxley, T. H. (1874). On the Hypothesis that Animals are Automata, and its History, The Fortnightly Review, n.s.16:555-580. Reprinted in Method and Results: Essays by Thomas H. Huxley (New York: D. Appleton and Company, 1898). Nagel, T. (1974). What is it like to be a bat? The Philosophical Review LXXXIII, 4 (October 1974): 435-50. <http://web.archive.org/19990218140703/members.aol.com/NeoNoetics/Nagel_Bat.html> Rey, Georges, (1997). Contemporary Philosophy of Mind.Blackwell: Oxford Sellars W. (1956). Empiricism and the Philosophy of Mind, In: Feigl H and Scriven M (eds) The Foundations of Science and the Concepts of Psychology and Psychoanalysis: Minnesota Studies in the Philosophy of Science, Vol. 1. Minneapolis: University of Minnesota Press: 253-329 Whitehead, A.N. (1920). The Concept of Nature. Chapter 3: Time. <http://spartan.ac.brocku.ca/~lward/Whitehead/Whitehead_1920/White1_03.html> **Direct Realism** - Austin, J.L. (1962) Sense and Sensibilia, ed. by Geoffrey J. Warnock (Oxford, 1962) - Aydede, M. (2001) Naturalism, introspection, and direct realism about pain. Consciousness and Emotion, Vol. 2, No. 1, 2001, pp. 29--73. <http://web.clas.ufl.edu/users/maydede/pain.pdf> - Chapman, C.R., and Y. Nakamura (1999). A Passion of the Soul: An Introduction to Pain for Consciousness Researchers. Consciousness and Cognition, 8: 391-422. - Dennett, D. (1991a). Consciousness Explained. Boston: Little, Brown - Dennett, D. (1991b). Lovely and suspect qualities. Commentary on David Rosenthal, \"The Independence of Consciousness and Sensory Quality\" in E. Villanueva, ed., Consciousness, (SOFIA Conference, Buenos Aires), Atascadero, CA: Ridgeview 1991. <http://ase.tufts.edu/cogstud/papers/lovely&s.htm> - Fowler C A (1986): "An event approach to the study of speech perception from a direct-realist perspective", J of Phonetics 14(1):3-28. - Gibson, J. J. (1966) The Senses Considered as Perceptual Systems. Houghton Mifflin Company,Boston. - Gibson, J. J. (1979) Ecological Approach to Visual Perception.: Lawrence Erlbaum Associates Publishers, Hillsdate. - Gregory, R.L. 1988. Consciousness in science and philosophy: conscience and con-science. Chapter 12 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. - Le Morvan, Pierre (2004). Arguments against direct realism and how to counter them. *The American Philosophical Quarterly*, *41*(3), 221-234.\] (pdf) <http://www.tcnj.edu/~lemorvan/DR_web.pdf> - Michaels, C. F. and Carello, C. (1981). Direct Perception. Century Psychology Series. Prentice-Hall. . 1981. Download this book at <http://ione.psy.uconn.edu/~psy254/MC.pdf> - Oliveira, André L. G. and Oliveira, Luis F. (2002) Toward an ecological conception of timbre. In Proceedings Auditory Perception Cognition and Action Meeting 2002, Kansas City. <http://cogprints.org/2713/> - Skinner, B. F. Science and Human Behavior . New York: Macmillan, 1953. - Skinner, B. F. 1971. Beyond Freedom and Dignity. New York: Knopf. - Skinner, B. F. 1948. Walden Two. New York: Macmillan. - Tye, M. (2004). ANOTHER LOOK AT REPRESENTATIONALISM ABOUT PAIN. Consciousness and Emotion 2004, special issue on pain, edited by Murat Aydede (with replies by M. Aydede, N. Block, B. Maund, and P. Noordhof <http://sun.soci.niu.edu/~phildept/MT/RepresentationalismAndPain.pdf> - Vygotsky, L.S.(1925) Consciousness as a problem in the psychology of behavior. Undiscovered Vygotsky: Etudes on the pre-history of cultural-historical psychology (European Studies in the History of Science and Ideas. Vol. 8), pp. 251--281. Peter Lang Publishing. <http://www.marxists.org/archive/vygotsky/works/1925/consciousness.htm> - Ziff, Paul. \"About Behaviourism.\" Analysis 18 (1958): 132-136. Quoted by Larry Hauser in the Internet Encyclopedia of Philosophy. <http://www.utm.edu/research/iep/b/behavior.htm#B>. F. Skinner: Radical Behaviorism **Indirect Realism** - Moutoussis, K. and Zeki, S. (1997). A direct demonstration of perceptual asynchrony in vision. Proceedings of the Royal Society of London, Series B: Biological Sciences, 264, 393 - 399. - Rizzo, M., Nawrot, M. & Zihl, J. (1995). Motion and shape perception in cerebral akinetopsia.Brain, 118. 1105-1127. <http://nawrot.psych.ndsu.nodak.edu/Publications/Nawrot.pdf/RizzoNawrotZihl.1995.pdf> - Russell, B. (1912). Problems of Philosophy. Home University Library. <http://www.ditext.com/russell/rus1.html> - Tye, M. (2003) Qualia. Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/qualia/#Repqualia> Further reading: - Hume, D. (1739). A Treatise of Human Nature. <http://www.class.uidaho.edu/mickelsen/ToC/hume%20treatise%20ToC.htm> - Firth, R. (1949) Sense Data and the Percept Theory, Mind, 58 (1949); 59 (1950). (Describes early reasons for rejecting Indirect Realism) <http://www.ditext.com/firth/spt.html> - Grush, R. (2000). Self, world and space: The meaning and mechanisms of ego- and allocentric spatial representation. Brain and Mind 1(1):59-92. <http://mind.ucsd.edu/papers/sws/sws.html> [^1]: Clarke, D.S. *Panpsychism: Past and Recent Selected Readings*. State University of New York Press, 2004. p.1

# Consciousness Studies/The Conflict2#Indirect realism *This part of this section is about the where and when of the experience called consciousness. Is it in the world, in the brain or are the world and brain within it?* ## Phenomenal consciousness and access consciousness Block(1995) drew attention to the way that there appear to be two types of consciousness: *phenomenal* consciousness and *access* consciousness: `Phenomenal consciousness is experience; the phenomenally`\ `conscious  aspect of a state is what it is like to be in that`\ `state. The mark of access-consciousness, by contrast, is `\ `availability for use in reasoning and rationally guiding speech `\ `and action. (Block 1995).` *See the section on Ned Block\'s ideas for a deeper coverage of his approach to access and phenomenal consciousness.* Block uses Nagel\'s famous (1974) paper, \"What is it like to be a bat?\" as an exemplary description of phenomenal consciousness. Excellent descriptions have also been proffered by the empiricist philosophers who gave lengthy descriptions of consciousness as partly experience itself. Although Block has formalised the idea of phenomenal and access consciousness similar ideas have also been put forward by many philosophers including Kant and Whitehead. Access consciousness has two interpretations, in the first, used by Block, it applies to the functions that appear to operate on phenomenal consciousness. In the second, used by the behaviourists and eliminativists, it is some property of the functions of the brain that can be called \'consciousness\'. This division between phenomenal and functional aspects of consciousness is useful because it emphasises the idea of phenomenal consciousness as observation rather than action. Some philosophers such as Huxley in 1874, have taken the view that because phenomenal consciousness appears to have no function it is of no importance or cannot exist. James (1879) introduced the term \"epiphenomenalism\" to summarise the idea that consciousness has no function. The idea that phenomenal consciousness cannot exist is a type of *Eliminativism* (also known as Eliminative Materialism). Eliminativism owes much to the work of Sellars(1956) and Feyerbend (1963). Dennett (1978) applied Eliminativism to phenomenal consciousness and denies that pain is real. Others such as Rey(1997) have also applied eliminativism to phenomenal consciousness. Dennett (1988) redefines consciousness in terms of access consciousness alone, he argues that \"Everything real has properties, and since I don\'t deny the reality of conscious experience, I grant that conscious experience has properties\". Having related all consciousness to properties he then declares that these properties are actually judgements of properties. He considers judgements of the properties of consciousness to be identical to the properties themselves. He writes: `<font face="times">`{=html}\"The infallibilist line on qualia treats them as properties of one\'s experience one cannot in principle misdiscover, and this is a mysterious doctrine (at least as mysterious as papal infallibility) unless we shift the emphasis a little and treat qualia as logical constructs out of subjects\' qualia-judgments: a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F. \"`</font>`{=html} Having identified \"properties\" with \"judgement of properties\" he can then show that the judgements are insubstantial, hence the properties are insubstantial and hence the qualia are insubstantial or even non-existent. Dennett concludes that qualia can be rejected as non-existent: `<font face="times">`{=html}\"So when we look one last time at our original characterization of qualia, as ineffable, intrinsic, private, directly apprehensible properties of experience, we find that there is nothing to fill the bill. In their place are relatively or practically ineffable public properties we can refer to indirectly via reference to our private property-detectors\-- private only in the sense of idiosyncratic. And insofar as we wish to cling to our subjective authority about the occurrence within us of states of certain types or with certain properties, we can have some authority\--not infallibility or incorrigibility, but something better than sheer guessing\--but only if we restrict ourselves to relational, extrinsic properties like the power of certain internal states of ours to provoke acts of apparent re- identification. So contrary to what seems obvious at first blush, there simply are no qualia at all. \" (Dennett 1988)`</font>`{=html} Dennett\'s asserts that \"a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F\". This is a statement of the belief that qualia are the same as processes such as judgements. Processes such as judgements are flows of data where one state examines a previous state in a succession over time and embody what Whitehead called the \"materialist\" concept of time. Dennett does not consider how a scientific concept of time might affect his argument. Dennett\'s argument has been persuasive and there are now many philosophers and neuroscientists who believe that the problem of phenomenal consciousness does not exist. This means that, to them, what we call \'consciousness\' can only be a property of the functions performed by the brain and body. According to these philosophers only access consciousness exists. Those who support the idea of phenomenal consciousness also tend to frame it in terms of nineteenth century theory where one state examines a previous state in a succession over time, for instance Edelman(1993) places the past in memories at an instant and time within experience is explained as continuing modelling processes: `<font face="times">`{=html}\"Primary consciousness is the state of being mentally aware of things in the world\--of having mental images in the present. But it is not accompanied by any sense of a person with a past and a future\.... In contrast, higher-order consciousness involves the recognition by a thinking subject of his or her own acts or affections. It embodies a model of the personal, and of the past and the future as well as the present. It exhibits direct awareness\--the noninferential or immediate awareness of mental episodes without the involvement of sense organs or receptors. It is what we humans have in addition to primary consciousness. We are conscious of being conscious.\" `</font>`{=html} Block(2004) also suggests this flow from state to state in his idea of \"Reflexivity\" where our idea of familiarity with an object is due to one state being analysed by another: `<font face="times">`{=html}\"Thus in the "conscious" case, the subject must have a state that is about the subject's own perceptual experience (looking familiar) and thus conscious in what might be termed a "reflexive" sense. An experience is conscious in this sense just in case it is the object of another of the subject's states; for example, one has a thought to the effect that one has that experience. The reflexive sense of \'consciousness\' contrasts with phenomenality, which perhaps attaches to some states which are not the objects of other mental states. Reflexive consciousness might better be called 'awareness' than 'consciousness'. Reflexivity is phenomenality plus something else (reflection) and that opens up the possibility in principle for phenomenality without reflection. For example, it is at least conceptually possible for there to be two people in pain, one of whom is introspecting the pain the other not. (Perhaps infants or animals can have pain but don't introspect it.) The first is reflexively conscious of the pain, but both have phenomenally conscious states, since pain is by its very nature a phenomenally conscious state. \"`</font>`{=html} Both Block and Edelman allow phenomenal consciousness, our experience, as an unexplained phenomenon. Block, Edelman and also Dennett\'s ideas of consciousness are shown in the illustration below:  This model differs from the empirical reports of phenomenal consciousness that were considered earlier. According to the empirical reports the present moment in our experience is extended so the succession of outputs or stages of access consciousness could constitute the contents of phenomenal consciousness. In other words phenomenal consciousness is composed of periods of access consciousness. This is how it seems to the empiricist and in our own experience but how such a state could be explained in terms of brain activity is highly problematical. Given that nineteenth century ideas cannot explain such a state a scientific explanation will be required. The idea that phenomenal consciousness misrepresents or \"misdiscovers\" itself (Dennett 1988) deserves further discussion. According to materialism the present instant has no duration so can only be known in succeeding instants as a report or memory and this could be wrong. Whitehead considered that this viewpoint originates in an archaic view of science, particularly the concept of time in science: \"The eighteenth and nineteenth centuries accepted as their natural philosophy a certain circle of concepts which were as rigid and definite as those of the philosophy of the middle ages, and were accepted with as little critical research. I will call this natural philosophy \'materialism.\' Not only were men of science materialists, but also adherents of all schools of philosophy. The idealists only differed from the philosophic materialists on question of the alignment of nature in reference to mind. But no one had any doubt that the philosophy of nature considered in itself was of the type which I have called materialism. It is the philosophy which I have already examined in my two lectures of this course preceding the present one. It can be summarised as the belief that nature is an aggregate of material and that this material exists in some sense at each successive member of a one-dimensional series of extensionless instants of time. Furthermore the mutual relations of the material entities at each instant formed these entities into a spatial configuration in an unbounded space. It would seem that space\-\--on this theory-would be as instantaneous as the instants, and that some explanation is required of the relations between the successive instantaneous spaces. The materialistic theory is however silent on this point; and the succession of instantaneous spaces is tacitly combined into one persistent space. This theory is a purely intellectual rendering of experience which has had the luck to get itself formulated at the dawn of scientific thought. It has dominated the language and the imagination of science since science flourished in Alexandria, with the result that it is now hardly possible to speak without appearing to assume its immediate obviousness.\" (Whitehead 1920). ## Direct Realism and Direct Perception Direct Realism proposes that phenomenal experience is directly objects in the world without any intervening representation. It is motivated by the belief that the Problem of Regression, the Subject-Object Paradox and the recursion form of the Homunculus arguments show that phenomenal consciousness cannot occur in the brain alone. Direct Realists reason that if phenomenal consciousness cannot be things in the brain then it must be something outside the brain. There are two principle types of Direct Realism: Natural Dualism and Behaviourism (both Radical and Analytical). Some behaviourists use the term "Direct Perception" rather than Direct Realism and consider that only the invariant parts of perception are direct (see for instance Michaels and Carello 1981). Thomas Reid is generally regarded as the founder of Direct Realism. In his Natural Dualism he proposed that the soul is in direct contact with the contents of experience and these contents are things in the world beyond the body. The Direct Realism of Reid is summarised in the statement of his famous disciple Sir William Hamilton: \"In the simplest act of perception I am conscious of myself as the perceiving subject and of an external reality as the object perceived\". Reid\'s Natural Dualism has now been largely replaced by radical and analytical behaviourism which eschew the idea of a soul and propose that phenomenal consciousness, if it exists at all, is a behavioural reflex. The modern justification of Direct Realism mainly consists of arguments against Indirect Realism or Representationalism. Philosophers such as Austin (1962) and Le Morvan (2004) have summarised the Direct Realism debate and have identified the following arguments in favour of Indirect Realism and given rebuttals to each of them: 1\. The Causal Argument: perception involves a succession of causal events such as the reflection of photons, bleaching of retinal pigments etc. so perception must involve the end of this causal chain. The Direct Realist response is that, although there may be a causal chain in sensation this does not inevitably imply that the end of the chain is the content of phenomenal experience. 2\. The Time Lag Argument: it takes time for light to travel from an object to the senses, time for chemical changes in the retina etc\... The Direct Realist response is that direct perception may be referred back in time. 3\. The Partial Character of Perception Argument: we only perceive the surface of objects, and then only a part of the surface. As the whole object would be perceived directly perception must be indirect. The Direct Realist response is that direct perception could occur even if only parts of an object were perceived. 4\. The Perceptual Relativity Argument: things appear to be different shapes depending upon the point of view. The Direct Realist response is that if perception can occur backwards in time it should have no problem occurring back down a line of sight. However, Le Morvan\'s argument does not seem to encompass the geometrical nature of phenomenal experience, seeking to explain geometry in terms of movement. 5\. The Argument from Perceptual Illusion: A stick may appear bent when projecting from the surface of water. Direct Realists apply the argument used in (4) to this problem. The bent stick illusion is a physical event in the world beyond the eye rather than a normal optical illusion such as the Muller-Lyer illusion etc., see (6) for a discussion of optical illusions. 6\. The Argument from Hallucination: Hallucinations are not in the world beyond the body. This is highly problematical for Direct Realists especially when phenomena such as lucid dreams, dreams and visual imaginations are included along with hallucinations. Direct Realists classify these phenomena as not being perceptions or deny that they actually exist as phenomena. Indirect Realists would maintain that all of perception is a reconstruction and use optical illusions such as the Muller-Lyer, Ames Room etc. to justify this contention so the Direct Realist approach to hallucination, dreams etc. might seem like an unwillingness to accept Indirect Realism rather than an argument. 7\. The Dubitability Argument (cf: Indubitability argument): we cannot doubt current phenomenal experience but we can doubt the world beyond the body therefore phenomenal experience is not the world beyond the body. Direct Realists fall back on Presentism or functional Presentism to defeat this argument. If phenomenal experience is instantaneous and made anew at each instant then anything can be doubted. The points above have summarised the Direct Realist stance on visual perception. Other sensory modalities have also been considered in the Direct Realism debate. Fowler (1986) considered that sounds were attached to objects in the world. This idea is strange because sounds only seem to be closely attached to objects in the world when these objects are seen as well as heard. For example, when a subject is blindfolded it is found that there can be a large error in locating the position of a sound in the world, this is especially true for low frequency sounds. The Direct Realist approach has difficulty explaining the transition from sounds with an indefinite location when a subject is blindfolded to sounds that are bound to visual events when the blindfold is removed. It also runs into problems explaining how the sound of speech from a single loudspeaker can become bound to lip movements on a cinema screen. If the binding does not occur in the brain then where does it occur? Pain is particularly problematic for Direct Realism because, unlike colour vision where \'red\' is inferred to be a property of electrons or light, pain is an inner experience that is not a property of tissue damage. Tissue damage has properties such as bleeding, wheal formation etc. but pain seems to be phenomenal experience in the brain and \'phantom pain\' can occur without tissue damage (see Aydede (2001), Tye (2004) and Chapman, and Nakamura (1999) for further analysis). On closer inspection other sensations also appear to be inner experiences rather than direct sensations. For instance, the red crosses of different hues in the illustration below are all due to the same physical wavelengths of light. In this case the range of hues in experience is unrelated to the actual physical red on the page or screen. Another problem for Direct Realism is that it does not overcome the problems that it is supposed to solve. The argument for Direct Realism begins with the idea that there are severe problems with representationalism (the idea that phenomenal experience is in the brain) and that direct perception is an alternative that does not have these problems. However on closer inspection Direct Realism suffers from almost same problems as representationalism. If phenomenal experience is the world itself then Ryle\'s regress applies to the world itself and this can only be avoided by assuming that phenomenal experience is a subset of the world (i.e.: a representation) that receives input from other parts of the world that are not part of phenomenal experience. It is also commonly assumed that Direct Realism avoids the recursion argument because it is believed that the separation of the observer from the things that are observed is simply due to the geometry of the world. If such simple geometry is possible between the eye and the world then it should also be possible in the brain and a similar geometrical explanation could be invoked to avoid recursion in representations. These points are shown in the illustration below: image:Constuddir1.gif Scientists have a further problem with Direct Realism. The illustration below demonstrates that our scientific knowledge of the world differs markedly from our phenomenal experience. image:constuddirect.gif It is difficult to see how the form and content of phenomenal experience could supervene directly on the world beyond the body. The world inferred from measurements beyond the body seems to be a nebulous set of quantum phenomena that are arranged as probability fields in three dimensions at any instant. The objects in this real world are mostly space. The world of phenomenal experience on the other hand contains objects that are one-sided, and are like a 2 dimensional field of vectors directed simultaneously at an observation point which is apparently separate from them. Phenomenal experience is not three dimensional, the rear of objects is not available within it at any instant. Visual phenomenal experience seems to be a geometrical relationship between an abstract observation point and the reflection properties of the part of the world external to the body. It is a form that crudely overlies the angular separations in inferred reality, providing approximate directional data. It is not like things in themselves beyond the body, not even in type, being a set of directional vectors. (See the module on the neuroscience of perception for a discussion of depth perception). If the form and content of visual phenomenal experience are abstractions separated according to the angular positions of things in the world beyond the body then theories which propose that phenomenal experience is the world itself are problematical. It should be noted that things arranged according to angular positions can appear to overlie any group of similar things along a radius from the centre point.  If Direct Realists admit that things are as they appear to be, observed according to angular positions at a \'point eye\', then any representation of things on the inside of a sphere of any radius would appear similar. The geometry of the \'point eye\' is problematical whether the view contains the world itself or a representation of the world; it cannot be the movements of lumps of matter or energy and the point observation cannot be due to lumps all landing at a point. In other words the \'view\' is inconsistent with nineteenth century materialism and will require a scientific explanation. Radical and Analytical Behaviourism tackle the problem of the difference between the world inferred from measurements beyond the body and the phenomenal world by denying phenomenal consciousness and maintaining that access and reflex consciousness are all that exists or is necessary. Radical Behaviourism is an offshoot of psychological behaviourism and was established as a philosophical adjunct to Marxism by Vygotsky and popularised by Burrhus Frederic Skinner (see Skinner 1953). There is another movement in psychological behaviourism which is similar to Radical Behaviourism called Ecological Psychology (see Gibson 1966, 1979 and also Michaels and Carello 1981). Analytical Behaviourism is a philosophical movement established by Gilbert Ryle (see Ryle 1949). The core of Analytical and Radical Behaviourism is the assumption that consciousness exists for a durationless instant so that the Dubitability Argument and the Regression and Recursion Arguments can be applied (Ryle 1949, Skinner 1971 and see the sections on Ryle\'s Regress and the Subject-Object Paradox above). As a result the Direct Realist is able to insinuate that subjects only think that they have had a particular experience (cf: Dennett 1991a). It is intriguing that Eliminativists also maintain that experience is the world itself, for instance an insight into Dennett\'s idea of the mind is to be found on pages 407-408 of Consciousness Explained: \"It seemed to him, according to the text, as if his mind - his visual field - were filled with intricate details of gold-green buds an wiggling branches, but although this is how it seemed this was an illusion. No such \"plenum\" ever came into his mind; the plenum remained out in the world where it is didn\'t have to be represented, but could just be. When we marvel, in those moments of heightened self-consciousness, at the glorious richness of our conscious experience, the richness we marvel at is actually the richness of the world outside, in all its ravishing detail. It does not \"enter\" our conscious minds, but is simply available\" This is a clear description of Direct Realism (although Dennett does not describe himself as a direct realist). Radical Behaviourism is sometimes described as the dictum that the only psychological events that are of importance are those that occur outside the head. The absurdity of this has led to jokes: Q: What does one behaviorist say to another when they meet on the street? A: You\'re fine. How am I? Q: What does one behaviorist say to another after sex? A: That was great for you. How was it for me? (Ziff 1958) However Vygotsky, Skinner and other Radical Behaviourists hold that inner behaviour is possible so that events within the brain can result in reward or punishment. Vygotsky (1925) describes this approach: \"Consciousness is wholly reduced to the transmitting mechanisms of reflexes operating according to general laws, i.e., no processes other than reactions can be admitted into the organism. The way is also paved for the solution of the problem of self-awareness and self-observation. Inner perception and introspection are possible only thanks to the existence of a proprioceptive field and secondary reflexes, which are connected with it. This is always the echo of a reaction.\" Hence Radical Behaviourists are able to make the claim that what are believed to be representations with phenomenal content are processes. Even events such as pain can then be explained as reflexes involving organs within the skin. However, by opening the possibility that such reflexes could occur at any sense organ, including the eye, this makes Radical Behaviourism a mixed Direct Realist/Indirect Realist philosophy with consciousness as a process, not a separate thing such as phenomenal consciousness (see the section on representationalism and intentionality below). But this raises a serious issue for science: can the phenomenal consciousness that seems to contain our observations really be argued out of existence on the basis of a theory? As Gregory (1988) put it: " 'If you can't explain it -- deny it' is one strategy for dealing with embarrassing questions such as 'what is consciousness?' ". But is this the right strategy? Direct Realism fails to overcome the problems of regression and recursion inherent in representations. It proposes that phenomenal consciousness is identical to the physical world beyond the body but must then use a plethora of arguments to explain why this is evidently not so. When confronted with these problems its proponents resort to the argument that everything can be doubted and can misrepresent itself. Yet it is still widely believed. It should be noted that Direct Realism is espoused in Religious Natural Dualism, some forms of Augustinian theology, nineteenth century materialism and its offspring such as Marxism, post-modernism, post-Marxism, and various sociological movements. It is also necessary for some forms of Strong AI to occur. Perhaps this explains why few ideas have attracted as much attention and defence as Direct Realism. It is interesting to compare the Direct Realist and Indirect Realist interpretations of something as simple as a cartoon on television (such as the image below). According to Indirect Realism the cartoon would be a moving representation constructed in the brain using data from the senses. This leads to the prediction of brain mechanisms for modelling motions, combining colours, binding sound and vision etc., many of which have been verified. Can you demonstrate how the theory of Direct Realism could explain the phenomenal experience that contains the cartoon and produce a list of the predictions made by the theory?  In science a theory should be of predictive value, for instance, information theory describes how the state of a thing can be impressed on a carrier so that a signal can be transmitted from one place to another. This theory predicts what will happen when the signal arrives at its destination and how the state of the source can be inferred from the events at the destination, the total amount of information that can be transmitted etc. At the destination it is the form of the signal that is directly known by interaction and measurement, the form of the source is inferred. Direct Realism is a direct challenge to this information theory but does it deliver a more powerful predictive description of phenomenal consciousness or is experience always dependent on what happens to the information flow between things in the world and somewhere in the brain? Does direct realism have a physical theory? Ultimately it appears as if Direct Realism is about various understandings of Information Theory. For example, Austin (1962) discusses what we see when we see a church camouflaged as a barn and comments that: \"We see, of course, a church that now looks like a barn.\". Do we see a church or a barn? Scientific information theory is clear about this, the church is an entity composed of selected information from the quantum state of its constituents, the optical image of a camouflaged church is an arrangement of photons emanating from a screen on which it is projected, the retina has an arrangement of chemical and electrical events based on an optical image and conscious visual experience correlates with the arrangement of things on the retina. The fact that conscious experience also correlates with classifications of the retinal image as a barn or a church suggests that conscious experience is an arrangement of things in the brain based on both the retinal arrangement and the contents of a relational database. Austin\'s arguments have been mythologised as a final demonstration that \"sense data\" theories are false. However, as will be seen below, sense data theories merely claim that there is a succession of information states between an information state outside the body and that reported as conscious experience i.e.: subjects report that a church is camouflaged when it is camouflaged. ## Indirect Realism Indirect realism proposes that phenomenal consciousness exists and is a set of signals or **sense data**, usually in the brain. This was proposed by philosophers from Aristotle to Locke and was probably the most widespread idea of conscious experience until the eighteenth century. The idea of sense data is discussed in depth by Russell (1912). Russell\'s original definition is given below: `<font face="times new roman">`{=html}\"Let us give the name of \'sense-data\' to the things that are immediately known in sensation: such things as colours, sounds, smells, hardnesses, roughnesses, and so on. We shall give the name \'sensation\' to the experience of being immediately aware of these things. Thus, whenever we see a colour, we have a sensation of the colour, but the colour itself is a sense-datum, not a sensation. The colour is that of which we are immediately aware, and the awareness itself is the sensation. It is plain that if we are to know anything about the table, it must be by means of the sense-data \-- brown colour, oblong shape, smoothness, etc. \-- which we associate with the table; but, for the reasons which have been given, we cannot say that the table is the sense-data, or even that the sense-data are directly properties of the table.\"`</font>`{=html} Russell\'s definition is a materialist concept in which experience is always **of** something because the durationless instant of the present has always gone. As such it differs from some empiricist ideas where experience is not confined to the durationless instant. Science is Indirect Realist because it holds that the scientist can only make **measurements** of events in the world. These measurements give rise to signals as a result of interaction with the event. According to **decoherence theory** the signals are a state that is a mixture of the state of the measuring instrument and the state of the thing being measured. For example, the eyes are measuring instruments that are sensitive to photons, photons are signals containing a state that is based on the state of electrons in a surface and the state of electrons is based on the state of the surface etc. Scientific inference allows some aspects of the state of the surface to be inferred from the state of the photons. In modern Indirect Realism there is an attempt to distinguish the phenomenal content of conscious experience from the processing involved in accessing this phenomenal content. According to these theories phenomenal experience is an arrangement of signals that are the content of the experience. This arrangement forms a *representation* of things in the world so this form of indirect realism is known as **Representationalism**. Tye (2003) describes types of representationalist theory: `<font face="times new roman">`{=html}\"Representationalism, as I have presented it so far, is an identity thesis with respect to qualia: qualia are supposedly one and the same as certain representational contents.\"`</font>`{=html} Tye also describes variants of this idea of representationalism: `<font face="times new roman">`{=html}\"Sometimes it is held instead that qualia are one and the same as certain representational properties of experiences; and sometimes it is is argued that these representational properties are themselves irreducible (Siewert 1998). There is also a weaker version of representationalism, according to which it is metaphysically necessary that experiences exactly alike with respect to their representational contents are exactly alike with respect to their qualia. Obviously, this supervenience thesis leaves open the further question as to the essential nature of qualia.\"`</font>`{=html} (Tye 2003). In a scientific sense Direct Realists believe that phenomenal experience is the signals that occur next to things in the world beyond the body (which they call \"things in themselves\") and Indirect Realists usually believe that phenomenal experience is signals in the brain. It can be seen from the pattern of signal flow that the signals travelling into the brain preserve the spatial relationships of the original signals and encode the properties in the original signals. This means that the original signals next to the QM sources and the signals in the brain are equivalent provided the latter are oriented appropriately relative to signals from the body. Either set of signals could transmit or contain the same information. Both Direct and Indirect Realism cannot, at present, explain the physics of how a viewing point occurs in experience i.e.: how we seem to see through an apparent space to the signals that are the contents of experience. So the choice between Direct Realism and Indirect Realism reduces to whether there is only one set of signals or a chain of signals between the world and phenomenal experience. The philosophical arguments for Indirect Realism are listed below: 1\. Variable perspective: when we see things the view changes so what we see must be a different set of signals depending on the view rather than a constant object. 2\. Illusions: we can see through fingers and see a variety of colours where measurements tell us one exists. Direct Realists quote the \"bent stick illusion\", which is not really an illusion at all, being a physical event. 3\. Hallucinations: two people can have phenomenal experience containing a table. The first may be viewing a real table whereas the second may be hallucinating a table. If the tables are the same (phenomenally) then experience is indirect. 4\. Double vision: press the side of one eye, two images appear (cf Hume 1739) yet there are not two things in the world. 5\. Time gap arguments: according to materialism the past has gone. The things being seen no longer exist in the state that relates to the state in experience. In the extreme case, some stars in the night sky no longer exist but are still in experience so experience must be a derived signal. 6\. Secondary qualities such as pain, colour and smell do not exist as physical things in the source of signals and are likely to be properties of signals in the brain.  Indirect Realism has received strong support from recent discoveries in neuroscience, for example, it is now clear that both the colour and motion in phenomenal experience are added by cortical processes. In Cerebral **Achromatopsia** patients have suffered trauma to area V4 of the cerebral cortex and report seeing the world in greyscale with no colour vision and in Congenital Achromatopsia people do not even understand the meaning of \'colour\'. In an astonishing ailment called **Akinetopsia** patients perceive movement as a succession of stationary images (Rizzo *et al.* 1995). Akinetopsia is usually associated with damage to cortical area V5. Moutoussis and Zeki (1997) have demonstrated that the addition of colour occurs more rapidly than the addition of motion. The section on the Neuroscience of Consciousness describes these discoveries and many other aspects of the creation of phenomenal experience in the brain. Unfortunately knowledge of the whereabouts of the signals that are the content of conscious experience does not resolve the problem of phenomenal consciousness. Whether these signals are next to objects in the world or at the end of a chain of signals in the brain there still remains the problem of how they become arranged in the form of experience. If such a thing occurs at all. ### Intentionality and representation There is a materialist interpretation of representationalism in which representations are redefined as intentional states: `<font face="times new roman">`{=html}\"One way of explaining what is meant by 'intentionality' in the (more obscure) philosophical sense is this: it is that aspect of mental states or events that consists in their being of or about things (as pertains to the questions, 'What are you thinking of?' and 'What are you thinking about?'). Intentionality is the aboutness or directedness of mind (or states of mind) to things, objects, states of affairs, events. So if you are thinking about San Francisco, or about the increased cost of living there, or about your meeting someone there at Union Square---your mind, your thinking, is directed toward San Francisco, or the increased cost of living, or the meeting in Union Square. To think at all is to think of or about something in this sense. This 'directedness' conception of intentionality plays a prominent role in the influential philosophical writings of Franz Brentano and those whose views developed in response to his (to be discussed further in Section 3).\"(Siewert 2003)`</font>`{=html} This definition allows \"representation\" to be redefined as a data stream rather than a set of things arranged in some mental or neural state that represents things in space. Husserl thought this approach would allow a description of consciousness that \"carefully abstains from affirming the existence of anything in spatio-temporal reality\" (Siewert 2003) although it could be argued that a data stream such as any description can never escape the constraints of representation in time at some place. Unfortunately the concept of \"intentionality\" has become so diverse that it could be applied to almost any aspect of the description of consciousness. An interesting example of this is given by Loar (2001) where \"intentionality\" is considered to overlap \"representing\" and \"conceiving\": `<font face="times new roman">`{=html}\"A person\'s thoughts represent things to her \-- conceive things \-- in many ways: perceptually, memory-wise, descriptively, by naming, by analogy, by intuitive sorting, theoretically, abstractly, implicitly and explicitly. These various manners of conceiving have something in common: they have intentional properties, and they have them essentially. `</font>`{=html} The usage of the term \"intentional state\" has become so broad that it now means little more than a state that is about another state. References Siewert, C. (2003). Consciousness and Intentionality. The Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/consciousness-intentionality/> Also see Loar, B. (2001) "Phenomenal Intentionality as the Basis of Mental Content", in Reflections and Replies, ed. M. Hahn and B. Ramsberg, MIT. <http://www.nyu.edu/gsas/dept/philo/courses/concepts/loar.html> Williford, K. (2002) The intentionality of consciousness and the consciousness of intentionality. Intentionality: Past and Future, edited by Gábor Forrai and George Kampis, Amsterdam/New York: Rodopi. <http://web.stcloudstate.edu/kwwilliford/Intentionality%20of%20Consciousness.pdf> Byrne, A. (2001). Intentionalism Defended. Philosophical Review 110 (April 2001):199-240. <http://stripe.colorado.edu/~leeds/byrne.pdf> ### Cartesian materialism The term \"Cartesian materialism\" once meant the idea that the mind is in the brain (see for instance Block 1995). The term had largely fallen out of use in philosophy until revived by Daniel Dennett (1991) in the book *Consciousness Explained*. Dennett uses a very particular definition of the term in his discussions and also uses a particular definition of the word \"mind\". See the section on Daniel Dennett for Dennett\'s critique. Philosophers who adhere to the idea that the mind is in the brain tend to call themselves \"indirect realists\" or \"representationalists\" where the substrate of conscious experience is in the brain and would deny that Dennett\'s critique applies to their proposals. Dennett\'s critique makes the materialist assumption that if there is a representation in the brain then a further flow of material out of this representation would be required for the representation to become part of mind. ### Identity theories of mind The idea that mental states are brain states is known as the **identity theory of mind**. There are two sorts of identity theory, in **type** identity theory it is held that mental states are identical to brain states whereas in **token** identity theory it is held that mental states correlate with brain states. Type identity theory was attacked by Putnam in \"The Nature of Mental States\" where he pointed out that if mental states are functions then type identity theory would presuppose that animals that had the same mental states would need to have identical brain structures. He suggested that this is unlikely, it being more probable that animals have functional systems that perform similar overall functions but which are not identical. In other words, if it is assumed that conscious experience is a set of functions then token identity theory is more probable than type identity theory. Putnam\'s critique does not preclude identity theories of mind that involve \"passive ideas\" (i.e.: states that are not classical functions). Most identity theories of mind would be representational, the physical states representing the world in some way. All identity theories of mind involve Cartesian materialism in the sense of the mental states being brain states. According to identity theories the mind is in the brain. Putnam, H. (1967) The nature of mental states. In The Nature of Mind, edited by Rosenthal, pp. 197--203. Originally published as \"Psychological predicates in Art, Mind, and Religion\", edited by Capitan and Merill, pp. 37--48. ## Dualism Prior to considering the arguments surrounding dualism it is important to have a clear idea of \"information\" because many of these arguments have parallels with the difference between information as a set of states that can be transmitted and the substrate on which this information is expressed or from which the information is derived. See Elementary information and information systems theory. ### Cartesian dualism Descartes, a philosopher, analysed his experience and developed an empirical description of how it is arranged. He described mental images and perceptions as extended in space and with a duration. He called these extended things **ideas** (Cartesian ideas) and proposed that they are patterns in the brain. Descartes thought the pineal gland was the most likely location for these ideas because it is one of the few single organs in the brain. He also proposed that there is a rational soul that directly contacts these ideas: `<font face="times new roman">`{=html}\"Now among these figures, it is not those imprinted on the external sense organs, or on the internal surface of the brain, which should be taken to be ideas - but only those which are traced in the spirits on the surface of gland H *(where the seat of the imagination and the \'common sense\' is located)*. That is to say, it is only the latter figures which should be taken to be the forms or images which the rational soul united to this machine will consider directly when it imagines some object or perceives it by the senses.\" Descartes (1664)`</font>`{=html} See section on Descartes for more information and references. Descartes considered that the soul was a physical point, an unextended entity that acts like a mind\'s eye. He called this unextended place the *res cogitans* and concluded that it was a substance that differed from that of material things: `<font face="times new roman">`{=html}\".. I thence concluded that I was a substance whose whole essence or nature consists only in thinking, and which, that it may exist, has need of no place, nor is dependent on any material thing; so that \" I,\" that is to say, the mind by which I am what I am, is wholly distinct from the body, and is even more easily known than the latter, and is such, that although the latter were not, it would still continue to be all that it is.\"Descartes (1637)`</font>`{=html} This unextended substance that is not material gives the word \"substance\" a new meaning. It has been attacked as a concept by Locke, Hume, Berkely and many other philosophers. The concept of there being two substances, that which composes the physical world and that which composes the soul, is the origin of the word **Dualism** but dualism, as a concept, has been extended beyond this original meaning. Cartesian dualism is a type of **substance dualism**. Cartesian dualism is an attempt to explain our experience. According to Descartes something supernatural would be needed for an unextended viewing point to exist. Reid\'s **Natural Dualism** also has a point soul looking at things but proposes that the things in question are forms in the world rather than in the brain. ### Property dualism Another sort of dualism has arisen out of a particular interpretation of the regress and homunculus arguments. These arguments show that phenomenal experience is not due entirely to flows from place to place (i.e.: it is not due to classical processes and functions). Property dualism asserts that when matter is organized in the appropriate way (i.e. in the way that living human bodies are organized), mental properties emerge. As Goldman (1993) pointed out, qualitative experience does not seem to be needed in a functional description of a system: `<font face="times new roman">`{=html}\"For any functional description of a system that is in pain (or has an itch), it seems as if we can imagine another system with the same functional description but lacking the qualitative property of painfulness (or itchiness).\" `</font>`{=html} Certainly a functional system that merely reports the words \"I am in pain\" when it is dropped on the floor does not require any qualitative property of painfulness. The *absent qualia* arguments suggest that even in a large system there would be no need for qualitative properties for the performance of any classical function. Chalmers (1993) commenting on Goldman\'s point, said that this implies that **zombies** might exist, functional replicas of humans but without qualia. He then denied that a complete functional replica of a human could exist without also including qualia: `<font face="times new roman">`{=html}\"It seems to me that the only way to avoid this conclusion is to deny that Zombie Dave is a conceptual possibility; and the only principled way to deny that Zombie Dave is a conceptual possibility is to allow that functional organization is conceptually constitutive of qualitative content.\" Chalmers (1993).`</font>`{=html} In other words he identifies qualia with function. According to Chalmers (1996) qualia are a particular type of function: `<font face="times new roman">`{=html}\"I claim that conscious experience arises from fine-grained functional organization. More specifically, I will argue for a principle of organizational invariance, holding that given any system that has conscious experiences, then any system that has the same fine-grained functional organization will have qualitatively identical experiences. According to this principle, consciousness is an organizational invariant: a property that remains constant over all functional isomorphs of a given system. Whether the organization is realized in silicon chips, in the population of China, or in beer cans and ping-pong balls does not matter. As long as the functional organisation is right, conscious experience will be determined.\" p249`</font>`{=html} Chalmers\' idea of functional organisation has within it a sometimes vague implication that the functional units must have a particular form; for instance, in the development of his argument, he refers to "fine grained" replacement of organic functional units with inorganic units. Chalmers is actually making two major points, firstly that qualia occur during the motion of things (functions), secondly that qualia are independent of any particular substrate.\*\* For the first point to be consistent with materialism the qualia must have no effect on the function, they must be **epiphenomenal**. Epiphenomenal qualia would not be forbidden by the regress and homunculus arguments and would be akin to Berkeley\'s \"passive ideas\". Whether or not epiphenomenal qualia are physical depends upon the definition of the word \"physical\". If physical functions cause qualia but qualia cannot affect functions then the qualia are \"physical\" in the sense of being caused by physical events but might be regarded as non-physical in the sense of being isolated from further physical events. In philosophical terms they violate the principle of **Causal Closure**. However, there are other definitions of physicalism based on arguments such as **Methodological Naturalism** which hold that anything that can be investigated using the methods of natural science is a physical thing (see Stoljar 2001). Thus, although epiphenomenal qualia may not conform to materialism they may be encompassed by physicalism; as events that are related to material events they are awaiting a physical theory of how they emerge from a given function. The reader might consider whether phenomenal consciousness is indeed epiphenomenal. Empirical reports describe it as something that is different from the world beyond the body (see direct realism) - could we generate empirical reports of an epiphenomenon? The term **property dualism** describes how physical events might give rise to a set of properties that cannot be predicted from the fine structure of the physical system. The \"dualism\" is present because one set of events is related to two sets of properties, one of which is not related by materialism to the set of events. In the case of the proposal about consciousness outlined above an extra assumption, beyond materialism, would be needed to explain qualia. Property dualism might be defined as a theory that there could be a theory of consciousness but that this requires some new assumption. As far as the \"when and where\" of consciousness are concerned, property dualism states that it is somewhere in the processes performed by the organism and the parts of the organism. `<font size=1>`{=html} \*\* In terms of information processing, Chalmers is proposing that qualia are the enactment of a particular information processing structure.`</font>`{=html} - Block, N. (2006). Max Black\'s objection to mind-body identity. Oxford Review of Metaphysics No.3. <http://philrsss.anu.edu.au/BlockFest/MaxBlack.rtf> - Chalmers, D.J. (1993) Commentary on \"The Psychology of Folk Psychology\". Behavioral and Brain Sciences 16:35-36, 1993 - Chalmers, D.J. (1996) \"The Conscious Mind: In Search of a Fundamental Theory\". Oxford University Press. 1996. - Goldman, A.I., (1993). The Psychology of Folk Psychology. Behavioral and Brain Sciences 16: 15-28 (1993). <http://www.ecs.soton.ac.uk/~harnad/Papers/Py104/goldman.psyc.html> ### Predicate dualism Predicate dualism is the view espoused by most non-reductive physicalists, such as Donald Davidson(1980) and Jerry Fodor(1968), who maintain that while there is only one ontological category of substances and properties of substances (usually physical), the predicates that we use to describe mental events cannot be redescribed in terms of (or reduced to) physical predicates of natural languages. If we characterize predicate monism as the view subscribed to by eliminative materialists, who maintain that such intentional predicates as believe, desire, think, feel, etc., will eventually be eliminated from both the language of science and from ordinary language because the entities to which they refer do not exist, then predicate dualism is most easily defined as the negation of this position. Predicate dualists believe that so-called \"folk psychology\", with all of its propositional attitude ascriptions, is an ineliminable part of the enterprise of describing, explaining and understanding human mental states and behavior. Davidson, for example, subscribes to Anomalous Monism, according to which there can be no strict psycho-physical laws which connect mental and physical events under their descriptions as mental and physical events. However, all mental events also have physical descriptions. It is in terms of the latter that such events can be connected in law-like relations with other physical events. Mental predicates are irreducibly different in character (rational, holistic and necessary) from physical predicates (contingent, atomic and causal). (Section based on Wikipedia article) - Davidson, D (1980). Essays on Actions and Events. Oxford University Press. - Fodor,J. (1968) *Psychological Explanation*, Random House. . ### The interaction between mind and brain in dualism #### Interactionism Interactionism is the view that mental states, such as beliefs and desires, causally interact with physical states. This is a position which is very appealing to common-sense intuitions, notwithstanding the fact that it is very difficult to establish its validity or correctness by way of logical argumentation or empirical proof. It is appealing to common-sense because we are surrounded by such everyday occurrences as a child\'s touching a hot stove (physical event) which causes him to feel pain (mental event) and then yell and scream (physical event) which causes his parents to experience a sensation of fear and protectiveness (mental event) and so on. #### Epiphenomalism According to epiphenomenalism, all mental events are caused by a physical event and have no physical consequences. So, a mental event of deciding to pick up a rock (call it \"M\") is caused by the firing of specific neurons in the brain (call it \"P\"), however when the arm and hand move to pick up a rock (call it \"E\") this is only caused by P. The physical causes are in principle reducible to fundamental physics, and therefore mental causes are eliminated using this reductionist explanation. If P causes M and E, there is no overdetermination in the explanation for E. #### Parallelism Psycho-physical parallelism is a very unusual view about the interaction between mental and physical events which was most prominently, and perhaps only truly, advocated by Gottfried Wilhelm von Leibniz. Like Malebranche and others before him, Leibniz recognized the weaknesses of Descartes\' account of causal interaction taking place in a physical location in the brain. Malebranche decided that such a material basis of interaction between material and immaterial was impossible and therefore formulated his doctrine of occasionalism, stating that the interactions were really caused by the intervention of God on each individual occasion. Leibniz idea is that God has created a pre-established harmony such that it only seems as if physical and mental events cause, and are caused by, one another. In reality, mental causes only have mental effects and physical causes only have physical effects. Hence the term parallelism is used to describe this view. #### Occasionalism Occasionalism argues that bodily events are the occasion of an act by the Creator causing a corresponding mental event, and vice versa. Any such view requires a theological structure as a premise. #### Further reading - Robinson, Howard, \"Dualism\", The Stanford Encyclopedia of Philosophy (Fall 2003 Edition), Edward N. Zalta (ed.), <http://plato.stanford.edu/archives/fall2003/entries/dualism/> - Robinson, H. (2003) \"Dualism\", in S. Stich and T. Warfield (eds) The Blackwell Guide to Philosophy of Mind, Blackwell, Oxford, 85-101. - Amoroso, R.L. (2010) \"The complementarity of Mind and Body: Realizing the Dream of Descartes, Einstein and Eccles\", New York: Nova Science Publishers, `, ``https://www.novapublishers.com/catalog/product_info.php?products_id=12759` ## Idealism According to Idealism only the mental truly exists. The form and content of personal conscious experience might be related to the structure of the world and brain in several ways. It could be a **solipsism** or be the mind of God. *This is a **stub** and needs expansion*. ## Panpsychism ### Etymology Ancient Greek *pan* (πᾶν : \"all, everything, whole\") and *psyche* (ψυχή : \"soul, mind\").[^1] Psyche is the from ψύχω (*psukhō*, \"I blow\") and means mind or \'life-breath\'. Philip Goff, a proponent of panpsychism, carves out a distinction between panexperientialism and pancognitivism. Panexperientialism is the belief that *experience* is ubiquitous, while pancognitivism is the belief that *cognition* is ubiquitous. Most modern purponents of panpsychism, such as Annaka Harris and David Chalmers, are careful to distance themselves from pancognitivism. In some interpretations, such as monadism, Panpsychism and Idealism can overlap because the universe is conceived as being composed of an infinity of point consciousnesses that each contain information about the whole universe. The form and content of personal conscious experience might be related to the structure of the world and brain in many ways. *This is a **stub** and needs expansion*. ## References Seager W. & Allen-Hermanson (2001). 'Panpsychism.' Online document: Stanford Encyclopedia of Philosophy, \[online\], <http://plato.stanford.edu/entries/panpsychism/>, \[accessed 10/2005\] **Supervenience** - Chalmers, D.J. (1996). The Conscious Mind. Oxford University Press. **The problem of regression** - Ryle, G. (1949) The Concept of Mind. The University of Chicago Press, 1949. **The homunculus argument** - Gregory, R.L. (1990) Eye and Brain: The Psychology of Seeing, Oxford University Press Inc. New York. - Gregory, T.L. (1987). The Oxford Companion to Mind. Oxford University Press. **Subject-object paradox** - James, W. (1904)Does \'Consciousness\' Exist? Journal of Philosophy, Psychology, and Scientific Methods, 1, 477-491. - Hegel, G.W.F. PHILOSOPHY OF MIND: SECTION I. MIND SUBJECTIVE B. PHENOMENOLOGY OF MIND CONSCIOUSNESS Part Three of the Encyclopaedia of the Philosophical Sciences - Velmans, M. (1996) Consciousness and the \"Casual Paradox\". Behavioral and Brain Sciences, 19 (3): 538-542. - Bermudez, J.L. (1999) The Paradox of Self-Consciousness (representation and Mind) Psycoloquy: 10,#35 **Ontological status** - Bierman, D.J. (2004) Non Conscious Processes Preceding Intuitive decisions <http://m0134.fmg.uva.nl/~djb/publications/2004/Intuition_bialsymp2004.pdf> - Damasio, A.R. (1994). Descartes\' error: Emotion, reason and the human brain. New York: Grosset/Putnam Book. - Kant, I. Critique of Pure Reason <http://www.arts.cuhk.edu.hk/Philosophy/Kant/cpr/> **Phenomenal consciousness and access consciousness** Block, N. (1995) On a confusion about a function of consciousness. Behavioral and Brain Sciences 18 (2): 227-287. <http://www.bbsonline.org/documents/a/00/00/04/31/bbs00000431-00/bbs.block.html> Block, N. (2004). *The Encyclopedia of Cognitive Science*. <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/ecs.pdf> Dennett, D. (1978). Why You Can\'t Make a Computer that Feels Pain, in: Brainstorms. Cambridge, MA: MIT Press: 190-229. Dennett, D. (1988). Quining Qualia. in A. Marcel and E. Bisiach, eds, Consciousness in Modern Science, Oxford University Press 1988. Reprinted in W. Lycan, ed., Mind and Cognition: A Reader, MIT Press, 1990, A. Goldman, ed. Readings in Philosophy and Cognitive Science, MIT Press, 1993. <http://ase.tufts.edu/cogstud/papers/quinqual.htm> Edelman, G.M. (1993). Bright Air, Brilliant Fire: On the Matter of the Mind. New York: Feyerabend, P. (1963). Mental Events and the Brain, Journal of Philosophy 40:295-6. Huxley, T. H. (1874). On the Hypothesis that Animals are Automata, and its History, The Fortnightly Review, n.s.16:555-580. Reprinted in Method and Results: Essays by Thomas H. Huxley (New York: D. Appleton and Company, 1898). Nagel, T. (1974). What is it like to be a bat? The Philosophical Review LXXXIII, 4 (October 1974): 435-50. <http://web.archive.org/19990218140703/members.aol.com/NeoNoetics/Nagel_Bat.html> Rey, Georges, (1997). Contemporary Philosophy of Mind.Blackwell: Oxford Sellars W. (1956). Empiricism and the Philosophy of Mind, In: Feigl H and Scriven M (eds) The Foundations of Science and the Concepts of Psychology and Psychoanalysis: Minnesota Studies in the Philosophy of Science, Vol. 1. Minneapolis: University of Minnesota Press: 253-329 Whitehead, A.N. (1920). The Concept of Nature. Chapter 3: Time. <http://spartan.ac.brocku.ca/~lward/Whitehead/Whitehead_1920/White1_03.html> **Direct Realism** - Austin, J.L. (1962) Sense and Sensibilia, ed. by Geoffrey J. Warnock (Oxford, 1962) - Aydede, M. (2001) Naturalism, introspection, and direct realism about pain. Consciousness and Emotion, Vol. 2, No. 1, 2001, pp. 29--73. <http://web.clas.ufl.edu/users/maydede/pain.pdf> - Chapman, C.R., and Y. Nakamura (1999). A Passion of the Soul: An Introduction to Pain for Consciousness Researchers. Consciousness and Cognition, 8: 391-422. - Dennett, D. (1991a). Consciousness Explained. Boston: Little, Brown - Dennett, D. (1991b). Lovely and suspect qualities. Commentary on David Rosenthal, \"The Independence of Consciousness and Sensory Quality\" in E. Villanueva, ed., Consciousness, (SOFIA Conference, Buenos Aires), Atascadero, CA: Ridgeview 1991. <http://ase.tufts.edu/cogstud/papers/lovely&s.htm> - Fowler C A (1986): "An event approach to the study of speech perception from a direct-realist perspective", J of Phonetics 14(1):3-28. - Gibson, J. J. (1966) The Senses Considered as Perceptual Systems. Houghton Mifflin Company,Boston. - Gibson, J. J. (1979) Ecological Approach to Visual Perception.: Lawrence Erlbaum Associates Publishers, Hillsdate. - Gregory, R.L. 1988. Consciousness in science and philosophy: conscience and con-science. Chapter 12 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. - Le Morvan, Pierre (2004). Arguments against direct realism and how to counter them. *The American Philosophical Quarterly*, *41*(3), 221-234.\] (pdf) <http://www.tcnj.edu/~lemorvan/DR_web.pdf> - Michaels, C. F. and Carello, C. (1981). Direct Perception. Century Psychology Series. Prentice-Hall. . 1981. Download this book at <http://ione.psy.uconn.edu/~psy254/MC.pdf> - Oliveira, André L. G. and Oliveira, Luis F. (2002) Toward an ecological conception of timbre. In Proceedings Auditory Perception Cognition and Action Meeting 2002, Kansas City. <http://cogprints.org/2713/> - Skinner, B. F. Science and Human Behavior . New York: Macmillan, 1953. - Skinner, B. F. 1971. Beyond Freedom and Dignity. New York: Knopf. - Skinner, B. F. 1948. Walden Two. New York: Macmillan. - Tye, M. (2004). ANOTHER LOOK AT REPRESENTATIONALISM ABOUT PAIN. Consciousness and Emotion 2004, special issue on pain, edited by Murat Aydede (with replies by M. Aydede, N. Block, B. Maund, and P. Noordhof <http://sun.soci.niu.edu/~phildept/MT/RepresentationalismAndPain.pdf> - Vygotsky, L.S.(1925) Consciousness as a problem in the psychology of behavior. Undiscovered Vygotsky: Etudes on the pre-history of cultural-historical psychology (European Studies in the History of Science and Ideas. Vol. 8), pp. 251--281. Peter Lang Publishing. <http://www.marxists.org/archive/vygotsky/works/1925/consciousness.htm> - Ziff, Paul. \"About Behaviourism.\" Analysis 18 (1958): 132-136. Quoted by Larry Hauser in the Internet Encyclopedia of Philosophy. <http://www.utm.edu/research/iep/b/behavior.htm#B>. F. Skinner: Radical Behaviorism **Indirect Realism** - Moutoussis, K. and Zeki, S. (1997). A direct demonstration of perceptual asynchrony in vision. Proceedings of the Royal Society of London, Series B: Biological Sciences, 264, 393 - 399. - Rizzo, M., Nawrot, M. & Zihl, J. (1995). Motion and shape perception in cerebral akinetopsia.Brain, 118. 1105-1127. <http://nawrot.psych.ndsu.nodak.edu/Publications/Nawrot.pdf/RizzoNawrotZihl.1995.pdf> - Russell, B. (1912). Problems of Philosophy. Home University Library. <http://www.ditext.com/russell/rus1.html> - Tye, M. (2003) Qualia. Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/qualia/#Repqualia> Further reading: - Hume, D. (1739). A Treatise of Human Nature. <http://www.class.uidaho.edu/mickelsen/ToC/hume%20treatise%20ToC.htm> - Firth, R. (1949) Sense Data and the Percept Theory, Mind, 58 (1949); 59 (1950). (Describes early reasons for rejecting Indirect Realism) <http://www.ditext.com/firth/spt.html> - Grush, R. (2000). Self, world and space: The meaning and mechanisms of ego- and allocentric spatial representation. Brain and Mind 1(1):59-92. <http://mind.ucsd.edu/papers/sws/sws.html> [^1]: Clarke, D.S. *Panpsychism: Past and Recent Selected Readings*. State University of New York Press, 2004. p.1

# Consciousness Studies/The Conflict2#Dualism *This part of this section is about the where and when of the experience called consciousness. Is it in the world, in the brain or are the world and brain within it?* ## Phenomenal consciousness and access consciousness Block(1995) drew attention to the way that there appear to be two types of consciousness: *phenomenal* consciousness and *access* consciousness: `Phenomenal consciousness is experience; the phenomenally`\ `conscious  aspect of a state is what it is like to be in that`\ `state. The mark of access-consciousness, by contrast, is `\ `availability for use in reasoning and rationally guiding speech `\ `and action. (Block 1995).` *See the section on Ned Block\'s ideas for a deeper coverage of his approach to access and phenomenal consciousness.* Block uses Nagel\'s famous (1974) paper, \"What is it like to be a bat?\" as an exemplary description of phenomenal consciousness. Excellent descriptions have also been proffered by the empiricist philosophers who gave lengthy descriptions of consciousness as partly experience itself. Although Block has formalised the idea of phenomenal and access consciousness similar ideas have also been put forward by many philosophers including Kant and Whitehead. Access consciousness has two interpretations, in the first, used by Block, it applies to the functions that appear to operate on phenomenal consciousness. In the second, used by the behaviourists and eliminativists, it is some property of the functions of the brain that can be called \'consciousness\'. This division between phenomenal and functional aspects of consciousness is useful because it emphasises the idea of phenomenal consciousness as observation rather than action. Some philosophers such as Huxley in 1874, have taken the view that because phenomenal consciousness appears to have no function it is of no importance or cannot exist. James (1879) introduced the term \"epiphenomenalism\" to summarise the idea that consciousness has no function. The idea that phenomenal consciousness cannot exist is a type of *Eliminativism* (also known as Eliminative Materialism). Eliminativism owes much to the work of Sellars(1956) and Feyerbend (1963). Dennett (1978) applied Eliminativism to phenomenal consciousness and denies that pain is real. Others such as Rey(1997) have also applied eliminativism to phenomenal consciousness. Dennett (1988) redefines consciousness in terms of access consciousness alone, he argues that \"Everything real has properties, and since I don\'t deny the reality of conscious experience, I grant that conscious experience has properties\". Having related all consciousness to properties he then declares that these properties are actually judgements of properties. He considers judgements of the properties of consciousness to be identical to the properties themselves. He writes: `<font face="times">`{=html}\"The infallibilist line on qualia treats them as properties of one\'s experience one cannot in principle misdiscover, and this is a mysterious doctrine (at least as mysterious as papal infallibility) unless we shift the emphasis a little and treat qualia as logical constructs out of subjects\' qualia-judgments: a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F. \"`</font>`{=html} Having identified \"properties\" with \"judgement of properties\" he can then show that the judgements are insubstantial, hence the properties are insubstantial and hence the qualia are insubstantial or even non-existent. Dennett concludes that qualia can be rejected as non-existent: `<font face="times">`{=html}\"So when we look one last time at our original characterization of qualia, as ineffable, intrinsic, private, directly apprehensible properties of experience, we find that there is nothing to fill the bill. In their place are relatively or practically ineffable public properties we can refer to indirectly via reference to our private property-detectors\-- private only in the sense of idiosyncratic. And insofar as we wish to cling to our subjective authority about the occurrence within us of states of certain types or with certain properties, we can have some authority\--not infallibility or incorrigibility, but something better than sheer guessing\--but only if we restrict ourselves to relational, extrinsic properties like the power of certain internal states of ours to provoke acts of apparent re- identification. So contrary to what seems obvious at first blush, there simply are no qualia at all. \" (Dennett 1988)`</font>`{=html} Dennett\'s asserts that \"a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F\". This is a statement of the belief that qualia are the same as processes such as judgements. Processes such as judgements are flows of data where one state examines a previous state in a succession over time and embody what Whitehead called the \"materialist\" concept of time. Dennett does not consider how a scientific concept of time might affect his argument. Dennett\'s argument has been persuasive and there are now many philosophers and neuroscientists who believe that the problem of phenomenal consciousness does not exist. This means that, to them, what we call \'consciousness\' can only be a property of the functions performed by the brain and body. According to these philosophers only access consciousness exists. Those who support the idea of phenomenal consciousness also tend to frame it in terms of nineteenth century theory where one state examines a previous state in a succession over time, for instance Edelman(1993) places the past in memories at an instant and time within experience is explained as continuing modelling processes: `<font face="times">`{=html}\"Primary consciousness is the state of being mentally aware of things in the world\--of having mental images in the present. But it is not accompanied by any sense of a person with a past and a future\.... In contrast, higher-order consciousness involves the recognition by a thinking subject of his or her own acts or affections. It embodies a model of the personal, and of the past and the future as well as the present. It exhibits direct awareness\--the noninferential or immediate awareness of mental episodes without the involvement of sense organs or receptors. It is what we humans have in addition to primary consciousness. We are conscious of being conscious.\" `</font>`{=html} Block(2004) also suggests this flow from state to state in his idea of \"Reflexivity\" where our idea of familiarity with an object is due to one state being analysed by another: `<font face="times">`{=html}\"Thus in the "conscious" case, the subject must have a state that is about the subject's own perceptual experience (looking familiar) and thus conscious in what might be termed a "reflexive" sense. An experience is conscious in this sense just in case it is the object of another of the subject's states; for example, one has a thought to the effect that one has that experience. The reflexive sense of \'consciousness\' contrasts with phenomenality, which perhaps attaches to some states which are not the objects of other mental states. Reflexive consciousness might better be called 'awareness' than 'consciousness'. Reflexivity is phenomenality plus something else (reflection) and that opens up the possibility in principle for phenomenality without reflection. For example, it is at least conceptually possible for there to be two people in pain, one of whom is introspecting the pain the other not. (Perhaps infants or animals can have pain but don't introspect it.) The first is reflexively conscious of the pain, but both have phenomenally conscious states, since pain is by its very nature a phenomenally conscious state. \"`</font>`{=html} Both Block and Edelman allow phenomenal consciousness, our experience, as an unexplained phenomenon. Block, Edelman and also Dennett\'s ideas of consciousness are shown in the illustration below:  This model differs from the empirical reports of phenomenal consciousness that were considered earlier. According to the empirical reports the present moment in our experience is extended so the succession of outputs or stages of access consciousness could constitute the contents of phenomenal consciousness. In other words phenomenal consciousness is composed of periods of access consciousness. This is how it seems to the empiricist and in our own experience but how such a state could be explained in terms of brain activity is highly problematical. Given that nineteenth century ideas cannot explain such a state a scientific explanation will be required. The idea that phenomenal consciousness misrepresents or \"misdiscovers\" itself (Dennett 1988) deserves further discussion. According to materialism the present instant has no duration so can only be known in succeeding instants as a report or memory and this could be wrong. Whitehead considered that this viewpoint originates in an archaic view of science, particularly the concept of time in science: \"The eighteenth and nineteenth centuries accepted as their natural philosophy a certain circle of concepts which were as rigid and definite as those of the philosophy of the middle ages, and were accepted with as little critical research. I will call this natural philosophy \'materialism.\' Not only were men of science materialists, but also adherents of all schools of philosophy. The idealists only differed from the philosophic materialists on question of the alignment of nature in reference to mind. But no one had any doubt that the philosophy of nature considered in itself was of the type which I have called materialism. It is the philosophy which I have already examined in my two lectures of this course preceding the present one. It can be summarised as the belief that nature is an aggregate of material and that this material exists in some sense at each successive member of a one-dimensional series of extensionless instants of time. Furthermore the mutual relations of the material entities at each instant formed these entities into a spatial configuration in an unbounded space. It would seem that space\-\--on this theory-would be as instantaneous as the instants, and that some explanation is required of the relations between the successive instantaneous spaces. The materialistic theory is however silent on this point; and the succession of instantaneous spaces is tacitly combined into one persistent space. This theory is a purely intellectual rendering of experience which has had the luck to get itself formulated at the dawn of scientific thought. It has dominated the language and the imagination of science since science flourished in Alexandria, with the result that it is now hardly possible to speak without appearing to assume its immediate obviousness.\" (Whitehead 1920). ## Direct Realism and Direct Perception Direct Realism proposes that phenomenal experience is directly objects in the world without any intervening representation. It is motivated by the belief that the Problem of Regression, the Subject-Object Paradox and the recursion form of the Homunculus arguments show that phenomenal consciousness cannot occur in the brain alone. Direct Realists reason that if phenomenal consciousness cannot be things in the brain then it must be something outside the brain. There are two principle types of Direct Realism: Natural Dualism and Behaviourism (both Radical and Analytical). Some behaviourists use the term "Direct Perception" rather than Direct Realism and consider that only the invariant parts of perception are direct (see for instance Michaels and Carello 1981). Thomas Reid is generally regarded as the founder of Direct Realism. In his Natural Dualism he proposed that the soul is in direct contact with the contents of experience and these contents are things in the world beyond the body. The Direct Realism of Reid is summarised in the statement of his famous disciple Sir William Hamilton: \"In the simplest act of perception I am conscious of myself as the perceiving subject and of an external reality as the object perceived\". Reid\'s Natural Dualism has now been largely replaced by radical and analytical behaviourism which eschew the idea of a soul and propose that phenomenal consciousness, if it exists at all, is a behavioural reflex. The modern justification of Direct Realism mainly consists of arguments against Indirect Realism or Representationalism. Philosophers such as Austin (1962) and Le Morvan (2004) have summarised the Direct Realism debate and have identified the following arguments in favour of Indirect Realism and given rebuttals to each of them: 1\. The Causal Argument: perception involves a succession of causal events such as the reflection of photons, bleaching of retinal pigments etc. so perception must involve the end of this causal chain. The Direct Realist response is that, although there may be a causal chain in sensation this does not inevitably imply that the end of the chain is the content of phenomenal experience. 2\. The Time Lag Argument: it takes time for light to travel from an object to the senses, time for chemical changes in the retina etc\... The Direct Realist response is that direct perception may be referred back in time. 3\. The Partial Character of Perception Argument: we only perceive the surface of objects, and then only a part of the surface. As the whole object would be perceived directly perception must be indirect. The Direct Realist response is that direct perception could occur even if only parts of an object were perceived. 4\. The Perceptual Relativity Argument: things appear to be different shapes depending upon the point of view. The Direct Realist response is that if perception can occur backwards in time it should have no problem occurring back down a line of sight. However, Le Morvan\'s argument does not seem to encompass the geometrical nature of phenomenal experience, seeking to explain geometry in terms of movement. 5\. The Argument from Perceptual Illusion: A stick may appear bent when projecting from the surface of water. Direct Realists apply the argument used in (4) to this problem. The bent stick illusion is a physical event in the world beyond the eye rather than a normal optical illusion such as the Muller-Lyer illusion etc., see (6) for a discussion of optical illusions. 6\. The Argument from Hallucination: Hallucinations are not in the world beyond the body. This is highly problematical for Direct Realists especially when phenomena such as lucid dreams, dreams and visual imaginations are included along with hallucinations. Direct Realists classify these phenomena as not being perceptions or deny that they actually exist as phenomena. Indirect Realists would maintain that all of perception is a reconstruction and use optical illusions such as the Muller-Lyer, Ames Room etc. to justify this contention so the Direct Realist approach to hallucination, dreams etc. might seem like an unwillingness to accept Indirect Realism rather than an argument. 7\. The Dubitability Argument (cf: Indubitability argument): we cannot doubt current phenomenal experience but we can doubt the world beyond the body therefore phenomenal experience is not the world beyond the body. Direct Realists fall back on Presentism or functional Presentism to defeat this argument. If phenomenal experience is instantaneous and made anew at each instant then anything can be doubted. The points above have summarised the Direct Realist stance on visual perception. Other sensory modalities have also been considered in the Direct Realism debate. Fowler (1986) considered that sounds were attached to objects in the world. This idea is strange because sounds only seem to be closely attached to objects in the world when these objects are seen as well as heard. For example, when a subject is blindfolded it is found that there can be a large error in locating the position of a sound in the world, this is especially true for low frequency sounds. The Direct Realist approach has difficulty explaining the transition from sounds with an indefinite location when a subject is blindfolded to sounds that are bound to visual events when the blindfold is removed. It also runs into problems explaining how the sound of speech from a single loudspeaker can become bound to lip movements on a cinema screen. If the binding does not occur in the brain then where does it occur? Pain is particularly problematic for Direct Realism because, unlike colour vision where \'red\' is inferred to be a property of electrons or light, pain is an inner experience that is not a property of tissue damage. Tissue damage has properties such as bleeding, wheal formation etc. but pain seems to be phenomenal experience in the brain and \'phantom pain\' can occur without tissue damage (see Aydede (2001), Tye (2004) and Chapman, and Nakamura (1999) for further analysis). On closer inspection other sensations also appear to be inner experiences rather than direct sensations. For instance, the red crosses of different hues in the illustration below are all due to the same physical wavelengths of light. In this case the range of hues in experience is unrelated to the actual physical red on the page or screen. Another problem for Direct Realism is that it does not overcome the problems that it is supposed to solve. The argument for Direct Realism begins with the idea that there are severe problems with representationalism (the idea that phenomenal experience is in the brain) and that direct perception is an alternative that does not have these problems. However on closer inspection Direct Realism suffers from almost same problems as representationalism. If phenomenal experience is the world itself then Ryle\'s regress applies to the world itself and this can only be avoided by assuming that phenomenal experience is a subset of the world (i.e.: a representation) that receives input from other parts of the world that are not part of phenomenal experience. It is also commonly assumed that Direct Realism avoids the recursion argument because it is believed that the separation of the observer from the things that are observed is simply due to the geometry of the world. If such simple geometry is possible between the eye and the world then it should also be possible in the brain and a similar geometrical explanation could be invoked to avoid recursion in representations. These points are shown in the illustration below: image:Constuddir1.gif Scientists have a further problem with Direct Realism. The illustration below demonstrates that our scientific knowledge of the world differs markedly from our phenomenal experience. image:constuddirect.gif It is difficult to see how the form and content of phenomenal experience could supervene directly on the world beyond the body. The world inferred from measurements beyond the body seems to be a nebulous set of quantum phenomena that are arranged as probability fields in three dimensions at any instant. The objects in this real world are mostly space. The world of phenomenal experience on the other hand contains objects that are one-sided, and are like a 2 dimensional field of vectors directed simultaneously at an observation point which is apparently separate from them. Phenomenal experience is not three dimensional, the rear of objects is not available within it at any instant. Visual phenomenal experience seems to be a geometrical relationship between an abstract observation point and the reflection properties of the part of the world external to the body. It is a form that crudely overlies the angular separations in inferred reality, providing approximate directional data. It is not like things in themselves beyond the body, not even in type, being a set of directional vectors. (See the module on the neuroscience of perception for a discussion of depth perception). If the form and content of visual phenomenal experience are abstractions separated according to the angular positions of things in the world beyond the body then theories which propose that phenomenal experience is the world itself are problematical. It should be noted that things arranged according to angular positions can appear to overlie any group of similar things along a radius from the centre point.  If Direct Realists admit that things are as they appear to be, observed according to angular positions at a \'point eye\', then any representation of things on the inside of a sphere of any radius would appear similar. The geometry of the \'point eye\' is problematical whether the view contains the world itself or a representation of the world; it cannot be the movements of lumps of matter or energy and the point observation cannot be due to lumps all landing at a point. In other words the \'view\' is inconsistent with nineteenth century materialism and will require a scientific explanation. Radical and Analytical Behaviourism tackle the problem of the difference between the world inferred from measurements beyond the body and the phenomenal world by denying phenomenal consciousness and maintaining that access and reflex consciousness are all that exists or is necessary. Radical Behaviourism is an offshoot of psychological behaviourism and was established as a philosophical adjunct to Marxism by Vygotsky and popularised by Burrhus Frederic Skinner (see Skinner 1953). There is another movement in psychological behaviourism which is similar to Radical Behaviourism called Ecological Psychology (see Gibson 1966, 1979 and also Michaels and Carello 1981). Analytical Behaviourism is a philosophical movement established by Gilbert Ryle (see Ryle 1949). The core of Analytical and Radical Behaviourism is the assumption that consciousness exists for a durationless instant so that the Dubitability Argument and the Regression and Recursion Arguments can be applied (Ryle 1949, Skinner 1971 and see the sections on Ryle\'s Regress and the Subject-Object Paradox above). As a result the Direct Realist is able to insinuate that subjects only think that they have had a particular experience (cf: Dennett 1991a). It is intriguing that Eliminativists also maintain that experience is the world itself, for instance an insight into Dennett\'s idea of the mind is to be found on pages 407-408 of Consciousness Explained: \"It seemed to him, according to the text, as if his mind - his visual field - were filled with intricate details of gold-green buds an wiggling branches, but although this is how it seemed this was an illusion. No such \"plenum\" ever came into his mind; the plenum remained out in the world where it is didn\'t have to be represented, but could just be. When we marvel, in those moments of heightened self-consciousness, at the glorious richness of our conscious experience, the richness we marvel at is actually the richness of the world outside, in all its ravishing detail. It does not \"enter\" our conscious minds, but is simply available\" This is a clear description of Direct Realism (although Dennett does not describe himself as a direct realist). Radical Behaviourism is sometimes described as the dictum that the only psychological events that are of importance are those that occur outside the head. The absurdity of this has led to jokes: Q: What does one behaviorist say to another when they meet on the street? A: You\'re fine. How am I? Q: What does one behaviorist say to another after sex? A: That was great for you. How was it for me? (Ziff 1958) However Vygotsky, Skinner and other Radical Behaviourists hold that inner behaviour is possible so that events within the brain can result in reward or punishment. Vygotsky (1925) describes this approach: \"Consciousness is wholly reduced to the transmitting mechanisms of reflexes operating according to general laws, i.e., no processes other than reactions can be admitted into the organism. The way is also paved for the solution of the problem of self-awareness and self-observation. Inner perception and introspection are possible only thanks to the existence of a proprioceptive field and secondary reflexes, which are connected with it. This is always the echo of a reaction.\" Hence Radical Behaviourists are able to make the claim that what are believed to be representations with phenomenal content are processes. Even events such as pain can then be explained as reflexes involving organs within the skin. However, by opening the possibility that such reflexes could occur at any sense organ, including the eye, this makes Radical Behaviourism a mixed Direct Realist/Indirect Realist philosophy with consciousness as a process, not a separate thing such as phenomenal consciousness (see the section on representationalism and intentionality below). But this raises a serious issue for science: can the phenomenal consciousness that seems to contain our observations really be argued out of existence on the basis of a theory? As Gregory (1988) put it: " 'If you can't explain it -- deny it' is one strategy for dealing with embarrassing questions such as 'what is consciousness?' ". But is this the right strategy? Direct Realism fails to overcome the problems of regression and recursion inherent in representations. It proposes that phenomenal consciousness is identical to the physical world beyond the body but must then use a plethora of arguments to explain why this is evidently not so. When confronted with these problems its proponents resort to the argument that everything can be doubted and can misrepresent itself. Yet it is still widely believed. It should be noted that Direct Realism is espoused in Religious Natural Dualism, some forms of Augustinian theology, nineteenth century materialism and its offspring such as Marxism, post-modernism, post-Marxism, and various sociological movements. It is also necessary for some forms of Strong AI to occur. Perhaps this explains why few ideas have attracted as much attention and defence as Direct Realism. It is interesting to compare the Direct Realist and Indirect Realist interpretations of something as simple as a cartoon on television (such as the image below). According to Indirect Realism the cartoon would be a moving representation constructed in the brain using data from the senses. This leads to the prediction of brain mechanisms for modelling motions, combining colours, binding sound and vision etc., many of which have been verified. Can you demonstrate how the theory of Direct Realism could explain the phenomenal experience that contains the cartoon and produce a list of the predictions made by the theory?  In science a theory should be of predictive value, for instance, information theory describes how the state of a thing can be impressed on a carrier so that a signal can be transmitted from one place to another. This theory predicts what will happen when the signal arrives at its destination and how the state of the source can be inferred from the events at the destination, the total amount of information that can be transmitted etc. At the destination it is the form of the signal that is directly known by interaction and measurement, the form of the source is inferred. Direct Realism is a direct challenge to this information theory but does it deliver a more powerful predictive description of phenomenal consciousness or is experience always dependent on what happens to the information flow between things in the world and somewhere in the brain? Does direct realism have a physical theory? Ultimately it appears as if Direct Realism is about various understandings of Information Theory. For example, Austin (1962) discusses what we see when we see a church camouflaged as a barn and comments that: \"We see, of course, a church that now looks like a barn.\". Do we see a church or a barn? Scientific information theory is clear about this, the church is an entity composed of selected information from the quantum state of its constituents, the optical image of a camouflaged church is an arrangement of photons emanating from a screen on which it is projected, the retina has an arrangement of chemical and electrical events based on an optical image and conscious visual experience correlates with the arrangement of things on the retina. The fact that conscious experience also correlates with classifications of the retinal image as a barn or a church suggests that conscious experience is an arrangement of things in the brain based on both the retinal arrangement and the contents of a relational database. Austin\'s arguments have been mythologised as a final demonstration that \"sense data\" theories are false. However, as will be seen below, sense data theories merely claim that there is a succession of information states between an information state outside the body and that reported as conscious experience i.e.: subjects report that a church is camouflaged when it is camouflaged. ## Indirect Realism Indirect realism proposes that phenomenal consciousness exists and is a set of signals or **sense data**, usually in the brain. This was proposed by philosophers from Aristotle to Locke and was probably the most widespread idea of conscious experience until the eighteenth century. The idea of sense data is discussed in depth by Russell (1912). Russell\'s original definition is given below: `<font face="times new roman">`{=html}\"Let us give the name of \'sense-data\' to the things that are immediately known in sensation: such things as colours, sounds, smells, hardnesses, roughnesses, and so on. We shall give the name \'sensation\' to the experience of being immediately aware of these things. Thus, whenever we see a colour, we have a sensation of the colour, but the colour itself is a sense-datum, not a sensation. The colour is that of which we are immediately aware, and the awareness itself is the sensation. It is plain that if we are to know anything about the table, it must be by means of the sense-data \-- brown colour, oblong shape, smoothness, etc. \-- which we associate with the table; but, for the reasons which have been given, we cannot say that the table is the sense-data, or even that the sense-data are directly properties of the table.\"`</font>`{=html} Russell\'s definition is a materialist concept in which experience is always **of** something because the durationless instant of the present has always gone. As such it differs from some empiricist ideas where experience is not confined to the durationless instant. Science is Indirect Realist because it holds that the scientist can only make **measurements** of events in the world. These measurements give rise to signals as a result of interaction with the event. According to **decoherence theory** the signals are a state that is a mixture of the state of the measuring instrument and the state of the thing being measured. For example, the eyes are measuring instruments that are sensitive to photons, photons are signals containing a state that is based on the state of electrons in a surface and the state of electrons is based on the state of the surface etc. Scientific inference allows some aspects of the state of the surface to be inferred from the state of the photons. In modern Indirect Realism there is an attempt to distinguish the phenomenal content of conscious experience from the processing involved in accessing this phenomenal content. According to these theories phenomenal experience is an arrangement of signals that are the content of the experience. This arrangement forms a *representation* of things in the world so this form of indirect realism is known as **Representationalism**. Tye (2003) describes types of representationalist theory: `<font face="times new roman">`{=html}\"Representationalism, as I have presented it so far, is an identity thesis with respect to qualia: qualia are supposedly one and the same as certain representational contents.\"`</font>`{=html} Tye also describes variants of this idea of representationalism: `<font face="times new roman">`{=html}\"Sometimes it is held instead that qualia are one and the same as certain representational properties of experiences; and sometimes it is is argued that these representational properties are themselves irreducible (Siewert 1998). There is also a weaker version of representationalism, according to which it is metaphysically necessary that experiences exactly alike with respect to their representational contents are exactly alike with respect to their qualia. Obviously, this supervenience thesis leaves open the further question as to the essential nature of qualia.\"`</font>`{=html} (Tye 2003). In a scientific sense Direct Realists believe that phenomenal experience is the signals that occur next to things in the world beyond the body (which they call \"things in themselves\") and Indirect Realists usually believe that phenomenal experience is signals in the brain. It can be seen from the pattern of signal flow that the signals travelling into the brain preserve the spatial relationships of the original signals and encode the properties in the original signals. This means that the original signals next to the QM sources and the signals in the brain are equivalent provided the latter are oriented appropriately relative to signals from the body. Either set of signals could transmit or contain the same information. Both Direct and Indirect Realism cannot, at present, explain the physics of how a viewing point occurs in experience i.e.: how we seem to see through an apparent space to the signals that are the contents of experience. So the choice between Direct Realism and Indirect Realism reduces to whether there is only one set of signals or a chain of signals between the world and phenomenal experience. The philosophical arguments for Indirect Realism are listed below: 1\. Variable perspective: when we see things the view changes so what we see must be a different set of signals depending on the view rather than a constant object. 2\. Illusions: we can see through fingers and see a variety of colours where measurements tell us one exists. Direct Realists quote the \"bent stick illusion\", which is not really an illusion at all, being a physical event. 3\. Hallucinations: two people can have phenomenal experience containing a table. The first may be viewing a real table whereas the second may be hallucinating a table. If the tables are the same (phenomenally) then experience is indirect. 4\. Double vision: press the side of one eye, two images appear (cf Hume 1739) yet there are not two things in the world. 5\. Time gap arguments: according to materialism the past has gone. The things being seen no longer exist in the state that relates to the state in experience. In the extreme case, some stars in the night sky no longer exist but are still in experience so experience must be a derived signal. 6\. Secondary qualities such as pain, colour and smell do not exist as physical things in the source of signals and are likely to be properties of signals in the brain.  Indirect Realism has received strong support from recent discoveries in neuroscience, for example, it is now clear that both the colour and motion in phenomenal experience are added by cortical processes. In Cerebral **Achromatopsia** patients have suffered trauma to area V4 of the cerebral cortex and report seeing the world in greyscale with no colour vision and in Congenital Achromatopsia people do not even understand the meaning of \'colour\'. In an astonishing ailment called **Akinetopsia** patients perceive movement as a succession of stationary images (Rizzo *et al.* 1995). Akinetopsia is usually associated with damage to cortical area V5. Moutoussis and Zeki (1997) have demonstrated that the addition of colour occurs more rapidly than the addition of motion. The section on the Neuroscience of Consciousness describes these discoveries and many other aspects of the creation of phenomenal experience in the brain. Unfortunately knowledge of the whereabouts of the signals that are the content of conscious experience does not resolve the problem of phenomenal consciousness. Whether these signals are next to objects in the world or at the end of a chain of signals in the brain there still remains the problem of how they become arranged in the form of experience. If such a thing occurs at all. ### Intentionality and representation There is a materialist interpretation of representationalism in which representations are redefined as intentional states: `<font face="times new roman">`{=html}\"One way of explaining what is meant by 'intentionality' in the (more obscure) philosophical sense is this: it is that aspect of mental states or events that consists in their being of or about things (as pertains to the questions, 'What are you thinking of?' and 'What are you thinking about?'). Intentionality is the aboutness or directedness of mind (or states of mind) to things, objects, states of affairs, events. So if you are thinking about San Francisco, or about the increased cost of living there, or about your meeting someone there at Union Square---your mind, your thinking, is directed toward San Francisco, or the increased cost of living, or the meeting in Union Square. To think at all is to think of or about something in this sense. This 'directedness' conception of intentionality plays a prominent role in the influential philosophical writings of Franz Brentano and those whose views developed in response to his (to be discussed further in Section 3).\"(Siewert 2003)`</font>`{=html} This definition allows \"representation\" to be redefined as a data stream rather than a set of things arranged in some mental or neural state that represents things in space. Husserl thought this approach would allow a description of consciousness that \"carefully abstains from affirming the existence of anything in spatio-temporal reality\" (Siewert 2003) although it could be argued that a data stream such as any description can never escape the constraints of representation in time at some place. Unfortunately the concept of \"intentionality\" has become so diverse that it could be applied to almost any aspect of the description of consciousness. An interesting example of this is given by Loar (2001) where \"intentionality\" is considered to overlap \"representing\" and \"conceiving\": `<font face="times new roman">`{=html}\"A person\'s thoughts represent things to her \-- conceive things \-- in many ways: perceptually, memory-wise, descriptively, by naming, by analogy, by intuitive sorting, theoretically, abstractly, implicitly and explicitly. These various manners of conceiving have something in common: they have intentional properties, and they have them essentially. `</font>`{=html} The usage of the term \"intentional state\" has become so broad that it now means little more than a state that is about another state. References Siewert, C. (2003). Consciousness and Intentionality. The Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/consciousness-intentionality/> Also see Loar, B. (2001) "Phenomenal Intentionality as the Basis of Mental Content", in Reflections and Replies, ed. M. Hahn and B. Ramsberg, MIT. <http://www.nyu.edu/gsas/dept/philo/courses/concepts/loar.html> Williford, K. (2002) The intentionality of consciousness and the consciousness of intentionality. Intentionality: Past and Future, edited by Gábor Forrai and George Kampis, Amsterdam/New York: Rodopi. <http://web.stcloudstate.edu/kwwilliford/Intentionality%20of%20Consciousness.pdf> Byrne, A. (2001). Intentionalism Defended. Philosophical Review 110 (April 2001):199-240. <http://stripe.colorado.edu/~leeds/byrne.pdf> ### Cartesian materialism The term \"Cartesian materialism\" once meant the idea that the mind is in the brain (see for instance Block 1995). The term had largely fallen out of use in philosophy until revived by Daniel Dennett (1991) in the book *Consciousness Explained*. Dennett uses a very particular definition of the term in his discussions and also uses a particular definition of the word \"mind\". See the section on Daniel Dennett for Dennett\'s critique. Philosophers who adhere to the idea that the mind is in the brain tend to call themselves \"indirect realists\" or \"representationalists\" where the substrate of conscious experience is in the brain and would deny that Dennett\'s critique applies to their proposals. Dennett\'s critique makes the materialist assumption that if there is a representation in the brain then a further flow of material out of this representation would be required for the representation to become part of mind. ### Identity theories of mind The idea that mental states are brain states is known as the **identity theory of mind**. There are two sorts of identity theory, in **type** identity theory it is held that mental states are identical to brain states whereas in **token** identity theory it is held that mental states correlate with brain states. Type identity theory was attacked by Putnam in \"The Nature of Mental States\" where he pointed out that if mental states are functions then type identity theory would presuppose that animals that had the same mental states would need to have identical brain structures. He suggested that this is unlikely, it being more probable that animals have functional systems that perform similar overall functions but which are not identical. In other words, if it is assumed that conscious experience is a set of functions then token identity theory is more probable than type identity theory. Putnam\'s critique does not preclude identity theories of mind that involve \"passive ideas\" (i.e.: states that are not classical functions). Most identity theories of mind would be representational, the physical states representing the world in some way. All identity theories of mind involve Cartesian materialism in the sense of the mental states being brain states. According to identity theories the mind is in the brain. Putnam, H. (1967) The nature of mental states. In The Nature of Mind, edited by Rosenthal, pp. 197--203. Originally published as \"Psychological predicates in Art, Mind, and Religion\", edited by Capitan and Merill, pp. 37--48. ## Dualism Prior to considering the arguments surrounding dualism it is important to have a clear idea of \"information\" because many of these arguments have parallels with the difference between information as a set of states that can be transmitted and the substrate on which this information is expressed or from which the information is derived. See Elementary information and information systems theory. ### Cartesian dualism Descartes, a philosopher, analysed his experience and developed an empirical description of how it is arranged. He described mental images and perceptions as extended in space and with a duration. He called these extended things **ideas** (Cartesian ideas) and proposed that they are patterns in the brain. Descartes thought the pineal gland was the most likely location for these ideas because it is one of the few single organs in the brain. He also proposed that there is a rational soul that directly contacts these ideas: `<font face="times new roman">`{=html}\"Now among these figures, it is not those imprinted on the external sense organs, or on the internal surface of the brain, which should be taken to be ideas - but only those which are traced in the spirits on the surface of gland H *(where the seat of the imagination and the \'common sense\' is located)*. That is to say, it is only the latter figures which should be taken to be the forms or images which the rational soul united to this machine will consider directly when it imagines some object or perceives it by the senses.\" Descartes (1664)`</font>`{=html} See section on Descartes for more information and references. Descartes considered that the soul was a physical point, an unextended entity that acts like a mind\'s eye. He called this unextended place the *res cogitans* and concluded that it was a substance that differed from that of material things: `<font face="times new roman">`{=html}\".. I thence concluded that I was a substance whose whole essence or nature consists only in thinking, and which, that it may exist, has need of no place, nor is dependent on any material thing; so that \" I,\" that is to say, the mind by which I am what I am, is wholly distinct from the body, and is even more easily known than the latter, and is such, that although the latter were not, it would still continue to be all that it is.\"Descartes (1637)`</font>`{=html} This unextended substance that is not material gives the word \"substance\" a new meaning. It has been attacked as a concept by Locke, Hume, Berkely and many other philosophers. The concept of there being two substances, that which composes the physical world and that which composes the soul, is the origin of the word **Dualism** but dualism, as a concept, has been extended beyond this original meaning. Cartesian dualism is a type of **substance dualism**. Cartesian dualism is an attempt to explain our experience. According to Descartes something supernatural would be needed for an unextended viewing point to exist. Reid\'s **Natural Dualism** also has a point soul looking at things but proposes that the things in question are forms in the world rather than in the brain. ### Property dualism Another sort of dualism has arisen out of a particular interpretation of the regress and homunculus arguments. These arguments show that phenomenal experience is not due entirely to flows from place to place (i.e.: it is not due to classical processes and functions). Property dualism asserts that when matter is organized in the appropriate way (i.e. in the way that living human bodies are organized), mental properties emerge. As Goldman (1993) pointed out, qualitative experience does not seem to be needed in a functional description of a system: `<font face="times new roman">`{=html}\"For any functional description of a system that is in pain (or has an itch), it seems as if we can imagine another system with the same functional description but lacking the qualitative property of painfulness (or itchiness).\" `</font>`{=html} Certainly a functional system that merely reports the words \"I am in pain\" when it is dropped on the floor does not require any qualitative property of painfulness. The *absent qualia* arguments suggest that even in a large system there would be no need for qualitative properties for the performance of any classical function. Chalmers (1993) commenting on Goldman\'s point, said that this implies that **zombies** might exist, functional replicas of humans but without qualia. He then denied that a complete functional replica of a human could exist without also including qualia: `<font face="times new roman">`{=html}\"It seems to me that the only way to avoid this conclusion is to deny that Zombie Dave is a conceptual possibility; and the only principled way to deny that Zombie Dave is a conceptual possibility is to allow that functional organization is conceptually constitutive of qualitative content.\" Chalmers (1993).`</font>`{=html} In other words he identifies qualia with function. According to Chalmers (1996) qualia are a particular type of function: `<font face="times new roman">`{=html}\"I claim that conscious experience arises from fine-grained functional organization. More specifically, I will argue for a principle of organizational invariance, holding that given any system that has conscious experiences, then any system that has the same fine-grained functional organization will have qualitatively identical experiences. According to this principle, consciousness is an organizational invariant: a property that remains constant over all functional isomorphs of a given system. Whether the organization is realized in silicon chips, in the population of China, or in beer cans and ping-pong balls does not matter. As long as the functional organisation is right, conscious experience will be determined.\" p249`</font>`{=html} Chalmers\' idea of functional organisation has within it a sometimes vague implication that the functional units must have a particular form; for instance, in the development of his argument, he refers to "fine grained" replacement of organic functional units with inorganic units. Chalmers is actually making two major points, firstly that qualia occur during the motion of things (functions), secondly that qualia are independent of any particular substrate.\*\* For the first point to be consistent with materialism the qualia must have no effect on the function, they must be **epiphenomenal**. Epiphenomenal qualia would not be forbidden by the regress and homunculus arguments and would be akin to Berkeley\'s \"passive ideas\". Whether or not epiphenomenal qualia are physical depends upon the definition of the word \"physical\". If physical functions cause qualia but qualia cannot affect functions then the qualia are \"physical\" in the sense of being caused by physical events but might be regarded as non-physical in the sense of being isolated from further physical events. In philosophical terms they violate the principle of **Causal Closure**. However, there are other definitions of physicalism based on arguments such as **Methodological Naturalism** which hold that anything that can be investigated using the methods of natural science is a physical thing (see Stoljar 2001). Thus, although epiphenomenal qualia may not conform to materialism they may be encompassed by physicalism; as events that are related to material events they are awaiting a physical theory of how they emerge from a given function. The reader might consider whether phenomenal consciousness is indeed epiphenomenal. Empirical reports describe it as something that is different from the world beyond the body (see direct realism) - could we generate empirical reports of an epiphenomenon? The term **property dualism** describes how physical events might give rise to a set of properties that cannot be predicted from the fine structure of the physical system. The \"dualism\" is present because one set of events is related to two sets of properties, one of which is not related by materialism to the set of events. In the case of the proposal about consciousness outlined above an extra assumption, beyond materialism, would be needed to explain qualia. Property dualism might be defined as a theory that there could be a theory of consciousness but that this requires some new assumption. As far as the \"when and where\" of consciousness are concerned, property dualism states that it is somewhere in the processes performed by the organism and the parts of the organism. `<font size=1>`{=html} \*\* In terms of information processing, Chalmers is proposing that qualia are the enactment of a particular information processing structure.`</font>`{=html} - Block, N. (2006). Max Black\'s objection to mind-body identity. Oxford Review of Metaphysics No.3. <http://philrsss.anu.edu.au/BlockFest/MaxBlack.rtf> - Chalmers, D.J. (1993) Commentary on \"The Psychology of Folk Psychology\". Behavioral and Brain Sciences 16:35-36, 1993 - Chalmers, D.J. (1996) \"The Conscious Mind: In Search of a Fundamental Theory\". Oxford University Press. 1996. - Goldman, A.I., (1993). The Psychology of Folk Psychology. Behavioral and Brain Sciences 16: 15-28 (1993). <http://www.ecs.soton.ac.uk/~harnad/Papers/Py104/goldman.psyc.html> ### Predicate dualism Predicate dualism is the view espoused by most non-reductive physicalists, such as Donald Davidson(1980) and Jerry Fodor(1968), who maintain that while there is only one ontological category of substances and properties of substances (usually physical), the predicates that we use to describe mental events cannot be redescribed in terms of (or reduced to) physical predicates of natural languages. If we characterize predicate monism as the view subscribed to by eliminative materialists, who maintain that such intentional predicates as believe, desire, think, feel, etc., will eventually be eliminated from both the language of science and from ordinary language because the entities to which they refer do not exist, then predicate dualism is most easily defined as the negation of this position. Predicate dualists believe that so-called \"folk psychology\", with all of its propositional attitude ascriptions, is an ineliminable part of the enterprise of describing, explaining and understanding human mental states and behavior. Davidson, for example, subscribes to Anomalous Monism, according to which there can be no strict psycho-physical laws which connect mental and physical events under their descriptions as mental and physical events. However, all mental events also have physical descriptions. It is in terms of the latter that such events can be connected in law-like relations with other physical events. Mental predicates are irreducibly different in character (rational, holistic and necessary) from physical predicates (contingent, atomic and causal). (Section based on Wikipedia article) - Davidson, D (1980). Essays on Actions and Events. Oxford University Press. - Fodor,J. (1968) *Psychological Explanation*, Random House. . ### The interaction between mind and brain in dualism #### Interactionism Interactionism is the view that mental states, such as beliefs and desires, causally interact with physical states. This is a position which is very appealing to common-sense intuitions, notwithstanding the fact that it is very difficult to establish its validity or correctness by way of logical argumentation or empirical proof. It is appealing to common-sense because we are surrounded by such everyday occurrences as a child\'s touching a hot stove (physical event) which causes him to feel pain (mental event) and then yell and scream (physical event) which causes his parents to experience a sensation of fear and protectiveness (mental event) and so on. #### Epiphenomalism According to epiphenomenalism, all mental events are caused by a physical event and have no physical consequences. So, a mental event of deciding to pick up a rock (call it \"M\") is caused by the firing of specific neurons in the brain (call it \"P\"), however when the arm and hand move to pick up a rock (call it \"E\") this is only caused by P. The physical causes are in principle reducible to fundamental physics, and therefore mental causes are eliminated using this reductionist explanation. If P causes M and E, there is no overdetermination in the explanation for E. #### Parallelism Psycho-physical parallelism is a very unusual view about the interaction between mental and physical events which was most prominently, and perhaps only truly, advocated by Gottfried Wilhelm von Leibniz. Like Malebranche and others before him, Leibniz recognized the weaknesses of Descartes\' account of causal interaction taking place in a physical location in the brain. Malebranche decided that such a material basis of interaction between material and immaterial was impossible and therefore formulated his doctrine of occasionalism, stating that the interactions were really caused by the intervention of God on each individual occasion. Leibniz idea is that God has created a pre-established harmony such that it only seems as if physical and mental events cause, and are caused by, one another. In reality, mental causes only have mental effects and physical causes only have physical effects. Hence the term parallelism is used to describe this view. #### Occasionalism Occasionalism argues that bodily events are the occasion of an act by the Creator causing a corresponding mental event, and vice versa. Any such view requires a theological structure as a premise. #### Further reading - Robinson, Howard, \"Dualism\", The Stanford Encyclopedia of Philosophy (Fall 2003 Edition), Edward N. Zalta (ed.), <http://plato.stanford.edu/archives/fall2003/entries/dualism/> - Robinson, H. (2003) \"Dualism\", in S. Stich and T. Warfield (eds) The Blackwell Guide to Philosophy of Mind, Blackwell, Oxford, 85-101. - Amoroso, R.L. (2010) \"The complementarity of Mind and Body: Realizing the Dream of Descartes, Einstein and Eccles\", New York: Nova Science Publishers, `, ``https://www.novapublishers.com/catalog/product_info.php?products_id=12759` ## Idealism According to Idealism only the mental truly exists. The form and content of personal conscious experience might be related to the structure of the world and brain in several ways. It could be a **solipsism** or be the mind of God. *This is a **stub** and needs expansion*. ## Panpsychism ### Etymology Ancient Greek *pan* (πᾶν : \"all, everything, whole\") and *psyche* (ψυχή : \"soul, mind\").[^1] Psyche is the from ψύχω (*psukhō*, \"I blow\") and means mind or \'life-breath\'. Philip Goff, a proponent of panpsychism, carves out a distinction between panexperientialism and pancognitivism. Panexperientialism is the belief that *experience* is ubiquitous, while pancognitivism is the belief that *cognition* is ubiquitous. Most modern purponents of panpsychism, such as Annaka Harris and David Chalmers, are careful to distance themselves from pancognitivism. In some interpretations, such as monadism, Panpsychism and Idealism can overlap because the universe is conceived as being composed of an infinity of point consciousnesses that each contain information about the whole universe. The form and content of personal conscious experience might be related to the structure of the world and brain in many ways. *This is a **stub** and needs expansion*. ## References Seager W. & Allen-Hermanson (2001). 'Panpsychism.' Online document: Stanford Encyclopedia of Philosophy, \[online\], <http://plato.stanford.edu/entries/panpsychism/>, \[accessed 10/2005\] **Supervenience** - Chalmers, D.J. (1996). The Conscious Mind. Oxford University Press. **The problem of regression** - Ryle, G. (1949) The Concept of Mind. The University of Chicago Press, 1949. **The homunculus argument** - Gregory, R.L. (1990) Eye and Brain: The Psychology of Seeing, Oxford University Press Inc. New York. - Gregory, T.L. (1987). The Oxford Companion to Mind. Oxford University Press. **Subject-object paradox** - James, W. (1904)Does \'Consciousness\' Exist? Journal of Philosophy, Psychology, and Scientific Methods, 1, 477-491. - Hegel, G.W.F. PHILOSOPHY OF MIND: SECTION I. MIND SUBJECTIVE B. PHENOMENOLOGY OF MIND CONSCIOUSNESS Part Three of the Encyclopaedia of the Philosophical Sciences - Velmans, M. (1996) Consciousness and the \"Casual Paradox\". Behavioral and Brain Sciences, 19 (3): 538-542. - Bermudez, J.L. (1999) The Paradox of Self-Consciousness (representation and Mind) Psycoloquy: 10,#35 **Ontological status** - Bierman, D.J. (2004) Non Conscious Processes Preceding Intuitive decisions <http://m0134.fmg.uva.nl/~djb/publications/2004/Intuition_bialsymp2004.pdf> - Damasio, A.R. (1994). Descartes\' error: Emotion, reason and the human brain. New York: Grosset/Putnam Book. - Kant, I. Critique of Pure Reason <http://www.arts.cuhk.edu.hk/Philosophy/Kant/cpr/> **Phenomenal consciousness and access consciousness** Block, N. (1995) On a confusion about a function of consciousness. Behavioral and Brain Sciences 18 (2): 227-287. <http://www.bbsonline.org/documents/a/00/00/04/31/bbs00000431-00/bbs.block.html> Block, N. (2004). *The Encyclopedia of Cognitive Science*. <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/ecs.pdf> Dennett, D. (1978). Why You Can\'t Make a Computer that Feels Pain, in: Brainstorms. Cambridge, MA: MIT Press: 190-229. Dennett, D. (1988). Quining Qualia. in A. Marcel and E. Bisiach, eds, Consciousness in Modern Science, Oxford University Press 1988. Reprinted in W. Lycan, ed., Mind and Cognition: A Reader, MIT Press, 1990, A. Goldman, ed. Readings in Philosophy and Cognitive Science, MIT Press, 1993. <http://ase.tufts.edu/cogstud/papers/quinqual.htm> Edelman, G.M. (1993). Bright Air, Brilliant Fire: On the Matter of the Mind. New York: Feyerabend, P. (1963). Mental Events and the Brain, Journal of Philosophy 40:295-6. Huxley, T. H. (1874). On the Hypothesis that Animals are Automata, and its History, The Fortnightly Review, n.s.16:555-580. Reprinted in Method and Results: Essays by Thomas H. Huxley (New York: D. Appleton and Company, 1898). Nagel, T. (1974). What is it like to be a bat? The Philosophical Review LXXXIII, 4 (October 1974): 435-50. <http://web.archive.org/19990218140703/members.aol.com/NeoNoetics/Nagel_Bat.html> Rey, Georges, (1997). Contemporary Philosophy of Mind.Blackwell: Oxford Sellars W. (1956). Empiricism and the Philosophy of Mind, In: Feigl H and Scriven M (eds) The Foundations of Science and the Concepts of Psychology and Psychoanalysis: Minnesota Studies in the Philosophy of Science, Vol. 1. Minneapolis: University of Minnesota Press: 253-329 Whitehead, A.N. (1920). The Concept of Nature. Chapter 3: Time. <http://spartan.ac.brocku.ca/~lward/Whitehead/Whitehead_1920/White1_03.html> **Direct Realism** - Austin, J.L. (1962) Sense and Sensibilia, ed. by Geoffrey J. Warnock (Oxford, 1962) - Aydede, M. (2001) Naturalism, introspection, and direct realism about pain. Consciousness and Emotion, Vol. 2, No. 1, 2001, pp. 29--73. <http://web.clas.ufl.edu/users/maydede/pain.pdf> - Chapman, C.R., and Y. Nakamura (1999). A Passion of the Soul: An Introduction to Pain for Consciousness Researchers. Consciousness and Cognition, 8: 391-422. - Dennett, D. (1991a). Consciousness Explained. Boston: Little, Brown - Dennett, D. (1991b). Lovely and suspect qualities. Commentary on David Rosenthal, \"The Independence of Consciousness and Sensory Quality\" in E. Villanueva, ed., Consciousness, (SOFIA Conference, Buenos Aires), Atascadero, CA: Ridgeview 1991. <http://ase.tufts.edu/cogstud/papers/lovely&s.htm> - Fowler C A (1986): "An event approach to the study of speech perception from a direct-realist perspective", J of Phonetics 14(1):3-28. - Gibson, J. J. (1966) The Senses Considered as Perceptual Systems. Houghton Mifflin Company,Boston. - Gibson, J. J. (1979) Ecological Approach to Visual Perception.: Lawrence Erlbaum Associates Publishers, Hillsdate. - Gregory, R.L. 1988. Consciousness in science and philosophy: conscience and con-science. Chapter 12 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. - Le Morvan, Pierre (2004). Arguments against direct realism and how to counter them. *The American Philosophical Quarterly*, *41*(3), 221-234.\] (pdf) <http://www.tcnj.edu/~lemorvan/DR_web.pdf> - Michaels, C. F. and Carello, C. (1981). Direct Perception. Century Psychology Series. Prentice-Hall. . 1981. Download this book at <http://ione.psy.uconn.edu/~psy254/MC.pdf> - Oliveira, André L. G. and Oliveira, Luis F. (2002) Toward an ecological conception of timbre. In Proceedings Auditory Perception Cognition and Action Meeting 2002, Kansas City. <http://cogprints.org/2713/> - Skinner, B. F. Science and Human Behavior . New York: Macmillan, 1953. - Skinner, B. F. 1971. Beyond Freedom and Dignity. New York: Knopf. - Skinner, B. F. 1948. Walden Two. New York: Macmillan. - Tye, M. (2004). ANOTHER LOOK AT REPRESENTATIONALISM ABOUT PAIN. Consciousness and Emotion 2004, special issue on pain, edited by Murat Aydede (with replies by M. Aydede, N. Block, B. Maund, and P. Noordhof <http://sun.soci.niu.edu/~phildept/MT/RepresentationalismAndPain.pdf> - Vygotsky, L.S.(1925) Consciousness as a problem in the psychology of behavior. Undiscovered Vygotsky: Etudes on the pre-history of cultural-historical psychology (European Studies in the History of Science and Ideas. Vol. 8), pp. 251--281. Peter Lang Publishing. <http://www.marxists.org/archive/vygotsky/works/1925/consciousness.htm> - Ziff, Paul. \"About Behaviourism.\" Analysis 18 (1958): 132-136. Quoted by Larry Hauser in the Internet Encyclopedia of Philosophy. <http://www.utm.edu/research/iep/b/behavior.htm#B>. F. Skinner: Radical Behaviorism **Indirect Realism** - Moutoussis, K. and Zeki, S. (1997). A direct demonstration of perceptual asynchrony in vision. Proceedings of the Royal Society of London, Series B: Biological Sciences, 264, 393 - 399. - Rizzo, M., Nawrot, M. & Zihl, J. (1995). Motion and shape perception in cerebral akinetopsia.Brain, 118. 1105-1127. <http://nawrot.psych.ndsu.nodak.edu/Publications/Nawrot.pdf/RizzoNawrotZihl.1995.pdf> - Russell, B. (1912). Problems of Philosophy. Home University Library. <http://www.ditext.com/russell/rus1.html> - Tye, M. (2003) Qualia. Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/qualia/#Repqualia> Further reading: - Hume, D. (1739). A Treatise of Human Nature. <http://www.class.uidaho.edu/mickelsen/ToC/hume%20treatise%20ToC.htm> - Firth, R. (1949) Sense Data and the Percept Theory, Mind, 58 (1949); 59 (1950). (Describes early reasons for rejecting Indirect Realism) <http://www.ditext.com/firth/spt.html> - Grush, R. (2000). Self, world and space: The meaning and mechanisms of ego- and allocentric spatial representation. Brain and Mind 1(1):59-92. <http://mind.ucsd.edu/papers/sws/sws.html> [^1]: Clarke, D.S. *Panpsychism: Past and Recent Selected Readings*. State University of New York Press, 2004. p.1

# Consciousness Studies/The Conflict2#Idealism *This part of this section is about the where and when of the experience called consciousness. Is it in the world, in the brain or are the world and brain within it?* ## Phenomenal consciousness and access consciousness Block(1995) drew attention to the way that there appear to be two types of consciousness: *phenomenal* consciousness and *access* consciousness: `Phenomenal consciousness is experience; the phenomenally`\ `conscious  aspect of a state is what it is like to be in that`\ `state. The mark of access-consciousness, by contrast, is `\ `availability for use in reasoning and rationally guiding speech `\ `and action. (Block 1995).` *See the section on Ned Block\'s ideas for a deeper coverage of his approach to access and phenomenal consciousness.* Block uses Nagel\'s famous (1974) paper, \"What is it like to be a bat?\" as an exemplary description of phenomenal consciousness. Excellent descriptions have also been proffered by the empiricist philosophers who gave lengthy descriptions of consciousness as partly experience itself. Although Block has formalised the idea of phenomenal and access consciousness similar ideas have also been put forward by many philosophers including Kant and Whitehead. Access consciousness has two interpretations, in the first, used by Block, it applies to the functions that appear to operate on phenomenal consciousness. In the second, used by the behaviourists and eliminativists, it is some property of the functions of the brain that can be called \'consciousness\'. This division between phenomenal and functional aspects of consciousness is useful because it emphasises the idea of phenomenal consciousness as observation rather than action. Some philosophers such as Huxley in 1874, have taken the view that because phenomenal consciousness appears to have no function it is of no importance or cannot exist. James (1879) introduced the term \"epiphenomenalism\" to summarise the idea that consciousness has no function. The idea that phenomenal consciousness cannot exist is a type of *Eliminativism* (also known as Eliminative Materialism). Eliminativism owes much to the work of Sellars(1956) and Feyerbend (1963). Dennett (1978) applied Eliminativism to phenomenal consciousness and denies that pain is real. Others such as Rey(1997) have also applied eliminativism to phenomenal consciousness. Dennett (1988) redefines consciousness in terms of access consciousness alone, he argues that \"Everything real has properties, and since I don\'t deny the reality of conscious experience, I grant that conscious experience has properties\". Having related all consciousness to properties he then declares that these properties are actually judgements of properties. He considers judgements of the properties of consciousness to be identical to the properties themselves. He writes: `<font face="times">`{=html}\"The infallibilist line on qualia treats them as properties of one\'s experience one cannot in principle misdiscover, and this is a mysterious doctrine (at least as mysterious as papal infallibility) unless we shift the emphasis a little and treat qualia as logical constructs out of subjects\' qualia-judgments: a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F. \"`</font>`{=html} Having identified \"properties\" with \"judgement of properties\" he can then show that the judgements are insubstantial, hence the properties are insubstantial and hence the qualia are insubstantial or even non-existent. Dennett concludes that qualia can be rejected as non-existent: `<font face="times">`{=html}\"So when we look one last time at our original characterization of qualia, as ineffable, intrinsic, private, directly apprehensible properties of experience, we find that there is nothing to fill the bill. In their place are relatively or practically ineffable public properties we can refer to indirectly via reference to our private property-detectors\-- private only in the sense of idiosyncratic. And insofar as we wish to cling to our subjective authority about the occurrence within us of states of certain types or with certain properties, we can have some authority\--not infallibility or incorrigibility, but something better than sheer guessing\--but only if we restrict ourselves to relational, extrinsic properties like the power of certain internal states of ours to provoke acts of apparent re- identification. So contrary to what seems obvious at first blush, there simply are no qualia at all. \" (Dennett 1988)`</font>`{=html} Dennett\'s asserts that \"a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F\". This is a statement of the belief that qualia are the same as processes such as judgements. Processes such as judgements are flows of data where one state examines a previous state in a succession over time and embody what Whitehead called the \"materialist\" concept of time. Dennett does not consider how a scientific concept of time might affect his argument. Dennett\'s argument has been persuasive and there are now many philosophers and neuroscientists who believe that the problem of phenomenal consciousness does not exist. This means that, to them, what we call \'consciousness\' can only be a property of the functions performed by the brain and body. According to these philosophers only access consciousness exists. Those who support the idea of phenomenal consciousness also tend to frame it in terms of nineteenth century theory where one state examines a previous state in a succession over time, for instance Edelman(1993) places the past in memories at an instant and time within experience is explained as continuing modelling processes: `<font face="times">`{=html}\"Primary consciousness is the state of being mentally aware of things in the world\--of having mental images in the present. But it is not accompanied by any sense of a person with a past and a future\.... In contrast, higher-order consciousness involves the recognition by a thinking subject of his or her own acts or affections. It embodies a model of the personal, and of the past and the future as well as the present. It exhibits direct awareness\--the noninferential or immediate awareness of mental episodes without the involvement of sense organs or receptors. It is what we humans have in addition to primary consciousness. We are conscious of being conscious.\" `</font>`{=html} Block(2004) also suggests this flow from state to state in his idea of \"Reflexivity\" where our idea of familiarity with an object is due to one state being analysed by another: `<font face="times">`{=html}\"Thus in the "conscious" case, the subject must have a state that is about the subject's own perceptual experience (looking familiar) and thus conscious in what might be termed a "reflexive" sense. An experience is conscious in this sense just in case it is the object of another of the subject's states; for example, one has a thought to the effect that one has that experience. The reflexive sense of \'consciousness\' contrasts with phenomenality, which perhaps attaches to some states which are not the objects of other mental states. Reflexive consciousness might better be called 'awareness' than 'consciousness'. Reflexivity is phenomenality plus something else (reflection) and that opens up the possibility in principle for phenomenality without reflection. For example, it is at least conceptually possible for there to be two people in pain, one of whom is introspecting the pain the other not. (Perhaps infants or animals can have pain but don't introspect it.) The first is reflexively conscious of the pain, but both have phenomenally conscious states, since pain is by its very nature a phenomenally conscious state. \"`</font>`{=html} Both Block and Edelman allow phenomenal consciousness, our experience, as an unexplained phenomenon. Block, Edelman and also Dennett\'s ideas of consciousness are shown in the illustration below:  This model differs from the empirical reports of phenomenal consciousness that were considered earlier. According to the empirical reports the present moment in our experience is extended so the succession of outputs or stages of access consciousness could constitute the contents of phenomenal consciousness. In other words phenomenal consciousness is composed of periods of access consciousness. This is how it seems to the empiricist and in our own experience but how such a state could be explained in terms of brain activity is highly problematical. Given that nineteenth century ideas cannot explain such a state a scientific explanation will be required. The idea that phenomenal consciousness misrepresents or \"misdiscovers\" itself (Dennett 1988) deserves further discussion. According to materialism the present instant has no duration so can only be known in succeeding instants as a report or memory and this could be wrong. Whitehead considered that this viewpoint originates in an archaic view of science, particularly the concept of time in science: \"The eighteenth and nineteenth centuries accepted as their natural philosophy a certain circle of concepts which were as rigid and definite as those of the philosophy of the middle ages, and were accepted with as little critical research. I will call this natural philosophy \'materialism.\' Not only were men of science materialists, but also adherents of all schools of philosophy. The idealists only differed from the philosophic materialists on question of the alignment of nature in reference to mind. But no one had any doubt that the philosophy of nature considered in itself was of the type which I have called materialism. It is the philosophy which I have already examined in my two lectures of this course preceding the present one. It can be summarised as the belief that nature is an aggregate of material and that this material exists in some sense at each successive member of a one-dimensional series of extensionless instants of time. Furthermore the mutual relations of the material entities at each instant formed these entities into a spatial configuration in an unbounded space. It would seem that space\-\--on this theory-would be as instantaneous as the instants, and that some explanation is required of the relations between the successive instantaneous spaces. The materialistic theory is however silent on this point; and the succession of instantaneous spaces is tacitly combined into one persistent space. This theory is a purely intellectual rendering of experience which has had the luck to get itself formulated at the dawn of scientific thought. It has dominated the language and the imagination of science since science flourished in Alexandria, with the result that it is now hardly possible to speak without appearing to assume its immediate obviousness.\" (Whitehead 1920). ## Direct Realism and Direct Perception Direct Realism proposes that phenomenal experience is directly objects in the world without any intervening representation. It is motivated by the belief that the Problem of Regression, the Subject-Object Paradox and the recursion form of the Homunculus arguments show that phenomenal consciousness cannot occur in the brain alone. Direct Realists reason that if phenomenal consciousness cannot be things in the brain then it must be something outside the brain. There are two principle types of Direct Realism: Natural Dualism and Behaviourism (both Radical and Analytical). Some behaviourists use the term "Direct Perception" rather than Direct Realism and consider that only the invariant parts of perception are direct (see for instance Michaels and Carello 1981). Thomas Reid is generally regarded as the founder of Direct Realism. In his Natural Dualism he proposed that the soul is in direct contact with the contents of experience and these contents are things in the world beyond the body. The Direct Realism of Reid is summarised in the statement of his famous disciple Sir William Hamilton: \"In the simplest act of perception I am conscious of myself as the perceiving subject and of an external reality as the object perceived\". Reid\'s Natural Dualism has now been largely replaced by radical and analytical behaviourism which eschew the idea of a soul and propose that phenomenal consciousness, if it exists at all, is a behavioural reflex. The modern justification of Direct Realism mainly consists of arguments against Indirect Realism or Representationalism. Philosophers such as Austin (1962) and Le Morvan (2004) have summarised the Direct Realism debate and have identified the following arguments in favour of Indirect Realism and given rebuttals to each of them: 1\. The Causal Argument: perception involves a succession of causal events such as the reflection of photons, bleaching of retinal pigments etc. so perception must involve the end of this causal chain. The Direct Realist response is that, although there may be a causal chain in sensation this does not inevitably imply that the end of the chain is the content of phenomenal experience. 2\. The Time Lag Argument: it takes time for light to travel from an object to the senses, time for chemical changes in the retina etc\... The Direct Realist response is that direct perception may be referred back in time. 3\. The Partial Character of Perception Argument: we only perceive the surface of objects, and then only a part of the surface. As the whole object would be perceived directly perception must be indirect. The Direct Realist response is that direct perception could occur even if only parts of an object were perceived. 4\. The Perceptual Relativity Argument: things appear to be different shapes depending upon the point of view. The Direct Realist response is that if perception can occur backwards in time it should have no problem occurring back down a line of sight. However, Le Morvan\'s argument does not seem to encompass the geometrical nature of phenomenal experience, seeking to explain geometry in terms of movement. 5\. The Argument from Perceptual Illusion: A stick may appear bent when projecting from the surface of water. Direct Realists apply the argument used in (4) to this problem. The bent stick illusion is a physical event in the world beyond the eye rather than a normal optical illusion such as the Muller-Lyer illusion etc., see (6) for a discussion of optical illusions. 6\. The Argument from Hallucination: Hallucinations are not in the world beyond the body. This is highly problematical for Direct Realists especially when phenomena such as lucid dreams, dreams and visual imaginations are included along with hallucinations. Direct Realists classify these phenomena as not being perceptions or deny that they actually exist as phenomena. Indirect Realists would maintain that all of perception is a reconstruction and use optical illusions such as the Muller-Lyer, Ames Room etc. to justify this contention so the Direct Realist approach to hallucination, dreams etc. might seem like an unwillingness to accept Indirect Realism rather than an argument. 7\. The Dubitability Argument (cf: Indubitability argument): we cannot doubt current phenomenal experience but we can doubt the world beyond the body therefore phenomenal experience is not the world beyond the body. Direct Realists fall back on Presentism or functional Presentism to defeat this argument. If phenomenal experience is instantaneous and made anew at each instant then anything can be doubted. The points above have summarised the Direct Realist stance on visual perception. Other sensory modalities have also been considered in the Direct Realism debate. Fowler (1986) considered that sounds were attached to objects in the world. This idea is strange because sounds only seem to be closely attached to objects in the world when these objects are seen as well as heard. For example, when a subject is blindfolded it is found that there can be a large error in locating the position of a sound in the world, this is especially true for low frequency sounds. The Direct Realist approach has difficulty explaining the transition from sounds with an indefinite location when a subject is blindfolded to sounds that are bound to visual events when the blindfold is removed. It also runs into problems explaining how the sound of speech from a single loudspeaker can become bound to lip movements on a cinema screen. If the binding does not occur in the brain then where does it occur? Pain is particularly problematic for Direct Realism because, unlike colour vision where \'red\' is inferred to be a property of electrons or light, pain is an inner experience that is not a property of tissue damage. Tissue damage has properties such as bleeding, wheal formation etc. but pain seems to be phenomenal experience in the brain and \'phantom pain\' can occur without tissue damage (see Aydede (2001), Tye (2004) and Chapman, and Nakamura (1999) for further analysis). On closer inspection other sensations also appear to be inner experiences rather than direct sensations. For instance, the red crosses of different hues in the illustration below are all due to the same physical wavelengths of light. In this case the range of hues in experience is unrelated to the actual physical red on the page or screen. Another problem for Direct Realism is that it does not overcome the problems that it is supposed to solve. The argument for Direct Realism begins with the idea that there are severe problems with representationalism (the idea that phenomenal experience is in the brain) and that direct perception is an alternative that does not have these problems. However on closer inspection Direct Realism suffers from almost same problems as representationalism. If phenomenal experience is the world itself then Ryle\'s regress applies to the world itself and this can only be avoided by assuming that phenomenal experience is a subset of the world (i.e.: a representation) that receives input from other parts of the world that are not part of phenomenal experience. It is also commonly assumed that Direct Realism avoids the recursion argument because it is believed that the separation of the observer from the things that are observed is simply due to the geometry of the world. If such simple geometry is possible between the eye and the world then it should also be possible in the brain and a similar geometrical explanation could be invoked to avoid recursion in representations. These points are shown in the illustration below: image:Constuddir1.gif Scientists have a further problem with Direct Realism. The illustration below demonstrates that our scientific knowledge of the world differs markedly from our phenomenal experience. image:constuddirect.gif It is difficult to see how the form and content of phenomenal experience could supervene directly on the world beyond the body. The world inferred from measurements beyond the body seems to be a nebulous set of quantum phenomena that are arranged as probability fields in three dimensions at any instant. The objects in this real world are mostly space. The world of phenomenal experience on the other hand contains objects that are one-sided, and are like a 2 dimensional field of vectors directed simultaneously at an observation point which is apparently separate from them. Phenomenal experience is not three dimensional, the rear of objects is not available within it at any instant. Visual phenomenal experience seems to be a geometrical relationship between an abstract observation point and the reflection properties of the part of the world external to the body. It is a form that crudely overlies the angular separations in inferred reality, providing approximate directional data. It is not like things in themselves beyond the body, not even in type, being a set of directional vectors. (See the module on the neuroscience of perception for a discussion of depth perception). If the form and content of visual phenomenal experience are abstractions separated according to the angular positions of things in the world beyond the body then theories which propose that phenomenal experience is the world itself are problematical. It should be noted that things arranged according to angular positions can appear to overlie any group of similar things along a radius from the centre point.  If Direct Realists admit that things are as they appear to be, observed according to angular positions at a \'point eye\', then any representation of things on the inside of a sphere of any radius would appear similar. The geometry of the \'point eye\' is problematical whether the view contains the world itself or a representation of the world; it cannot be the movements of lumps of matter or energy and the point observation cannot be due to lumps all landing at a point. In other words the \'view\' is inconsistent with nineteenth century materialism and will require a scientific explanation. Radical and Analytical Behaviourism tackle the problem of the difference between the world inferred from measurements beyond the body and the phenomenal world by denying phenomenal consciousness and maintaining that access and reflex consciousness are all that exists or is necessary. Radical Behaviourism is an offshoot of psychological behaviourism and was established as a philosophical adjunct to Marxism by Vygotsky and popularised by Burrhus Frederic Skinner (see Skinner 1953). There is another movement in psychological behaviourism which is similar to Radical Behaviourism called Ecological Psychology (see Gibson 1966, 1979 and also Michaels and Carello 1981). Analytical Behaviourism is a philosophical movement established by Gilbert Ryle (see Ryle 1949). The core of Analytical and Radical Behaviourism is the assumption that consciousness exists for a durationless instant so that the Dubitability Argument and the Regression and Recursion Arguments can be applied (Ryle 1949, Skinner 1971 and see the sections on Ryle\'s Regress and the Subject-Object Paradox above). As a result the Direct Realist is able to insinuate that subjects only think that they have had a particular experience (cf: Dennett 1991a). It is intriguing that Eliminativists also maintain that experience is the world itself, for instance an insight into Dennett\'s idea of the mind is to be found on pages 407-408 of Consciousness Explained: \"It seemed to him, according to the text, as if his mind - his visual field - were filled with intricate details of gold-green buds an wiggling branches, but although this is how it seemed this was an illusion. No such \"plenum\" ever came into his mind; the plenum remained out in the world where it is didn\'t have to be represented, but could just be. When we marvel, in those moments of heightened self-consciousness, at the glorious richness of our conscious experience, the richness we marvel at is actually the richness of the world outside, in all its ravishing detail. It does not \"enter\" our conscious minds, but is simply available\" This is a clear description of Direct Realism (although Dennett does not describe himself as a direct realist). Radical Behaviourism is sometimes described as the dictum that the only psychological events that are of importance are those that occur outside the head. The absurdity of this has led to jokes: Q: What does one behaviorist say to another when they meet on the street? A: You\'re fine. How am I? Q: What does one behaviorist say to another after sex? A: That was great for you. How was it for me? (Ziff 1958) However Vygotsky, Skinner and other Radical Behaviourists hold that inner behaviour is possible so that events within the brain can result in reward or punishment. Vygotsky (1925) describes this approach: \"Consciousness is wholly reduced to the transmitting mechanisms of reflexes operating according to general laws, i.e., no processes other than reactions can be admitted into the organism. The way is also paved for the solution of the problem of self-awareness and self-observation. Inner perception and introspection are possible only thanks to the existence of a proprioceptive field and secondary reflexes, which are connected with it. This is always the echo of a reaction.\" Hence Radical Behaviourists are able to make the claim that what are believed to be representations with phenomenal content are processes. Even events such as pain can then be explained as reflexes involving organs within the skin. However, by opening the possibility that such reflexes could occur at any sense organ, including the eye, this makes Radical Behaviourism a mixed Direct Realist/Indirect Realist philosophy with consciousness as a process, not a separate thing such as phenomenal consciousness (see the section on representationalism and intentionality below). But this raises a serious issue for science: can the phenomenal consciousness that seems to contain our observations really be argued out of existence on the basis of a theory? As Gregory (1988) put it: " 'If you can't explain it -- deny it' is one strategy for dealing with embarrassing questions such as 'what is consciousness?' ". But is this the right strategy? Direct Realism fails to overcome the problems of regression and recursion inherent in representations. It proposes that phenomenal consciousness is identical to the physical world beyond the body but must then use a plethora of arguments to explain why this is evidently not so. When confronted with these problems its proponents resort to the argument that everything can be doubted and can misrepresent itself. Yet it is still widely believed. It should be noted that Direct Realism is espoused in Religious Natural Dualism, some forms of Augustinian theology, nineteenth century materialism and its offspring such as Marxism, post-modernism, post-Marxism, and various sociological movements. It is also necessary for some forms of Strong AI to occur. Perhaps this explains why few ideas have attracted as much attention and defence as Direct Realism. It is interesting to compare the Direct Realist and Indirect Realist interpretations of something as simple as a cartoon on television (such as the image below). According to Indirect Realism the cartoon would be a moving representation constructed in the brain using data from the senses. This leads to the prediction of brain mechanisms for modelling motions, combining colours, binding sound and vision etc., many of which have been verified. Can you demonstrate how the theory of Direct Realism could explain the phenomenal experience that contains the cartoon and produce a list of the predictions made by the theory?  In science a theory should be of predictive value, for instance, information theory describes how the state of a thing can be impressed on a carrier so that a signal can be transmitted from one place to another. This theory predicts what will happen when the signal arrives at its destination and how the state of the source can be inferred from the events at the destination, the total amount of information that can be transmitted etc. At the destination it is the form of the signal that is directly known by interaction and measurement, the form of the source is inferred. Direct Realism is a direct challenge to this information theory but does it deliver a more powerful predictive description of phenomenal consciousness or is experience always dependent on what happens to the information flow between things in the world and somewhere in the brain? Does direct realism have a physical theory? Ultimately it appears as if Direct Realism is about various understandings of Information Theory. For example, Austin (1962) discusses what we see when we see a church camouflaged as a barn and comments that: \"We see, of course, a church that now looks like a barn.\". Do we see a church or a barn? Scientific information theory is clear about this, the church is an entity composed of selected information from the quantum state of its constituents, the optical image of a camouflaged church is an arrangement of photons emanating from a screen on which it is projected, the retina has an arrangement of chemical and electrical events based on an optical image and conscious visual experience correlates with the arrangement of things on the retina. The fact that conscious experience also correlates with classifications of the retinal image as a barn or a church suggests that conscious experience is an arrangement of things in the brain based on both the retinal arrangement and the contents of a relational database. Austin\'s arguments have been mythologised as a final demonstration that \"sense data\" theories are false. However, as will be seen below, sense data theories merely claim that there is a succession of information states between an information state outside the body and that reported as conscious experience i.e.: subjects report that a church is camouflaged when it is camouflaged. ## Indirect Realism Indirect realism proposes that phenomenal consciousness exists and is a set of signals or **sense data**, usually in the brain. This was proposed by philosophers from Aristotle to Locke and was probably the most widespread idea of conscious experience until the eighteenth century. The idea of sense data is discussed in depth by Russell (1912). Russell\'s original definition is given below: `<font face="times new roman">`{=html}\"Let us give the name of \'sense-data\' to the things that are immediately known in sensation: such things as colours, sounds, smells, hardnesses, roughnesses, and so on. We shall give the name \'sensation\' to the experience of being immediately aware of these things. Thus, whenever we see a colour, we have a sensation of the colour, but the colour itself is a sense-datum, not a sensation. The colour is that of which we are immediately aware, and the awareness itself is the sensation. It is plain that if we are to know anything about the table, it must be by means of the sense-data \-- brown colour, oblong shape, smoothness, etc. \-- which we associate with the table; but, for the reasons which have been given, we cannot say that the table is the sense-data, or even that the sense-data are directly properties of the table.\"`</font>`{=html} Russell\'s definition is a materialist concept in which experience is always **of** something because the durationless instant of the present has always gone. As such it differs from some empiricist ideas where experience is not confined to the durationless instant. Science is Indirect Realist because it holds that the scientist can only make **measurements** of events in the world. These measurements give rise to signals as a result of interaction with the event. According to **decoherence theory** the signals are a state that is a mixture of the state of the measuring instrument and the state of the thing being measured. For example, the eyes are measuring instruments that are sensitive to photons, photons are signals containing a state that is based on the state of electrons in a surface and the state of electrons is based on the state of the surface etc. Scientific inference allows some aspects of the state of the surface to be inferred from the state of the photons. In modern Indirect Realism there is an attempt to distinguish the phenomenal content of conscious experience from the processing involved in accessing this phenomenal content. According to these theories phenomenal experience is an arrangement of signals that are the content of the experience. This arrangement forms a *representation* of things in the world so this form of indirect realism is known as **Representationalism**. Tye (2003) describes types of representationalist theory: `<font face="times new roman">`{=html}\"Representationalism, as I have presented it so far, is an identity thesis with respect to qualia: qualia are supposedly one and the same as certain representational contents.\"`</font>`{=html} Tye also describes variants of this idea of representationalism: `<font face="times new roman">`{=html}\"Sometimes it is held instead that qualia are one and the same as certain representational properties of experiences; and sometimes it is is argued that these representational properties are themselves irreducible (Siewert 1998). There is also a weaker version of representationalism, according to which it is metaphysically necessary that experiences exactly alike with respect to their representational contents are exactly alike with respect to their qualia. Obviously, this supervenience thesis leaves open the further question as to the essential nature of qualia.\"`</font>`{=html} (Tye 2003). In a scientific sense Direct Realists believe that phenomenal experience is the signals that occur next to things in the world beyond the body (which they call \"things in themselves\") and Indirect Realists usually believe that phenomenal experience is signals in the brain. It can be seen from the pattern of signal flow that the signals travelling into the brain preserve the spatial relationships of the original signals and encode the properties in the original signals. This means that the original signals next to the QM sources and the signals in the brain are equivalent provided the latter are oriented appropriately relative to signals from the body. Either set of signals could transmit or contain the same information. Both Direct and Indirect Realism cannot, at present, explain the physics of how a viewing point occurs in experience i.e.: how we seem to see through an apparent space to the signals that are the contents of experience. So the choice between Direct Realism and Indirect Realism reduces to whether there is only one set of signals or a chain of signals between the world and phenomenal experience. The philosophical arguments for Indirect Realism are listed below: 1\. Variable perspective: when we see things the view changes so what we see must be a different set of signals depending on the view rather than a constant object. 2\. Illusions: we can see through fingers and see a variety of colours where measurements tell us one exists. Direct Realists quote the \"bent stick illusion\", which is not really an illusion at all, being a physical event. 3\. Hallucinations: two people can have phenomenal experience containing a table. The first may be viewing a real table whereas the second may be hallucinating a table. If the tables are the same (phenomenally) then experience is indirect. 4\. Double vision: press the side of one eye, two images appear (cf Hume 1739) yet there are not two things in the world. 5\. Time gap arguments: according to materialism the past has gone. The things being seen no longer exist in the state that relates to the state in experience. In the extreme case, some stars in the night sky no longer exist but are still in experience so experience must be a derived signal. 6\. Secondary qualities such as pain, colour and smell do not exist as physical things in the source of signals and are likely to be properties of signals in the brain.  Indirect Realism has received strong support from recent discoveries in neuroscience, for example, it is now clear that both the colour and motion in phenomenal experience are added by cortical processes. In Cerebral **Achromatopsia** patients have suffered trauma to area V4 of the cerebral cortex and report seeing the world in greyscale with no colour vision and in Congenital Achromatopsia people do not even understand the meaning of \'colour\'. In an astonishing ailment called **Akinetopsia** patients perceive movement as a succession of stationary images (Rizzo *et al.* 1995). Akinetopsia is usually associated with damage to cortical area V5. Moutoussis and Zeki (1997) have demonstrated that the addition of colour occurs more rapidly than the addition of motion. The section on the Neuroscience of Consciousness describes these discoveries and many other aspects of the creation of phenomenal experience in the brain. Unfortunately knowledge of the whereabouts of the signals that are the content of conscious experience does not resolve the problem of phenomenal consciousness. Whether these signals are next to objects in the world or at the end of a chain of signals in the brain there still remains the problem of how they become arranged in the form of experience. If such a thing occurs at all. ### Intentionality and representation There is a materialist interpretation of representationalism in which representations are redefined as intentional states: `<font face="times new roman">`{=html}\"One way of explaining what is meant by 'intentionality' in the (more obscure) philosophical sense is this: it is that aspect of mental states or events that consists in their being of or about things (as pertains to the questions, 'What are you thinking of?' and 'What are you thinking about?'). Intentionality is the aboutness or directedness of mind (or states of mind) to things, objects, states of affairs, events. So if you are thinking about San Francisco, or about the increased cost of living there, or about your meeting someone there at Union Square---your mind, your thinking, is directed toward San Francisco, or the increased cost of living, or the meeting in Union Square. To think at all is to think of or about something in this sense. This 'directedness' conception of intentionality plays a prominent role in the influential philosophical writings of Franz Brentano and those whose views developed in response to his (to be discussed further in Section 3).\"(Siewert 2003)`</font>`{=html} This definition allows \"representation\" to be redefined as a data stream rather than a set of things arranged in some mental or neural state that represents things in space. Husserl thought this approach would allow a description of consciousness that \"carefully abstains from affirming the existence of anything in spatio-temporal reality\" (Siewert 2003) although it could be argued that a data stream such as any description can never escape the constraints of representation in time at some place. Unfortunately the concept of \"intentionality\" has become so diverse that it could be applied to almost any aspect of the description of consciousness. An interesting example of this is given by Loar (2001) where \"intentionality\" is considered to overlap \"representing\" and \"conceiving\": `<font face="times new roman">`{=html}\"A person\'s thoughts represent things to her \-- conceive things \-- in many ways: perceptually, memory-wise, descriptively, by naming, by analogy, by intuitive sorting, theoretically, abstractly, implicitly and explicitly. These various manners of conceiving have something in common: they have intentional properties, and they have them essentially. `</font>`{=html} The usage of the term \"intentional state\" has become so broad that it now means little more than a state that is about another state. References Siewert, C. (2003). Consciousness and Intentionality. The Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/consciousness-intentionality/> Also see Loar, B. (2001) "Phenomenal Intentionality as the Basis of Mental Content", in Reflections and Replies, ed. M. Hahn and B. Ramsberg, MIT. <http://www.nyu.edu/gsas/dept/philo/courses/concepts/loar.html> Williford, K. (2002) The intentionality of consciousness and the consciousness of intentionality. Intentionality: Past and Future, edited by Gábor Forrai and George Kampis, Amsterdam/New York: Rodopi. <http://web.stcloudstate.edu/kwwilliford/Intentionality%20of%20Consciousness.pdf> Byrne, A. (2001). Intentionalism Defended. Philosophical Review 110 (April 2001):199-240. <http://stripe.colorado.edu/~leeds/byrne.pdf> ### Cartesian materialism The term \"Cartesian materialism\" once meant the idea that the mind is in the brain (see for instance Block 1995). The term had largely fallen out of use in philosophy until revived by Daniel Dennett (1991) in the book *Consciousness Explained*. Dennett uses a very particular definition of the term in his discussions and also uses a particular definition of the word \"mind\". See the section on Daniel Dennett for Dennett\'s critique. Philosophers who adhere to the idea that the mind is in the brain tend to call themselves \"indirect realists\" or \"representationalists\" where the substrate of conscious experience is in the brain and would deny that Dennett\'s critique applies to their proposals. Dennett\'s critique makes the materialist assumption that if there is a representation in the brain then a further flow of material out of this representation would be required for the representation to become part of mind. ### Identity theories of mind The idea that mental states are brain states is known as the **identity theory of mind**. There are two sorts of identity theory, in **type** identity theory it is held that mental states are identical to brain states whereas in **token** identity theory it is held that mental states correlate with brain states. Type identity theory was attacked by Putnam in \"The Nature of Mental States\" where he pointed out that if mental states are functions then type identity theory would presuppose that animals that had the same mental states would need to have identical brain structures. He suggested that this is unlikely, it being more probable that animals have functional systems that perform similar overall functions but which are not identical. In other words, if it is assumed that conscious experience is a set of functions then token identity theory is more probable than type identity theory. Putnam\'s critique does not preclude identity theories of mind that involve \"passive ideas\" (i.e.: states that are not classical functions). Most identity theories of mind would be representational, the physical states representing the world in some way. All identity theories of mind involve Cartesian materialism in the sense of the mental states being brain states. According to identity theories the mind is in the brain. Putnam, H. (1967) The nature of mental states. In The Nature of Mind, edited by Rosenthal, pp. 197--203. Originally published as \"Psychological predicates in Art, Mind, and Religion\", edited by Capitan and Merill, pp. 37--48. ## Dualism Prior to considering the arguments surrounding dualism it is important to have a clear idea of \"information\" because many of these arguments have parallels with the difference between information as a set of states that can be transmitted and the substrate on which this information is expressed or from which the information is derived. See Elementary information and information systems theory. ### Cartesian dualism Descartes, a philosopher, analysed his experience and developed an empirical description of how it is arranged. He described mental images and perceptions as extended in space and with a duration. He called these extended things **ideas** (Cartesian ideas) and proposed that they are patterns in the brain. Descartes thought the pineal gland was the most likely location for these ideas because it is one of the few single organs in the brain. He also proposed that there is a rational soul that directly contacts these ideas: `<font face="times new roman">`{=html}\"Now among these figures, it is not those imprinted on the external sense organs, or on the internal surface of the brain, which should be taken to be ideas - but only those which are traced in the spirits on the surface of gland H *(where the seat of the imagination and the \'common sense\' is located)*. That is to say, it is only the latter figures which should be taken to be the forms or images which the rational soul united to this machine will consider directly when it imagines some object or perceives it by the senses.\" Descartes (1664)`</font>`{=html} See section on Descartes for more information and references. Descartes considered that the soul was a physical point, an unextended entity that acts like a mind\'s eye. He called this unextended place the *res cogitans* and concluded that it was a substance that differed from that of material things: `<font face="times new roman">`{=html}\".. I thence concluded that I was a substance whose whole essence or nature consists only in thinking, and which, that it may exist, has need of no place, nor is dependent on any material thing; so that \" I,\" that is to say, the mind by which I am what I am, is wholly distinct from the body, and is even more easily known than the latter, and is such, that although the latter were not, it would still continue to be all that it is.\"Descartes (1637)`</font>`{=html} This unextended substance that is not material gives the word \"substance\" a new meaning. It has been attacked as a concept by Locke, Hume, Berkely and many other philosophers. The concept of there being two substances, that which composes the physical world and that which composes the soul, is the origin of the word **Dualism** but dualism, as a concept, has been extended beyond this original meaning. Cartesian dualism is a type of **substance dualism**. Cartesian dualism is an attempt to explain our experience. According to Descartes something supernatural would be needed for an unextended viewing point to exist. Reid\'s **Natural Dualism** also has a point soul looking at things but proposes that the things in question are forms in the world rather than in the brain. ### Property dualism Another sort of dualism has arisen out of a particular interpretation of the regress and homunculus arguments. These arguments show that phenomenal experience is not due entirely to flows from place to place (i.e.: it is not due to classical processes and functions). Property dualism asserts that when matter is organized in the appropriate way (i.e. in the way that living human bodies are organized), mental properties emerge. As Goldman (1993) pointed out, qualitative experience does not seem to be needed in a functional description of a system: `<font face="times new roman">`{=html}\"For any functional description of a system that is in pain (or has an itch), it seems as if we can imagine another system with the same functional description but lacking the qualitative property of painfulness (or itchiness).\" `</font>`{=html} Certainly a functional system that merely reports the words \"I am in pain\" when it is dropped on the floor does not require any qualitative property of painfulness. The *absent qualia* arguments suggest that even in a large system there would be no need for qualitative properties for the performance of any classical function. Chalmers (1993) commenting on Goldman\'s point, said that this implies that **zombies** might exist, functional replicas of humans but without qualia. He then denied that a complete functional replica of a human could exist without also including qualia: `<font face="times new roman">`{=html}\"It seems to me that the only way to avoid this conclusion is to deny that Zombie Dave is a conceptual possibility; and the only principled way to deny that Zombie Dave is a conceptual possibility is to allow that functional organization is conceptually constitutive of qualitative content.\" Chalmers (1993).`</font>`{=html} In other words he identifies qualia with function. According to Chalmers (1996) qualia are a particular type of function: `<font face="times new roman">`{=html}\"I claim that conscious experience arises from fine-grained functional organization. More specifically, I will argue for a principle of organizational invariance, holding that given any system that has conscious experiences, then any system that has the same fine-grained functional organization will have qualitatively identical experiences. According to this principle, consciousness is an organizational invariant: a property that remains constant over all functional isomorphs of a given system. Whether the organization is realized in silicon chips, in the population of China, or in beer cans and ping-pong balls does not matter. As long as the functional organisation is right, conscious experience will be determined.\" p249`</font>`{=html} Chalmers\' idea of functional organisation has within it a sometimes vague implication that the functional units must have a particular form; for instance, in the development of his argument, he refers to "fine grained" replacement of organic functional units with inorganic units. Chalmers is actually making two major points, firstly that qualia occur during the motion of things (functions), secondly that qualia are independent of any particular substrate.\*\* For the first point to be consistent with materialism the qualia must have no effect on the function, they must be **epiphenomenal**. Epiphenomenal qualia would not be forbidden by the regress and homunculus arguments and would be akin to Berkeley\'s \"passive ideas\". Whether or not epiphenomenal qualia are physical depends upon the definition of the word \"physical\". If physical functions cause qualia but qualia cannot affect functions then the qualia are \"physical\" in the sense of being caused by physical events but might be regarded as non-physical in the sense of being isolated from further physical events. In philosophical terms they violate the principle of **Causal Closure**. However, there are other definitions of physicalism based on arguments such as **Methodological Naturalism** which hold that anything that can be investigated using the methods of natural science is a physical thing (see Stoljar 2001). Thus, although epiphenomenal qualia may not conform to materialism they may be encompassed by physicalism; as events that are related to material events they are awaiting a physical theory of how they emerge from a given function. The reader might consider whether phenomenal consciousness is indeed epiphenomenal. Empirical reports describe it as something that is different from the world beyond the body (see direct realism) - could we generate empirical reports of an epiphenomenon? The term **property dualism** describes how physical events might give rise to a set of properties that cannot be predicted from the fine structure of the physical system. The \"dualism\" is present because one set of events is related to two sets of properties, one of which is not related by materialism to the set of events. In the case of the proposal about consciousness outlined above an extra assumption, beyond materialism, would be needed to explain qualia. Property dualism might be defined as a theory that there could be a theory of consciousness but that this requires some new assumption. As far as the \"when and where\" of consciousness are concerned, property dualism states that it is somewhere in the processes performed by the organism and the parts of the organism. `<font size=1>`{=html} \*\* In terms of information processing, Chalmers is proposing that qualia are the enactment of a particular information processing structure.`</font>`{=html} - Block, N. (2006). Max Black\'s objection to mind-body identity. Oxford Review of Metaphysics No.3. <http://philrsss.anu.edu.au/BlockFest/MaxBlack.rtf> - Chalmers, D.J. (1993) Commentary on \"The Psychology of Folk Psychology\". Behavioral and Brain Sciences 16:35-36, 1993 - Chalmers, D.J. (1996) \"The Conscious Mind: In Search of a Fundamental Theory\". Oxford University Press. 1996. - Goldman, A.I., (1993). The Psychology of Folk Psychology. Behavioral and Brain Sciences 16: 15-28 (1993). <http://www.ecs.soton.ac.uk/~harnad/Papers/Py104/goldman.psyc.html> ### Predicate dualism Predicate dualism is the view espoused by most non-reductive physicalists, such as Donald Davidson(1980) and Jerry Fodor(1968), who maintain that while there is only one ontological category of substances and properties of substances (usually physical), the predicates that we use to describe mental events cannot be redescribed in terms of (or reduced to) physical predicates of natural languages. If we characterize predicate monism as the view subscribed to by eliminative materialists, who maintain that such intentional predicates as believe, desire, think, feel, etc., will eventually be eliminated from both the language of science and from ordinary language because the entities to which they refer do not exist, then predicate dualism is most easily defined as the negation of this position. Predicate dualists believe that so-called \"folk psychology\", with all of its propositional attitude ascriptions, is an ineliminable part of the enterprise of describing, explaining and understanding human mental states and behavior. Davidson, for example, subscribes to Anomalous Monism, according to which there can be no strict psycho-physical laws which connect mental and physical events under their descriptions as mental and physical events. However, all mental events also have physical descriptions. It is in terms of the latter that such events can be connected in law-like relations with other physical events. Mental predicates are irreducibly different in character (rational, holistic and necessary) from physical predicates (contingent, atomic and causal). (Section based on Wikipedia article) - Davidson, D (1980). Essays on Actions and Events. Oxford University Press. - Fodor,J. (1968) *Psychological Explanation*, Random House. . ### The interaction between mind and brain in dualism #### Interactionism Interactionism is the view that mental states, such as beliefs and desires, causally interact with physical states. This is a position which is very appealing to common-sense intuitions, notwithstanding the fact that it is very difficult to establish its validity or correctness by way of logical argumentation or empirical proof. It is appealing to common-sense because we are surrounded by such everyday occurrences as a child\'s touching a hot stove (physical event) which causes him to feel pain (mental event) and then yell and scream (physical event) which causes his parents to experience a sensation of fear and protectiveness (mental event) and so on. #### Epiphenomalism According to epiphenomenalism, all mental events are caused by a physical event and have no physical consequences. So, a mental event of deciding to pick up a rock (call it \"M\") is caused by the firing of specific neurons in the brain (call it \"P\"), however when the arm and hand move to pick up a rock (call it \"E\") this is only caused by P. The physical causes are in principle reducible to fundamental physics, and therefore mental causes are eliminated using this reductionist explanation. If P causes M and E, there is no overdetermination in the explanation for E. #### Parallelism Psycho-physical parallelism is a very unusual view about the interaction between mental and physical events which was most prominently, and perhaps only truly, advocated by Gottfried Wilhelm von Leibniz. Like Malebranche and others before him, Leibniz recognized the weaknesses of Descartes\' account of causal interaction taking place in a physical location in the brain. Malebranche decided that such a material basis of interaction between material and immaterial was impossible and therefore formulated his doctrine of occasionalism, stating that the interactions were really caused by the intervention of God on each individual occasion. Leibniz idea is that God has created a pre-established harmony such that it only seems as if physical and mental events cause, and are caused by, one another. In reality, mental causes only have mental effects and physical causes only have physical effects. Hence the term parallelism is used to describe this view. #### Occasionalism Occasionalism argues that bodily events are the occasion of an act by the Creator causing a corresponding mental event, and vice versa. Any such view requires a theological structure as a premise. #### Further reading - Robinson, Howard, \"Dualism\", The Stanford Encyclopedia of Philosophy (Fall 2003 Edition), Edward N. Zalta (ed.), <http://plato.stanford.edu/archives/fall2003/entries/dualism/> - Robinson, H. (2003) \"Dualism\", in S. Stich and T. Warfield (eds) The Blackwell Guide to Philosophy of Mind, Blackwell, Oxford, 85-101. - Amoroso, R.L. (2010) \"The complementarity of Mind and Body: Realizing the Dream of Descartes, Einstein and Eccles\", New York: Nova Science Publishers, `, ``https://www.novapublishers.com/catalog/product_info.php?products_id=12759` ## Idealism According to Idealism only the mental truly exists. The form and content of personal conscious experience might be related to the structure of the world and brain in several ways. It could be a **solipsism** or be the mind of God. *This is a **stub** and needs expansion*. ## Panpsychism ### Etymology Ancient Greek *pan* (πᾶν : \"all, everything, whole\") and *psyche* (ψυχή : \"soul, mind\").[^1] Psyche is the from ψύχω (*psukhō*, \"I blow\") and means mind or \'life-breath\'. Philip Goff, a proponent of panpsychism, carves out a distinction between panexperientialism and pancognitivism. Panexperientialism is the belief that *experience* is ubiquitous, while pancognitivism is the belief that *cognition* is ubiquitous. Most modern purponents of panpsychism, such as Annaka Harris and David Chalmers, are careful to distance themselves from pancognitivism. In some interpretations, such as monadism, Panpsychism and Idealism can overlap because the universe is conceived as being composed of an infinity of point consciousnesses that each contain information about the whole universe. The form and content of personal conscious experience might be related to the structure of the world and brain in many ways. *This is a **stub** and needs expansion*. ## References Seager W. & Allen-Hermanson (2001). 'Panpsychism.' Online document: Stanford Encyclopedia of Philosophy, \[online\], <http://plato.stanford.edu/entries/panpsychism/>, \[accessed 10/2005\] **Supervenience** - Chalmers, D.J. (1996). The Conscious Mind. Oxford University Press. **The problem of regression** - Ryle, G. (1949) The Concept of Mind. The University of Chicago Press, 1949. **The homunculus argument** - Gregory, R.L. (1990) Eye and Brain: The Psychology of Seeing, Oxford University Press Inc. New York. - Gregory, T.L. (1987). The Oxford Companion to Mind. Oxford University Press. **Subject-object paradox** - James, W. (1904)Does \'Consciousness\' Exist? Journal of Philosophy, Psychology, and Scientific Methods, 1, 477-491. - Hegel, G.W.F. PHILOSOPHY OF MIND: SECTION I. MIND SUBJECTIVE B. PHENOMENOLOGY OF MIND CONSCIOUSNESS Part Three of the Encyclopaedia of the Philosophical Sciences - Velmans, M. (1996) Consciousness and the \"Casual Paradox\". Behavioral and Brain Sciences, 19 (3): 538-542. - Bermudez, J.L. (1999) The Paradox of Self-Consciousness (representation and Mind) Psycoloquy: 10,#35 **Ontological status** - Bierman, D.J. (2004) Non Conscious Processes Preceding Intuitive decisions <http://m0134.fmg.uva.nl/~djb/publications/2004/Intuition_bialsymp2004.pdf> - Damasio, A.R. (1994). Descartes\' error: Emotion, reason and the human brain. New York: Grosset/Putnam Book. - Kant, I. Critique of Pure Reason <http://www.arts.cuhk.edu.hk/Philosophy/Kant/cpr/> **Phenomenal consciousness and access consciousness** Block, N. (1995) On a confusion about a function of consciousness. Behavioral and Brain Sciences 18 (2): 227-287. <http://www.bbsonline.org/documents/a/00/00/04/31/bbs00000431-00/bbs.block.html> Block, N. (2004). *The Encyclopedia of Cognitive Science*. <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/ecs.pdf> Dennett, D. (1978). Why You Can\'t Make a Computer that Feels Pain, in: Brainstorms. Cambridge, MA: MIT Press: 190-229. Dennett, D. (1988). Quining Qualia. in A. Marcel and E. Bisiach, eds, Consciousness in Modern Science, Oxford University Press 1988. Reprinted in W. Lycan, ed., Mind and Cognition: A Reader, MIT Press, 1990, A. Goldman, ed. Readings in Philosophy and Cognitive Science, MIT Press, 1993. <http://ase.tufts.edu/cogstud/papers/quinqual.htm> Edelman, G.M. (1993). Bright Air, Brilliant Fire: On the Matter of the Mind. New York: Feyerabend, P. (1963). Mental Events and the Brain, Journal of Philosophy 40:295-6. Huxley, T. H. (1874). On the Hypothesis that Animals are Automata, and its History, The Fortnightly Review, n.s.16:555-580. Reprinted in Method and Results: Essays by Thomas H. Huxley (New York: D. Appleton and Company, 1898). Nagel, T. (1974). What is it like to be a bat? The Philosophical Review LXXXIII, 4 (October 1974): 435-50. <http://web.archive.org/19990218140703/members.aol.com/NeoNoetics/Nagel_Bat.html> Rey, Georges, (1997). Contemporary Philosophy of Mind.Blackwell: Oxford Sellars W. (1956). Empiricism and the Philosophy of Mind, In: Feigl H and Scriven M (eds) The Foundations of Science and the Concepts of Psychology and Psychoanalysis: Minnesota Studies in the Philosophy of Science, Vol. 1. Minneapolis: University of Minnesota Press: 253-329 Whitehead, A.N. (1920). The Concept of Nature. Chapter 3: Time. <http://spartan.ac.brocku.ca/~lward/Whitehead/Whitehead_1920/White1_03.html> **Direct Realism** - Austin, J.L. (1962) Sense and Sensibilia, ed. by Geoffrey J. Warnock (Oxford, 1962) - Aydede, M. (2001) Naturalism, introspection, and direct realism about pain. Consciousness and Emotion, Vol. 2, No. 1, 2001, pp. 29--73. <http://web.clas.ufl.edu/users/maydede/pain.pdf> - Chapman, C.R., and Y. Nakamura (1999). A Passion of the Soul: An Introduction to Pain for Consciousness Researchers. Consciousness and Cognition, 8: 391-422. - Dennett, D. (1991a). Consciousness Explained. Boston: Little, Brown - Dennett, D. (1991b). Lovely and suspect qualities. Commentary on David Rosenthal, \"The Independence of Consciousness and Sensory Quality\" in E. Villanueva, ed., Consciousness, (SOFIA Conference, Buenos Aires), Atascadero, CA: Ridgeview 1991. <http://ase.tufts.edu/cogstud/papers/lovely&s.htm> - Fowler C A (1986): "An event approach to the study of speech perception from a direct-realist perspective", J of Phonetics 14(1):3-28. - Gibson, J. J. (1966) The Senses Considered as Perceptual Systems. Houghton Mifflin Company,Boston. - Gibson, J. J. (1979) Ecological Approach to Visual Perception.: Lawrence Erlbaum Associates Publishers, Hillsdate. - Gregory, R.L. 1988. Consciousness in science and philosophy: conscience and con-science. Chapter 12 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. - Le Morvan, Pierre (2004). Arguments against direct realism and how to counter them. *The American Philosophical Quarterly*, *41*(3), 221-234.\] (pdf) <http://www.tcnj.edu/~lemorvan/DR_web.pdf> - Michaels, C. F. and Carello, C. (1981). Direct Perception. Century Psychology Series. Prentice-Hall. . 1981. Download this book at <http://ione.psy.uconn.edu/~psy254/MC.pdf> - Oliveira, André L. G. and Oliveira, Luis F. (2002) Toward an ecological conception of timbre. In Proceedings Auditory Perception Cognition and Action Meeting 2002, Kansas City. <http://cogprints.org/2713/> - Skinner, B. F. Science and Human Behavior . New York: Macmillan, 1953. - Skinner, B. F. 1971. Beyond Freedom and Dignity. New York: Knopf. - Skinner, B. F. 1948. Walden Two. New York: Macmillan. - Tye, M. (2004). ANOTHER LOOK AT REPRESENTATIONALISM ABOUT PAIN. Consciousness and Emotion 2004, special issue on pain, edited by Murat Aydede (with replies by M. Aydede, N. Block, B. Maund, and P. Noordhof <http://sun.soci.niu.edu/~phildept/MT/RepresentationalismAndPain.pdf> - Vygotsky, L.S.(1925) Consciousness as a problem in the psychology of behavior. Undiscovered Vygotsky: Etudes on the pre-history of cultural-historical psychology (European Studies in the History of Science and Ideas. Vol. 8), pp. 251--281. Peter Lang Publishing. <http://www.marxists.org/archive/vygotsky/works/1925/consciousness.htm> - Ziff, Paul. \"About Behaviourism.\" Analysis 18 (1958): 132-136. Quoted by Larry Hauser in the Internet Encyclopedia of Philosophy. <http://www.utm.edu/research/iep/b/behavior.htm#B>. F. Skinner: Radical Behaviorism **Indirect Realism** - Moutoussis, K. and Zeki, S. (1997). A direct demonstration of perceptual asynchrony in vision. Proceedings of the Royal Society of London, Series B: Biological Sciences, 264, 393 - 399. - Rizzo, M., Nawrot, M. & Zihl, J. (1995). Motion and shape perception in cerebral akinetopsia.Brain, 118. 1105-1127. <http://nawrot.psych.ndsu.nodak.edu/Publications/Nawrot.pdf/RizzoNawrotZihl.1995.pdf> - Russell, B. (1912). Problems of Philosophy. Home University Library. <http://www.ditext.com/russell/rus1.html> - Tye, M. (2003) Qualia. Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/qualia/#Repqualia> Further reading: - Hume, D. (1739). A Treatise of Human Nature. <http://www.class.uidaho.edu/mickelsen/ToC/hume%20treatise%20ToC.htm> - Firth, R. (1949) Sense Data and the Percept Theory, Mind, 58 (1949); 59 (1950). (Describes early reasons for rejecting Indirect Realism) <http://www.ditext.com/firth/spt.html> - Grush, R. (2000). Self, world and space: The meaning and mechanisms of ego- and allocentric spatial representation. Brain and Mind 1(1):59-92. <http://mind.ucsd.edu/papers/sws/sws.html> [^1]: Clarke, D.S. *Panpsychism: Past and Recent Selected Readings*. State University of New York Press, 2004. p.1

# Consciousness Studies/The Conflict2#Panpsychism *This part of this section is about the where and when of the experience called consciousness. Is it in the world, in the brain or are the world and brain within it?* ## Phenomenal consciousness and access consciousness Block(1995) drew attention to the way that there appear to be two types of consciousness: *phenomenal* consciousness and *access* consciousness: `Phenomenal consciousness is experience; the phenomenally`\ `conscious  aspect of a state is what it is like to be in that`\ `state. The mark of access-consciousness, by contrast, is `\ `availability for use in reasoning and rationally guiding speech `\ `and action. (Block 1995).` *See the section on Ned Block\'s ideas for a deeper coverage of his approach to access and phenomenal consciousness.* Block uses Nagel\'s famous (1974) paper, \"What is it like to be a bat?\" as an exemplary description of phenomenal consciousness. Excellent descriptions have also been proffered by the empiricist philosophers who gave lengthy descriptions of consciousness as partly experience itself. Although Block has formalised the idea of phenomenal and access consciousness similar ideas have also been put forward by many philosophers including Kant and Whitehead. Access consciousness has two interpretations, in the first, used by Block, it applies to the functions that appear to operate on phenomenal consciousness. In the second, used by the behaviourists and eliminativists, it is some property of the functions of the brain that can be called \'consciousness\'. This division between phenomenal and functional aspects of consciousness is useful because it emphasises the idea of phenomenal consciousness as observation rather than action. Some philosophers such as Huxley in 1874, have taken the view that because phenomenal consciousness appears to have no function it is of no importance or cannot exist. James (1879) introduced the term \"epiphenomenalism\" to summarise the idea that consciousness has no function. The idea that phenomenal consciousness cannot exist is a type of *Eliminativism* (also known as Eliminative Materialism). Eliminativism owes much to the work of Sellars(1956) and Feyerbend (1963). Dennett (1978) applied Eliminativism to phenomenal consciousness and denies that pain is real. Others such as Rey(1997) have also applied eliminativism to phenomenal consciousness. Dennett (1988) redefines consciousness in terms of access consciousness alone, he argues that \"Everything real has properties, and since I don\'t deny the reality of conscious experience, I grant that conscious experience has properties\". Having related all consciousness to properties he then declares that these properties are actually judgements of properties. He considers judgements of the properties of consciousness to be identical to the properties themselves. He writes: `<font face="times">`{=html}\"The infallibilist line on qualia treats them as properties of one\'s experience one cannot in principle misdiscover, and this is a mysterious doctrine (at least as mysterious as papal infallibility) unless we shift the emphasis a little and treat qualia as logical constructs out of subjects\' qualia-judgments: a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F. \"`</font>`{=html} Having identified \"properties\" with \"judgement of properties\" he can then show that the judgements are insubstantial, hence the properties are insubstantial and hence the qualia are insubstantial or even non-existent. Dennett concludes that qualia can be rejected as non-existent: `<font face="times">`{=html}\"So when we look one last time at our original characterization of qualia, as ineffable, intrinsic, private, directly apprehensible properties of experience, we find that there is nothing to fill the bill. In their place are relatively or practically ineffable public properties we can refer to indirectly via reference to our private property-detectors\-- private only in the sense of idiosyncratic. And insofar as we wish to cling to our subjective authority about the occurrence within us of states of certain types or with certain properties, we can have some authority\--not infallibility or incorrigibility, but something better than sheer guessing\--but only if we restrict ourselves to relational, extrinsic properties like the power of certain internal states of ours to provoke acts of apparent re- identification. So contrary to what seems obvious at first blush, there simply are no qualia at all. \" (Dennett 1988)`</font>`{=html} Dennett\'s asserts that \"a subject\'s experience has the quale F if and only if the subject judges his experience to have quale F\". This is a statement of the belief that qualia are the same as processes such as judgements. Processes such as judgements are flows of data where one state examines a previous state in a succession over time and embody what Whitehead called the \"materialist\" concept of time. Dennett does not consider how a scientific concept of time might affect his argument. Dennett\'s argument has been persuasive and there are now many philosophers and neuroscientists who believe that the problem of phenomenal consciousness does not exist. This means that, to them, what we call \'consciousness\' can only be a property of the functions performed by the brain and body. According to these philosophers only access consciousness exists. Those who support the idea of phenomenal consciousness also tend to frame it in terms of nineteenth century theory where one state examines a previous state in a succession over time, for instance Edelman(1993) places the past in memories at an instant and time within experience is explained as continuing modelling processes: `<font face="times">`{=html}\"Primary consciousness is the state of being mentally aware of things in the world\--of having mental images in the present. But it is not accompanied by any sense of a person with a past and a future\.... In contrast, higher-order consciousness involves the recognition by a thinking subject of his or her own acts or affections. It embodies a model of the personal, and of the past and the future as well as the present. It exhibits direct awareness\--the noninferential or immediate awareness of mental episodes without the involvement of sense organs or receptors. It is what we humans have in addition to primary consciousness. We are conscious of being conscious.\" `</font>`{=html} Block(2004) also suggests this flow from state to state in his idea of \"Reflexivity\" where our idea of familiarity with an object is due to one state being analysed by another: `<font face="times">`{=html}\"Thus in the "conscious" case, the subject must have a state that is about the subject's own perceptual experience (looking familiar) and thus conscious in what might be termed a "reflexive" sense. An experience is conscious in this sense just in case it is the object of another of the subject's states; for example, one has a thought to the effect that one has that experience. The reflexive sense of \'consciousness\' contrasts with phenomenality, which perhaps attaches to some states which are not the objects of other mental states. Reflexive consciousness might better be called 'awareness' than 'consciousness'. Reflexivity is phenomenality plus something else (reflection) and that opens up the possibility in principle for phenomenality without reflection. For example, it is at least conceptually possible for there to be two people in pain, one of whom is introspecting the pain the other not. (Perhaps infants or animals can have pain but don't introspect it.) The first is reflexively conscious of the pain, but both have phenomenally conscious states, since pain is by its very nature a phenomenally conscious state. \"`</font>`{=html} Both Block and Edelman allow phenomenal consciousness, our experience, as an unexplained phenomenon. Block, Edelman and also Dennett\'s ideas of consciousness are shown in the illustration below:  This model differs from the empirical reports of phenomenal consciousness that were considered earlier. According to the empirical reports the present moment in our experience is extended so the succession of outputs or stages of access consciousness could constitute the contents of phenomenal consciousness. In other words phenomenal consciousness is composed of periods of access consciousness. This is how it seems to the empiricist and in our own experience but how such a state could be explained in terms of brain activity is highly problematical. Given that nineteenth century ideas cannot explain such a state a scientific explanation will be required. The idea that phenomenal consciousness misrepresents or \"misdiscovers\" itself (Dennett 1988) deserves further discussion. According to materialism the present instant has no duration so can only be known in succeeding instants as a report or memory and this could be wrong. Whitehead considered that this viewpoint originates in an archaic view of science, particularly the concept of time in science: \"The eighteenth and nineteenth centuries accepted as their natural philosophy a certain circle of concepts which were as rigid and definite as those of the philosophy of the middle ages, and were accepted with as little critical research. I will call this natural philosophy \'materialism.\' Not only were men of science materialists, but also adherents of all schools of philosophy. The idealists only differed from the philosophic materialists on question of the alignment of nature in reference to mind. But no one had any doubt that the philosophy of nature considered in itself was of the type which I have called materialism. It is the philosophy which I have already examined in my two lectures of this course preceding the present one. It can be summarised as the belief that nature is an aggregate of material and that this material exists in some sense at each successive member of a one-dimensional series of extensionless instants of time. Furthermore the mutual relations of the material entities at each instant formed these entities into a spatial configuration in an unbounded space. It would seem that space\-\--on this theory-would be as instantaneous as the instants, and that some explanation is required of the relations between the successive instantaneous spaces. The materialistic theory is however silent on this point; and the succession of instantaneous spaces is tacitly combined into one persistent space. This theory is a purely intellectual rendering of experience which has had the luck to get itself formulated at the dawn of scientific thought. It has dominated the language and the imagination of science since science flourished in Alexandria, with the result that it is now hardly possible to speak without appearing to assume its immediate obviousness.\" (Whitehead 1920). ## Direct Realism and Direct Perception Direct Realism proposes that phenomenal experience is directly objects in the world without any intervening representation. It is motivated by the belief that the Problem of Regression, the Subject-Object Paradox and the recursion form of the Homunculus arguments show that phenomenal consciousness cannot occur in the brain alone. Direct Realists reason that if phenomenal consciousness cannot be things in the brain then it must be something outside the brain. There are two principle types of Direct Realism: Natural Dualism and Behaviourism (both Radical and Analytical). Some behaviourists use the term "Direct Perception" rather than Direct Realism and consider that only the invariant parts of perception are direct (see for instance Michaels and Carello 1981). Thomas Reid is generally regarded as the founder of Direct Realism. In his Natural Dualism he proposed that the soul is in direct contact with the contents of experience and these contents are things in the world beyond the body. The Direct Realism of Reid is summarised in the statement of his famous disciple Sir William Hamilton: \"In the simplest act of perception I am conscious of myself as the perceiving subject and of an external reality as the object perceived\". Reid\'s Natural Dualism has now been largely replaced by radical and analytical behaviourism which eschew the idea of a soul and propose that phenomenal consciousness, if it exists at all, is a behavioural reflex. The modern justification of Direct Realism mainly consists of arguments against Indirect Realism or Representationalism. Philosophers such as Austin (1962) and Le Morvan (2004) have summarised the Direct Realism debate and have identified the following arguments in favour of Indirect Realism and given rebuttals to each of them: 1\. The Causal Argument: perception involves a succession of causal events such as the reflection of photons, bleaching of retinal pigments etc. so perception must involve the end of this causal chain. The Direct Realist response is that, although there may be a causal chain in sensation this does not inevitably imply that the end of the chain is the content of phenomenal experience. 2\. The Time Lag Argument: it takes time for light to travel from an object to the senses, time for chemical changes in the retina etc\... The Direct Realist response is that direct perception may be referred back in time. 3\. The Partial Character of Perception Argument: we only perceive the surface of objects, and then only a part of the surface. As the whole object would be perceived directly perception must be indirect. The Direct Realist response is that direct perception could occur even if only parts of an object were perceived. 4\. The Perceptual Relativity Argument: things appear to be different shapes depending upon the point of view. The Direct Realist response is that if perception can occur backwards in time it should have no problem occurring back down a line of sight. However, Le Morvan\'s argument does not seem to encompass the geometrical nature of phenomenal experience, seeking to explain geometry in terms of movement. 5\. The Argument from Perceptual Illusion: A stick may appear bent when projecting from the surface of water. Direct Realists apply the argument used in (4) to this problem. The bent stick illusion is a physical event in the world beyond the eye rather than a normal optical illusion such as the Muller-Lyer illusion etc., see (6) for a discussion of optical illusions. 6\. The Argument from Hallucination: Hallucinations are not in the world beyond the body. This is highly problematical for Direct Realists especially when phenomena such as lucid dreams, dreams and visual imaginations are included along with hallucinations. Direct Realists classify these phenomena as not being perceptions or deny that they actually exist as phenomena. Indirect Realists would maintain that all of perception is a reconstruction and use optical illusions such as the Muller-Lyer, Ames Room etc. to justify this contention so the Direct Realist approach to hallucination, dreams etc. might seem like an unwillingness to accept Indirect Realism rather than an argument. 7\. The Dubitability Argument (cf: Indubitability argument): we cannot doubt current phenomenal experience but we can doubt the world beyond the body therefore phenomenal experience is not the world beyond the body. Direct Realists fall back on Presentism or functional Presentism to defeat this argument. If phenomenal experience is instantaneous and made anew at each instant then anything can be doubted. The points above have summarised the Direct Realist stance on visual perception. Other sensory modalities have also been considered in the Direct Realism debate. Fowler (1986) considered that sounds were attached to objects in the world. This idea is strange because sounds only seem to be closely attached to objects in the world when these objects are seen as well as heard. For example, when a subject is blindfolded it is found that there can be a large error in locating the position of a sound in the world, this is especially true for low frequency sounds. The Direct Realist approach has difficulty explaining the transition from sounds with an indefinite location when a subject is blindfolded to sounds that are bound to visual events when the blindfold is removed. It also runs into problems explaining how the sound of speech from a single loudspeaker can become bound to lip movements on a cinema screen. If the binding does not occur in the brain then where does it occur? Pain is particularly problematic for Direct Realism because, unlike colour vision where \'red\' is inferred to be a property of electrons or light, pain is an inner experience that is not a property of tissue damage. Tissue damage has properties such as bleeding, wheal formation etc. but pain seems to be phenomenal experience in the brain and \'phantom pain\' can occur without tissue damage (see Aydede (2001), Tye (2004) and Chapman, and Nakamura (1999) for further analysis). On closer inspection other sensations also appear to be inner experiences rather than direct sensations. For instance, the red crosses of different hues in the illustration below are all due to the same physical wavelengths of light. In this case the range of hues in experience is unrelated to the actual physical red on the page or screen. Another problem for Direct Realism is that it does not overcome the problems that it is supposed to solve. The argument for Direct Realism begins with the idea that there are severe problems with representationalism (the idea that phenomenal experience is in the brain) and that direct perception is an alternative that does not have these problems. However on closer inspection Direct Realism suffers from almost same problems as representationalism. If phenomenal experience is the world itself then Ryle\'s regress applies to the world itself and this can only be avoided by assuming that phenomenal experience is a subset of the world (i.e.: a representation) that receives input from other parts of the world that are not part of phenomenal experience. It is also commonly assumed that Direct Realism avoids the recursion argument because it is believed that the separation of the observer from the things that are observed is simply due to the geometry of the world. If such simple geometry is possible between the eye and the world then it should also be possible in the brain and a similar geometrical explanation could be invoked to avoid recursion in representations. These points are shown in the illustration below: image:Constuddir1.gif Scientists have a further problem with Direct Realism. The illustration below demonstrates that our scientific knowledge of the world differs markedly from our phenomenal experience. image:constuddirect.gif It is difficult to see how the form and content of phenomenal experience could supervene directly on the world beyond the body. The world inferred from measurements beyond the body seems to be a nebulous set of quantum phenomena that are arranged as probability fields in three dimensions at any instant. The objects in this real world are mostly space. The world of phenomenal experience on the other hand contains objects that are one-sided, and are like a 2 dimensional field of vectors directed simultaneously at an observation point which is apparently separate from them. Phenomenal experience is not three dimensional, the rear of objects is not available within it at any instant. Visual phenomenal experience seems to be a geometrical relationship between an abstract observation point and the reflection properties of the part of the world external to the body. It is a form that crudely overlies the angular separations in inferred reality, providing approximate directional data. It is not like things in themselves beyond the body, not even in type, being a set of directional vectors. (See the module on the neuroscience of perception for a discussion of depth perception). If the form and content of visual phenomenal experience are abstractions separated according to the angular positions of things in the world beyond the body then theories which propose that phenomenal experience is the world itself are problematical. It should be noted that things arranged according to angular positions can appear to overlie any group of similar things along a radius from the centre point.  If Direct Realists admit that things are as they appear to be, observed according to angular positions at a \'point eye\', then any representation of things on the inside of a sphere of any radius would appear similar. The geometry of the \'point eye\' is problematical whether the view contains the world itself or a representation of the world; it cannot be the movements of lumps of matter or energy and the point observation cannot be due to lumps all landing at a point. In other words the \'view\' is inconsistent with nineteenth century materialism and will require a scientific explanation. Radical and Analytical Behaviourism tackle the problem of the difference between the world inferred from measurements beyond the body and the phenomenal world by denying phenomenal consciousness and maintaining that access and reflex consciousness are all that exists or is necessary. Radical Behaviourism is an offshoot of psychological behaviourism and was established as a philosophical adjunct to Marxism by Vygotsky and popularised by Burrhus Frederic Skinner (see Skinner 1953). There is another movement in psychological behaviourism which is similar to Radical Behaviourism called Ecological Psychology (see Gibson 1966, 1979 and also Michaels and Carello 1981). Analytical Behaviourism is a philosophical movement established by Gilbert Ryle (see Ryle 1949). The core of Analytical and Radical Behaviourism is the assumption that consciousness exists for a durationless instant so that the Dubitability Argument and the Regression and Recursion Arguments can be applied (Ryle 1949, Skinner 1971 and see the sections on Ryle\'s Regress and the Subject-Object Paradox above). As a result the Direct Realist is able to insinuate that subjects only think that they have had a particular experience (cf: Dennett 1991a). It is intriguing that Eliminativists also maintain that experience is the world itself, for instance an insight into Dennett\'s idea of the mind is to be found on pages 407-408 of Consciousness Explained: \"It seemed to him, according to the text, as if his mind - his visual field - were filled with intricate details of gold-green buds an wiggling branches, but although this is how it seemed this was an illusion. No such \"plenum\" ever came into his mind; the plenum remained out in the world where it is didn\'t have to be represented, but could just be. When we marvel, in those moments of heightened self-consciousness, at the glorious richness of our conscious experience, the richness we marvel at is actually the richness of the world outside, in all its ravishing detail. It does not \"enter\" our conscious minds, but is simply available\" This is a clear description of Direct Realism (although Dennett does not describe himself as a direct realist). Radical Behaviourism is sometimes described as the dictum that the only psychological events that are of importance are those that occur outside the head. The absurdity of this has led to jokes: Q: What does one behaviorist say to another when they meet on the street? A: You\'re fine. How am I? Q: What does one behaviorist say to another after sex? A: That was great for you. How was it for me? (Ziff 1958) However Vygotsky, Skinner and other Radical Behaviourists hold that inner behaviour is possible so that events within the brain can result in reward or punishment. Vygotsky (1925) describes this approach: \"Consciousness is wholly reduced to the transmitting mechanisms of reflexes operating according to general laws, i.e., no processes other than reactions can be admitted into the organism. The way is also paved for the solution of the problem of self-awareness and self-observation. Inner perception and introspection are possible only thanks to the existence of a proprioceptive field and secondary reflexes, which are connected with it. This is always the echo of a reaction.\" Hence Radical Behaviourists are able to make the claim that what are believed to be representations with phenomenal content are processes. Even events such as pain can then be explained as reflexes involving organs within the skin. However, by opening the possibility that such reflexes could occur at any sense organ, including the eye, this makes Radical Behaviourism a mixed Direct Realist/Indirect Realist philosophy with consciousness as a process, not a separate thing such as phenomenal consciousness (see the section on representationalism and intentionality below). But this raises a serious issue for science: can the phenomenal consciousness that seems to contain our observations really be argued out of existence on the basis of a theory? As Gregory (1988) put it: " 'If you can't explain it -- deny it' is one strategy for dealing with embarrassing questions such as 'what is consciousness?' ". But is this the right strategy? Direct Realism fails to overcome the problems of regression and recursion inherent in representations. It proposes that phenomenal consciousness is identical to the physical world beyond the body but must then use a plethora of arguments to explain why this is evidently not so. When confronted with these problems its proponents resort to the argument that everything can be doubted and can misrepresent itself. Yet it is still widely believed. It should be noted that Direct Realism is espoused in Religious Natural Dualism, some forms of Augustinian theology, nineteenth century materialism and its offspring such as Marxism, post-modernism, post-Marxism, and various sociological movements. It is also necessary for some forms of Strong AI to occur. Perhaps this explains why few ideas have attracted as much attention and defence as Direct Realism. It is interesting to compare the Direct Realist and Indirect Realist interpretations of something as simple as a cartoon on television (such as the image below). According to Indirect Realism the cartoon would be a moving representation constructed in the brain using data from the senses. This leads to the prediction of brain mechanisms for modelling motions, combining colours, binding sound and vision etc., many of which have been verified. Can you demonstrate how the theory of Direct Realism could explain the phenomenal experience that contains the cartoon and produce a list of the predictions made by the theory?  In science a theory should be of predictive value, for instance, information theory describes how the state of a thing can be impressed on a carrier so that a signal can be transmitted from one place to another. This theory predicts what will happen when the signal arrives at its destination and how the state of the source can be inferred from the events at the destination, the total amount of information that can be transmitted etc. At the destination it is the form of the signal that is directly known by interaction and measurement, the form of the source is inferred. Direct Realism is a direct challenge to this information theory but does it deliver a more powerful predictive description of phenomenal consciousness or is experience always dependent on what happens to the information flow between things in the world and somewhere in the brain? Does direct realism have a physical theory? Ultimately it appears as if Direct Realism is about various understandings of Information Theory. For example, Austin (1962) discusses what we see when we see a church camouflaged as a barn and comments that: \"We see, of course, a church that now looks like a barn.\". Do we see a church or a barn? Scientific information theory is clear about this, the church is an entity composed of selected information from the quantum state of its constituents, the optical image of a camouflaged church is an arrangement of photons emanating from a screen on which it is projected, the retina has an arrangement of chemical and electrical events based on an optical image and conscious visual experience correlates with the arrangement of things on the retina. The fact that conscious experience also correlates with classifications of the retinal image as a barn or a church suggests that conscious experience is an arrangement of things in the brain based on both the retinal arrangement and the contents of a relational database. Austin\'s arguments have been mythologised as a final demonstration that \"sense data\" theories are false. However, as will be seen below, sense data theories merely claim that there is a succession of information states between an information state outside the body and that reported as conscious experience i.e.: subjects report that a church is camouflaged when it is camouflaged. ## Indirect Realism Indirect realism proposes that phenomenal consciousness exists and is a set of signals or **sense data**, usually in the brain. This was proposed by philosophers from Aristotle to Locke and was probably the most widespread idea of conscious experience until the eighteenth century. The idea of sense data is discussed in depth by Russell (1912). Russell\'s original definition is given below: `<font face="times new roman">`{=html}\"Let us give the name of \'sense-data\' to the things that are immediately known in sensation: such things as colours, sounds, smells, hardnesses, roughnesses, and so on. We shall give the name \'sensation\' to the experience of being immediately aware of these things. Thus, whenever we see a colour, we have a sensation of the colour, but the colour itself is a sense-datum, not a sensation. The colour is that of which we are immediately aware, and the awareness itself is the sensation. It is plain that if we are to know anything about the table, it must be by means of the sense-data \-- brown colour, oblong shape, smoothness, etc. \-- which we associate with the table; but, for the reasons which have been given, we cannot say that the table is the sense-data, or even that the sense-data are directly properties of the table.\"`</font>`{=html} Russell\'s definition is a materialist concept in which experience is always **of** something because the durationless instant of the present has always gone. As such it differs from some empiricist ideas where experience is not confined to the durationless instant. Science is Indirect Realist because it holds that the scientist can only make **measurements** of events in the world. These measurements give rise to signals as a result of interaction with the event. According to **decoherence theory** the signals are a state that is a mixture of the state of the measuring instrument and the state of the thing being measured. For example, the eyes are measuring instruments that are sensitive to photons, photons are signals containing a state that is based on the state of electrons in a surface and the state of electrons is based on the state of the surface etc. Scientific inference allows some aspects of the state of the surface to be inferred from the state of the photons. In modern Indirect Realism there is an attempt to distinguish the phenomenal content of conscious experience from the processing involved in accessing this phenomenal content. According to these theories phenomenal experience is an arrangement of signals that are the content of the experience. This arrangement forms a *representation* of things in the world so this form of indirect realism is known as **Representationalism**. Tye (2003) describes types of representationalist theory: `<font face="times new roman">`{=html}\"Representationalism, as I have presented it so far, is an identity thesis with respect to qualia: qualia are supposedly one and the same as certain representational contents.\"`</font>`{=html} Tye also describes variants of this idea of representationalism: `<font face="times new roman">`{=html}\"Sometimes it is held instead that qualia are one and the same as certain representational properties of experiences; and sometimes it is is argued that these representational properties are themselves irreducible (Siewert 1998). There is also a weaker version of representationalism, according to which it is metaphysically necessary that experiences exactly alike with respect to their representational contents are exactly alike with respect to their qualia. Obviously, this supervenience thesis leaves open the further question as to the essential nature of qualia.\"`</font>`{=html} (Tye 2003). In a scientific sense Direct Realists believe that phenomenal experience is the signals that occur next to things in the world beyond the body (which they call \"things in themselves\") and Indirect Realists usually believe that phenomenal experience is signals in the brain. It can be seen from the pattern of signal flow that the signals travelling into the brain preserve the spatial relationships of the original signals and encode the properties in the original signals. This means that the original signals next to the QM sources and the signals in the brain are equivalent provided the latter are oriented appropriately relative to signals from the body. Either set of signals could transmit or contain the same information. Both Direct and Indirect Realism cannot, at present, explain the physics of how a viewing point occurs in experience i.e.: how we seem to see through an apparent space to the signals that are the contents of experience. So the choice between Direct Realism and Indirect Realism reduces to whether there is only one set of signals or a chain of signals between the world and phenomenal experience. The philosophical arguments for Indirect Realism are listed below: 1\. Variable perspective: when we see things the view changes so what we see must be a different set of signals depending on the view rather than a constant object. 2\. Illusions: we can see through fingers and see a variety of colours where measurements tell us one exists. Direct Realists quote the \"bent stick illusion\", which is not really an illusion at all, being a physical event. 3\. Hallucinations: two people can have phenomenal experience containing a table. The first may be viewing a real table whereas the second may be hallucinating a table. If the tables are the same (phenomenally) then experience is indirect. 4\. Double vision: press the side of one eye, two images appear (cf Hume 1739) yet there are not two things in the world. 5\. Time gap arguments: according to materialism the past has gone. The things being seen no longer exist in the state that relates to the state in experience. In the extreme case, some stars in the night sky no longer exist but are still in experience so experience must be a derived signal. 6\. Secondary qualities such as pain, colour and smell do not exist as physical things in the source of signals and are likely to be properties of signals in the brain.  Indirect Realism has received strong support from recent discoveries in neuroscience, for example, it is now clear that both the colour and motion in phenomenal experience are added by cortical processes. In Cerebral **Achromatopsia** patients have suffered trauma to area V4 of the cerebral cortex and report seeing the world in greyscale with no colour vision and in Congenital Achromatopsia people do not even understand the meaning of \'colour\'. In an astonishing ailment called **Akinetopsia** patients perceive movement as a succession of stationary images (Rizzo *et al.* 1995). Akinetopsia is usually associated with damage to cortical area V5. Moutoussis and Zeki (1997) have demonstrated that the addition of colour occurs more rapidly than the addition of motion. The section on the Neuroscience of Consciousness describes these discoveries and many other aspects of the creation of phenomenal experience in the brain. Unfortunately knowledge of the whereabouts of the signals that are the content of conscious experience does not resolve the problem of phenomenal consciousness. Whether these signals are next to objects in the world or at the end of a chain of signals in the brain there still remains the problem of how they become arranged in the form of experience. If such a thing occurs at all. ### Intentionality and representation There is a materialist interpretation of representationalism in which representations are redefined as intentional states: `<font face="times new roman">`{=html}\"One way of explaining what is meant by 'intentionality' in the (more obscure) philosophical sense is this: it is that aspect of mental states or events that consists in their being of or about things (as pertains to the questions, 'What are you thinking of?' and 'What are you thinking about?'). Intentionality is the aboutness or directedness of mind (or states of mind) to things, objects, states of affairs, events. So if you are thinking about San Francisco, or about the increased cost of living there, or about your meeting someone there at Union Square---your mind, your thinking, is directed toward San Francisco, or the increased cost of living, or the meeting in Union Square. To think at all is to think of or about something in this sense. This 'directedness' conception of intentionality plays a prominent role in the influential philosophical writings of Franz Brentano and those whose views developed in response to his (to be discussed further in Section 3).\"(Siewert 2003)`</font>`{=html} This definition allows \"representation\" to be redefined as a data stream rather than a set of things arranged in some mental or neural state that represents things in space. Husserl thought this approach would allow a description of consciousness that \"carefully abstains from affirming the existence of anything in spatio-temporal reality\" (Siewert 2003) although it could be argued that a data stream such as any description can never escape the constraints of representation in time at some place. Unfortunately the concept of \"intentionality\" has become so diverse that it could be applied to almost any aspect of the description of consciousness. An interesting example of this is given by Loar (2001) where \"intentionality\" is considered to overlap \"representing\" and \"conceiving\": `<font face="times new roman">`{=html}\"A person\'s thoughts represent things to her \-- conceive things \-- in many ways: perceptually, memory-wise, descriptively, by naming, by analogy, by intuitive sorting, theoretically, abstractly, implicitly and explicitly. These various manners of conceiving have something in common: they have intentional properties, and they have them essentially. `</font>`{=html} The usage of the term \"intentional state\" has become so broad that it now means little more than a state that is about another state. References Siewert, C. (2003). Consciousness and Intentionality. The Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/consciousness-intentionality/> Also see Loar, B. (2001) "Phenomenal Intentionality as the Basis of Mental Content", in Reflections and Replies, ed. M. Hahn and B. Ramsberg, MIT. <http://www.nyu.edu/gsas/dept/philo/courses/concepts/loar.html> Williford, K. (2002) The intentionality of consciousness and the consciousness of intentionality. Intentionality: Past and Future, edited by Gábor Forrai and George Kampis, Amsterdam/New York: Rodopi. <http://web.stcloudstate.edu/kwwilliford/Intentionality%20of%20Consciousness.pdf> Byrne, A. (2001). Intentionalism Defended. Philosophical Review 110 (April 2001):199-240. <http://stripe.colorado.edu/~leeds/byrne.pdf> ### Cartesian materialism The term \"Cartesian materialism\" once meant the idea that the mind is in the brain (see for instance Block 1995). The term had largely fallen out of use in philosophy until revived by Daniel Dennett (1991) in the book *Consciousness Explained*. Dennett uses a very particular definition of the term in his discussions and also uses a particular definition of the word \"mind\". See the section on Daniel Dennett for Dennett\'s critique. Philosophers who adhere to the idea that the mind is in the brain tend to call themselves \"indirect realists\" or \"representationalists\" where the substrate of conscious experience is in the brain and would deny that Dennett\'s critique applies to their proposals. Dennett\'s critique makes the materialist assumption that if there is a representation in the brain then a further flow of material out of this representation would be required for the representation to become part of mind. ### Identity theories of mind The idea that mental states are brain states is known as the **identity theory of mind**. There are two sorts of identity theory, in **type** identity theory it is held that mental states are identical to brain states whereas in **token** identity theory it is held that mental states correlate with brain states. Type identity theory was attacked by Putnam in \"The Nature of Mental States\" where he pointed out that if mental states are functions then type identity theory would presuppose that animals that had the same mental states would need to have identical brain structures. He suggested that this is unlikely, it being more probable that animals have functional systems that perform similar overall functions but which are not identical. In other words, if it is assumed that conscious experience is a set of functions then token identity theory is more probable than type identity theory. Putnam\'s critique does not preclude identity theories of mind that involve \"passive ideas\" (i.e.: states that are not classical functions). Most identity theories of mind would be representational, the physical states representing the world in some way. All identity theories of mind involve Cartesian materialism in the sense of the mental states being brain states. According to identity theories the mind is in the brain. Putnam, H. (1967) The nature of mental states. In The Nature of Mind, edited by Rosenthal, pp. 197--203. Originally published as \"Psychological predicates in Art, Mind, and Religion\", edited by Capitan and Merill, pp. 37--48. ## Dualism Prior to considering the arguments surrounding dualism it is important to have a clear idea of \"information\" because many of these arguments have parallels with the difference between information as a set of states that can be transmitted and the substrate on which this information is expressed or from which the information is derived. See Elementary information and information systems theory. ### Cartesian dualism Descartes, a philosopher, analysed his experience and developed an empirical description of how it is arranged. He described mental images and perceptions as extended in space and with a duration. He called these extended things **ideas** (Cartesian ideas) and proposed that they are patterns in the brain. Descartes thought the pineal gland was the most likely location for these ideas because it is one of the few single organs in the brain. He also proposed that there is a rational soul that directly contacts these ideas: `<font face="times new roman">`{=html}\"Now among these figures, it is not those imprinted on the external sense organs, or on the internal surface of the brain, which should be taken to be ideas - but only those which are traced in the spirits on the surface of gland H *(where the seat of the imagination and the \'common sense\' is located)*. That is to say, it is only the latter figures which should be taken to be the forms or images which the rational soul united to this machine will consider directly when it imagines some object or perceives it by the senses.\" Descartes (1664)`</font>`{=html} See section on Descartes for more information and references. Descartes considered that the soul was a physical point, an unextended entity that acts like a mind\'s eye. He called this unextended place the *res cogitans* and concluded that it was a substance that differed from that of material things: `<font face="times new roman">`{=html}\".. I thence concluded that I was a substance whose whole essence or nature consists only in thinking, and which, that it may exist, has need of no place, nor is dependent on any material thing; so that \" I,\" that is to say, the mind by which I am what I am, is wholly distinct from the body, and is even more easily known than the latter, and is such, that although the latter were not, it would still continue to be all that it is.\"Descartes (1637)`</font>`{=html} This unextended substance that is not material gives the word \"substance\" a new meaning. It has been attacked as a concept by Locke, Hume, Berkely and many other philosophers. The concept of there being two substances, that which composes the physical world and that which composes the soul, is the origin of the word **Dualism** but dualism, as a concept, has been extended beyond this original meaning. Cartesian dualism is a type of **substance dualism**. Cartesian dualism is an attempt to explain our experience. According to Descartes something supernatural would be needed for an unextended viewing point to exist. Reid\'s **Natural Dualism** also has a point soul looking at things but proposes that the things in question are forms in the world rather than in the brain. ### Property dualism Another sort of dualism has arisen out of a particular interpretation of the regress and homunculus arguments. These arguments show that phenomenal experience is not due entirely to flows from place to place (i.e.: it is not due to classical processes and functions). Property dualism asserts that when matter is organized in the appropriate way (i.e. in the way that living human bodies are organized), mental properties emerge. As Goldman (1993) pointed out, qualitative experience does not seem to be needed in a functional description of a system: `<font face="times new roman">`{=html}\"For any functional description of a system that is in pain (or has an itch), it seems as if we can imagine another system with the same functional description but lacking the qualitative property of painfulness (or itchiness).\" `</font>`{=html} Certainly a functional system that merely reports the words \"I am in pain\" when it is dropped on the floor does not require any qualitative property of painfulness. The *absent qualia* arguments suggest that even in a large system there would be no need for qualitative properties for the performance of any classical function. Chalmers (1993) commenting on Goldman\'s point, said that this implies that **zombies** might exist, functional replicas of humans but without qualia. He then denied that a complete functional replica of a human could exist without also including qualia: `<font face="times new roman">`{=html}\"It seems to me that the only way to avoid this conclusion is to deny that Zombie Dave is a conceptual possibility; and the only principled way to deny that Zombie Dave is a conceptual possibility is to allow that functional organization is conceptually constitutive of qualitative content.\" Chalmers (1993).`</font>`{=html} In other words he identifies qualia with function. According to Chalmers (1996) qualia are a particular type of function: `<font face="times new roman">`{=html}\"I claim that conscious experience arises from fine-grained functional organization. More specifically, I will argue for a principle of organizational invariance, holding that given any system that has conscious experiences, then any system that has the same fine-grained functional organization will have qualitatively identical experiences. According to this principle, consciousness is an organizational invariant: a property that remains constant over all functional isomorphs of a given system. Whether the organization is realized in silicon chips, in the population of China, or in beer cans and ping-pong balls does not matter. As long as the functional organisation is right, conscious experience will be determined.\" p249`</font>`{=html} Chalmers\' idea of functional organisation has within it a sometimes vague implication that the functional units must have a particular form; for instance, in the development of his argument, he refers to "fine grained" replacement of organic functional units with inorganic units. Chalmers is actually making two major points, firstly that qualia occur during the motion of things (functions), secondly that qualia are independent of any particular substrate.\*\* For the first point to be consistent with materialism the qualia must have no effect on the function, they must be **epiphenomenal**. Epiphenomenal qualia would not be forbidden by the regress and homunculus arguments and would be akin to Berkeley\'s \"passive ideas\". Whether or not epiphenomenal qualia are physical depends upon the definition of the word \"physical\". If physical functions cause qualia but qualia cannot affect functions then the qualia are \"physical\" in the sense of being caused by physical events but might be regarded as non-physical in the sense of being isolated from further physical events. In philosophical terms they violate the principle of **Causal Closure**. However, there are other definitions of physicalism based on arguments such as **Methodological Naturalism** which hold that anything that can be investigated using the methods of natural science is a physical thing (see Stoljar 2001). Thus, although epiphenomenal qualia may not conform to materialism they may be encompassed by physicalism; as events that are related to material events they are awaiting a physical theory of how they emerge from a given function. The reader might consider whether phenomenal consciousness is indeed epiphenomenal. Empirical reports describe it as something that is different from the world beyond the body (see direct realism) - could we generate empirical reports of an epiphenomenon? The term **property dualism** describes how physical events might give rise to a set of properties that cannot be predicted from the fine structure of the physical system. The \"dualism\" is present because one set of events is related to two sets of properties, one of which is not related by materialism to the set of events. In the case of the proposal about consciousness outlined above an extra assumption, beyond materialism, would be needed to explain qualia. Property dualism might be defined as a theory that there could be a theory of consciousness but that this requires some new assumption. As far as the \"when and where\" of consciousness are concerned, property dualism states that it is somewhere in the processes performed by the organism and the parts of the organism. `<font size=1>`{=html} \*\* In terms of information processing, Chalmers is proposing that qualia are the enactment of a particular information processing structure.`</font>`{=html} - Block, N. (2006). Max Black\'s objection to mind-body identity. Oxford Review of Metaphysics No.3. <http://philrsss.anu.edu.au/BlockFest/MaxBlack.rtf> - Chalmers, D.J. (1993) Commentary on \"The Psychology of Folk Psychology\". Behavioral and Brain Sciences 16:35-36, 1993 - Chalmers, D.J. (1996) \"The Conscious Mind: In Search of a Fundamental Theory\". Oxford University Press. 1996. - Goldman, A.I., (1993). The Psychology of Folk Psychology. Behavioral and Brain Sciences 16: 15-28 (1993). <http://www.ecs.soton.ac.uk/~harnad/Papers/Py104/goldman.psyc.html> ### Predicate dualism Predicate dualism is the view espoused by most non-reductive physicalists, such as Donald Davidson(1980) and Jerry Fodor(1968), who maintain that while there is only one ontological category of substances and properties of substances (usually physical), the predicates that we use to describe mental events cannot be redescribed in terms of (or reduced to) physical predicates of natural languages. If we characterize predicate monism as the view subscribed to by eliminative materialists, who maintain that such intentional predicates as believe, desire, think, feel, etc., will eventually be eliminated from both the language of science and from ordinary language because the entities to which they refer do not exist, then predicate dualism is most easily defined as the negation of this position. Predicate dualists believe that so-called \"folk psychology\", with all of its propositional attitude ascriptions, is an ineliminable part of the enterprise of describing, explaining and understanding human mental states and behavior. Davidson, for example, subscribes to Anomalous Monism, according to which there can be no strict psycho-physical laws which connect mental and physical events under their descriptions as mental and physical events. However, all mental events also have physical descriptions. It is in terms of the latter that such events can be connected in law-like relations with other physical events. Mental predicates are irreducibly different in character (rational, holistic and necessary) from physical predicates (contingent, atomic and causal). (Section based on Wikipedia article) - Davidson, D (1980). Essays on Actions and Events. Oxford University Press. - Fodor,J. (1968) *Psychological Explanation*, Random House. . ### The interaction between mind and brain in dualism #### Interactionism Interactionism is the view that mental states, such as beliefs and desires, causally interact with physical states. This is a position which is very appealing to common-sense intuitions, notwithstanding the fact that it is very difficult to establish its validity or correctness by way of logical argumentation or empirical proof. It is appealing to common-sense because we are surrounded by such everyday occurrences as a child\'s touching a hot stove (physical event) which causes him to feel pain (mental event) and then yell and scream (physical event) which causes his parents to experience a sensation of fear and protectiveness (mental event) and so on. #### Epiphenomalism According to epiphenomenalism, all mental events are caused by a physical event and have no physical consequences. So, a mental event of deciding to pick up a rock (call it \"M\") is caused by the firing of specific neurons in the brain (call it \"P\"), however when the arm and hand move to pick up a rock (call it \"E\") this is only caused by P. The physical causes are in principle reducible to fundamental physics, and therefore mental causes are eliminated using this reductionist explanation. If P causes M and E, there is no overdetermination in the explanation for E. #### Parallelism Psycho-physical parallelism is a very unusual view about the interaction between mental and physical events which was most prominently, and perhaps only truly, advocated by Gottfried Wilhelm von Leibniz. Like Malebranche and others before him, Leibniz recognized the weaknesses of Descartes\' account of causal interaction taking place in a physical location in the brain. Malebranche decided that such a material basis of interaction between material and immaterial was impossible and therefore formulated his doctrine of occasionalism, stating that the interactions were really caused by the intervention of God on each individual occasion. Leibniz idea is that God has created a pre-established harmony such that it only seems as if physical and mental events cause, and are caused by, one another. In reality, mental causes only have mental effects and physical causes only have physical effects. Hence the term parallelism is used to describe this view. #### Occasionalism Occasionalism argues that bodily events are the occasion of an act by the Creator causing a corresponding mental event, and vice versa. Any such view requires a theological structure as a premise. #### Further reading - Robinson, Howard, \"Dualism\", The Stanford Encyclopedia of Philosophy (Fall 2003 Edition), Edward N. Zalta (ed.), <http://plato.stanford.edu/archives/fall2003/entries/dualism/> - Robinson, H. (2003) \"Dualism\", in S. Stich and T. Warfield (eds) The Blackwell Guide to Philosophy of Mind, Blackwell, Oxford, 85-101. - Amoroso, R.L. (2010) \"The complementarity of Mind and Body: Realizing the Dream of Descartes, Einstein and Eccles\", New York: Nova Science Publishers, `, ``https://www.novapublishers.com/catalog/product_info.php?products_id=12759` ## Idealism According to Idealism only the mental truly exists. The form and content of personal conscious experience might be related to the structure of the world and brain in several ways. It could be a **solipsism** or be the mind of God. *This is a **stub** and needs expansion*. ## Panpsychism ### Etymology Ancient Greek *pan* (πᾶν : \"all, everything, whole\") and *psyche* (ψυχή : \"soul, mind\").[^1] Psyche is the from ψύχω (*psukhō*, \"I blow\") and means mind or \'life-breath\'. Philip Goff, a proponent of panpsychism, carves out a distinction between panexperientialism and pancognitivism. Panexperientialism is the belief that *experience* is ubiquitous, while pancognitivism is the belief that *cognition* is ubiquitous. Most modern purponents of panpsychism, such as Annaka Harris and David Chalmers, are careful to distance themselves from pancognitivism. In some interpretations, such as monadism, Panpsychism and Idealism can overlap because the universe is conceived as being composed of an infinity of point consciousnesses that each contain information about the whole universe. The form and content of personal conscious experience might be related to the structure of the world and brain in many ways. *This is a **stub** and needs expansion*. ## References Seager W. & Allen-Hermanson (2001). 'Panpsychism.' Online document: Stanford Encyclopedia of Philosophy, \[online\], <http://plato.stanford.edu/entries/panpsychism/>, \[accessed 10/2005\] **Supervenience** - Chalmers, D.J. (1996). The Conscious Mind. Oxford University Press. **The problem of regression** - Ryle, G. (1949) The Concept of Mind. The University of Chicago Press, 1949. **The homunculus argument** - Gregory, R.L. (1990) Eye and Brain: The Psychology of Seeing, Oxford University Press Inc. New York. - Gregory, T.L. (1987). The Oxford Companion to Mind. Oxford University Press. **Subject-object paradox** - James, W. (1904)Does \'Consciousness\' Exist? Journal of Philosophy, Psychology, and Scientific Methods, 1, 477-491. - Hegel, G.W.F. PHILOSOPHY OF MIND: SECTION I. MIND SUBJECTIVE B. PHENOMENOLOGY OF MIND CONSCIOUSNESS Part Three of the Encyclopaedia of the Philosophical Sciences - Velmans, M. (1996) Consciousness and the \"Casual Paradox\". Behavioral and Brain Sciences, 19 (3): 538-542. - Bermudez, J.L. (1999) The Paradox of Self-Consciousness (representation and Mind) Psycoloquy: 10,#35 **Ontological status** - Bierman, D.J. (2004) Non Conscious Processes Preceding Intuitive decisions <http://m0134.fmg.uva.nl/~djb/publications/2004/Intuition_bialsymp2004.pdf> - Damasio, A.R. (1994). Descartes\' error: Emotion, reason and the human brain. New York: Grosset/Putnam Book. - Kant, I. Critique of Pure Reason <http://www.arts.cuhk.edu.hk/Philosophy/Kant/cpr/> **Phenomenal consciousness and access consciousness** Block, N. (1995) On a confusion about a function of consciousness. Behavioral and Brain Sciences 18 (2): 227-287. <http://www.bbsonline.org/documents/a/00/00/04/31/bbs00000431-00/bbs.block.html> Block, N. (2004). *The Encyclopedia of Cognitive Science*. <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/ecs.pdf> Dennett, D. (1978). Why You Can\'t Make a Computer that Feels Pain, in: Brainstorms. Cambridge, MA: MIT Press: 190-229. Dennett, D. (1988). Quining Qualia. in A. Marcel and E. Bisiach, eds, Consciousness in Modern Science, Oxford University Press 1988. Reprinted in W. Lycan, ed., Mind and Cognition: A Reader, MIT Press, 1990, A. Goldman, ed. Readings in Philosophy and Cognitive Science, MIT Press, 1993. <http://ase.tufts.edu/cogstud/papers/quinqual.htm> Edelman, G.M. (1993). Bright Air, Brilliant Fire: On the Matter of the Mind. New York: Feyerabend, P. (1963). Mental Events and the Brain, Journal of Philosophy 40:295-6. Huxley, T. H. (1874). On the Hypothesis that Animals are Automata, and its History, The Fortnightly Review, n.s.16:555-580. Reprinted in Method and Results: Essays by Thomas H. Huxley (New York: D. Appleton and Company, 1898). Nagel, T. (1974). What is it like to be a bat? The Philosophical Review LXXXIII, 4 (October 1974): 435-50. <http://web.archive.org/19990218140703/members.aol.com/NeoNoetics/Nagel_Bat.html> Rey, Georges, (1997). Contemporary Philosophy of Mind.Blackwell: Oxford Sellars W. (1956). Empiricism and the Philosophy of Mind, In: Feigl H and Scriven M (eds) The Foundations of Science and the Concepts of Psychology and Psychoanalysis: Minnesota Studies in the Philosophy of Science, Vol. 1. Minneapolis: University of Minnesota Press: 253-329 Whitehead, A.N. (1920). The Concept of Nature. Chapter 3: Time. <http://spartan.ac.brocku.ca/~lward/Whitehead/Whitehead_1920/White1_03.html> **Direct Realism** - Austin, J.L. (1962) Sense and Sensibilia, ed. by Geoffrey J. Warnock (Oxford, 1962) - Aydede, M. (2001) Naturalism, introspection, and direct realism about pain. Consciousness and Emotion, Vol. 2, No. 1, 2001, pp. 29--73. <http://web.clas.ufl.edu/users/maydede/pain.pdf> - Chapman, C.R., and Y. Nakamura (1999). A Passion of the Soul: An Introduction to Pain for Consciousness Researchers. Consciousness and Cognition, 8: 391-422. - Dennett, D. (1991a). Consciousness Explained. Boston: Little, Brown - Dennett, D. (1991b). Lovely and suspect qualities. Commentary on David Rosenthal, \"The Independence of Consciousness and Sensory Quality\" in E. Villanueva, ed., Consciousness, (SOFIA Conference, Buenos Aires), Atascadero, CA: Ridgeview 1991. <http://ase.tufts.edu/cogstud/papers/lovely&s.htm> - Fowler C A (1986): "An event approach to the study of speech perception from a direct-realist perspective", J of Phonetics 14(1):3-28. - Gibson, J. J. (1966) The Senses Considered as Perceptual Systems. Houghton Mifflin Company,Boston. - Gibson, J. J. (1979) Ecological Approach to Visual Perception.: Lawrence Erlbaum Associates Publishers, Hillsdate. - Gregory, R.L. 1988. Consciousness in science and philosophy: conscience and con-science. Chapter 12 in Consciousness in Contemporary Science. (Editors: Marcel, A.J. and Bisiach, E.). Oxford Science Publications. - Le Morvan, Pierre (2004). Arguments against direct realism and how to counter them. *The American Philosophical Quarterly*, *41*(3), 221-234.\] (pdf) <http://www.tcnj.edu/~lemorvan/DR_web.pdf> - Michaels, C. F. and Carello, C. (1981). Direct Perception. Century Psychology Series. Prentice-Hall. . 1981. Download this book at <http://ione.psy.uconn.edu/~psy254/MC.pdf> - Oliveira, André L. G. and Oliveira, Luis F. (2002) Toward an ecological conception of timbre. In Proceedings Auditory Perception Cognition and Action Meeting 2002, Kansas City. <http://cogprints.org/2713/> - Skinner, B. F. Science and Human Behavior . New York: Macmillan, 1953. - Skinner, B. F. 1971. Beyond Freedom and Dignity. New York: Knopf. - Skinner, B. F. 1948. Walden Two. New York: Macmillan. - Tye, M. (2004). ANOTHER LOOK AT REPRESENTATIONALISM ABOUT PAIN. Consciousness and Emotion 2004, special issue on pain, edited by Murat Aydede (with replies by M. Aydede, N. Block, B. Maund, and P. Noordhof <http://sun.soci.niu.edu/~phildept/MT/RepresentationalismAndPain.pdf> - Vygotsky, L.S.(1925) Consciousness as a problem in the psychology of behavior. Undiscovered Vygotsky: Etudes on the pre-history of cultural-historical psychology (European Studies in the History of Science and Ideas. Vol. 8), pp. 251--281. Peter Lang Publishing. <http://www.marxists.org/archive/vygotsky/works/1925/consciousness.htm> - Ziff, Paul. \"About Behaviourism.\" Analysis 18 (1958): 132-136. Quoted by Larry Hauser in the Internet Encyclopedia of Philosophy. <http://www.utm.edu/research/iep/b/behavior.htm#B>. F. Skinner: Radical Behaviorism **Indirect Realism** - Moutoussis, K. and Zeki, S. (1997). A direct demonstration of perceptual asynchrony in vision. Proceedings of the Royal Society of London, Series B: Biological Sciences, 264, 393 - 399. - Rizzo, M., Nawrot, M. & Zihl, J. (1995). Motion and shape perception in cerebral akinetopsia.Brain, 118. 1105-1127. <http://nawrot.psych.ndsu.nodak.edu/Publications/Nawrot.pdf/RizzoNawrotZihl.1995.pdf> - Russell, B. (1912). Problems of Philosophy. Home University Library. <http://www.ditext.com/russell/rus1.html> - Tye, M. (2003) Qualia. Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/qualia/#Repqualia> Further reading: - Hume, D. (1739). A Treatise of Human Nature. <http://www.class.uidaho.edu/mickelsen/ToC/hume%20treatise%20ToC.htm> - Firth, R. (1949) Sense Data and the Percept Theory, Mind, 58 (1949); 59 (1950). (Describes early reasons for rejecting Indirect Realism) <http://www.ditext.com/firth/spt.html> - Grush, R. (2000). Self, world and space: The meaning and mechanisms of ego- and allocentric spatial representation. Brain and Mind 1(1):59-92. <http://mind.ucsd.edu/papers/sws/sws.html> [^1]: Clarke, D.S. *Panpsychism: Past and Recent Selected Readings*. State University of New York Press, 2004. p.1

# Consciousness Studies/The Philosophical Problem ## The philosophical problem of phenomenal consciousness Chalmers (1996) encapsulated the philosophical problem of phenomenal consciousness, describing it as the *Hard Problem*. The Hard Problem can be concisely defined as \"how to explain a state of consciousness in terms of its neurological basis\" Block (2004). A state is an arrangement of things in space over a period of time. It is possible that the Hard Problem has not been solved because the concepts of \"space\", \"time\" and \"things\" are intensely problematic in both science and philosophy. Some philosophers have argued that *changes* in state are equivalent to \"mental states\". That consciousness experience always involves acts, such as acts of acquaintance (Russell 1912). But what is a succession of states in the brain or the physical world? As an extension of the idea of \"acts\" as mental states many philosophers have argued that the functional description of a system does not need to contain any reference to qualia within that system. Such ideas, based on nineteenth century materialism, have been expressed by Huxley, Ryle, Smart, Goldman and many others. However, although qualia are not required for classical functions, such as most computations or servo-control, it is far from clear whether this is true for all functions. If a function is described as any thing that mediates a change in state it should be realised that \"change\" itself is not fully understood in philosophy or science and that some systems, such as quantum mechanical systems, contain state changes that are far from understood. It will be seen below that our scientific knowledge is not yet sufficiently complete to allow the claim that all, or even any, changes can occur without qualia. Whether a philosopher or scientist is dualist, materialist or physicalist they should have some insight into current theories about the physical world. Certainly, if they are considering the problem of \"how to explain a state of consciousness in terms of its neurological basis\" then some idea of a \"neurological basis\" is essential. The objective of this section is to give an account of the problems of space, time and content and to describe how these affect the problem of consciousness. ## Epiphenomenalism and the problem of change Philosophers have noticed since the time of Leibniz that phenomenal consciousness does not seem to be required for the brain to produce action. As an example there are numerous reflexes that can occur without any awareness that they are happening. In fact it is difficult to think of any response to a stimulus that requires phenomenal consciousness and could not, in principle, be performed in the absence of conscious intervention. T.H. Huxley is often regarded as the originator of the term **epiphenomenalism** to describe how consciousness seems extraneous to processes in the materialist interpretation of the world although the term may have originated in James\' description of Huxley\'s (1874) ideas. According to nineteenth century science changes in state cannot explain the existence of phenomenal consciousness so superficially it may appear as if phenomenal consciousness is unnecessary. However, it may come as a shock to the reader to discover that nineteenth century science is also unable to account for any change in state. In the materialist paradigm time is construed to be a succession of instants of no duration, each of which is entirely separate from the others. As a result no instant can cause a change in another instant. It is not only conscious experience that is epiphenomenal, each instant of the nineteenth century concept of the world is epiphenomenal because it cannot give rise to the next instant. On the one hand it seems that conscious experience is not required for a nineteenth century model of behaviour and on the other hand nineteenth century science seems to be impossible without extraneous input from a conscious observer who contains the idea of change. The problem of change is closely related to the problem of time which is discussed in depth below. (See Change and Inconsistency, Stanford Encyclopedia of Philosophy). The reader might consider whether phenomenal consciousness is indeed epiphenomenal. Empirical reports describe it as something that is different from the world beyond the body (see direct realism) - but could we generate empirical reports of an epiphenomenon? If we do indeed generate empirical reports of phenomenal consciousness is there some non-materialist, physical\*\* connection between phenomenal consciousness and the functional state? In the analysis that follows it is essential that the reader does not dismiss the possibility that conscious experience is largely non-functional in a classical sense. The idea that observation is not action should not be dismissed out of hand. Indeed the claim that something cannot be true if it is \"epiphenomenal\" in a classical sense is astonishing in the context of modern quantum physics. Everettian approaches (and offshoots like the Bohmian, Consistent Histories and operational (decoherence) approaches) to quantum physics all allow that the classical world is epiphenomenal (cf: Page 1997, Stapp 1998). The Copenhagen Interpretation, however, was less clear on this issue. It is curious that problems with the nature of phenomenal consciousness are also problems with nineteenth century science - Aristotlean regress in the mind is part of the wider problem of epistemological regress and epiphenomenalism is part of the wider problem of change. Perhaps nineteenth century science is not an appropriate foundation for understanding consciousness. Recommended reading: Mortensen, C. (2002) Change. The Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/change/> Page, D.N. (1997). Sensible Quantum Mechanics: Are Only Perceptions Probabilistic? <http://arxiv.org/abs/quant-ph/9506010> Rivas, T., & Dongen, H. van (2003). Exit Epiphenomenalism: The Demolition of a Refuge Stapp, (1998). Quantum Ontology and Mind-Matter Synthesis.\[Appeared in proceedings of X-th Max Born Symposium, eds, Blanchard and Jadczyk, Vol 517 Lecture notes in Physics series, Springer-Verlag, 1999 (Quantum Future:from Volta and Como to the present and beyond) \] <http://arxiv.org/PS_cache/quant-ph/pdf/9905/9905053.pdf> (\*\*) cf: gravity may affect the rate at which clocks tick without the occurrence of any collisions between particles or anything that can be called a \"process\". ## The problem of time *This section should be read after reading a quick introduction to special relativity* ### The past century of ideas about time McTaggart in 1908 set out some of the problems with our idea of time in his classic paper *The Unreality of Time*. He drew attention to the way that a sequence of things in a list does not describe time because a sequence of things is constant yet events are always changing. These considerations led him to propose that there are three different sequences of things, or series, that are commonly used to describe events. McTaggart\'s three different time series are summarized in the illustration below.  He argued that only the \'A Series\' is a temporal series because it is only in the A Series that change occurs so that events can be given the labels \'future\', \'present\' and \'past\'. He pointed out that although the A Series is used for determining the direction and sequence of events it is not itself \'in time\' because it contains relations that are neither a part of the C Series nor the B Series. This led him to propose that time is unreal because change involves a movement along the time series so cannot be fixed within it. Franck (1994) argued on the basis of Atmanspacher\'s models of universes with real and imaginary geometries that McTaggart\'s \'unreality\' of time could be avoided by proposing a second, imaginary, time dimension. `"What McTaggart in fact demonstrates is that it is impossible to `\ `account for temporality within a strictly one-dimensional concept `\ `of time."(Franck 1994).` This idea is illustrated below:  This idea of time being two dimensional is not new and has also been advanced by such luminaries as Hermann Weyl and CD Broad. Weyl (1920) made the following statement that is extremely apposite to consciousness studies, he wrote that reality is a: `"...four-dimensional continuum which is neither 'time' nor 'space'. `\ `Only the consciousness that passes on in one portion of this world `\ `experiences the detached piece which comes to meet it and passes `\ `behind it, as history, that is, as a process that is going forward `\ `in time and takes place in space." (Weyl 1920).` McTaggart\'s objection to time is felt intuitively by anyone who has contemplated the *Block Universe* of Relativity Theory. If the universe is four dimensional with three space dimensions and one time dimension it would be fixed forever and the observer would be frozen within it. This would occur whether the time dimension was arranged according to Galilean Relativity or Modern Relativity. Peter Lynds in 2003 has drawn attention to the \'frozen\' nature of the observer in a four dimensional universe. He proposes, like Kevin Brown in his popular mathpages, that time must be approached from the viewpoint of quantum physics because simple four dimensional universes would give rise to \'frozen, static\' instants and hence no change could occur. Lynds argues that if quantum physics is introduced then no event can have a definite moment of occurrence and that change occurs because of this quantum indeterminacy: `<font face="times new roman">`{=html}I would suggest that there is possibly much more to be gleaned from the connection between quantum physics and the inherent need for physical continuity, and even go as far to speculate that the dependent relationship may be the underlying explanation for quantum jumping and with static indivisible mathematical time values directly related to the process of quantum collapse. Time will tell.\"`</font>`{=html}(Lynds 2003). Our knowledge of quantum uncertainty can be traced back to De Broglie\'s highly successful model of individual particle motions. This model was based on Special Relativity theory and it predicted a wave nature for particles. The Heisenberg Uncertainty Principle can be shown to be a consequence of this wave nature. See the illustration below:  The illustration is based on de Broglie (1925) and Pollock (2004). So Lynds\' argument that change is due to the uncertainty principle is actually an argument that change is due to differing planes of simultaneity between systems that are in relative motion. Kevin Brown is aware of this; he summarises the effect of uncertainty due to special relativity and points out that it provides a resolution of Zeno\'s arrow paradox: `"The theory of special relativity answers Zeno's concern over the `\ `lack of an instantaneous difference between a moving and a non-moving `\ `arrow by positing a fundamental re-structuring the basic way in which `\ `space and time fit together, such that there really is an instantaneous `\ `difference between a moving and a non-moving object, insofar as it `\ `makes sense to speak of "an instant" of a physical system with mutually `\ `moving elements.  Objects in relative motion have different planes of `\ `simultaneity, with all the familiar relativistic consequences, so not `\ `only does a moving object look different to the world, but the world `\ `looks different to a moving object." (Brown 19??)` Another approach to the way that time has a direction is to suggest that the possible outcomes in quantum mechanics are located in \"disjoint space-time regions which exclude one another\" (McCall 2000). This does not explain the A Series however because the observer would not have any sense of \'becoming\' or temporality as a result of the existence of regions that could not be observed. ### Presentism and Four-Dimensionalism In the past century the philosophical battle lines have been drawn between the Presentists, who believe that only the durationless instant of the present exists and the Four Dimensionalists who consider that things are extended in both space and time (see Rea (2004)). There are two types of Presentism, in its extreme form it is the belief that the past and future are truly non-existent, that what we call time is not an axis for arranging things but a series of changes and records in an *enduring* present. In its less extreme form, which might be called *functional presentism*, the present is a durationless instant that can never be connected to the future or past except through predictions and records. In consciousness studies it is the conventional theory that brain activity occurs in the present instant and that the past can only occur as memories retrieved into this durationless present. So, in consciousness studies functional Presentism seems to be the accepted paradigm. Presentism cannot explain change. Each instant is durationless and frozen. That said, as seen above, four dimensionalism cannot explain the observation of change although it can explain the difference between moving and stationary objects. Fortunately the debate has been largely resolved by recent scientific experiments which show that time exists and hence Presentism is unlikely. ### The existence of time The issue of whether or not time exists is critical to consciousness studies. If we exist at an instant without duration then how can we know we exist? Clay (1882) coined the term \'specious present\' to describe how we seem to exist for a short period containing the immediate past: \"All the notes of a bar of a song seem to the listener to be contained in the present. All the changes of place of a meteor seem to the beholder to be contained in the present. At the instant of the termination of such series, no part of the time measured by them seems to be a past. Time, then, considered relatively to human apprehension, consists of four parts, viz., the obvious past, the specious present, the real present, and the future.\" So conscious, phenomenal experience has things that are apparently extended in time. But does time exist? Recent experiments in quantum physics should change our view of time forever. Lindner *et al.* (2005) have explored the problem of time by investigating quantum interference between interferometer slits that are separated by time rather than space. In the famous, spatial \'double slit experiment\' in quantum physics single electrons are directed at an apparatus that has the equivalent of two tiny slits separated by a small gap. The electrons pass through the apparatus one at a time and produce flashes of light on a screen or changes in a photographic plate. The electrons produce series of bands on the screen that are typical of interference effects. So each electron is deflected as if it has passed through both slits and interfered with itself.  This experiment provided some of the earliest evidence for the wave-packet nature of the electron. In an amazing technical tour de force Lindner *et al.* (2005) have extended the idea of the spatial double slit experiment to an investigation of time. In the double slit experiment in time electrons are produced in an inert gas by extremely short laser pulses. The pulses stimulate a single atom and there is a probability of this atom releasing an electron at each oscillation of the pulse. The apparatus is described by Paulus *et al.* (2003). The probability (see note 1) of an electron being ejected to the left or right of the apparatus can be adjusted by adjusting the optical pulse. Pulses can be applied with a duration of a few femtoseconds and these create \'slits\' extending over an interval of about 500 attoseconds (500 x 10-18 seconds). A single electron has a probability of being emitted at each of the slits. The probability of the single electron going in a particular direction after both slits have been created depends upon the interaction of the probabilities of being emitted in a particular direction at each single slit. As expected, an interference pattern was generated as a result of single electrons interfering with themselves across different times.  This experiment is remarkable because it provides direct evidence that time exists in a similar fashion to the way that space exists. It is consistent with Feynman\'s theory of Quantum Electrodynamics where all possible paths, both in time and space, interact to produce the final trajectory of a particle and consistent with modern Special Relativity, on which QED is based, where the trajectories of particles occur in an extended four dimensional space-time. The experiment has not attracted as much attention as it might have done because most physicists are not Presentists. To physicists the experiment is yet another confirmation of modern physics. However it has impressed many: \"This experiment should be included in every textbook on quantum mechanics,\" says Wolfgang Schleich, a quantum physicist at the University of Ulm in Germany. \"It certainly will be in mine.\" (PhysicsWeb) Why should a concrete demonstration that time exists affect consciousness studies? The simple answer is that, as Kant, Gombrich, Clay, James and many others have spotted, there can be no conscious, phenomenal experience without time. The fact that time exists should provide new insights and liberate theorists in the field of consciousness studies from the problems of recursion and regression that are inherent in Presentism. Meanwhile Quantum Theorists are pressing on with the problem of how an organised spacetime could emerge from quantum chaos (cf: Ambjorn *et al.* (2004)) and even how mind might be involved in the emergence of time itself (cf: Romer (2004)). ### The nature of time #### The nature of classical time In the eighteenth century it became apparent that Euclid\'s parallel postulate could not be explained in terms of the other postulates. The parallel postulate is equivalent to the statement that exactly one line can be drawn through any point not on a given line in such a way that it is parallel to the given line (this is Playfair\'s simple version). It is also known as the fifth postulate. The attempts to prove the parallel postulate led to the development of non-Euclidean geometry. It was then possible to show that the parallel postulate is a special case within a range of geometrical forms from spherical geometry, through Euclidean geometry to the hyperbolic geometry of Bolyai and Lobatschefsky. Furthermore it was shown by Taurinus that the axioms of Euclidean geometry, with the exception of the fifth postulate, applied on the surface of a sphere with an imaginary radius. This motivated Hermann Minkowski to propose that Einstein\'s new theory of relativity was in fact due to the universe being a \'space-time\' with four dimensions rather than just a space in which things change (see Walter 1999). In 1909 Minkowski said that: `"Henceforth space by itself and time by itself, are doomed to fade `\ `away into mere shadows, and only a kind of union of the two will `\ `preserve an independent reality". (Minkowski 1909).` The earliest idea of the four dimensional universe involved time as an axis with displacements measured in units of the square root of minus one (cf: Einstein (1920)): time was considered to be displacements along the imaginary plane. However, from the moment of Minkowski\'s proposal mathematicians were aware that other interpretations of time could give almost identical physical results. According to the differential geometry developed during the nineteenth century a space is defined in terms of a *metric tensor* which is a matrix of factors that determine how displacements in each independent direction vary with displacements in the other directions. The metric tensor then specifies a *metric* which is an equation that describes the length of a displacement in any direction in terms of the independent directions, or *dimensions*. A derivation of the metric tensor and how it can be used to calculate the metric is given in the /Appendix/. The metric of the space considered by Euclid is Pythagoras\' theorem where the length of any displacement is given in terms of the displacements along the three independent axes, or dimensions: $s^2 = x^2 + y^2 + z^2$ It is interesting to explore *imaginary time* from the point of view of consciousness studies. Minkowski\'s original idea for the geometry of the world proposed that any displacement was a displacement in both time and space given by a four dimensional version of Pythagoras\' theorem: $s^2 = x^2 + y^2 + z^2 + (ict)^2$ which, given that $i^2 = -1$ equals: $s^2 = x^2 + y^2 + z^2 - (ct)^2$ Where *i* is the square root of minus one, *c* is a constant for converting metres to seconds and t is the displacement in time. The space-time is considered to be flat and all displacements are measured from the origin. The interesting feature of Minkowski space-time with imaginary time is that displacements in time can *subtract* from displacements in space. If we set $r^2 = x^2 + y^2 + z^2$ (where *r* is the radius of a sphere around the origin then: $s^2 = r^2 - (ct)^2$ Notice that $s^2 = 0$ when $r^2 = (ct)^2$ so if imaginary time existed there would be times and separations within a spherical volume of things where **everything is at a point as well as distributed in space**. This idea has distinct similarites with the *res cogitans* mentioned by Descartes, and the *point soul* of Reid and Malebranche etc., however, this feature of Minkowski\'s space-time has not been popular with physicists for some good reasons. Blandford and Thorne point out some of the problems: `<font face="times new roman">`{=html} One approach, often used in elementary textbooks \[and also used in Goldstein\'s (1980) Classical Mechanics and in the first edition of Jackson\'s Classical Electrodynamics\], is to set $x^0 = it$, where $i = \sqrt{-1}$ and correspondingly make the time basis vector be imaginary,\... When this approach is adopted, the resulting formalism does not care whether indices are placed up or down; one can place them wherever one\'s stomach or liver dictate without asking one\'s brain. However, this $x^0 = it$ approach has severe disadvantages: (i) it hides the true physical geometry of Minkowski spacetime, (ii) it cannot be extended in any reasonable manner to non-orthonormal bases in flat spacetime, and (iii) it cannot be extended in any reasonable manner to the curvilinear coordinates that one must use in general relativity. For this reason, most advanced texts \[including the second and third editions of Jackson (1999)\] and all general relativity texts take an alternative approach, which we also adopt in this book. This alternative approach requires introducing two different types of components for vectors, and analogously for tensors: contravariant components denoted by superscripts, and covariant components denoted by subscripts.\"`</font>`{=html} Blandford & Thorne (2004). What Blandford and Thorne are saying is that the metric of space-time appears to be the result of the interaction of two coordinate systems and cannot be explained by a single coordinate system with imaginary time. When a more complicated geometrical analysis is applied it is evident that there are two possibilities for the time coordinate. In the first the metric can be **assumed** from the outset to be $s^2 = x^2 + y^2 + z^2 - (ct)^2$ and the metric tensor simply adjusted by inserting -1 in the principle diagonal so that the negative sign in front of the time coordinate occurs. With this assumption and adjustment the time coordinate can be assumed to be *real*. In the second possibility the time coordinate in the world can be assumed to be imaginary and the time coordinate of the observer can be assumed to be real. This gives rise to the same metric tensor and metric as the first possibility but does not assume the resulting metric from the outset. The three ideas of classical time (imaginary, real and mixed) are shown in the illustration below:  The light cone is divided into three regions: events on the surface of the light cone, such as photons converging on the observer, are said to be *lightlike* separated from the observer, events inside the future or past light cones are said to be *timelike separated* and events outside the lightcone are said to be *spacelike* separated from the observer. The physical **theory of relativity** consists of four dimensional geometry plus the assumption of causality and the assumption that physical laws are invariant between observers. It should be noted that space-time could contain preferred frames of reference and is not, by itself, a theory of relativity. The assumption that physical laws are invariant between observers leads to the postulate that nothing can travel faster than *c* metres per second. This means that the constant *c*, which in Minkowski space-time is the conversion factor from seconds to metres then has a new significance as the maximum velocity. A result of *c* being a maximum velocity is that nothing can travel from regions of the light cone that are spacelike separated to the observer at coordinates (0,0,0,0). This is problematic for observers if time is real because, as Stein (1968) wrote: `<font face="times new roman">`{=html}"in Einstein-Minkowski space-time an event\'s present is constituted by itself alone." `</font>`{=html} (Stein 1968). However, to each of us it seems that the present is characterised by *many* things simultaneously. As will be discussed below, this simultaneity of present things also results in the appearance of phenomenal space. But in Minkowski space-time with real time the plane of simultaneity is entirely space-like separated from the observation point. If real time is accepted it would appear that we cannot have the space of phenomenal experience. The regions of the light-cone and the spacelike separation of present events are shown in the illustration below:  So can the time in Minkowski space-time be real? If time were in some way related to the imaginary plane then all the content of the surface of the light cone could be simultaneously at the position of the observer and phenomenal experience containing space is possible, but then general relativity may be problematic. So can the time in Minkowski space-time be imaginary? There is another problem with Minkowski space-time known as the \"Rietdijk-Putnam-Penrose\" argument or the Andromeda paradox (Penrose 1989). Moving observers have different planes of simultaneity. The plane of simultaneity of an observer moving towards you slopes upward relative to your plane of simultaneity (see the illustration on \"De Broglie waves\" above). Suppose an alien civilisation in the Andromeda galaxy decided to launch a fleet of spacecraft intent on the invasion of earth just as you passed Jim in your car. Your plane of simultaneity would slope upwards ever so slightly compared with Jim\'s, Jim\'s plane of simultaneity could contain earlier events on Andromeda than yours. At the distance of the Andromeda galaxy it could be another week or two for the Andromedean\'s to launch their invasion fleet in Jim\'s slice of the universe. Penrose considers that this example shows that the events in the universe must be fixed: `<font face="times new roman">`{=html}\"Two people pass each other on the street; and according to one of the two people, an Andromedean space fleet has already set off on its journey, while to the other, the decision as to whether or not the journey will actually take place has not yet been made. How can there still be some uncertainty as to the outcome of that decision? If to either person the decision has already been made, then surely there cannot be any uncertainty. The launching of the space fleet is an inevitability.\"`</font>`{=html} (Penrose 1989). If the decision to invade and a time previous to this decision are both part of the present instant on earth then, in a 4D classical universe, the decision to invade must be inevitable. This lack of free will in a 4D universe is known as chronogeometrical determinism (Toretti 1983). However, as de Broglie demonstrated, it is sloping planes of simultaneity that do indeed introduce uncertainty into our universe. It should also be noted that nothing on the plane of simultaneity is observable to the owner of that plane because, to observe it would involve the transmission of data at velocities greater than the speed of light. Petkov (2002)considers a version of the Andromeda paradox in depth. He concludes that: `<font face="times new roman">`{=html}\"If the relativity of simultaneity is explicitly discussed in terms of the dimensionality of reality, the fact that observers in relative motion have different sets of simultaneous events can be explained either by assuming that existence is also relativized (preserving the views of the present and objective becoming) or by considering existence absolute which means that reality is a 4D world. Although the option of relativizing existence appears completely unacceptable from a philosophical point of view, that option is eliminated within the framework of SR by demonstrating that the twin paradox would not be possible if existence were not absolute.\"`</font>`{=html} According to Petkov Special Relativity describes the universe as a frozen space-time where things are eternally arranged in four dimensions. Petkov introduces the possibility of change as a feature of consciousness and in support of this quotes Weyl\'s intuition that only the conscious observer moves in time. ## Relationalism, Substantivalism, the Hole Argument and General Covariance ### Relationalism and Substantivalism The view that the universe could be an extended space and time with things in it, a sort of unbounded container, is known as **substantivalism**. It was championed by Newton and Clarke in the seventeenth century. The view that the space and time in the universe depends upon the relations between the objects in the universe is known as **relationalism** and was championed by Leibniz. Leibniz attacked substantivalism by arguing that if there were two universes which only differed by things in one universe being displaced by five feet compared with things in the other universe then there is no reason why the two universes should be discernably different. Newton supported substantivalism by arguing that when the water in a bucket rotates it adopts a concave surface that is independent of other motions and provides evidence of the possibility of absolute motion. This argument is called the *bucket argument*. Newton also introduces the *globe argument* in which he proposes that the state of motion of two globes connected by a taut thread can be gauged from the tension in the thread alone. When the globes are stationary with respect to each other there is no tension in the thread. Ernst Mach in 1893 introduced a relationalist account of the bucket argument by claiming that the water rotates in relation to the fixed stars. He stated this in what has become known as Mach\'s principle: \"The inertia of any system is the result of the interaction of that system and the rest of the universe. In other words, every particle in the universe ultimately has an effect on every other particle.\" The relationalist position is interesting from the viewpoint of consciousness studies because phenomenal consciousness appears as a projection that overlies physical space. As an example, the stars on the ceiling of a planetarium appear to be at huge distances from the observer even though they are reflected lights that are only a few metres away. In general a projection where positions depend upon angular separations will be subject to relationalism. It is also probable that the space of phenomenal consciousness is a continuum of some field in the brain, if this is the case then the way we conceive of space as an existent entity is actually a conception involving the angular relations between the perturbations of the substance that is the field. Substantivalism would then literally be space as a substance. It is intriguing in this respect that Kant believed that space was a form of intuition and hence a property of mind. Kant raised another type of argument for the justification of absolute space. He asked whether *handedness* was due to relations or a property of space. The right and left hands are enantiomorphs (mirror images). The relations within the right and left hands are identical but they still differ, for instance a right hand cannot be moved on to a left hand so that it exactly overlies it. Kant proposed that handedness was property inherent in space itself rather than a set of relations. Gardner introduced a version of Kant\'s problem with the \"Ozma\" argument: \"Is there any way to communicate the meaning of the word \"left\" by a language transmitted in the form of pulsating signals? By the terms of the problem we may say anything we please to our listeners, ask them to perform any experiment whatever, with one proviso: there is to be no asymmetric object or structure that we and they can observe in common.\" (Gardner 1990). Although it is probably impossible to provide an answer to the Ozma argument it is possible to relate handedness to a conceptual point observer who spans more than an instant of time. If a point observer is at the centre of a field of inward pointing space-time vectors then relative to any given vector there are positive and negative angular separations. The body is asymmetric and the point observer would lie within this so always have available a \'head\' direction or a \'foot direction\' and hence a left and right. Unlike the time extended observer an instantaneous observer would not contain vectors that contained directional information and would be no more than a collection of points in space. Pooley (2002) discusses handedness in depth and introduces the problem of parity violation in the Weak Interaction. ### General Covariance and the Hole Argument The proposal that the universe is four dimensional does not in itself produce a full physical theory. The assumptions of causality and the invariance of physical laws between observers are also required to create modern Relativity Theory. The second assumption, that the laws of physics are the same for all observers is closely related to the requirement of **general covariance**. The principle of general covariance requires that a manifold of events can be smoothly mapped to another manifold of the same dimension and back again. This mapping should always give the same result. General covariance is assumed in General Relativity. Einstein realised that there was an apparent problem with this assumption in certain circumstances. In his **hole argument** he considers a special region of space-time that is devoid of matter and where the stress-energy tensor vanishes. He then labels the same events outside the hole with two different coordinate systems. These coordinate systems could differ by something as simple as having origins that are separate so the difference is entirely passive. Both systems will give the same values for the gravitational field outside the hole. It turns out however that that the systems predict different fields within the hole (see MacDonald (2001) for the calculation and Norton (1993), (1999) for a discussion). Einstein overcame this problem by considering active mappings where particles are actually transferred through the hole. He concluded that the points where particles meet can be transformed according to general covariance and hence a relativistic theory could indeed be constructed. Solutions to the field equations that were inconsistent with the points defined by interacting particles were discarded as non-physical. The hole argument led Einstein to abandon the idea of space and time as something separate from the material content of the universe. The General Theory of Relativity becomes a theory of **observables**. He wrote that: `<font face="times new roman">`{=html}\"That the requirement of general covariance, which takes away from space and time the last remnant of physical objectivity, is a natural one, will be seen from the following reflection. All our space-time verifications invariably amount to a determination of space-time coincidences. If, for example, events consisted merely in the motion of material points, then ultimately nothing would be observable but the meetings of two or more of these points. Moreover, the results of our measurings are nothing but verifications of such meetings of the material points of our measuring instruments with other material points, coincidences between the hands of the a clock and points on the clock dial, and observed point-events happening at the same place at the same time. The introduction of a system of reference serves no other purpose than to facilitate the description of the totality of such coincidences\".`</font>`{=html} (Einstein 1916). This is what would be expected from a four dimensional block universe with real time. It is a frozen universe of the type discussed earlier. As Earman (2002) puts it when discussing change: `<font face="times new roman">`{=html}\"First, the roots of the problem lie in classical GTR, and even if it was decided that it is a mistake to quantize GTR, there would remain the problem of reconciling the frozen dynamics of GTR with the B-series notion of change that is supported not only by common sense but by every physical theory prior to GTR. Second, although the aspect of the problem that grabs attention is that of time and change, no solution will be forthcoming without tackling the more general issue of what an "observable" of classical GTR is.\"`</font>`{=html} In such a universe action at a distance is not possible. From the viewpoint of consciousness studies the limitation of physical concepts to interactions between particles is a restatement of Ryle\'s regress and the recursion version of the homunculus problem. If events are no more than space-time coincidences then we are doomed to the endless transfer of data from point to point without any conscious observation. This seems to forbid any true simultaneity in experience and means that only measurements are possible. The reduction of physics to the study of particle interactions is fully relationalist and allows space-time to become a property of these interactions rather than vice-versa. Once it becomes possible to consider space-time as a dependent property it is then feasible to equate *observation* with *measurement*. Observation is normally the representation of an event in an observer\'s space-time coordinate system. Measurement is the change in state of a system in response to an encounter with an event. If we maintain that space-time does not exist and can be replaced by encounters between particles then observation can be replaced by measurement. This may well be a way forward for some approximations to physical reality and may allow us to understand how a space-time is selected within an observer. As part of this approach the word \"observable\" is often used interchangeably with \"measurable\". ## Quantum theory and time ### The general problem of QM and time Quantum physics provides many fundamental insights into the nature of time. At the simplest level the energy-time version of the Heisenberg Uncertainty Principle predicts that Quantum Mechanical (QM) interference should occur between a particle and earlier versions of itself. Such interference has been observed (see \"The existence of time\" above). Two of the most complete reviews of the problem of time in quantum theory available at present are Zeh (2001) and Isham (1993). Perhaps the most interesting aspect of QM and time is that it can provide an argument that time does not exist in the universe as a whole. The argument can be approached from many directions (See Rovelli 2003) but is clear in the Wheeler-de Witt equation which describes the wavefunction of the entire universe. This wavefunction has no reference to time. De Witt explained the emergence of time by proposing that the universe can be divided into an observer with measuring instruments and the rest of the universe so that the rest of the universe changes with respect to the observer. Rovelli (2003) supports this idea of partition, he considers in depth the problems of the \"hole argument\" and quantum physics and notes that, given the assumption that events are just successions of relations: \"`<font face="times new roman">`{=html}The unique account of the state of the world of the classical theory is thus shattered into a multiplicity of accounts, one for each possible \"observing\" physical system. Quantum mechanics is a theory about the physical description of physical systems relative to other systems, and this is a complete description of the world.`</font>`{=html} (Rovelli 2003). Barbour (1997) and Hartle and Gell-Mann have both proposed that an observer is a partition or region with memories that contain the trace of histories. The histories would represent a B Series. Unfortunately this leaves the A Series unexplained so time would have a direction but there would be no \'becoming\'. Hawking introduces the observer into the problem of time by asking what sort of universe is compatible with human life. This application of the **Anthropic Principle** leads to constraints on the form of the universe, for instance the universe should have galaxies and last for more than a few million years. The Anthropic Principle is actually a restatement of the observer problem - if being an observer leads to a certain division of the universe into observer and observed then the observed part will have the form given by the Anthropic Principle. Hartle and Hawking () also tackled the \"boundary problem\" of cosmology by proposing that there is no boundary. This proposal involves adding a fifth, time-like, dimension on the imaginary plane so that the universe at its beginning is a **de Sitter** or **anti de Sitter** space-time. A de Sitter space-time is characterised by the metric: $ds^2 = dx^2 + dy^2 + dz^2 + (idt)^2 + du^2$ An anti de Sitter space time has the metric: $ds^2 = dx^2 + dy^2 + dz^2 + (idt)^2 - du^2$ A de Sitter space time is fascinating from the view point of consciousness studies because it contains three space-like dimensions, one real, time-like dimension (u) and one imaginary time-like dimension. This might give the real and imaginary time-like axes that Franck proposed were needed to produce the McTaggart A Series. However, the extra dimension could only be related to the observer in the universe as it is at present because the extra dimension does not appear to be required to explain measurables. ### The interpretation of QM Time is also of interest in the interpretation of quantum mechanics and entanglement. There are many interpretations of QM such as the **Operational Interpretation** (Decoherence Theory), the **Transactional Interpretation**, the **Relational Interpretation**, the **Many Worlds Interpretation**, the **Copenhagen Interpretation**, the **Bohm Interpretation**, the **Many Minds Interpretation** etc. Some of these interpretations, such as the Transactional Interpretation, allow the connection of entangled quantum states backwards in time along the path of particles. Decoherence theory is of particular interest because it allows the calculation of how long an entangled state can persist. Tegmark (2000) and Hagan *et al.* (2002) have used this technique to calculate the decoherence time of entanglement in microtubules and have differed by a factor of $10^{10}$ because of differing assumptions about the biophysics of microtubules in the brain. ## Time and conscious experience In a four dimensional universe time is an independent direction for arranging things. As an independent direction things arranged in time do not overlie things arranged in space. This also appears to be the case in conscious experience where whole words or \"bars of a tune\" can be experienced arranged in time. This extension in time is easy to experience but the independence of the time dimension is difficult to conceive, for instance Le Poidevin (2000) reflects that: > \"If events e1 and e2 are registered in a single specious present, > then we perceive them both as present, and so as simultaneous. But we > do not see, e.g., the successive positions of a moving object as > simultaneous, for if we did we would see a blurred object and not a > moving one.\" This assumes that arrangements in time do not occur in an independent direction for arranging things and hence would overlay space. In fact the mystery of conscious experience is deeply related to how we can experience many things as events that are separate from each other. Our experience of two dimensional patterns containing many things is as much a mystery as how we experience temporal patterns extended in time. The problem is illustrated below:  It is as if patterns in conscious experience are being viewed from a point in at least four dimensions. How our experience can be like the \'view\' of a conceptual point observer at the apex of a light cone without the data being overlaid and obscured is a profound mystery, obviously the data cannot be transferred into the apparent observation point and appears as nebulous vectors directed at the point. Some philosophers have noticed this problem. (*This is a stub, requires an elaboration of Specious Present Theory and Husserl\'s ideas*) Le Poidevin (2000). The experience and perception of time. Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu//archives/spr2001/entries/time-experience/#4> Readers who are unfamiliar with the developments to Newtonian mechanics that occurred in the eighteenth and nineteenth centuries should read Consciousness Studies/The Philosophical Problem/Appendixs See overleaf for the philosophical problem continued..: ## The problems of space, qualia, machine and digital consciousness Click on the above link. ## Notes and References More\...

# Consciousness Studies/The Philosophical Problem#The philosophical problem ## The philosophical problem of phenomenal consciousness Chalmers (1996) encapsulated the philosophical problem of phenomenal consciousness, describing it as the *Hard Problem*. The Hard Problem can be concisely defined as \"how to explain a state of consciousness in terms of its neurological basis\" Block (2004). A state is an arrangement of things in space over a period of time. It is possible that the Hard Problem has not been solved because the concepts of \"space\", \"time\" and \"things\" are intensely problematic in both science and philosophy. Some philosophers have argued that *changes* in state are equivalent to \"mental states\". That consciousness experience always involves acts, such as acts of acquaintance (Russell 1912). But what is a succession of states in the brain or the physical world? As an extension of the idea of \"acts\" as mental states many philosophers have argued that the functional description of a system does not need to contain any reference to qualia within that system. Such ideas, based on nineteenth century materialism, have been expressed by Huxley, Ryle, Smart, Goldman and many others. However, although qualia are not required for classical functions, such as most computations or servo-control, it is far from clear whether this is true for all functions. If a function is described as any thing that mediates a change in state it should be realised that \"change\" itself is not fully understood in philosophy or science and that some systems, such as quantum mechanical systems, contain state changes that are far from understood. It will be seen below that our scientific knowledge is not yet sufficiently complete to allow the claim that all, or even any, changes can occur without qualia. Whether a philosopher or scientist is dualist, materialist or physicalist they should have some insight into current theories about the physical world. Certainly, if they are considering the problem of \"how to explain a state of consciousness in terms of its neurological basis\" then some idea of a \"neurological basis\" is essential. The objective of this section is to give an account of the problems of space, time and content and to describe how these affect the problem of consciousness. ## Epiphenomenalism and the problem of change Philosophers have noticed since the time of Leibniz that phenomenal consciousness does not seem to be required for the brain to produce action. As an example there are numerous reflexes that can occur without any awareness that they are happening. In fact it is difficult to think of any response to a stimulus that requires phenomenal consciousness and could not, in principle, be performed in the absence of conscious intervention. T.H. Huxley is often regarded as the originator of the term **epiphenomenalism** to describe how consciousness seems extraneous to processes in the materialist interpretation of the world although the term may have originated in James\' description of Huxley\'s (1874) ideas. According to nineteenth century science changes in state cannot explain the existence of phenomenal consciousness so superficially it may appear as if phenomenal consciousness is unnecessary. However, it may come as a shock to the reader to discover that nineteenth century science is also unable to account for any change in state. In the materialist paradigm time is construed to be a succession of instants of no duration, each of which is entirely separate from the others. As a result no instant can cause a change in another instant. It is not only conscious experience that is epiphenomenal, each instant of the nineteenth century concept of the world is epiphenomenal because it cannot give rise to the next instant. On the one hand it seems that conscious experience is not required for a nineteenth century model of behaviour and on the other hand nineteenth century science seems to be impossible without extraneous input from a conscious observer who contains the idea of change. The problem of change is closely related to the problem of time which is discussed in depth below. (See Change and Inconsistency, Stanford Encyclopedia of Philosophy). The reader might consider whether phenomenal consciousness is indeed epiphenomenal. Empirical reports describe it as something that is different from the world beyond the body (see direct realism) - but could we generate empirical reports of an epiphenomenon? If we do indeed generate empirical reports of phenomenal consciousness is there some non-materialist, physical\*\* connection between phenomenal consciousness and the functional state? In the analysis that follows it is essential that the reader does not dismiss the possibility that conscious experience is largely non-functional in a classical sense. The idea that observation is not action should not be dismissed out of hand. Indeed the claim that something cannot be true if it is \"epiphenomenal\" in a classical sense is astonishing in the context of modern quantum physics. Everettian approaches (and offshoots like the Bohmian, Consistent Histories and operational (decoherence) approaches) to quantum physics all allow that the classical world is epiphenomenal (cf: Page 1997, Stapp 1998). The Copenhagen Interpretation, however, was less clear on this issue. It is curious that problems with the nature of phenomenal consciousness are also problems with nineteenth century science - Aristotlean regress in the mind is part of the wider problem of epistemological regress and epiphenomenalism is part of the wider problem of change. Perhaps nineteenth century science is not an appropriate foundation for understanding consciousness. Recommended reading: Mortensen, C. (2002) Change. The Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/change/> Page, D.N. (1997). Sensible Quantum Mechanics: Are Only Perceptions Probabilistic? <http://arxiv.org/abs/quant-ph/9506010> Rivas, T., & Dongen, H. van (2003). Exit Epiphenomenalism: The Demolition of a Refuge Stapp, (1998). Quantum Ontology and Mind-Matter Synthesis.\[Appeared in proceedings of X-th Max Born Symposium, eds, Blanchard and Jadczyk, Vol 517 Lecture notes in Physics series, Springer-Verlag, 1999 (Quantum Future:from Volta and Como to the present and beyond) \] <http://arxiv.org/PS_cache/quant-ph/pdf/9905/9905053.pdf> (\*\*) cf: gravity may affect the rate at which clocks tick without the occurrence of any collisions between particles or anything that can be called a \"process\". ## The problem of time *This section should be read after reading a quick introduction to special relativity* ### The past century of ideas about time McTaggart in 1908 set out some of the problems with our idea of time in his classic paper *The Unreality of Time*. He drew attention to the way that a sequence of things in a list does not describe time because a sequence of things is constant yet events are always changing. These considerations led him to propose that there are three different sequences of things, or series, that are commonly used to describe events. McTaggart\'s three different time series are summarized in the illustration below.  He argued that only the \'A Series\' is a temporal series because it is only in the A Series that change occurs so that events can be given the labels \'future\', \'present\' and \'past\'. He pointed out that although the A Series is used for determining the direction and sequence of events it is not itself \'in time\' because it contains relations that are neither a part of the C Series nor the B Series. This led him to propose that time is unreal because change involves a movement along the time series so cannot be fixed within it. Franck (1994) argued on the basis of Atmanspacher\'s models of universes with real and imaginary geometries that McTaggart\'s \'unreality\' of time could be avoided by proposing a second, imaginary, time dimension. `"What McTaggart in fact demonstrates is that it is impossible to `\ `account for temporality within a strictly one-dimensional concept `\ `of time."(Franck 1994).` This idea is illustrated below:  This idea of time being two dimensional is not new and has also been advanced by such luminaries as Hermann Weyl and CD Broad. Weyl (1920) made the following statement that is extremely apposite to consciousness studies, he wrote that reality is a: `"...four-dimensional continuum which is neither 'time' nor 'space'. `\ `Only the consciousness that passes on in one portion of this world `\ `experiences the detached piece which comes to meet it and passes `\ `behind it, as history, that is, as a process that is going forward `\ `in time and takes place in space." (Weyl 1920).` McTaggart\'s objection to time is felt intuitively by anyone who has contemplated the *Block Universe* of Relativity Theory. If the universe is four dimensional with three space dimensions and one time dimension it would be fixed forever and the observer would be frozen within it. This would occur whether the time dimension was arranged according to Galilean Relativity or Modern Relativity. Peter Lynds in 2003 has drawn attention to the \'frozen\' nature of the observer in a four dimensional universe. He proposes, like Kevin Brown in his popular mathpages, that time must be approached from the viewpoint of quantum physics because simple four dimensional universes would give rise to \'frozen, static\' instants and hence no change could occur. Lynds argues that if quantum physics is introduced then no event can have a definite moment of occurrence and that change occurs because of this quantum indeterminacy: `<font face="times new roman">`{=html}I would suggest that there is possibly much more to be gleaned from the connection between quantum physics and the inherent need for physical continuity, and even go as far to speculate that the dependent relationship may be the underlying explanation for quantum jumping and with static indivisible mathematical time values directly related to the process of quantum collapse. Time will tell.\"`</font>`{=html}(Lynds 2003). Our knowledge of quantum uncertainty can be traced back to De Broglie\'s highly successful model of individual particle motions. This model was based on Special Relativity theory and it predicted a wave nature for particles. The Heisenberg Uncertainty Principle can be shown to be a consequence of this wave nature. See the illustration below:  The illustration is based on de Broglie (1925) and Pollock (2004). So Lynds\' argument that change is due to the uncertainty principle is actually an argument that change is due to differing planes of simultaneity between systems that are in relative motion. Kevin Brown is aware of this; he summarises the effect of uncertainty due to special relativity and points out that it provides a resolution of Zeno\'s arrow paradox: `"The theory of special relativity answers Zeno's concern over the `\ `lack of an instantaneous difference between a moving and a non-moving `\ `arrow by positing a fundamental re-structuring the basic way in which `\ `space and time fit together, such that there really is an instantaneous `\ `difference between a moving and a non-moving object, insofar as it `\ `makes sense to speak of "an instant" of a physical system with mutually `\ `moving elements.  Objects in relative motion have different planes of `\ `simultaneity, with all the familiar relativistic consequences, so not `\ `only does a moving object look different to the world, but the world `\ `looks different to a moving object." (Brown 19??)` Another approach to the way that time has a direction is to suggest that the possible outcomes in quantum mechanics are located in \"disjoint space-time regions which exclude one another\" (McCall 2000). This does not explain the A Series however because the observer would not have any sense of \'becoming\' or temporality as a result of the existence of regions that could not be observed. ### Presentism and Four-Dimensionalism In the past century the philosophical battle lines have been drawn between the Presentists, who believe that only the durationless instant of the present exists and the Four Dimensionalists who consider that things are extended in both space and time (see Rea (2004)). There are two types of Presentism, in its extreme form it is the belief that the past and future are truly non-existent, that what we call time is not an axis for arranging things but a series of changes and records in an *enduring* present. In its less extreme form, which might be called *functional presentism*, the present is a durationless instant that can never be connected to the future or past except through predictions and records. In consciousness studies it is the conventional theory that brain activity occurs in the present instant and that the past can only occur as memories retrieved into this durationless present. So, in consciousness studies functional Presentism seems to be the accepted paradigm. Presentism cannot explain change. Each instant is durationless and frozen. That said, as seen above, four dimensionalism cannot explain the observation of change although it can explain the difference between moving and stationary objects. Fortunately the debate has been largely resolved by recent scientific experiments which show that time exists and hence Presentism is unlikely. ### The existence of time The issue of whether or not time exists is critical to consciousness studies. If we exist at an instant without duration then how can we know we exist? Clay (1882) coined the term \'specious present\' to describe how we seem to exist for a short period containing the immediate past: \"All the notes of a bar of a song seem to the listener to be contained in the present. All the changes of place of a meteor seem to the beholder to be contained in the present. At the instant of the termination of such series, no part of the time measured by them seems to be a past. Time, then, considered relatively to human apprehension, consists of four parts, viz., the obvious past, the specious present, the real present, and the future.\" So conscious, phenomenal experience has things that are apparently extended in time. But does time exist? Recent experiments in quantum physics should change our view of time forever. Lindner *et al.* (2005) have explored the problem of time by investigating quantum interference between interferometer slits that are separated by time rather than space. In the famous, spatial \'double slit experiment\' in quantum physics single electrons are directed at an apparatus that has the equivalent of two tiny slits separated by a small gap. The electrons pass through the apparatus one at a time and produce flashes of light on a screen or changes in a photographic plate. The electrons produce series of bands on the screen that are typical of interference effects. So each electron is deflected as if it has passed through both slits and interfered with itself.  This experiment provided some of the earliest evidence for the wave-packet nature of the electron. In an amazing technical tour de force Lindner *et al.* (2005) have extended the idea of the spatial double slit experiment to an investigation of time. In the double slit experiment in time electrons are produced in an inert gas by extremely short laser pulses. The pulses stimulate a single atom and there is a probability of this atom releasing an electron at each oscillation of the pulse. The apparatus is described by Paulus *et al.* (2003). The probability (see note 1) of an electron being ejected to the left or right of the apparatus can be adjusted by adjusting the optical pulse. Pulses can be applied with a duration of a few femtoseconds and these create \'slits\' extending over an interval of about 500 attoseconds (500 x 10-18 seconds). A single electron has a probability of being emitted at each of the slits. The probability of the single electron going in a particular direction after both slits have been created depends upon the interaction of the probabilities of being emitted in a particular direction at each single slit. As expected, an interference pattern was generated as a result of single electrons interfering with themselves across different times.  This experiment is remarkable because it provides direct evidence that time exists in a similar fashion to the way that space exists. It is consistent with Feynman\'s theory of Quantum Electrodynamics where all possible paths, both in time and space, interact to produce the final trajectory of a particle and consistent with modern Special Relativity, on which QED is based, where the trajectories of particles occur in an extended four dimensional space-time. The experiment has not attracted as much attention as it might have done because most physicists are not Presentists. To physicists the experiment is yet another confirmation of modern physics. However it has impressed many: \"This experiment should be included in every textbook on quantum mechanics,\" says Wolfgang Schleich, a quantum physicist at the University of Ulm in Germany. \"It certainly will be in mine.\" (PhysicsWeb) Why should a concrete demonstration that time exists affect consciousness studies? The simple answer is that, as Kant, Gombrich, Clay, James and many others have spotted, there can be no conscious, phenomenal experience without time. The fact that time exists should provide new insights and liberate theorists in the field of consciousness studies from the problems of recursion and regression that are inherent in Presentism. Meanwhile Quantum Theorists are pressing on with the problem of how an organised spacetime could emerge from quantum chaos (cf: Ambjorn *et al.* (2004)) and even how mind might be involved in the emergence of time itself (cf: Romer (2004)). ### The nature of time #### The nature of classical time In the eighteenth century it became apparent that Euclid\'s parallel postulate could not be explained in terms of the other postulates. The parallel postulate is equivalent to the statement that exactly one line can be drawn through any point not on a given line in such a way that it is parallel to the given line (this is Playfair\'s simple version). It is also known as the fifth postulate. The attempts to prove the parallel postulate led to the development of non-Euclidean geometry. It was then possible to show that the parallel postulate is a special case within a range of geometrical forms from spherical geometry, through Euclidean geometry to the hyperbolic geometry of Bolyai and Lobatschefsky. Furthermore it was shown by Taurinus that the axioms of Euclidean geometry, with the exception of the fifth postulate, applied on the surface of a sphere with an imaginary radius. This motivated Hermann Minkowski to propose that Einstein\'s new theory of relativity was in fact due to the universe being a \'space-time\' with four dimensions rather than just a space in which things change (see Walter 1999). In 1909 Minkowski said that: `"Henceforth space by itself and time by itself, are doomed to fade `\ `away into mere shadows, and only a kind of union of the two will `\ `preserve an independent reality". (Minkowski 1909).` The earliest idea of the four dimensional universe involved time as an axis with displacements measured in units of the square root of minus one (cf: Einstein (1920)): time was considered to be displacements along the imaginary plane. However, from the moment of Minkowski\'s proposal mathematicians were aware that other interpretations of time could give almost identical physical results. According to the differential geometry developed during the nineteenth century a space is defined in terms of a *metric tensor* which is a matrix of factors that determine how displacements in each independent direction vary with displacements in the other directions. The metric tensor then specifies a *metric* which is an equation that describes the length of a displacement in any direction in terms of the independent directions, or *dimensions*. A derivation of the metric tensor and how it can be used to calculate the metric is given in the /Appendix/. The metric of the space considered by Euclid is Pythagoras\' theorem where the length of any displacement is given in terms of the displacements along the three independent axes, or dimensions: $s^2 = x^2 + y^2 + z^2$ It is interesting to explore *imaginary time* from the point of view of consciousness studies. Minkowski\'s original idea for the geometry of the world proposed that any displacement was a displacement in both time and space given by a four dimensional version of Pythagoras\' theorem: $s^2 = x^2 + y^2 + z^2 + (ict)^2$ which, given that $i^2 = -1$ equals: $s^2 = x^2 + y^2 + z^2 - (ct)^2$ Where *i* is the square root of minus one, *c* is a constant for converting metres to seconds and t is the displacement in time. The space-time is considered to be flat and all displacements are measured from the origin. The interesting feature of Minkowski space-time with imaginary time is that displacements in time can *subtract* from displacements in space. If we set $r^2 = x^2 + y^2 + z^2$ (where *r* is the radius of a sphere around the origin then: $s^2 = r^2 - (ct)^2$ Notice that $s^2 = 0$ when $r^2 = (ct)^2$ so if imaginary time existed there would be times and separations within a spherical volume of things where **everything is at a point as well as distributed in space**. This idea has distinct similarites with the *res cogitans* mentioned by Descartes, and the *point soul* of Reid and Malebranche etc., however, this feature of Minkowski\'s space-time has not been popular with physicists for some good reasons. Blandford and Thorne point out some of the problems: `<font face="times new roman">`{=html} One approach, often used in elementary textbooks \[and also used in Goldstein\'s (1980) Classical Mechanics and in the first edition of Jackson\'s Classical Electrodynamics\], is to set $x^0 = it$, where $i = \sqrt{-1}$ and correspondingly make the time basis vector be imaginary,\... When this approach is adopted, the resulting formalism does not care whether indices are placed up or down; one can place them wherever one\'s stomach or liver dictate without asking one\'s brain. However, this $x^0 = it$ approach has severe disadvantages: (i) it hides the true physical geometry of Minkowski spacetime, (ii) it cannot be extended in any reasonable manner to non-orthonormal bases in flat spacetime, and (iii) it cannot be extended in any reasonable manner to the curvilinear coordinates that one must use in general relativity. For this reason, most advanced texts \[including the second and third editions of Jackson (1999)\] and all general relativity texts take an alternative approach, which we also adopt in this book. This alternative approach requires introducing two different types of components for vectors, and analogously for tensors: contravariant components denoted by superscripts, and covariant components denoted by subscripts.\"`</font>`{=html} Blandford & Thorne (2004). What Blandford and Thorne are saying is that the metric of space-time appears to be the result of the interaction of two coordinate systems and cannot be explained by a single coordinate system with imaginary time. When a more complicated geometrical analysis is applied it is evident that there are two possibilities for the time coordinate. In the first the metric can be **assumed** from the outset to be $s^2 = x^2 + y^2 + z^2 - (ct)^2$ and the metric tensor simply adjusted by inserting -1 in the principle diagonal so that the negative sign in front of the time coordinate occurs. With this assumption and adjustment the time coordinate can be assumed to be *real*. In the second possibility the time coordinate in the world can be assumed to be imaginary and the time coordinate of the observer can be assumed to be real. This gives rise to the same metric tensor and metric as the first possibility but does not assume the resulting metric from the outset. The three ideas of classical time (imaginary, real and mixed) are shown in the illustration below:  The light cone is divided into three regions: events on the surface of the light cone, such as photons converging on the observer, are said to be *lightlike* separated from the observer, events inside the future or past light cones are said to be *timelike separated* and events outside the lightcone are said to be *spacelike* separated from the observer. The physical **theory of relativity** consists of four dimensional geometry plus the assumption of causality and the assumption that physical laws are invariant between observers. It should be noted that space-time could contain preferred frames of reference and is not, by itself, a theory of relativity. The assumption that physical laws are invariant between observers leads to the postulate that nothing can travel faster than *c* metres per second. This means that the constant *c*, which in Minkowski space-time is the conversion factor from seconds to metres then has a new significance as the maximum velocity. A result of *c* being a maximum velocity is that nothing can travel from regions of the light cone that are spacelike separated to the observer at coordinates (0,0,0,0). This is problematic for observers if time is real because, as Stein (1968) wrote: `<font face="times new roman">`{=html}"in Einstein-Minkowski space-time an event\'s present is constituted by itself alone." `</font>`{=html} (Stein 1968). However, to each of us it seems that the present is characterised by *many* things simultaneously. As will be discussed below, this simultaneity of present things also results in the appearance of phenomenal space. But in Minkowski space-time with real time the plane of simultaneity is entirely space-like separated from the observation point. If real time is accepted it would appear that we cannot have the space of phenomenal experience. The regions of the light-cone and the spacelike separation of present events are shown in the illustration below:  So can the time in Minkowski space-time be real? If time were in some way related to the imaginary plane then all the content of the surface of the light cone could be simultaneously at the position of the observer and phenomenal experience containing space is possible, but then general relativity may be problematic. So can the time in Minkowski space-time be imaginary? There is another problem with Minkowski space-time known as the \"Rietdijk-Putnam-Penrose\" argument or the Andromeda paradox (Penrose 1989). Moving observers have different planes of simultaneity. The plane of simultaneity of an observer moving towards you slopes upward relative to your plane of simultaneity (see the illustration on \"De Broglie waves\" above). Suppose an alien civilisation in the Andromeda galaxy decided to launch a fleet of spacecraft intent on the invasion of earth just as you passed Jim in your car. Your plane of simultaneity would slope upwards ever so slightly compared with Jim\'s, Jim\'s plane of simultaneity could contain earlier events on Andromeda than yours. At the distance of the Andromeda galaxy it could be another week or two for the Andromedean\'s to launch their invasion fleet in Jim\'s slice of the universe. Penrose considers that this example shows that the events in the universe must be fixed: `<font face="times new roman">`{=html}\"Two people pass each other on the street; and according to one of the two people, an Andromedean space fleet has already set off on its journey, while to the other, the decision as to whether or not the journey will actually take place has not yet been made. How can there still be some uncertainty as to the outcome of that decision? If to either person the decision has already been made, then surely there cannot be any uncertainty. The launching of the space fleet is an inevitability.\"`</font>`{=html} (Penrose 1989). If the decision to invade and a time previous to this decision are both part of the present instant on earth then, in a 4D classical universe, the decision to invade must be inevitable. This lack of free will in a 4D universe is known as chronogeometrical determinism (Toretti 1983). However, as de Broglie demonstrated, it is sloping planes of simultaneity that do indeed introduce uncertainty into our universe. It should also be noted that nothing on the plane of simultaneity is observable to the owner of that plane because, to observe it would involve the transmission of data at velocities greater than the speed of light. Petkov (2002)considers a version of the Andromeda paradox in depth. He concludes that: `<font face="times new roman">`{=html}\"If the relativity of simultaneity is explicitly discussed in terms of the dimensionality of reality, the fact that observers in relative motion have different sets of simultaneous events can be explained either by assuming that existence is also relativized (preserving the views of the present and objective becoming) or by considering existence absolute which means that reality is a 4D world. Although the option of relativizing existence appears completely unacceptable from a philosophical point of view, that option is eliminated within the framework of SR by demonstrating that the twin paradox would not be possible if existence were not absolute.\"`</font>`{=html} According to Petkov Special Relativity describes the universe as a frozen space-time where things are eternally arranged in four dimensions. Petkov introduces the possibility of change as a feature of consciousness and in support of this quotes Weyl\'s intuition that only the conscious observer moves in time. ## Relationalism, Substantivalism, the Hole Argument and General Covariance ### Relationalism and Substantivalism The view that the universe could be an extended space and time with things in it, a sort of unbounded container, is known as **substantivalism**. It was championed by Newton and Clarke in the seventeenth century. The view that the space and time in the universe depends upon the relations between the objects in the universe is known as **relationalism** and was championed by Leibniz. Leibniz attacked substantivalism by arguing that if there were two universes which only differed by things in one universe being displaced by five feet compared with things in the other universe then there is no reason why the two universes should be discernably different. Newton supported substantivalism by arguing that when the water in a bucket rotates it adopts a concave surface that is independent of other motions and provides evidence of the possibility of absolute motion. This argument is called the *bucket argument*. Newton also introduces the *globe argument* in which he proposes that the state of motion of two globes connected by a taut thread can be gauged from the tension in the thread alone. When the globes are stationary with respect to each other there is no tension in the thread. Ernst Mach in 1893 introduced a relationalist account of the bucket argument by claiming that the water rotates in relation to the fixed stars. He stated this in what has become known as Mach\'s principle: \"The inertia of any system is the result of the interaction of that system and the rest of the universe. In other words, every particle in the universe ultimately has an effect on every other particle.\" The relationalist position is interesting from the viewpoint of consciousness studies because phenomenal consciousness appears as a projection that overlies physical space. As an example, the stars on the ceiling of a planetarium appear to be at huge distances from the observer even though they are reflected lights that are only a few metres away. In general a projection where positions depend upon angular separations will be subject to relationalism. It is also probable that the space of phenomenal consciousness is a continuum of some field in the brain, if this is the case then the way we conceive of space as an existent entity is actually a conception involving the angular relations between the perturbations of the substance that is the field. Substantivalism would then literally be space as a substance. It is intriguing in this respect that Kant believed that space was a form of intuition and hence a property of mind. Kant raised another type of argument for the justification of absolute space. He asked whether *handedness* was due to relations or a property of space. The right and left hands are enantiomorphs (mirror images). The relations within the right and left hands are identical but they still differ, for instance a right hand cannot be moved on to a left hand so that it exactly overlies it. Kant proposed that handedness was property inherent in space itself rather than a set of relations. Gardner introduced a version of Kant\'s problem with the \"Ozma\" argument: \"Is there any way to communicate the meaning of the word \"left\" by a language transmitted in the form of pulsating signals? By the terms of the problem we may say anything we please to our listeners, ask them to perform any experiment whatever, with one proviso: there is to be no asymmetric object or structure that we and they can observe in common.\" (Gardner 1990). Although it is probably impossible to provide an answer to the Ozma argument it is possible to relate handedness to a conceptual point observer who spans more than an instant of time. If a point observer is at the centre of a field of inward pointing space-time vectors then relative to any given vector there are positive and negative angular separations. The body is asymmetric and the point observer would lie within this so always have available a \'head\' direction or a \'foot direction\' and hence a left and right. Unlike the time extended observer an instantaneous observer would not contain vectors that contained directional information and would be no more than a collection of points in space. Pooley (2002) discusses handedness in depth and introduces the problem of parity violation in the Weak Interaction. ### General Covariance and the Hole Argument The proposal that the universe is four dimensional does not in itself produce a full physical theory. The assumptions of causality and the invariance of physical laws between observers are also required to create modern Relativity Theory. The second assumption, that the laws of physics are the same for all observers is closely related to the requirement of **general covariance**. The principle of general covariance requires that a manifold of events can be smoothly mapped to another manifold of the same dimension and back again. This mapping should always give the same result. General covariance is assumed in General Relativity. Einstein realised that there was an apparent problem with this assumption in certain circumstances. In his **hole argument** he considers a special region of space-time that is devoid of matter and where the stress-energy tensor vanishes. He then labels the same events outside the hole with two different coordinate systems. These coordinate systems could differ by something as simple as having origins that are separate so the difference is entirely passive. Both systems will give the same values for the gravitational field outside the hole. It turns out however that that the systems predict different fields within the hole (see MacDonald (2001) for the calculation and Norton (1993), (1999) for a discussion). Einstein overcame this problem by considering active mappings where particles are actually transferred through the hole. He concluded that the points where particles meet can be transformed according to general covariance and hence a relativistic theory could indeed be constructed. Solutions to the field equations that were inconsistent with the points defined by interacting particles were discarded as non-physical. The hole argument led Einstein to abandon the idea of space and time as something separate from the material content of the universe. The General Theory of Relativity becomes a theory of **observables**. He wrote that: `<font face="times new roman">`{=html}\"That the requirement of general covariance, which takes away from space and time the last remnant of physical objectivity, is a natural one, will be seen from the following reflection. All our space-time verifications invariably amount to a determination of space-time coincidences. If, for example, events consisted merely in the motion of material points, then ultimately nothing would be observable but the meetings of two or more of these points. Moreover, the results of our measurings are nothing but verifications of such meetings of the material points of our measuring instruments with other material points, coincidences between the hands of the a clock and points on the clock dial, and observed point-events happening at the same place at the same time. The introduction of a system of reference serves no other purpose than to facilitate the description of the totality of such coincidences\".`</font>`{=html} (Einstein 1916). This is what would be expected from a four dimensional block universe with real time. It is a frozen universe of the type discussed earlier. As Earman (2002) puts it when discussing change: `<font face="times new roman">`{=html}\"First, the roots of the problem lie in classical GTR, and even if it was decided that it is a mistake to quantize GTR, there would remain the problem of reconciling the frozen dynamics of GTR with the B-series notion of change that is supported not only by common sense but by every physical theory prior to GTR. Second, although the aspect of the problem that grabs attention is that of time and change, no solution will be forthcoming without tackling the more general issue of what an "observable" of classical GTR is.\"`</font>`{=html} In such a universe action at a distance is not possible. From the viewpoint of consciousness studies the limitation of physical concepts to interactions between particles is a restatement of Ryle\'s regress and the recursion version of the homunculus problem. If events are no more than space-time coincidences then we are doomed to the endless transfer of data from point to point without any conscious observation. This seems to forbid any true simultaneity in experience and means that only measurements are possible. The reduction of physics to the study of particle interactions is fully relationalist and allows space-time to become a property of these interactions rather than vice-versa. Once it becomes possible to consider space-time as a dependent property it is then feasible to equate *observation* with *measurement*. Observation is normally the representation of an event in an observer\'s space-time coordinate system. Measurement is the change in state of a system in response to an encounter with an event. If we maintain that space-time does not exist and can be replaced by encounters between particles then observation can be replaced by measurement. This may well be a way forward for some approximations to physical reality and may allow us to understand how a space-time is selected within an observer. As part of this approach the word \"observable\" is often used interchangeably with \"measurable\". ## Quantum theory and time ### The general problem of QM and time Quantum physics provides many fundamental insights into the nature of time. At the simplest level the energy-time version of the Heisenberg Uncertainty Principle predicts that Quantum Mechanical (QM) interference should occur between a particle and earlier versions of itself. Such interference has been observed (see \"The existence of time\" above). Two of the most complete reviews of the problem of time in quantum theory available at present are Zeh (2001) and Isham (1993). Perhaps the most interesting aspect of QM and time is that it can provide an argument that time does not exist in the universe as a whole. The argument can be approached from many directions (See Rovelli 2003) but is clear in the Wheeler-de Witt equation which describes the wavefunction of the entire universe. This wavefunction has no reference to time. De Witt explained the emergence of time by proposing that the universe can be divided into an observer with measuring instruments and the rest of the universe so that the rest of the universe changes with respect to the observer. Rovelli (2003) supports this idea of partition, he considers in depth the problems of the \"hole argument\" and quantum physics and notes that, given the assumption that events are just successions of relations: \"`<font face="times new roman">`{=html}The unique account of the state of the world of the classical theory is thus shattered into a multiplicity of accounts, one for each possible \"observing\" physical system. Quantum mechanics is a theory about the physical description of physical systems relative to other systems, and this is a complete description of the world.`</font>`{=html} (Rovelli 2003). Barbour (1997) and Hartle and Gell-Mann have both proposed that an observer is a partition or region with memories that contain the trace of histories. The histories would represent a B Series. Unfortunately this leaves the A Series unexplained so time would have a direction but there would be no \'becoming\'. Hawking introduces the observer into the problem of time by asking what sort of universe is compatible with human life. This application of the **Anthropic Principle** leads to constraints on the form of the universe, for instance the universe should have galaxies and last for more than a few million years. The Anthropic Principle is actually a restatement of the observer problem - if being an observer leads to a certain division of the universe into observer and observed then the observed part will have the form given by the Anthropic Principle. Hartle and Hawking () also tackled the \"boundary problem\" of cosmology by proposing that there is no boundary. This proposal involves adding a fifth, time-like, dimension on the imaginary plane so that the universe at its beginning is a **de Sitter** or **anti de Sitter** space-time. A de Sitter space-time is characterised by the metric: $ds^2 = dx^2 + dy^2 + dz^2 + (idt)^2 + du^2$ An anti de Sitter space time has the metric: $ds^2 = dx^2 + dy^2 + dz^2 + (idt)^2 - du^2$ A de Sitter space time is fascinating from the view point of consciousness studies because it contains three space-like dimensions, one real, time-like dimension (u) and one imaginary time-like dimension. This might give the real and imaginary time-like axes that Franck proposed were needed to produce the McTaggart A Series. However, the extra dimension could only be related to the observer in the universe as it is at present because the extra dimension does not appear to be required to explain measurables. ### The interpretation of QM Time is also of interest in the interpretation of quantum mechanics and entanglement. There are many interpretations of QM such as the **Operational Interpretation** (Decoherence Theory), the **Transactional Interpretation**, the **Relational Interpretation**, the **Many Worlds Interpretation**, the **Copenhagen Interpretation**, the **Bohm Interpretation**, the **Many Minds Interpretation** etc. Some of these interpretations, such as the Transactional Interpretation, allow the connection of entangled quantum states backwards in time along the path of particles. Decoherence theory is of particular interest because it allows the calculation of how long an entangled state can persist. Tegmark (2000) and Hagan *et al.* (2002) have used this technique to calculate the decoherence time of entanglement in microtubules and have differed by a factor of $10^{10}$ because of differing assumptions about the biophysics of microtubules in the brain. ## Time and conscious experience In a four dimensional universe time is an independent direction for arranging things. As an independent direction things arranged in time do not overlie things arranged in space. This also appears to be the case in conscious experience where whole words or \"bars of a tune\" can be experienced arranged in time. This extension in time is easy to experience but the independence of the time dimension is difficult to conceive, for instance Le Poidevin (2000) reflects that: > \"If events e1 and e2 are registered in a single specious present, > then we perceive them both as present, and so as simultaneous. But we > do not see, e.g., the successive positions of a moving object as > simultaneous, for if we did we would see a blurred object and not a > moving one.\" This assumes that arrangements in time do not occur in an independent direction for arranging things and hence would overlay space. In fact the mystery of conscious experience is deeply related to how we can experience many things as events that are separate from each other. Our experience of two dimensional patterns containing many things is as much a mystery as how we experience temporal patterns extended in time. The problem is illustrated below:  It is as if patterns in conscious experience are being viewed from a point in at least four dimensions. How our experience can be like the \'view\' of a conceptual point observer at the apex of a light cone without the data being overlaid and obscured is a profound mystery, obviously the data cannot be transferred into the apparent observation point and appears as nebulous vectors directed at the point. Some philosophers have noticed this problem. (*This is a stub, requires an elaboration of Specious Present Theory and Husserl\'s ideas*) Le Poidevin (2000). The experience and perception of time. Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu//archives/spr2001/entries/time-experience/#4> Readers who are unfamiliar with the developments to Newtonian mechanics that occurred in the eighteenth and nineteenth centuries should read Consciousness Studies/The Philosophical Problem/Appendixs See overleaf for the philosophical problem continued..: ## The problems of space, qualia, machine and digital consciousness Click on the above link. ## Notes and References More\...

# Consciousness Studies/The Philosophical Problem#The problem of time ## The philosophical problem of phenomenal consciousness Chalmers (1996) encapsulated the philosophical problem of phenomenal consciousness, describing it as the *Hard Problem*. The Hard Problem can be concisely defined as \"how to explain a state of consciousness in terms of its neurological basis\" Block (2004). A state is an arrangement of things in space over a period of time. It is possible that the Hard Problem has not been solved because the concepts of \"space\", \"time\" and \"things\" are intensely problematic in both science and philosophy. Some philosophers have argued that *changes* in state are equivalent to \"mental states\". That consciousness experience always involves acts, such as acts of acquaintance (Russell 1912). But what is a succession of states in the brain or the physical world? As an extension of the idea of \"acts\" as mental states many philosophers have argued that the functional description of a system does not need to contain any reference to qualia within that system. Such ideas, based on nineteenth century materialism, have been expressed by Huxley, Ryle, Smart, Goldman and many others. However, although qualia are not required for classical functions, such as most computations or servo-control, it is far from clear whether this is true for all functions. If a function is described as any thing that mediates a change in state it should be realised that \"change\" itself is not fully understood in philosophy or science and that some systems, such as quantum mechanical systems, contain state changes that are far from understood. It will be seen below that our scientific knowledge is not yet sufficiently complete to allow the claim that all, or even any, changes can occur without qualia. Whether a philosopher or scientist is dualist, materialist or physicalist they should have some insight into current theories about the physical world. Certainly, if they are considering the problem of \"how to explain a state of consciousness in terms of its neurological basis\" then some idea of a \"neurological basis\" is essential. The objective of this section is to give an account of the problems of space, time and content and to describe how these affect the problem of consciousness. ## Epiphenomenalism and the problem of change Philosophers have noticed since the time of Leibniz that phenomenal consciousness does not seem to be required for the brain to produce action. As an example there are numerous reflexes that can occur without any awareness that they are happening. In fact it is difficult to think of any response to a stimulus that requires phenomenal consciousness and could not, in principle, be performed in the absence of conscious intervention. T.H. Huxley is often regarded as the originator of the term **epiphenomenalism** to describe how consciousness seems extraneous to processes in the materialist interpretation of the world although the term may have originated in James\' description of Huxley\'s (1874) ideas. According to nineteenth century science changes in state cannot explain the existence of phenomenal consciousness so superficially it may appear as if phenomenal consciousness is unnecessary. However, it may come as a shock to the reader to discover that nineteenth century science is also unable to account for any change in state. In the materialist paradigm time is construed to be a succession of instants of no duration, each of which is entirely separate from the others. As a result no instant can cause a change in another instant. It is not only conscious experience that is epiphenomenal, each instant of the nineteenth century concept of the world is epiphenomenal because it cannot give rise to the next instant. On the one hand it seems that conscious experience is not required for a nineteenth century model of behaviour and on the other hand nineteenth century science seems to be impossible without extraneous input from a conscious observer who contains the idea of change. The problem of change is closely related to the problem of time which is discussed in depth below. (See Change and Inconsistency, Stanford Encyclopedia of Philosophy). The reader might consider whether phenomenal consciousness is indeed epiphenomenal. Empirical reports describe it as something that is different from the world beyond the body (see direct realism) - but could we generate empirical reports of an epiphenomenon? If we do indeed generate empirical reports of phenomenal consciousness is there some non-materialist, physical\*\* connection between phenomenal consciousness and the functional state? In the analysis that follows it is essential that the reader does not dismiss the possibility that conscious experience is largely non-functional in a classical sense. The idea that observation is not action should not be dismissed out of hand. Indeed the claim that something cannot be true if it is \"epiphenomenal\" in a classical sense is astonishing in the context of modern quantum physics. Everettian approaches (and offshoots like the Bohmian, Consistent Histories and operational (decoherence) approaches) to quantum physics all allow that the classical world is epiphenomenal (cf: Page 1997, Stapp 1998). The Copenhagen Interpretation, however, was less clear on this issue. It is curious that problems with the nature of phenomenal consciousness are also problems with nineteenth century science - Aristotlean regress in the mind is part of the wider problem of epistemological regress and epiphenomenalism is part of the wider problem of change. Perhaps nineteenth century science is not an appropriate foundation for understanding consciousness. Recommended reading: Mortensen, C. (2002) Change. The Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu/entries/change/> Page, D.N. (1997). Sensible Quantum Mechanics: Are Only Perceptions Probabilistic? <http://arxiv.org/abs/quant-ph/9506010> Rivas, T., & Dongen, H. van (2003). Exit Epiphenomenalism: The Demolition of a Refuge Stapp, (1998). Quantum Ontology and Mind-Matter Synthesis.\[Appeared in proceedings of X-th Max Born Symposium, eds, Blanchard and Jadczyk, Vol 517 Lecture notes in Physics series, Springer-Verlag, 1999 (Quantum Future:from Volta and Como to the present and beyond) \] <http://arxiv.org/PS_cache/quant-ph/pdf/9905/9905053.pdf> (\*\*) cf: gravity may affect the rate at which clocks tick without the occurrence of any collisions between particles or anything that can be called a \"process\". ## The problem of time *This section should be read after reading a quick introduction to special relativity* ### The past century of ideas about time McTaggart in 1908 set out some of the problems with our idea of time in his classic paper *The Unreality of Time*. He drew attention to the way that a sequence of things in a list does not describe time because a sequence of things is constant yet events are always changing. These considerations led him to propose that there are three different sequences of things, or series, that are commonly used to describe events. McTaggart\'s three different time series are summarized in the illustration below.  He argued that only the \'A Series\' is a temporal series because it is only in the A Series that change occurs so that events can be given the labels \'future\', \'present\' and \'past\'. He pointed out that although the A Series is used for determining the direction and sequence of events it is not itself \'in time\' because it contains relations that are neither a part of the C Series nor the B Series. This led him to propose that time is unreal because change involves a movement along the time series so cannot be fixed within it. Franck (1994) argued on the basis of Atmanspacher\'s models of universes with real and imaginary geometries that McTaggart\'s \'unreality\' of time could be avoided by proposing a second, imaginary, time dimension. `"What McTaggart in fact demonstrates is that it is impossible to `\ `account for temporality within a strictly one-dimensional concept `\ `of time."(Franck 1994).` This idea is illustrated below:  This idea of time being two dimensional is not new and has also been advanced by such luminaries as Hermann Weyl and CD Broad. Weyl (1920) made the following statement that is extremely apposite to consciousness studies, he wrote that reality is a: `"...four-dimensional continuum which is neither 'time' nor 'space'. `\ `Only the consciousness that passes on in one portion of this world `\ `experiences the detached piece which comes to meet it and passes `\ `behind it, as history, that is, as a process that is going forward `\ `in time and takes place in space." (Weyl 1920).` McTaggart\'s objection to time is felt intuitively by anyone who has contemplated the *Block Universe* of Relativity Theory. If the universe is four dimensional with three space dimensions and one time dimension it would be fixed forever and the observer would be frozen within it. This would occur whether the time dimension was arranged according to Galilean Relativity or Modern Relativity. Peter Lynds in 2003 has drawn attention to the \'frozen\' nature of the observer in a four dimensional universe. He proposes, like Kevin Brown in his popular mathpages, that time must be approached from the viewpoint of quantum physics because simple four dimensional universes would give rise to \'frozen, static\' instants and hence no change could occur. Lynds argues that if quantum physics is introduced then no event can have a definite moment of occurrence and that change occurs because of this quantum indeterminacy: `<font face="times new roman">`{=html}I would suggest that there is possibly much more to be gleaned from the connection between quantum physics and the inherent need for physical continuity, and even go as far to speculate that the dependent relationship may be the underlying explanation for quantum jumping and with static indivisible mathematical time values directly related to the process of quantum collapse. Time will tell.\"`</font>`{=html}(Lynds 2003). Our knowledge of quantum uncertainty can be traced back to De Broglie\'s highly successful model of individual particle motions. This model was based on Special Relativity theory and it predicted a wave nature for particles. The Heisenberg Uncertainty Principle can be shown to be a consequence of this wave nature. See the illustration below:  The illustration is based on de Broglie (1925) and Pollock (2004). So Lynds\' argument that change is due to the uncertainty principle is actually an argument that change is due to differing planes of simultaneity between systems that are in relative motion. Kevin Brown is aware of this; he summarises the effect of uncertainty due to special relativity and points out that it provides a resolution of Zeno\'s arrow paradox: `"The theory of special relativity answers Zeno's concern over the `\ `lack of an instantaneous difference between a moving and a non-moving `\ `arrow by positing a fundamental re-structuring the basic way in which `\ `space and time fit together, such that there really is an instantaneous `\ `difference between a moving and a non-moving object, insofar as it `\ `makes sense to speak of "an instant" of a physical system with mutually `\ `moving elements.  Objects in relative motion have different planes of `\ `simultaneity, with all the familiar relativistic consequences, so not `\ `only does a moving object look different to the world, but the world `\ `looks different to a moving object." (Brown 19??)` Another approach to the way that time has a direction is to suggest that the possible outcomes in quantum mechanics are located in \"disjoint space-time regions which exclude one another\" (McCall 2000). This does not explain the A Series however because the observer would not have any sense of \'becoming\' or temporality as a result of the existence of regions that could not be observed. ### Presentism and Four-Dimensionalism In the past century the philosophical battle lines have been drawn between the Presentists, who believe that only the durationless instant of the present exists and the Four Dimensionalists who consider that things are extended in both space and time (see Rea (2004)). There are two types of Presentism, in its extreme form it is the belief that the past and future are truly non-existent, that what we call time is not an axis for arranging things but a series of changes and records in an *enduring* present. In its less extreme form, which might be called *functional presentism*, the present is a durationless instant that can never be connected to the future or past except through predictions and records. In consciousness studies it is the conventional theory that brain activity occurs in the present instant and that the past can only occur as memories retrieved into this durationless present. So, in consciousness studies functional Presentism seems to be the accepted paradigm. Presentism cannot explain change. Each instant is durationless and frozen. That said, as seen above, four dimensionalism cannot explain the observation of change although it can explain the difference between moving and stationary objects. Fortunately the debate has been largely resolved by recent scientific experiments which show that time exists and hence Presentism is unlikely. ### The existence of time The issue of whether or not time exists is critical to consciousness studies. If we exist at an instant without duration then how can we know we exist? Clay (1882) coined the term \'specious present\' to describe how we seem to exist for a short period containing the immediate past: \"All the notes of a bar of a song seem to the listener to be contained in the present. All the changes of place of a meteor seem to the beholder to be contained in the present. At the instant of the termination of such series, no part of the time measured by them seems to be a past. Time, then, considered relatively to human apprehension, consists of four parts, viz., the obvious past, the specious present, the real present, and the future.\" So conscious, phenomenal experience has things that are apparently extended in time. But does time exist? Recent experiments in quantum physics should change our view of time forever. Lindner *et al.* (2005) have explored the problem of time by investigating quantum interference between interferometer slits that are separated by time rather than space. In the famous, spatial \'double slit experiment\' in quantum physics single electrons are directed at an apparatus that has the equivalent of two tiny slits separated by a small gap. The electrons pass through the apparatus one at a time and produce flashes of light on a screen or changes in a photographic plate. The electrons produce series of bands on the screen that are typical of interference effects. So each electron is deflected as if it has passed through both slits and interfered with itself.  This experiment provided some of the earliest evidence for the wave-packet nature of the electron. In an amazing technical tour de force Lindner *et al.* (2005) have extended the idea of the spatial double slit experiment to an investigation of time. In the double slit experiment in time electrons are produced in an inert gas by extremely short laser pulses. The pulses stimulate a single atom and there is a probability of this atom releasing an electron at each oscillation of the pulse. The apparatus is described by Paulus *et al.* (2003). The probability (see note 1) of an electron being ejected to the left or right of the apparatus can be adjusted by adjusting the optical pulse. Pulses can be applied with a duration of a few femtoseconds and these create \'slits\' extending over an interval of about 500 attoseconds (500 x 10-18 seconds). A single electron has a probability of being emitted at each of the slits. The probability of the single electron going in a particular direction after both slits have been created depends upon the interaction of the probabilities of being emitted in a particular direction at each single slit. As expected, an interference pattern was generated as a result of single electrons interfering with themselves across different times.  This experiment is remarkable because it provides direct evidence that time exists in a similar fashion to the way that space exists. It is consistent with Feynman\'s theory of Quantum Electrodynamics where all possible paths, both in time and space, interact to produce the final trajectory of a particle and consistent with modern Special Relativity, on which QED is based, where the trajectories of particles occur in an extended four dimensional space-time. The experiment has not attracted as much attention as it might have done because most physicists are not Presentists. To physicists the experiment is yet another confirmation of modern physics. However it has impressed many: \"This experiment should be included in every textbook on quantum mechanics,\" says Wolfgang Schleich, a quantum physicist at the University of Ulm in Germany. \"It certainly will be in mine.\" (PhysicsWeb) Why should a concrete demonstration that time exists affect consciousness studies? The simple answer is that, as Kant, Gombrich, Clay, James and many others have spotted, there can be no conscious, phenomenal experience without time. The fact that time exists should provide new insights and liberate theorists in the field of consciousness studies from the problems of recursion and regression that are inherent in Presentism. Meanwhile Quantum Theorists are pressing on with the problem of how an organised spacetime could emerge from quantum chaos (cf: Ambjorn *et al.* (2004)) and even how mind might be involved in the emergence of time itself (cf: Romer (2004)). ### The nature of time #### The nature of classical time In the eighteenth century it became apparent that Euclid\'s parallel postulate could not be explained in terms of the other postulates. The parallel postulate is equivalent to the statement that exactly one line can be drawn through any point not on a given line in such a way that it is parallel to the given line (this is Playfair\'s simple version). It is also known as the fifth postulate. The attempts to prove the parallel postulate led to the development of non-Euclidean geometry. It was then possible to show that the parallel postulate is a special case within a range of geometrical forms from spherical geometry, through Euclidean geometry to the hyperbolic geometry of Bolyai and Lobatschefsky. Furthermore it was shown by Taurinus that the axioms of Euclidean geometry, with the exception of the fifth postulate, applied on the surface of a sphere with an imaginary radius. This motivated Hermann Minkowski to propose that Einstein\'s new theory of relativity was in fact due to the universe being a \'space-time\' with four dimensions rather than just a space in which things change (see Walter 1999). In 1909 Minkowski said that: `"Henceforth space by itself and time by itself, are doomed to fade `\ `away into mere shadows, and only a kind of union of the two will `\ `preserve an independent reality". (Minkowski 1909).` The earliest idea of the four dimensional universe involved time as an axis with displacements measured in units of the square root of minus one (cf: Einstein (1920)): time was considered to be displacements along the imaginary plane. However, from the moment of Minkowski\'s proposal mathematicians were aware that other interpretations of time could give almost identical physical results. According to the differential geometry developed during the nineteenth century a space is defined in terms of a *metric tensor* which is a matrix of factors that determine how displacements in each independent direction vary with displacements in the other directions. The metric tensor then specifies a *metric* which is an equation that describes the length of a displacement in any direction in terms of the independent directions, or *dimensions*. A derivation of the metric tensor and how it can be used to calculate the metric is given in the /Appendix/. The metric of the space considered by Euclid is Pythagoras\' theorem where the length of any displacement is given in terms of the displacements along the three independent axes, or dimensions: $s^2 = x^2 + y^2 + z^2$ It is interesting to explore *imaginary time* from the point of view of consciousness studies. Minkowski\'s original idea for the geometry of the world proposed that any displacement was a displacement in both time and space given by a four dimensional version of Pythagoras\' theorem: $s^2 = x^2 + y^2 + z^2 + (ict)^2$ which, given that $i^2 = -1$ equals: $s^2 = x^2 + y^2 + z^2 - (ct)^2$ Where *i* is the square root of minus one, *c* is a constant for converting metres to seconds and t is the displacement in time. The space-time is considered to be flat and all displacements are measured from the origin. The interesting feature of Minkowski space-time with imaginary time is that displacements in time can *subtract* from displacements in space. If we set $r^2 = x^2 + y^2 + z^2$ (where *r* is the radius of a sphere around the origin then: $s^2 = r^2 - (ct)^2$ Notice that $s^2 = 0$ when $r^2 = (ct)^2$ so if imaginary time existed there would be times and separations within a spherical volume of things where **everything is at a point as well as distributed in space**. This idea has distinct similarites with the *res cogitans* mentioned by Descartes, and the *point soul* of Reid and Malebranche etc., however, this feature of Minkowski\'s space-time has not been popular with physicists for some good reasons. Blandford and Thorne point out some of the problems: `<font face="times new roman">`{=html} One approach, often used in elementary textbooks \[and also used in Goldstein\'s (1980) Classical Mechanics and in the first edition of Jackson\'s Classical Electrodynamics\], is to set $x^0 = it$, where $i = \sqrt{-1}$ and correspondingly make the time basis vector be imaginary,\... When this approach is adopted, the resulting formalism does not care whether indices are placed up or down; one can place them wherever one\'s stomach or liver dictate without asking one\'s brain. However, this $x^0 = it$ approach has severe disadvantages: (i) it hides the true physical geometry of Minkowski spacetime, (ii) it cannot be extended in any reasonable manner to non-orthonormal bases in flat spacetime, and (iii) it cannot be extended in any reasonable manner to the curvilinear coordinates that one must use in general relativity. For this reason, most advanced texts \[including the second and third editions of Jackson (1999)\] and all general relativity texts take an alternative approach, which we also adopt in this book. This alternative approach requires introducing two different types of components for vectors, and analogously for tensors: contravariant components denoted by superscripts, and covariant components denoted by subscripts.\"`</font>`{=html} Blandford & Thorne (2004). What Blandford and Thorne are saying is that the metric of space-time appears to be the result of the interaction of two coordinate systems and cannot be explained by a single coordinate system with imaginary time. When a more complicated geometrical analysis is applied it is evident that there are two possibilities for the time coordinate. In the first the metric can be **assumed** from the outset to be $s^2 = x^2 + y^2 + z^2 - (ct)^2$ and the metric tensor simply adjusted by inserting -1 in the principle diagonal so that the negative sign in front of the time coordinate occurs. With this assumption and adjustment the time coordinate can be assumed to be *real*. In the second possibility the time coordinate in the world can be assumed to be imaginary and the time coordinate of the observer can be assumed to be real. This gives rise to the same metric tensor and metric as the first possibility but does not assume the resulting metric from the outset. The three ideas of classical time (imaginary, real and mixed) are shown in the illustration below:  The light cone is divided into three regions: events on the surface of the light cone, such as photons converging on the observer, are said to be *lightlike* separated from the observer, events inside the future or past light cones are said to be *timelike separated* and events outside the lightcone are said to be *spacelike* separated from the observer. The physical **theory of relativity** consists of four dimensional geometry plus the assumption of causality and the assumption that physical laws are invariant between observers. It should be noted that space-time could contain preferred frames of reference and is not, by itself, a theory of relativity. The assumption that physical laws are invariant between observers leads to the postulate that nothing can travel faster than *c* metres per second. This means that the constant *c*, which in Minkowski space-time is the conversion factor from seconds to metres then has a new significance as the maximum velocity. A result of *c* being a maximum velocity is that nothing can travel from regions of the light cone that are spacelike separated to the observer at coordinates (0,0,0,0). This is problematic for observers if time is real because, as Stein (1968) wrote: `<font face="times new roman">`{=html}"in Einstein-Minkowski space-time an event\'s present is constituted by itself alone." `</font>`{=html} (Stein 1968). However, to each of us it seems that the present is characterised by *many* things simultaneously. As will be discussed below, this simultaneity of present things also results in the appearance of phenomenal space. But in Minkowski space-time with real time the plane of simultaneity is entirely space-like separated from the observation point. If real time is accepted it would appear that we cannot have the space of phenomenal experience. The regions of the light-cone and the spacelike separation of present events are shown in the illustration below:  So can the time in Minkowski space-time be real? If time were in some way related to the imaginary plane then all the content of the surface of the light cone could be simultaneously at the position of the observer and phenomenal experience containing space is possible, but then general relativity may be problematic. So can the time in Minkowski space-time be imaginary? There is another problem with Minkowski space-time known as the \"Rietdijk-Putnam-Penrose\" argument or the Andromeda paradox (Penrose 1989). Moving observers have different planes of simultaneity. The plane of simultaneity of an observer moving towards you slopes upward relative to your plane of simultaneity (see the illustration on \"De Broglie waves\" above). Suppose an alien civilisation in the Andromeda galaxy decided to launch a fleet of spacecraft intent on the invasion of earth just as you passed Jim in your car. Your plane of simultaneity would slope upwards ever so slightly compared with Jim\'s, Jim\'s plane of simultaneity could contain earlier events on Andromeda than yours. At the distance of the Andromeda galaxy it could be another week or two for the Andromedean\'s to launch their invasion fleet in Jim\'s slice of the universe. Penrose considers that this example shows that the events in the universe must be fixed: `<font face="times new roman">`{=html}\"Two people pass each other on the street; and according to one of the two people, an Andromedean space fleet has already set off on its journey, while to the other, the decision as to whether or not the journey will actually take place has not yet been made. How can there still be some uncertainty as to the outcome of that decision? If to either person the decision has already been made, then surely there cannot be any uncertainty. The launching of the space fleet is an inevitability.\"`</font>`{=html} (Penrose 1989). If the decision to invade and a time previous to this decision are both part of the present instant on earth then, in a 4D classical universe, the decision to invade must be inevitable. This lack of free will in a 4D universe is known as chronogeometrical determinism (Toretti 1983). However, as de Broglie demonstrated, it is sloping planes of simultaneity that do indeed introduce uncertainty into our universe. It should also be noted that nothing on the plane of simultaneity is observable to the owner of that plane because, to observe it would involve the transmission of data at velocities greater than the speed of light. Petkov (2002)considers a version of the Andromeda paradox in depth. He concludes that: `<font face="times new roman">`{=html}\"If the relativity of simultaneity is explicitly discussed in terms of the dimensionality of reality, the fact that observers in relative motion have different sets of simultaneous events can be explained either by assuming that existence is also relativized (preserving the views of the present and objective becoming) or by considering existence absolute which means that reality is a 4D world. Although the option of relativizing existence appears completely unacceptable from a philosophical point of view, that option is eliminated within the framework of SR by demonstrating that the twin paradox would not be possible if existence were not absolute.\"`</font>`{=html} According to Petkov Special Relativity describes the universe as a frozen space-time where things are eternally arranged in four dimensions. Petkov introduces the possibility of change as a feature of consciousness and in support of this quotes Weyl\'s intuition that only the conscious observer moves in time. ## Relationalism, Substantivalism, the Hole Argument and General Covariance ### Relationalism and Substantivalism The view that the universe could be an extended space and time with things in it, a sort of unbounded container, is known as **substantivalism**. It was championed by Newton and Clarke in the seventeenth century. The view that the space and time in the universe depends upon the relations between the objects in the universe is known as **relationalism** and was championed by Leibniz. Leibniz attacked substantivalism by arguing that if there were two universes which only differed by things in one universe being displaced by five feet compared with things in the other universe then there is no reason why the two universes should be discernably different. Newton supported substantivalism by arguing that when the water in a bucket rotates it adopts a concave surface that is independent of other motions and provides evidence of the possibility of absolute motion. This argument is called the *bucket argument*. Newton also introduces the *globe argument* in which he proposes that the state of motion of two globes connected by a taut thread can be gauged from the tension in the thread alone. When the globes are stationary with respect to each other there is no tension in the thread. Ernst Mach in 1893 introduced a relationalist account of the bucket argument by claiming that the water rotates in relation to the fixed stars. He stated this in what has become known as Mach\'s principle: \"The inertia of any system is the result of the interaction of that system and the rest of the universe. In other words, every particle in the universe ultimately has an effect on every other particle.\" The relationalist position is interesting from the viewpoint of consciousness studies because phenomenal consciousness appears as a projection that overlies physical space. As an example, the stars on the ceiling of a planetarium appear to be at huge distances from the observer even though they are reflected lights that are only a few metres away. In general a projection where positions depend upon angular separations will be subject to relationalism. It is also probable that the space of phenomenal consciousness is a continuum of some field in the brain, if this is the case then the way we conceive of space as an existent entity is actually a conception involving the angular relations between the perturbations of the substance that is the field. Substantivalism would then literally be space as a substance. It is intriguing in this respect that Kant believed that space was a form of intuition and hence a property of mind. Kant raised another type of argument for the justification of absolute space. He asked whether *handedness* was due to relations or a property of space. The right and left hands are enantiomorphs (mirror images). The relations within the right and left hands are identical but they still differ, for instance a right hand cannot be moved on to a left hand so that it exactly overlies it. Kant proposed that handedness was property inherent in space itself rather than a set of relations. Gardner introduced a version of Kant\'s problem with the \"Ozma\" argument: \"Is there any way to communicate the meaning of the word \"left\" by a language transmitted in the form of pulsating signals? By the terms of the problem we may say anything we please to our listeners, ask them to perform any experiment whatever, with one proviso: there is to be no asymmetric object or structure that we and they can observe in common.\" (Gardner 1990). Although it is probably impossible to provide an answer to the Ozma argument it is possible to relate handedness to a conceptual point observer who spans more than an instant of time. If a point observer is at the centre of a field of inward pointing space-time vectors then relative to any given vector there are positive and negative angular separations. The body is asymmetric and the point observer would lie within this so always have available a \'head\' direction or a \'foot direction\' and hence a left and right. Unlike the time extended observer an instantaneous observer would not contain vectors that contained directional information and would be no more than a collection of points in space. Pooley (2002) discusses handedness in depth and introduces the problem of parity violation in the Weak Interaction. ### General Covariance and the Hole Argument The proposal that the universe is four dimensional does not in itself produce a full physical theory. The assumptions of causality and the invariance of physical laws between observers are also required to create modern Relativity Theory. The second assumption, that the laws of physics are the same for all observers is closely related to the requirement of **general covariance**. The principle of general covariance requires that a manifold of events can be smoothly mapped to another manifold of the same dimension and back again. This mapping should always give the same result. General covariance is assumed in General Relativity. Einstein realised that there was an apparent problem with this assumption in certain circumstances. In his **hole argument** he considers a special region of space-time that is devoid of matter and where the stress-energy tensor vanishes. He then labels the same events outside the hole with two different coordinate systems. These coordinate systems could differ by something as simple as having origins that are separate so the difference is entirely passive. Both systems will give the same values for the gravitational field outside the hole. It turns out however that that the systems predict different fields within the hole (see MacDonald (2001) for the calculation and Norton (1993), (1999) for a discussion). Einstein overcame this problem by considering active mappings where particles are actually transferred through the hole. He concluded that the points where particles meet can be transformed according to general covariance and hence a relativistic theory could indeed be constructed. Solutions to the field equations that were inconsistent with the points defined by interacting particles were discarded as non-physical. The hole argument led Einstein to abandon the idea of space and time as something separate from the material content of the universe. The General Theory of Relativity becomes a theory of **observables**. He wrote that: `<font face="times new roman">`{=html}\"That the requirement of general covariance, which takes away from space and time the last remnant of physical objectivity, is a natural one, will be seen from the following reflection. All our space-time verifications invariably amount to a determination of space-time coincidences. If, for example, events consisted merely in the motion of material points, then ultimately nothing would be observable but the meetings of two or more of these points. Moreover, the results of our measurings are nothing but verifications of such meetings of the material points of our measuring instruments with other material points, coincidences between the hands of the a clock and points on the clock dial, and observed point-events happening at the same place at the same time. The introduction of a system of reference serves no other purpose than to facilitate the description of the totality of such coincidences\".`</font>`{=html} (Einstein 1916). This is what would be expected from a four dimensional block universe with real time. It is a frozen universe of the type discussed earlier. As Earman (2002) puts it when discussing change: `<font face="times new roman">`{=html}\"First, the roots of the problem lie in classical GTR, and even if it was decided that it is a mistake to quantize GTR, there would remain the problem of reconciling the frozen dynamics of GTR with the B-series notion of change that is supported not only by common sense but by every physical theory prior to GTR. Second, although the aspect of the problem that grabs attention is that of time and change, no solution will be forthcoming without tackling the more general issue of what an "observable" of classical GTR is.\"`</font>`{=html} In such a universe action at a distance is not possible. From the viewpoint of consciousness studies the limitation of physical concepts to interactions between particles is a restatement of Ryle\'s regress and the recursion version of the homunculus problem. If events are no more than space-time coincidences then we are doomed to the endless transfer of data from point to point without any conscious observation. This seems to forbid any true simultaneity in experience and means that only measurements are possible. The reduction of physics to the study of particle interactions is fully relationalist and allows space-time to become a property of these interactions rather than vice-versa. Once it becomes possible to consider space-time as a dependent property it is then feasible to equate *observation* with *measurement*. Observation is normally the representation of an event in an observer\'s space-time coordinate system. Measurement is the change in state of a system in response to an encounter with an event. If we maintain that space-time does not exist and can be replaced by encounters between particles then observation can be replaced by measurement. This may well be a way forward for some approximations to physical reality and may allow us to understand how a space-time is selected within an observer. As part of this approach the word \"observable\" is often used interchangeably with \"measurable\". ## Quantum theory and time ### The general problem of QM and time Quantum physics provides many fundamental insights into the nature of time. At the simplest level the energy-time version of the Heisenberg Uncertainty Principle predicts that Quantum Mechanical (QM) interference should occur between a particle and earlier versions of itself. Such interference has been observed (see \"The existence of time\" above). Two of the most complete reviews of the problem of time in quantum theory available at present are Zeh (2001) and Isham (1993). Perhaps the most interesting aspect of QM and time is that it can provide an argument that time does not exist in the universe as a whole. The argument can be approached from many directions (See Rovelli 2003) but is clear in the Wheeler-de Witt equation which describes the wavefunction of the entire universe. This wavefunction has no reference to time. De Witt explained the emergence of time by proposing that the universe can be divided into an observer with measuring instruments and the rest of the universe so that the rest of the universe changes with respect to the observer. Rovelli (2003) supports this idea of partition, he considers in depth the problems of the \"hole argument\" and quantum physics and notes that, given the assumption that events are just successions of relations: \"`<font face="times new roman">`{=html}The unique account of the state of the world of the classical theory is thus shattered into a multiplicity of accounts, one for each possible \"observing\" physical system. Quantum mechanics is a theory about the physical description of physical systems relative to other systems, and this is a complete description of the world.`</font>`{=html} (Rovelli 2003). Barbour (1997) and Hartle and Gell-Mann have both proposed that an observer is a partition or region with memories that contain the trace of histories. The histories would represent a B Series. Unfortunately this leaves the A Series unexplained so time would have a direction but there would be no \'becoming\'. Hawking introduces the observer into the problem of time by asking what sort of universe is compatible with human life. This application of the **Anthropic Principle** leads to constraints on the form of the universe, for instance the universe should have galaxies and last for more than a few million years. The Anthropic Principle is actually a restatement of the observer problem - if being an observer leads to a certain division of the universe into observer and observed then the observed part will have the form given by the Anthropic Principle. Hartle and Hawking () also tackled the \"boundary problem\" of cosmology by proposing that there is no boundary. This proposal involves adding a fifth, time-like, dimension on the imaginary plane so that the universe at its beginning is a **de Sitter** or **anti de Sitter** space-time. A de Sitter space-time is characterised by the metric: $ds^2 = dx^2 + dy^2 + dz^2 + (idt)^2 + du^2$ An anti de Sitter space time has the metric: $ds^2 = dx^2 + dy^2 + dz^2 + (idt)^2 - du^2$ A de Sitter space time is fascinating from the view point of consciousness studies because it contains three space-like dimensions, one real, time-like dimension (u) and one imaginary time-like dimension. This might give the real and imaginary time-like axes that Franck proposed were needed to produce the McTaggart A Series. However, the extra dimension could only be related to the observer in the universe as it is at present because the extra dimension does not appear to be required to explain measurables. ### The interpretation of QM Time is also of interest in the interpretation of quantum mechanics and entanglement. There are many interpretations of QM such as the **Operational Interpretation** (Decoherence Theory), the **Transactional Interpretation**, the **Relational Interpretation**, the **Many Worlds Interpretation**, the **Copenhagen Interpretation**, the **Bohm Interpretation**, the **Many Minds Interpretation** etc. Some of these interpretations, such as the Transactional Interpretation, allow the connection of entangled quantum states backwards in time along the path of particles. Decoherence theory is of particular interest because it allows the calculation of how long an entangled state can persist. Tegmark (2000) and Hagan *et al.* (2002) have used this technique to calculate the decoherence time of entanglement in microtubules and have differed by a factor of $10^{10}$ because of differing assumptions about the biophysics of microtubules in the brain. ## Time and conscious experience In a four dimensional universe time is an independent direction for arranging things. As an independent direction things arranged in time do not overlie things arranged in space. This also appears to be the case in conscious experience where whole words or \"bars of a tune\" can be experienced arranged in time. This extension in time is easy to experience but the independence of the time dimension is difficult to conceive, for instance Le Poidevin (2000) reflects that: > \"If events e1 and e2 are registered in a single specious present, > then we perceive them both as present, and so as simultaneous. But we > do not see, e.g., the successive positions of a moving object as > simultaneous, for if we did we would see a blurred object and not a > moving one.\" This assumes that arrangements in time do not occur in an independent direction for arranging things and hence would overlay space. In fact the mystery of conscious experience is deeply related to how we can experience many things as events that are separate from each other. Our experience of two dimensional patterns containing many things is as much a mystery as how we experience temporal patterns extended in time. The problem is illustrated below:  It is as if patterns in conscious experience are being viewed from a point in at least four dimensions. How our experience can be like the \'view\' of a conceptual point observer at the apex of a light cone without the data being overlaid and obscured is a profound mystery, obviously the data cannot be transferred into the apparent observation point and appears as nebulous vectors directed at the point. Some philosophers have noticed this problem. (*This is a stub, requires an elaboration of Specious Present Theory and Husserl\'s ideas*) Le Poidevin (2000). The experience and perception of time. Stanford Encyclopedia of Philosophy. <http://plato.stanford.edu//archives/spr2001/entries/time-experience/#4> Readers who are unfamiliar with the developments to Newtonian mechanics that occurred in the eighteenth and nineteenth centuries should read Consciousness Studies/The Philosophical Problem/Appendixs See overleaf for the philosophical problem continued..: ## The problems of space, qualia, machine and digital consciousness Click on the above link. ## Notes and References More\...

# Consciousness Studies/The Philosophical Problem Continued#The problem of space ## The problem of space The problem of Relationalism and Substantivalism has been discussed earlier. In this section the concept of space will be explored in more depth. Space is apparent to us all. It is the existence of many simultaneous things at an instant. If we see a ship and hear a dog barking on our left there is space. If we look at a checkerboard there is space. This occurrence of space in phenomenal experience is similar to the measurement of space in the world: things that are simultaneously at the ends of a metre rule are a metre apart; if there is more than one object at a given instant the objects are separated by space. Physicists have found that the mathematics of **vector spaces** describes much of the arrangement of things in the world. In a vector space the independent directions for arranging things are called **dimensions**. At any instant physical space has three clearly observable dimensions. It has been known for millennia that the three dimensions observable at an instant are interrelated by **Pythagoras\' Theorem**: Pythagoras\' theorem on a plane shows that the length of any displacement is related to the sum of the squares of the displacements in the independent directions (x and y): $h^2 = x^2 + y^2$ Pythagoras\' theorem in three dimensions is: $h^2 = x^2 + y^2 + z^2$ The advances in geometry in the nineteenth century showed that Pythagoras\' theorem was a special case of a **metric**, an equation that describes displacements in terms of the dimensions available. In the twentieth century it was realised that time was another independent direction for arranging things that was interrelated to the other three dimensions. The world is now described as a **four dimensional manifold**. The illustration below shows how different numbers of dimensions affect the arrangement of things.  It is sometimes suggested that our idea of space is due to some sort of memory that is read out sequentially. This is unlikely because, at any instant a one dimensional form cannot be made to overlie a two dimensional form and a two dimensional form cannot overlie a three dimensional form etc. One dimensional forms are not *congruent* with two dimensional forms. This means that a one dimensional form such as *virtual memory* cannot, at any instant, overlie two dimensional forms such as occur in phenomenal experience and hence experience does not supervene on the idea of virtual memory (See section on functionalism as a one dimensional Turing Machine). Curiously the idea of *mental space* is often denied. McGinn(1995) gives such a denial: `<font face="times new roman">`{=html}We perceive, by our various sense organs, a variety of material objects laid out in space, taking up certain volumes and separated by certain distances. We thus conceive of these perceptual objects as spatial entities; perception informs us directly of their spatiality. But conscious subjects and their mental states are not in this way perceptual objects. We do not see or hear or smell or touch them, and a fortiori do not perceive them as spatially individuated.(2) This holds both for the first- and third-person perspectives. Since we do not observe our own states of consciousness, nor those of others, we do not apprehend these states as spatial. `</font>`{=html} McGinn(1995). This denial is strange because it begins by describing phenomenal experience as clearly spatial and then proceeds to argue that there is some other thing, the \"mental state\", which is non-spatial. This seems to contradict our everday life where our experience is our experience, there is no other experience. The issue is whether this experience is things in themselves (Direct Realism) or some other form in the brain (Indirect Realism). The illustration below shows how space occurs in phenomenal experience; it sidesteps the issue of the location of the contents of phenomenal consciousness.  McGinn (1995) gives a description of how phenomenal experience cannot be overlaid by a 3D model of events in the brain: `<font face="times new roman">`{=html}\"Consider a visual experience, E, as of a yellow flash. Associated with E in the cortex is a complex of neural structures and events, N, which does admit of spatial description. N occurs, say, an inch from the back of the head; it extends over some specific area of the cortex; it has some kind of configuration or contour; it is composed of spatial parts that aggregate into a structured whole; it exists in three spatial dimensions; it excludes other neural complexes from its spatial location. N is a regular denizen of space, as much as any other physical entity. But E seems not to have any of these spatial characteristics: it is not located at any specific place; it takes up no particular volume of space; it has no shape; it is not made up of spatially distributed parts; it has no spatial dimensionality; it is not solid. Even to ask for its spatial properties is to commit some sort of category mistake, analogous to asking for the spatial properties of numbers. E seems not to be the kind of thing that falls under spatial predicates. It falls under temporal predicates\... `</font>`{=html}McGinn(1995) He concludes that a 3D form can only be rearranged into the form of the things in experience over a succession of instants (\"It falls under temporal predicates\"). This is highly suggestive of phenomenal experience having more than three dimensions in the same way as an ordinary physical thing or field has more than three dimensions. ## The problem of qualia A quality of an object such as its colour, roughness, temperature etc. is known as a **quale**, the plural of quale is **qualia**. Qualia are the contents of phenomenal consciousness. The term \"qualia\" is sometimes extended to all mental aspects of an object such as roundness, size and even relative position. ### The physics of qualia According to physicalism qualia must be things in the universe. But what are \"things in the universe\" and which of these are qualia? If we wish to explain phenomenal experience we must first decide whether experience is a measurement or things themselves. Measurement begins with a quantum mechanical interaction between an instrument and a set of particles, this then creates a *signal* which is a change in the state of the instrument. As an example, a mercury thermometer interacts with the fluid around it which results in a signal in the form of a moving column of mercury in the thermometer. As another example, a measuring rule is aligned with the two ends of an object by a servomechanism that interacts with photons from the rule and the object, the signal being the markings that align with the end of the object. The signal can be a flow of charge or photons or a chemical change etc. Sensory experience begins with the interaction between an object that acts as a measuring instrument and a set of particles such as photons or scent molecules etc. In the Direct Realist case the signal would be the change at the interface between the bulk of a material (a crude measuring device) and a set of particles such as photons, in the Indirect Realist case it would be some signal in the brain derived from the initial signal. In either case phenomenal consciousness would be some form, an arrangement of the set of signals themselves. The signals in measuring events arise as a result of interactions between QM phenomena and a measuring apparatus composed of relatively large structures. These structures (called *the environment*) produce signals at definite locations. This chain of fixing positions is known as **decoherence** (see Zurek (2003) or Bacciagaluppi (2004) for a review). This means that measuring events fix the positions of signals and these represent the positions of QM events. (Some physical particles such as photons are subject to little decoherence during propagation, even in water (cf: Anglin & Zurek (1996)).) So signals in measuring devices usually have highly restrained positions. Now consider the final signals, the one\'s in phenomenal consciousness. To an observer of the brain they should be, very nearly, in their classical positions within the brain unless they consist of photons or are subject to some special effect such as has been proposed for microtubules. The brain acts as a measuring device causing decoherence. But despite this even signals composed of sodium ions, which should decohere rapidly in water, have a tiny, but finite, probability of remaining in a coherent state. If your conscious experience is the signals and not the fabric of the brain are you the set of signals that interacts with the brain fabric almost immediately, the set that interacts after a minute or the set that almost never interacts? To an outside observer you must be the main chance, the rapidly interacting signals, but to the signals themselves all possibilities exist. Which one are you? Certainly any interaction between the signals and the mutually observed world must involve decoherence but the external observer would find it difficult to determine whether a particular interaction was due to signals that had interacted immediately or ones that were delayed (or delayed in an alternate QM reality). This problem is part of the *preferred basis problem* that will be discussed later. Zurek (2003)assumes that phenomenal experience is identical to measurements. The observer is then both the signal and the apparatus that encloses the signal. He summarises the resultant idea of the completely determined observer who is fully integrated into the measured world: `<font face="times new roman">`{=html}The 'higher functions' of observers - e.g., consciousness, etc. - may be at present poorly understood, but it is safe to assume that they reflect physical processes in the information processing hardware of the brain. Hence, mental processes are in effect objective, as they leave an indelible imprint on the environment: The observer has no chance of perceiving either his memory, or any other macroscopic part of the Universe in some arbitrary superposition. \"`</font>`{=html} Zurek (2003) Notice the phrase \"perceiving .. his memory\" - as neuroscientists we must ask \"how\"? By more measurements? There are no more measurements when things are arranged in phenomenal consciousness, the information has nowhere else to go. However, according to the empiricist philosophers the arrangements of the signals in phenomenal consciousness do extend through time in a definite order at any instant. Is it this order that determines the positions of signals in the brain or is it the brain that determines this order? Physicalism leads us to an idea of the content of consciousness as an arrangement of quantum fields like the content of the brain or the content of the world. The arrangement of the quantum fields at an instant in experience is probably related to the arrangement of measured events at a succession of instants in the world. According to the account given above, the contents of conscious experience, the qualia, are signals derived from the world that compose conscious experience with the interesting problem that they are themselves the experience and are not fixed in space and time by further measurement. ### The philosophy of qualia The term \"qualia\" was introduced by C.I. Lewis in 1929: `<font face="times new roman">`{=html}This given element in a single experience of an object is what will be meant by \"a presentation.\" Such a presentation is, obviously, an event and historically unique. But for most of the purposes of analyzing knowledge one presentation of a half-dollar held at right angles to the line of vision, etc., will be as good as another. If, then, I speak of \" the presentation\" of this or that, it will be on the supposition that the reader can provide his own illustration. No identification of the event itself with the repeatable content of it is intended.`</font>`{=html} `<font face="times new roman">`{=html}In any presentation, this content is either a specific quale (such as the immediacy of redness or loudness) or something analyzable into a complex of such. The presentation as an event is, of course, unique, but the qualia which make it up are not. They are recognizable from one to another experience.(CI Lewis, *Mind and the World Order*, 1941 edition Chapter 2)`</font>`{=html} Tye (2003) gives the following definition of qualia: `<font face="times new roman">`{=html}\"Experiences vary widely. For example, I run my fingers over sandpaper, smell a skunk, feel a sharp pain in my finger, seem to see bright purple, become extremely angry. In each of these cases, I am the subject of a mental state with a very distinctive subjective character. There is something it is like for me to undergo each state, some phenomenology that it has. Philosophers often use the term \'qualia\' to refer to the introspectively accessible properties of experiences that characterize what it is like to have them. In this standard, broad sense of the term, it is very difficult to deny that there are qualia.\"`</font>`{=html} Tye(2003). In philosophy objects are considered to have perceived features such as shape and colour, weight and texture which are called sensible qualities. Sensible qualities are divided into intrinsic, or primary, qualities that are properties of the object itself and extrinsic, or secondary, qualities which are related to the sensations produced in the observer. Shape is generally considered to be a primary quality whereas colour is often considered to be a secondary quality. It is generally considered that secondary qualities correspond to qualia (Smith 1990, Shoemaker 1990) and the two terms are often used synonymously. Although secondary qualities may be qualia, the term \"qualia\" may include things other than perceptions such as pain etc. that are, arguably, not secondary qualities. Primary qualities might also give rise to experience that is distinct from, say, the shape of an object itself. Although \"qualia\" is a recent term, the philosophical debate about the nature of secondary qualities, such as colours, and the nature of conscious experience itself has been around for millennia. It seems that the visual system gives rise to experience even in the absence of previous visual stimulation. For example, when someone recovers from blindness they have an experience that contains shapes and colours even though these have little meaning: `<font face="times new roman">`{=html}\"When he first saw, he was so far from making any judgement of distances, that he thought all object whatever touched his eyes\.... he knew not the shape of anything, nor any one thing from another, however different in shape and magnitude.. We thought he soon knew what pictures represented, which were shewed to him, but we found afterwards we were mistaken; for about two months after he was couched, he discovered at once they represented solid bodiess, when to that time he considered them only as party-coloured panes, or surfaces diversified with variety of paint.\"`</font>`{=html} William Cheselden (1728) Qualia are the components of experience, whatever the mode of input to that experience. Strawson (1994) includes content such as accompanies suddenly remembering or thinking of something as examples of qualia. There is thought to be an *explanatory gap* associated with qualia (Levine 1983), as an example it is hard to imagine how the experience called pain could be a set of impulses in the brain. Some philosophers have attempted to bridge this gap by invoking Direct Realism, proposing that our experience is in some way \'transparent\' so that we experience the world or the injured limb directly (i.e.: there is an assumption that things flow within phenomenal experience into a centre point and we see right through this flow!). This idea has led to a deduction that phenomenal experience is a set of things and qualities are these things, not deductions about or experiences based on these things. As Tye (2003) puts it: `<font face="times new roman">`{=html}These observations suggest that qualia, conceived of as the immediately \'felt\' qualities of experiences of which we are cognizant when we attend to them introspectively, do not really exist. The qualities of which we are aware are not qualities of experiences at all, but rather qualities that, if they are qualities of anything, are qualities of things in the world (as in the case of perceptual experiences) or of regions of our bodies (as in the case of bodily sensations). This is not to say that experiences do not have qualia. The point is that qualia are not qualities of experiences. `</font>`{=html} However, the outstanding issue for Tye\'s analysis is where in the world the thing that is called a quale exists - on a thing in the world beyond the body, on the retina, in the cortex, in the thalamus? Tye seems to be suggesting that \"in the world\" can only be beyond the retina but given that a television can have a colour and a retina can have a colour why should we insist that the colour in conscious experience is always *of* the thing being represented via the DVD or videotape? That colour should always be a property of an original coloured object seems strange, why is it not a property of the pigment in a photo of the object, a property of an led in a computer screen displaying an image of the photo, a property of the pigments in the retina viewing the computer, the impulses in the visual cortex etc.? As was seen in the previous section, only signals are available in the classical world of conscious observation. The \"reality\" of the things that generate signals is not available. So whether experience is a signal at the position of what we call an \"oak tree\" or a signal in the eye due to photons reflected from the tree or a signal in the brain the same sort of phenomena would apply. Qualia would be a field, an arrangement of signals, not processes based on these signals. Some philosophers hold that qualia are a field of signals derived from the original signals that are next to the quantum phenomena that compose an object. In other words they propose that qualia are not the first signals in the chain from whatever composes an object to the observer. These philosophers are known as Representationalists and the emphasis on secondary signals allows a contribution from the brain etc. to the field of signals that is conscious experience. Modern representationalists such as Tye (1995), Lehar(2003) and Dretske(2003) emphasise the idea that qualia are actual things that represent objects rather than concepts or experiences of things. As Dretske puts it: `<font face="times new roman">`{=html}\"..the features that define what it is like to have an experience are properties that the objects we experience (not our experience of them) have.`</font>`{=html}(Dretske 2003). Lehar(2003) uses modern language to express the empiricist notion that the signals that comprise qualia are more likely to be in our brains than elsewhere, according to Lehar the objects we experience must be informational replicas in our heads: `<font face="times new roman">`{=html}\"The central message of Gestalt theory therefore is that the primary function of perceptual processing is the generation of a miniature, virtual-reality replica of the external world inside our head, and that the world we see around us is not the real external world, but is exactly that miniature internal replica\" (Lehar 2003).`</font>`{=html} Direct Realists and Representationalists share the same view that qualia are an actual, physical field of things somewhere in the world. Some functionalists and eliminativists take a different view, believing that qualia do not exist except as judgements of properties that are used in interactions (i.e.: as disembodied information - see the section on Direct Realism). Lewis, C.I. (1929) Mind and the World-Order. <http://www.ditext.com/lewis/mwo2.html> Smith, A.D. (1990) Of Primary and Secondary Qualities, Philosophical Review 99 (1990). ### More about qualia

# Consciousness Studies/The Philosophical Problem Continued#The problem of qualia ## The problem of space The problem of Relationalism and Substantivalism has been discussed earlier. In this section the concept of space will be explored in more depth. Space is apparent to us all. It is the existence of many simultaneous things at an instant. If we see a ship and hear a dog barking on our left there is space. If we look at a checkerboard there is space. This occurrence of space in phenomenal experience is similar to the measurement of space in the world: things that are simultaneously at the ends of a metre rule are a metre apart; if there is more than one object at a given instant the objects are separated by space. Physicists have found that the mathematics of **vector spaces** describes much of the arrangement of things in the world. In a vector space the independent directions for arranging things are called **dimensions**. At any instant physical space has three clearly observable dimensions. It has been known for millennia that the three dimensions observable at an instant are interrelated by **Pythagoras\' Theorem**: Pythagoras\' theorem on a plane shows that the length of any displacement is related to the sum of the squares of the displacements in the independent directions (x and y): $h^2 = x^2 + y^2$ Pythagoras\' theorem in three dimensions is: $h^2 = x^2 + y^2 + z^2$ The advances in geometry in the nineteenth century showed that Pythagoras\' theorem was a special case of a **metric**, an equation that describes displacements in terms of the dimensions available. In the twentieth century it was realised that time was another independent direction for arranging things that was interrelated to the other three dimensions. The world is now described as a **four dimensional manifold**. The illustration below shows how different numbers of dimensions affect the arrangement of things.  It is sometimes suggested that our idea of space is due to some sort of memory that is read out sequentially. This is unlikely because, at any instant a one dimensional form cannot be made to overlie a two dimensional form and a two dimensional form cannot overlie a three dimensional form etc. One dimensional forms are not *congruent* with two dimensional forms. This means that a one dimensional form such as *virtual memory* cannot, at any instant, overlie two dimensional forms such as occur in phenomenal experience and hence experience does not supervene on the idea of virtual memory (See section on functionalism as a one dimensional Turing Machine). Curiously the idea of *mental space* is often denied. McGinn(1995) gives such a denial: `<font face="times new roman">`{=html}We perceive, by our various sense organs, a variety of material objects laid out in space, taking up certain volumes and separated by certain distances. We thus conceive of these perceptual objects as spatial entities; perception informs us directly of their spatiality. But conscious subjects and their mental states are not in this way perceptual objects. We do not see or hear or smell or touch them, and a fortiori do not perceive them as spatially individuated.(2) This holds both for the first- and third-person perspectives. Since we do not observe our own states of consciousness, nor those of others, we do not apprehend these states as spatial. `</font>`{=html} McGinn(1995). This denial is strange because it begins by describing phenomenal experience as clearly spatial and then proceeds to argue that there is some other thing, the \"mental state\", which is non-spatial. This seems to contradict our everday life where our experience is our experience, there is no other experience. The issue is whether this experience is things in themselves (Direct Realism) or some other form in the brain (Indirect Realism). The illustration below shows how space occurs in phenomenal experience; it sidesteps the issue of the location of the contents of phenomenal consciousness.  McGinn (1995) gives a description of how phenomenal experience cannot be overlaid by a 3D model of events in the brain: `<font face="times new roman">`{=html}\"Consider a visual experience, E, as of a yellow flash. Associated with E in the cortex is a complex of neural structures and events, N, which does admit of spatial description. N occurs, say, an inch from the back of the head; it extends over some specific area of the cortex; it has some kind of configuration or contour; it is composed of spatial parts that aggregate into a structured whole; it exists in three spatial dimensions; it excludes other neural complexes from its spatial location. N is a regular denizen of space, as much as any other physical entity. But E seems not to have any of these spatial characteristics: it is not located at any specific place; it takes up no particular volume of space; it has no shape; it is not made up of spatially distributed parts; it has no spatial dimensionality; it is not solid. Even to ask for its spatial properties is to commit some sort of category mistake, analogous to asking for the spatial properties of numbers. E seems not to be the kind of thing that falls under spatial predicates. It falls under temporal predicates\... `</font>`{=html}McGinn(1995) He concludes that a 3D form can only be rearranged into the form of the things in experience over a succession of instants (\"It falls under temporal predicates\"). This is highly suggestive of phenomenal experience having more than three dimensions in the same way as an ordinary physical thing or field has more than three dimensions. ## The problem of qualia A quality of an object such as its colour, roughness, temperature etc. is known as a **quale**, the plural of quale is **qualia**. Qualia are the contents of phenomenal consciousness. The term \"qualia\" is sometimes extended to all mental aspects of an object such as roundness, size and even relative position. ### The physics of qualia According to physicalism qualia must be things in the universe. But what are \"things in the universe\" and which of these are qualia? If we wish to explain phenomenal experience we must first decide whether experience is a measurement or things themselves. Measurement begins with a quantum mechanical interaction between an instrument and a set of particles, this then creates a *signal* which is a change in the state of the instrument. As an example, a mercury thermometer interacts with the fluid around it which results in a signal in the form of a moving column of mercury in the thermometer. As another example, a measuring rule is aligned with the two ends of an object by a servomechanism that interacts with photons from the rule and the object, the signal being the markings that align with the end of the object. The signal can be a flow of charge or photons or a chemical change etc. Sensory experience begins with the interaction between an object that acts as a measuring instrument and a set of particles such as photons or scent molecules etc. In the Direct Realist case the signal would be the change at the interface between the bulk of a material (a crude measuring device) and a set of particles such as photons, in the Indirect Realist case it would be some signal in the brain derived from the initial signal. In either case phenomenal consciousness would be some form, an arrangement of the set of signals themselves. The signals in measuring events arise as a result of interactions between QM phenomena and a measuring apparatus composed of relatively large structures. These structures (called *the environment*) produce signals at definite locations. This chain of fixing positions is known as **decoherence** (see Zurek (2003) or Bacciagaluppi (2004) for a review). This means that measuring events fix the positions of signals and these represent the positions of QM events. (Some physical particles such as photons are subject to little decoherence during propagation, even in water (cf: Anglin & Zurek (1996)).) So signals in measuring devices usually have highly restrained positions. Now consider the final signals, the one\'s in phenomenal consciousness. To an observer of the brain they should be, very nearly, in their classical positions within the brain unless they consist of photons or are subject to some special effect such as has been proposed for microtubules. The brain acts as a measuring device causing decoherence. But despite this even signals composed of sodium ions, which should decohere rapidly in water, have a tiny, but finite, probability of remaining in a coherent state. If your conscious experience is the signals and not the fabric of the brain are you the set of signals that interacts with the brain fabric almost immediately, the set that interacts after a minute or the set that almost never interacts? To an outside observer you must be the main chance, the rapidly interacting signals, but to the signals themselves all possibilities exist. Which one are you? Certainly any interaction between the signals and the mutually observed world must involve decoherence but the external observer would find it difficult to determine whether a particular interaction was due to signals that had interacted immediately or ones that were delayed (or delayed in an alternate QM reality). This problem is part of the *preferred basis problem* that will be discussed later. Zurek (2003)assumes that phenomenal experience is identical to measurements. The observer is then both the signal and the apparatus that encloses the signal. He summarises the resultant idea of the completely determined observer who is fully integrated into the measured world: `<font face="times new roman">`{=html}The 'higher functions' of observers - e.g., consciousness, etc. - may be at present poorly understood, but it is safe to assume that they reflect physical processes in the information processing hardware of the brain. Hence, mental processes are in effect objective, as they leave an indelible imprint on the environment: The observer has no chance of perceiving either his memory, or any other macroscopic part of the Universe in some arbitrary superposition. \"`</font>`{=html} Zurek (2003) Notice the phrase \"perceiving .. his memory\" - as neuroscientists we must ask \"how\"? By more measurements? There are no more measurements when things are arranged in phenomenal consciousness, the information has nowhere else to go. However, according to the empiricist philosophers the arrangements of the signals in phenomenal consciousness do extend through time in a definite order at any instant. Is it this order that determines the positions of signals in the brain or is it the brain that determines this order? Physicalism leads us to an idea of the content of consciousness as an arrangement of quantum fields like the content of the brain or the content of the world. The arrangement of the quantum fields at an instant in experience is probably related to the arrangement of measured events at a succession of instants in the world. According to the account given above, the contents of conscious experience, the qualia, are signals derived from the world that compose conscious experience with the interesting problem that they are themselves the experience and are not fixed in space and time by further measurement. ### The philosophy of qualia The term \"qualia\" was introduced by C.I. Lewis in 1929: `<font face="times new roman">`{=html}This given element in a single experience of an object is what will be meant by \"a presentation.\" Such a presentation is, obviously, an event and historically unique. But for most of the purposes of analyzing knowledge one presentation of a half-dollar held at right angles to the line of vision, etc., will be as good as another. If, then, I speak of \" the presentation\" of this or that, it will be on the supposition that the reader can provide his own illustration. No identification of the event itself with the repeatable content of it is intended.`</font>`{=html} `<font face="times new roman">`{=html}In any presentation, this content is either a specific quale (such as the immediacy of redness or loudness) or something analyzable into a complex of such. The presentation as an event is, of course, unique, but the qualia which make it up are not. They are recognizable from one to another experience.(CI Lewis, *Mind and the World Order*, 1941 edition Chapter 2)`</font>`{=html} Tye (2003) gives the following definition of qualia: `<font face="times new roman">`{=html}\"Experiences vary widely. For example, I run my fingers over sandpaper, smell a skunk, feel a sharp pain in my finger, seem to see bright purple, become extremely angry. In each of these cases, I am the subject of a mental state with a very distinctive subjective character. There is something it is like for me to undergo each state, some phenomenology that it has. Philosophers often use the term \'qualia\' to refer to the introspectively accessible properties of experiences that characterize what it is like to have them. In this standard, broad sense of the term, it is very difficult to deny that there are qualia.\"`</font>`{=html} Tye(2003). In philosophy objects are considered to have perceived features such as shape and colour, weight and texture which are called sensible qualities. Sensible qualities are divided into intrinsic, or primary, qualities that are properties of the object itself and extrinsic, or secondary, qualities which are related to the sensations produced in the observer. Shape is generally considered to be a primary quality whereas colour is often considered to be a secondary quality. It is generally considered that secondary qualities correspond to qualia (Smith 1990, Shoemaker 1990) and the two terms are often used synonymously. Although secondary qualities may be qualia, the term \"qualia\" may include things other than perceptions such as pain etc. that are, arguably, not secondary qualities. Primary qualities might also give rise to experience that is distinct from, say, the shape of an object itself. Although \"qualia\" is a recent term, the philosophical debate about the nature of secondary qualities, such as colours, and the nature of conscious experience itself has been around for millennia. It seems that the visual system gives rise to experience even in the absence of previous visual stimulation. For example, when someone recovers from blindness they have an experience that contains shapes and colours even though these have little meaning: `<font face="times new roman">`{=html}\"When he first saw, he was so far from making any judgement of distances, that he thought all object whatever touched his eyes\.... he knew not the shape of anything, nor any one thing from another, however different in shape and magnitude.. We thought he soon knew what pictures represented, which were shewed to him, but we found afterwards we were mistaken; for about two months after he was couched, he discovered at once they represented solid bodiess, when to that time he considered them only as party-coloured panes, or surfaces diversified with variety of paint.\"`</font>`{=html} William Cheselden (1728) Qualia are the components of experience, whatever the mode of input to that experience. Strawson (1994) includes content such as accompanies suddenly remembering or thinking of something as examples of qualia. There is thought to be an *explanatory gap* associated with qualia (Levine 1983), as an example it is hard to imagine how the experience called pain could be a set of impulses in the brain. Some philosophers have attempted to bridge this gap by invoking Direct Realism, proposing that our experience is in some way \'transparent\' so that we experience the world or the injured limb directly (i.e.: there is an assumption that things flow within phenomenal experience into a centre point and we see right through this flow!). This idea has led to a deduction that phenomenal experience is a set of things and qualities are these things, not deductions about or experiences based on these things. As Tye (2003) puts it: `<font face="times new roman">`{=html}These observations suggest that qualia, conceived of as the immediately \'felt\' qualities of experiences of which we are cognizant when we attend to them introspectively, do not really exist. The qualities of which we are aware are not qualities of experiences at all, but rather qualities that, if they are qualities of anything, are qualities of things in the world (as in the case of perceptual experiences) or of regions of our bodies (as in the case of bodily sensations). This is not to say that experiences do not have qualia. The point is that qualia are not qualities of experiences. `</font>`{=html} However, the outstanding issue for Tye\'s analysis is where in the world the thing that is called a quale exists - on a thing in the world beyond the body, on the retina, in the cortex, in the thalamus? Tye seems to be suggesting that \"in the world\" can only be beyond the retina but given that a television can have a colour and a retina can have a colour why should we insist that the colour in conscious experience is always *of* the thing being represented via the DVD or videotape? That colour should always be a property of an original coloured object seems strange, why is it not a property of the pigment in a photo of the object, a property of an led in a computer screen displaying an image of the photo, a property of the pigments in the retina viewing the computer, the impulses in the visual cortex etc.? As was seen in the previous section, only signals are available in the classical world of conscious observation. The \"reality\" of the things that generate signals is not available. So whether experience is a signal at the position of what we call an \"oak tree\" or a signal in the eye due to photons reflected from the tree or a signal in the brain the same sort of phenomena would apply. Qualia would be a field, an arrangement of signals, not processes based on these signals. Some philosophers hold that qualia are a field of signals derived from the original signals that are next to the quantum phenomena that compose an object. In other words they propose that qualia are not the first signals in the chain from whatever composes an object to the observer. These philosophers are known as Representationalists and the emphasis on secondary signals allows a contribution from the brain etc. to the field of signals that is conscious experience. Modern representationalists such as Tye (1995), Lehar(2003) and Dretske(2003) emphasise the idea that qualia are actual things that represent objects rather than concepts or experiences of things. As Dretske puts it: `<font face="times new roman">`{=html}\"..the features that define what it is like to have an experience are properties that the objects we experience (not our experience of them) have.`</font>`{=html}(Dretske 2003). Lehar(2003) uses modern language to express the empiricist notion that the signals that comprise qualia are more likely to be in our brains than elsewhere, according to Lehar the objects we experience must be informational replicas in our heads: `<font face="times new roman">`{=html}\"The central message of Gestalt theory therefore is that the primary function of perceptual processing is the generation of a miniature, virtual-reality replica of the external world inside our head, and that the world we see around us is not the real external world, but is exactly that miniature internal replica\" (Lehar 2003).`</font>`{=html} Direct Realists and Representationalists share the same view that qualia are an actual, physical field of things somewhere in the world. Some functionalists and eliminativists take a different view, believing that qualia do not exist except as judgements of properties that are used in interactions (i.e.: as disembodied information - see the section on Direct Realism). Lewis, C.I. (1929) Mind and the World-Order. <http://www.ditext.com/lewis/mwo2.html> Smith, A.D. (1990) Of Primary and Secondary Qualities, Philosophical Review 99 (1990). ### More about qualia

# Consciousness Studies/Measurement In Quantum Physics And The Preferred Basis Problem ## The Measurement Problem In quantum physics the probability of an event is deduced by taking the square of the **amplitude** for an event to happen. The term \"amplitude for an event\" arises because of the way that the Schrödinger equation is derived using the mathematics of ordinary, classical waves where the amplitude over a small area is related to the number of photons hitting the area. In the case of light, the probability of a photon hitting that area will be related to the ratio of the number of photons hitting the area divided by the total number of photons released. The number of photons hitting an area per second is the intensity or amplitude of the light on the area, hence the probability of finding a photon is related to \"amplitude\". However, the Schrödinger equation is not a classical wave equation. It does not determine events, it simply tells us the probability of an event. In fact the Schrödinger equation in itself does not tell us that an event occurs at all, it is only when a measurement is made that an event occurs. The measurement is said to cause *state vector reduction*. This role of measurement in quantum theory is known as the **measurement problem**. The measurement problem asks how a definite event can arise out of a theory that only predicts a continuous probability for events. Two broad classes of theory have been advanced to explain the measurement problem. In the first it is proposed that observation produces a sudden change in the quantum system so that a particle becomes localised or has a definite momentum. This type of explanation is known as *collapse of the wavefunction*. In the second it is proposed that the probabilistic Schrödinger equation is always correct and that, for some reason, the observer only observes one particular outcome for an event. This type of explanation is known as the *relative state interpretation*. In the past thirty years relative state interpretations, especially Everett\'s relative state interpretation have become favoured amongst quantum physicists. ## The quantum probability problem The measurement problem is particularly problematical when a single particle is considered. Quantum theory differs from classical theory because it is found that a single photon seems to be able to interfere with itself. If there are many photons then probabilities can be expressed in terms of the ratio of the number hitting a particular place to the total number released but if there is only one photon then this does not make sense. When only one photon is released from a light source quantum theory still gives us a probability for a photon to hit a particular area but what does this mean at any instant if there is indeed only one photon? If the Everettian interpretation of quantum mechanics is invoked then it might seem that the probability of the photon hitting an area in your particular universe is related to the occurrences of the photon in all the other universes. But in the Everrettian interpretation even the improbable universes occur. This leads to a problem known as the quantum **probability problem**: `If the universe splits after a measurement, with every possible `\ `measurement outcome realised in some branch, then how can it make `\ `sense to talk about the probabilities of each outcome? Each `\ `outcome occurs.` This means that if our phenomenal consciousness is a set of events then there would be endless copies of these sets of events, almost all of which are almost entirely improbable to an observer outside the brain but all of which exist according to an Everrettian Interpretation. Which set is you? Why should \'you\' conform to what happens in the environment around you? ## The preferred basis problem It could be held that you assess probabilities in terms of the branch of the universe in which you find yourself but then why do you find yourself in a particular branch? Decoherence Theory is one approach to these questions. In decoherence theory the environment is a complex form that can only interact with particles in particular ways. As a result quantum phenomena are rapidly smoothed out in a series of micro-measurements so that the macro-scale universe appears quasi-classical. The form of the environment is known as the preferred basis for quantum decoherence. This then leads to the **preferred basis problem** in which it is asked how the environment occurs or whether the state of the environment depends on any other system. According to most forms of decoherence theory \'you\' are a part of the environment and hence determined by the preferred basis. From the viewpoint of phenomenal consciousness this does not seem unreasonable because it has always been understood that the conscious observer does not observe things as quantum superpositions. The conscious observation is a classical observation. However, the arguments that are used to derive this idea of the classical, conscious observer contain dubious assumptions that may be hindering the progress of quantum physics. The assumption that the conscious observer is simply an information system is particularly dubious: `<font face="times new roman">`{=html}\"Here we are using aware in a down - to - earth sense: Quite simply, observers know what they know. Their information processing machinery (that must underlie higher functions of the mind such as \"consciousness\") can readily consult the content of their memory. `</font>`{=html}(Zurek 2003). This assumption is the same as assuming that the conscious observer is a set of measurements rather than an observation. It makes the rest of Zurek\'s argument about decoherence and the observer into a tautology - given that observations are measurements then observations will be like measurements. However, conscious observation is not simply a change of state in a neuron, a \"measurement\", it is the entire manifold of conscious experience. In his 2003 review of this topic Zurek makes clear an important feature of information theory when he states that: `There is no information without representation.` So the contents of conscious observation are states that correspond to states of the environment in the brain (i.e.: measurements). But how do these states in the brain arise? The issue that arises here is whether the representation, the contents of consciousness, is entirely due to the environment or due to some degree to the form of conscious observation. Suppose we make the reasonable assumption that conscious observation is due to some physical field in the dendrites of neurons rather than in the action potentials that transmit the state of the neurons from place to place. This field would not necessarily be constrained by decoherence; there are many possibilities for the field, for instance, it could be a radio frequency field due to impulses or some other electromagnetic field (cf: Anglin & Zurek (1996)) or some quantum state of macromolecules etc.. Such a field might contain many superposed possibilities for the state of the underlying neurons and although these would not affect sensations, they could affect the firing patterns of neurons and create actions in the world that are not determined by the environmental \"preferred basis\". Zeh (2000) provides a mature review of the problem of conscious observation. For example he realises that memory is not the same as consciousness: `<font face="times new roman">`{=html}\"The genuine carriers of consciousness \... must not in general be expected to represent memory states, as there do not seem to be permanent contents of consciousness.\"`</font>`{=html} and notes of memory states that they must enter some other system to become part of observation: `<font face="times new roman">`{=html}\"To most of these states, however, the true physical carrier of consciousness somewhere in the brain may still represent an external observer system, with whom they have to interact in order to be perceived. Regardless of whether the ultimate observer systems are quasi-classical or possess essential quantum aspects, consciousness can only be related to factor states (of systems assumed to be localized in the brain) that appear in branches (robust components) of the global wave function --- provided the Schrodinger equation is exact. Environmental decoherence represents entanglement (but not any "distortion" --- of the brain, in this case), while ensembles of wave functions, representing various potential (unpredictable) outcomes, would require a dynamical collapse (that has never been observed).\"`</font>`{=html} However, Zeh (2003) points out that events may be irreversibly determined by decoherence before information from them reaches the observer. This might give rise to a multiple worlds and multiple minds mixture for the universe, the multiple minds being superposed states of the part of the world that is the mind. Such an interpretation would be consistent with the *apparently* epiphenomenal nature of mind. A mind that interacts only weakly with the consensus physical world, perhaps only approving or rejecting passing actions would be an ideal candidate for a QM multiple minds hypothesis. ## Further reading and references - Anglin, J.R. & Zurek, J.H. (1996). Decoherence of quantum fields: decoherence and predictability. Phys.Rev. D53 (1996) 7327-7335 <http://arxiv.org/PS_cache/quant-ph/pdf/9510/9510021.pdf> - Baker, D.J. (2004). Lingering Problems with Probability in Everettian Quantum Mechanics <http://www.princeton.edu/~hhalvors/teaching/phi538_f2004/LingeringProbsEverett.pdf> - Lockwood, M. (1996) Many Minds Interpretations of quantum mechanics. The British Journal of the Philosophy of Science. 47: 2 (159-188). <http://www.ibiblio.org/weidai/Many_Minds.pdf> - Pearl, P. (1997). True collapse and false collapse. Published in Quantum Classical Correspondence: Proceedings of the 4th Drexel Symposium on Quantum Nonintegrability, Philadelphia, PA, USA, September 8--11, 1994, pp. 51--68. Edited by Da Hsuan Feng and Bei Lok Hu. Cambridge, MA: International Press, 1997. <http://arxiv.org/PS_cache/quant-ph/pdf/9805/9805049.pdf> - Squires, E.J. (1996). What are quantum theorists doing at a conference on consciousness? <http://arxiv.org/PS_cache/quant-ph/pdf/9602/9602006.pdf> - Zeh, H. D. (1979). Quantum Theory and Time Asymmetry. Foundations of Physics, Vol 9, pp 803--818 (1979). - Zeh, H.D. (2000) THE PROBLEM OF CONSCIOUS OBSERVATION IN QUANTUM MECHANICAL DESCRIPTION. Epistemological Letters of the Ferdinand-Gonseth Association in Biel (Switzerland) Letter No 63.0.1981, updated 2000. <http://arxiv.org/abs/quant-ph/9908084> - Zeh, H.D. (2003). Decoherence and the Appearance of a Classical World in Quantum Theory, second edition, Authors:. E. Joos, H.D. Zeh, C. Kiefer D. Giulini, J. Kupsch, and I.-O. Stamatescu. Chapter 2: Basic Concepts and their Interpretation. <http://www.rzuser.uni-heidelberg.de/~as3/index.html> - Zurek, W.H. (2003). Decoherence, einselection and the quantum origins of the classical. Rev. Mod. Phys. 75, 715 (2003) <http://arxiv.org/abs/quant-ph/0105127>

# Consciousness Studies/The Neuroscience Of Consciousness *\"All parts of the brain may well be involved in normal conscious processes but the indispensable substratum of consciousness lies outside the cerebral cortex, probably in the diencephalon\" Penfield 1937.* *\"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\" Baars et al 1998.* ## Introduction *It is recommended that readers review ../The Philosophical Problem/ before reading the sections on the neuroscience of consciousness.* One of the most exciting discoveries of neuroscience is that nearly all of the brain performs functions that are not part of conscious experience. In everyday life we are usually unaware of breathing or heartbeats yet there are parts of the brain dedicated to these functions. When we pick up a pencil we have no experience of the fine control of individual muscles yet large areas of cortex and cerebellum implement this. Things do not appear as greyscale and then have the colour poured into them although this strange colour addition is done in the visual cortex. Most of the brain is non-conscious but how is the \"ghost in the machine\", the mind, created by and linked into the mostly non-conscious brain? Although most of the processes in the brain are non-conscious there can be little doubt that the output of sensory processes contribute to experience. For example, although we do not experience the process of adding colour to visual data in cortical area V4 we do experience coloured forms and although we have little inkling of the hugely complex creation of words in the temporal/frontal lobes we do experience verbal thoughts. Our experience is an integrated output of most of the brain processes that deal with sensation as well as dreams, thoughts and emotions. But how and where does this experience occur? The signals that compose phenomenal consciousness have not been elucidated. Perhaps the least likely signals for this role are electrical impulses in nerve fibres because they are distributed unevenly in time and space and can even be absent for relatively long periods. Furthermore, electrical impulses across the membranes of neurons have an all or nothing character; they cannot be easily superimposed on one another. There are many other possibilities however, such as: the electrical fields on the dendrites of neurons, the fields of chemicals spreading out from synapses, the radio-frequency emissions of action potentials, events in the microtubules in cells, the depolarisations of glia, the varying fields measured by EEG devices, the quantum superposition of brain states etc\... Phenomenal consciousness could exist in the dendritic field of ten neurons receiving 100,000 synapses or as an oscillation of fields over the whole brain. The substrate of phenomenal consciousness could be staring us in the face as a state of the whole brain or be like a needle in a haystack, lurking in a tiny region of brain, unsuspected and undiscovered. Given that there is no widely accepted theory of phenomenal consciousness Crick (1994) and Crick and Koch (1998) approached the problem of the location of the substrate of consciousness by proposing that scientists search for the **Neural Correlates of Consciousness**. These neural correlates consist of events in the brain that accompany events in conscious experience. References: Crick, F. (1994). The Astonishing Hypothesis. New York: Scribners. Crick, F. & Koch, C. (1998).Consciousness and Neuroscience. Cerebral Cortex, 8:97-107, 1998 <http://www.klab.caltech.edu/~koch/crick-koch-cc-97.html> ## Neuroanatomy ### General layout of the CNS The Central Nervous System (CNS) consists of the spinal cord, the brain and the retina. The CNS consists of two major groups of active cells, the **neurons** and the **glia**. The neurons conduct short impulses of electricity along their membranes called **\'action potentials** and encode data as frequency modulated signals (i.e.: different intensities of stimulation are converted into different rates of firing). The glia modify the connections between neurons and can respond to neuron activity by a change of voltage across their membranes. Glia also have many other roles such as sustaining neurons and providing electrical insulation. Neurons have three principal parts: the **cell body**, the **dendrites** and the **axon**. Impulses flow from the cell body to the axon. The axon can be over a metre long and bundles of axons form **nerve fibres**. Where an axon makes contact with the dendrites or cell body of another neuron there is a special sort of junction called a **synapse**. Transmission of data across synapses is usually mediated by chemical signals. Areas of the brain where there are many cell bodies have a beige/grey tinge and are called **grey matter**. Areas that contain mainly nerve fibres are called **white matter**. Masses of grey matter outside of the surface of the cerebral cortex or the cerebellum are called **nuclei**. The brain is of central interest in consciousness studies because consciousness persists even when the spinal cord is sectioned at the neck. The brain can be divided into five distinct divisions or *\'vesicles* on the basis of embryological development. These are the myelencephalon, metencephalon, mesencephalon, diencephalon and telencephalon (See the illustration below).  : Myelencephalon: Medulla oblongata. : Metencephalon: pons and cerebellum. : Mesencephalon: midbrain (tectum containing the superior colliculus and inferior colliculus, red nucleus, substantia nigra, cerebellar peduncles. : Diencephalon: thalamus, epithalamus, hypothalamus, subthalamus. : Telencephalon: corpus striatum, cerebral hemispheres. These divisions tend to obscure the physical anatomy of the brain which looks like a rod of spinal cord with a swelling at the top due to the thalamus and corpus striatum. Around the top of the rod is a globe of deeply indented cerebral cortex and at the back there is the puckered mass of cerebellum. The physical anatomy is shown in greater detail in the illustration below where the thalamus and corpus striatum have been splayed out to show more detail.  The thalamus is a complex organ with numerous nuclei. 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 The cerebral hemispheres consist of a thin layer of nerve cell bodies on the surface (the cerebral cortex) with a mass of white, interconnecting fibres below (the cerebral medulla). Each hemisphere is divided into four principle **lobes** as shown in the illustration below:  The cortex is a set of interconnected processors. The general layout of the cortex with the location of the processors is shown in the illustration below:  The pathways in the brain tend to preserve the **topography** of the sense organs so that particular groups of cells on the retina, cochlear or body have corresponding groups of cells in the thalamus or cortex. The retina is said to have a topological mapping onto the thalamus so that the projection of the optic nerve is said to be **retinotopic**. Nerve fibres that go to a part of the brain are called **afferents** and fibres that come from a part of the brain are called **efferents**. The cortex and thalamus/striatum are intimately linked by millions of connecting fibres and there is also a direct connection from the motor cortex to the spinal cord. ### Sensory pathways Information from the sense organs travels along the appropriate sensory nerve (optic, auditory, spinal etc.) and once in the brain is divided into three principal paths that connect either with the thalamus, the cerebellum or the reticular formation. There are thalamic nuclei for each broad type of sensation and these have reciprocal connections with specific areas of cortex that deal with the appropriate mode of sensation. The large mass of nerve fibres that mediate the connection between the thalamus and cortex are known as the thalamo-cortical and cortico-thalamic tracts. There tend to be more sensory nerve fibres returning from the cortex to the thalamus than connect from the thalamus to the cortex so it is difficult to determine whether the cortex is the destination of sensory data or a region that supplies extra processing power to thalamic nuclei. The cerebellum mediates reflex control of complex movements and receives input from most of the sense organs. The reticular formation is a group of loosely distributed neurons in the medulla, pons and mesencephalon. It receives a large amount of autonomic input and also input from all the sense organs. The intralaminar nuclei of the thalamus are the principal destination of reticular output to higher centres. In the most primitive vertebrates the reticular formation performs most of the higher control functions of the animal. The reticular formation is implicated in the maintenance of sleep-wake cycles and activates the higher centres. This activity has attracted the label **ascending reticular activating system** (ARAS) to describe how the activity of higher centres is controlled by reticular input. This title is unfortunate from the point of view of consciousness studies because it implies that conscious experience is a result of activating the cortex when it could be due to turning on or off particular systems all the way from the reticular formation to the cortex. Destruction of the reticular formation leads to coma. ### Motor and output pathways Motor control of the body below the skull is accomplished by three principle routes. The motor cortex of the frontal lobes and related cortex in the parietal lobes can control movement directly via nerves known as the cortico-spinal tract (also called the pyramidal tract). The activity of the motor cortex is modified and controlled by a loop that passes through the corpus striatum, the substantia nigra and the subthalamic nucleus and returns to the cortex. These controlling nuclei are, along with the amygdala, known as the **basal ganglia**. The cerebellum and the corpus striatum provide complex reflex control of the body through nerves that travel through the red nucleus and form the rubro-spinal tract. The vestibular nucleus, which processes signals related to balance and posture, has direct connections with the periphery via the vestibulo-spinal tract. Apart from the routes for controlling motor activity there are also other outputs from the brain, for instance the autonomic nervous system is intimately linked with the reticular formation which has areas that control blood pressure, respiratory rhythm etc. ## Topological mapping and cortical columns !Sensorimotor homunculus{width="400"}The cerebral cortex has a highly convoluted surface that provides a large area of tissue. The parts of the cortex that are used for motor and sensory functions are organised so that different areas correspond to different zones of the body. This **topological** organisation is shown classically by a drawing of the *sensorimotor homunculus* such as that shown on the right. Within a given area of the cortex there are further subdivisions. For example, the occipital cortex corresponds to the eyes of the sensorimotor homunculus and it is further organised so that areas of the retina have corresponding areas on the cortex. This mapping of the layout of the retina onto the cortex is known as **topological mapping**. It results in a corresponding mapping of the receptive field of the eye onto the cortex. The mapping is like an image on the surface of the brain tissue and the visual scene that is presented to a subject can be recovered by using fMRI along with computer analysis (Miyawaki *et al.* 2008). The human cortex is fairly deep, containing 100-200 neurons from the surface to the white matter. It is divided into six histological and functional layers. These layers can be further subdivided. In 1957 Mountcastle used microelectrode measurements to show that activity of small zones of cortex about 0.1 to 1 mm in diameter corresponded to particular points in the receptive field. These functional columns of cortical tissue are called **cortical columns**.  The diagram above shows the organisation of **ocular dominance columns**. Each column represents a particular part of the receptive field of a single eye. The columns for left and right eyes are linked together in lines. The lines of ocular dominance form a pattern like a fingerprint on the surface of the cortex. The same part of cortex can have overlapping columns for different functions. For instance there are columns that react to particular orientations of edges at particular places in the visual field. These columns tend to be located together on the cortex forming a **pinwheel** of columns that cover all orientations at a particular receptive field position.  There are also topologically arranged columns for colour, spatial frequency etc. Yoichi Miyawaki, Hajime Uchida, Okito Yamashita, Masa-aki Sato, Yusuke Morito, Hiroki C. Tanabe, Norihiro Sadato and Yukiyasu Kamitani. (2008). Visual Image Reconstruction from Human Brain Activity using a Combination of Multiscale Local Image Decoders. Neuron, Volume 60, Issue 5, 10 December 2008, Pages 915-929 **Modules** - The neurophysiology of sensation and perception - The cortex and thalamus - Rivalries and synchronisation

# Consciousness Studies/The Neuroscience Of Consciousness#Introduction *\"All parts of the brain may well be involved in normal conscious processes but the indispensable substratum of consciousness lies outside the cerebral cortex, probably in the diencephalon\" Penfield 1937.* *\"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\" Baars et al 1998.* ## Introduction *It is recommended that readers review ../The Philosophical Problem/ before reading the sections on the neuroscience of consciousness.* One of the most exciting discoveries of neuroscience is that nearly all of the brain performs functions that are not part of conscious experience. In everyday life we are usually unaware of breathing or heartbeats yet there are parts of the brain dedicated to these functions. When we pick up a pencil we have no experience of the fine control of individual muscles yet large areas of cortex and cerebellum implement this. Things do not appear as greyscale and then have the colour poured into them although this strange colour addition is done in the visual cortex. Most of the brain is non-conscious but how is the \"ghost in the machine\", the mind, created by and linked into the mostly non-conscious brain? Although most of the processes in the brain are non-conscious there can be little doubt that the output of sensory processes contribute to experience. For example, although we do not experience the process of adding colour to visual data in cortical area V4 we do experience coloured forms and although we have little inkling of the hugely complex creation of words in the temporal/frontal lobes we do experience verbal thoughts. Our experience is an integrated output of most of the brain processes that deal with sensation as well as dreams, thoughts and emotions. But how and where does this experience occur? The signals that compose phenomenal consciousness have not been elucidated. Perhaps the least likely signals for this role are electrical impulses in nerve fibres because they are distributed unevenly in time and space and can even be absent for relatively long periods. Furthermore, electrical impulses across the membranes of neurons have an all or nothing character; they cannot be easily superimposed on one another. There are many other possibilities however, such as: the electrical fields on the dendrites of neurons, the fields of chemicals spreading out from synapses, the radio-frequency emissions of action potentials, events in the microtubules in cells, the depolarisations of glia, the varying fields measured by EEG devices, the quantum superposition of brain states etc\... Phenomenal consciousness could exist in the dendritic field of ten neurons receiving 100,000 synapses or as an oscillation of fields over the whole brain. The substrate of phenomenal consciousness could be staring us in the face as a state of the whole brain or be like a needle in a haystack, lurking in a tiny region of brain, unsuspected and undiscovered. Given that there is no widely accepted theory of phenomenal consciousness Crick (1994) and Crick and Koch (1998) approached the problem of the location of the substrate of consciousness by proposing that scientists search for the **Neural Correlates of Consciousness**. These neural correlates consist of events in the brain that accompany events in conscious experience. References: Crick, F. (1994). The Astonishing Hypothesis. New York: Scribners. Crick, F. & Koch, C. (1998).Consciousness and Neuroscience. Cerebral Cortex, 8:97-107, 1998 <http://www.klab.caltech.edu/~koch/crick-koch-cc-97.html> ## Neuroanatomy ### General layout of the CNS The Central Nervous System (CNS) consists of the spinal cord, the brain and the retina. The CNS consists of two major groups of active cells, the **neurons** and the **glia**. The neurons conduct short impulses of electricity along their membranes called **\'action potentials** and encode data as frequency modulated signals (i.e.: different intensities of stimulation are converted into different rates of firing). The glia modify the connections between neurons and can respond to neuron activity by a change of voltage across their membranes. Glia also have many other roles such as sustaining neurons and providing electrical insulation. Neurons have three principal parts: the **cell body**, the **dendrites** and the **axon**. Impulses flow from the cell body to the axon. The axon can be over a metre long and bundles of axons form **nerve fibres**. Where an axon makes contact with the dendrites or cell body of another neuron there is a special sort of junction called a **synapse**. Transmission of data across synapses is usually mediated by chemical signals. Areas of the brain where there are many cell bodies have a beige/grey tinge and are called **grey matter**. Areas that contain mainly nerve fibres are called **white matter**. Masses of grey matter outside of the surface of the cerebral cortex or the cerebellum are called **nuclei**. The brain is of central interest in consciousness studies because consciousness persists even when the spinal cord is sectioned at the neck. The brain can be divided into five distinct divisions or *\'vesicles* on the basis of embryological development. These are the myelencephalon, metencephalon, mesencephalon, diencephalon and telencephalon (See the illustration below).  : Myelencephalon: Medulla oblongata. : Metencephalon: pons and cerebellum. : Mesencephalon: midbrain (tectum containing the superior colliculus and inferior colliculus, red nucleus, substantia nigra, cerebellar peduncles. : Diencephalon: thalamus, epithalamus, hypothalamus, subthalamus. : Telencephalon: corpus striatum, cerebral hemispheres. These divisions tend to obscure the physical anatomy of the brain which looks like a rod of spinal cord with a swelling at the top due to the thalamus and corpus striatum. Around the top of the rod is a globe of deeply indented cerebral cortex and at the back there is the puckered mass of cerebellum. The physical anatomy is shown in greater detail in the illustration below where the thalamus and corpus striatum have been splayed out to show more detail.  The thalamus is a complex organ with numerous nuclei. 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SIZE=2>`{=html}(motor)`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ``` `<FONT SIZE=2>`{=html}Ventral lateral`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ``` `<FONT SIZE=2>`{=html}VL`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ``` `<FONT SIZE=2>`{=html}Motor`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} </TABLE> ``` The location of these nuclei is shown in the illustration below:  The cerebral hemispheres consist of a thin layer of nerve cell bodies on the surface (the cerebral cortex) with a mass of white, interconnecting fibres below (the cerebral medulla). Each hemisphere is divided into four principle **lobes** as shown in the illustration below:  The cortex is a set of interconnected processors. The general layout of the cortex with the location of the processors is shown in the illustration below:  The pathways in the brain tend to preserve the **topography** of the sense organs so that particular groups of cells on the retina, cochlear or body have corresponding groups of cells in the thalamus or cortex. The retina is said to have a topological mapping onto the thalamus so that the projection of the optic nerve is said to be **retinotopic**. Nerve fibres that go to a part of the brain are called **afferents** and fibres that come from a part of the brain are called **efferents**. The cortex and thalamus/striatum are intimately linked by millions of connecting fibres and there is also a direct connection from the motor cortex to the spinal cord. ### Sensory pathways Information from the sense organs travels along the appropriate sensory nerve (optic, auditory, spinal etc.) and once in the brain is divided into three principal paths that connect either with the thalamus, the cerebellum or the reticular formation. There are thalamic nuclei for each broad type of sensation and these have reciprocal connections with specific areas of cortex that deal with the appropriate mode of sensation. The large mass of nerve fibres that mediate the connection between the thalamus and cortex are known as the thalamo-cortical and cortico-thalamic tracts. There tend to be more sensory nerve fibres returning from the cortex to the thalamus than connect from the thalamus to the cortex so it is difficult to determine whether the cortex is the destination of sensory data or a region that supplies extra processing power to thalamic nuclei. The cerebellum mediates reflex control of complex movements and receives input from most of the sense organs. The reticular formation is a group of loosely distributed neurons in the medulla, pons and mesencephalon. It receives a large amount of autonomic input and also input from all the sense organs. The intralaminar nuclei of the thalamus are the principal destination of reticular output to higher centres. In the most primitive vertebrates the reticular formation performs most of the higher control functions of the animal. The reticular formation is implicated in the maintenance of sleep-wake cycles and activates the higher centres. This activity has attracted the label **ascending reticular activating system** (ARAS) to describe how the activity of higher centres is controlled by reticular input. This title is unfortunate from the point of view of consciousness studies because it implies that conscious experience is a result of activating the cortex when it could be due to turning on or off particular systems all the way from the reticular formation to the cortex. Destruction of the reticular formation leads to coma. ### Motor and output pathways Motor control of the body below the skull is accomplished by three principle routes. The motor cortex of the frontal lobes and related cortex in the parietal lobes can control movement directly via nerves known as the cortico-spinal tract (also called the pyramidal tract). The activity of the motor cortex is modified and controlled by a loop that passes through the corpus striatum, the substantia nigra and the subthalamic nucleus and returns to the cortex. These controlling nuclei are, along with the amygdala, known as the **basal ganglia**. The cerebellum and the corpus striatum provide complex reflex control of the body through nerves that travel through the red nucleus and form the rubro-spinal tract. The vestibular nucleus, which processes signals related to balance and posture, has direct connections with the periphery via the vestibulo-spinal tract. Apart from the routes for controlling motor activity there are also other outputs from the brain, for instance the autonomic nervous system is intimately linked with the reticular formation which has areas that control blood pressure, respiratory rhythm etc. ## Topological mapping and cortical columns !Sensorimotor homunculus{width="400"}The cerebral cortex has a highly convoluted surface that provides a large area of tissue. The parts of the cortex that are used for motor and sensory functions are organised so that different areas correspond to different zones of the body. This **topological** organisation is shown classically by a drawing of the *sensorimotor homunculus* such as that shown on the right. Within a given area of the cortex there are further subdivisions. For example, the occipital cortex corresponds to the eyes of the sensorimotor homunculus and it is further organised so that areas of the retina have corresponding areas on the cortex. This mapping of the layout of the retina onto the cortex is known as **topological mapping**. It results in a corresponding mapping of the receptive field of the eye onto the cortex. The mapping is like an image on the surface of the brain tissue and the visual scene that is presented to a subject can be recovered by using fMRI along with computer analysis (Miyawaki *et al.* 2008). The human cortex is fairly deep, containing 100-200 neurons from the surface to the white matter. It is divided into six histological and functional layers. These layers can be further subdivided. In 1957 Mountcastle used microelectrode measurements to show that activity of small zones of cortex about 0.1 to 1 mm in diameter corresponded to particular points in the receptive field. These functional columns of cortical tissue are called **cortical columns**.  The diagram above shows the organisation of **ocular dominance columns**. Each column represents a particular part of the receptive field of a single eye. The columns for left and right eyes are linked together in lines. The lines of ocular dominance form a pattern like a fingerprint on the surface of the cortex. The same part of cortex can have overlapping columns for different functions. For instance there are columns that react to particular orientations of edges at particular places in the visual field. These columns tend to be located together on the cortex forming a **pinwheel** of columns that cover all orientations at a particular receptive field position.  There are also topologically arranged columns for colour, spatial frequency etc. Yoichi Miyawaki, Hajime Uchida, Okito Yamashita, Masa-aki Sato, Yusuke Morito, Hiroki C. Tanabe, Norihiro Sadato and Yukiyasu Kamitani. (2008). Visual Image Reconstruction from Human Brain Activity using a Combination of Multiscale Local Image Decoders. Neuron, Volume 60, Issue 5, 10 December 2008, Pages 915-929 **Modules** - The neurophysiology of sensation and perception - The cortex and thalamus - Rivalries and synchronisation

# Consciousness Studies/The Neuroscience Of Consciousness#The substrate of experience *\"All parts of the brain may well be involved in normal conscious processes but the indispensable substratum of consciousness lies outside the cerebral cortex, probably in the diencephalon\" Penfield 1937.* *\"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\" Baars et al 1998.* ## Introduction *It is recommended that readers review ../The Philosophical Problem/ before reading the sections on the neuroscience of consciousness.* One of the most exciting discoveries of neuroscience is that nearly all of the brain performs functions that are not part of conscious experience. In everyday life we are usually unaware of breathing or heartbeats yet there are parts of the brain dedicated to these functions. When we pick up a pencil we have no experience of the fine control of individual muscles yet large areas of cortex and cerebellum implement this. Things do not appear as greyscale and then have the colour poured into them although this strange colour addition is done in the visual cortex. Most of the brain is non-conscious but how is the \"ghost in the machine\", the mind, created by and linked into the mostly non-conscious brain? Although most of the processes in the brain are non-conscious there can be little doubt that the output of sensory processes contribute to experience. For example, although we do not experience the process of adding colour to visual data in cortical area V4 we do experience coloured forms and although we have little inkling of the hugely complex creation of words in the temporal/frontal lobes we do experience verbal thoughts. Our experience is an integrated output of most of the brain processes that deal with sensation as well as dreams, thoughts and emotions. But how and where does this experience occur? The signals that compose phenomenal consciousness have not been elucidated. Perhaps the least likely signals for this role are electrical impulses in nerve fibres because they are distributed unevenly in time and space and can even be absent for relatively long periods. Furthermore, electrical impulses across the membranes of neurons have an all or nothing character; they cannot be easily superimposed on one another. There are many other possibilities however, such as: the electrical fields on the dendrites of neurons, the fields of chemicals spreading out from synapses, the radio-frequency emissions of action potentials, events in the microtubules in cells, the depolarisations of glia, the varying fields measured by EEG devices, the quantum superposition of brain states etc\... Phenomenal consciousness could exist in the dendritic field of ten neurons receiving 100,000 synapses or as an oscillation of fields over the whole brain. The substrate of phenomenal consciousness could be staring us in the face as a state of the whole brain or be like a needle in a haystack, lurking in a tiny region of brain, unsuspected and undiscovered. Given that there is no widely accepted theory of phenomenal consciousness Crick (1994) and Crick and Koch (1998) approached the problem of the location of the substrate of consciousness by proposing that scientists search for the **Neural Correlates of Consciousness**. These neural correlates consist of events in the brain that accompany events in conscious experience. References: Crick, F. (1994). The Astonishing Hypothesis. New York: Scribners. Crick, F. & Koch, C. (1998).Consciousness and Neuroscience. Cerebral Cortex, 8:97-107, 1998 <http://www.klab.caltech.edu/~koch/crick-koch-cc-97.html> ## Neuroanatomy ### General layout of the CNS The Central Nervous System (CNS) consists of the spinal cord, the brain and the retina. The CNS consists of two major groups of active cells, the **neurons** and the **glia**. The neurons conduct short impulses of electricity along their membranes called **\'action potentials** and encode data as frequency modulated signals (i.e.: different intensities of stimulation are converted into different rates of firing). The glia modify the connections between neurons and can respond to neuron activity by a change of voltage across their membranes. Glia also have many other roles such as sustaining neurons and providing electrical insulation. Neurons have three principal parts: the **cell body**, the **dendrites** and the **axon**. Impulses flow from the cell body to the axon. The axon can be over a metre long and bundles of axons form **nerve fibres**. Where an axon makes contact with the dendrites or cell body of another neuron there is a special sort of junction called a **synapse**. Transmission of data across synapses is usually mediated by chemical signals. Areas of the brain where there are many cell bodies have a beige/grey tinge and are called **grey matter**. Areas that contain mainly nerve fibres are called **white matter**. Masses of grey matter outside of the surface of the cerebral cortex or the cerebellum are called **nuclei**. The brain is of central interest in consciousness studies because consciousness persists even when the spinal cord is sectioned at the neck. The brain can be divided into five distinct divisions or *\'vesicles* on the basis of embryological development. These are the myelencephalon, metencephalon, mesencephalon, diencephalon and telencephalon (See the illustration below).  : Myelencephalon: Medulla oblongata. : Metencephalon: pons and cerebellum. : Mesencephalon: midbrain (tectum containing the superior colliculus and inferior colliculus, red nucleus, substantia nigra, cerebellar peduncles. : Diencephalon: thalamus, epithalamus, hypothalamus, subthalamus. : Telencephalon: corpus striatum, cerebral hemispheres. These divisions tend to obscure the physical anatomy of the brain which looks like a rod of spinal cord with a swelling at the top due to the thalamus and corpus striatum. Around the top of the rod is a globe of deeply indented cerebral cortex and at the back there is the puckered mass of cerebellum. The physical anatomy is shown in greater detail in the illustration below where the thalamus and corpus striatum have been splayed out to show more detail.  The thalamus is a complex organ with numerous nuclei. 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SIZE=2>`{=html}(motor)`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ``` `<FONT SIZE=2>`{=html}Ventral lateral`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ``` `<FONT SIZE=2>`{=html}VL`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ``` `<FONT SIZE=2>`{=html}Motor`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} </TABLE> ``` The location of these nuclei is shown in the illustration below:  The cerebral hemispheres consist of a thin layer of nerve cell bodies on the surface (the cerebral cortex) with a mass of white, interconnecting fibres below (the cerebral medulla). Each hemisphere is divided into four principle **lobes** as shown in the illustration below:  The cortex is a set of interconnected processors. The general layout of the cortex with the location of the processors is shown in the illustration below:  The pathways in the brain tend to preserve the **topography** of the sense organs so that particular groups of cells on the retina, cochlear or body have corresponding groups of cells in the thalamus or cortex. The retina is said to have a topological mapping onto the thalamus so that the projection of the optic nerve is said to be **retinotopic**. Nerve fibres that go to a part of the brain are called **afferents** and fibres that come from a part of the brain are called **efferents**. The cortex and thalamus/striatum are intimately linked by millions of connecting fibres and there is also a direct connection from the motor cortex to the spinal cord. ### Sensory pathways Information from the sense organs travels along the appropriate sensory nerve (optic, auditory, spinal etc.) and once in the brain is divided into three principal paths that connect either with the thalamus, the cerebellum or the reticular formation. There are thalamic nuclei for each broad type of sensation and these have reciprocal connections with specific areas of cortex that deal with the appropriate mode of sensation. The large mass of nerve fibres that mediate the connection between the thalamus and cortex are known as the thalamo-cortical and cortico-thalamic tracts. There tend to be more sensory nerve fibres returning from the cortex to the thalamus than connect from the thalamus to the cortex so it is difficult to determine whether the cortex is the destination of sensory data or a region that supplies extra processing power to thalamic nuclei. The cerebellum mediates reflex control of complex movements and receives input from most of the sense organs. The reticular formation is a group of loosely distributed neurons in the medulla, pons and mesencephalon. It receives a large amount of autonomic input and also input from all the sense organs. The intralaminar nuclei of the thalamus are the principal destination of reticular output to higher centres. In the most primitive vertebrates the reticular formation performs most of the higher control functions of the animal. The reticular formation is implicated in the maintenance of sleep-wake cycles and activates the higher centres. This activity has attracted the label **ascending reticular activating system** (ARAS) to describe how the activity of higher centres is controlled by reticular input. This title is unfortunate from the point of view of consciousness studies because it implies that conscious experience is a result of activating the cortex when it could be due to turning on or off particular systems all the way from the reticular formation to the cortex. Destruction of the reticular formation leads to coma. ### Motor and output pathways Motor control of the body below the skull is accomplished by three principle routes. The motor cortex of the frontal lobes and related cortex in the parietal lobes can control movement directly via nerves known as the cortico-spinal tract (also called the pyramidal tract). The activity of the motor cortex is modified and controlled by a loop that passes through the corpus striatum, the substantia nigra and the subthalamic nucleus and returns to the cortex. These controlling nuclei are, along with the amygdala, known as the **basal ganglia**. The cerebellum and the corpus striatum provide complex reflex control of the body through nerves that travel through the red nucleus and form the rubro-spinal tract. The vestibular nucleus, which processes signals related to balance and posture, has direct connections with the periphery via the vestibulo-spinal tract. Apart from the routes for controlling motor activity there are also other outputs from the brain, for instance the autonomic nervous system is intimately linked with the reticular formation which has areas that control blood pressure, respiratory rhythm etc. ## Topological mapping and cortical columns !Sensorimotor homunculus{width="400"}The cerebral cortex has a highly convoluted surface that provides a large area of tissue. The parts of the cortex that are used for motor and sensory functions are organised so that different areas correspond to different zones of the body. This **topological** organisation is shown classically by a drawing of the *sensorimotor homunculus* such as that shown on the right. Within a given area of the cortex there are further subdivisions. For example, the occipital cortex corresponds to the eyes of the sensorimotor homunculus and it is further organised so that areas of the retina have corresponding areas on the cortex. This mapping of the layout of the retina onto the cortex is known as **topological mapping**. It results in a corresponding mapping of the receptive field of the eye onto the cortex. The mapping is like an image on the surface of the brain tissue and the visual scene that is presented to a subject can be recovered by using fMRI along with computer analysis (Miyawaki *et al.* 2008). The human cortex is fairly deep, containing 100-200 neurons from the surface to the white matter. It is divided into six histological and functional layers. These layers can be further subdivided. In 1957 Mountcastle used microelectrode measurements to show that activity of small zones of cortex about 0.1 to 1 mm in diameter corresponded to particular points in the receptive field. These functional columns of cortical tissue are called **cortical columns**.  The diagram above shows the organisation of **ocular dominance columns**. Each column represents a particular part of the receptive field of a single eye. The columns for left and right eyes are linked together in lines. The lines of ocular dominance form a pattern like a fingerprint on the surface of the cortex. The same part of cortex can have overlapping columns for different functions. For instance there are columns that react to particular orientations of edges at particular places in the visual field. These columns tend to be located together on the cortex forming a **pinwheel** of columns that cover all orientations at a particular receptive field position.  There are also topologically arranged columns for colour, spatial frequency etc. Yoichi Miyawaki, Hajime Uchida, Okito Yamashita, Masa-aki Sato, Yusuke Morito, Hiroki C. Tanabe, Norihiro Sadato and Yukiyasu Kamitani. (2008). Visual Image Reconstruction from Human Brain Activity using a Combination of Multiscale Local Image Decoders. Neuron, Volume 60, Issue 5, 10 December 2008, Pages 915-929 **Modules** - The neurophysiology of sensation and perception - The cortex and thalamus - Rivalries and synchronisation

# Consciousness Studies/The Neuroscience Of Consciousness#Neuroanatomy *\"All parts of the brain may well be involved in normal conscious processes but the indispensable substratum of consciousness lies outside the cerebral cortex, probably in the diencephalon\" Penfield 1937.* *\"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\" Baars et al 1998.* ## Introduction *It is recommended that readers review ../The Philosophical Problem/ before reading the sections on the neuroscience of consciousness.* One of the most exciting discoveries of neuroscience is that nearly all of the brain performs functions that are not part of conscious experience. In everyday life we are usually unaware of breathing or heartbeats yet there are parts of the brain dedicated to these functions. When we pick up a pencil we have no experience of the fine control of individual muscles yet large areas of cortex and cerebellum implement this. Things do not appear as greyscale and then have the colour poured into them although this strange colour addition is done in the visual cortex. Most of the brain is non-conscious but how is the \"ghost in the machine\", the mind, created by and linked into the mostly non-conscious brain? Although most of the processes in the brain are non-conscious there can be little doubt that the output of sensory processes contribute to experience. For example, although we do not experience the process of adding colour to visual data in cortical area V4 we do experience coloured forms and although we have little inkling of the hugely complex creation of words in the temporal/frontal lobes we do experience verbal thoughts. Our experience is an integrated output of most of the brain processes that deal with sensation as well as dreams, thoughts and emotions. But how and where does this experience occur? The signals that compose phenomenal consciousness have not been elucidated. Perhaps the least likely signals for this role are electrical impulses in nerve fibres because they are distributed unevenly in time and space and can even be absent for relatively long periods. Furthermore, electrical impulses across the membranes of neurons have an all or nothing character; they cannot be easily superimposed on one another. There are many other possibilities however, such as: the electrical fields on the dendrites of neurons, the fields of chemicals spreading out from synapses, the radio-frequency emissions of action potentials, events in the microtubules in cells, the depolarisations of glia, the varying fields measured by EEG devices, the quantum superposition of brain states etc\... Phenomenal consciousness could exist in the dendritic field of ten neurons receiving 100,000 synapses or as an oscillation of fields over the whole brain. The substrate of phenomenal consciousness could be staring us in the face as a state of the whole brain or be like a needle in a haystack, lurking in a tiny region of brain, unsuspected and undiscovered. Given that there is no widely accepted theory of phenomenal consciousness Crick (1994) and Crick and Koch (1998) approached the problem of the location of the substrate of consciousness by proposing that scientists search for the **Neural Correlates of Consciousness**. These neural correlates consist of events in the brain that accompany events in conscious experience. References: Crick, F. (1994). The Astonishing Hypothesis. New York: Scribners. Crick, F. & Koch, C. (1998).Consciousness and Neuroscience. Cerebral Cortex, 8:97-107, 1998 <http://www.klab.caltech.edu/~koch/crick-koch-cc-97.html> ## Neuroanatomy ### General layout of the CNS The Central Nervous System (CNS) consists of the spinal cord, the brain and the retina. The CNS consists of two major groups of active cells, the **neurons** and the **glia**. The neurons conduct short impulses of electricity along their membranes called **\'action potentials** and encode data as frequency modulated signals (i.e.: different intensities of stimulation are converted into different rates of firing). The glia modify the connections between neurons and can respond to neuron activity by a change of voltage across their membranes. Glia also have many other roles such as sustaining neurons and providing electrical insulation. Neurons have three principal parts: the **cell body**, the **dendrites** and the **axon**. Impulses flow from the cell body to the axon. The axon can be over a metre long and bundles of axons form **nerve fibres**. Where an axon makes contact with the dendrites or cell body of another neuron there is a special sort of junction called a **synapse**. Transmission of data across synapses is usually mediated by chemical signals. Areas of the brain where there are many cell bodies have a beige/grey tinge and are called **grey matter**. Areas that contain mainly nerve fibres are called **white matter**. Masses of grey matter outside of the surface of the cerebral cortex or the cerebellum are called **nuclei**. The brain is of central interest in consciousness studies because consciousness persists even when the spinal cord is sectioned at the neck. The brain can be divided into five distinct divisions or *\'vesicles* on the basis of embryological development. These are the myelencephalon, metencephalon, mesencephalon, diencephalon and telencephalon (See the illustration below).  : Myelencephalon: Medulla oblongata. : Metencephalon: pons and cerebellum. : Mesencephalon: midbrain (tectum containing the superior colliculus and inferior colliculus, red nucleus, substantia nigra, cerebellar peduncles. : Diencephalon: thalamus, epithalamus, hypothalamus, subthalamus. : Telencephalon: corpus striatum, cerebral hemispheres. These divisions tend to obscure the physical anatomy of the brain which looks like a rod of spinal cord with a swelling at the top due to the thalamus and corpus striatum. Around the top of the rod is a globe of deeply indented cerebral cortex and at the back there is the puckered mass of cerebellum. The physical anatomy is shown in greater detail in the illustration below where the thalamus and corpus striatum have been splayed out to show more detail.  The thalamus is a complex organ with numerous nuclei. 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SIZE=2>`{=html}(motor)`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ``` `<FONT SIZE=2>`{=html}Ventral lateral`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ``` `<FONT SIZE=2>`{=html}VL`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ``` `<FONT SIZE=2>`{=html}Motor`</FONT>`{=html} ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} <TD VALIGN="TOP"> ```   ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} </TABLE> ``` The location of these nuclei is shown in the illustration below:  The cerebral hemispheres consist of a thin layer of nerve cell bodies on the surface (the cerebral cortex) with a mass of white, interconnecting fibres below (the cerebral medulla). Each hemisphere is divided into four principle **lobes** as shown in the illustration below:  The cortex is a set of interconnected processors. The general layout of the cortex with the location of the processors is shown in the illustration below:  The pathways in the brain tend to preserve the **topography** of the sense organs so that particular groups of cells on the retina, cochlear or body have corresponding groups of cells in the thalamus or cortex. The retina is said to have a topological mapping onto the thalamus so that the projection of the optic nerve is said to be **retinotopic**. Nerve fibres that go to a part of the brain are called **afferents** and fibres that come from a part of the brain are called **efferents**. The cortex and thalamus/striatum are intimately linked by millions of connecting fibres and there is also a direct connection from the motor cortex to the spinal cord. ### Sensory pathways Information from the sense organs travels along the appropriate sensory nerve (optic, auditory, spinal etc.) and once in the brain is divided into three principal paths that connect either with the thalamus, the cerebellum or the reticular formation. There are thalamic nuclei for each broad type of sensation and these have reciprocal connections with specific areas of cortex that deal with the appropriate mode of sensation. The large mass of nerve fibres that mediate the connection between the thalamus and cortex are known as the thalamo-cortical and cortico-thalamic tracts. There tend to be more sensory nerve fibres returning from the cortex to the thalamus than connect from the thalamus to the cortex so it is difficult to determine whether the cortex is the destination of sensory data or a region that supplies extra processing power to thalamic nuclei. The cerebellum mediates reflex control of complex movements and receives input from most of the sense organs. The reticular formation is a group of loosely distributed neurons in the medulla, pons and mesencephalon. It receives a large amount of autonomic input and also input from all the sense organs. The intralaminar nuclei of the thalamus are the principal destination of reticular output to higher centres. In the most primitive vertebrates the reticular formation performs most of the higher control functions of the animal. The reticular formation is implicated in the maintenance of sleep-wake cycles and activates the higher centres. This activity has attracted the label **ascending reticular activating system** (ARAS) to describe how the activity of higher centres is controlled by reticular input. This title is unfortunate from the point of view of consciousness studies because it implies that conscious experience is a result of activating the cortex when it could be due to turning on or off particular systems all the way from the reticular formation to the cortex. Destruction of the reticular formation leads to coma. ### Motor and output pathways Motor control of the body below the skull is accomplished by three principle routes. The motor cortex of the frontal lobes and related cortex in the parietal lobes can control movement directly via nerves known as the cortico-spinal tract (also called the pyramidal tract). The activity of the motor cortex is modified and controlled by a loop that passes through the corpus striatum, the substantia nigra and the subthalamic nucleus and returns to the cortex. These controlling nuclei are, along with the amygdala, known as the **basal ganglia**. The cerebellum and the corpus striatum provide complex reflex control of the body through nerves that travel through the red nucleus and form the rubro-spinal tract. The vestibular nucleus, which processes signals related to balance and posture, has direct connections with the periphery via the vestibulo-spinal tract. Apart from the routes for controlling motor activity there are also other outputs from the brain, for instance the autonomic nervous system is intimately linked with the reticular formation which has areas that control blood pressure, respiratory rhythm etc. ## Topological mapping and cortical columns !Sensorimotor homunculus{width="400"}The cerebral cortex has a highly convoluted surface that provides a large area of tissue. The parts of the cortex that are used for motor and sensory functions are organised so that different areas correspond to different zones of the body. This **topological** organisation is shown classically by a drawing of the *sensorimotor homunculus* such as that shown on the right. Within a given area of the cortex there are further subdivisions. For example, the occipital cortex corresponds to the eyes of the sensorimotor homunculus and it is further organised so that areas of the retina have corresponding areas on the cortex. This mapping of the layout of the retina onto the cortex is known as **topological mapping**. It results in a corresponding mapping of the receptive field of the eye onto the cortex. The mapping is like an image on the surface of the brain tissue and the visual scene that is presented to a subject can be recovered by using fMRI along with computer analysis (Miyawaki *et al.* 2008). The human cortex is fairly deep, containing 100-200 neurons from the surface to the white matter. It is divided into six histological and functional layers. These layers can be further subdivided. In 1957 Mountcastle used microelectrode measurements to show that activity of small zones of cortex about 0.1 to 1 mm in diameter corresponded to particular points in the receptive field. These functional columns of cortical tissue are called **cortical columns**.  The diagram above shows the organisation of **ocular dominance columns**. Each column represents a particular part of the receptive field of a single eye. The columns for left and right eyes are linked together in lines. The lines of ocular dominance form a pattern like a fingerprint on the surface of the cortex. The same part of cortex can have overlapping columns for different functions. For instance there are columns that react to particular orientations of edges at particular places in the visual field. These columns tend to be located together on the cortex forming a **pinwheel** of columns that cover all orientations at a particular receptive field position.  There are also topologically arranged columns for colour, spatial frequency etc. Yoichi Miyawaki, Hajime Uchida, Okito Yamashita, Masa-aki Sato, Yusuke Morito, Hiroki C. Tanabe, Norihiro Sadato and Yukiyasu Kamitani. (2008). Visual Image Reconstruction from Human Brain Activity using a Combination of Multiscale Local Image Decoders. Neuron, Volume 60, Issue 5, 10 December 2008, Pages 915-929 **Modules** - The neurophysiology of sensation and perception - The cortex and thalamus - Rivalries and synchronisation

# Consciousness Studies/The Neuroscience Of Consciousness#Topological mapping and cortical columns *\"All parts of the brain may well be involved in normal conscious processes but the indispensable substratum of consciousness lies outside the cerebral cortex, probably in the diencephalon\" Penfield 1937.* *\"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\" Baars et al 1998.* ## Introduction *It is recommended that readers review ../The Philosophical Problem/ before reading the sections on the neuroscience of consciousness.* One of the most exciting discoveries of neuroscience is that nearly all of the brain performs functions that are not part of conscious experience. In everyday life we are usually unaware of breathing or heartbeats yet there are parts of the brain dedicated to these functions. When we pick up a pencil we have no experience of the fine control of individual muscles yet large areas of cortex and cerebellum implement this. Things do not appear as greyscale and then have the colour poured into them although this strange colour addition is done in the visual cortex. Most of the brain is non-conscious but how is the \"ghost in the machine\", the mind, created by and linked into the mostly non-conscious brain? Although most of the processes in the brain are non-conscious there can be little doubt that the output of sensory processes contribute to experience. For example, although we do not experience the process of adding colour to visual data in cortical area V4 we do experience coloured forms and although we have little inkling of the hugely complex creation of words in the temporal/frontal lobes we do experience verbal thoughts. Our experience is an integrated output of most of the brain processes that deal with sensation as well as dreams, thoughts and emotions. But how and where does this experience occur? The signals that compose phenomenal consciousness have not been elucidated. Perhaps the least likely signals for this role are electrical impulses in nerve fibres because they are distributed unevenly in time and space and can even be absent for relatively long periods. Furthermore, electrical impulses across the membranes of neurons have an all or nothing character; they cannot be easily superimposed on one another. There are many other possibilities however, such as: the electrical fields on the dendrites of neurons, the fields of chemicals spreading out from synapses, the radio-frequency emissions of action potentials, events in the microtubules in cells, the depolarisations of glia, the varying fields measured by EEG devices, the quantum superposition of brain states etc\... Phenomenal consciousness could exist in the dendritic field of ten neurons receiving 100,000 synapses or as an oscillation of fields over the whole brain. The substrate of phenomenal consciousness could be staring us in the face as a state of the whole brain or be like a needle in a haystack, lurking in a tiny region of brain, unsuspected and undiscovered. Given that there is no widely accepted theory of phenomenal consciousness Crick (1994) and Crick and Koch (1998) approached the problem of the location of the substrate of consciousness by proposing that scientists search for the **Neural Correlates of Consciousness**. These neural correlates consist of events in the brain that accompany events in conscious experience. References: Crick, F. (1994). The Astonishing Hypothesis. New York: Scribners. Crick, F. & Koch, C. (1998).Consciousness and Neuroscience. Cerebral Cortex, 8:97-107, 1998 <http://www.klab.caltech.edu/~koch/crick-koch-cc-97.html> ## Neuroanatomy ### General layout of the CNS The Central Nervous System (CNS) consists of the spinal cord, the brain and the retina. The CNS consists of two major groups of active cells, the **neurons** and the **glia**. The neurons conduct short impulses of electricity along their membranes called **\'action potentials** and encode data as frequency modulated signals (i.e.: different intensities of stimulation are converted into different rates of firing). The glia modify the connections between neurons and can respond to neuron activity by a change of voltage across their membranes. Glia also have many other roles such as sustaining neurons and providing electrical insulation. Neurons have three principal parts: the **cell body**, the **dendrites** and the **axon**. Impulses flow from the cell body to the axon. The axon can be over a metre long and bundles of axons form **nerve fibres**. Where an axon makes contact with the dendrites or cell body of another neuron there is a special sort of junction called a **synapse**. Transmission of data across synapses is usually mediated by chemical signals. Areas of the brain where there are many cell bodies have a beige/grey tinge and are called **grey matter**. Areas that contain mainly nerve fibres are called **white matter**. Masses of grey matter outside of the surface of the cerebral cortex or the cerebellum are called **nuclei**. The brain is of central interest in consciousness studies because consciousness persists even when the spinal cord is sectioned at the neck. The brain can be divided into five distinct divisions or *\'vesicles* on the basis of embryological development. These are the myelencephalon, metencephalon, mesencephalon, diencephalon and telencephalon (See the illustration below).  : Myelencephalon: Medulla oblongata. : Metencephalon: pons and cerebellum. : Mesencephalon: midbrain (tectum containing the superior colliculus and inferior colliculus, red nucleus, substantia nigra, cerebellar peduncles. : Diencephalon: thalamus, epithalamus, hypothalamus, subthalamus. : Telencephalon: corpus striatum, cerebral hemispheres. These divisions tend to obscure the physical anatomy of the brain which looks like a rod of spinal cord with a swelling at the top due to the thalamus and corpus striatum. Around the top of the rod is a globe of deeply indented cerebral cortex and at the back there is the puckered mass of cerebellum. The physical anatomy is shown in greater detail in the illustration below where the thalamus and corpus striatum have been splayed out to show more detail.  The thalamus is a complex organ with numerous nuclei. 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 The cerebral hemispheres consist of a thin layer of nerve cell bodies on the surface (the cerebral cortex) with a mass of white, interconnecting fibres below (the cerebral medulla). Each hemisphere is divided into four principle **lobes** as shown in the illustration below:  The cortex is a set of interconnected processors. The general layout of the cortex with the location of the processors is shown in the illustration below:  The pathways in the brain tend to preserve the **topography** of the sense organs so that particular groups of cells on the retina, cochlear or body have corresponding groups of cells in the thalamus or cortex. The retina is said to have a topological mapping onto the thalamus so that the projection of the optic nerve is said to be **retinotopic**. Nerve fibres that go to a part of the brain are called **afferents** and fibres that come from a part of the brain are called **efferents**. The cortex and thalamus/striatum are intimately linked by millions of connecting fibres and there is also a direct connection from the motor cortex to the spinal cord. ### Sensory pathways Information from the sense organs travels along the appropriate sensory nerve (optic, auditory, spinal etc.) and once in the brain is divided into three principal paths that connect either with the thalamus, the cerebellum or the reticular formation. There are thalamic nuclei for each broad type of sensation and these have reciprocal connections with specific areas of cortex that deal with the appropriate mode of sensation. The large mass of nerve fibres that mediate the connection between the thalamus and cortex are known as the thalamo-cortical and cortico-thalamic tracts. There tend to be more sensory nerve fibres returning from the cortex to the thalamus than connect from the thalamus to the cortex so it is difficult to determine whether the cortex is the destination of sensory data or a region that supplies extra processing power to thalamic nuclei. The cerebellum mediates reflex control of complex movements and receives input from most of the sense organs. The reticular formation is a group of loosely distributed neurons in the medulla, pons and mesencephalon. It receives a large amount of autonomic input and also input from all the sense organs. The intralaminar nuclei of the thalamus are the principal destination of reticular output to higher centres. In the most primitive vertebrates the reticular formation performs most of the higher control functions of the animal. The reticular formation is implicated in the maintenance of sleep-wake cycles and activates the higher centres. This activity has attracted the label **ascending reticular activating system** (ARAS) to describe how the activity of higher centres is controlled by reticular input. This title is unfortunate from the point of view of consciousness studies because it implies that conscious experience is a result of activating the cortex when it could be due to turning on or off particular systems all the way from the reticular formation to the cortex. Destruction of the reticular formation leads to coma. ### Motor and output pathways Motor control of the body below the skull is accomplished by three principle routes. The motor cortex of the frontal lobes and related cortex in the parietal lobes can control movement directly via nerves known as the cortico-spinal tract (also called the pyramidal tract). The activity of the motor cortex is modified and controlled by a loop that passes through the corpus striatum, the substantia nigra and the subthalamic nucleus and returns to the cortex. These controlling nuclei are, along with the amygdala, known as the **basal ganglia**. The cerebellum and the corpus striatum provide complex reflex control of the body through nerves that travel through the red nucleus and form the rubro-spinal tract. The vestibular nucleus, which processes signals related to balance and posture, has direct connections with the periphery via the vestibulo-spinal tract. Apart from the routes for controlling motor activity there are also other outputs from the brain, for instance the autonomic nervous system is intimately linked with the reticular formation which has areas that control blood pressure, respiratory rhythm etc. ## Topological mapping and cortical columns !Sensorimotor homunculus{width="400"}The cerebral cortex has a highly convoluted surface that provides a large area of tissue. The parts of the cortex that are used for motor and sensory functions are organised so that different areas correspond to different zones of the body. This **topological** organisation is shown classically by a drawing of the *sensorimotor homunculus* such as that shown on the right. Within a given area of the cortex there are further subdivisions. For example, the occipital cortex corresponds to the eyes of the sensorimotor homunculus and it is further organised so that areas of the retina have corresponding areas on the cortex. This mapping of the layout of the retina onto the cortex is known as **topological mapping**. It results in a corresponding mapping of the receptive field of the eye onto the cortex. The mapping is like an image on the surface of the brain tissue and the visual scene that is presented to a subject can be recovered by using fMRI along with computer analysis (Miyawaki *et al.* 2008). The human cortex is fairly deep, containing 100-200 neurons from the surface to the white matter. It is divided into six histological and functional layers. These layers can be further subdivided. In 1957 Mountcastle used microelectrode measurements to show that activity of small zones of cortex about 0.1 to 1 mm in diameter corresponded to particular points in the receptive field. These functional columns of cortical tissue are called **cortical columns**.  The diagram above shows the organisation of **ocular dominance columns**. Each column represents a particular part of the receptive field of a single eye. The columns for left and right eyes are linked together in lines. The lines of ocular dominance form a pattern like a fingerprint on the surface of the cortex. The same part of cortex can have overlapping columns for different functions. For instance there are columns that react to particular orientations of edges at particular places in the visual field. These columns tend to be located together on the cortex forming a **pinwheel** of columns that cover all orientations at a particular receptive field position.  There are also topologically arranged columns for colour, spatial frequency etc. Yoichi Miyawaki, Hajime Uchida, Okito Yamashita, Masa-aki Sato, Yusuke Morito, Hiroki C. Tanabe, Norihiro Sadato and Yukiyasu Kamitani. (2008). Visual Image Reconstruction from Human Brain Activity using a Combination of Multiscale Local Image Decoders. Neuron, Volume 60, Issue 5, 10 December 2008, Pages 915-929 **Modules** - The neurophysiology of sensation and perception - The cortex and thalamus - Rivalries and synchronisation

# Consciousness Studies/The Neurophysiology Of Sensation And Perception ## Vision ### The human eye The eye is a remarkable optical instrument that is often poorly understood by students of consciousness. The most popular misconception is that there is a \'focus\' within the eye through which all the light rays pass! The purpose of this article is to describe our knowledge of the optics of the eye so that such misconceptions can be avoided.  The eye consists of several surfaces at which refraction occurs: air-cornea, cornea-aqueous humour, aqueous humour-lens, lens-vitreous humour. The crude image forming capability of the eye can be represented quite accurately by the *reduced eye* model which involves a single optical surface (air-cornea). Optometrists use more accurate models such as the Gullstrand Schematic Eye, the Le Grand Theoretical and the LeGrand Simplified Eye. The lens system at the front of the eye forms an inverted image on the retina. The eye is about 23 mm deep from the front of the cornea to the back of the retina. The refractive index of the components of the lens system varies from about 1.33 to 1.39. Light from every point of a field of view falls all over the surface of the eye. There is no \'point eye\' and there is no ordered image between objects in the view and the retina except on the retina. The image on the eye has the form of an inverted mapping of 3D objects to a 2D surface. This is also the form of conscious experience so the images on the retinas are the closest physical analogues of phenomenal, visual, conscious experience (see Perspective below). ### Perspective Perspective describes how light from three dimensional objects is mapped onto a two dimensional surface as a result of the action of lenses of the type found in the eye.  Perspective is used by artists to create the impression of viewing a 3D scene. To do this they create a 2D image that is similar to the image on the retina that would be created by the 3D scene.  Naive Realists and many Direct Realists believe that the 2D perspective view is the way things are actually arranged in the world. Of course, things in the world differ from images because they are arranged in three dimensions. ### Colour The colour of an object can be represented by its **spectral power distribution** which is a plot of the power available at each wavelength. The unit of light power is the watt but the unit that is used to measure subjective illumination is the **candela**. One candela is the illumination due to light of a wavelength of 555 nanometres and a radiant intensity of 1/683 watts per steradian in the direction being measured. A steradian is a solid angle at the centre of sphere of one metre radius that is subtended by one square metre of the surface. The curious number 1/683 occurs because the unit was originally based on light emitted from a square centimetre of molten platinum. The wavelength of 555 nm is chosen because this is the wavelength of peak sensitivity for light adapted (photopic) vision over a large group of subjects. Light adapted vision is largely due to photosensitive cells in the retina called **cones**. The candela is fixed as a standard SI Unit for light at a wavelength of 555 nanometres. The **lumen** is a subjective measure of the flux of light energy passing through a solid angle (a steradian). 683 lumens of light at 555 nm are equivalent to a watt passing through the solid angle. At a wavelength of about 520 nm only 500 lumens of luminous flux occur per watt because the visual system is less sensitive at this wavelength. The curve of sensitivity of the visual system to light is known as the **V-lambda Curve**. At a wavelength of about 510 nm the same radiant intensity is seen as being half as bright as at a wavelength of 555 nm.  Dark adapted (scotopic) vision has a peak sensitivity at a wavelength of 507 nm and is largely due to photosensitive cells called **rods** in the retina. Spectral Luminous Efficacy Curves are also used to express how the sensitivity to light varies with wavelength. Phenomenal colours are due to mixtures of **spectral colours** of varying intensities. A **spectral colour** corresponds to a wavelength of light found on the electromagnetic spectrum of visible light. Colours have three attributes: **brightness**, **saturation** and **hue**. The brightness of a colour depends on the illuminance and the reflectivity of the surface. The saturation depends on the amount of white present, for instance white and red make pink. The hue is similar to spectral colour but can consist of some combinations - for instance magenta is a hue but combines two spectral colours: red and blue. It should be noted that experiences that contain colour are dependent on the properties of the visual system as much as on the wavelengths of light being reflected. Any set of three colours that can be added together to give white are known as **primary colours**. There are a large number of colours that can be combined to make white, or almost any other colour. This means that a set of surfaces that all appear white could reflect a wide range of different wavelengths of light. There are numerous systems for predicting how colours will combine to make other colours; the CIE Chromaticity Diagram, the Munsell Colour System and the Ostwald Colour System have all been used. The 1931 CIE Chromaticity Diagram is shown below: {width="400"} See Chromaticity diagram for more information. ### The retina The retina contains photoreceptive cells called rods and cones and several types of neurons. The rods are generally sensitive to light and there are three varieties of cones sensitive to long, medium and short wavelengths of light (L, M and S type cones). Some of the ganglion cells in the retina (about 2%) are also slightly light sensitive and provide input for the control of circadian rhythms. A schematic diagram of the retina is shown below.  The photoreceptors hyperpolarise (their membrane potential becomes more negative) in response to illumination. Bipolar cells make direct contact with the photoreceptors and come in two types, *on* and *off*. The on-bipolar cells are also known as *invaginating* bipolars and the off-bipolars as *flat bipolars*. On-bipolars depolarise when light falls on the photoreceptors and off-bipolars hyperpolarise. Action potentials do not occur in the bipolar or photoreceptor cells. The retinal neurons perform considerable preprocessing before submitting information to the brain. The network of horizontal and ganglion neurons act to produce an output of action potentials that is sensitive to boundaries between areas of differing illumination (edge detection) and to motion. Kuffler in 1953 discovered that many retinal ganglion cells are responsive to differences in illumination on the retina. This **centre-surround** processing is shown in the illustration below.  The centre-surround effect is due to **lateral inhibition** by horizontally arranged cells in the retina. The structure of the response fields of ganglion cells is important in everyday processing and increases the definition of boundaries in the visual field. Sometimes it gives rise to effects that are not directly related to the physical content of the visual field. The most famous of these effects is the Hermann Illusion. The Hermann Grid Illusion is a set of black squares separated by white lines. Where the white lines cross it appears as if there are grey dots.  The grey dots are due to the relative suppression of on-centre ganglion cells where the white lines cross. This is explained in the illustration below.  Notice how the grey dots disappear when the crossed white lines are at the centre of the visual field. This is due to way that ganglion cell fields are much smaller in the fovea. There are many other retinal illusions. White\'s illusion is particularly strong and was believed to be due to centre-surround activity but is now thought to have a complex origin.  The grey lines really are the same shade of grey in the illustration. Mach\'s Illusion is another example of a centre-surround effect. Centre-surround effects can also occur with colour fields, red/green and yellow/blue contrasts having a similar effect to light/dark contrasts. Lateral inhibition and the resultant centre-surround effect increases the number of cells that respond to boundaries and edges in the visual field. If it did not occur then small boundaries might be missed entirely if these fell on areas of the retina outside of the fovea. The result of this effect is everywhere in our normal visual phenomenal experience so not only is visual experience a mapping of 3D on to a 2D surface, it also contains shading and brightening at edges that will not be found by photometers that measure objective light intensities. Photoreceptors become less responsive after continuous exposure to bright light. This gives rise to **afterimages**. Afterimages are usually of the opponent colour (white light gives a dark afterimage, yellow light gives a blue afterimage, red gives a green afterimage etc.). Afterimages when the eyes are open are generally due to a lack of response to a particular frequency of light within the white light that bathes the retina. It is clear that visual phenomenal experience is related more directly to the layout and type of activity in the retinal cells than to things in the visual field beyond the eye. ### Visual pathways  ### The lateral geniculate nucleus Retinal ganglion cells project to the Lateral Geniculate Nuclei which are small bumps on the back of the thalamus. (Only 10-15% of the input to the LGN comes from the retina, most (c.80%) comes from the visual cortex). The neurons in the LGN are arranged retinotopically so preserve the layout of events on the surface of the retina. The LGN are arranged in 6 layers. The top two are known as Magnocellular layers (about 100,000 neurons with large cell bodies) and the bottom four are called Parvocellular layers (about 1,000,000 neurons with small cell bodies). Between the main layers are the Koniocellular layers that consist of large numbers of tiny neurons. The left Lateral Geniculate Nucleus receives input from the right visual field and the right LGN receives input from the left visual field. Each nucleus receives input from both eyes but this input is segregated so that input from the eye on the same side goes to layers 1, 3, 5 and from the other side to layers 2,4, 6. The magnocellular layers contain neurons that have a large receptive field, are sensitive to contrast, a transient response and are not colour sensitive. The parvocellular layers contains neurons that have small receptive fields, are colour sensitive, have a prolonged response and are less sensitive to contrast. The LGN pathway from the retina is largely connected to the striate part of the visual cortex (cortical area V1) via a set of fibres called the optic radiation. There are reciprocal connections between the Thalamic Reticular Nucleus and the LGN. The LGN are also interconnected with the Superior Colliculus and brainstem. The LGN may be involved in controlling which areas of the visual field are subjected to attention (O\'Connor *et al.* 2002). ### The visual cortex The input from the LGN goes mainly to area V1 of the cortex. The cortex is arranged in six layers and divided up into **columns**. Each column in the visual cortex corresponds to a particular area of the retina in one eye. The columns are arranged in rows called **hypercolumns**. Each column within a hypercolumn responds to a different orientation of an optical stimulus at a given location (so responds to edges/boundaries that are oriented in the visual field). Hypercolumns from each eye are arranged alternately and form a small block of cortex called a **pinwheel**. At the centre of each pinwheel are colour sensitive cells that are usually not orientation sensitive. These coincide with the \"blobs\" that are seen when visual cortex is viewed using cytochrome oxidase dependent stains. It is important to note that the \"hypercolumns\" merge into one another and respond to line stimuli that cover an area of retina so they may be physiological rather than anatomical entities. The blind spot in each eye is represented by an area of visual cortex that only receives monocular input from the other eye (Tong & Engel 2001). The effect of the blind spot is illustrated below:  Normally it seems that the blindspot is \'filled in\' with background when one eye is used. However, Lou & Chen (2003) demonstrated that subjects could respond to quite complex figures in the blind spot, although how far they were investigating \'blindsight\' rather than visual experience in the blind spot is difficult to determine. Different layers in the visual cortex have outputs that go to different locations. Layer 6 sends nerve fibres to the Lateral Geniculate Nuclei and thalamus, layer 5 to superior colliculus and pons, layer 2 & 3 to other cortical areas. There are two important outputs to other cortical areas, the **ventral stream** and the **dorsal stream**. The ventral stream processes colour, form and objects. It proceeds to the inferior (lower) temporal cortex. The dorsal stream processes motion, position and spatial relationships. It proceeds towards the parietal cortex. Lesions in the ventral stream can result in patients knowing where an object is located but being unable to enumerate its properties, on the other hand, lesions to the dorsal stream can result in patients being able to label an object but unable to tell exactly where it is located. There is also a large output from the visual cortex back to the thalamus, this output contains more fibres than the thalamo-cortical input. ### Depth perception The world is three dimensional but the image on the back of the retinas is two dimensional. How does the brain give the subject a perception of depth? Depth perception relies on **cues** which are data about the displacement of things relative to the body. These cues consist of: - the convergence of the eyes - the accommodation of the lens - binocular disparity -the difference between the images on the retinas- this was first suggested by Wheatstone. - motion parallax - distant objects move slower when the observer moves - first suggested by Helmholtz. - optical flow - the rate of expansion/contraction of a scene with movement towards or away from it (Lee & Aronson 1974). - binocular occlusion - parts of a scene are invisible to each eye. - body motion provides cues about near objects. - vanishing points - the convergence of parallel lines. - numerous other cues such as size constancy, texture etc. Binocular disparity has been most extensively studied as a source of depth cues. When the eyes converge to focus on an object in from of them there is very little disparity in the images of that object on the two retinas. The angle at the object formed between the lines that project back to the pupils is known as the **vergence** at the object. The sphere where all objects have the same vergence is known as the **horopter**.  When the disparity between the retinas is small a single image occurs in phenomenal experience which is accompanied by a sensation of objects with depth. This is known as **stereopsis**. If the disparity between the retinas is large double vision ensues, this is known as **diplopia**. The curious feature of stereopsis is that we can see no more of the object than is visible on the retinas and certainly cannot see behind the object. Stereopsis is more like a stretching of 2D space than actual 3D. The **empirical horopter** is a zone where things are seen without diplopia. The empirical and **Veith Muller** (geometric) horopters are different. This difference is the result of both processing by the CNS and optical factors. **Physiological diplopia** refers to the stimulation of receptors in different parts of the retinas of the two eyes by the same object. Physiological diplopia does not always give rise to subjective diplopia, objects close to the empirical horopter do not give rise to double vision and the zone in which this occurs is known as **Panum\'s Fusion Area**. It is widest for objects that are distributed away from the nose (with \'temporal\' locations) and for objects that are slow moving and poorly focussed. In the review by Cutting and Vishton (1995) the contributions of each type of cue is discussed. Cutting and Vishton also present evidence that there are several zones of depth perception that are informed by different sets of cues. These are **personal space**, which is the zone of things within arms reach, **action space**, which is the zone in which we interact and where our motions have a large impact on the perceived layout, and **vista space** which is the zone beyond about 30m that is informed by long range cues. The interesting feature of 3D perceptual space is that it is not seen. The sides of a solid object appear as intrusions or lateral extensions in 2D space, when we close an eye that has access to the side of the object and then open it again the side grows out into 2D space. The lack of \'seeing\' depth is also evident when we close one eye when looking at a vista - nothing seems to change even though stereopsis has gone. This leaves the problem of what it is that constitutes the \'feeling\' of depth. We have feelings that we can fall into space or move into it or around in it. Depth seems to be defined by premotor modelling and the potential for occupancy by our bodies and limbs. As such it involves qualia that are different from those of vision and more akin to those that accompany movement, as an example, if you reach out to touch something, move the hand back, then consider the distance to the object it is evident that a feeling of the movement is still present. Is depth a quale of movement modelled during the extended present of perception? - Cutting, J.E. & Vishton, P.M. (1995) Perceiving layout and knowing distances: The integration, relative potency, and contextual use of different information about depth. In W. Epstein & S. Rogers (eds.) Handbook of perception and cognition, Vol 5; Perception of space and motion. (pp. 69-117). San Diego, CA: Academic Press. <http://pmvish.people.wm.edu/cutting&vishton1995.pdf> ```{=html} <!-- --> ``` - Gregory, R.L. (1997). Knowledge in perception and illusion. From: Phil. Trans. R. Soc. Lond. B (1997) 352, 1121--1128. <http://www.richardgregory.org/papers/knowl_illusion/knowledge-in-perception.pdf> ```{=html} <!-- --> ``` - Hubel, D.H. (1981). EVOLUTION OF IDEAS ON THE PRIMARY VISUAL CORTEX, 1955-1978: A BIASED HISTORICAL ACCOUNT. <http://nobelprize.org/medicine/laureates/1981/hubel-lecture.pdf> ```{=html} <!-- --> ``` - Lou, L. & Chen, J. (2003). Attention and Blind-Spot Phenomenology. PSYCHE, 9(02), January 2003. <http://psyche.cs.monash.edu.au/v9/psyche-9-02-lou.html> ```{=html} <!-- --> ``` - O\'Connor, D.H., Fukui, M.M., Pinsk, M.A. & Kastner, S. (2002). Attention modulates responses in the human lateral geniculate nucleus. Nature Neuroscience 5, 1203 - 1209 (2002). <http://www.nature.com/neuro/journal/v5/n11/full/nn957.html#B34> ```{=html} <!-- --> ``` - Tong, F., & Engel, S. A. (2001). Interocular rivalry revealed in the human cortical blind-spot representation. Nature, 411, 195-199. <http://www.psy.vanderbilt.edu/tonglab/publications/Tong&Engel2001.pdf> ```{=html} <!-- --> ``` - Tong, F. (2003). PRIMARY VISUAL CORTEX AND VISUAL AWARENESS. Nature Reviews of Neuroscience. 4:219-229. <http://www.psy.vanderbilt.edu/tonglab/publications/Tong_NRN2003.pdf> **Modules** - The cortex and thalamus - Rivalries and synchronisation

# Consciousness Studies/The Neurophysiology Of Sensation And Perception#Vision ## Vision ### The human eye The eye is a remarkable optical instrument that is often poorly understood by students of consciousness. The most popular misconception is that there is a \'focus\' within the eye through which all the light rays pass! The purpose of this article is to describe our knowledge of the optics of the eye so that such misconceptions can be avoided.  The eye consists of several surfaces at which refraction occurs: air-cornea, cornea-aqueous humour, aqueous humour-lens, lens-vitreous humour. The crude image forming capability of the eye can be represented quite accurately by the *reduced eye* model which involves a single optical surface (air-cornea). Optometrists use more accurate models such as the Gullstrand Schematic Eye, the Le Grand Theoretical and the LeGrand Simplified Eye. The lens system at the front of the eye forms an inverted image on the retina. The eye is about 23 mm deep from the front of the cornea to the back of the retina. The refractive index of the components of the lens system varies from about 1.33 to 1.39. Light from every point of a field of view falls all over the surface of the eye. There is no \'point eye\' and there is no ordered image between objects in the view and the retina except on the retina. The image on the eye has the form of an inverted mapping of 3D objects to a 2D surface. This is also the form of conscious experience so the images on the retinas are the closest physical analogues of phenomenal, visual, conscious experience (see Perspective below). ### Perspective Perspective describes how light from three dimensional objects is mapped onto a two dimensional surface as a result of the action of lenses of the type found in the eye.  Perspective is used by artists to create the impression of viewing a 3D scene. To do this they create a 2D image that is similar to the image on the retina that would be created by the 3D scene.  Naive Realists and many Direct Realists believe that the 2D perspective view is the way things are actually arranged in the world. Of course, things in the world differ from images because they are arranged in three dimensions. ### Colour The colour of an object can be represented by its **spectral power distribution** which is a plot of the power available at each wavelength. The unit of light power is the watt but the unit that is used to measure subjective illumination is the **candela**. One candela is the illumination due to light of a wavelength of 555 nanometres and a radiant intensity of 1/683 watts per steradian in the direction being measured. A steradian is a solid angle at the centre of sphere of one metre radius that is subtended by one square metre of the surface. The curious number 1/683 occurs because the unit was originally based on light emitted from a square centimetre of molten platinum. The wavelength of 555 nm is chosen because this is the wavelength of peak sensitivity for light adapted (photopic) vision over a large group of subjects. Light adapted vision is largely due to photosensitive cells in the retina called **cones**. The candela is fixed as a standard SI Unit for light at a wavelength of 555 nanometres. The **lumen** is a subjective measure of the flux of light energy passing through a solid angle (a steradian). 683 lumens of light at 555 nm are equivalent to a watt passing through the solid angle. At a wavelength of about 520 nm only 500 lumens of luminous flux occur per watt because the visual system is less sensitive at this wavelength. The curve of sensitivity of the visual system to light is known as the **V-lambda Curve**. At a wavelength of about 510 nm the same radiant intensity is seen as being half as bright as at a wavelength of 555 nm.  Dark adapted (scotopic) vision has a peak sensitivity at a wavelength of 507 nm and is largely due to photosensitive cells called **rods** in the retina. Spectral Luminous Efficacy Curves are also used to express how the sensitivity to light varies with wavelength. Phenomenal colours are due to mixtures of **spectral colours** of varying intensities. A **spectral colour** corresponds to a wavelength of light found on the electromagnetic spectrum of visible light. Colours have three attributes: **brightness**, **saturation** and **hue**. The brightness of a colour depends on the illuminance and the reflectivity of the surface. The saturation depends on the amount of white present, for instance white and red make pink. The hue is similar to spectral colour but can consist of some combinations - for instance magenta is a hue but combines two spectral colours: red and blue. It should be noted that experiences that contain colour are dependent on the properties of the visual system as much as on the wavelengths of light being reflected. Any set of three colours that can be added together to give white are known as **primary colours**. There are a large number of colours that can be combined to make white, or almost any other colour. This means that a set of surfaces that all appear white could reflect a wide range of different wavelengths of light. There are numerous systems for predicting how colours will combine to make other colours; the CIE Chromaticity Diagram, the Munsell Colour System and the Ostwald Colour System have all been used. The 1931 CIE Chromaticity Diagram is shown below: {width="400"} See Chromaticity diagram for more information. ### The retina The retina contains photoreceptive cells called rods and cones and several types of neurons. The rods are generally sensitive to light and there are three varieties of cones sensitive to long, medium and short wavelengths of light (L, M and S type cones). Some of the ganglion cells in the retina (about 2%) are also slightly light sensitive and provide input for the control of circadian rhythms. A schematic diagram of the retina is shown below.  The photoreceptors hyperpolarise (their membrane potential becomes more negative) in response to illumination. Bipolar cells make direct contact with the photoreceptors and come in two types, *on* and *off*. The on-bipolar cells are also known as *invaginating* bipolars and the off-bipolars as *flat bipolars*. On-bipolars depolarise when light falls on the photoreceptors and off-bipolars hyperpolarise. Action potentials do not occur in the bipolar or photoreceptor cells. The retinal neurons perform considerable preprocessing before submitting information to the brain. The network of horizontal and ganglion neurons act to produce an output of action potentials that is sensitive to boundaries between areas of differing illumination (edge detection) and to motion. Kuffler in 1953 discovered that many retinal ganglion cells are responsive to differences in illumination on the retina. This **centre-surround** processing is shown in the illustration below.  The centre-surround effect is due to **lateral inhibition** by horizontally arranged cells in the retina. The structure of the response fields of ganglion cells is important in everyday processing and increases the definition of boundaries in the visual field. Sometimes it gives rise to effects that are not directly related to the physical content of the visual field. The most famous of these effects is the Hermann Illusion. The Hermann Grid Illusion is a set of black squares separated by white lines. Where the white lines cross it appears as if there are grey dots.  The grey dots are due to the relative suppression of on-centre ganglion cells where the white lines cross. This is explained in the illustration below.  Notice how the grey dots disappear when the crossed white lines are at the centre of the visual field. This is due to way that ganglion cell fields are much smaller in the fovea. There are many other retinal illusions. White\'s illusion is particularly strong and was believed to be due to centre-surround activity but is now thought to have a complex origin.  The grey lines really are the same shade of grey in the illustration. Mach\'s Illusion is another example of a centre-surround effect. Centre-surround effects can also occur with colour fields, red/green and yellow/blue contrasts having a similar effect to light/dark contrasts. Lateral inhibition and the resultant centre-surround effect increases the number of cells that respond to boundaries and edges in the visual field. If it did not occur then small boundaries might be missed entirely if these fell on areas of the retina outside of the fovea. The result of this effect is everywhere in our normal visual phenomenal experience so not only is visual experience a mapping of 3D on to a 2D surface, it also contains shading and brightening at edges that will not be found by photometers that measure objective light intensities. Photoreceptors become less responsive after continuous exposure to bright light. This gives rise to **afterimages**. Afterimages are usually of the opponent colour (white light gives a dark afterimage, yellow light gives a blue afterimage, red gives a green afterimage etc.). Afterimages when the eyes are open are generally due to a lack of response to a particular frequency of light within the white light that bathes the retina. It is clear that visual phenomenal experience is related more directly to the layout and type of activity in the retinal cells than to things in the visual field beyond the eye. ### Visual pathways  ### The lateral geniculate nucleus Retinal ganglion cells project to the Lateral Geniculate Nuclei which are small bumps on the back of the thalamus. (Only 10-15% of the input to the LGN comes from the retina, most (c.80%) comes from the visual cortex). The neurons in the LGN are arranged retinotopically so preserve the layout of events on the surface of the retina. The LGN are arranged in 6 layers. The top two are known as Magnocellular layers (about 100,000 neurons with large cell bodies) and the bottom four are called Parvocellular layers (about 1,000,000 neurons with small cell bodies). Between the main layers are the Koniocellular layers that consist of large numbers of tiny neurons. The left Lateral Geniculate Nucleus receives input from the right visual field and the right LGN receives input from the left visual field. Each nucleus receives input from both eyes but this input is segregated so that input from the eye on the same side goes to layers 1, 3, 5 and from the other side to layers 2,4, 6. The magnocellular layers contain neurons that have a large receptive field, are sensitive to contrast, a transient response and are not colour sensitive. The parvocellular layers contains neurons that have small receptive fields, are colour sensitive, have a prolonged response and are less sensitive to contrast. The LGN pathway from the retina is largely connected to the striate part of the visual cortex (cortical area V1) via a set of fibres called the optic radiation. There are reciprocal connections between the Thalamic Reticular Nucleus and the LGN. The LGN are also interconnected with the Superior Colliculus and brainstem. The LGN may be involved in controlling which areas of the visual field are subjected to attention (O\'Connor *et al.* 2002). ### The visual cortex The input from the LGN goes mainly to area V1 of the cortex. The cortex is arranged in six layers and divided up into **columns**. Each column in the visual cortex corresponds to a particular area of the retina in one eye. The columns are arranged in rows called **hypercolumns**. Each column within a hypercolumn responds to a different orientation of an optical stimulus at a given location (so responds to edges/boundaries that are oriented in the visual field). Hypercolumns from each eye are arranged alternately and form a small block of cortex called a **pinwheel**. At the centre of each pinwheel are colour sensitive cells that are usually not orientation sensitive. These coincide with the \"blobs\" that are seen when visual cortex is viewed using cytochrome oxidase dependent stains. It is important to note that the \"hypercolumns\" merge into one another and respond to line stimuli that cover an area of retina so they may be physiological rather than anatomical entities. The blind spot in each eye is represented by an area of visual cortex that only receives monocular input from the other eye (Tong & Engel 2001). The effect of the blind spot is illustrated below:  Normally it seems that the blindspot is \'filled in\' with background when one eye is used. However, Lou & Chen (2003) demonstrated that subjects could respond to quite complex figures in the blind spot, although how far they were investigating \'blindsight\' rather than visual experience in the blind spot is difficult to determine. Different layers in the visual cortex have outputs that go to different locations. Layer 6 sends nerve fibres to the Lateral Geniculate Nuclei and thalamus, layer 5 to superior colliculus and pons, layer 2 & 3 to other cortical areas. There are two important outputs to other cortical areas, the **ventral stream** and the **dorsal stream**. The ventral stream processes colour, form and objects. It proceeds to the inferior (lower) temporal cortex. The dorsal stream processes motion, position and spatial relationships. It proceeds towards the parietal cortex. Lesions in the ventral stream can result in patients knowing where an object is located but being unable to enumerate its properties, on the other hand, lesions to the dorsal stream can result in patients being able to label an object but unable to tell exactly where it is located. There is also a large output from the visual cortex back to the thalamus, this output contains more fibres than the thalamo-cortical input. ### Depth perception The world is three dimensional but the image on the back of the retinas is two dimensional. How does the brain give the subject a perception of depth? Depth perception relies on **cues** which are data about the displacement of things relative to the body. These cues consist of: - the convergence of the eyes - the accommodation of the lens - binocular disparity -the difference between the images on the retinas- this was first suggested by Wheatstone. - motion parallax - distant objects move slower when the observer moves - first suggested by Helmholtz. - optical flow - the rate of expansion/contraction of a scene with movement towards or away from it (Lee & Aronson 1974). - binocular occlusion - parts of a scene are invisible to each eye. - body motion provides cues about near objects. - vanishing points - the convergence of parallel lines. - numerous other cues such as size constancy, texture etc. Binocular disparity has been most extensively studied as a source of depth cues. When the eyes converge to focus on an object in from of them there is very little disparity in the images of that object on the two retinas. The angle at the object formed between the lines that project back to the pupils is known as the **vergence** at the object. The sphere where all objects have the same vergence is known as the **horopter**.  When the disparity between the retinas is small a single image occurs in phenomenal experience which is accompanied by a sensation of objects with depth. This is known as **stereopsis**. If the disparity between the retinas is large double vision ensues, this is known as **diplopia**. The curious feature of stereopsis is that we can see no more of the object than is visible on the retinas and certainly cannot see behind the object. Stereopsis is more like a stretching of 2D space than actual 3D. The **empirical horopter** is a zone where things are seen without diplopia. The empirical and **Veith Muller** (geometric) horopters are different. This difference is the result of both processing by the CNS and optical factors. **Physiological diplopia** refers to the stimulation of receptors in different parts of the retinas of the two eyes by the same object. Physiological diplopia does not always give rise to subjective diplopia, objects close to the empirical horopter do not give rise to double vision and the zone in which this occurs is known as **Panum\'s Fusion Area**. It is widest for objects that are distributed away from the nose (with \'temporal\' locations) and for objects that are slow moving and poorly focussed. In the review by Cutting and Vishton (1995) the contributions of each type of cue is discussed. Cutting and Vishton also present evidence that there are several zones of depth perception that are informed by different sets of cues. These are **personal space**, which is the zone of things within arms reach, **action space**, which is the zone in which we interact and where our motions have a large impact on the perceived layout, and **vista space** which is the zone beyond about 30m that is informed by long range cues. The interesting feature of 3D perceptual space is that it is not seen. The sides of a solid object appear as intrusions or lateral extensions in 2D space, when we close an eye that has access to the side of the object and then open it again the side grows out into 2D space. The lack of \'seeing\' depth is also evident when we close one eye when looking at a vista - nothing seems to change even though stereopsis has gone. This leaves the problem of what it is that constitutes the \'feeling\' of depth. We have feelings that we can fall into space or move into it or around in it. Depth seems to be defined by premotor modelling and the potential for occupancy by our bodies and limbs. As such it involves qualia that are different from those of vision and more akin to those that accompany movement, as an example, if you reach out to touch something, move the hand back, then consider the distance to the object it is evident that a feeling of the movement is still present. Is depth a quale of movement modelled during the extended present of perception? - Cutting, J.E. & Vishton, P.M. (1995) Perceiving layout and knowing distances: The integration, relative potency, and contextual use of different information about depth. In W. Epstein & S. Rogers (eds.) Handbook of perception and cognition, Vol 5; Perception of space and motion. (pp. 69-117). San Diego, CA: Academic Press. <http://pmvish.people.wm.edu/cutting&vishton1995.pdf> ```{=html} <!-- --> ``` - Gregory, R.L. (1997). Knowledge in perception and illusion. From: Phil. Trans. R. Soc. Lond. B (1997) 352, 1121--1128. <http://www.richardgregory.org/papers/knowl_illusion/knowledge-in-perception.pdf> ```{=html} <!-- --> ``` - Hubel, D.H. (1981). EVOLUTION OF IDEAS ON THE PRIMARY VISUAL CORTEX, 1955-1978: A BIASED HISTORICAL ACCOUNT. <http://nobelprize.org/medicine/laureates/1981/hubel-lecture.pdf> ```{=html} <!-- --> ``` - Lou, L. & Chen, J. (2003). Attention and Blind-Spot Phenomenology. PSYCHE, 9(02), January 2003. <http://psyche.cs.monash.edu.au/v9/psyche-9-02-lou.html> ```{=html} <!-- --> ``` - O\'Connor, D.H., Fukui, M.M., Pinsk, M.A. & Kastner, S. (2002). Attention modulates responses in the human lateral geniculate nucleus. Nature Neuroscience 5, 1203 - 1209 (2002). <http://www.nature.com/neuro/journal/v5/n11/full/nn957.html#B34> ```{=html} <!-- --> ``` - Tong, F., & Engel, S. A. (2001). Interocular rivalry revealed in the human cortical blind-spot representation. Nature, 411, 195-199. <http://www.psy.vanderbilt.edu/tonglab/publications/Tong&Engel2001.pdf> ```{=html} <!-- --> ``` - Tong, F. (2003). PRIMARY VISUAL CORTEX AND VISUAL AWARENESS. Nature Reviews of Neuroscience. 4:219-229. <http://www.psy.vanderbilt.edu/tonglab/publications/Tong_NRN2003.pdf> **Modules** - The cortex and thalamus - Rivalries and synchronisation

# Consciousness Studies/The Neurophysiology Of Sensation And Perception#Depth perception ## Vision ### The human eye The eye is a remarkable optical instrument that is often poorly understood by students of consciousness. The most popular misconception is that there is a \'focus\' within the eye through which all the light rays pass! The purpose of this article is to describe our knowledge of the optics of the eye so that such misconceptions can be avoided.  The eye consists of several surfaces at which refraction occurs: air-cornea, cornea-aqueous humour, aqueous humour-lens, lens-vitreous humour. The crude image forming capability of the eye can be represented quite accurately by the *reduced eye* model which involves a single optical surface (air-cornea). Optometrists use more accurate models such as the Gullstrand Schematic Eye, the Le Grand Theoretical and the LeGrand Simplified Eye. The lens system at the front of the eye forms an inverted image on the retina. The eye is about 23 mm deep from the front of the cornea to the back of the retina. The refractive index of the components of the lens system varies from about 1.33 to 1.39. Light from every point of a field of view falls all over the surface of the eye. There is no \'point eye\' and there is no ordered image between objects in the view and the retina except on the retina. The image on the eye has the form of an inverted mapping of 3D objects to a 2D surface. This is also the form of conscious experience so the images on the retinas are the closest physical analogues of phenomenal, visual, conscious experience (see Perspective below). ### Perspective Perspective describes how light from three dimensional objects is mapped onto a two dimensional surface as a result of the action of lenses of the type found in the eye.  Perspective is used by artists to create the impression of viewing a 3D scene. To do this they create a 2D image that is similar to the image on the retina that would be created by the 3D scene.  Naive Realists and many Direct Realists believe that the 2D perspective view is the way things are actually arranged in the world. Of course, things in the world differ from images because they are arranged in three dimensions. ### Colour The colour of an object can be represented by its **spectral power distribution** which is a plot of the power available at each wavelength. The unit of light power is the watt but the unit that is used to measure subjective illumination is the **candela**. One candela is the illumination due to light of a wavelength of 555 nanometres and a radiant intensity of 1/683 watts per steradian in the direction being measured. A steradian is a solid angle at the centre of sphere of one metre radius that is subtended by one square metre of the surface. The curious number 1/683 occurs because the unit was originally based on light emitted from a square centimetre of molten platinum. The wavelength of 555 nm is chosen because this is the wavelength of peak sensitivity for light adapted (photopic) vision over a large group of subjects. Light adapted vision is largely due to photosensitive cells in the retina called **cones**. The candela is fixed as a standard SI Unit for light at a wavelength of 555 nanometres. The **lumen** is a subjective measure of the flux of light energy passing through a solid angle (a steradian). 683 lumens of light at 555 nm are equivalent to a watt passing through the solid angle. At a wavelength of about 520 nm only 500 lumens of luminous flux occur per watt because the visual system is less sensitive at this wavelength. The curve of sensitivity of the visual system to light is known as the **V-lambda Curve**. At a wavelength of about 510 nm the same radiant intensity is seen as being half as bright as at a wavelength of 555 nm.  Dark adapted (scotopic) vision has a peak sensitivity at a wavelength of 507 nm and is largely due to photosensitive cells called **rods** in the retina. Spectral Luminous Efficacy Curves are also used to express how the sensitivity to light varies with wavelength. Phenomenal colours are due to mixtures of **spectral colours** of varying intensities. A **spectral colour** corresponds to a wavelength of light found on the electromagnetic spectrum of visible light. Colours have three attributes: **brightness**, **saturation** and **hue**. The brightness of a colour depends on the illuminance and the reflectivity of the surface. The saturation depends on the amount of white present, for instance white and red make pink. The hue is similar to spectral colour but can consist of some combinations - for instance magenta is a hue but combines two spectral colours: red and blue. It should be noted that experiences that contain colour are dependent on the properties of the visual system as much as on the wavelengths of light being reflected. Any set of three colours that can be added together to give white are known as **primary colours**. There are a large number of colours that can be combined to make white, or almost any other colour. This means that a set of surfaces that all appear white could reflect a wide range of different wavelengths of light. There are numerous systems for predicting how colours will combine to make other colours; the CIE Chromaticity Diagram, the Munsell Colour System and the Ostwald Colour System have all been used. The 1931 CIE Chromaticity Diagram is shown below: {width="400"} See Chromaticity diagram for more information. ### The retina The retina contains photoreceptive cells called rods and cones and several types of neurons. The rods are generally sensitive to light and there are three varieties of cones sensitive to long, medium and short wavelengths of light (L, M and S type cones). Some of the ganglion cells in the retina (about 2%) are also slightly light sensitive and provide input for the control of circadian rhythms. A schematic diagram of the retina is shown below.  The photoreceptors hyperpolarise (their membrane potential becomes more negative) in response to illumination. Bipolar cells make direct contact with the photoreceptors and come in two types, *on* and *off*. The on-bipolar cells are also known as *invaginating* bipolars and the off-bipolars as *flat bipolars*. On-bipolars depolarise when light falls on the photoreceptors and off-bipolars hyperpolarise. Action potentials do not occur in the bipolar or photoreceptor cells. The retinal neurons perform considerable preprocessing before submitting information to the brain. The network of horizontal and ganglion neurons act to produce an output of action potentials that is sensitive to boundaries between areas of differing illumination (edge detection) and to motion. Kuffler in 1953 discovered that many retinal ganglion cells are responsive to differences in illumination on the retina. This **centre-surround** processing is shown in the illustration below.  The centre-surround effect is due to **lateral inhibition** by horizontally arranged cells in the retina. The structure of the response fields of ganglion cells is important in everyday processing and increases the definition of boundaries in the visual field. Sometimes it gives rise to effects that are not directly related to the physical content of the visual field. The most famous of these effects is the Hermann Illusion. The Hermann Grid Illusion is a set of black squares separated by white lines. Where the white lines cross it appears as if there are grey dots.  The grey dots are due to the relative suppression of on-centre ganglion cells where the white lines cross. This is explained in the illustration below.  Notice how the grey dots disappear when the crossed white lines are at the centre of the visual field. This is due to way that ganglion cell fields are much smaller in the fovea. There are many other retinal illusions. White\'s illusion is particularly strong and was believed to be due to centre-surround activity but is now thought to have a complex origin.  The grey lines really are the same shade of grey in the illustration. Mach\'s Illusion is another example of a centre-surround effect. Centre-surround effects can also occur with colour fields, red/green and yellow/blue contrasts having a similar effect to light/dark contrasts. Lateral inhibition and the resultant centre-surround effect increases the number of cells that respond to boundaries and edges in the visual field. If it did not occur then small boundaries might be missed entirely if these fell on areas of the retina outside of the fovea. The result of this effect is everywhere in our normal visual phenomenal experience so not only is visual experience a mapping of 3D on to a 2D surface, it also contains shading and brightening at edges that will not be found by photometers that measure objective light intensities. Photoreceptors become less responsive after continuous exposure to bright light. This gives rise to **afterimages**. Afterimages are usually of the opponent colour (white light gives a dark afterimage, yellow light gives a blue afterimage, red gives a green afterimage etc.). Afterimages when the eyes are open are generally due to a lack of response to a particular frequency of light within the white light that bathes the retina. It is clear that visual phenomenal experience is related more directly to the layout and type of activity in the retinal cells than to things in the visual field beyond the eye. ### Visual pathways  ### The lateral geniculate nucleus Retinal ganglion cells project to the Lateral Geniculate Nuclei which are small bumps on the back of the thalamus. (Only 10-15% of the input to the LGN comes from the retina, most (c.80%) comes from the visual cortex). The neurons in the LGN are arranged retinotopically so preserve the layout of events on the surface of the retina. The LGN are arranged in 6 layers. The top two are known as Magnocellular layers (about 100,000 neurons with large cell bodies) and the bottom four are called Parvocellular layers (about 1,000,000 neurons with small cell bodies). Between the main layers are the Koniocellular layers that consist of large numbers of tiny neurons. The left Lateral Geniculate Nucleus receives input from the right visual field and the right LGN receives input from the left visual field. Each nucleus receives input from both eyes but this input is segregated so that input from the eye on the same side goes to layers 1, 3, 5 and from the other side to layers 2,4, 6. The magnocellular layers contain neurons that have a large receptive field, are sensitive to contrast, a transient response and are not colour sensitive. The parvocellular layers contains neurons that have small receptive fields, are colour sensitive, have a prolonged response and are less sensitive to contrast. The LGN pathway from the retina is largely connected to the striate part of the visual cortex (cortical area V1) via a set of fibres called the optic radiation. There are reciprocal connections between the Thalamic Reticular Nucleus and the LGN. The LGN are also interconnected with the Superior Colliculus and brainstem. The LGN may be involved in controlling which areas of the visual field are subjected to attention (O\'Connor *et al.* 2002). ### The visual cortex The input from the LGN goes mainly to area V1 of the cortex. The cortex is arranged in six layers and divided up into **columns**. Each column in the visual cortex corresponds to a particular area of the retina in one eye. The columns are arranged in rows called **hypercolumns**. Each column within a hypercolumn responds to a different orientation of an optical stimulus at a given location (so responds to edges/boundaries that are oriented in the visual field). Hypercolumns from each eye are arranged alternately and form a small block of cortex called a **pinwheel**. At the centre of each pinwheel are colour sensitive cells that are usually not orientation sensitive. These coincide with the \"blobs\" that are seen when visual cortex is viewed using cytochrome oxidase dependent stains. It is important to note that the \"hypercolumns\" merge into one another and respond to line stimuli that cover an area of retina so they may be physiological rather than anatomical entities. The blind spot in each eye is represented by an area of visual cortex that only receives monocular input from the other eye (Tong & Engel 2001). The effect of the blind spot is illustrated below:  Normally it seems that the blindspot is \'filled in\' with background when one eye is used. However, Lou & Chen (2003) demonstrated that subjects could respond to quite complex figures in the blind spot, although how far they were investigating \'blindsight\' rather than visual experience in the blind spot is difficult to determine. Different layers in the visual cortex have outputs that go to different locations. Layer 6 sends nerve fibres to the Lateral Geniculate Nuclei and thalamus, layer 5 to superior colliculus and pons, layer 2 & 3 to other cortical areas. There are two important outputs to other cortical areas, the **ventral stream** and the **dorsal stream**. The ventral stream processes colour, form and objects. It proceeds to the inferior (lower) temporal cortex. The dorsal stream processes motion, position and spatial relationships. It proceeds towards the parietal cortex. Lesions in the ventral stream can result in patients knowing where an object is located but being unable to enumerate its properties, on the other hand, lesions to the dorsal stream can result in patients being able to label an object but unable to tell exactly where it is located. There is also a large output from the visual cortex back to the thalamus, this output contains more fibres than the thalamo-cortical input. ### Depth perception The world is three dimensional but the image on the back of the retinas is two dimensional. How does the brain give the subject a perception of depth? Depth perception relies on **cues** which are data about the displacement of things relative to the body. These cues consist of: - the convergence of the eyes - the accommodation of the lens - binocular disparity -the difference between the images on the retinas- this was first suggested by Wheatstone. - motion parallax - distant objects move slower when the observer moves - first suggested by Helmholtz. - optical flow - the rate of expansion/contraction of a scene with movement towards or away from it (Lee & Aronson 1974). - binocular occlusion - parts of a scene are invisible to each eye. - body motion provides cues about near objects. - vanishing points - the convergence of parallel lines. - numerous other cues such as size constancy, texture etc. Binocular disparity has been most extensively studied as a source of depth cues. When the eyes converge to focus on an object in from of them there is very little disparity in the images of that object on the two retinas. The angle at the object formed between the lines that project back to the pupils is known as the **vergence** at the object. The sphere where all objects have the same vergence is known as the **horopter**.  When the disparity between the retinas is small a single image occurs in phenomenal experience which is accompanied by a sensation of objects with depth. This is known as **stereopsis**. If the disparity between the retinas is large double vision ensues, this is known as **diplopia**. The curious feature of stereopsis is that we can see no more of the object than is visible on the retinas and certainly cannot see behind the object. Stereopsis is more like a stretching of 2D space than actual 3D. The **empirical horopter** is a zone where things are seen without diplopia. The empirical and **Veith Muller** (geometric) horopters are different. This difference is the result of both processing by the CNS and optical factors. **Physiological diplopia** refers to the stimulation of receptors in different parts of the retinas of the two eyes by the same object. Physiological diplopia does not always give rise to subjective diplopia, objects close to the empirical horopter do not give rise to double vision and the zone in which this occurs is known as **Panum\'s Fusion Area**. It is widest for objects that are distributed away from the nose (with \'temporal\' locations) and for objects that are slow moving and poorly focussed. In the review by Cutting and Vishton (1995) the contributions of each type of cue is discussed. Cutting and Vishton also present evidence that there are several zones of depth perception that are informed by different sets of cues. These are **personal space**, which is the zone of things within arms reach, **action space**, which is the zone in which we interact and where our motions have a large impact on the perceived layout, and **vista space** which is the zone beyond about 30m that is informed by long range cues. The interesting feature of 3D perceptual space is that it is not seen. The sides of a solid object appear as intrusions or lateral extensions in 2D space, when we close an eye that has access to the side of the object and then open it again the side grows out into 2D space. The lack of \'seeing\' depth is also evident when we close one eye when looking at a vista - nothing seems to change even though stereopsis has gone. This leaves the problem of what it is that constitutes the \'feeling\' of depth. We have feelings that we can fall into space or move into it or around in it. Depth seems to be defined by premotor modelling and the potential for occupancy by our bodies and limbs. As such it involves qualia that are different from those of vision and more akin to those that accompany movement, as an example, if you reach out to touch something, move the hand back, then consider the distance to the object it is evident that a feeling of the movement is still present. Is depth a quale of movement modelled during the extended present of perception? - Cutting, J.E. & Vishton, P.M. (1995) Perceiving layout and knowing distances: The integration, relative potency, and contextual use of different information about depth. In W. Epstein & S. Rogers (eds.) Handbook of perception and cognition, Vol 5; Perception of space and motion. (pp. 69-117). San Diego, CA: Academic Press. <http://pmvish.people.wm.edu/cutting&vishton1995.pdf> ```{=html} <!-- --> ``` - Gregory, R.L. (1997). Knowledge in perception and illusion. From: Phil. Trans. R. Soc. Lond. B (1997) 352, 1121--1128. <http://www.richardgregory.org/papers/knowl_illusion/knowledge-in-perception.pdf> ```{=html} <!-- --> ``` - Hubel, D.H. (1981). EVOLUTION OF IDEAS ON THE PRIMARY VISUAL CORTEX, 1955-1978: A BIASED HISTORICAL ACCOUNT. <http://nobelprize.org/medicine/laureates/1981/hubel-lecture.pdf> ```{=html} <!-- --> ``` - Lou, L. & Chen, J. (2003). Attention and Blind-Spot Phenomenology. PSYCHE, 9(02), January 2003. <http://psyche.cs.monash.edu.au/v9/psyche-9-02-lou.html> ```{=html} <!-- --> ``` - O\'Connor, D.H., Fukui, M.M., Pinsk, M.A. & Kastner, S. (2002). Attention modulates responses in the human lateral geniculate nucleus. Nature Neuroscience 5, 1203 - 1209 (2002). <http://www.nature.com/neuro/journal/v5/n11/full/nn957.html#B34> ```{=html} <!-- --> ``` - Tong, F., & Engel, S. A. (2001). Interocular rivalry revealed in the human cortical blind-spot representation. Nature, 411, 195-199. <http://www.psy.vanderbilt.edu/tonglab/publications/Tong&Engel2001.pdf> ```{=html} <!-- --> ``` - Tong, F. (2003). PRIMARY VISUAL CORTEX AND VISUAL AWARENESS. Nature Reviews of Neuroscience. 4:219-229. <http://www.psy.vanderbilt.edu/tonglab/publications/Tong_NRN2003.pdf> **Modules** - The cortex and thalamus - Rivalries and synchronisation

# Consciousness Studies/Neuroscience 1 ## The cortex and consciousness The cerebral cortex consists of a set of specialised areas that process different aspects of sensation and motor control. There are about ten times as many nerve fibres going from the cortex to the thalamus as there are from the thalamus to the cortex (Destexhe 2000).  Histologically the cerebral cortex is a layer of greyish neurons overlying a huge mass of white nerve fibres, the cerebral medulla. The cortex consists of six main layers. The upper layers receive input from the relays in the thalamus such as the lateral geniculate, from the thalamus in general and from other areas of cortex plus a few specialised inputs from other locations. The lower layers give rise to output fibres that largely connect with the thalamus and other areas of cortex although particular specialised processors in the cortex may also have direct connections elsewhere such as to motor nuclei.  The cerebral cortex has many functions and is divided up into numerous separate processors. The most important function of the cortex from the point of view of consciousness studies is that it creates models. As was seen in Part I, philosophers debate whether these models are actually experienced consciously but in the neurophysiological literature it is normally assumed that we do experience models and rehearsals such as inner speech and imaginings. There is considerable evidence that the parts of the brain that deal with imagining (modelling) things are also the parts that deal with perception (i.e.: modelling the world). The overlap between imagination and normal perception is not complete because, as Tong(2003), in a review of visual consciousness, put it: \"Internally generated experiences share some, but not all, of the phenomenal properties of actual perception\". There is also considerable overlap between the areas used for imaginary speech (thought) and actual speech, areas dealing with the control of sensation and of the tongue etc. being used in actual speech but not in imagined speech (Fu *et al.* 2002). Kreiman *et al.* (2000) investigated the activity of single neurons in humans and also found that the brain activity evoked by visual imagination overlapped that which occurs upon direct stimulation by the same image. Our conscious experience consists of the output of the cortical modelling and perceptual processes. The cerebral cortex itself appears to be non-conscious. The evidence for the non-conscious nature of the cerebral cortex consists of lesion studies in which large amounts of cortex can be removed without removing consciousness and physiological studies in which it is demonstrated that the cerebral cortex can be active without conscious experience. Lesion studies have shown that up to 60% of the cerebral cortex can be removed without abolishing consciousness (Austin and Grant 1958). An entire hemisphere can be removed or much of the front or back of the cerebral cortex can be cut off yet consciousness persists. Fiset *et al.* (1999) and Cariani (2000) have shown that cortical activity can be normal or even elevated during the unconscious state of general anaesthesia. Alkire *et al.* (1996) also showed that cortical activity related to word recognition occurred during general anaesthesia. Libet *et al.* (1967) found that there could be cerebral cortical activity in response to weak stimulation of the skin without any conscious awareness of the stimulus. This work provides a neurophysiological basis for subliminal (non-conscious) perception and also shows that large areas of the cerebral cortex can be active without conscious experience. The insensitivity of experience to cortical activity has been further confirmed by Libet *et al.* (1979). They electrically stimulated the cerebral cortex of conscious patients and discovered that the stimulus must be continued for about 0.5 seconds for subjects to report a conscious experience of the stimulation. Libet\'s findings have been analysed at length but there still appears to be a 0.25 to 0.5 secs delay (Klein 2002). It has been demonstrated that cerebral cortical activity is not synonymous with conscious experience but why should there be a delay of up to 0.5 seconds or so between cortical stimulation and a conscious percept? What is the cortex doing in the 0.5 seconds between the start of stimulation and the report of awareness of the stimulation? It is probably synchronising its various processors and creating a waking dream, a structured set of events that accounts for the activity. The synchronisation of cerebral cortical processes will be discussed later, but what evidence is there for the cerebral cortex constructing a waking dream, or model, to describe the world? The \'Attentional Blink\' (Raymond *et al.* 1992) is consistent with the concept of the cerebral cortex being a device that creates models. In the \'Attentional Blink\' the identification of an object impairs the identification of a second object that is presented within 0.5 seconds of the first. Raymond *et al.* used a stream of letters (11 letters per second) and the identification of a first letter impaired the identification of a subsequent \'probe\' letter in the stream. If the probe letter followed the first letter within about 180 msecs it could easily be identified, suggesting that chunks of about 180 msecs of data stream are modelled together. Christmann & Leuthold (2004) have theorised that the \'Attentional Blink\' involves perceptual and central components of visual processing. This is supported by the fMRI studies of Marois *et al.* (2004) who presented subjects with faces mounted on scenes of places. The scenes of places often went undetected by subjects but they activated regions of the medial temporal cortex involved in high-level scene representations, the parahippocampal place area (PPA). When the scenes of places were detected by the subjects there was activity in the frontal cortex and the PPA activity was increased. These experiments are consistent with the idea of a cerebral cortex that is a multiprocessor system that creates consistent models of the environment. Bregman\'s (1990) auditory continuity illusion is another example of how sensory events are modelled. If a pure tone is followed by broadband noise and the noise followed by the same pure tone it seems as if the tone occurs throughout the period of noise. If the noise is not followed by the pure tone there is no sound of the tone during the period of noise. This effect is similar to the results found by Libet because a delay of several hundred milliseconds between sensory stimulation and conscious experience is needed to account for the apparent rewriting of history after the second tone appears. Dennett and Kinsbourne (1992) argued strongly against modelling as the source of conscious experience. They discussed two illusions, the \"cutaneous rabbit illusion\", in which the subject is tapped successively in such a way that some illusory taps appear and the \"phi illusion\" in which successively illuminated lights appear as a motion of the light. Dennett and Kinsbourne declared that there should be no cerebral cortical filling in of the gaps in the these illusions. Both these illusions have now been investigated. Blankenburg *et al.* (2006) found that cerebral cortical activity occurred at the locations expected for the missing taps in the \"cutaneous rabbit\" illusion and Larsen *et al.* (2006) found that the areas of cerebral cortex that would be stimulated by a moving light were active during the \"phi illusion\". ## The delay before consciousness of \"voluntary\" actions The 0.5 second delay required for the cortex to model an event has implications for the role of conscious experience in the control of our lives. If experience is about 0.5 seconds behind the true present instant then how can we be said to control anything? The brain must be acting automatically whilst performing most tasks. The 0.5 second delay also seems to contradict our everyday experience. We certainly feel like we are aware of things in less than 0.5 seconds, for example, the direct stimulation of sense organs seems to be experienced much more rapidly than the delayed experience of cortical stimulation. In fact subjects report that they are conscious of stimuli, such as being touched or seeing flashing lights, within 0.1 to 0.2 seconds of the event. So how can subjects report events within 0.2 seconds even though it seems to take 0.5 seconds for the cortex to generate activity that can be experienced? The simplest explanation is that the reaction occurs automatically within 0.2 seconds and then the conscious experience of this reaction occurs 0.3 seconds later. This gives a total 0.5 seconds delay before conscious experience whilst allowing fast reactions. Libet *et al.* extended their experiments by stimulating a \"relay nucleus\" in the thalamus that intercepts signals from the senses before they reach the somatosensory cortex. It was found that when this nucleus was stimulated for 0.5 seconds the subjects reported that the stimulus occurred 0.2 seconds after it had begun. When the nucleus was stimulated for less than 0.5 seconds the subjects did not report any sensation. This supports the concept of a 0.5 second delay whilst the cortex puts a stimulus in context before it is experienced. These experiments show that our experience is an output of cortical processing rather than the processing itself. If our conscious experience is non-cortical then this raises the possibility that the non-conscious cerebral cortex can perform actions without conscious control. Of course, the cortex does this all the time when we are indulging in skilled or routine behaviour. The ability of the non-conscious cortex is quite remarkable; for instance car drivers sometimes discover that they have driven for several miles without conscious experience of driving, even at the level of having no recollection of the route. !Typical recording of the readiness potential.{width="150"}Although it might be accepted that much of our everyday behaviour is automatic is there any behaviour that is definitely initiated by conscious experience? This is probably a pointless question because consciousness is about observation, not action; however, despite this there have been several experiments that have attempted to determine the relationship between consciousness and action. In 1964 Kornhuber and Deecke performed a series of experiments that measured the electrical activity from the scalp (EEG) during voluntary actions. They averaged many EEG\'s from subjects who were about to move a finger and discovered that there is an increase in scalp potential before the movement takes place. The increase in potential can start as long as 2 seconds or so before the movement and is known as the \"readiness potential\" (Bereitschaftspotential). The readiness potential is strange because it seems to contradict our conscious experience; we do not decide to move a hand and then wait 2 seconds before the hand moves. It seems that the non-conscious brain may be taking things into its own hands. Libet *et al.* (1983) extended the readiness potential experiments by asking subjects to observe a Wundt clock whilst flexing a finger. The Wundt clock had a spot of light that moved around a circle every 2.56 seconds and allowed the subjects to obtain timings that were related to their mental experiences. When the subjects flexed a finger it was found that the readiness potential occurred about 0.5 seconds before the finger moved and the subjects reported they were going to move the finger about 0.2 seconds before the movement. This suggested that a subject\'s cerebral cortex was preparing for the movement about 0.3 seconds before the subject was conscious of this. Libet\'s experiments have been reproduced elsewhere (see Keller & Heckhausen 1990). (It is important to note that the subjects in Libet\'s experiment were asked to wait until they felt the urge to move the finger.) These results are consistent with the idea of the cortex as a modelling system that constructs a consistent model of events to pass on to whatever mediates conscious experience. More recently fMRI and direct electrode recording have borne out the readiness potential experiments. Soon *et al.* (2008) allowed subjects to decide to press either a left or right button. They used fMRI to show that there was spatially organised activity in the polar frontal cortex and parietal cortex (from precuneus into posterior cingulate cortex) that predicted the conscious left/right decision and preceded it by about **seven seconds**. Rektor *et al.* (2001) used direct electrode recordings to show a 2 second latency. Haggard & Eimer (1999) and also Trevena and Miller (2002, 2009) have identified a \"Lateralized Readiness Potential\" that is correlated with the movement of a particular hand (left or right) in their EEG experiments and Trevena and Miller claim that this potential always follows the making of a conscious decision and precedes the actions being studied. However, Soon *et al.* (2008) showed that fMRI can predict which button will be used well before any conscious decision is reported. (See Haggard (2008) for a review of conscious volition). ## Perception, Imagination, Memory and Dreams ### More about Models Our dreams are clearly models that form a \'dreamworld\' but the idea that perception might be like a dream that is updated by sensation is not so obvious. Experience seems to be an active model of the world (virtual reality) based on sense data rather than a simple mapping of retinal and other sensory data. This is demonstrated by visual illusions such as the Ames Room, Spoke Illusion and Muller Lyer illusions shown below:  Notice how the circle is distorted without any distortion in the \'spokes\', it is as if the circle has been treated as a separate object by the processes in the brain that rearranged it. In all of these illusions the brain has rearranged large areas of the visual field and has managed the input as a collection of \'objects\' that are manipulated separately. Even movement seems to occur in some figures showing that the brain models the position of things:  The creation of a model is also demonstrated by the illusion of movement experienced when we watch the cinema or television. This is due to the cortical modelling that is known as \'short-range apparent motion\' rather than flicker fusion or persistence of vision. It is intriguing that, although it has been known for decades that the joining together of static images in our minds is due to modelling activity in the brain the myth that it is due to persistence of vision or flicker fusion is universal. As Anderson and Anderson (1993) noted: `Indeed, in the past decade, psychoanalytic-Marxist film scholars `\ `have retained the  model implied by persistence of vision: theirs `\ `is a passive viewer, a spectator who is "positioned," unwittingly `\ `"sutured" into the text, and victimized by excess ideology.` Our experience of the cinema is like a dream updated by sensation rather than sensation updated by interpretation. In fact the most compelling evidence for the modelling power of the brain is the existence of dreams; our dreams are often models of worlds that do not exist and involve little or no sensory input yet can involve effects as powerful as any television drama. Short range apparent motion occurs when the interval between presentations of an object is brief (c. 50-100 msecs). Motion modelling in response to longer intervals is known as long range apparent motion. There is evidence that the modelling in short range apparent motion is enhanced if the moving patterns are similar to moving human forms (such as patterns of dots outlining a person)(Thornton *et al.* 1998). The accuracy of predicting movement can actually improve if the interval between presentations is increased when human forms are used. Motion modelling can also be seen in visual illusions such as the *Waterfall Illusion* (motion aftereffect). The waterfall illusion is commonly seen after viewing a sequence of scrolling credits on the television; when the credits stop rolling it appears as if they briefly move in the opposite direction. Tootel *et al.* (1995) have used fMRI to show that this is correlated with activity in the motion modelling area of visual cortex (area MT/V5). The waterfall illusion is also associated with an intriguing aftereffect known as **storage of the motion aftereffect**. Normal motion aftereffects last for up to about ten seconds after the stimulus, however, if the subjects close their eyes for the normal duration of the aftereffect then reopen them they see the illusion for almost the normal duration. Culham *et al.* (1999) used fMRI to show that activity in area MT/V5 was low during the period when the eyes were closed then increased dramatically when the eyes were opened. This is strongly suggestive of a modelling mechanism outside MT/V5 that has adapted to motion and then models stationary data with movement in the wrong direction. Visual area MT/V5 is also involved in the separation of moving visual scenes into *sprites* or objects that move together as a whole within a scene (Muckli *et al.* 2002). The way that mental models may be the basis of ordinary reasoning was outlined by Johnson-Laird (1980), based on earlier work by Kenneth Craik. Studies of \'change blindness\' and \'inattentional blindness\', where subjects fail to spot outrageous changes in their environment, also demonstrate that we experience a model and suggest that the brain must analyse an object to incorporate it fully into the model (See for instance Rensink (2000), Simons & Rensink (2005)). ### Brain areas used in perception overlap those used in imagination and recall Functional Magnetic Resonance Imaging (fMRI) has shown that similar areas of brain are used during perception involving the senses as during imagination (Tong 2003, Kosslyn and Thompson 2003). The substrate of the mental images that occur in both modes of brain activity has not yet been found. This overlap of the brain areas used in perception with those used in imagination, memory and recall has been demonstrated in a wide range of experiments. Ganis *et al.* (2004) used fairly complex perceptual and imagination tasks that activated large areas of the brain, they found an overlap between the brain areas activated during perception and imagery. The principle areas that were different in the two tasks were found in the primary sensory areas of the visual cortex. Other areas in the visual cortex and activity in the rest of the brain showed a remarkable degree of overlap. The authors suggested that the differences in the activity of primary visual cortex may have been due to differences between the perceptual and imaginary stimuli such as speed of onset etc. The hippocampus was not activated. It is intriguing that, contrary to object imagery, spatial imagery such as predicting when a cross on a screen would fall on an imaginary letter actually seems to inhibit activity in sensory visual cortex (Aleman *et al.*). Both fMRI and blocking with transcranial magnetic stimulation (TMS) showed that the posterior parietal cortex was involved in the spatial imagery. Imagery involving places and faces activates the place and face areas that are activated during perception (Ishai *et al.* 2000). The recall and recognition of things also seems to involve very similar brain areas to those used during perception. Wheeler and Buckner (2003) showed that areas involved in perception were also involved in the recall of the perceptual stimuli. Recall causes activation of areas used in perception but also seems to use areas that may be particularly related to the process of recall iself, such as the left parietal cortex (Konishi *et al.* 2000) (Brodmann\'s area 40/39). Frontal and parietal regions are involved in the recognition of whether stimuli have been experienced before. Image generation during sleep seems to differ from that during imagination and recall. In particular it seems to involve a few well defined areas of cortex and considerable activation of the posterior thalamus. Sleep studies have shown that people dream throughout sleep. However, dreams are more frequent during the REM (rapid eye movement) periods of sleep than the NREM (non-REM) periods. Dreams are reported after 70-95% of awakenings in REM sleep and 5-10% of awakenings in NREM sleep. REM dreams are more visual than NREM dreams which are more \'thoughtlike\' (Solms 2000). Thoughtlike events (mentation) are reported after 43% of awakenings from NREM sleep. Solms (1997) found that patients who had lesions in the parietal-temporo-occipital junction reported a cessation of visual images in dreams. Solms also found that patients with lesions in the white matter inferior to the frontal horns of the lateral ventricles, in the ventromesial quadrant of the frontal lobes, also reported loss of dreaming. Loss of dreaming is also reported by leucotomised patients with frontal ventromesial damage. Damasio *et al.* (1985) and Solms (1997) also reported that some patients with damage to the medial prefrontal cortex, the anterior cingulate cortex, and the basal forebrain became confused about what was real life and what was dreaming (waking dreams occurred). Studies using fMRI show that the sensory occipital lobe (BA 18) and posterior thalamus, especially the lateral geniculate nuclei, are activated in REM sleep, weaker activations of the posterior cingulate, putamen and midbrain were also found (Wehrle *et al.* 2005, Loveblad *et al.* 1999). These findings are consistent with activation of the ponto-geniculo-occipital system (PGO) during REM. So dreams may be more like primary activations of sensory cortex than imagining or recall. This suggests that dreams have a thalamic origin or are managed via connections from the cortex through the thalamus to the visual cortex. Hallucinations seem to differ from dreams. In Charles Bonnett Syndrome patients can have clear hallucinations. These, like imaginations, seem to involve areas of the visual cortex that deal with processed data, for instance hallucinations of faces activate the \"face area\" rather than visual cortical area V1 (Ffytche *et al.* 1998). ### Suppression of data acquisition during saccades - perception as a patchwork If you look at yourself in the mirror you will not see your eyes moving even though they will be darting all over the view of your face. Even when you deliberately look from place to place your eyes will appear steady. The natural darting of the eyes from place to place as you view a scene is known as \"saccadic\" movement of the eyes. The suppression of the visual image during the motion of the eyes is known as \"saccadic suppression\" or \"saccadic masking\". The suppression of the acquisition of image data extends to suppression of awareness of flashes of light during saccades, this effect is known as \"flash suppression\", however, flash suppression seems to apply only to rather dull flashes (Volkman (1962). The suppression during saccades is probably due to suppression of the magnocellular pathway (the motion sensitive pathway) in the lateral geniculate nucleus (Burr *et al.* (1996). The most intriguing feature of this suppression of data acquisition during saccades is that each snapshot that is obtained between saccades can only contain a relatively small amount of information. This is because the fovea, which is the most sensitive area of the eye, is tiny (about 1mm diameter) and only receives input from a few degrees of the visual field. As a result what we consider to be a uniform scene in our minds is actually a patchwork of intersaccade snapshots. Another aspect of saccades is that the timing of events is referred back to the beginning of the saccade. This effect is known as \"saccadic chronostasis\". For example, if an object changes colour during a saccade the observer feels as if the colour change occurred at the beginning of the saccade, so extending the amount of time that the object possesses the changed colour. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception (see Yarrow *et al.* 2006). Burr D, Morrone M, Ross J. (1996) Selective suppression of the magnocellular visual pathway during saccades\]\'\', Behavioral Brain Research 80 1-8 (1996) <http://www.pisavisionlab.org/downloads/BBRReview96.pdf> Volkman, F. (1962). Vision during voluntary saccadic eye movements. J. Opt Soc. Am. 52:571-578. 1962. Yarrow, K, Whiteley, L, Rothwell, J.C & Haggard,P. (2006) Spatial consequences of bridging the saccadic gap. Vision Res. 2006 February; 46(4): 545--555. <http://www.hexicon.co.uk/Kielan/papers/Moving_chrono.pdf> ## Blindsight Blindsight studies illuminate the relationship between the cerebral cortex and our experience. When the visual cortex is removed subjects become almost totally blind. If the visual cortex on one side is removed subjects become relatively blind in the contra-lateral hemifield. One of the most revealing studies of blindsight is Marcel\'s 1998 paper: \" Blindsight and shape perception: deficit of visual consciousness or visual function?\". It is useful when considering blindsight to contemplate for a while the appearance of the world with both eyes closed and then with one eye closed. When both eyes are closed our experience is of a darkish space radiating out from our heads, with one eye closed we tend to ignore the darkish areas that cannot be seen even though they are still present. Marcel notes that patients who have a right blind field still have an underlying visual field on the right side and that this can even contain conscious visual experience. This sounds a bit like the darkish space that we all experience if deprived of visual input on one side. As Marcel says: \"A question that naturally arises is whether the loss is a \'total\' loss of visual consciousness in the blind field. It is often assumed to be so, especially by those who discuss blindsight without carefully reading the literature or working with the subjects. One can immediately respond negatively to the question..\" The consciousness of the completion of Kanizsa figures in blindsight patients is particularly indicative of the preservation of the field even though the content was largely missing. A Kanizsa figure is shown below:  If we put Marcel\'s observations together with cortical anatomy and function it seems that the space of our experience is located outside of the cerebral cortex. The cortex generates much of visual and other content but it does not generate the space. ## The Role of the Thalamus The thalamus is connected to the entire bottom layer of the cerebral cortex. It is the nexus of the various cortical processors as well as a recipient of independent input from most of the rest of the brain.  The thalamus is subdivided into numerous small and medium sized nuclei that between them receive inputs from every process in the nervous system (the white fibres in the illustration above largely penetrate the thalamus). The thalamic nuclei are interconnected which means that any of them could, potentially host activity from anywhere in the body or brain. Although the founders of neurology such as Hughlings Jackson and Penfield & Jasper located conscious experience in the diencephalon, including the thalamus, this is no longer the conventional wisdom. The small size of the thalamic nuclei means that they cannot support the processes that are assumed to compose access consciousness, however, even some of the smallest thalamic nuclei host millions of synapses so size would not be an obstacle if the thalamus contains the substrate of phenomenal consciousness. Indeed, the diencephalon and the thalamus in particular can be shown to be excellent candidates for a possible location of phenomenal experience.  `<font size=1>`{=html} The Intralaminar Nuclei of the thalamus. The white space above and to the left of RN is the third ventricle. MD=mediodorsal nucleus. CM=Centromedian nucleus, RN=red nucleus (not part of thalamus) The black areas are stained white fibres. Picture from: <http://www.neurophys.wisc.edu/> University of Wisconsin and Michigan State Comparative Mammalian Brain Collections. Preparation of image has been funded by the National Science Foundation, as well as by the National Institutes of Health. May only be used with these acknowledgements.`</font>`{=html} If the thalamus contains a location for conscious experience then lesions should abolish this experience. Unlike the cerebral hemispheres, lesions of the thalamus do indeed seem to abolish consciousness. The area that is most sensitive to lesions contains the Intralaminar Nuclei, especially the Parafascicular and Centromedian Nuclei. If these are damaged bilaterally patients suffer death, coma, akinetic mutism, hypersomnia, dementia and other equally serious impairments of consciousness that depend upon the size and placement of the lesions (Bogen 1995, Schiff & Plum 1999). In cases of fatal familial insomnia, in which patients exhibit many of these symptoms, there is marked neuron loss in the Intralaminar Nuclei (Budka 1998). The effect of interrupting the blood supply to the medial thalamus depends upon the severity of the damage. There is frequently initial coma. The recovery after coma is often incomplete, Krolak-Salmon *et al.* (2000) described bilateral paramedian thalamic infarcts as normally being \"followed by persisting dementia with severe mnemic disturbance, global aspontaneity and apathy.\" The symptoms of bilateral damage to the ILN can be so severe that it is possible that, even after recovery from coma, some patients may cease to be conscious and are being coordinated by automatic cortical processes. Bjornstad *et al.* (2003) and Woernera *et al.* (2005) both reported that the initial coma after bilateral paramedian infarct was accompanied by a similar pattern of EEG activity to stage 2 sleep. Woernera *et al.* (2005) also discovered that painful stimuli gave rise to a range of EEG activity, transiently breaking the stage 2 sleep pattern but without recovery of consciousness. Unfortunately even in those patients who recover consciousness Kumral *et al.* (2001) report that \"Cognitive functions in patients with bilateral paramedian infarction did not change significantly during the follow-up, in contrast to those with infarcts in varied arterial territories\" although Krolak-Salmon *et al.* (2000) did report a single patient who made a total recovery. Laureys *et al.* (2002) investigated recovery from \'persistent vegetative state\' (wakefulness without awareness). They found that overall cortical metabolism remained almost constant during recovery but that the metabolism in the prefrontal and association cortices became correlated with thalamic ILN and precuneus activity. Again confirming that thalamo-cortico-thalamic activity is required for consciousness and that cortical activity by itself is not conscious. Yamamoto *et al.* (2005) investigated persistent vegetative state and found that deep brain stimulation (25Hz) of the centromedian-parafascicular complex (19 cases) or mesencephalic reticular formation (2 cases) resulted in 8 of the patients emerging from persistent vegetative state. It is interesting that zolpidem, a GABA agonist, has recently been found to reverse PVS in some patients (Claus & Nel 2006). The effect is rapid and might be used to demonstrate the correlations that occur on recovery from PVS. As Bogen(1995) demonstrates, the ILN receive inputs, either directly or indirectly, from every part of the CNS but what do they do? Interest in the thalamus has recently been revived by the theories of Newman & Baars (1993), Baars, Newman, & Taylor1998) and Crick & Koch (1990). In Baars, Newman and Taylors\' (1998) theory it is suggested that \"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\". They also propose that the \"nucleus reticularis thalami\" (Thalamic Reticular Nucleus, TRN), which is a thin sheet of neurons that covers the thalamus, is involved in a selective attention system. This concept is reinforced by the way that point stimulation of the TRN causes focal activity in the overlying cortex (MacDonald *et al.* 1998) and the way the TRN is organised topographically (i.e.: has activity that is like an electrical image of receptor fields). The thalamus is ideally placed for integrating brain activity, if tiny parts of the thalamus are removed consciousness is abolished and the thalamus is involved in attention and the global integration of cortical activity. Any impartial judge might pronounce that the site of conscious experience has been found, possibly in the ILN of the thalamus, but no one can say how it works. ## General Anaesthesia and the Thalamus General anaesthesia should result in a profound depression of activity in the ILN if these are indeed the sites of the conscious state. White & Alkire (2003) administered halothane or isoflurane to volunteers and used positron emission tomography (PET) to monitor brain activity. They found severe depression of activity in the thalamus. The depression appeared to be higher in the non-specific nuclei than in the relay nuclei of the thalamus. In other words the anaesthesia is neither turning off the cortex nor turning off the input to the cortex but it is turning off an important part of the thalamus. Fiset *et al.* (1999) have also demonstrated a similar pattern of medial thalamic inactivity and cortical activity in propofol anaesthesia. Suppression of cortical activity is not the cause of unconsciousness; for instance, the anaesthetic agent chloralose leads to increased neural activity in the cortex relative to conscious patients (Cariani 2000). ## The function of consciousness When we walk our conscious experience does not contain data about the control of the spinal, cerebellar and vestibular reflexes that keep us on an even keel. When we reach out for a cup our conscious experience only contains data related to the need for the cup, not data about the elaborate control system that enables the action. When we talk the words just come into mind, we do not painstakingly control the syntax and vocal chords. When our attention shifts the conscious experience containing the shift happens after the attention has shifted. This passive nature of experience recurs throughout the neuroscience of consciousness from the \"readiness potential\" to the \"auditory continuity illusion\". So what does conscious observation do? The medical evidence of the lack of consciousness in some forms of delirium, mutism, PVS etc. suggest that the role of conscious observation is to stabilise the brain so that it acts as a coordinated whole. Conscious observation is an orderly arrangement of events, a stable groundform that reflects the environment and composes the stage for action. It could be speculated that if quantum events were prominent in brain function then such a groundform would be essential but even a classical brain might require a stabilising form that could be continuously compared with the world beyond the body. A stable form of neural information that contains bound data from the senses and internal neural processes is likely to have a role in the functioning of the organism. There is now an *integration consensus* that proposes that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent (see review in Baars, 2002). However, it has remained unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect. Morsella (2005) proposed a *Supramodular Interaction Theory* (SIT) that contrasts the task demands of consciously penetrable processes (e.g.: those that can be part of conscious experience such as pain, conflicting urges, and the delay of gratification) and consciously impenetrable processes (e.g.: intersensory conflicts, peristalsis, and the pupillary reflex). With this contrastive approach, SIT builds upon the integration consensus by specifying which kinds of interaction require conscious processing and which kinds do not (e.g., some intersensory processes). SIT proposes that conscious processes are required to integrate high-level systems in the brain that are vying for (specifically) skeletomotor control, as described by the principle of *parallel responses into skeletal muscle* (PRISM). Accordingly, regarding processes such as digestion and excretion, one is conscious of only those phases of the processes that require coordination with skeletomotor plans (e.g., chewing or micturating) and none of those that do not (e.g., peristalsis). From this standpoint, consciousness functions above the level of the traditional module to "cross-talk" among high-level, specialized and often multi-modal, systems. **References** Baars, B. J. (2002). The conscious access hypothesis: Origins and recent evidence. *Trends in Cognitive Sciences, 6,* 47 -- 52. Morsella, E. (2005). The function of phenomenal states: Supramodular interaction theory. *Psychological Review, 112,* 1000 - 1021. More\... Click here for Rivalries and synchronisation, bibliography and references

# Consciousness Studies/Neuroscience 1#The cortex and consciousness ## The cortex and consciousness The cerebral cortex consists of a set of specialised areas that process different aspects of sensation and motor control. There are about ten times as many nerve fibres going from the cortex to the thalamus as there are from the thalamus to the cortex (Destexhe 2000).  Histologically the cerebral cortex is a layer of greyish neurons overlying a huge mass of white nerve fibres, the cerebral medulla. The cortex consists of six main layers. The upper layers receive input from the relays in the thalamus such as the lateral geniculate, from the thalamus in general and from other areas of cortex plus a few specialised inputs from other locations. The lower layers give rise to output fibres that largely connect with the thalamus and other areas of cortex although particular specialised processors in the cortex may also have direct connections elsewhere such as to motor nuclei.  The cerebral cortex has many functions and is divided up into numerous separate processors. The most important function of the cortex from the point of view of consciousness studies is that it creates models. As was seen in Part I, philosophers debate whether these models are actually experienced consciously but in the neurophysiological literature it is normally assumed that we do experience models and rehearsals such as inner speech and imaginings. There is considerable evidence that the parts of the brain that deal with imagining (modelling) things are also the parts that deal with perception (i.e.: modelling the world). The overlap between imagination and normal perception is not complete because, as Tong(2003), in a review of visual consciousness, put it: \"Internally generated experiences share some, but not all, of the phenomenal properties of actual perception\". There is also considerable overlap between the areas used for imaginary speech (thought) and actual speech, areas dealing with the control of sensation and of the tongue etc. being used in actual speech but not in imagined speech (Fu *et al.* 2002). Kreiman *et al.* (2000) investigated the activity of single neurons in humans and also found that the brain activity evoked by visual imagination overlapped that which occurs upon direct stimulation by the same image. Our conscious experience consists of the output of the cortical modelling and perceptual processes. The cerebral cortex itself appears to be non-conscious. The evidence for the non-conscious nature of the cerebral cortex consists of lesion studies in which large amounts of cortex can be removed without removing consciousness and physiological studies in which it is demonstrated that the cerebral cortex can be active without conscious experience. Lesion studies have shown that up to 60% of the cerebral cortex can be removed without abolishing consciousness (Austin and Grant 1958). An entire hemisphere can be removed or much of the front or back of the cerebral cortex can be cut off yet consciousness persists. Fiset *et al.* (1999) and Cariani (2000) have shown that cortical activity can be normal or even elevated during the unconscious state of general anaesthesia. Alkire *et al.* (1996) also showed that cortical activity related to word recognition occurred during general anaesthesia. Libet *et al.* (1967) found that there could be cerebral cortical activity in response to weak stimulation of the skin without any conscious awareness of the stimulus. This work provides a neurophysiological basis for subliminal (non-conscious) perception and also shows that large areas of the cerebral cortex can be active without conscious experience. The insensitivity of experience to cortical activity has been further confirmed by Libet *et al.* (1979). They electrically stimulated the cerebral cortex of conscious patients and discovered that the stimulus must be continued for about 0.5 seconds for subjects to report a conscious experience of the stimulation. Libet\'s findings have been analysed at length but there still appears to be a 0.25 to 0.5 secs delay (Klein 2002). It has been demonstrated that cerebral cortical activity is not synonymous with conscious experience but why should there be a delay of up to 0.5 seconds or so between cortical stimulation and a conscious percept? What is the cortex doing in the 0.5 seconds between the start of stimulation and the report of awareness of the stimulation? It is probably synchronising its various processors and creating a waking dream, a structured set of events that accounts for the activity. The synchronisation of cerebral cortical processes will be discussed later, but what evidence is there for the cerebral cortex constructing a waking dream, or model, to describe the world? The \'Attentional Blink\' (Raymond *et al.* 1992) is consistent with the concept of the cerebral cortex being a device that creates models. In the \'Attentional Blink\' the identification of an object impairs the identification of a second object that is presented within 0.5 seconds of the first. Raymond *et al.* used a stream of letters (11 letters per second) and the identification of a first letter impaired the identification of a subsequent \'probe\' letter in the stream. If the probe letter followed the first letter within about 180 msecs it could easily be identified, suggesting that chunks of about 180 msecs of data stream are modelled together. Christmann & Leuthold (2004) have theorised that the \'Attentional Blink\' involves perceptual and central components of visual processing. This is supported by the fMRI studies of Marois *et al.* (2004) who presented subjects with faces mounted on scenes of places. The scenes of places often went undetected by subjects but they activated regions of the medial temporal cortex involved in high-level scene representations, the parahippocampal place area (PPA). When the scenes of places were detected by the subjects there was activity in the frontal cortex and the PPA activity was increased. These experiments are consistent with the idea of a cerebral cortex that is a multiprocessor system that creates consistent models of the environment. Bregman\'s (1990) auditory continuity illusion is another example of how sensory events are modelled. If a pure tone is followed by broadband noise and the noise followed by the same pure tone it seems as if the tone occurs throughout the period of noise. If the noise is not followed by the pure tone there is no sound of the tone during the period of noise. This effect is similar to the results found by Libet because a delay of several hundred milliseconds between sensory stimulation and conscious experience is needed to account for the apparent rewriting of history after the second tone appears. Dennett and Kinsbourne (1992) argued strongly against modelling as the source of conscious experience. They discussed two illusions, the \"cutaneous rabbit illusion\", in which the subject is tapped successively in such a way that some illusory taps appear and the \"phi illusion\" in which successively illuminated lights appear as a motion of the light. Dennett and Kinsbourne declared that there should be no cerebral cortical filling in of the gaps in the these illusions. Both these illusions have now been investigated. Blankenburg *et al.* (2006) found that cerebral cortical activity occurred at the locations expected for the missing taps in the \"cutaneous rabbit\" illusion and Larsen *et al.* (2006) found that the areas of cerebral cortex that would be stimulated by a moving light were active during the \"phi illusion\". ## The delay before consciousness of \"voluntary\" actions The 0.5 second delay required for the cortex to model an event has implications for the role of conscious experience in the control of our lives. If experience is about 0.5 seconds behind the true present instant then how can we be said to control anything? The brain must be acting automatically whilst performing most tasks. The 0.5 second delay also seems to contradict our everyday experience. We certainly feel like we are aware of things in less than 0.5 seconds, for example, the direct stimulation of sense organs seems to be experienced much more rapidly than the delayed experience of cortical stimulation. In fact subjects report that they are conscious of stimuli, such as being touched or seeing flashing lights, within 0.1 to 0.2 seconds of the event. So how can subjects report events within 0.2 seconds even though it seems to take 0.5 seconds for the cortex to generate activity that can be experienced? The simplest explanation is that the reaction occurs automatically within 0.2 seconds and then the conscious experience of this reaction occurs 0.3 seconds later. This gives a total 0.5 seconds delay before conscious experience whilst allowing fast reactions. Libet *et al.* extended their experiments by stimulating a \"relay nucleus\" in the thalamus that intercepts signals from the senses before they reach the somatosensory cortex. It was found that when this nucleus was stimulated for 0.5 seconds the subjects reported that the stimulus occurred 0.2 seconds after it had begun. When the nucleus was stimulated for less than 0.5 seconds the subjects did not report any sensation. This supports the concept of a 0.5 second delay whilst the cortex puts a stimulus in context before it is experienced. These experiments show that our experience is an output of cortical processing rather than the processing itself. If our conscious experience is non-cortical then this raises the possibility that the non-conscious cerebral cortex can perform actions without conscious control. Of course, the cortex does this all the time when we are indulging in skilled or routine behaviour. The ability of the non-conscious cortex is quite remarkable; for instance car drivers sometimes discover that they have driven for several miles without conscious experience of driving, even at the level of having no recollection of the route. !Typical recording of the readiness potential.{width="150"}Although it might be accepted that much of our everyday behaviour is automatic is there any behaviour that is definitely initiated by conscious experience? This is probably a pointless question because consciousness is about observation, not action; however, despite this there have been several experiments that have attempted to determine the relationship between consciousness and action. In 1964 Kornhuber and Deecke performed a series of experiments that measured the electrical activity from the scalp (EEG) during voluntary actions. They averaged many EEG\'s from subjects who were about to move a finger and discovered that there is an increase in scalp potential before the movement takes place. The increase in potential can start as long as 2 seconds or so before the movement and is known as the \"readiness potential\" (Bereitschaftspotential). The readiness potential is strange because it seems to contradict our conscious experience; we do not decide to move a hand and then wait 2 seconds before the hand moves. It seems that the non-conscious brain may be taking things into its own hands. Libet *et al.* (1983) extended the readiness potential experiments by asking subjects to observe a Wundt clock whilst flexing a finger. The Wundt clock had a spot of light that moved around a circle every 2.56 seconds and allowed the subjects to obtain timings that were related to their mental experiences. When the subjects flexed a finger it was found that the readiness potential occurred about 0.5 seconds before the finger moved and the subjects reported they were going to move the finger about 0.2 seconds before the movement. This suggested that a subject\'s cerebral cortex was preparing for the movement about 0.3 seconds before the subject was conscious of this. Libet\'s experiments have been reproduced elsewhere (see Keller & Heckhausen 1990). (It is important to note that the subjects in Libet\'s experiment were asked to wait until they felt the urge to move the finger.) These results are consistent with the idea of the cortex as a modelling system that constructs a consistent model of events to pass on to whatever mediates conscious experience. More recently fMRI and direct electrode recording have borne out the readiness potential experiments. Soon *et al.* (2008) allowed subjects to decide to press either a left or right button. They used fMRI to show that there was spatially organised activity in the polar frontal cortex and parietal cortex (from precuneus into posterior cingulate cortex) that predicted the conscious left/right decision and preceded it by about **seven seconds**. Rektor *et al.* (2001) used direct electrode recordings to show a 2 second latency. Haggard & Eimer (1999) and also Trevena and Miller (2002, 2009) have identified a \"Lateralized Readiness Potential\" that is correlated with the movement of a particular hand (left or right) in their EEG experiments and Trevena and Miller claim that this potential always follows the making of a conscious decision and precedes the actions being studied. However, Soon *et al.* (2008) showed that fMRI can predict which button will be used well before any conscious decision is reported. (See Haggard (2008) for a review of conscious volition). ## Perception, Imagination, Memory and Dreams ### More about Models Our dreams are clearly models that form a \'dreamworld\' but the idea that perception might be like a dream that is updated by sensation is not so obvious. Experience seems to be an active model of the world (virtual reality) based on sense data rather than a simple mapping of retinal and other sensory data. This is demonstrated by visual illusions such as the Ames Room, Spoke Illusion and Muller Lyer illusions shown below:  Notice how the circle is distorted without any distortion in the \'spokes\', it is as if the circle has been treated as a separate object by the processes in the brain that rearranged it. In all of these illusions the brain has rearranged large areas of the visual field and has managed the input as a collection of \'objects\' that are manipulated separately. Even movement seems to occur in some figures showing that the brain models the position of things:  The creation of a model is also demonstrated by the illusion of movement experienced when we watch the cinema or television. This is due to the cortical modelling that is known as \'short-range apparent motion\' rather than flicker fusion or persistence of vision. It is intriguing that, although it has been known for decades that the joining together of static images in our minds is due to modelling activity in the brain the myth that it is due to persistence of vision or flicker fusion is universal. As Anderson and Anderson (1993) noted: `Indeed, in the past decade, psychoanalytic-Marxist film scholars `\ `have retained the  model implied by persistence of vision: theirs `\ `is a passive viewer, a spectator who is "positioned," unwittingly `\ `"sutured" into the text, and victimized by excess ideology.` Our experience of the cinema is like a dream updated by sensation rather than sensation updated by interpretation. In fact the most compelling evidence for the modelling power of the brain is the existence of dreams; our dreams are often models of worlds that do not exist and involve little or no sensory input yet can involve effects as powerful as any television drama. Short range apparent motion occurs when the interval between presentations of an object is brief (c. 50-100 msecs). Motion modelling in response to longer intervals is known as long range apparent motion. There is evidence that the modelling in short range apparent motion is enhanced if the moving patterns are similar to moving human forms (such as patterns of dots outlining a person)(Thornton *et al.* 1998). The accuracy of predicting movement can actually improve if the interval between presentations is increased when human forms are used. Motion modelling can also be seen in visual illusions such as the *Waterfall Illusion* (motion aftereffect). The waterfall illusion is commonly seen after viewing a sequence of scrolling credits on the television; when the credits stop rolling it appears as if they briefly move in the opposite direction. Tootel *et al.* (1995) have used fMRI to show that this is correlated with activity in the motion modelling area of visual cortex (area MT/V5). The waterfall illusion is also associated with an intriguing aftereffect known as **storage of the motion aftereffect**. Normal motion aftereffects last for up to about ten seconds after the stimulus, however, if the subjects close their eyes for the normal duration of the aftereffect then reopen them they see the illusion for almost the normal duration. Culham *et al.* (1999) used fMRI to show that activity in area MT/V5 was low during the period when the eyes were closed then increased dramatically when the eyes were opened. This is strongly suggestive of a modelling mechanism outside MT/V5 that has adapted to motion and then models stationary data with movement in the wrong direction. Visual area MT/V5 is also involved in the separation of moving visual scenes into *sprites* or objects that move together as a whole within a scene (Muckli *et al.* 2002). The way that mental models may be the basis of ordinary reasoning was outlined by Johnson-Laird (1980), based on earlier work by Kenneth Craik. Studies of \'change blindness\' and \'inattentional blindness\', where subjects fail to spot outrageous changes in their environment, also demonstrate that we experience a model and suggest that the brain must analyse an object to incorporate it fully into the model (See for instance Rensink (2000), Simons & Rensink (2005)). ### Brain areas used in perception overlap those used in imagination and recall Functional Magnetic Resonance Imaging (fMRI) has shown that similar areas of brain are used during perception involving the senses as during imagination (Tong 2003, Kosslyn and Thompson 2003). The substrate of the mental images that occur in both modes of brain activity has not yet been found. This overlap of the brain areas used in perception with those used in imagination, memory and recall has been demonstrated in a wide range of experiments. Ganis *et al.* (2004) used fairly complex perceptual and imagination tasks that activated large areas of the brain, they found an overlap between the brain areas activated during perception and imagery. The principle areas that were different in the two tasks were found in the primary sensory areas of the visual cortex. Other areas in the visual cortex and activity in the rest of the brain showed a remarkable degree of overlap. The authors suggested that the differences in the activity of primary visual cortex may have been due to differences between the perceptual and imaginary stimuli such as speed of onset etc. The hippocampus was not activated. It is intriguing that, contrary to object imagery, spatial imagery such as predicting when a cross on a screen would fall on an imaginary letter actually seems to inhibit activity in sensory visual cortex (Aleman *et al.*). Both fMRI and blocking with transcranial magnetic stimulation (TMS) showed that the posterior parietal cortex was involved in the spatial imagery. Imagery involving places and faces activates the place and face areas that are activated during perception (Ishai *et al.* 2000). The recall and recognition of things also seems to involve very similar brain areas to those used during perception. Wheeler and Buckner (2003) showed that areas involved in perception were also involved in the recall of the perceptual stimuli. Recall causes activation of areas used in perception but also seems to use areas that may be particularly related to the process of recall iself, such as the left parietal cortex (Konishi *et al.* 2000) (Brodmann\'s area 40/39). Frontal and parietal regions are involved in the recognition of whether stimuli have been experienced before. Image generation during sleep seems to differ from that during imagination and recall. In particular it seems to involve a few well defined areas of cortex and considerable activation of the posterior thalamus. Sleep studies have shown that people dream throughout sleep. However, dreams are more frequent during the REM (rapid eye movement) periods of sleep than the NREM (non-REM) periods. Dreams are reported after 70-95% of awakenings in REM sleep and 5-10% of awakenings in NREM sleep. REM dreams are more visual than NREM dreams which are more \'thoughtlike\' (Solms 2000). Thoughtlike events (mentation) are reported after 43% of awakenings from NREM sleep. Solms (1997) found that patients who had lesions in the parietal-temporo-occipital junction reported a cessation of visual images in dreams. Solms also found that patients with lesions in the white matter inferior to the frontal horns of the lateral ventricles, in the ventromesial quadrant of the frontal lobes, also reported loss of dreaming. Loss of dreaming is also reported by leucotomised patients with frontal ventromesial damage. Damasio *et al.* (1985) and Solms (1997) also reported that some patients with damage to the medial prefrontal cortex, the anterior cingulate cortex, and the basal forebrain became confused about what was real life and what was dreaming (waking dreams occurred). Studies using fMRI show that the sensory occipital lobe (BA 18) and posterior thalamus, especially the lateral geniculate nuclei, are activated in REM sleep, weaker activations of the posterior cingulate, putamen and midbrain were also found (Wehrle *et al.* 2005, Loveblad *et al.* 1999). These findings are consistent with activation of the ponto-geniculo-occipital system (PGO) during REM. So dreams may be more like primary activations of sensory cortex than imagining or recall. This suggests that dreams have a thalamic origin or are managed via connections from the cortex through the thalamus to the visual cortex. Hallucinations seem to differ from dreams. In Charles Bonnett Syndrome patients can have clear hallucinations. These, like imaginations, seem to involve areas of the visual cortex that deal with processed data, for instance hallucinations of faces activate the \"face area\" rather than visual cortical area V1 (Ffytche *et al.* 1998). ### Suppression of data acquisition during saccades - perception as a patchwork If you look at yourself in the mirror you will not see your eyes moving even though they will be darting all over the view of your face. Even when you deliberately look from place to place your eyes will appear steady. The natural darting of the eyes from place to place as you view a scene is known as \"saccadic\" movement of the eyes. The suppression of the visual image during the motion of the eyes is known as \"saccadic suppression\" or \"saccadic masking\". The suppression of the acquisition of image data extends to suppression of awareness of flashes of light during saccades, this effect is known as \"flash suppression\", however, flash suppression seems to apply only to rather dull flashes (Volkman (1962). The suppression during saccades is probably due to suppression of the magnocellular pathway (the motion sensitive pathway) in the lateral geniculate nucleus (Burr *et al.* (1996). The most intriguing feature of this suppression of data acquisition during saccades is that each snapshot that is obtained between saccades can only contain a relatively small amount of information. This is because the fovea, which is the most sensitive area of the eye, is tiny (about 1mm diameter) and only receives input from a few degrees of the visual field. As a result what we consider to be a uniform scene in our minds is actually a patchwork of intersaccade snapshots. Another aspect of saccades is that the timing of events is referred back to the beginning of the saccade. This effect is known as \"saccadic chronostasis\". For example, if an object changes colour during a saccade the observer feels as if the colour change occurred at the beginning of the saccade, so extending the amount of time that the object possesses the changed colour. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception (see Yarrow *et al.* 2006). Burr D, Morrone M, Ross J. (1996) Selective suppression of the magnocellular visual pathway during saccades\]\'\', Behavioral Brain Research 80 1-8 (1996) <http://www.pisavisionlab.org/downloads/BBRReview96.pdf> Volkman, F. (1962). Vision during voluntary saccadic eye movements. J. Opt Soc. Am. 52:571-578. 1962. Yarrow, K, Whiteley, L, Rothwell, J.C & Haggard,P. (2006) Spatial consequences of bridging the saccadic gap. Vision Res. 2006 February; 46(4): 545--555. <http://www.hexicon.co.uk/Kielan/papers/Moving_chrono.pdf> ## Blindsight Blindsight studies illuminate the relationship between the cerebral cortex and our experience. When the visual cortex is removed subjects become almost totally blind. If the visual cortex on one side is removed subjects become relatively blind in the contra-lateral hemifield. One of the most revealing studies of blindsight is Marcel\'s 1998 paper: \" Blindsight and shape perception: deficit of visual consciousness or visual function?\". It is useful when considering blindsight to contemplate for a while the appearance of the world with both eyes closed and then with one eye closed. When both eyes are closed our experience is of a darkish space radiating out from our heads, with one eye closed we tend to ignore the darkish areas that cannot be seen even though they are still present. Marcel notes that patients who have a right blind field still have an underlying visual field on the right side and that this can even contain conscious visual experience. This sounds a bit like the darkish space that we all experience if deprived of visual input on one side. As Marcel says: \"A question that naturally arises is whether the loss is a \'total\' loss of visual consciousness in the blind field. It is often assumed to be so, especially by those who discuss blindsight without carefully reading the literature or working with the subjects. One can immediately respond negatively to the question..\" The consciousness of the completion of Kanizsa figures in blindsight patients is particularly indicative of the preservation of the field even though the content was largely missing. A Kanizsa figure is shown below:  If we put Marcel\'s observations together with cortical anatomy and function it seems that the space of our experience is located outside of the cerebral cortex. The cortex generates much of visual and other content but it does not generate the space. ## The Role of the Thalamus The thalamus is connected to the entire bottom layer of the cerebral cortex. It is the nexus of the various cortical processors as well as a recipient of independent input from most of the rest of the brain.  The thalamus is subdivided into numerous small and medium sized nuclei that between them receive inputs from every process in the nervous system (the white fibres in the illustration above largely penetrate the thalamus). The thalamic nuclei are interconnected which means that any of them could, potentially host activity from anywhere in the body or brain. Although the founders of neurology such as Hughlings Jackson and Penfield & Jasper located conscious experience in the diencephalon, including the thalamus, this is no longer the conventional wisdom. The small size of the thalamic nuclei means that they cannot support the processes that are assumed to compose access consciousness, however, even some of the smallest thalamic nuclei host millions of synapses so size would not be an obstacle if the thalamus contains the substrate of phenomenal consciousness. Indeed, the diencephalon and the thalamus in particular can be shown to be excellent candidates for a possible location of phenomenal experience.  `<font size=1>`{=html} The Intralaminar Nuclei of the thalamus. The white space above and to the left of RN is the third ventricle. MD=mediodorsal nucleus. CM=Centromedian nucleus, RN=red nucleus (not part of thalamus) The black areas are stained white fibres. Picture from: <http://www.neurophys.wisc.edu/> University of Wisconsin and Michigan State Comparative Mammalian Brain Collections. Preparation of image has been funded by the National Science Foundation, as well as by the National Institutes of Health. May only be used with these acknowledgements.`</font>`{=html} If the thalamus contains a location for conscious experience then lesions should abolish this experience. Unlike the cerebral hemispheres, lesions of the thalamus do indeed seem to abolish consciousness. The area that is most sensitive to lesions contains the Intralaminar Nuclei, especially the Parafascicular and Centromedian Nuclei. If these are damaged bilaterally patients suffer death, coma, akinetic mutism, hypersomnia, dementia and other equally serious impairments of consciousness that depend upon the size and placement of the lesions (Bogen 1995, Schiff & Plum 1999). In cases of fatal familial insomnia, in which patients exhibit many of these symptoms, there is marked neuron loss in the Intralaminar Nuclei (Budka 1998). The effect of interrupting the blood supply to the medial thalamus depends upon the severity of the damage. There is frequently initial coma. The recovery after coma is often incomplete, Krolak-Salmon *et al.* (2000) described bilateral paramedian thalamic infarcts as normally being \"followed by persisting dementia with severe mnemic disturbance, global aspontaneity and apathy.\" The symptoms of bilateral damage to the ILN can be so severe that it is possible that, even after recovery from coma, some patients may cease to be conscious and are being coordinated by automatic cortical processes. Bjornstad *et al.* (2003) and Woernera *et al.* (2005) both reported that the initial coma after bilateral paramedian infarct was accompanied by a similar pattern of EEG activity to stage 2 sleep. Woernera *et al.* (2005) also discovered that painful stimuli gave rise to a range of EEG activity, transiently breaking the stage 2 sleep pattern but without recovery of consciousness. Unfortunately even in those patients who recover consciousness Kumral *et al.* (2001) report that \"Cognitive functions in patients with bilateral paramedian infarction did not change significantly during the follow-up, in contrast to those with infarcts in varied arterial territories\" although Krolak-Salmon *et al.* (2000) did report a single patient who made a total recovery. Laureys *et al.* (2002) investigated recovery from \'persistent vegetative state\' (wakefulness without awareness). They found that overall cortical metabolism remained almost constant during recovery but that the metabolism in the prefrontal and association cortices became correlated with thalamic ILN and precuneus activity. Again confirming that thalamo-cortico-thalamic activity is required for consciousness and that cortical activity by itself is not conscious. Yamamoto *et al.* (2005) investigated persistent vegetative state and found that deep brain stimulation (25Hz) of the centromedian-parafascicular complex (19 cases) or mesencephalic reticular formation (2 cases) resulted in 8 of the patients emerging from persistent vegetative state. It is interesting that zolpidem, a GABA agonist, has recently been found to reverse PVS in some patients (Claus & Nel 2006). The effect is rapid and might be used to demonstrate the correlations that occur on recovery from PVS. As Bogen(1995) demonstrates, the ILN receive inputs, either directly or indirectly, from every part of the CNS but what do they do? Interest in the thalamus has recently been revived by the theories of Newman & Baars (1993), Baars, Newman, & Taylor1998) and Crick & Koch (1990). In Baars, Newman and Taylors\' (1998) theory it is suggested that \"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\". They also propose that the \"nucleus reticularis thalami\" (Thalamic Reticular Nucleus, TRN), which is a thin sheet of neurons that covers the thalamus, is involved in a selective attention system. This concept is reinforced by the way that point stimulation of the TRN causes focal activity in the overlying cortex (MacDonald *et al.* 1998) and the way the TRN is organised topographically (i.e.: has activity that is like an electrical image of receptor fields). The thalamus is ideally placed for integrating brain activity, if tiny parts of the thalamus are removed consciousness is abolished and the thalamus is involved in attention and the global integration of cortical activity. Any impartial judge might pronounce that the site of conscious experience has been found, possibly in the ILN of the thalamus, but no one can say how it works. ## General Anaesthesia and the Thalamus General anaesthesia should result in a profound depression of activity in the ILN if these are indeed the sites of the conscious state. White & Alkire (2003) administered halothane or isoflurane to volunteers and used positron emission tomography (PET) to monitor brain activity. They found severe depression of activity in the thalamus. The depression appeared to be higher in the non-specific nuclei than in the relay nuclei of the thalamus. In other words the anaesthesia is neither turning off the cortex nor turning off the input to the cortex but it is turning off an important part of the thalamus. Fiset *et al.* (1999) have also demonstrated a similar pattern of medial thalamic inactivity and cortical activity in propofol anaesthesia. Suppression of cortical activity is not the cause of unconsciousness; for instance, the anaesthetic agent chloralose leads to increased neural activity in the cortex relative to conscious patients (Cariani 2000). ## The function of consciousness When we walk our conscious experience does not contain data about the control of the spinal, cerebellar and vestibular reflexes that keep us on an even keel. When we reach out for a cup our conscious experience only contains data related to the need for the cup, not data about the elaborate control system that enables the action. When we talk the words just come into mind, we do not painstakingly control the syntax and vocal chords. When our attention shifts the conscious experience containing the shift happens after the attention has shifted. This passive nature of experience recurs throughout the neuroscience of consciousness from the \"readiness potential\" to the \"auditory continuity illusion\". So what does conscious observation do? The medical evidence of the lack of consciousness in some forms of delirium, mutism, PVS etc. suggest that the role of conscious observation is to stabilise the brain so that it acts as a coordinated whole. Conscious observation is an orderly arrangement of events, a stable groundform that reflects the environment and composes the stage for action. It could be speculated that if quantum events were prominent in brain function then such a groundform would be essential but even a classical brain might require a stabilising form that could be continuously compared with the world beyond the body. A stable form of neural information that contains bound data from the senses and internal neural processes is likely to have a role in the functioning of the organism. There is now an *integration consensus* that proposes that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent (see review in Baars, 2002). However, it has remained unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect. Morsella (2005) proposed a *Supramodular Interaction Theory* (SIT) that contrasts the task demands of consciously penetrable processes (e.g.: those that can be part of conscious experience such as pain, conflicting urges, and the delay of gratification) and consciously impenetrable processes (e.g.: intersensory conflicts, peristalsis, and the pupillary reflex). With this contrastive approach, SIT builds upon the integration consensus by specifying which kinds of interaction require conscious processing and which kinds do not (e.g., some intersensory processes). SIT proposes that conscious processes are required to integrate high-level systems in the brain that are vying for (specifically) skeletomotor control, as described by the principle of *parallel responses into skeletal muscle* (PRISM). Accordingly, regarding processes such as digestion and excretion, one is conscious of only those phases of the processes that require coordination with skeletomotor plans (e.g., chewing or micturating) and none of those that do not (e.g., peristalsis). From this standpoint, consciousness functions above the level of the traditional module to "cross-talk" among high-level, specialized and often multi-modal, systems. **References** Baars, B. J. (2002). The conscious access hypothesis: Origins and recent evidence. *Trends in Cognitive Sciences, 6,* 47 -- 52. Morsella, E. (2005). The function of phenomenal states: Supramodular interaction theory. *Psychological Review, 112,* 1000 - 1021. More\... Click here for Rivalries and synchronisation, bibliography and references

# Consciousness Studies/Neuroscience 1#Perception, Imagination, Memory and Dreams ## The cortex and consciousness The cerebral cortex consists of a set of specialised areas that process different aspects of sensation and motor control. There are about ten times as many nerve fibres going from the cortex to the thalamus as there are from the thalamus to the cortex (Destexhe 2000).  Histologically the cerebral cortex is a layer of greyish neurons overlying a huge mass of white nerve fibres, the cerebral medulla. The cortex consists of six main layers. The upper layers receive input from the relays in the thalamus such as the lateral geniculate, from the thalamus in general and from other areas of cortex plus a few specialised inputs from other locations. The lower layers give rise to output fibres that largely connect with the thalamus and other areas of cortex although particular specialised processors in the cortex may also have direct connections elsewhere such as to motor nuclei.  The cerebral cortex has many functions and is divided up into numerous separate processors. The most important function of the cortex from the point of view of consciousness studies is that it creates models. As was seen in Part I, philosophers debate whether these models are actually experienced consciously but in the neurophysiological literature it is normally assumed that we do experience models and rehearsals such as inner speech and imaginings. There is considerable evidence that the parts of the brain that deal with imagining (modelling) things are also the parts that deal with perception (i.e.: modelling the world). The overlap between imagination and normal perception is not complete because, as Tong(2003), in a review of visual consciousness, put it: \"Internally generated experiences share some, but not all, of the phenomenal properties of actual perception\". There is also considerable overlap between the areas used for imaginary speech (thought) and actual speech, areas dealing with the control of sensation and of the tongue etc. being used in actual speech but not in imagined speech (Fu *et al.* 2002). Kreiman *et al.* (2000) investigated the activity of single neurons in humans and also found that the brain activity evoked by visual imagination overlapped that which occurs upon direct stimulation by the same image. Our conscious experience consists of the output of the cortical modelling and perceptual processes. The cerebral cortex itself appears to be non-conscious. The evidence for the non-conscious nature of the cerebral cortex consists of lesion studies in which large amounts of cortex can be removed without removing consciousness and physiological studies in which it is demonstrated that the cerebral cortex can be active without conscious experience. Lesion studies have shown that up to 60% of the cerebral cortex can be removed without abolishing consciousness (Austin and Grant 1958). An entire hemisphere can be removed or much of the front or back of the cerebral cortex can be cut off yet consciousness persists. Fiset *et al.* (1999) and Cariani (2000) have shown that cortical activity can be normal or even elevated during the unconscious state of general anaesthesia. Alkire *et al.* (1996) also showed that cortical activity related to word recognition occurred during general anaesthesia. Libet *et al.* (1967) found that there could be cerebral cortical activity in response to weak stimulation of the skin without any conscious awareness of the stimulus. This work provides a neurophysiological basis for subliminal (non-conscious) perception and also shows that large areas of the cerebral cortex can be active without conscious experience. The insensitivity of experience to cortical activity has been further confirmed by Libet *et al.* (1979). They electrically stimulated the cerebral cortex of conscious patients and discovered that the stimulus must be continued for about 0.5 seconds for subjects to report a conscious experience of the stimulation. Libet\'s findings have been analysed at length but there still appears to be a 0.25 to 0.5 secs delay (Klein 2002). It has been demonstrated that cerebral cortical activity is not synonymous with conscious experience but why should there be a delay of up to 0.5 seconds or so between cortical stimulation and a conscious percept? What is the cortex doing in the 0.5 seconds between the start of stimulation and the report of awareness of the stimulation? It is probably synchronising its various processors and creating a waking dream, a structured set of events that accounts for the activity. The synchronisation of cerebral cortical processes will be discussed later, but what evidence is there for the cerebral cortex constructing a waking dream, or model, to describe the world? The \'Attentional Blink\' (Raymond *et al.* 1992) is consistent with the concept of the cerebral cortex being a device that creates models. In the \'Attentional Blink\' the identification of an object impairs the identification of a second object that is presented within 0.5 seconds of the first. Raymond *et al.* used a stream of letters (11 letters per second) and the identification of a first letter impaired the identification of a subsequent \'probe\' letter in the stream. If the probe letter followed the first letter within about 180 msecs it could easily be identified, suggesting that chunks of about 180 msecs of data stream are modelled together. Christmann & Leuthold (2004) have theorised that the \'Attentional Blink\' involves perceptual and central components of visual processing. This is supported by the fMRI studies of Marois *et al.* (2004) who presented subjects with faces mounted on scenes of places. The scenes of places often went undetected by subjects but they activated regions of the medial temporal cortex involved in high-level scene representations, the parahippocampal place area (PPA). When the scenes of places were detected by the subjects there was activity in the frontal cortex and the PPA activity was increased. These experiments are consistent with the idea of a cerebral cortex that is a multiprocessor system that creates consistent models of the environment. Bregman\'s (1990) auditory continuity illusion is another example of how sensory events are modelled. If a pure tone is followed by broadband noise and the noise followed by the same pure tone it seems as if the tone occurs throughout the period of noise. If the noise is not followed by the pure tone there is no sound of the tone during the period of noise. This effect is similar to the results found by Libet because a delay of several hundred milliseconds between sensory stimulation and conscious experience is needed to account for the apparent rewriting of history after the second tone appears. Dennett and Kinsbourne (1992) argued strongly against modelling as the source of conscious experience. They discussed two illusions, the \"cutaneous rabbit illusion\", in which the subject is tapped successively in such a way that some illusory taps appear and the \"phi illusion\" in which successively illuminated lights appear as a motion of the light. Dennett and Kinsbourne declared that there should be no cerebral cortical filling in of the gaps in the these illusions. Both these illusions have now been investigated. Blankenburg *et al.* (2006) found that cerebral cortical activity occurred at the locations expected for the missing taps in the \"cutaneous rabbit\" illusion and Larsen *et al.* (2006) found that the areas of cerebral cortex that would be stimulated by a moving light were active during the \"phi illusion\". ## The delay before consciousness of \"voluntary\" actions The 0.5 second delay required for the cortex to model an event has implications for the role of conscious experience in the control of our lives. If experience is about 0.5 seconds behind the true present instant then how can we be said to control anything? The brain must be acting automatically whilst performing most tasks. The 0.5 second delay also seems to contradict our everyday experience. We certainly feel like we are aware of things in less than 0.5 seconds, for example, the direct stimulation of sense organs seems to be experienced much more rapidly than the delayed experience of cortical stimulation. In fact subjects report that they are conscious of stimuli, such as being touched or seeing flashing lights, within 0.1 to 0.2 seconds of the event. So how can subjects report events within 0.2 seconds even though it seems to take 0.5 seconds for the cortex to generate activity that can be experienced? The simplest explanation is that the reaction occurs automatically within 0.2 seconds and then the conscious experience of this reaction occurs 0.3 seconds later. This gives a total 0.5 seconds delay before conscious experience whilst allowing fast reactions. Libet *et al.* extended their experiments by stimulating a \"relay nucleus\" in the thalamus that intercepts signals from the senses before they reach the somatosensory cortex. It was found that when this nucleus was stimulated for 0.5 seconds the subjects reported that the stimulus occurred 0.2 seconds after it had begun. When the nucleus was stimulated for less than 0.5 seconds the subjects did not report any sensation. This supports the concept of a 0.5 second delay whilst the cortex puts a stimulus in context before it is experienced. These experiments show that our experience is an output of cortical processing rather than the processing itself. If our conscious experience is non-cortical then this raises the possibility that the non-conscious cerebral cortex can perform actions without conscious control. Of course, the cortex does this all the time when we are indulging in skilled or routine behaviour. The ability of the non-conscious cortex is quite remarkable; for instance car drivers sometimes discover that they have driven for several miles without conscious experience of driving, even at the level of having no recollection of the route. !Typical recording of the readiness potential.{width="150"}Although it might be accepted that much of our everyday behaviour is automatic is there any behaviour that is definitely initiated by conscious experience? This is probably a pointless question because consciousness is about observation, not action; however, despite this there have been several experiments that have attempted to determine the relationship between consciousness and action. In 1964 Kornhuber and Deecke performed a series of experiments that measured the electrical activity from the scalp (EEG) during voluntary actions. They averaged many EEG\'s from subjects who were about to move a finger and discovered that there is an increase in scalp potential before the movement takes place. The increase in potential can start as long as 2 seconds or so before the movement and is known as the \"readiness potential\" (Bereitschaftspotential). The readiness potential is strange because it seems to contradict our conscious experience; we do not decide to move a hand and then wait 2 seconds before the hand moves. It seems that the non-conscious brain may be taking things into its own hands. Libet *et al.* (1983) extended the readiness potential experiments by asking subjects to observe a Wundt clock whilst flexing a finger. The Wundt clock had a spot of light that moved around a circle every 2.56 seconds and allowed the subjects to obtain timings that were related to their mental experiences. When the subjects flexed a finger it was found that the readiness potential occurred about 0.5 seconds before the finger moved and the subjects reported they were going to move the finger about 0.2 seconds before the movement. This suggested that a subject\'s cerebral cortex was preparing for the movement about 0.3 seconds before the subject was conscious of this. Libet\'s experiments have been reproduced elsewhere (see Keller & Heckhausen 1990). (It is important to note that the subjects in Libet\'s experiment were asked to wait until they felt the urge to move the finger.) These results are consistent with the idea of the cortex as a modelling system that constructs a consistent model of events to pass on to whatever mediates conscious experience. More recently fMRI and direct electrode recording have borne out the readiness potential experiments. Soon *et al.* (2008) allowed subjects to decide to press either a left or right button. They used fMRI to show that there was spatially organised activity in the polar frontal cortex and parietal cortex (from precuneus into posterior cingulate cortex) that predicted the conscious left/right decision and preceded it by about **seven seconds**. Rektor *et al.* (2001) used direct electrode recordings to show a 2 second latency. Haggard & Eimer (1999) and also Trevena and Miller (2002, 2009) have identified a \"Lateralized Readiness Potential\" that is correlated with the movement of a particular hand (left or right) in their EEG experiments and Trevena and Miller claim that this potential always follows the making of a conscious decision and precedes the actions being studied. However, Soon *et al.* (2008) showed that fMRI can predict which button will be used well before any conscious decision is reported. (See Haggard (2008) for a review of conscious volition). ## Perception, Imagination, Memory and Dreams ### More about Models Our dreams are clearly models that form a \'dreamworld\' but the idea that perception might be like a dream that is updated by sensation is not so obvious. Experience seems to be an active model of the world (virtual reality) based on sense data rather than a simple mapping of retinal and other sensory data. This is demonstrated by visual illusions such as the Ames Room, Spoke Illusion and Muller Lyer illusions shown below:  Notice how the circle is distorted without any distortion in the \'spokes\', it is as if the circle has been treated as a separate object by the processes in the brain that rearranged it. In all of these illusions the brain has rearranged large areas of the visual field and has managed the input as a collection of \'objects\' that are manipulated separately. Even movement seems to occur in some figures showing that the brain models the position of things:  The creation of a model is also demonstrated by the illusion of movement experienced when we watch the cinema or television. This is due to the cortical modelling that is known as \'short-range apparent motion\' rather than flicker fusion or persistence of vision. It is intriguing that, although it has been known for decades that the joining together of static images in our minds is due to modelling activity in the brain the myth that it is due to persistence of vision or flicker fusion is universal. As Anderson and Anderson (1993) noted: `Indeed, in the past decade, psychoanalytic-Marxist film scholars `\ `have retained the  model implied by persistence of vision: theirs `\ `is a passive viewer, a spectator who is "positioned," unwittingly `\ `"sutured" into the text, and victimized by excess ideology.` Our experience of the cinema is like a dream updated by sensation rather than sensation updated by interpretation. In fact the most compelling evidence for the modelling power of the brain is the existence of dreams; our dreams are often models of worlds that do not exist and involve little or no sensory input yet can involve effects as powerful as any television drama. Short range apparent motion occurs when the interval between presentations of an object is brief (c. 50-100 msecs). Motion modelling in response to longer intervals is known as long range apparent motion. There is evidence that the modelling in short range apparent motion is enhanced if the moving patterns are similar to moving human forms (such as patterns of dots outlining a person)(Thornton *et al.* 1998). The accuracy of predicting movement can actually improve if the interval between presentations is increased when human forms are used. Motion modelling can also be seen in visual illusions such as the *Waterfall Illusion* (motion aftereffect). The waterfall illusion is commonly seen after viewing a sequence of scrolling credits on the television; when the credits stop rolling it appears as if they briefly move in the opposite direction. Tootel *et al.* (1995) have used fMRI to show that this is correlated with activity in the motion modelling area of visual cortex (area MT/V5). The waterfall illusion is also associated with an intriguing aftereffect known as **storage of the motion aftereffect**. Normal motion aftereffects last for up to about ten seconds after the stimulus, however, if the subjects close their eyes for the normal duration of the aftereffect then reopen them they see the illusion for almost the normal duration. Culham *et al.* (1999) used fMRI to show that activity in area MT/V5 was low during the period when the eyes were closed then increased dramatically when the eyes were opened. This is strongly suggestive of a modelling mechanism outside MT/V5 that has adapted to motion and then models stationary data with movement in the wrong direction. Visual area MT/V5 is also involved in the separation of moving visual scenes into *sprites* or objects that move together as a whole within a scene (Muckli *et al.* 2002). The way that mental models may be the basis of ordinary reasoning was outlined by Johnson-Laird (1980), based on earlier work by Kenneth Craik. Studies of \'change blindness\' and \'inattentional blindness\', where subjects fail to spot outrageous changes in their environment, also demonstrate that we experience a model and suggest that the brain must analyse an object to incorporate it fully into the model (See for instance Rensink (2000), Simons & Rensink (2005)). ### Brain areas used in perception overlap those used in imagination and recall Functional Magnetic Resonance Imaging (fMRI) has shown that similar areas of brain are used during perception involving the senses as during imagination (Tong 2003, Kosslyn and Thompson 2003). The substrate of the mental images that occur in both modes of brain activity has not yet been found. This overlap of the brain areas used in perception with those used in imagination, memory and recall has been demonstrated in a wide range of experiments. Ganis *et al.* (2004) used fairly complex perceptual and imagination tasks that activated large areas of the brain, they found an overlap between the brain areas activated during perception and imagery. The principle areas that were different in the two tasks were found in the primary sensory areas of the visual cortex. Other areas in the visual cortex and activity in the rest of the brain showed a remarkable degree of overlap. The authors suggested that the differences in the activity of primary visual cortex may have been due to differences between the perceptual and imaginary stimuli such as speed of onset etc. The hippocampus was not activated. It is intriguing that, contrary to object imagery, spatial imagery such as predicting when a cross on a screen would fall on an imaginary letter actually seems to inhibit activity in sensory visual cortex (Aleman *et al.*). Both fMRI and blocking with transcranial magnetic stimulation (TMS) showed that the posterior parietal cortex was involved in the spatial imagery. Imagery involving places and faces activates the place and face areas that are activated during perception (Ishai *et al.* 2000). The recall and recognition of things also seems to involve very similar brain areas to those used during perception. Wheeler and Buckner (2003) showed that areas involved in perception were also involved in the recall of the perceptual stimuli. Recall causes activation of areas used in perception but also seems to use areas that may be particularly related to the process of recall iself, such as the left parietal cortex (Konishi *et al.* 2000) (Brodmann\'s area 40/39). Frontal and parietal regions are involved in the recognition of whether stimuli have been experienced before. Image generation during sleep seems to differ from that during imagination and recall. In particular it seems to involve a few well defined areas of cortex and considerable activation of the posterior thalamus. Sleep studies have shown that people dream throughout sleep. However, dreams are more frequent during the REM (rapid eye movement) periods of sleep than the NREM (non-REM) periods. Dreams are reported after 70-95% of awakenings in REM sleep and 5-10% of awakenings in NREM sleep. REM dreams are more visual than NREM dreams which are more \'thoughtlike\' (Solms 2000). Thoughtlike events (mentation) are reported after 43% of awakenings from NREM sleep. Solms (1997) found that patients who had lesions in the parietal-temporo-occipital junction reported a cessation of visual images in dreams. Solms also found that patients with lesions in the white matter inferior to the frontal horns of the lateral ventricles, in the ventromesial quadrant of the frontal lobes, also reported loss of dreaming. Loss of dreaming is also reported by leucotomised patients with frontal ventromesial damage. Damasio *et al.* (1985) and Solms (1997) also reported that some patients with damage to the medial prefrontal cortex, the anterior cingulate cortex, and the basal forebrain became confused about what was real life and what was dreaming (waking dreams occurred). Studies using fMRI show that the sensory occipital lobe (BA 18) and posterior thalamus, especially the lateral geniculate nuclei, are activated in REM sleep, weaker activations of the posterior cingulate, putamen and midbrain were also found (Wehrle *et al.* 2005, Loveblad *et al.* 1999). These findings are consistent with activation of the ponto-geniculo-occipital system (PGO) during REM. So dreams may be more like primary activations of sensory cortex than imagining or recall. This suggests that dreams have a thalamic origin or are managed via connections from the cortex through the thalamus to the visual cortex. Hallucinations seem to differ from dreams. In Charles Bonnett Syndrome patients can have clear hallucinations. These, like imaginations, seem to involve areas of the visual cortex that deal with processed data, for instance hallucinations of faces activate the \"face area\" rather than visual cortical area V1 (Ffytche *et al.* 1998). ### Suppression of data acquisition during saccades - perception as a patchwork If you look at yourself in the mirror you will not see your eyes moving even though they will be darting all over the view of your face. Even when you deliberately look from place to place your eyes will appear steady. The natural darting of the eyes from place to place as you view a scene is known as \"saccadic\" movement of the eyes. The suppression of the visual image during the motion of the eyes is known as \"saccadic suppression\" or \"saccadic masking\". The suppression of the acquisition of image data extends to suppression of awareness of flashes of light during saccades, this effect is known as \"flash suppression\", however, flash suppression seems to apply only to rather dull flashes (Volkman (1962). The suppression during saccades is probably due to suppression of the magnocellular pathway (the motion sensitive pathway) in the lateral geniculate nucleus (Burr *et al.* (1996). The most intriguing feature of this suppression of data acquisition during saccades is that each snapshot that is obtained between saccades can only contain a relatively small amount of information. This is because the fovea, which is the most sensitive area of the eye, is tiny (about 1mm diameter) and only receives input from a few degrees of the visual field. As a result what we consider to be a uniform scene in our minds is actually a patchwork of intersaccade snapshots. Another aspect of saccades is that the timing of events is referred back to the beginning of the saccade. This effect is known as \"saccadic chronostasis\". For example, if an object changes colour during a saccade the observer feels as if the colour change occurred at the beginning of the saccade, so extending the amount of time that the object possesses the changed colour. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception (see Yarrow *et al.* 2006). Burr D, Morrone M, Ross J. (1996) Selective suppression of the magnocellular visual pathway during saccades\]\'\', Behavioral Brain Research 80 1-8 (1996) <http://www.pisavisionlab.org/downloads/BBRReview96.pdf> Volkman, F. (1962). Vision during voluntary saccadic eye movements. J. Opt Soc. Am. 52:571-578. 1962. Yarrow, K, Whiteley, L, Rothwell, J.C & Haggard,P. (2006) Spatial consequences of bridging the saccadic gap. Vision Res. 2006 February; 46(4): 545--555. <http://www.hexicon.co.uk/Kielan/papers/Moving_chrono.pdf> ## Blindsight Blindsight studies illuminate the relationship between the cerebral cortex and our experience. When the visual cortex is removed subjects become almost totally blind. If the visual cortex on one side is removed subjects become relatively blind in the contra-lateral hemifield. One of the most revealing studies of blindsight is Marcel\'s 1998 paper: \" Blindsight and shape perception: deficit of visual consciousness or visual function?\". It is useful when considering blindsight to contemplate for a while the appearance of the world with both eyes closed and then with one eye closed. When both eyes are closed our experience is of a darkish space radiating out from our heads, with one eye closed we tend to ignore the darkish areas that cannot be seen even though they are still present. Marcel notes that patients who have a right blind field still have an underlying visual field on the right side and that this can even contain conscious visual experience. This sounds a bit like the darkish space that we all experience if deprived of visual input on one side. As Marcel says: \"A question that naturally arises is whether the loss is a \'total\' loss of visual consciousness in the blind field. It is often assumed to be so, especially by those who discuss blindsight without carefully reading the literature or working with the subjects. One can immediately respond negatively to the question..\" The consciousness of the completion of Kanizsa figures in blindsight patients is particularly indicative of the preservation of the field even though the content was largely missing. A Kanizsa figure is shown below:  If we put Marcel\'s observations together with cortical anatomy and function it seems that the space of our experience is located outside of the cerebral cortex. The cortex generates much of visual and other content but it does not generate the space. ## The Role of the Thalamus The thalamus is connected to the entire bottom layer of the cerebral cortex. It is the nexus of the various cortical processors as well as a recipient of independent input from most of the rest of the brain.  The thalamus is subdivided into numerous small and medium sized nuclei that between them receive inputs from every process in the nervous system (the white fibres in the illustration above largely penetrate the thalamus). The thalamic nuclei are interconnected which means that any of them could, potentially host activity from anywhere in the body or brain. Although the founders of neurology such as Hughlings Jackson and Penfield & Jasper located conscious experience in the diencephalon, including the thalamus, this is no longer the conventional wisdom. The small size of the thalamic nuclei means that they cannot support the processes that are assumed to compose access consciousness, however, even some of the smallest thalamic nuclei host millions of synapses so size would not be an obstacle if the thalamus contains the substrate of phenomenal consciousness. Indeed, the diencephalon and the thalamus in particular can be shown to be excellent candidates for a possible location of phenomenal experience.  `<font size=1>`{=html} The Intralaminar Nuclei of the thalamus. The white space above and to the left of RN is the third ventricle. MD=mediodorsal nucleus. CM=Centromedian nucleus, RN=red nucleus (not part of thalamus) The black areas are stained white fibres. Picture from: <http://www.neurophys.wisc.edu/> University of Wisconsin and Michigan State Comparative Mammalian Brain Collections. Preparation of image has been funded by the National Science Foundation, as well as by the National Institutes of Health. May only be used with these acknowledgements.`</font>`{=html} If the thalamus contains a location for conscious experience then lesions should abolish this experience. Unlike the cerebral hemispheres, lesions of the thalamus do indeed seem to abolish consciousness. The area that is most sensitive to lesions contains the Intralaminar Nuclei, especially the Parafascicular and Centromedian Nuclei. If these are damaged bilaterally patients suffer death, coma, akinetic mutism, hypersomnia, dementia and other equally serious impairments of consciousness that depend upon the size and placement of the lesions (Bogen 1995, Schiff & Plum 1999). In cases of fatal familial insomnia, in which patients exhibit many of these symptoms, there is marked neuron loss in the Intralaminar Nuclei (Budka 1998). The effect of interrupting the blood supply to the medial thalamus depends upon the severity of the damage. There is frequently initial coma. The recovery after coma is often incomplete, Krolak-Salmon *et al.* (2000) described bilateral paramedian thalamic infarcts as normally being \"followed by persisting dementia with severe mnemic disturbance, global aspontaneity and apathy.\" The symptoms of bilateral damage to the ILN can be so severe that it is possible that, even after recovery from coma, some patients may cease to be conscious and are being coordinated by automatic cortical processes. Bjornstad *et al.* (2003) and Woernera *et al.* (2005) both reported that the initial coma after bilateral paramedian infarct was accompanied by a similar pattern of EEG activity to stage 2 sleep. Woernera *et al.* (2005) also discovered that painful stimuli gave rise to a range of EEG activity, transiently breaking the stage 2 sleep pattern but without recovery of consciousness. Unfortunately even in those patients who recover consciousness Kumral *et al.* (2001) report that \"Cognitive functions in patients with bilateral paramedian infarction did not change significantly during the follow-up, in contrast to those with infarcts in varied arterial territories\" although Krolak-Salmon *et al.* (2000) did report a single patient who made a total recovery. Laureys *et al.* (2002) investigated recovery from \'persistent vegetative state\' (wakefulness without awareness). They found that overall cortical metabolism remained almost constant during recovery but that the metabolism in the prefrontal and association cortices became correlated with thalamic ILN and precuneus activity. Again confirming that thalamo-cortico-thalamic activity is required for consciousness and that cortical activity by itself is not conscious. Yamamoto *et al.* (2005) investigated persistent vegetative state and found that deep brain stimulation (25Hz) of the centromedian-parafascicular complex (19 cases) or mesencephalic reticular formation (2 cases) resulted in 8 of the patients emerging from persistent vegetative state. It is interesting that zolpidem, a GABA agonist, has recently been found to reverse PVS in some patients (Claus & Nel 2006). The effect is rapid and might be used to demonstrate the correlations that occur on recovery from PVS. As Bogen(1995) demonstrates, the ILN receive inputs, either directly or indirectly, from every part of the CNS but what do they do? Interest in the thalamus has recently been revived by the theories of Newman & Baars (1993), Baars, Newman, & Taylor1998) and Crick & Koch (1990). In Baars, Newman and Taylors\' (1998) theory it is suggested that \"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\". They also propose that the \"nucleus reticularis thalami\" (Thalamic Reticular Nucleus, TRN), which is a thin sheet of neurons that covers the thalamus, is involved in a selective attention system. This concept is reinforced by the way that point stimulation of the TRN causes focal activity in the overlying cortex (MacDonald *et al.* 1998) and the way the TRN is organised topographically (i.e.: has activity that is like an electrical image of receptor fields). The thalamus is ideally placed for integrating brain activity, if tiny parts of the thalamus are removed consciousness is abolished and the thalamus is involved in attention and the global integration of cortical activity. Any impartial judge might pronounce that the site of conscious experience has been found, possibly in the ILN of the thalamus, but no one can say how it works. ## General Anaesthesia and the Thalamus General anaesthesia should result in a profound depression of activity in the ILN if these are indeed the sites of the conscious state. White & Alkire (2003) administered halothane or isoflurane to volunteers and used positron emission tomography (PET) to monitor brain activity. They found severe depression of activity in the thalamus. The depression appeared to be higher in the non-specific nuclei than in the relay nuclei of the thalamus. In other words the anaesthesia is neither turning off the cortex nor turning off the input to the cortex but it is turning off an important part of the thalamus. Fiset *et al.* (1999) have also demonstrated a similar pattern of medial thalamic inactivity and cortical activity in propofol anaesthesia. Suppression of cortical activity is not the cause of unconsciousness; for instance, the anaesthetic agent chloralose leads to increased neural activity in the cortex relative to conscious patients (Cariani 2000). ## The function of consciousness When we walk our conscious experience does not contain data about the control of the spinal, cerebellar and vestibular reflexes that keep us on an even keel. When we reach out for a cup our conscious experience only contains data related to the need for the cup, not data about the elaborate control system that enables the action. When we talk the words just come into mind, we do not painstakingly control the syntax and vocal chords. When our attention shifts the conscious experience containing the shift happens after the attention has shifted. This passive nature of experience recurs throughout the neuroscience of consciousness from the \"readiness potential\" to the \"auditory continuity illusion\". So what does conscious observation do? The medical evidence of the lack of consciousness in some forms of delirium, mutism, PVS etc. suggest that the role of conscious observation is to stabilise the brain so that it acts as a coordinated whole. Conscious observation is an orderly arrangement of events, a stable groundform that reflects the environment and composes the stage for action. It could be speculated that if quantum events were prominent in brain function then such a groundform would be essential but even a classical brain might require a stabilising form that could be continuously compared with the world beyond the body. A stable form of neural information that contains bound data from the senses and internal neural processes is likely to have a role in the functioning of the organism. There is now an *integration consensus* that proposes that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent (see review in Baars, 2002). However, it has remained unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect. Morsella (2005) proposed a *Supramodular Interaction Theory* (SIT) that contrasts the task demands of consciously penetrable processes (e.g.: those that can be part of conscious experience such as pain, conflicting urges, and the delay of gratification) and consciously impenetrable processes (e.g.: intersensory conflicts, peristalsis, and the pupillary reflex). With this contrastive approach, SIT builds upon the integration consensus by specifying which kinds of interaction require conscious processing and which kinds do not (e.g., some intersensory processes). SIT proposes that conscious processes are required to integrate high-level systems in the brain that are vying for (specifically) skeletomotor control, as described by the principle of *parallel responses into skeletal muscle* (PRISM). Accordingly, regarding processes such as digestion and excretion, one is conscious of only those phases of the processes that require coordination with skeletomotor plans (e.g., chewing or micturating) and none of those that do not (e.g., peristalsis). From this standpoint, consciousness functions above the level of the traditional module to "cross-talk" among high-level, specialized and often multi-modal, systems. **References** Baars, B. J. (2002). The conscious access hypothesis: Origins and recent evidence. *Trends in Cognitive Sciences, 6,* 47 -- 52. Morsella, E. (2005). The function of phenomenal states: Supramodular interaction theory. *Psychological Review, 112,* 1000 - 1021. More\... Click here for Rivalries and synchronisation, bibliography and references

# Consciousness Studies/Neuroscience 1#More about Models ## The cortex and consciousness The cerebral cortex consists of a set of specialised areas that process different aspects of sensation and motor control. There are about ten times as many nerve fibres going from the cortex to the thalamus as there are from the thalamus to the cortex (Destexhe 2000).  Histologically the cerebral cortex is a layer of greyish neurons overlying a huge mass of white nerve fibres, the cerebral medulla. The cortex consists of six main layers. The upper layers receive input from the relays in the thalamus such as the lateral geniculate, from the thalamus in general and from other areas of cortex plus a few specialised inputs from other locations. The lower layers give rise to output fibres that largely connect with the thalamus and other areas of cortex although particular specialised processors in the cortex may also have direct connections elsewhere such as to motor nuclei.  The cerebral cortex has many functions and is divided up into numerous separate processors. The most important function of the cortex from the point of view of consciousness studies is that it creates models. As was seen in Part I, philosophers debate whether these models are actually experienced consciously but in the neurophysiological literature it is normally assumed that we do experience models and rehearsals such as inner speech and imaginings. There is considerable evidence that the parts of the brain that deal with imagining (modelling) things are also the parts that deal with perception (i.e.: modelling the world). The overlap between imagination and normal perception is not complete because, as Tong(2003), in a review of visual consciousness, put it: \"Internally generated experiences share some, but not all, of the phenomenal properties of actual perception\". There is also considerable overlap between the areas used for imaginary speech (thought) and actual speech, areas dealing with the control of sensation and of the tongue etc. being used in actual speech but not in imagined speech (Fu *et al.* 2002). Kreiman *et al.* (2000) investigated the activity of single neurons in humans and also found that the brain activity evoked by visual imagination overlapped that which occurs upon direct stimulation by the same image. Our conscious experience consists of the output of the cortical modelling and perceptual processes. The cerebral cortex itself appears to be non-conscious. The evidence for the non-conscious nature of the cerebral cortex consists of lesion studies in which large amounts of cortex can be removed without removing consciousness and physiological studies in which it is demonstrated that the cerebral cortex can be active without conscious experience. Lesion studies have shown that up to 60% of the cerebral cortex can be removed without abolishing consciousness (Austin and Grant 1958). An entire hemisphere can be removed or much of the front or back of the cerebral cortex can be cut off yet consciousness persists. Fiset *et al.* (1999) and Cariani (2000) have shown that cortical activity can be normal or even elevated during the unconscious state of general anaesthesia. Alkire *et al.* (1996) also showed that cortical activity related to word recognition occurred during general anaesthesia. Libet *et al.* (1967) found that there could be cerebral cortical activity in response to weak stimulation of the skin without any conscious awareness of the stimulus. This work provides a neurophysiological basis for subliminal (non-conscious) perception and also shows that large areas of the cerebral cortex can be active without conscious experience. The insensitivity of experience to cortical activity has been further confirmed by Libet *et al.* (1979). They electrically stimulated the cerebral cortex of conscious patients and discovered that the stimulus must be continued for about 0.5 seconds for subjects to report a conscious experience of the stimulation. Libet\'s findings have been analysed at length but there still appears to be a 0.25 to 0.5 secs delay (Klein 2002). It has been demonstrated that cerebral cortical activity is not synonymous with conscious experience but why should there be a delay of up to 0.5 seconds or so between cortical stimulation and a conscious percept? What is the cortex doing in the 0.5 seconds between the start of stimulation and the report of awareness of the stimulation? It is probably synchronising its various processors and creating a waking dream, a structured set of events that accounts for the activity. The synchronisation of cerebral cortical processes will be discussed later, but what evidence is there for the cerebral cortex constructing a waking dream, or model, to describe the world? The \'Attentional Blink\' (Raymond *et al.* 1992) is consistent with the concept of the cerebral cortex being a device that creates models. In the \'Attentional Blink\' the identification of an object impairs the identification of a second object that is presented within 0.5 seconds of the first. Raymond *et al.* used a stream of letters (11 letters per second) and the identification of a first letter impaired the identification of a subsequent \'probe\' letter in the stream. If the probe letter followed the first letter within about 180 msecs it could easily be identified, suggesting that chunks of about 180 msecs of data stream are modelled together. Christmann & Leuthold (2004) have theorised that the \'Attentional Blink\' involves perceptual and central components of visual processing. This is supported by the fMRI studies of Marois *et al.* (2004) who presented subjects with faces mounted on scenes of places. The scenes of places often went undetected by subjects but they activated regions of the medial temporal cortex involved in high-level scene representations, the parahippocampal place area (PPA). When the scenes of places were detected by the subjects there was activity in the frontal cortex and the PPA activity was increased. These experiments are consistent with the idea of a cerebral cortex that is a multiprocessor system that creates consistent models of the environment. Bregman\'s (1990) auditory continuity illusion is another example of how sensory events are modelled. If a pure tone is followed by broadband noise and the noise followed by the same pure tone it seems as if the tone occurs throughout the period of noise. If the noise is not followed by the pure tone there is no sound of the tone during the period of noise. This effect is similar to the results found by Libet because a delay of several hundred milliseconds between sensory stimulation and conscious experience is needed to account for the apparent rewriting of history after the second tone appears. Dennett and Kinsbourne (1992) argued strongly against modelling as the source of conscious experience. They discussed two illusions, the \"cutaneous rabbit illusion\", in which the subject is tapped successively in such a way that some illusory taps appear and the \"phi illusion\" in which successively illuminated lights appear as a motion of the light. Dennett and Kinsbourne declared that there should be no cerebral cortical filling in of the gaps in the these illusions. Both these illusions have now been investigated. Blankenburg *et al.* (2006) found that cerebral cortical activity occurred at the locations expected for the missing taps in the \"cutaneous rabbit\" illusion and Larsen *et al.* (2006) found that the areas of cerebral cortex that would be stimulated by a moving light were active during the \"phi illusion\". ## The delay before consciousness of \"voluntary\" actions The 0.5 second delay required for the cortex to model an event has implications for the role of conscious experience in the control of our lives. If experience is about 0.5 seconds behind the true present instant then how can we be said to control anything? The brain must be acting automatically whilst performing most tasks. The 0.5 second delay also seems to contradict our everyday experience. We certainly feel like we are aware of things in less than 0.5 seconds, for example, the direct stimulation of sense organs seems to be experienced much more rapidly than the delayed experience of cortical stimulation. In fact subjects report that they are conscious of stimuli, such as being touched or seeing flashing lights, within 0.1 to 0.2 seconds of the event. So how can subjects report events within 0.2 seconds even though it seems to take 0.5 seconds for the cortex to generate activity that can be experienced? The simplest explanation is that the reaction occurs automatically within 0.2 seconds and then the conscious experience of this reaction occurs 0.3 seconds later. This gives a total 0.5 seconds delay before conscious experience whilst allowing fast reactions. Libet *et al.* extended their experiments by stimulating a \"relay nucleus\" in the thalamus that intercepts signals from the senses before they reach the somatosensory cortex. It was found that when this nucleus was stimulated for 0.5 seconds the subjects reported that the stimulus occurred 0.2 seconds after it had begun. When the nucleus was stimulated for less than 0.5 seconds the subjects did not report any sensation. This supports the concept of a 0.5 second delay whilst the cortex puts a stimulus in context before it is experienced. These experiments show that our experience is an output of cortical processing rather than the processing itself. If our conscious experience is non-cortical then this raises the possibility that the non-conscious cerebral cortex can perform actions without conscious control. Of course, the cortex does this all the time when we are indulging in skilled or routine behaviour. The ability of the non-conscious cortex is quite remarkable; for instance car drivers sometimes discover that they have driven for several miles without conscious experience of driving, even at the level of having no recollection of the route. !Typical recording of the readiness potential.{width="150"}Although it might be accepted that much of our everyday behaviour is automatic is there any behaviour that is definitely initiated by conscious experience? This is probably a pointless question because consciousness is about observation, not action; however, despite this there have been several experiments that have attempted to determine the relationship between consciousness and action. In 1964 Kornhuber and Deecke performed a series of experiments that measured the electrical activity from the scalp (EEG) during voluntary actions. They averaged many EEG\'s from subjects who were about to move a finger and discovered that there is an increase in scalp potential before the movement takes place. The increase in potential can start as long as 2 seconds or so before the movement and is known as the \"readiness potential\" (Bereitschaftspotential). The readiness potential is strange because it seems to contradict our conscious experience; we do not decide to move a hand and then wait 2 seconds before the hand moves. It seems that the non-conscious brain may be taking things into its own hands. Libet *et al.* (1983) extended the readiness potential experiments by asking subjects to observe a Wundt clock whilst flexing a finger. The Wundt clock had a spot of light that moved around a circle every 2.56 seconds and allowed the subjects to obtain timings that were related to their mental experiences. When the subjects flexed a finger it was found that the readiness potential occurred about 0.5 seconds before the finger moved and the subjects reported they were going to move the finger about 0.2 seconds before the movement. This suggested that a subject\'s cerebral cortex was preparing for the movement about 0.3 seconds before the subject was conscious of this. Libet\'s experiments have been reproduced elsewhere (see Keller & Heckhausen 1990). (It is important to note that the subjects in Libet\'s experiment were asked to wait until they felt the urge to move the finger.) These results are consistent with the idea of the cortex as a modelling system that constructs a consistent model of events to pass on to whatever mediates conscious experience. More recently fMRI and direct electrode recording have borne out the readiness potential experiments. Soon *et al.* (2008) allowed subjects to decide to press either a left or right button. They used fMRI to show that there was spatially organised activity in the polar frontal cortex and parietal cortex (from precuneus into posterior cingulate cortex) that predicted the conscious left/right decision and preceded it by about **seven seconds**. Rektor *et al.* (2001) used direct electrode recordings to show a 2 second latency. Haggard & Eimer (1999) and also Trevena and Miller (2002, 2009) have identified a \"Lateralized Readiness Potential\" that is correlated with the movement of a particular hand (left or right) in their EEG experiments and Trevena and Miller claim that this potential always follows the making of a conscious decision and precedes the actions being studied. However, Soon *et al.* (2008) showed that fMRI can predict which button will be used well before any conscious decision is reported. (See Haggard (2008) for a review of conscious volition). ## Perception, Imagination, Memory and Dreams ### More about Models Our dreams are clearly models that form a \'dreamworld\' but the idea that perception might be like a dream that is updated by sensation is not so obvious. Experience seems to be an active model of the world (virtual reality) based on sense data rather than a simple mapping of retinal and other sensory data. This is demonstrated by visual illusions such as the Ames Room, Spoke Illusion and Muller Lyer illusions shown below:  Notice how the circle is distorted without any distortion in the \'spokes\', it is as if the circle has been treated as a separate object by the processes in the brain that rearranged it. In all of these illusions the brain has rearranged large areas of the visual field and has managed the input as a collection of \'objects\' that are manipulated separately. Even movement seems to occur in some figures showing that the brain models the position of things:  The creation of a model is also demonstrated by the illusion of movement experienced when we watch the cinema or television. This is due to the cortical modelling that is known as \'short-range apparent motion\' rather than flicker fusion or persistence of vision. It is intriguing that, although it has been known for decades that the joining together of static images in our minds is due to modelling activity in the brain the myth that it is due to persistence of vision or flicker fusion is universal. As Anderson and Anderson (1993) noted: `Indeed, in the past decade, psychoanalytic-Marxist film scholars `\ `have retained the  model implied by persistence of vision: theirs `\ `is a passive viewer, a spectator who is "positioned," unwittingly `\ `"sutured" into the text, and victimized by excess ideology.` Our experience of the cinema is like a dream updated by sensation rather than sensation updated by interpretation. In fact the most compelling evidence for the modelling power of the brain is the existence of dreams; our dreams are often models of worlds that do not exist and involve little or no sensory input yet can involve effects as powerful as any television drama. Short range apparent motion occurs when the interval between presentations of an object is brief (c. 50-100 msecs). Motion modelling in response to longer intervals is known as long range apparent motion. There is evidence that the modelling in short range apparent motion is enhanced if the moving patterns are similar to moving human forms (such as patterns of dots outlining a person)(Thornton *et al.* 1998). The accuracy of predicting movement can actually improve if the interval between presentations is increased when human forms are used. Motion modelling can also be seen in visual illusions such as the *Waterfall Illusion* (motion aftereffect). The waterfall illusion is commonly seen after viewing a sequence of scrolling credits on the television; when the credits stop rolling it appears as if they briefly move in the opposite direction. Tootel *et al.* (1995) have used fMRI to show that this is correlated with activity in the motion modelling area of visual cortex (area MT/V5). The waterfall illusion is also associated with an intriguing aftereffect known as **storage of the motion aftereffect**. Normal motion aftereffects last for up to about ten seconds after the stimulus, however, if the subjects close their eyes for the normal duration of the aftereffect then reopen them they see the illusion for almost the normal duration. Culham *et al.* (1999) used fMRI to show that activity in area MT/V5 was low during the period when the eyes were closed then increased dramatically when the eyes were opened. This is strongly suggestive of a modelling mechanism outside MT/V5 that has adapted to motion and then models stationary data with movement in the wrong direction. Visual area MT/V5 is also involved in the separation of moving visual scenes into *sprites* or objects that move together as a whole within a scene (Muckli *et al.* 2002). The way that mental models may be the basis of ordinary reasoning was outlined by Johnson-Laird (1980), based on earlier work by Kenneth Craik. Studies of \'change blindness\' and \'inattentional blindness\', where subjects fail to spot outrageous changes in their environment, also demonstrate that we experience a model and suggest that the brain must analyse an object to incorporate it fully into the model (See for instance Rensink (2000), Simons & Rensink (2005)). ### Brain areas used in perception overlap those used in imagination and recall Functional Magnetic Resonance Imaging (fMRI) has shown that similar areas of brain are used during perception involving the senses as during imagination (Tong 2003, Kosslyn and Thompson 2003). The substrate of the mental images that occur in both modes of brain activity has not yet been found. This overlap of the brain areas used in perception with those used in imagination, memory and recall has been demonstrated in a wide range of experiments. Ganis *et al.* (2004) used fairly complex perceptual and imagination tasks that activated large areas of the brain, they found an overlap between the brain areas activated during perception and imagery. The principle areas that were different in the two tasks were found in the primary sensory areas of the visual cortex. Other areas in the visual cortex and activity in the rest of the brain showed a remarkable degree of overlap. The authors suggested that the differences in the activity of primary visual cortex may have been due to differences between the perceptual and imaginary stimuli such as speed of onset etc. The hippocampus was not activated. It is intriguing that, contrary to object imagery, spatial imagery such as predicting when a cross on a screen would fall on an imaginary letter actually seems to inhibit activity in sensory visual cortex (Aleman *et al.*). Both fMRI and blocking with transcranial magnetic stimulation (TMS) showed that the posterior parietal cortex was involved in the spatial imagery. Imagery involving places and faces activates the place and face areas that are activated during perception (Ishai *et al.* 2000). The recall and recognition of things also seems to involve very similar brain areas to those used during perception. Wheeler and Buckner (2003) showed that areas involved in perception were also involved in the recall of the perceptual stimuli. Recall causes activation of areas used in perception but also seems to use areas that may be particularly related to the process of recall iself, such as the left parietal cortex (Konishi *et al.* 2000) (Brodmann\'s area 40/39). Frontal and parietal regions are involved in the recognition of whether stimuli have been experienced before. Image generation during sleep seems to differ from that during imagination and recall. In particular it seems to involve a few well defined areas of cortex and considerable activation of the posterior thalamus. Sleep studies have shown that people dream throughout sleep. However, dreams are more frequent during the REM (rapid eye movement) periods of sleep than the NREM (non-REM) periods. Dreams are reported after 70-95% of awakenings in REM sleep and 5-10% of awakenings in NREM sleep. REM dreams are more visual than NREM dreams which are more \'thoughtlike\' (Solms 2000). Thoughtlike events (mentation) are reported after 43% of awakenings from NREM sleep. Solms (1997) found that patients who had lesions in the parietal-temporo-occipital junction reported a cessation of visual images in dreams. Solms also found that patients with lesions in the white matter inferior to the frontal horns of the lateral ventricles, in the ventromesial quadrant of the frontal lobes, also reported loss of dreaming. Loss of dreaming is also reported by leucotomised patients with frontal ventromesial damage. Damasio *et al.* (1985) and Solms (1997) also reported that some patients with damage to the medial prefrontal cortex, the anterior cingulate cortex, and the basal forebrain became confused about what was real life and what was dreaming (waking dreams occurred). Studies using fMRI show that the sensory occipital lobe (BA 18) and posterior thalamus, especially the lateral geniculate nuclei, are activated in REM sleep, weaker activations of the posterior cingulate, putamen and midbrain were also found (Wehrle *et al.* 2005, Loveblad *et al.* 1999). These findings are consistent with activation of the ponto-geniculo-occipital system (PGO) during REM. So dreams may be more like primary activations of sensory cortex than imagining or recall. This suggests that dreams have a thalamic origin or are managed via connections from the cortex through the thalamus to the visual cortex. Hallucinations seem to differ from dreams. In Charles Bonnett Syndrome patients can have clear hallucinations. These, like imaginations, seem to involve areas of the visual cortex that deal with processed data, for instance hallucinations of faces activate the \"face area\" rather than visual cortical area V1 (Ffytche *et al.* 1998). ### Suppression of data acquisition during saccades - perception as a patchwork If you look at yourself in the mirror you will not see your eyes moving even though they will be darting all over the view of your face. Even when you deliberately look from place to place your eyes will appear steady. The natural darting of the eyes from place to place as you view a scene is known as \"saccadic\" movement of the eyes. The suppression of the visual image during the motion of the eyes is known as \"saccadic suppression\" or \"saccadic masking\". The suppression of the acquisition of image data extends to suppression of awareness of flashes of light during saccades, this effect is known as \"flash suppression\", however, flash suppression seems to apply only to rather dull flashes (Volkman (1962). The suppression during saccades is probably due to suppression of the magnocellular pathway (the motion sensitive pathway) in the lateral geniculate nucleus (Burr *et al.* (1996). The most intriguing feature of this suppression of data acquisition during saccades is that each snapshot that is obtained between saccades can only contain a relatively small amount of information. This is because the fovea, which is the most sensitive area of the eye, is tiny (about 1mm diameter) and only receives input from a few degrees of the visual field. As a result what we consider to be a uniform scene in our minds is actually a patchwork of intersaccade snapshots. Another aspect of saccades is that the timing of events is referred back to the beginning of the saccade. This effect is known as \"saccadic chronostasis\". For example, if an object changes colour during a saccade the observer feels as if the colour change occurred at the beginning of the saccade, so extending the amount of time that the object possesses the changed colour. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception (see Yarrow *et al.* 2006). Burr D, Morrone M, Ross J. (1996) Selective suppression of the magnocellular visual pathway during saccades\]\'\', Behavioral Brain Research 80 1-8 (1996) <http://www.pisavisionlab.org/downloads/BBRReview96.pdf> Volkman, F. (1962). Vision during voluntary saccadic eye movements. J. Opt Soc. Am. 52:571-578. 1962. Yarrow, K, Whiteley, L, Rothwell, J.C & Haggard,P. (2006) Spatial consequences of bridging the saccadic gap. Vision Res. 2006 February; 46(4): 545--555. <http://www.hexicon.co.uk/Kielan/papers/Moving_chrono.pdf> ## Blindsight Blindsight studies illuminate the relationship between the cerebral cortex and our experience. When the visual cortex is removed subjects become almost totally blind. If the visual cortex on one side is removed subjects become relatively blind in the contra-lateral hemifield. One of the most revealing studies of blindsight is Marcel\'s 1998 paper: \" Blindsight and shape perception: deficit of visual consciousness or visual function?\". It is useful when considering blindsight to contemplate for a while the appearance of the world with both eyes closed and then with one eye closed. When both eyes are closed our experience is of a darkish space radiating out from our heads, with one eye closed we tend to ignore the darkish areas that cannot be seen even though they are still present. Marcel notes that patients who have a right blind field still have an underlying visual field on the right side and that this can even contain conscious visual experience. This sounds a bit like the darkish space that we all experience if deprived of visual input on one side. As Marcel says: \"A question that naturally arises is whether the loss is a \'total\' loss of visual consciousness in the blind field. It is often assumed to be so, especially by those who discuss blindsight without carefully reading the literature or working with the subjects. One can immediately respond negatively to the question..\" The consciousness of the completion of Kanizsa figures in blindsight patients is particularly indicative of the preservation of the field even though the content was largely missing. A Kanizsa figure is shown below:  If we put Marcel\'s observations together with cortical anatomy and function it seems that the space of our experience is located outside of the cerebral cortex. The cortex generates much of visual and other content but it does not generate the space. ## The Role of the Thalamus The thalamus is connected to the entire bottom layer of the cerebral cortex. It is the nexus of the various cortical processors as well as a recipient of independent input from most of the rest of the brain.  The thalamus is subdivided into numerous small and medium sized nuclei that between them receive inputs from every process in the nervous system (the white fibres in the illustration above largely penetrate the thalamus). The thalamic nuclei are interconnected which means that any of them could, potentially host activity from anywhere in the body or brain. Although the founders of neurology such as Hughlings Jackson and Penfield & Jasper located conscious experience in the diencephalon, including the thalamus, this is no longer the conventional wisdom. The small size of the thalamic nuclei means that they cannot support the processes that are assumed to compose access consciousness, however, even some of the smallest thalamic nuclei host millions of synapses so size would not be an obstacle if the thalamus contains the substrate of phenomenal consciousness. Indeed, the diencephalon and the thalamus in particular can be shown to be excellent candidates for a possible location of phenomenal experience.  `<font size=1>`{=html} The Intralaminar Nuclei of the thalamus. The white space above and to the left of RN is the third ventricle. MD=mediodorsal nucleus. CM=Centromedian nucleus, RN=red nucleus (not part of thalamus) The black areas are stained white fibres. Picture from: <http://www.neurophys.wisc.edu/> University of Wisconsin and Michigan State Comparative Mammalian Brain Collections. Preparation of image has been funded by the National Science Foundation, as well as by the National Institutes of Health. May only be used with these acknowledgements.`</font>`{=html} If the thalamus contains a location for conscious experience then lesions should abolish this experience. Unlike the cerebral hemispheres, lesions of the thalamus do indeed seem to abolish consciousness. The area that is most sensitive to lesions contains the Intralaminar Nuclei, especially the Parafascicular and Centromedian Nuclei. If these are damaged bilaterally patients suffer death, coma, akinetic mutism, hypersomnia, dementia and other equally serious impairments of consciousness that depend upon the size and placement of the lesions (Bogen 1995, Schiff & Plum 1999). In cases of fatal familial insomnia, in which patients exhibit many of these symptoms, there is marked neuron loss in the Intralaminar Nuclei (Budka 1998). The effect of interrupting the blood supply to the medial thalamus depends upon the severity of the damage. There is frequently initial coma. The recovery after coma is often incomplete, Krolak-Salmon *et al.* (2000) described bilateral paramedian thalamic infarcts as normally being \"followed by persisting dementia with severe mnemic disturbance, global aspontaneity and apathy.\" The symptoms of bilateral damage to the ILN can be so severe that it is possible that, even after recovery from coma, some patients may cease to be conscious and are being coordinated by automatic cortical processes. Bjornstad *et al.* (2003) and Woernera *et al.* (2005) both reported that the initial coma after bilateral paramedian infarct was accompanied by a similar pattern of EEG activity to stage 2 sleep. Woernera *et al.* (2005) also discovered that painful stimuli gave rise to a range of EEG activity, transiently breaking the stage 2 sleep pattern but without recovery of consciousness. Unfortunately even in those patients who recover consciousness Kumral *et al.* (2001) report that \"Cognitive functions in patients with bilateral paramedian infarction did not change significantly during the follow-up, in contrast to those with infarcts in varied arterial territories\" although Krolak-Salmon *et al.* (2000) did report a single patient who made a total recovery. Laureys *et al.* (2002) investigated recovery from \'persistent vegetative state\' (wakefulness without awareness). They found that overall cortical metabolism remained almost constant during recovery but that the metabolism in the prefrontal and association cortices became correlated with thalamic ILN and precuneus activity. Again confirming that thalamo-cortico-thalamic activity is required for consciousness and that cortical activity by itself is not conscious. Yamamoto *et al.* (2005) investigated persistent vegetative state and found that deep brain stimulation (25Hz) of the centromedian-parafascicular complex (19 cases) or mesencephalic reticular formation (2 cases) resulted in 8 of the patients emerging from persistent vegetative state. It is interesting that zolpidem, a GABA agonist, has recently been found to reverse PVS in some patients (Claus & Nel 2006). The effect is rapid and might be used to demonstrate the correlations that occur on recovery from PVS. As Bogen(1995) demonstrates, the ILN receive inputs, either directly or indirectly, from every part of the CNS but what do they do? Interest in the thalamus has recently been revived by the theories of Newman & Baars (1993), Baars, Newman, & Taylor1998) and Crick & Koch (1990). In Baars, Newman and Taylors\' (1998) theory it is suggested that \"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\". They also propose that the \"nucleus reticularis thalami\" (Thalamic Reticular Nucleus, TRN), which is a thin sheet of neurons that covers the thalamus, is involved in a selective attention system. This concept is reinforced by the way that point stimulation of the TRN causes focal activity in the overlying cortex (MacDonald *et al.* 1998) and the way the TRN is organised topographically (i.e.: has activity that is like an electrical image of receptor fields). The thalamus is ideally placed for integrating brain activity, if tiny parts of the thalamus are removed consciousness is abolished and the thalamus is involved in attention and the global integration of cortical activity. Any impartial judge might pronounce that the site of conscious experience has been found, possibly in the ILN of the thalamus, but no one can say how it works. ## General Anaesthesia and the Thalamus General anaesthesia should result in a profound depression of activity in the ILN if these are indeed the sites of the conscious state. White & Alkire (2003) administered halothane or isoflurane to volunteers and used positron emission tomography (PET) to monitor brain activity. They found severe depression of activity in the thalamus. The depression appeared to be higher in the non-specific nuclei than in the relay nuclei of the thalamus. In other words the anaesthesia is neither turning off the cortex nor turning off the input to the cortex but it is turning off an important part of the thalamus. Fiset *et al.* (1999) have also demonstrated a similar pattern of medial thalamic inactivity and cortical activity in propofol anaesthesia. Suppression of cortical activity is not the cause of unconsciousness; for instance, the anaesthetic agent chloralose leads to increased neural activity in the cortex relative to conscious patients (Cariani 2000). ## The function of consciousness When we walk our conscious experience does not contain data about the control of the spinal, cerebellar and vestibular reflexes that keep us on an even keel. When we reach out for a cup our conscious experience only contains data related to the need for the cup, not data about the elaborate control system that enables the action. When we talk the words just come into mind, we do not painstakingly control the syntax and vocal chords. When our attention shifts the conscious experience containing the shift happens after the attention has shifted. This passive nature of experience recurs throughout the neuroscience of consciousness from the \"readiness potential\" to the \"auditory continuity illusion\". So what does conscious observation do? The medical evidence of the lack of consciousness in some forms of delirium, mutism, PVS etc. suggest that the role of conscious observation is to stabilise the brain so that it acts as a coordinated whole. Conscious observation is an orderly arrangement of events, a stable groundform that reflects the environment and composes the stage for action. It could be speculated that if quantum events were prominent in brain function then such a groundform would be essential but even a classical brain might require a stabilising form that could be continuously compared with the world beyond the body. A stable form of neural information that contains bound data from the senses and internal neural processes is likely to have a role in the functioning of the organism. There is now an *integration consensus* that proposes that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent (see review in Baars, 2002). However, it has remained unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect. Morsella (2005) proposed a *Supramodular Interaction Theory* (SIT) that contrasts the task demands of consciously penetrable processes (e.g.: those that can be part of conscious experience such as pain, conflicting urges, and the delay of gratification) and consciously impenetrable processes (e.g.: intersensory conflicts, peristalsis, and the pupillary reflex). With this contrastive approach, SIT builds upon the integration consensus by specifying which kinds of interaction require conscious processing and which kinds do not (e.g., some intersensory processes). SIT proposes that conscious processes are required to integrate high-level systems in the brain that are vying for (specifically) skeletomotor control, as described by the principle of *parallel responses into skeletal muscle* (PRISM). Accordingly, regarding processes such as digestion and excretion, one is conscious of only those phases of the processes that require coordination with skeletomotor plans (e.g., chewing or micturating) and none of those that do not (e.g., peristalsis). From this standpoint, consciousness functions above the level of the traditional module to "cross-talk" among high-level, specialized and often multi-modal, systems. **References** Baars, B. J. (2002). The conscious access hypothesis: Origins and recent evidence. *Trends in Cognitive Sciences, 6,* 47 -- 52. Morsella, E. (2005). The function of phenomenal states: Supramodular interaction theory. *Psychological Review, 112,* 1000 - 1021. More\... Click here for Rivalries and synchronisation, bibliography and references

# Consciousness Studies/Neuroscience 1#Blindsight ## The cortex and consciousness The cerebral cortex consists of a set of specialised areas that process different aspects of sensation and motor control. There are about ten times as many nerve fibres going from the cortex to the thalamus as there are from the thalamus to the cortex (Destexhe 2000).  Histologically the cerebral cortex is a layer of greyish neurons overlying a huge mass of white nerve fibres, the cerebral medulla. The cortex consists of six main layers. The upper layers receive input from the relays in the thalamus such as the lateral geniculate, from the thalamus in general and from other areas of cortex plus a few specialised inputs from other locations. The lower layers give rise to output fibres that largely connect with the thalamus and other areas of cortex although particular specialised processors in the cortex may also have direct connections elsewhere such as to motor nuclei.  The cerebral cortex has many functions and is divided up into numerous separate processors. The most important function of the cortex from the point of view of consciousness studies is that it creates models. As was seen in Part I, philosophers debate whether these models are actually experienced consciously but in the neurophysiological literature it is normally assumed that we do experience models and rehearsals such as inner speech and imaginings. There is considerable evidence that the parts of the brain that deal with imagining (modelling) things are also the parts that deal with perception (i.e.: modelling the world). The overlap between imagination and normal perception is not complete because, as Tong(2003), in a review of visual consciousness, put it: \"Internally generated experiences share some, but not all, of the phenomenal properties of actual perception\". There is also considerable overlap between the areas used for imaginary speech (thought) and actual speech, areas dealing with the control of sensation and of the tongue etc. being used in actual speech but not in imagined speech (Fu *et al.* 2002). Kreiman *et al.* (2000) investigated the activity of single neurons in humans and also found that the brain activity evoked by visual imagination overlapped that which occurs upon direct stimulation by the same image. Our conscious experience consists of the output of the cortical modelling and perceptual processes. The cerebral cortex itself appears to be non-conscious. The evidence for the non-conscious nature of the cerebral cortex consists of lesion studies in which large amounts of cortex can be removed without removing consciousness and physiological studies in which it is demonstrated that the cerebral cortex can be active without conscious experience. Lesion studies have shown that up to 60% of the cerebral cortex can be removed without abolishing consciousness (Austin and Grant 1958). An entire hemisphere can be removed or much of the front or back of the cerebral cortex can be cut off yet consciousness persists. Fiset *et al.* (1999) and Cariani (2000) have shown that cortical activity can be normal or even elevated during the unconscious state of general anaesthesia. Alkire *et al.* (1996) also showed that cortical activity related to word recognition occurred during general anaesthesia. Libet *et al.* (1967) found that there could be cerebral cortical activity in response to weak stimulation of the skin without any conscious awareness of the stimulus. This work provides a neurophysiological basis for subliminal (non-conscious) perception and also shows that large areas of the cerebral cortex can be active without conscious experience. The insensitivity of experience to cortical activity has been further confirmed by Libet *et al.* (1979). They electrically stimulated the cerebral cortex of conscious patients and discovered that the stimulus must be continued for about 0.5 seconds for subjects to report a conscious experience of the stimulation. Libet\'s findings have been analysed at length but there still appears to be a 0.25 to 0.5 secs delay (Klein 2002). It has been demonstrated that cerebral cortical activity is not synonymous with conscious experience but why should there be a delay of up to 0.5 seconds or so between cortical stimulation and a conscious percept? What is the cortex doing in the 0.5 seconds between the start of stimulation and the report of awareness of the stimulation? It is probably synchronising its various processors and creating a waking dream, a structured set of events that accounts for the activity. The synchronisation of cerebral cortical processes will be discussed later, but what evidence is there for the cerebral cortex constructing a waking dream, or model, to describe the world? The \'Attentional Blink\' (Raymond *et al.* 1992) is consistent with the concept of the cerebral cortex being a device that creates models. In the \'Attentional Blink\' the identification of an object impairs the identification of a second object that is presented within 0.5 seconds of the first. Raymond *et al.* used a stream of letters (11 letters per second) and the identification of a first letter impaired the identification of a subsequent \'probe\' letter in the stream. If the probe letter followed the first letter within about 180 msecs it could easily be identified, suggesting that chunks of about 180 msecs of data stream are modelled together. Christmann & Leuthold (2004) have theorised that the \'Attentional Blink\' involves perceptual and central components of visual processing. This is supported by the fMRI studies of Marois *et al.* (2004) who presented subjects with faces mounted on scenes of places. The scenes of places often went undetected by subjects but they activated regions of the medial temporal cortex involved in high-level scene representations, the parahippocampal place area (PPA). When the scenes of places were detected by the subjects there was activity in the frontal cortex and the PPA activity was increased. These experiments are consistent with the idea of a cerebral cortex that is a multiprocessor system that creates consistent models of the environment. Bregman\'s (1990) auditory continuity illusion is another example of how sensory events are modelled. If a pure tone is followed by broadband noise and the noise followed by the same pure tone it seems as if the tone occurs throughout the period of noise. If the noise is not followed by the pure tone there is no sound of the tone during the period of noise. This effect is similar to the results found by Libet because a delay of several hundred milliseconds between sensory stimulation and conscious experience is needed to account for the apparent rewriting of history after the second tone appears. Dennett and Kinsbourne (1992) argued strongly against modelling as the source of conscious experience. They discussed two illusions, the \"cutaneous rabbit illusion\", in which the subject is tapped successively in such a way that some illusory taps appear and the \"phi illusion\" in which successively illuminated lights appear as a motion of the light. Dennett and Kinsbourne declared that there should be no cerebral cortical filling in of the gaps in the these illusions. Both these illusions have now been investigated. Blankenburg *et al.* (2006) found that cerebral cortical activity occurred at the locations expected for the missing taps in the \"cutaneous rabbit\" illusion and Larsen *et al.* (2006) found that the areas of cerebral cortex that would be stimulated by a moving light were active during the \"phi illusion\". ## The delay before consciousness of \"voluntary\" actions The 0.5 second delay required for the cortex to model an event has implications for the role of conscious experience in the control of our lives. If experience is about 0.5 seconds behind the true present instant then how can we be said to control anything? The brain must be acting automatically whilst performing most tasks. The 0.5 second delay also seems to contradict our everyday experience. We certainly feel like we are aware of things in less than 0.5 seconds, for example, the direct stimulation of sense organs seems to be experienced much more rapidly than the delayed experience of cortical stimulation. In fact subjects report that they are conscious of stimuli, such as being touched or seeing flashing lights, within 0.1 to 0.2 seconds of the event. So how can subjects report events within 0.2 seconds even though it seems to take 0.5 seconds for the cortex to generate activity that can be experienced? The simplest explanation is that the reaction occurs automatically within 0.2 seconds and then the conscious experience of this reaction occurs 0.3 seconds later. This gives a total 0.5 seconds delay before conscious experience whilst allowing fast reactions. Libet *et al.* extended their experiments by stimulating a \"relay nucleus\" in the thalamus that intercepts signals from the senses before they reach the somatosensory cortex. It was found that when this nucleus was stimulated for 0.5 seconds the subjects reported that the stimulus occurred 0.2 seconds after it had begun. When the nucleus was stimulated for less than 0.5 seconds the subjects did not report any sensation. This supports the concept of a 0.5 second delay whilst the cortex puts a stimulus in context before it is experienced. These experiments show that our experience is an output of cortical processing rather than the processing itself. If our conscious experience is non-cortical then this raises the possibility that the non-conscious cerebral cortex can perform actions without conscious control. Of course, the cortex does this all the time when we are indulging in skilled or routine behaviour. The ability of the non-conscious cortex is quite remarkable; for instance car drivers sometimes discover that they have driven for several miles without conscious experience of driving, even at the level of having no recollection of the route. !Typical recording of the readiness potential.{width="150"}Although it might be accepted that much of our everyday behaviour is automatic is there any behaviour that is definitely initiated by conscious experience? This is probably a pointless question because consciousness is about observation, not action; however, despite this there have been several experiments that have attempted to determine the relationship between consciousness and action. In 1964 Kornhuber and Deecke performed a series of experiments that measured the electrical activity from the scalp (EEG) during voluntary actions. They averaged many EEG\'s from subjects who were about to move a finger and discovered that there is an increase in scalp potential before the movement takes place. The increase in potential can start as long as 2 seconds or so before the movement and is known as the \"readiness potential\" (Bereitschaftspotential). The readiness potential is strange because it seems to contradict our conscious experience; we do not decide to move a hand and then wait 2 seconds before the hand moves. It seems that the non-conscious brain may be taking things into its own hands. Libet *et al.* (1983) extended the readiness potential experiments by asking subjects to observe a Wundt clock whilst flexing a finger. The Wundt clock had a spot of light that moved around a circle every 2.56 seconds and allowed the subjects to obtain timings that were related to their mental experiences. When the subjects flexed a finger it was found that the readiness potential occurred about 0.5 seconds before the finger moved and the subjects reported they were going to move the finger about 0.2 seconds before the movement. This suggested that a subject\'s cerebral cortex was preparing for the movement about 0.3 seconds before the subject was conscious of this. Libet\'s experiments have been reproduced elsewhere (see Keller & Heckhausen 1990). (It is important to note that the subjects in Libet\'s experiment were asked to wait until they felt the urge to move the finger.) These results are consistent with the idea of the cortex as a modelling system that constructs a consistent model of events to pass on to whatever mediates conscious experience. More recently fMRI and direct electrode recording have borne out the readiness potential experiments. Soon *et al.* (2008) allowed subjects to decide to press either a left or right button. They used fMRI to show that there was spatially organised activity in the polar frontal cortex and parietal cortex (from precuneus into posterior cingulate cortex) that predicted the conscious left/right decision and preceded it by about **seven seconds**. Rektor *et al.* (2001) used direct electrode recordings to show a 2 second latency. Haggard & Eimer (1999) and also Trevena and Miller (2002, 2009) have identified a \"Lateralized Readiness Potential\" that is correlated with the movement of a particular hand (left or right) in their EEG experiments and Trevena and Miller claim that this potential always follows the making of a conscious decision and precedes the actions being studied. However, Soon *et al.* (2008) showed that fMRI can predict which button will be used well before any conscious decision is reported. (See Haggard (2008) for a review of conscious volition). ## Perception, Imagination, Memory and Dreams ### More about Models Our dreams are clearly models that form a \'dreamworld\' but the idea that perception might be like a dream that is updated by sensation is not so obvious. Experience seems to be an active model of the world (virtual reality) based on sense data rather than a simple mapping of retinal and other sensory data. This is demonstrated by visual illusions such as the Ames Room, Spoke Illusion and Muller Lyer illusions shown below:  Notice how the circle is distorted without any distortion in the \'spokes\', it is as if the circle has been treated as a separate object by the processes in the brain that rearranged it. In all of these illusions the brain has rearranged large areas of the visual field and has managed the input as a collection of \'objects\' that are manipulated separately. Even movement seems to occur in some figures showing that the brain models the position of things:  The creation of a model is also demonstrated by the illusion of movement experienced when we watch the cinema or television. This is due to the cortical modelling that is known as \'short-range apparent motion\' rather than flicker fusion or persistence of vision. It is intriguing that, although it has been known for decades that the joining together of static images in our minds is due to modelling activity in the brain the myth that it is due to persistence of vision or flicker fusion is universal. As Anderson and Anderson (1993) noted: `Indeed, in the past decade, psychoanalytic-Marxist film scholars `\ `have retained the  model implied by persistence of vision: theirs `\ `is a passive viewer, a spectator who is "positioned," unwittingly `\ `"sutured" into the text, and victimized by excess ideology.` Our experience of the cinema is like a dream updated by sensation rather than sensation updated by interpretation. In fact the most compelling evidence for the modelling power of the brain is the existence of dreams; our dreams are often models of worlds that do not exist and involve little or no sensory input yet can involve effects as powerful as any television drama. Short range apparent motion occurs when the interval between presentations of an object is brief (c. 50-100 msecs). Motion modelling in response to longer intervals is known as long range apparent motion. There is evidence that the modelling in short range apparent motion is enhanced if the moving patterns are similar to moving human forms (such as patterns of dots outlining a person)(Thornton *et al.* 1998). The accuracy of predicting movement can actually improve if the interval between presentations is increased when human forms are used. Motion modelling can also be seen in visual illusions such as the *Waterfall Illusion* (motion aftereffect). The waterfall illusion is commonly seen after viewing a sequence of scrolling credits on the television; when the credits stop rolling it appears as if they briefly move in the opposite direction. Tootel *et al.* (1995) have used fMRI to show that this is correlated with activity in the motion modelling area of visual cortex (area MT/V5). The waterfall illusion is also associated with an intriguing aftereffect known as **storage of the motion aftereffect**. Normal motion aftereffects last for up to about ten seconds after the stimulus, however, if the subjects close their eyes for the normal duration of the aftereffect then reopen them they see the illusion for almost the normal duration. Culham *et al.* (1999) used fMRI to show that activity in area MT/V5 was low during the period when the eyes were closed then increased dramatically when the eyes were opened. This is strongly suggestive of a modelling mechanism outside MT/V5 that has adapted to motion and then models stationary data with movement in the wrong direction. Visual area MT/V5 is also involved in the separation of moving visual scenes into *sprites* or objects that move together as a whole within a scene (Muckli *et al.* 2002). The way that mental models may be the basis of ordinary reasoning was outlined by Johnson-Laird (1980), based on earlier work by Kenneth Craik. Studies of \'change blindness\' and \'inattentional blindness\', where subjects fail to spot outrageous changes in their environment, also demonstrate that we experience a model and suggest that the brain must analyse an object to incorporate it fully into the model (See for instance Rensink (2000), Simons & Rensink (2005)). ### Brain areas used in perception overlap those used in imagination and recall Functional Magnetic Resonance Imaging (fMRI) has shown that similar areas of brain are used during perception involving the senses as during imagination (Tong 2003, Kosslyn and Thompson 2003). The substrate of the mental images that occur in both modes of brain activity has not yet been found. This overlap of the brain areas used in perception with those used in imagination, memory and recall has been demonstrated in a wide range of experiments. Ganis *et al.* (2004) used fairly complex perceptual and imagination tasks that activated large areas of the brain, they found an overlap between the brain areas activated during perception and imagery. The principle areas that were different in the two tasks were found in the primary sensory areas of the visual cortex. Other areas in the visual cortex and activity in the rest of the brain showed a remarkable degree of overlap. The authors suggested that the differences in the activity of primary visual cortex may have been due to differences between the perceptual and imaginary stimuli such as speed of onset etc. The hippocampus was not activated. It is intriguing that, contrary to object imagery, spatial imagery such as predicting when a cross on a screen would fall on an imaginary letter actually seems to inhibit activity in sensory visual cortex (Aleman *et al.*). Both fMRI and blocking with transcranial magnetic stimulation (TMS) showed that the posterior parietal cortex was involved in the spatial imagery. Imagery involving places and faces activates the place and face areas that are activated during perception (Ishai *et al.* 2000). The recall and recognition of things also seems to involve very similar brain areas to those used during perception. Wheeler and Buckner (2003) showed that areas involved in perception were also involved in the recall of the perceptual stimuli. Recall causes activation of areas used in perception but also seems to use areas that may be particularly related to the process of recall iself, such as the left parietal cortex (Konishi *et al.* 2000) (Brodmann\'s area 40/39). Frontal and parietal regions are involved in the recognition of whether stimuli have been experienced before. Image generation during sleep seems to differ from that during imagination and recall. In particular it seems to involve a few well defined areas of cortex and considerable activation of the posterior thalamus. Sleep studies have shown that people dream throughout sleep. However, dreams are more frequent during the REM (rapid eye movement) periods of sleep than the NREM (non-REM) periods. Dreams are reported after 70-95% of awakenings in REM sleep and 5-10% of awakenings in NREM sleep. REM dreams are more visual than NREM dreams which are more \'thoughtlike\' (Solms 2000). Thoughtlike events (mentation) are reported after 43% of awakenings from NREM sleep. Solms (1997) found that patients who had lesions in the parietal-temporo-occipital junction reported a cessation of visual images in dreams. Solms also found that patients with lesions in the white matter inferior to the frontal horns of the lateral ventricles, in the ventromesial quadrant of the frontal lobes, also reported loss of dreaming. Loss of dreaming is also reported by leucotomised patients with frontal ventromesial damage. Damasio *et al.* (1985) and Solms (1997) also reported that some patients with damage to the medial prefrontal cortex, the anterior cingulate cortex, and the basal forebrain became confused about what was real life and what was dreaming (waking dreams occurred). Studies using fMRI show that the sensory occipital lobe (BA 18) and posterior thalamus, especially the lateral geniculate nuclei, are activated in REM sleep, weaker activations of the posterior cingulate, putamen and midbrain were also found (Wehrle *et al.* 2005, Loveblad *et al.* 1999). These findings are consistent with activation of the ponto-geniculo-occipital system (PGO) during REM. So dreams may be more like primary activations of sensory cortex than imagining or recall. This suggests that dreams have a thalamic origin or are managed via connections from the cortex through the thalamus to the visual cortex. Hallucinations seem to differ from dreams. In Charles Bonnett Syndrome patients can have clear hallucinations. These, like imaginations, seem to involve areas of the visual cortex that deal with processed data, for instance hallucinations of faces activate the \"face area\" rather than visual cortical area V1 (Ffytche *et al.* 1998). ### Suppression of data acquisition during saccades - perception as a patchwork If you look at yourself in the mirror you will not see your eyes moving even though they will be darting all over the view of your face. Even when you deliberately look from place to place your eyes will appear steady. The natural darting of the eyes from place to place as you view a scene is known as \"saccadic\" movement of the eyes. The suppression of the visual image during the motion of the eyes is known as \"saccadic suppression\" or \"saccadic masking\". The suppression of the acquisition of image data extends to suppression of awareness of flashes of light during saccades, this effect is known as \"flash suppression\", however, flash suppression seems to apply only to rather dull flashes (Volkman (1962). The suppression during saccades is probably due to suppression of the magnocellular pathway (the motion sensitive pathway) in the lateral geniculate nucleus (Burr *et al.* (1996). The most intriguing feature of this suppression of data acquisition during saccades is that each snapshot that is obtained between saccades can only contain a relatively small amount of information. This is because the fovea, which is the most sensitive area of the eye, is tiny (about 1mm diameter) and only receives input from a few degrees of the visual field. As a result what we consider to be a uniform scene in our minds is actually a patchwork of intersaccade snapshots. Another aspect of saccades is that the timing of events is referred back to the beginning of the saccade. This effect is known as \"saccadic chronostasis\". For example, if an object changes colour during a saccade the observer feels as if the colour change occurred at the beginning of the saccade, so extending the amount of time that the object possesses the changed colour. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception (see Yarrow *et al.* 2006). Burr D, Morrone M, Ross J. (1996) Selective suppression of the magnocellular visual pathway during saccades\]\'\', Behavioral Brain Research 80 1-8 (1996) <http://www.pisavisionlab.org/downloads/BBRReview96.pdf> Volkman, F. (1962). Vision during voluntary saccadic eye movements. J. Opt Soc. Am. 52:571-578. 1962. Yarrow, K, Whiteley, L, Rothwell, J.C & Haggard,P. (2006) Spatial consequences of bridging the saccadic gap. Vision Res. 2006 February; 46(4): 545--555. <http://www.hexicon.co.uk/Kielan/papers/Moving_chrono.pdf> ## Blindsight Blindsight studies illuminate the relationship between the cerebral cortex and our experience. When the visual cortex is removed subjects become almost totally blind. If the visual cortex on one side is removed subjects become relatively blind in the contra-lateral hemifield. One of the most revealing studies of blindsight is Marcel\'s 1998 paper: \" Blindsight and shape perception: deficit of visual consciousness or visual function?\". It is useful when considering blindsight to contemplate for a while the appearance of the world with both eyes closed and then with one eye closed. When both eyes are closed our experience is of a darkish space radiating out from our heads, with one eye closed we tend to ignore the darkish areas that cannot be seen even though they are still present. Marcel notes that patients who have a right blind field still have an underlying visual field on the right side and that this can even contain conscious visual experience. This sounds a bit like the darkish space that we all experience if deprived of visual input on one side. As Marcel says: \"A question that naturally arises is whether the loss is a \'total\' loss of visual consciousness in the blind field. It is often assumed to be so, especially by those who discuss blindsight without carefully reading the literature or working with the subjects. One can immediately respond negatively to the question..\" The consciousness of the completion of Kanizsa figures in blindsight patients is particularly indicative of the preservation of the field even though the content was largely missing. A Kanizsa figure is shown below:  If we put Marcel\'s observations together with cortical anatomy and function it seems that the space of our experience is located outside of the cerebral cortex. The cortex generates much of visual and other content but it does not generate the space. ## The Role of the Thalamus The thalamus is connected to the entire bottom layer of the cerebral cortex. It is the nexus of the various cortical processors as well as a recipient of independent input from most of the rest of the brain.  The thalamus is subdivided into numerous small and medium sized nuclei that between them receive inputs from every process in the nervous system (the white fibres in the illustration above largely penetrate the thalamus). The thalamic nuclei are interconnected which means that any of them could, potentially host activity from anywhere in the body or brain. Although the founders of neurology such as Hughlings Jackson and Penfield & Jasper located conscious experience in the diencephalon, including the thalamus, this is no longer the conventional wisdom. The small size of the thalamic nuclei means that they cannot support the processes that are assumed to compose access consciousness, however, even some of the smallest thalamic nuclei host millions of synapses so size would not be an obstacle if the thalamus contains the substrate of phenomenal consciousness. Indeed, the diencephalon and the thalamus in particular can be shown to be excellent candidates for a possible location of phenomenal experience.  `<font size=1>`{=html} The Intralaminar Nuclei of the thalamus. The white space above and to the left of RN is the third ventricle. MD=mediodorsal nucleus. CM=Centromedian nucleus, RN=red nucleus (not part of thalamus) The black areas are stained white fibres. Picture from: <http://www.neurophys.wisc.edu/> University of Wisconsin and Michigan State Comparative Mammalian Brain Collections. Preparation of image has been funded by the National Science Foundation, as well as by the National Institutes of Health. May only be used with these acknowledgements.`</font>`{=html} If the thalamus contains a location for conscious experience then lesions should abolish this experience. Unlike the cerebral hemispheres, lesions of the thalamus do indeed seem to abolish consciousness. The area that is most sensitive to lesions contains the Intralaminar Nuclei, especially the Parafascicular and Centromedian Nuclei. If these are damaged bilaterally patients suffer death, coma, akinetic mutism, hypersomnia, dementia and other equally serious impairments of consciousness that depend upon the size and placement of the lesions (Bogen 1995, Schiff & Plum 1999). In cases of fatal familial insomnia, in which patients exhibit many of these symptoms, there is marked neuron loss in the Intralaminar Nuclei (Budka 1998). The effect of interrupting the blood supply to the medial thalamus depends upon the severity of the damage. There is frequently initial coma. The recovery after coma is often incomplete, Krolak-Salmon *et al.* (2000) described bilateral paramedian thalamic infarcts as normally being \"followed by persisting dementia with severe mnemic disturbance, global aspontaneity and apathy.\" The symptoms of bilateral damage to the ILN can be so severe that it is possible that, even after recovery from coma, some patients may cease to be conscious and are being coordinated by automatic cortical processes. Bjornstad *et al.* (2003) and Woernera *et al.* (2005) both reported that the initial coma after bilateral paramedian infarct was accompanied by a similar pattern of EEG activity to stage 2 sleep. Woernera *et al.* (2005) also discovered that painful stimuli gave rise to a range of EEG activity, transiently breaking the stage 2 sleep pattern but without recovery of consciousness. Unfortunately even in those patients who recover consciousness Kumral *et al.* (2001) report that \"Cognitive functions in patients with bilateral paramedian infarction did not change significantly during the follow-up, in contrast to those with infarcts in varied arterial territories\" although Krolak-Salmon *et al.* (2000) did report a single patient who made a total recovery. Laureys *et al.* (2002) investigated recovery from \'persistent vegetative state\' (wakefulness without awareness). They found that overall cortical metabolism remained almost constant during recovery but that the metabolism in the prefrontal and association cortices became correlated with thalamic ILN and precuneus activity. Again confirming that thalamo-cortico-thalamic activity is required for consciousness and that cortical activity by itself is not conscious. Yamamoto *et al.* (2005) investigated persistent vegetative state and found that deep brain stimulation (25Hz) of the centromedian-parafascicular complex (19 cases) or mesencephalic reticular formation (2 cases) resulted in 8 of the patients emerging from persistent vegetative state. It is interesting that zolpidem, a GABA agonist, has recently been found to reverse PVS in some patients (Claus & Nel 2006). The effect is rapid and might be used to demonstrate the correlations that occur on recovery from PVS. As Bogen(1995) demonstrates, the ILN receive inputs, either directly or indirectly, from every part of the CNS but what do they do? Interest in the thalamus has recently been revived by the theories of Newman & Baars (1993), Baars, Newman, & Taylor1998) and Crick & Koch (1990). In Baars, Newman and Taylors\' (1998) theory it is suggested that \"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\". They also propose that the \"nucleus reticularis thalami\" (Thalamic Reticular Nucleus, TRN), which is a thin sheet of neurons that covers the thalamus, is involved in a selective attention system. This concept is reinforced by the way that point stimulation of the TRN causes focal activity in the overlying cortex (MacDonald *et al.* 1998) and the way the TRN is organised topographically (i.e.: has activity that is like an electrical image of receptor fields). The thalamus is ideally placed for integrating brain activity, if tiny parts of the thalamus are removed consciousness is abolished and the thalamus is involved in attention and the global integration of cortical activity. Any impartial judge might pronounce that the site of conscious experience has been found, possibly in the ILN of the thalamus, but no one can say how it works. ## General Anaesthesia and the Thalamus General anaesthesia should result in a profound depression of activity in the ILN if these are indeed the sites of the conscious state. White & Alkire (2003) administered halothane or isoflurane to volunteers and used positron emission tomography (PET) to monitor brain activity. They found severe depression of activity in the thalamus. The depression appeared to be higher in the non-specific nuclei than in the relay nuclei of the thalamus. In other words the anaesthesia is neither turning off the cortex nor turning off the input to the cortex but it is turning off an important part of the thalamus. Fiset *et al.* (1999) have also demonstrated a similar pattern of medial thalamic inactivity and cortical activity in propofol anaesthesia. Suppression of cortical activity is not the cause of unconsciousness; for instance, the anaesthetic agent chloralose leads to increased neural activity in the cortex relative to conscious patients (Cariani 2000). ## The function of consciousness When we walk our conscious experience does not contain data about the control of the spinal, cerebellar and vestibular reflexes that keep us on an even keel. When we reach out for a cup our conscious experience only contains data related to the need for the cup, not data about the elaborate control system that enables the action. When we talk the words just come into mind, we do not painstakingly control the syntax and vocal chords. When our attention shifts the conscious experience containing the shift happens after the attention has shifted. This passive nature of experience recurs throughout the neuroscience of consciousness from the \"readiness potential\" to the \"auditory continuity illusion\". So what does conscious observation do? The medical evidence of the lack of consciousness in some forms of delirium, mutism, PVS etc. suggest that the role of conscious observation is to stabilise the brain so that it acts as a coordinated whole. Conscious observation is an orderly arrangement of events, a stable groundform that reflects the environment and composes the stage for action. It could be speculated that if quantum events were prominent in brain function then such a groundform would be essential but even a classical brain might require a stabilising form that could be continuously compared with the world beyond the body. A stable form of neural information that contains bound data from the senses and internal neural processes is likely to have a role in the functioning of the organism. There is now an *integration consensus* that proposes that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent (see review in Baars, 2002). However, it has remained unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect. Morsella (2005) proposed a *Supramodular Interaction Theory* (SIT) that contrasts the task demands of consciously penetrable processes (e.g.: those that can be part of conscious experience such as pain, conflicting urges, and the delay of gratification) and consciously impenetrable processes (e.g.: intersensory conflicts, peristalsis, and the pupillary reflex). With this contrastive approach, SIT builds upon the integration consensus by specifying which kinds of interaction require conscious processing and which kinds do not (e.g., some intersensory processes). SIT proposes that conscious processes are required to integrate high-level systems in the brain that are vying for (specifically) skeletomotor control, as described by the principle of *parallel responses into skeletal muscle* (PRISM). Accordingly, regarding processes such as digestion and excretion, one is conscious of only those phases of the processes that require coordination with skeletomotor plans (e.g., chewing or micturating) and none of those that do not (e.g., peristalsis). From this standpoint, consciousness functions above the level of the traditional module to "cross-talk" among high-level, specialized and often multi-modal, systems. **References** Baars, B. J. (2002). The conscious access hypothesis: Origins and recent evidence. *Trends in Cognitive Sciences, 6,* 47 -- 52. Morsella, E. (2005). The function of phenomenal states: Supramodular interaction theory. *Psychological Review, 112,* 1000 - 1021. More\... Click here for Rivalries and synchronisation, bibliography and references

# Consciousness Studies/Neuroscience 1#The Role of the Thalamus ## The cortex and consciousness The cerebral cortex consists of a set of specialised areas that process different aspects of sensation and motor control. There are about ten times as many nerve fibres going from the cortex to the thalamus as there are from the thalamus to the cortex (Destexhe 2000).  Histologically the cerebral cortex is a layer of greyish neurons overlying a huge mass of white nerve fibres, the cerebral medulla. The cortex consists of six main layers. The upper layers receive input from the relays in the thalamus such as the lateral geniculate, from the thalamus in general and from other areas of cortex plus a few specialised inputs from other locations. The lower layers give rise to output fibres that largely connect with the thalamus and other areas of cortex although particular specialised processors in the cortex may also have direct connections elsewhere such as to motor nuclei.  The cerebral cortex has many functions and is divided up into numerous separate processors. The most important function of the cortex from the point of view of consciousness studies is that it creates models. As was seen in Part I, philosophers debate whether these models are actually experienced consciously but in the neurophysiological literature it is normally assumed that we do experience models and rehearsals such as inner speech and imaginings. There is considerable evidence that the parts of the brain that deal with imagining (modelling) things are also the parts that deal with perception (i.e.: modelling the world). The overlap between imagination and normal perception is not complete because, as Tong(2003), in a review of visual consciousness, put it: \"Internally generated experiences share some, but not all, of the phenomenal properties of actual perception\". There is also considerable overlap between the areas used for imaginary speech (thought) and actual speech, areas dealing with the control of sensation and of the tongue etc. being used in actual speech but not in imagined speech (Fu *et al.* 2002). Kreiman *et al.* (2000) investigated the activity of single neurons in humans and also found that the brain activity evoked by visual imagination overlapped that which occurs upon direct stimulation by the same image. Our conscious experience consists of the output of the cortical modelling and perceptual processes. The cerebral cortex itself appears to be non-conscious. The evidence for the non-conscious nature of the cerebral cortex consists of lesion studies in which large amounts of cortex can be removed without removing consciousness and physiological studies in which it is demonstrated that the cerebral cortex can be active without conscious experience. Lesion studies have shown that up to 60% of the cerebral cortex can be removed without abolishing consciousness (Austin and Grant 1958). An entire hemisphere can be removed or much of the front or back of the cerebral cortex can be cut off yet consciousness persists. Fiset *et al.* (1999) and Cariani (2000) have shown that cortical activity can be normal or even elevated during the unconscious state of general anaesthesia. Alkire *et al.* (1996) also showed that cortical activity related to word recognition occurred during general anaesthesia. Libet *et al.* (1967) found that there could be cerebral cortical activity in response to weak stimulation of the skin without any conscious awareness of the stimulus. This work provides a neurophysiological basis for subliminal (non-conscious) perception and also shows that large areas of the cerebral cortex can be active without conscious experience. The insensitivity of experience to cortical activity has been further confirmed by Libet *et al.* (1979). They electrically stimulated the cerebral cortex of conscious patients and discovered that the stimulus must be continued for about 0.5 seconds for subjects to report a conscious experience of the stimulation. Libet\'s findings have been analysed at length but there still appears to be a 0.25 to 0.5 secs delay (Klein 2002). It has been demonstrated that cerebral cortical activity is not synonymous with conscious experience but why should there be a delay of up to 0.5 seconds or so between cortical stimulation and a conscious percept? What is the cortex doing in the 0.5 seconds between the start of stimulation and the report of awareness of the stimulation? It is probably synchronising its various processors and creating a waking dream, a structured set of events that accounts for the activity. The synchronisation of cerebral cortical processes will be discussed later, but what evidence is there for the cerebral cortex constructing a waking dream, or model, to describe the world? The \'Attentional Blink\' (Raymond *et al.* 1992) is consistent with the concept of the cerebral cortex being a device that creates models. In the \'Attentional Blink\' the identification of an object impairs the identification of a second object that is presented within 0.5 seconds of the first. Raymond *et al.* used a stream of letters (11 letters per second) and the identification of a first letter impaired the identification of a subsequent \'probe\' letter in the stream. If the probe letter followed the first letter within about 180 msecs it could easily be identified, suggesting that chunks of about 180 msecs of data stream are modelled together. Christmann & Leuthold (2004) have theorised that the \'Attentional Blink\' involves perceptual and central components of visual processing. This is supported by the fMRI studies of Marois *et al.* (2004) who presented subjects with faces mounted on scenes of places. The scenes of places often went undetected by subjects but they activated regions of the medial temporal cortex involved in high-level scene representations, the parahippocampal place area (PPA). When the scenes of places were detected by the subjects there was activity in the frontal cortex and the PPA activity was increased. These experiments are consistent with the idea of a cerebral cortex that is a multiprocessor system that creates consistent models of the environment. Bregman\'s (1990) auditory continuity illusion is another example of how sensory events are modelled. If a pure tone is followed by broadband noise and the noise followed by the same pure tone it seems as if the tone occurs throughout the period of noise. If the noise is not followed by the pure tone there is no sound of the tone during the period of noise. This effect is similar to the results found by Libet because a delay of several hundred milliseconds between sensory stimulation and conscious experience is needed to account for the apparent rewriting of history after the second tone appears. Dennett and Kinsbourne (1992) argued strongly against modelling as the source of conscious experience. They discussed two illusions, the \"cutaneous rabbit illusion\", in which the subject is tapped successively in such a way that some illusory taps appear and the \"phi illusion\" in which successively illuminated lights appear as a motion of the light. Dennett and Kinsbourne declared that there should be no cerebral cortical filling in of the gaps in the these illusions. Both these illusions have now been investigated. Blankenburg *et al.* (2006) found that cerebral cortical activity occurred at the locations expected for the missing taps in the \"cutaneous rabbit\" illusion and Larsen *et al.* (2006) found that the areas of cerebral cortex that would be stimulated by a moving light were active during the \"phi illusion\". ## The delay before consciousness of \"voluntary\" actions The 0.5 second delay required for the cortex to model an event has implications for the role of conscious experience in the control of our lives. If experience is about 0.5 seconds behind the true present instant then how can we be said to control anything? The brain must be acting automatically whilst performing most tasks. The 0.5 second delay also seems to contradict our everyday experience. We certainly feel like we are aware of things in less than 0.5 seconds, for example, the direct stimulation of sense organs seems to be experienced much more rapidly than the delayed experience of cortical stimulation. In fact subjects report that they are conscious of stimuli, such as being touched or seeing flashing lights, within 0.1 to 0.2 seconds of the event. So how can subjects report events within 0.2 seconds even though it seems to take 0.5 seconds for the cortex to generate activity that can be experienced? The simplest explanation is that the reaction occurs automatically within 0.2 seconds and then the conscious experience of this reaction occurs 0.3 seconds later. This gives a total 0.5 seconds delay before conscious experience whilst allowing fast reactions. Libet *et al.* extended their experiments by stimulating a \"relay nucleus\" in the thalamus that intercepts signals from the senses before they reach the somatosensory cortex. It was found that when this nucleus was stimulated for 0.5 seconds the subjects reported that the stimulus occurred 0.2 seconds after it had begun. When the nucleus was stimulated for less than 0.5 seconds the subjects did not report any sensation. This supports the concept of a 0.5 second delay whilst the cortex puts a stimulus in context before it is experienced. These experiments show that our experience is an output of cortical processing rather than the processing itself. If our conscious experience is non-cortical then this raises the possibility that the non-conscious cerebral cortex can perform actions without conscious control. Of course, the cortex does this all the time when we are indulging in skilled or routine behaviour. The ability of the non-conscious cortex is quite remarkable; for instance car drivers sometimes discover that they have driven for several miles without conscious experience of driving, even at the level of having no recollection of the route. !Typical recording of the readiness potential.{width="150"}Although it might be accepted that much of our everyday behaviour is automatic is there any behaviour that is definitely initiated by conscious experience? This is probably a pointless question because consciousness is about observation, not action; however, despite this there have been several experiments that have attempted to determine the relationship between consciousness and action. In 1964 Kornhuber and Deecke performed a series of experiments that measured the electrical activity from the scalp (EEG) during voluntary actions. They averaged many EEG\'s from subjects who were about to move a finger and discovered that there is an increase in scalp potential before the movement takes place. The increase in potential can start as long as 2 seconds or so before the movement and is known as the \"readiness potential\" (Bereitschaftspotential). The readiness potential is strange because it seems to contradict our conscious experience; we do not decide to move a hand and then wait 2 seconds before the hand moves. It seems that the non-conscious brain may be taking things into its own hands. Libet *et al.* (1983) extended the readiness potential experiments by asking subjects to observe a Wundt clock whilst flexing a finger. The Wundt clock had a spot of light that moved around a circle every 2.56 seconds and allowed the subjects to obtain timings that were related to their mental experiences. When the subjects flexed a finger it was found that the readiness potential occurred about 0.5 seconds before the finger moved and the subjects reported they were going to move the finger about 0.2 seconds before the movement. This suggested that a subject\'s cerebral cortex was preparing for the movement about 0.3 seconds before the subject was conscious of this. Libet\'s experiments have been reproduced elsewhere (see Keller & Heckhausen 1990). (It is important to note that the subjects in Libet\'s experiment were asked to wait until they felt the urge to move the finger.) These results are consistent with the idea of the cortex as a modelling system that constructs a consistent model of events to pass on to whatever mediates conscious experience. More recently fMRI and direct electrode recording have borne out the readiness potential experiments. Soon *et al.* (2008) allowed subjects to decide to press either a left or right button. They used fMRI to show that there was spatially organised activity in the polar frontal cortex and parietal cortex (from precuneus into posterior cingulate cortex) that predicted the conscious left/right decision and preceded it by about **seven seconds**. Rektor *et al.* (2001) used direct electrode recordings to show a 2 second latency. Haggard & Eimer (1999) and also Trevena and Miller (2002, 2009) have identified a \"Lateralized Readiness Potential\" that is correlated with the movement of a particular hand (left or right) in their EEG experiments and Trevena and Miller claim that this potential always follows the making of a conscious decision and precedes the actions being studied. However, Soon *et al.* (2008) showed that fMRI can predict which button will be used well before any conscious decision is reported. (See Haggard (2008) for a review of conscious volition). ## Perception, Imagination, Memory and Dreams ### More about Models Our dreams are clearly models that form a \'dreamworld\' but the idea that perception might be like a dream that is updated by sensation is not so obvious. Experience seems to be an active model of the world (virtual reality) based on sense data rather than a simple mapping of retinal and other sensory data. This is demonstrated by visual illusions such as the Ames Room, Spoke Illusion and Muller Lyer illusions shown below:  Notice how the circle is distorted without any distortion in the \'spokes\', it is as if the circle has been treated as a separate object by the processes in the brain that rearranged it. In all of these illusions the brain has rearranged large areas of the visual field and has managed the input as a collection of \'objects\' that are manipulated separately. Even movement seems to occur in some figures showing that the brain models the position of things:  The creation of a model is also demonstrated by the illusion of movement experienced when we watch the cinema or television. This is due to the cortical modelling that is known as \'short-range apparent motion\' rather than flicker fusion or persistence of vision. It is intriguing that, although it has been known for decades that the joining together of static images in our minds is due to modelling activity in the brain the myth that it is due to persistence of vision or flicker fusion is universal. As Anderson and Anderson (1993) noted: `Indeed, in the past decade, psychoanalytic-Marxist film scholars `\ `have retained the  model implied by persistence of vision: theirs `\ `is a passive viewer, a spectator who is "positioned," unwittingly `\ `"sutured" into the text, and victimized by excess ideology.` Our experience of the cinema is like a dream updated by sensation rather than sensation updated by interpretation. In fact the most compelling evidence for the modelling power of the brain is the existence of dreams; our dreams are often models of worlds that do not exist and involve little or no sensory input yet can involve effects as powerful as any television drama. Short range apparent motion occurs when the interval between presentations of an object is brief (c. 50-100 msecs). Motion modelling in response to longer intervals is known as long range apparent motion. There is evidence that the modelling in short range apparent motion is enhanced if the moving patterns are similar to moving human forms (such as patterns of dots outlining a person)(Thornton *et al.* 1998). The accuracy of predicting movement can actually improve if the interval between presentations is increased when human forms are used. Motion modelling can also be seen in visual illusions such as the *Waterfall Illusion* (motion aftereffect). The waterfall illusion is commonly seen after viewing a sequence of scrolling credits on the television; when the credits stop rolling it appears as if they briefly move in the opposite direction. Tootel *et al.* (1995) have used fMRI to show that this is correlated with activity in the motion modelling area of visual cortex (area MT/V5). The waterfall illusion is also associated with an intriguing aftereffect known as **storage of the motion aftereffect**. Normal motion aftereffects last for up to about ten seconds after the stimulus, however, if the subjects close their eyes for the normal duration of the aftereffect then reopen them they see the illusion for almost the normal duration. Culham *et al.* (1999) used fMRI to show that activity in area MT/V5 was low during the period when the eyes were closed then increased dramatically when the eyes were opened. This is strongly suggestive of a modelling mechanism outside MT/V5 that has adapted to motion and then models stationary data with movement in the wrong direction. Visual area MT/V5 is also involved in the separation of moving visual scenes into *sprites* or objects that move together as a whole within a scene (Muckli *et al.* 2002). The way that mental models may be the basis of ordinary reasoning was outlined by Johnson-Laird (1980), based on earlier work by Kenneth Craik. Studies of \'change blindness\' and \'inattentional blindness\', where subjects fail to spot outrageous changes in their environment, also demonstrate that we experience a model and suggest that the brain must analyse an object to incorporate it fully into the model (See for instance Rensink (2000), Simons & Rensink (2005)). ### Brain areas used in perception overlap those used in imagination and recall Functional Magnetic Resonance Imaging (fMRI) has shown that similar areas of brain are used during perception involving the senses as during imagination (Tong 2003, Kosslyn and Thompson 2003). The substrate of the mental images that occur in both modes of brain activity has not yet been found. This overlap of the brain areas used in perception with those used in imagination, memory and recall has been demonstrated in a wide range of experiments. Ganis *et al.* (2004) used fairly complex perceptual and imagination tasks that activated large areas of the brain, they found an overlap between the brain areas activated during perception and imagery. The principle areas that were different in the two tasks were found in the primary sensory areas of the visual cortex. Other areas in the visual cortex and activity in the rest of the brain showed a remarkable degree of overlap. The authors suggested that the differences in the activity of primary visual cortex may have been due to differences between the perceptual and imaginary stimuli such as speed of onset etc. The hippocampus was not activated. It is intriguing that, contrary to object imagery, spatial imagery such as predicting when a cross on a screen would fall on an imaginary letter actually seems to inhibit activity in sensory visual cortex (Aleman *et al.*). Both fMRI and blocking with transcranial magnetic stimulation (TMS) showed that the posterior parietal cortex was involved in the spatial imagery. Imagery involving places and faces activates the place and face areas that are activated during perception (Ishai *et al.* 2000). The recall and recognition of things also seems to involve very similar brain areas to those used during perception. Wheeler and Buckner (2003) showed that areas involved in perception were also involved in the recall of the perceptual stimuli. Recall causes activation of areas used in perception but also seems to use areas that may be particularly related to the process of recall iself, such as the left parietal cortex (Konishi *et al.* 2000) (Brodmann\'s area 40/39). Frontal and parietal regions are involved in the recognition of whether stimuli have been experienced before. Image generation during sleep seems to differ from that during imagination and recall. In particular it seems to involve a few well defined areas of cortex and considerable activation of the posterior thalamus. Sleep studies have shown that people dream throughout sleep. However, dreams are more frequent during the REM (rapid eye movement) periods of sleep than the NREM (non-REM) periods. Dreams are reported after 70-95% of awakenings in REM sleep and 5-10% of awakenings in NREM sleep. REM dreams are more visual than NREM dreams which are more \'thoughtlike\' (Solms 2000). Thoughtlike events (mentation) are reported after 43% of awakenings from NREM sleep. Solms (1997) found that patients who had lesions in the parietal-temporo-occipital junction reported a cessation of visual images in dreams. Solms also found that patients with lesions in the white matter inferior to the frontal horns of the lateral ventricles, in the ventromesial quadrant of the frontal lobes, also reported loss of dreaming. Loss of dreaming is also reported by leucotomised patients with frontal ventromesial damage. Damasio *et al.* (1985) and Solms (1997) also reported that some patients with damage to the medial prefrontal cortex, the anterior cingulate cortex, and the basal forebrain became confused about what was real life and what was dreaming (waking dreams occurred). Studies using fMRI show that the sensory occipital lobe (BA 18) and posterior thalamus, especially the lateral geniculate nuclei, are activated in REM sleep, weaker activations of the posterior cingulate, putamen and midbrain were also found (Wehrle *et al.* 2005, Loveblad *et al.* 1999). These findings are consistent with activation of the ponto-geniculo-occipital system (PGO) during REM. So dreams may be more like primary activations of sensory cortex than imagining or recall. This suggests that dreams have a thalamic origin or are managed via connections from the cortex through the thalamus to the visual cortex. Hallucinations seem to differ from dreams. In Charles Bonnett Syndrome patients can have clear hallucinations. These, like imaginations, seem to involve areas of the visual cortex that deal with processed data, for instance hallucinations of faces activate the \"face area\" rather than visual cortical area V1 (Ffytche *et al.* 1998). ### Suppression of data acquisition during saccades - perception as a patchwork If you look at yourself in the mirror you will not see your eyes moving even though they will be darting all over the view of your face. Even when you deliberately look from place to place your eyes will appear steady. The natural darting of the eyes from place to place as you view a scene is known as \"saccadic\" movement of the eyes. The suppression of the visual image during the motion of the eyes is known as \"saccadic suppression\" or \"saccadic masking\". The suppression of the acquisition of image data extends to suppression of awareness of flashes of light during saccades, this effect is known as \"flash suppression\", however, flash suppression seems to apply only to rather dull flashes (Volkman (1962). The suppression during saccades is probably due to suppression of the magnocellular pathway (the motion sensitive pathway) in the lateral geniculate nucleus (Burr *et al.* (1996). The most intriguing feature of this suppression of data acquisition during saccades is that each snapshot that is obtained between saccades can only contain a relatively small amount of information. This is because the fovea, which is the most sensitive area of the eye, is tiny (about 1mm diameter) and only receives input from a few degrees of the visual field. As a result what we consider to be a uniform scene in our minds is actually a patchwork of intersaccade snapshots. Another aspect of saccades is that the timing of events is referred back to the beginning of the saccade. This effect is known as \"saccadic chronostasis\". For example, if an object changes colour during a saccade the observer feels as if the colour change occurred at the beginning of the saccade, so extending the amount of time that the object possesses the changed colour. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception (see Yarrow *et al.* 2006). Burr D, Morrone M, Ross J. (1996) Selective suppression of the magnocellular visual pathway during saccades\]\'\', Behavioral Brain Research 80 1-8 (1996) <http://www.pisavisionlab.org/downloads/BBRReview96.pdf> Volkman, F. (1962). Vision during voluntary saccadic eye movements. J. Opt Soc. Am. 52:571-578. 1962. Yarrow, K, Whiteley, L, Rothwell, J.C & Haggard,P. (2006) Spatial consequences of bridging the saccadic gap. Vision Res. 2006 February; 46(4): 545--555. <http://www.hexicon.co.uk/Kielan/papers/Moving_chrono.pdf> ## Blindsight Blindsight studies illuminate the relationship between the cerebral cortex and our experience. When the visual cortex is removed subjects become almost totally blind. If the visual cortex on one side is removed subjects become relatively blind in the contra-lateral hemifield. One of the most revealing studies of blindsight is Marcel\'s 1998 paper: \" Blindsight and shape perception: deficit of visual consciousness or visual function?\". It is useful when considering blindsight to contemplate for a while the appearance of the world with both eyes closed and then with one eye closed. When both eyes are closed our experience is of a darkish space radiating out from our heads, with one eye closed we tend to ignore the darkish areas that cannot be seen even though they are still present. Marcel notes that patients who have a right blind field still have an underlying visual field on the right side and that this can even contain conscious visual experience. This sounds a bit like the darkish space that we all experience if deprived of visual input on one side. As Marcel says: \"A question that naturally arises is whether the loss is a \'total\' loss of visual consciousness in the blind field. It is often assumed to be so, especially by those who discuss blindsight without carefully reading the literature or working with the subjects. One can immediately respond negatively to the question..\" The consciousness of the completion of Kanizsa figures in blindsight patients is particularly indicative of the preservation of the field even though the content was largely missing. A Kanizsa figure is shown below:  If we put Marcel\'s observations together with cortical anatomy and function it seems that the space of our experience is located outside of the cerebral cortex. The cortex generates much of visual and other content but it does not generate the space. ## The Role of the Thalamus The thalamus is connected to the entire bottom layer of the cerebral cortex. It is the nexus of the various cortical processors as well as a recipient of independent input from most of the rest of the brain.  The thalamus is subdivided into numerous small and medium sized nuclei that between them receive inputs from every process in the nervous system (the white fibres in the illustration above largely penetrate the thalamus). The thalamic nuclei are interconnected which means that any of them could, potentially host activity from anywhere in the body or brain. Although the founders of neurology such as Hughlings Jackson and Penfield & Jasper located conscious experience in the diencephalon, including the thalamus, this is no longer the conventional wisdom. The small size of the thalamic nuclei means that they cannot support the processes that are assumed to compose access consciousness, however, even some of the smallest thalamic nuclei host millions of synapses so size would not be an obstacle if the thalamus contains the substrate of phenomenal consciousness. Indeed, the diencephalon and the thalamus in particular can be shown to be excellent candidates for a possible location of phenomenal experience.  `<font size=1>`{=html} The Intralaminar Nuclei of the thalamus. The white space above and to the left of RN is the third ventricle. MD=mediodorsal nucleus. CM=Centromedian nucleus, RN=red nucleus (not part of thalamus) The black areas are stained white fibres. Picture from: <http://www.neurophys.wisc.edu/> University of Wisconsin and Michigan State Comparative Mammalian Brain Collections. Preparation of image has been funded by the National Science Foundation, as well as by the National Institutes of Health. May only be used with these acknowledgements.`</font>`{=html} If the thalamus contains a location for conscious experience then lesions should abolish this experience. Unlike the cerebral hemispheres, lesions of the thalamus do indeed seem to abolish consciousness. The area that is most sensitive to lesions contains the Intralaminar Nuclei, especially the Parafascicular and Centromedian Nuclei. If these are damaged bilaterally patients suffer death, coma, akinetic mutism, hypersomnia, dementia and other equally serious impairments of consciousness that depend upon the size and placement of the lesions (Bogen 1995, Schiff & Plum 1999). In cases of fatal familial insomnia, in which patients exhibit many of these symptoms, there is marked neuron loss in the Intralaminar Nuclei (Budka 1998). The effect of interrupting the blood supply to the medial thalamus depends upon the severity of the damage. There is frequently initial coma. The recovery after coma is often incomplete, Krolak-Salmon *et al.* (2000) described bilateral paramedian thalamic infarcts as normally being \"followed by persisting dementia with severe mnemic disturbance, global aspontaneity and apathy.\" The symptoms of bilateral damage to the ILN can be so severe that it is possible that, even after recovery from coma, some patients may cease to be conscious and are being coordinated by automatic cortical processes. Bjornstad *et al.* (2003) and Woernera *et al.* (2005) both reported that the initial coma after bilateral paramedian infarct was accompanied by a similar pattern of EEG activity to stage 2 sleep. Woernera *et al.* (2005) also discovered that painful stimuli gave rise to a range of EEG activity, transiently breaking the stage 2 sleep pattern but without recovery of consciousness. Unfortunately even in those patients who recover consciousness Kumral *et al.* (2001) report that \"Cognitive functions in patients with bilateral paramedian infarction did not change significantly during the follow-up, in contrast to those with infarcts in varied arterial territories\" although Krolak-Salmon *et al.* (2000) did report a single patient who made a total recovery. Laureys *et al.* (2002) investigated recovery from \'persistent vegetative state\' (wakefulness without awareness). They found that overall cortical metabolism remained almost constant during recovery but that the metabolism in the prefrontal and association cortices became correlated with thalamic ILN and precuneus activity. Again confirming that thalamo-cortico-thalamic activity is required for consciousness and that cortical activity by itself is not conscious. Yamamoto *et al.* (2005) investigated persistent vegetative state and found that deep brain stimulation (25Hz) of the centromedian-parafascicular complex (19 cases) or mesencephalic reticular formation (2 cases) resulted in 8 of the patients emerging from persistent vegetative state. It is interesting that zolpidem, a GABA agonist, has recently been found to reverse PVS in some patients (Claus & Nel 2006). The effect is rapid and might be used to demonstrate the correlations that occur on recovery from PVS. As Bogen(1995) demonstrates, the ILN receive inputs, either directly or indirectly, from every part of the CNS but what do they do? Interest in the thalamus has recently been revived by the theories of Newman & Baars (1993), Baars, Newman, & Taylor1998) and Crick & Koch (1990). In Baars, Newman and Taylors\' (1998) theory it is suggested that \"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\". They also propose that the \"nucleus reticularis thalami\" (Thalamic Reticular Nucleus, TRN), which is a thin sheet of neurons that covers the thalamus, is involved in a selective attention system. This concept is reinforced by the way that point stimulation of the TRN causes focal activity in the overlying cortex (MacDonald *et al.* 1998) and the way the TRN is organised topographically (i.e.: has activity that is like an electrical image of receptor fields). The thalamus is ideally placed for integrating brain activity, if tiny parts of the thalamus are removed consciousness is abolished and the thalamus is involved in attention and the global integration of cortical activity. Any impartial judge might pronounce that the site of conscious experience has been found, possibly in the ILN of the thalamus, but no one can say how it works. ## General Anaesthesia and the Thalamus General anaesthesia should result in a profound depression of activity in the ILN if these are indeed the sites of the conscious state. White & Alkire (2003) administered halothane or isoflurane to volunteers and used positron emission tomography (PET) to monitor brain activity. They found severe depression of activity in the thalamus. The depression appeared to be higher in the non-specific nuclei than in the relay nuclei of the thalamus. In other words the anaesthesia is neither turning off the cortex nor turning off the input to the cortex but it is turning off an important part of the thalamus. Fiset *et al.* (1999) have also demonstrated a similar pattern of medial thalamic inactivity and cortical activity in propofol anaesthesia. Suppression of cortical activity is not the cause of unconsciousness; for instance, the anaesthetic agent chloralose leads to increased neural activity in the cortex relative to conscious patients (Cariani 2000). ## The function of consciousness When we walk our conscious experience does not contain data about the control of the spinal, cerebellar and vestibular reflexes that keep us on an even keel. When we reach out for a cup our conscious experience only contains data related to the need for the cup, not data about the elaborate control system that enables the action. When we talk the words just come into mind, we do not painstakingly control the syntax and vocal chords. When our attention shifts the conscious experience containing the shift happens after the attention has shifted. This passive nature of experience recurs throughout the neuroscience of consciousness from the \"readiness potential\" to the \"auditory continuity illusion\". So what does conscious observation do? The medical evidence of the lack of consciousness in some forms of delirium, mutism, PVS etc. suggest that the role of conscious observation is to stabilise the brain so that it acts as a coordinated whole. Conscious observation is an orderly arrangement of events, a stable groundform that reflects the environment and composes the stage for action. It could be speculated that if quantum events were prominent in brain function then such a groundform would be essential but even a classical brain might require a stabilising form that could be continuously compared with the world beyond the body. A stable form of neural information that contains bound data from the senses and internal neural processes is likely to have a role in the functioning of the organism. There is now an *integration consensus* that proposes that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent (see review in Baars, 2002). However, it has remained unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect. Morsella (2005) proposed a *Supramodular Interaction Theory* (SIT) that contrasts the task demands of consciously penetrable processes (e.g.: those that can be part of conscious experience such as pain, conflicting urges, and the delay of gratification) and consciously impenetrable processes (e.g.: intersensory conflicts, peristalsis, and the pupillary reflex). With this contrastive approach, SIT builds upon the integration consensus by specifying which kinds of interaction require conscious processing and which kinds do not (e.g., some intersensory processes). SIT proposes that conscious processes are required to integrate high-level systems in the brain that are vying for (specifically) skeletomotor control, as described by the principle of *parallel responses into skeletal muscle* (PRISM). Accordingly, regarding processes such as digestion and excretion, one is conscious of only those phases of the processes that require coordination with skeletomotor plans (e.g., chewing or micturating) and none of those that do not (e.g., peristalsis). From this standpoint, consciousness functions above the level of the traditional module to "cross-talk" among high-level, specialized and often multi-modal, systems. **References** Baars, B. J. (2002). The conscious access hypothesis: Origins and recent evidence. *Trends in Cognitive Sciences, 6,* 47 -- 52. Morsella, E. (2005). The function of phenomenal states: Supramodular interaction theory. *Psychological Review, 112,* 1000 - 1021. More\... Click here for Rivalries and synchronisation, bibliography and references

# Consciousness Studies/Neuroscience 1#General Anaesthesia and the Thalamus ## The cortex and consciousness The cerebral cortex consists of a set of specialised areas that process different aspects of sensation and motor control. There are about ten times as many nerve fibres going from the cortex to the thalamus as there are from the thalamus to the cortex (Destexhe 2000).  Histologically the cerebral cortex is a layer of greyish neurons overlying a huge mass of white nerve fibres, the cerebral medulla. The cortex consists of six main layers. The upper layers receive input from the relays in the thalamus such as the lateral geniculate, from the thalamus in general and from other areas of cortex plus a few specialised inputs from other locations. The lower layers give rise to output fibres that largely connect with the thalamus and other areas of cortex although particular specialised processors in the cortex may also have direct connections elsewhere such as to motor nuclei.  The cerebral cortex has many functions and is divided up into numerous separate processors. The most important function of the cortex from the point of view of consciousness studies is that it creates models. As was seen in Part I, philosophers debate whether these models are actually experienced consciously but in the neurophysiological literature it is normally assumed that we do experience models and rehearsals such as inner speech and imaginings. There is considerable evidence that the parts of the brain that deal with imagining (modelling) things are also the parts that deal with perception (i.e.: modelling the world). The overlap between imagination and normal perception is not complete because, as Tong(2003), in a review of visual consciousness, put it: \"Internally generated experiences share some, but not all, of the phenomenal properties of actual perception\". There is also considerable overlap between the areas used for imaginary speech (thought) and actual speech, areas dealing with the control of sensation and of the tongue etc. being used in actual speech but not in imagined speech (Fu *et al.* 2002). Kreiman *et al.* (2000) investigated the activity of single neurons in humans and also found that the brain activity evoked by visual imagination overlapped that which occurs upon direct stimulation by the same image. Our conscious experience consists of the output of the cortical modelling and perceptual processes. The cerebral cortex itself appears to be non-conscious. The evidence for the non-conscious nature of the cerebral cortex consists of lesion studies in which large amounts of cortex can be removed without removing consciousness and physiological studies in which it is demonstrated that the cerebral cortex can be active without conscious experience. Lesion studies have shown that up to 60% of the cerebral cortex can be removed without abolishing consciousness (Austin and Grant 1958). An entire hemisphere can be removed or much of the front or back of the cerebral cortex can be cut off yet consciousness persists. Fiset *et al.* (1999) and Cariani (2000) have shown that cortical activity can be normal or even elevated during the unconscious state of general anaesthesia. Alkire *et al.* (1996) also showed that cortical activity related to word recognition occurred during general anaesthesia. Libet *et al.* (1967) found that there could be cerebral cortical activity in response to weak stimulation of the skin without any conscious awareness of the stimulus. This work provides a neurophysiological basis for subliminal (non-conscious) perception and also shows that large areas of the cerebral cortex can be active without conscious experience. The insensitivity of experience to cortical activity has been further confirmed by Libet *et al.* (1979). They electrically stimulated the cerebral cortex of conscious patients and discovered that the stimulus must be continued for about 0.5 seconds for subjects to report a conscious experience of the stimulation. Libet\'s findings have been analysed at length but there still appears to be a 0.25 to 0.5 secs delay (Klein 2002). It has been demonstrated that cerebral cortical activity is not synonymous with conscious experience but why should there be a delay of up to 0.5 seconds or so between cortical stimulation and a conscious percept? What is the cortex doing in the 0.5 seconds between the start of stimulation and the report of awareness of the stimulation? It is probably synchronising its various processors and creating a waking dream, a structured set of events that accounts for the activity. The synchronisation of cerebral cortical processes will be discussed later, but what evidence is there for the cerebral cortex constructing a waking dream, or model, to describe the world? The \'Attentional Blink\' (Raymond *et al.* 1992) is consistent with the concept of the cerebral cortex being a device that creates models. In the \'Attentional Blink\' the identification of an object impairs the identification of a second object that is presented within 0.5 seconds of the first. Raymond *et al.* used a stream of letters (11 letters per second) and the identification of a first letter impaired the identification of a subsequent \'probe\' letter in the stream. If the probe letter followed the first letter within about 180 msecs it could easily be identified, suggesting that chunks of about 180 msecs of data stream are modelled together. Christmann & Leuthold (2004) have theorised that the \'Attentional Blink\' involves perceptual and central components of visual processing. This is supported by the fMRI studies of Marois *et al.* (2004) who presented subjects with faces mounted on scenes of places. The scenes of places often went undetected by subjects but they activated regions of the medial temporal cortex involved in high-level scene representations, the parahippocampal place area (PPA). When the scenes of places were detected by the subjects there was activity in the frontal cortex and the PPA activity was increased. These experiments are consistent with the idea of a cerebral cortex that is a multiprocessor system that creates consistent models of the environment. Bregman\'s (1990) auditory continuity illusion is another example of how sensory events are modelled. If a pure tone is followed by broadband noise and the noise followed by the same pure tone it seems as if the tone occurs throughout the period of noise. If the noise is not followed by the pure tone there is no sound of the tone during the period of noise. This effect is similar to the results found by Libet because a delay of several hundred milliseconds between sensory stimulation and conscious experience is needed to account for the apparent rewriting of history after the second tone appears. Dennett and Kinsbourne (1992) argued strongly against modelling as the source of conscious experience. They discussed two illusions, the \"cutaneous rabbit illusion\", in which the subject is tapped successively in such a way that some illusory taps appear and the \"phi illusion\" in which successively illuminated lights appear as a motion of the light. Dennett and Kinsbourne declared that there should be no cerebral cortical filling in of the gaps in the these illusions. Both these illusions have now been investigated. Blankenburg *et al.* (2006) found that cerebral cortical activity occurred at the locations expected for the missing taps in the \"cutaneous rabbit\" illusion and Larsen *et al.* (2006) found that the areas of cerebral cortex that would be stimulated by a moving light were active during the \"phi illusion\". ## The delay before consciousness of \"voluntary\" actions The 0.5 second delay required for the cortex to model an event has implications for the role of conscious experience in the control of our lives. If experience is about 0.5 seconds behind the true present instant then how can we be said to control anything? The brain must be acting automatically whilst performing most tasks. The 0.5 second delay also seems to contradict our everyday experience. We certainly feel like we are aware of things in less than 0.5 seconds, for example, the direct stimulation of sense organs seems to be experienced much more rapidly than the delayed experience of cortical stimulation. In fact subjects report that they are conscious of stimuli, such as being touched or seeing flashing lights, within 0.1 to 0.2 seconds of the event. So how can subjects report events within 0.2 seconds even though it seems to take 0.5 seconds for the cortex to generate activity that can be experienced? The simplest explanation is that the reaction occurs automatically within 0.2 seconds and then the conscious experience of this reaction occurs 0.3 seconds later. This gives a total 0.5 seconds delay before conscious experience whilst allowing fast reactions. Libet *et al.* extended their experiments by stimulating a \"relay nucleus\" in the thalamus that intercepts signals from the senses before they reach the somatosensory cortex. It was found that when this nucleus was stimulated for 0.5 seconds the subjects reported that the stimulus occurred 0.2 seconds after it had begun. When the nucleus was stimulated for less than 0.5 seconds the subjects did not report any sensation. This supports the concept of a 0.5 second delay whilst the cortex puts a stimulus in context before it is experienced. These experiments show that our experience is an output of cortical processing rather than the processing itself. If our conscious experience is non-cortical then this raises the possibility that the non-conscious cerebral cortex can perform actions without conscious control. Of course, the cortex does this all the time when we are indulging in skilled or routine behaviour. The ability of the non-conscious cortex is quite remarkable; for instance car drivers sometimes discover that they have driven for several miles without conscious experience of driving, even at the level of having no recollection of the route. !Typical recording of the readiness potential.{width="150"}Although it might be accepted that much of our everyday behaviour is automatic is there any behaviour that is definitely initiated by conscious experience? This is probably a pointless question because consciousness is about observation, not action; however, despite this there have been several experiments that have attempted to determine the relationship between consciousness and action. In 1964 Kornhuber and Deecke performed a series of experiments that measured the electrical activity from the scalp (EEG) during voluntary actions. They averaged many EEG\'s from subjects who were about to move a finger and discovered that there is an increase in scalp potential before the movement takes place. The increase in potential can start as long as 2 seconds or so before the movement and is known as the \"readiness potential\" (Bereitschaftspotential). The readiness potential is strange because it seems to contradict our conscious experience; we do not decide to move a hand and then wait 2 seconds before the hand moves. It seems that the non-conscious brain may be taking things into its own hands. Libet *et al.* (1983) extended the readiness potential experiments by asking subjects to observe a Wundt clock whilst flexing a finger. The Wundt clock had a spot of light that moved around a circle every 2.56 seconds and allowed the subjects to obtain timings that were related to their mental experiences. When the subjects flexed a finger it was found that the readiness potential occurred about 0.5 seconds before the finger moved and the subjects reported they were going to move the finger about 0.2 seconds before the movement. This suggested that a subject\'s cerebral cortex was preparing for the movement about 0.3 seconds before the subject was conscious of this. Libet\'s experiments have been reproduced elsewhere (see Keller & Heckhausen 1990). (It is important to note that the subjects in Libet\'s experiment were asked to wait until they felt the urge to move the finger.) These results are consistent with the idea of the cortex as a modelling system that constructs a consistent model of events to pass on to whatever mediates conscious experience. More recently fMRI and direct electrode recording have borne out the readiness potential experiments. Soon *et al.* (2008) allowed subjects to decide to press either a left or right button. They used fMRI to show that there was spatially organised activity in the polar frontal cortex and parietal cortex (from precuneus into posterior cingulate cortex) that predicted the conscious left/right decision and preceded it by about **seven seconds**. Rektor *et al.* (2001) used direct electrode recordings to show a 2 second latency. Haggard & Eimer (1999) and also Trevena and Miller (2002, 2009) have identified a \"Lateralized Readiness Potential\" that is correlated with the movement of a particular hand (left or right) in their EEG experiments and Trevena and Miller claim that this potential always follows the making of a conscious decision and precedes the actions being studied. However, Soon *et al.* (2008) showed that fMRI can predict which button will be used well before any conscious decision is reported. (See Haggard (2008) for a review of conscious volition). ## Perception, Imagination, Memory and Dreams ### More about Models Our dreams are clearly models that form a \'dreamworld\' but the idea that perception might be like a dream that is updated by sensation is not so obvious. Experience seems to be an active model of the world (virtual reality) based on sense data rather than a simple mapping of retinal and other sensory data. This is demonstrated by visual illusions such as the Ames Room, Spoke Illusion and Muller Lyer illusions shown below:  Notice how the circle is distorted without any distortion in the \'spokes\', it is as if the circle has been treated as a separate object by the processes in the brain that rearranged it. In all of these illusions the brain has rearranged large areas of the visual field and has managed the input as a collection of \'objects\' that are manipulated separately. Even movement seems to occur in some figures showing that the brain models the position of things:  The creation of a model is also demonstrated by the illusion of movement experienced when we watch the cinema or television. This is due to the cortical modelling that is known as \'short-range apparent motion\' rather than flicker fusion or persistence of vision. It is intriguing that, although it has been known for decades that the joining together of static images in our minds is due to modelling activity in the brain the myth that it is due to persistence of vision or flicker fusion is universal. As Anderson and Anderson (1993) noted: `Indeed, in the past decade, psychoanalytic-Marxist film scholars `\ `have retained the  model implied by persistence of vision: theirs `\ `is a passive viewer, a spectator who is "positioned," unwittingly `\ `"sutured" into the text, and victimized by excess ideology.` Our experience of the cinema is like a dream updated by sensation rather than sensation updated by interpretation. In fact the most compelling evidence for the modelling power of the brain is the existence of dreams; our dreams are often models of worlds that do not exist and involve little or no sensory input yet can involve effects as powerful as any television drama. Short range apparent motion occurs when the interval between presentations of an object is brief (c. 50-100 msecs). Motion modelling in response to longer intervals is known as long range apparent motion. There is evidence that the modelling in short range apparent motion is enhanced if the moving patterns are similar to moving human forms (such as patterns of dots outlining a person)(Thornton *et al.* 1998). The accuracy of predicting movement can actually improve if the interval between presentations is increased when human forms are used. Motion modelling can also be seen in visual illusions such as the *Waterfall Illusion* (motion aftereffect). The waterfall illusion is commonly seen after viewing a sequence of scrolling credits on the television; when the credits stop rolling it appears as if they briefly move in the opposite direction. Tootel *et al.* (1995) have used fMRI to show that this is correlated with activity in the motion modelling area of visual cortex (area MT/V5). The waterfall illusion is also associated with an intriguing aftereffect known as **storage of the motion aftereffect**. Normal motion aftereffects last for up to about ten seconds after the stimulus, however, if the subjects close their eyes for the normal duration of the aftereffect then reopen them they see the illusion for almost the normal duration. Culham *et al.* (1999) used fMRI to show that activity in area MT/V5 was low during the period when the eyes were closed then increased dramatically when the eyes were opened. This is strongly suggestive of a modelling mechanism outside MT/V5 that has adapted to motion and then models stationary data with movement in the wrong direction. Visual area MT/V5 is also involved in the separation of moving visual scenes into *sprites* or objects that move together as a whole within a scene (Muckli *et al.* 2002). The way that mental models may be the basis of ordinary reasoning was outlined by Johnson-Laird (1980), based on earlier work by Kenneth Craik. Studies of \'change blindness\' and \'inattentional blindness\', where subjects fail to spot outrageous changes in their environment, also demonstrate that we experience a model and suggest that the brain must analyse an object to incorporate it fully into the model (See for instance Rensink (2000), Simons & Rensink (2005)). ### Brain areas used in perception overlap those used in imagination and recall Functional Magnetic Resonance Imaging (fMRI) has shown that similar areas of brain are used during perception involving the senses as during imagination (Tong 2003, Kosslyn and Thompson 2003). The substrate of the mental images that occur in both modes of brain activity has not yet been found. This overlap of the brain areas used in perception with those used in imagination, memory and recall has been demonstrated in a wide range of experiments. Ganis *et al.* (2004) used fairly complex perceptual and imagination tasks that activated large areas of the brain, they found an overlap between the brain areas activated during perception and imagery. The principle areas that were different in the two tasks were found in the primary sensory areas of the visual cortex. Other areas in the visual cortex and activity in the rest of the brain showed a remarkable degree of overlap. The authors suggested that the differences in the activity of primary visual cortex may have been due to differences between the perceptual and imaginary stimuli such as speed of onset etc. The hippocampus was not activated. It is intriguing that, contrary to object imagery, spatial imagery such as predicting when a cross on a screen would fall on an imaginary letter actually seems to inhibit activity in sensory visual cortex (Aleman *et al.*). Both fMRI and blocking with transcranial magnetic stimulation (TMS) showed that the posterior parietal cortex was involved in the spatial imagery. Imagery involving places and faces activates the place and face areas that are activated during perception (Ishai *et al.* 2000). The recall and recognition of things also seems to involve very similar brain areas to those used during perception. Wheeler and Buckner (2003) showed that areas involved in perception were also involved in the recall of the perceptual stimuli. Recall causes activation of areas used in perception but also seems to use areas that may be particularly related to the process of recall iself, such as the left parietal cortex (Konishi *et al.* 2000) (Brodmann\'s area 40/39). Frontal and parietal regions are involved in the recognition of whether stimuli have been experienced before. Image generation during sleep seems to differ from that during imagination and recall. In particular it seems to involve a few well defined areas of cortex and considerable activation of the posterior thalamus. Sleep studies have shown that people dream throughout sleep. However, dreams are more frequent during the REM (rapid eye movement) periods of sleep than the NREM (non-REM) periods. Dreams are reported after 70-95% of awakenings in REM sleep and 5-10% of awakenings in NREM sleep. REM dreams are more visual than NREM dreams which are more \'thoughtlike\' (Solms 2000). Thoughtlike events (mentation) are reported after 43% of awakenings from NREM sleep. Solms (1997) found that patients who had lesions in the parietal-temporo-occipital junction reported a cessation of visual images in dreams. Solms also found that patients with lesions in the white matter inferior to the frontal horns of the lateral ventricles, in the ventromesial quadrant of the frontal lobes, also reported loss of dreaming. Loss of dreaming is also reported by leucotomised patients with frontal ventromesial damage. Damasio *et al.* (1985) and Solms (1997) also reported that some patients with damage to the medial prefrontal cortex, the anterior cingulate cortex, and the basal forebrain became confused about what was real life and what was dreaming (waking dreams occurred). Studies using fMRI show that the sensory occipital lobe (BA 18) and posterior thalamus, especially the lateral geniculate nuclei, are activated in REM sleep, weaker activations of the posterior cingulate, putamen and midbrain were also found (Wehrle *et al.* 2005, Loveblad *et al.* 1999). These findings are consistent with activation of the ponto-geniculo-occipital system (PGO) during REM. So dreams may be more like primary activations of sensory cortex than imagining or recall. This suggests that dreams have a thalamic origin or are managed via connections from the cortex through the thalamus to the visual cortex. Hallucinations seem to differ from dreams. In Charles Bonnett Syndrome patients can have clear hallucinations. These, like imaginations, seem to involve areas of the visual cortex that deal with processed data, for instance hallucinations of faces activate the \"face area\" rather than visual cortical area V1 (Ffytche *et al.* 1998). ### Suppression of data acquisition during saccades - perception as a patchwork If you look at yourself in the mirror you will not see your eyes moving even though they will be darting all over the view of your face. Even when you deliberately look from place to place your eyes will appear steady. The natural darting of the eyes from place to place as you view a scene is known as \"saccadic\" movement of the eyes. The suppression of the visual image during the motion of the eyes is known as \"saccadic suppression\" or \"saccadic masking\". The suppression of the acquisition of image data extends to suppression of awareness of flashes of light during saccades, this effect is known as \"flash suppression\", however, flash suppression seems to apply only to rather dull flashes (Volkman (1962). The suppression during saccades is probably due to suppression of the magnocellular pathway (the motion sensitive pathway) in the lateral geniculate nucleus (Burr *et al.* (1996). The most intriguing feature of this suppression of data acquisition during saccades is that each snapshot that is obtained between saccades can only contain a relatively small amount of information. This is because the fovea, which is the most sensitive area of the eye, is tiny (about 1mm diameter) and only receives input from a few degrees of the visual field. As a result what we consider to be a uniform scene in our minds is actually a patchwork of intersaccade snapshots. Another aspect of saccades is that the timing of events is referred back to the beginning of the saccade. This effect is known as \"saccadic chronostasis\". For example, if an object changes colour during a saccade the observer feels as if the colour change occurred at the beginning of the saccade, so extending the amount of time that the object possesses the changed colour. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception (see Yarrow *et al.* 2006). Burr D, Morrone M, Ross J. (1996) Selective suppression of the magnocellular visual pathway during saccades\]\'\', Behavioral Brain Research 80 1-8 (1996) <http://www.pisavisionlab.org/downloads/BBRReview96.pdf> Volkman, F. (1962). Vision during voluntary saccadic eye movements. J. Opt Soc. Am. 52:571-578. 1962. Yarrow, K, Whiteley, L, Rothwell, J.C & Haggard,P. (2006) Spatial consequences of bridging the saccadic gap. Vision Res. 2006 February; 46(4): 545--555. <http://www.hexicon.co.uk/Kielan/papers/Moving_chrono.pdf> ## Blindsight Blindsight studies illuminate the relationship between the cerebral cortex and our experience. When the visual cortex is removed subjects become almost totally blind. If the visual cortex on one side is removed subjects become relatively blind in the contra-lateral hemifield. One of the most revealing studies of blindsight is Marcel\'s 1998 paper: \" Blindsight and shape perception: deficit of visual consciousness or visual function?\". It is useful when considering blindsight to contemplate for a while the appearance of the world with both eyes closed and then with one eye closed. When both eyes are closed our experience is of a darkish space radiating out from our heads, with one eye closed we tend to ignore the darkish areas that cannot be seen even though they are still present. Marcel notes that patients who have a right blind field still have an underlying visual field on the right side and that this can even contain conscious visual experience. This sounds a bit like the darkish space that we all experience if deprived of visual input on one side. As Marcel says: \"A question that naturally arises is whether the loss is a \'total\' loss of visual consciousness in the blind field. It is often assumed to be so, especially by those who discuss blindsight without carefully reading the literature or working with the subjects. One can immediately respond negatively to the question..\" The consciousness of the completion of Kanizsa figures in blindsight patients is particularly indicative of the preservation of the field even though the content was largely missing. A Kanizsa figure is shown below:  If we put Marcel\'s observations together with cortical anatomy and function it seems that the space of our experience is located outside of the cerebral cortex. The cortex generates much of visual and other content but it does not generate the space. ## The Role of the Thalamus The thalamus is connected to the entire bottom layer of the cerebral cortex. It is the nexus of the various cortical processors as well as a recipient of independent input from most of the rest of the brain.  The thalamus is subdivided into numerous small and medium sized nuclei that between them receive inputs from every process in the nervous system (the white fibres in the illustration above largely penetrate the thalamus). The thalamic nuclei are interconnected which means that any of them could, potentially host activity from anywhere in the body or brain. Although the founders of neurology such as Hughlings Jackson and Penfield & Jasper located conscious experience in the diencephalon, including the thalamus, this is no longer the conventional wisdom. The small size of the thalamic nuclei means that they cannot support the processes that are assumed to compose access consciousness, however, even some of the smallest thalamic nuclei host millions of synapses so size would not be an obstacle if the thalamus contains the substrate of phenomenal consciousness. Indeed, the diencephalon and the thalamus in particular can be shown to be excellent candidates for a possible location of phenomenal experience.  `<font size=1>`{=html} The Intralaminar Nuclei of the thalamus. The white space above and to the left of RN is the third ventricle. MD=mediodorsal nucleus. CM=Centromedian nucleus, RN=red nucleus (not part of thalamus) The black areas are stained white fibres. Picture from: <http://www.neurophys.wisc.edu/> University of Wisconsin and Michigan State Comparative Mammalian Brain Collections. Preparation of image has been funded by the National Science Foundation, as well as by the National Institutes of Health. May only be used with these acknowledgements.`</font>`{=html} If the thalamus contains a location for conscious experience then lesions should abolish this experience. Unlike the cerebral hemispheres, lesions of the thalamus do indeed seem to abolish consciousness. The area that is most sensitive to lesions contains the Intralaminar Nuclei, especially the Parafascicular and Centromedian Nuclei. If these are damaged bilaterally patients suffer death, coma, akinetic mutism, hypersomnia, dementia and other equally serious impairments of consciousness that depend upon the size and placement of the lesions (Bogen 1995, Schiff & Plum 1999). In cases of fatal familial insomnia, in which patients exhibit many of these symptoms, there is marked neuron loss in the Intralaminar Nuclei (Budka 1998). The effect of interrupting the blood supply to the medial thalamus depends upon the severity of the damage. There is frequently initial coma. The recovery after coma is often incomplete, Krolak-Salmon *et al.* (2000) described bilateral paramedian thalamic infarcts as normally being \"followed by persisting dementia with severe mnemic disturbance, global aspontaneity and apathy.\" The symptoms of bilateral damage to the ILN can be so severe that it is possible that, even after recovery from coma, some patients may cease to be conscious and are being coordinated by automatic cortical processes. Bjornstad *et al.* (2003) and Woernera *et al.* (2005) both reported that the initial coma after bilateral paramedian infarct was accompanied by a similar pattern of EEG activity to stage 2 sleep. Woernera *et al.* (2005) also discovered that painful stimuli gave rise to a range of EEG activity, transiently breaking the stage 2 sleep pattern but without recovery of consciousness. Unfortunately even in those patients who recover consciousness Kumral *et al.* (2001) report that \"Cognitive functions in patients with bilateral paramedian infarction did not change significantly during the follow-up, in contrast to those with infarcts in varied arterial territories\" although Krolak-Salmon *et al.* (2000) did report a single patient who made a total recovery. Laureys *et al.* (2002) investigated recovery from \'persistent vegetative state\' (wakefulness without awareness). They found that overall cortical metabolism remained almost constant during recovery but that the metabolism in the prefrontal and association cortices became correlated with thalamic ILN and precuneus activity. Again confirming that thalamo-cortico-thalamic activity is required for consciousness and that cortical activity by itself is not conscious. Yamamoto *et al.* (2005) investigated persistent vegetative state and found that deep brain stimulation (25Hz) of the centromedian-parafascicular complex (19 cases) or mesencephalic reticular formation (2 cases) resulted in 8 of the patients emerging from persistent vegetative state. It is interesting that zolpidem, a GABA agonist, has recently been found to reverse PVS in some patients (Claus & Nel 2006). The effect is rapid and might be used to demonstrate the correlations that occur on recovery from PVS. As Bogen(1995) demonstrates, the ILN receive inputs, either directly or indirectly, from every part of the CNS but what do they do? Interest in the thalamus has recently been revived by the theories of Newman & Baars (1993), Baars, Newman, & Taylor1998) and Crick & Koch (1990). In Baars, Newman and Taylors\' (1998) theory it is suggested that \"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\". They also propose that the \"nucleus reticularis thalami\" (Thalamic Reticular Nucleus, TRN), which is a thin sheet of neurons that covers the thalamus, is involved in a selective attention system. This concept is reinforced by the way that point stimulation of the TRN causes focal activity in the overlying cortex (MacDonald *et al.* 1998) and the way the TRN is organised topographically (i.e.: has activity that is like an electrical image of receptor fields). The thalamus is ideally placed for integrating brain activity, if tiny parts of the thalamus are removed consciousness is abolished and the thalamus is involved in attention and the global integration of cortical activity. Any impartial judge might pronounce that the site of conscious experience has been found, possibly in the ILN of the thalamus, but no one can say how it works. ## General Anaesthesia and the Thalamus General anaesthesia should result in a profound depression of activity in the ILN if these are indeed the sites of the conscious state. White & Alkire (2003) administered halothane or isoflurane to volunteers and used positron emission tomography (PET) to monitor brain activity. They found severe depression of activity in the thalamus. The depression appeared to be higher in the non-specific nuclei than in the relay nuclei of the thalamus. In other words the anaesthesia is neither turning off the cortex nor turning off the input to the cortex but it is turning off an important part of the thalamus. Fiset *et al.* (1999) have also demonstrated a similar pattern of medial thalamic inactivity and cortical activity in propofol anaesthesia. Suppression of cortical activity is not the cause of unconsciousness; for instance, the anaesthetic agent chloralose leads to increased neural activity in the cortex relative to conscious patients (Cariani 2000). ## The function of consciousness When we walk our conscious experience does not contain data about the control of the spinal, cerebellar and vestibular reflexes that keep us on an even keel. When we reach out for a cup our conscious experience only contains data related to the need for the cup, not data about the elaborate control system that enables the action. When we talk the words just come into mind, we do not painstakingly control the syntax and vocal chords. When our attention shifts the conscious experience containing the shift happens after the attention has shifted. This passive nature of experience recurs throughout the neuroscience of consciousness from the \"readiness potential\" to the \"auditory continuity illusion\". So what does conscious observation do? The medical evidence of the lack of consciousness in some forms of delirium, mutism, PVS etc. suggest that the role of conscious observation is to stabilise the brain so that it acts as a coordinated whole. Conscious observation is an orderly arrangement of events, a stable groundform that reflects the environment and composes the stage for action. It could be speculated that if quantum events were prominent in brain function then such a groundform would be essential but even a classical brain might require a stabilising form that could be continuously compared with the world beyond the body. A stable form of neural information that contains bound data from the senses and internal neural processes is likely to have a role in the functioning of the organism. There is now an *integration consensus* that proposes that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent (see review in Baars, 2002). However, it has remained unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect. Morsella (2005) proposed a *Supramodular Interaction Theory* (SIT) that contrasts the task demands of consciously penetrable processes (e.g.: those that can be part of conscious experience such as pain, conflicting urges, and the delay of gratification) and consciously impenetrable processes (e.g.: intersensory conflicts, peristalsis, and the pupillary reflex). With this contrastive approach, SIT builds upon the integration consensus by specifying which kinds of interaction require conscious processing and which kinds do not (e.g., some intersensory processes). SIT proposes that conscious processes are required to integrate high-level systems in the brain that are vying for (specifically) skeletomotor control, as described by the principle of *parallel responses into skeletal muscle* (PRISM). Accordingly, regarding processes such as digestion and excretion, one is conscious of only those phases of the processes that require coordination with skeletomotor plans (e.g., chewing or micturating) and none of those that do not (e.g., peristalsis). From this standpoint, consciousness functions above the level of the traditional module to "cross-talk" among high-level, specialized and often multi-modal, systems. **References** Baars, B. J. (2002). The conscious access hypothesis: Origins and recent evidence. *Trends in Cognitive Sciences, 6,* 47 -- 52. Morsella, E. (2005). The function of phenomenal states: Supramodular interaction theory. *Psychological Review, 112,* 1000 - 1021. More\... Click here for Rivalries and synchronisation, bibliography and references

# Consciousness Studies/Neuroscience 1#The function of consciousness ## The cortex and consciousness The cerebral cortex consists of a set of specialised areas that process different aspects of sensation and motor control. There are about ten times as many nerve fibres going from the cortex to the thalamus as there are from the thalamus to the cortex (Destexhe 2000).  Histologically the cerebral cortex is a layer of greyish neurons overlying a huge mass of white nerve fibres, the cerebral medulla. The cortex consists of six main layers. The upper layers receive input from the relays in the thalamus such as the lateral geniculate, from the thalamus in general and from other areas of cortex plus a few specialised inputs from other locations. The lower layers give rise to output fibres that largely connect with the thalamus and other areas of cortex although particular specialised processors in the cortex may also have direct connections elsewhere such as to motor nuclei.  The cerebral cortex has many functions and is divided up into numerous separate processors. The most important function of the cortex from the point of view of consciousness studies is that it creates models. As was seen in Part I, philosophers debate whether these models are actually experienced consciously but in the neurophysiological literature it is normally assumed that we do experience models and rehearsals such as inner speech and imaginings. There is considerable evidence that the parts of the brain that deal with imagining (modelling) things are also the parts that deal with perception (i.e.: modelling the world). The overlap between imagination and normal perception is not complete because, as Tong(2003), in a review of visual consciousness, put it: \"Internally generated experiences share some, but not all, of the phenomenal properties of actual perception\". There is also considerable overlap between the areas used for imaginary speech (thought) and actual speech, areas dealing with the control of sensation and of the tongue etc. being used in actual speech but not in imagined speech (Fu *et al.* 2002). Kreiman *et al.* (2000) investigated the activity of single neurons in humans and also found that the brain activity evoked by visual imagination overlapped that which occurs upon direct stimulation by the same image. Our conscious experience consists of the output of the cortical modelling and perceptual processes. The cerebral cortex itself appears to be non-conscious. The evidence for the non-conscious nature of the cerebral cortex consists of lesion studies in which large amounts of cortex can be removed without removing consciousness and physiological studies in which it is demonstrated that the cerebral cortex can be active without conscious experience. Lesion studies have shown that up to 60% of the cerebral cortex can be removed without abolishing consciousness (Austin and Grant 1958). An entire hemisphere can be removed or much of the front or back of the cerebral cortex can be cut off yet consciousness persists. Fiset *et al.* (1999) and Cariani (2000) have shown that cortical activity can be normal or even elevated during the unconscious state of general anaesthesia. Alkire *et al.* (1996) also showed that cortical activity related to word recognition occurred during general anaesthesia. Libet *et al.* (1967) found that there could be cerebral cortical activity in response to weak stimulation of the skin without any conscious awareness of the stimulus. This work provides a neurophysiological basis for subliminal (non-conscious) perception and also shows that large areas of the cerebral cortex can be active without conscious experience. The insensitivity of experience to cortical activity has been further confirmed by Libet *et al.* (1979). They electrically stimulated the cerebral cortex of conscious patients and discovered that the stimulus must be continued for about 0.5 seconds for subjects to report a conscious experience of the stimulation. Libet\'s findings have been analysed at length but there still appears to be a 0.25 to 0.5 secs delay (Klein 2002). It has been demonstrated that cerebral cortical activity is not synonymous with conscious experience but why should there be a delay of up to 0.5 seconds or so between cortical stimulation and a conscious percept? What is the cortex doing in the 0.5 seconds between the start of stimulation and the report of awareness of the stimulation? It is probably synchronising its various processors and creating a waking dream, a structured set of events that accounts for the activity. The synchronisation of cerebral cortical processes will be discussed later, but what evidence is there for the cerebral cortex constructing a waking dream, or model, to describe the world? The \'Attentional Blink\' (Raymond *et al.* 1992) is consistent with the concept of the cerebral cortex being a device that creates models. In the \'Attentional Blink\' the identification of an object impairs the identification of a second object that is presented within 0.5 seconds of the first. Raymond *et al.* used a stream of letters (11 letters per second) and the identification of a first letter impaired the identification of a subsequent \'probe\' letter in the stream. If the probe letter followed the first letter within about 180 msecs it could easily be identified, suggesting that chunks of about 180 msecs of data stream are modelled together. Christmann & Leuthold (2004) have theorised that the \'Attentional Blink\' involves perceptual and central components of visual processing. This is supported by the fMRI studies of Marois *et al.* (2004) who presented subjects with faces mounted on scenes of places. The scenes of places often went undetected by subjects but they activated regions of the medial temporal cortex involved in high-level scene representations, the parahippocampal place area (PPA). When the scenes of places were detected by the subjects there was activity in the frontal cortex and the PPA activity was increased. These experiments are consistent with the idea of a cerebral cortex that is a multiprocessor system that creates consistent models of the environment. Bregman\'s (1990) auditory continuity illusion is another example of how sensory events are modelled. If a pure tone is followed by broadband noise and the noise followed by the same pure tone it seems as if the tone occurs throughout the period of noise. If the noise is not followed by the pure tone there is no sound of the tone during the period of noise. This effect is similar to the results found by Libet because a delay of several hundred milliseconds between sensory stimulation and conscious experience is needed to account for the apparent rewriting of history after the second tone appears. Dennett and Kinsbourne (1992) argued strongly against modelling as the source of conscious experience. They discussed two illusions, the \"cutaneous rabbit illusion\", in which the subject is tapped successively in such a way that some illusory taps appear and the \"phi illusion\" in which successively illuminated lights appear as a motion of the light. Dennett and Kinsbourne declared that there should be no cerebral cortical filling in of the gaps in the these illusions. Both these illusions have now been investigated. Blankenburg *et al.* (2006) found that cerebral cortical activity occurred at the locations expected for the missing taps in the \"cutaneous rabbit\" illusion and Larsen *et al.* (2006) found that the areas of cerebral cortex that would be stimulated by a moving light were active during the \"phi illusion\". ## The delay before consciousness of \"voluntary\" actions The 0.5 second delay required for the cortex to model an event has implications for the role of conscious experience in the control of our lives. If experience is about 0.5 seconds behind the true present instant then how can we be said to control anything? The brain must be acting automatically whilst performing most tasks. The 0.5 second delay also seems to contradict our everyday experience. We certainly feel like we are aware of things in less than 0.5 seconds, for example, the direct stimulation of sense organs seems to be experienced much more rapidly than the delayed experience of cortical stimulation. In fact subjects report that they are conscious of stimuli, such as being touched or seeing flashing lights, within 0.1 to 0.2 seconds of the event. So how can subjects report events within 0.2 seconds even though it seems to take 0.5 seconds for the cortex to generate activity that can be experienced? The simplest explanation is that the reaction occurs automatically within 0.2 seconds and then the conscious experience of this reaction occurs 0.3 seconds later. This gives a total 0.5 seconds delay before conscious experience whilst allowing fast reactions. Libet *et al.* extended their experiments by stimulating a \"relay nucleus\" in the thalamus that intercepts signals from the senses before they reach the somatosensory cortex. It was found that when this nucleus was stimulated for 0.5 seconds the subjects reported that the stimulus occurred 0.2 seconds after it had begun. When the nucleus was stimulated for less than 0.5 seconds the subjects did not report any sensation. This supports the concept of a 0.5 second delay whilst the cortex puts a stimulus in context before it is experienced. These experiments show that our experience is an output of cortical processing rather than the processing itself. If our conscious experience is non-cortical then this raises the possibility that the non-conscious cerebral cortex can perform actions without conscious control. Of course, the cortex does this all the time when we are indulging in skilled or routine behaviour. The ability of the non-conscious cortex is quite remarkable; for instance car drivers sometimes discover that they have driven for several miles without conscious experience of driving, even at the level of having no recollection of the route. !Typical recording of the readiness potential.{width="150"}Although it might be accepted that much of our everyday behaviour is automatic is there any behaviour that is definitely initiated by conscious experience? This is probably a pointless question because consciousness is about observation, not action; however, despite this there have been several experiments that have attempted to determine the relationship between consciousness and action. In 1964 Kornhuber and Deecke performed a series of experiments that measured the electrical activity from the scalp (EEG) during voluntary actions. They averaged many EEG\'s from subjects who were about to move a finger and discovered that there is an increase in scalp potential before the movement takes place. The increase in potential can start as long as 2 seconds or so before the movement and is known as the \"readiness potential\" (Bereitschaftspotential). The readiness potential is strange because it seems to contradict our conscious experience; we do not decide to move a hand and then wait 2 seconds before the hand moves. It seems that the non-conscious brain may be taking things into its own hands. Libet *et al.* (1983) extended the readiness potential experiments by asking subjects to observe a Wundt clock whilst flexing a finger. The Wundt clock had a spot of light that moved around a circle every 2.56 seconds and allowed the subjects to obtain timings that were related to their mental experiences. When the subjects flexed a finger it was found that the readiness potential occurred about 0.5 seconds before the finger moved and the subjects reported they were going to move the finger about 0.2 seconds before the movement. This suggested that a subject\'s cerebral cortex was preparing for the movement about 0.3 seconds before the subject was conscious of this. Libet\'s experiments have been reproduced elsewhere (see Keller & Heckhausen 1990). (It is important to note that the subjects in Libet\'s experiment were asked to wait until they felt the urge to move the finger.) These results are consistent with the idea of the cortex as a modelling system that constructs a consistent model of events to pass on to whatever mediates conscious experience. More recently fMRI and direct electrode recording have borne out the readiness potential experiments. Soon *et al.* (2008) allowed subjects to decide to press either a left or right button. They used fMRI to show that there was spatially organised activity in the polar frontal cortex and parietal cortex (from precuneus into posterior cingulate cortex) that predicted the conscious left/right decision and preceded it by about **seven seconds**. Rektor *et al.* (2001) used direct electrode recordings to show a 2 second latency. Haggard & Eimer (1999) and also Trevena and Miller (2002, 2009) have identified a \"Lateralized Readiness Potential\" that is correlated with the movement of a particular hand (left or right) in their EEG experiments and Trevena and Miller claim that this potential always follows the making of a conscious decision and precedes the actions being studied. However, Soon *et al.* (2008) showed that fMRI can predict which button will be used well before any conscious decision is reported. (See Haggard (2008) for a review of conscious volition). ## Perception, Imagination, Memory and Dreams ### More about Models Our dreams are clearly models that form a \'dreamworld\' but the idea that perception might be like a dream that is updated by sensation is not so obvious. Experience seems to be an active model of the world (virtual reality) based on sense data rather than a simple mapping of retinal and other sensory data. This is demonstrated by visual illusions such as the Ames Room, Spoke Illusion and Muller Lyer illusions shown below:  Notice how the circle is distorted without any distortion in the \'spokes\', it is as if the circle has been treated as a separate object by the processes in the brain that rearranged it. In all of these illusions the brain has rearranged large areas of the visual field and has managed the input as a collection of \'objects\' that are manipulated separately. Even movement seems to occur in some figures showing that the brain models the position of things:  The creation of a model is also demonstrated by the illusion of movement experienced when we watch the cinema or television. This is due to the cortical modelling that is known as \'short-range apparent motion\' rather than flicker fusion or persistence of vision. It is intriguing that, although it has been known for decades that the joining together of static images in our minds is due to modelling activity in the brain the myth that it is due to persistence of vision or flicker fusion is universal. As Anderson and Anderson (1993) noted: `Indeed, in the past decade, psychoanalytic-Marxist film scholars `\ `have retained the  model implied by persistence of vision: theirs `\ `is a passive viewer, a spectator who is "positioned," unwittingly `\ `"sutured" into the text, and victimized by excess ideology.` Our experience of the cinema is like a dream updated by sensation rather than sensation updated by interpretation. In fact the most compelling evidence for the modelling power of the brain is the existence of dreams; our dreams are often models of worlds that do not exist and involve little or no sensory input yet can involve effects as powerful as any television drama. Short range apparent motion occurs when the interval between presentations of an object is brief (c. 50-100 msecs). Motion modelling in response to longer intervals is known as long range apparent motion. There is evidence that the modelling in short range apparent motion is enhanced if the moving patterns are similar to moving human forms (such as patterns of dots outlining a person)(Thornton *et al.* 1998). The accuracy of predicting movement can actually improve if the interval between presentations is increased when human forms are used. Motion modelling can also be seen in visual illusions such as the *Waterfall Illusion* (motion aftereffect). The waterfall illusion is commonly seen after viewing a sequence of scrolling credits on the television; when the credits stop rolling it appears as if they briefly move in the opposite direction. Tootel *et al.* (1995) have used fMRI to show that this is correlated with activity in the motion modelling area of visual cortex (area MT/V5). The waterfall illusion is also associated with an intriguing aftereffect known as **storage of the motion aftereffect**. Normal motion aftereffects last for up to about ten seconds after the stimulus, however, if the subjects close their eyes for the normal duration of the aftereffect then reopen them they see the illusion for almost the normal duration. Culham *et al.* (1999) used fMRI to show that activity in area MT/V5 was low during the period when the eyes were closed then increased dramatically when the eyes were opened. This is strongly suggestive of a modelling mechanism outside MT/V5 that has adapted to motion and then models stationary data with movement in the wrong direction. Visual area MT/V5 is also involved in the separation of moving visual scenes into *sprites* or objects that move together as a whole within a scene (Muckli *et al.* 2002). The way that mental models may be the basis of ordinary reasoning was outlined by Johnson-Laird (1980), based on earlier work by Kenneth Craik. Studies of \'change blindness\' and \'inattentional blindness\', where subjects fail to spot outrageous changes in their environment, also demonstrate that we experience a model and suggest that the brain must analyse an object to incorporate it fully into the model (See for instance Rensink (2000), Simons & Rensink (2005)). ### Brain areas used in perception overlap those used in imagination and recall Functional Magnetic Resonance Imaging (fMRI) has shown that similar areas of brain are used during perception involving the senses as during imagination (Tong 2003, Kosslyn and Thompson 2003). The substrate of the mental images that occur in both modes of brain activity has not yet been found. This overlap of the brain areas used in perception with those used in imagination, memory and recall has been demonstrated in a wide range of experiments. Ganis *et al.* (2004) used fairly complex perceptual and imagination tasks that activated large areas of the brain, they found an overlap between the brain areas activated during perception and imagery. The principle areas that were different in the two tasks were found in the primary sensory areas of the visual cortex. Other areas in the visual cortex and activity in the rest of the brain showed a remarkable degree of overlap. The authors suggested that the differences in the activity of primary visual cortex may have been due to differences between the perceptual and imaginary stimuli such as speed of onset etc. The hippocampus was not activated. It is intriguing that, contrary to object imagery, spatial imagery such as predicting when a cross on a screen would fall on an imaginary letter actually seems to inhibit activity in sensory visual cortex (Aleman *et al.*). Both fMRI and blocking with transcranial magnetic stimulation (TMS) showed that the posterior parietal cortex was involved in the spatial imagery. Imagery involving places and faces activates the place and face areas that are activated during perception (Ishai *et al.* 2000). The recall and recognition of things also seems to involve very similar brain areas to those used during perception. Wheeler and Buckner (2003) showed that areas involved in perception were also involved in the recall of the perceptual stimuli. Recall causes activation of areas used in perception but also seems to use areas that may be particularly related to the process of recall iself, such as the left parietal cortex (Konishi *et al.* 2000) (Brodmann\'s area 40/39). Frontal and parietal regions are involved in the recognition of whether stimuli have been experienced before. Image generation during sleep seems to differ from that during imagination and recall. In particular it seems to involve a few well defined areas of cortex and considerable activation of the posterior thalamus. Sleep studies have shown that people dream throughout sleep. However, dreams are more frequent during the REM (rapid eye movement) periods of sleep than the NREM (non-REM) periods. Dreams are reported after 70-95% of awakenings in REM sleep and 5-10% of awakenings in NREM sleep. REM dreams are more visual than NREM dreams which are more \'thoughtlike\' (Solms 2000). Thoughtlike events (mentation) are reported after 43% of awakenings from NREM sleep. Solms (1997) found that patients who had lesions in the parietal-temporo-occipital junction reported a cessation of visual images in dreams. Solms also found that patients with lesions in the white matter inferior to the frontal horns of the lateral ventricles, in the ventromesial quadrant of the frontal lobes, also reported loss of dreaming. Loss of dreaming is also reported by leucotomised patients with frontal ventromesial damage. Damasio *et al.* (1985) and Solms (1997) also reported that some patients with damage to the medial prefrontal cortex, the anterior cingulate cortex, and the basal forebrain became confused about what was real life and what was dreaming (waking dreams occurred). Studies using fMRI show that the sensory occipital lobe (BA 18) and posterior thalamus, especially the lateral geniculate nuclei, are activated in REM sleep, weaker activations of the posterior cingulate, putamen and midbrain were also found (Wehrle *et al.* 2005, Loveblad *et al.* 1999). These findings are consistent with activation of the ponto-geniculo-occipital system (PGO) during REM. So dreams may be more like primary activations of sensory cortex than imagining or recall. This suggests that dreams have a thalamic origin or are managed via connections from the cortex through the thalamus to the visual cortex. Hallucinations seem to differ from dreams. In Charles Bonnett Syndrome patients can have clear hallucinations. These, like imaginations, seem to involve areas of the visual cortex that deal with processed data, for instance hallucinations of faces activate the \"face area\" rather than visual cortical area V1 (Ffytche *et al.* 1998). ### Suppression of data acquisition during saccades - perception as a patchwork If you look at yourself in the mirror you will not see your eyes moving even though they will be darting all over the view of your face. Even when you deliberately look from place to place your eyes will appear steady. The natural darting of the eyes from place to place as you view a scene is known as \"saccadic\" movement of the eyes. The suppression of the visual image during the motion of the eyes is known as \"saccadic suppression\" or \"saccadic masking\". The suppression of the acquisition of image data extends to suppression of awareness of flashes of light during saccades, this effect is known as \"flash suppression\", however, flash suppression seems to apply only to rather dull flashes (Volkman (1962). The suppression during saccades is probably due to suppression of the magnocellular pathway (the motion sensitive pathway) in the lateral geniculate nucleus (Burr *et al.* (1996). The most intriguing feature of this suppression of data acquisition during saccades is that each snapshot that is obtained between saccades can only contain a relatively small amount of information. This is because the fovea, which is the most sensitive area of the eye, is tiny (about 1mm diameter) and only receives input from a few degrees of the visual field. As a result what we consider to be a uniform scene in our minds is actually a patchwork of intersaccade snapshots. Another aspect of saccades is that the timing of events is referred back to the beginning of the saccade. This effect is known as \"saccadic chronostasis\". For example, if an object changes colour during a saccade the observer feels as if the colour change occurred at the beginning of the saccade, so extending the amount of time that the object possesses the changed colour. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception (see Yarrow *et al.* 2006). Burr D, Morrone M, Ross J. (1996) Selective suppression of the magnocellular visual pathway during saccades\]\'\', Behavioral Brain Research 80 1-8 (1996) <http://www.pisavisionlab.org/downloads/BBRReview96.pdf> Volkman, F. (1962). Vision during voluntary saccadic eye movements. J. Opt Soc. Am. 52:571-578. 1962. Yarrow, K, Whiteley, L, Rothwell, J.C & Haggard,P. (2006) Spatial consequences of bridging the saccadic gap. Vision Res. 2006 February; 46(4): 545--555. <http://www.hexicon.co.uk/Kielan/papers/Moving_chrono.pdf> ## Blindsight Blindsight studies illuminate the relationship between the cerebral cortex and our experience. When the visual cortex is removed subjects become almost totally blind. If the visual cortex on one side is removed subjects become relatively blind in the contra-lateral hemifield. One of the most revealing studies of blindsight is Marcel\'s 1998 paper: \" Blindsight and shape perception: deficit of visual consciousness or visual function?\". It is useful when considering blindsight to contemplate for a while the appearance of the world with both eyes closed and then with one eye closed. When both eyes are closed our experience is of a darkish space radiating out from our heads, with one eye closed we tend to ignore the darkish areas that cannot be seen even though they are still present. Marcel notes that patients who have a right blind field still have an underlying visual field on the right side and that this can even contain conscious visual experience. This sounds a bit like the darkish space that we all experience if deprived of visual input on one side. As Marcel says: \"A question that naturally arises is whether the loss is a \'total\' loss of visual consciousness in the blind field. It is often assumed to be so, especially by those who discuss blindsight without carefully reading the literature or working with the subjects. One can immediately respond negatively to the question..\" The consciousness of the completion of Kanizsa figures in blindsight patients is particularly indicative of the preservation of the field even though the content was largely missing. A Kanizsa figure is shown below:  If we put Marcel\'s observations together with cortical anatomy and function it seems that the space of our experience is located outside of the cerebral cortex. The cortex generates much of visual and other content but it does not generate the space. ## The Role of the Thalamus The thalamus is connected to the entire bottom layer of the cerebral cortex. It is the nexus of the various cortical processors as well as a recipient of independent input from most of the rest of the brain.  The thalamus is subdivided into numerous small and medium sized nuclei that between them receive inputs from every process in the nervous system (the white fibres in the illustration above largely penetrate the thalamus). The thalamic nuclei are interconnected which means that any of them could, potentially host activity from anywhere in the body or brain. Although the founders of neurology such as Hughlings Jackson and Penfield & Jasper located conscious experience in the diencephalon, including the thalamus, this is no longer the conventional wisdom. The small size of the thalamic nuclei means that they cannot support the processes that are assumed to compose access consciousness, however, even some of the smallest thalamic nuclei host millions of synapses so size would not be an obstacle if the thalamus contains the substrate of phenomenal consciousness. Indeed, the diencephalon and the thalamus in particular can be shown to be excellent candidates for a possible location of phenomenal experience.  `<font size=1>`{=html} The Intralaminar Nuclei of the thalamus. The white space above and to the left of RN is the third ventricle. MD=mediodorsal nucleus. CM=Centromedian nucleus, RN=red nucleus (not part of thalamus) The black areas are stained white fibres. Picture from: <http://www.neurophys.wisc.edu/> University of Wisconsin and Michigan State Comparative Mammalian Brain Collections. Preparation of image has been funded by the National Science Foundation, as well as by the National Institutes of Health. May only be used with these acknowledgements.`</font>`{=html} If the thalamus contains a location for conscious experience then lesions should abolish this experience. Unlike the cerebral hemispheres, lesions of the thalamus do indeed seem to abolish consciousness. The area that is most sensitive to lesions contains the Intralaminar Nuclei, especially the Parafascicular and Centromedian Nuclei. If these are damaged bilaterally patients suffer death, coma, akinetic mutism, hypersomnia, dementia and other equally serious impairments of consciousness that depend upon the size and placement of the lesions (Bogen 1995, Schiff & Plum 1999). In cases of fatal familial insomnia, in which patients exhibit many of these symptoms, there is marked neuron loss in the Intralaminar Nuclei (Budka 1998). The effect of interrupting the blood supply to the medial thalamus depends upon the severity of the damage. There is frequently initial coma. The recovery after coma is often incomplete, Krolak-Salmon *et al.* (2000) described bilateral paramedian thalamic infarcts as normally being \"followed by persisting dementia with severe mnemic disturbance, global aspontaneity and apathy.\" The symptoms of bilateral damage to the ILN can be so severe that it is possible that, even after recovery from coma, some patients may cease to be conscious and are being coordinated by automatic cortical processes. Bjornstad *et al.* (2003) and Woernera *et al.* (2005) both reported that the initial coma after bilateral paramedian infarct was accompanied by a similar pattern of EEG activity to stage 2 sleep. Woernera *et al.* (2005) also discovered that painful stimuli gave rise to a range of EEG activity, transiently breaking the stage 2 sleep pattern but without recovery of consciousness. Unfortunately even in those patients who recover consciousness Kumral *et al.* (2001) report that \"Cognitive functions in patients with bilateral paramedian infarction did not change significantly during the follow-up, in contrast to those with infarcts in varied arterial territories\" although Krolak-Salmon *et al.* (2000) did report a single patient who made a total recovery. Laureys *et al.* (2002) investigated recovery from \'persistent vegetative state\' (wakefulness without awareness). They found that overall cortical metabolism remained almost constant during recovery but that the metabolism in the prefrontal and association cortices became correlated with thalamic ILN and precuneus activity. Again confirming that thalamo-cortico-thalamic activity is required for consciousness and that cortical activity by itself is not conscious. Yamamoto *et al.* (2005) investigated persistent vegetative state and found that deep brain stimulation (25Hz) of the centromedian-parafascicular complex (19 cases) or mesencephalic reticular formation (2 cases) resulted in 8 of the patients emerging from persistent vegetative state. It is interesting that zolpidem, a GABA agonist, has recently been found to reverse PVS in some patients (Claus & Nel 2006). The effect is rapid and might be used to demonstrate the correlations that occur on recovery from PVS. As Bogen(1995) demonstrates, the ILN receive inputs, either directly or indirectly, from every part of the CNS but what do they do? Interest in the thalamus has recently been revived by the theories of Newman & Baars (1993), Baars, Newman, & Taylor1998) and Crick & Koch (1990). In Baars, Newman and Taylors\' (1998) theory it is suggested that \"The brain stem-thalamocortical axis supports the state, but not the detailed contents of consciousness, which are produced by cortex\". They also propose that the \"nucleus reticularis thalami\" (Thalamic Reticular Nucleus, TRN), which is a thin sheet of neurons that covers the thalamus, is involved in a selective attention system. This concept is reinforced by the way that point stimulation of the TRN causes focal activity in the overlying cortex (MacDonald *et al.* 1998) and the way the TRN is organised topographically (i.e.: has activity that is like an electrical image of receptor fields). The thalamus is ideally placed for integrating brain activity, if tiny parts of the thalamus are removed consciousness is abolished and the thalamus is involved in attention and the global integration of cortical activity. Any impartial judge might pronounce that the site of conscious experience has been found, possibly in the ILN of the thalamus, but no one can say how it works. ## General Anaesthesia and the Thalamus General anaesthesia should result in a profound depression of activity in the ILN if these are indeed the sites of the conscious state. White & Alkire (2003) administered halothane or isoflurane to volunteers and used positron emission tomography (PET) to monitor brain activity. They found severe depression of activity in the thalamus. The depression appeared to be higher in the non-specific nuclei than in the relay nuclei of the thalamus. In other words the anaesthesia is neither turning off the cortex nor turning off the input to the cortex but it is turning off an important part of the thalamus. Fiset *et al.* (1999) have also demonstrated a similar pattern of medial thalamic inactivity and cortical activity in propofol anaesthesia. Suppression of cortical activity is not the cause of unconsciousness; for instance, the anaesthetic agent chloralose leads to increased neural activity in the cortex relative to conscious patients (Cariani 2000). ## The function of consciousness When we walk our conscious experience does not contain data about the control of the spinal, cerebellar and vestibular reflexes that keep us on an even keel. When we reach out for a cup our conscious experience only contains data related to the need for the cup, not data about the elaborate control system that enables the action. When we talk the words just come into mind, we do not painstakingly control the syntax and vocal chords. When our attention shifts the conscious experience containing the shift happens after the attention has shifted. This passive nature of experience recurs throughout the neuroscience of consciousness from the \"readiness potential\" to the \"auditory continuity illusion\". So what does conscious observation do? The medical evidence of the lack of consciousness in some forms of delirium, mutism, PVS etc. suggest that the role of conscious observation is to stabilise the brain so that it acts as a coordinated whole. Conscious observation is an orderly arrangement of events, a stable groundform that reflects the environment and composes the stage for action. It could be speculated that if quantum events were prominent in brain function then such a groundform would be essential but even a classical brain might require a stabilising form that could be continuously compared with the world beyond the body. A stable form of neural information that contains bound data from the senses and internal neural processes is likely to have a role in the functioning of the organism. There is now an *integration consensus* that proposes that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent (see review in Baars, 2002). However, it has remained unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect. Morsella (2005) proposed a *Supramodular Interaction Theory* (SIT) that contrasts the task demands of consciously penetrable processes (e.g.: those that can be part of conscious experience such as pain, conflicting urges, and the delay of gratification) and consciously impenetrable processes (e.g.: intersensory conflicts, peristalsis, and the pupillary reflex). With this contrastive approach, SIT builds upon the integration consensus by specifying which kinds of interaction require conscious processing and which kinds do not (e.g., some intersensory processes). SIT proposes that conscious processes are required to integrate high-level systems in the brain that are vying for (specifically) skeletomotor control, as described by the principle of *parallel responses into skeletal muscle* (PRISM). Accordingly, regarding processes such as digestion and excretion, one is conscious of only those phases of the processes that require coordination with skeletomotor plans (e.g., chewing or micturating) and none of those that do not (e.g., peristalsis). From this standpoint, consciousness functions above the level of the traditional module to "cross-talk" among high-level, specialized and often multi-modal, systems. **References** Baars, B. J. (2002). The conscious access hypothesis: Origins and recent evidence. *Trends in Cognitive Sciences, 6,* 47 -- 52. Morsella, E. (2005). The function of phenomenal states: Supramodular interaction theory. *Psychological Review, 112,* 1000 - 1021. More\... Click here for Rivalries and synchronisation, bibliography and references

# Consciousness Studies/Neuroscience 2 *Contributors: please include full data in the references section for all references in the text.* ```{=html} <div class="noprint"> ``` Home ```{=html} </div> ``` ## Perceptual \"filling in\" Perceptual \"filling in\" occurs when visual properties such as textures, colours, brightness or motion are extended in the visual field to areas where they do not have corresponding events in the world. The filling in of the blind spot by the properties of the field in the contralateral eye has already been discussed. The part of the visual field represented by the blind spot is also \"filled in\" in the case of monocular vision.  Shut the right eye and focus on the pink cross with the left eye, if the head is moved towards the pink cross there is a point at which the yellow disk disappears but the white lines are still present. In this \"filling in\" the visual field does not appear to be distorted. Fiorani *et al.* (1992) developed a technique for probing the cortical blind spot using vertical and horizontal bar stimuli. Matsumoto & komatsu (2005) used this technique on macaque monkeys. In the monocular case they found that as a bar was moved across the visual field so that it crossed the blind spot there was a sudden change in neural activity in the deep layers of the neurons in the blind spot area of V1. When the bar was moved across the same part of the visual field of the contralateral eye the neural activity in the blind spot area increased steadily as the bar was moved. The authors found that there were neurons in the deep layers of blind spot cortex that had elongated receptive fields that could respond to stimuli outside the blind spot and transfer this activation into the blind spot cortex. Filling in of a slightly different type occurs in \"scotoma\". In scotoma an area of the retina is damaged and unresonsive to visual stimuli, immediately after the damage patients report an area of visual field that is unresponsive to stimuli. After several months patients report that the area of field represented by the scotoma contains visual properties related to the physical world surrounding the area that would have formed an image on the scotoma. This results in a distortion of the visual field. (see for instance Gilbert(1993)). Direct measurements of activity in cortical area V1 show that the neurons that represented the area of the scotoma become sensitive to activity in the surrounding visual field. At the cortical level the scotoma is literally \"filled in\". There are many stimuli that cause \"filling in\". These stimuli are known as \"illusions\" because they produce phenomenal experience that has no correlate in the world outside the body. In the \"neon colour spreading illusion\" a lightly coloured circle appears where there should be a white background. Sasaki and Watanabe (2004) used fMRI to show that the part of the topographic map in cortical area V1 corresponding to the light coloured circle was activated.  Fiorani, M., Rosa, M.G.P., Gattas, R. & Rocha-Miranda, C.E. (1992). Dynamic surrounds of receptive fields in primate striate cortex: a physiological basis for perceptual completion? Proc. Natl. Acad. Sci. 89, 8547-8551. <http://www.pnas.org/cgi/content/abstract/89/18/8547> Gilbert, C.D. (1993). Circuitry, architecture and functional dynamics of visual cortex. Matsumoto, M & Komatsu, H. (2005). Neural responses in the macaque V1 to bar stimuli with various lengths presented on the blind spot. J neurophysiol. 93. 2374-2387. <http://jn.physiology.org/cgi/content/abstract/93/5/2374> Sasaki, Y & Watanabe, T. The primary visual cortex fills in colour. Proc. Natl. Acad. Sci. USA 101, 18251-18256. (2004). ## Binocular Rivalry, Pattern Rivalry and Binocular Fusion Sir Charles Wheatstone (1838) was the first scientist to systematically investigate binocular rivalry. Binocular rivalry occurs when different images are presented to the left and right eyes. The subject sees successively one image, a combined image and then the other image. The swapping of images can take a second or more. Binocular rivalry is of interest in consciousness research because the parts of the brain that contain the dominant image should also be those parts that are contributing to conscious experience. Binocular rivalry involves at least two components; the first switches from one image to a merged image and then to the other image and the second permits the view to be part of conscious experience.  The switching of one image for another may involve selecting one of the images as the percept or selecting one of the eyes. Blake *et al.* (1979) performed an experiment in which subjects could change the image at a given eye by pressing a button. When a particular image became dominant they pressed a button to change the image at the eye receiving the dominant image for the non-dominant image. They found that the subjects immediately experienced the second image as the dominant image. This suggests that binocular rivalry is selecting between eyes rather than images. Lehky in 1988 proposed that the switching may be occurring as a result of feedback between visual cortical area V1 and the Lateral Geniculate Nucleus (a thalamic relay - see Carandini *et al.* 2002) and Blake in 1989 also proposed that the switching occurred at the level of area V1. (Visual cortical area V1 receives visual input direct from the LGN.) Tong (2001) has argued that, in humans, the switching of images in binocular rivalry may occur at the earliest levels in the visual cortex. In particular, Tong and Engel (2001) used an elegant technique measuring the activity in the visual cortex that represents the blind spot of the eye to show that almost complete switching to the dominant image occurs at the level of visual cortical area V1. In support of this idea of switching at the level of V1 or even before the cortex, Kreimann *et al.* (2001, 2002) used direct electrode recordings in human cortex and found that the activity of most neurons changed with the percept. Other experiments have not shown a single locus in the brain where the suppressed sensory information gets switched out (Blake & Logothetis 2002, Leopold & Logothetis 1996, Gail et al., 2004). Functional MRI has also shown cortical activity outside of sensory visual cortex related to both images in binocular rivalry. Lumer *et al.* (1998) found that only the fronto-parietal areas of cortex switched with the percept, Fang & He (2005) found that activity relating to both suppressed and unsuppressed images were present in the dorsal stream of the visual system. Wunderlich *et al.* (2005) and Haynes *et al.* (2005) have both found suppression at the level of the lateral geniculate nucleus using fMRI in humans. Pasley *et al.* (2004) have shown that, even during suppression, fearful faces can produce activity in the amygdala (see Pessoa (2005) for a review). Rivalry alternations seem to be the result of widespread activity changes that cover large parts of the brain, including but not necessarily originating at the earliest sensory stages of visual processing. Most investigators have found that, once switching has occurred, there are areas of the brain that contain activity that is solely related to the percept but this varies from most of the cortex to largely more frontal regions depending upon the study. The most likely explanation for binocular rivalry is that the switching occurs at the level of the LGN as a result of feedback from the cortex. Pattern Rivalry is also of interest in consciousness research for the same reasons as binocular rivalry. In pattern rivalry a figure may have two or more forms that replace each other. Typical examples of such figures are the Necker cube and Rubin\'s face-vase. The similarity of the time course of the switching between percepts in binocular rivalry and pattern rivalry has led many authors to suggest that these involve the same mechanism. Logothetis *et al.* (1996) used novel dichoptic stimuli (different images to each eyes) to produce a form of rivalry that seems to involve switching at levels in the cerebral cortex that are more distal to the sensory stimulus than V1. Leopold and Logothetis (1999), on the basis of their work with monkeys, state that \"..many neurons throughout the visual system, both monocular and binocular, continue to respond to a stimulus even when it is perceptually suppressed.\". Kleinschmidt *et al.* (1998) investigated pattern rivalry with MRI and found activity in higher order visual areas during change of dominant pattern. Pettigrew (2001) also describes effects on rivalry due to thought and mood that may require involvement of large areas of cortex in the switching operation and stresses the way that V1 represents different visual fields in different hemispheres of the brain so that inter-hemispheric switching must also be considered. It seems likely that the change of dominant pattern or percept is associated with higher level cortical activity but once the dominant percept is established many of the visually responsive neurons in the cortex are switched over to the new percept. This might account for the similarities in timing of binocular and pattern rivalry and the disparate results found by the various groups of authors. In the words of Kleinschmidt *et al.* (1998): \"The transient activity fluctuations we found suggest that perceptual metastability elicited by ambiguous stimuli is associated with rapid redistributions of neural activity between separate specialized cortical and subcortical structures.\" Which permits both the idea of selecting particular eyes or percepts, perhaps by feedback that switches a thalamic relay on the basis of cortical processing of patterns. Once the cortex has switched the thalamic relay most of the neurons in V1 would become exposed to the dominant percept but there would still be a few neurons in the cortical visual system receiving data from the non dominant image. The investigations of binocular and pattern rivalry provide evidence that conscious visual experience is probably distal to V1 (i.e.: cortex or thalamus). Perceptual rivalry may be part of complex decision making rather than being simply a switch to blank out unwelcome input. It is clear from the Rubin face-vase that pattern rivalry is linked to recognition and would involve a complex delineation of forms within cortical processing. This would suggest that many areas of cortex should be involved before a particular percept is made dominant. Pettigrew (2001) argues that rivalry is the result of a complex phenomenon rather than being simply a switching event. Pettigrew\'s discovery that laughter abolishes rivalry also points to a complex cortical system for switching percepts. Pettigrew proposes that complex cortical processes control rivalry and that the actual switching of percepts is performed sub-cortically in the Ventral Tegmental Area. He concludes his review of the problem by noting that \"Rivalry may thus reflect fundamental aspects of perceptual decision making..\" Pettigrew (2001). Another effect, known as \"binocular fusion\", provides further compelling evidence for the non-conscious nature of the cerebral cortex. In binocular fusion images from both eyes are fused together to create a single image in experience. Moutoussis and Zeki (2002) used a form of binocular fusion in which images of faces were flashed at 100ms intervals to both eyes simultaneously. When both eyes received images of the same colour the subject could see the faces but when one eye received a green image on a red background and the other a red image on a green background the subjects reported seeing a uniform yellow field that contained no faces. fMRI scans of the subject\'s brains showed that when both eyes were exposed to images of the same colour the part of the brain that deals with faces was active and when each eye received images of different colours the same areas of brain showed activity. In other words the cortex contained strong activity related to faces whether or not faces were experienced. Moutoussis and Zeki found a similar effect when they used images of houses instead of images of faces. The authors concluded that: \"The present study further suggests that there are no separate processing and perceptual areas but rather that the same cortical regions are involved in both the processing and, when certain levels of activation are reached and probably in combination with the activation of other areas as well, the generation of a conscious visual percept\". This conclusion does not seem to be supported by the data. There is no evidence that any area of cortex contains the percept itself. The experiment shows that the cortex contains data relating to both red and green faces which suggests that the cortex is not the site of the conscious percept. The percept is most likely distal to the cortex perhaps in the thalamus or some other area that receives cortical sensory output. It is interesting that Fries *et al.* (1997) found that neurons that were activated by the dominant image in binocular rivalry fired synchronously whereas those that were activated by the non-dominant image did not. Thalamocorticothalamic oscillations are the most likely source for synchronising neurons over whole areas of cortex, suggesting that the conscious percept is located in the thalamus rather than the cortex. ## Synchronisation of Neural Processes Our experience seems to contain entities with their attributes attached to them at the correct places in space and time. When a dog barks we see its jaws open at the same time as the bark and both jaws and bark are at the same location. We take this for granted but the brain must be engaging in some complex processing to achieve this synchronised and appropriately positioned set of objects and events. The illustration below shows the two basic processes that might be used to synchronise events between the different specialised processors in the cerebral cortex and brain in general.  In the first option a complete model of sensation, dream etc. may be created and then allowed to become part of conscious experience. In the second model events are released into experience as fast as possible but are synchronous when recalled, having been synchronised in a storage buffer. There is a third option in which there is no synchronisation of events so that the output from different processors would occur at different times. The \'experience buffer\' would be a volume of brain in which a succession of events could be recorded. The buffer might either be updated in steps, the previous content being discarded, or continuously updated with the oldest content being lost continuously. In the first option events from different processes would always appear to be simultaneous unless the experience buffer were updated as a series of steps in which case any changes at around the moment of updating might appear in successive buffers. For instance, if change of position were processed before change in colour a circle on a screen that changed from green to red at the start of a motion might seem to be briefly green during the motion and then turn red. In the second model events from different processors might appear asynchronous at the moment of experience but synchronous when recalled. Colour vision and motion vision are processed in different parts of the visual cortex and in distinct parts of visual cortical areas V1 and V2. They are different processes and hence ideal for studying the synchronisation of cortical activity. Moutoussis and Zeki (1997) presented subjects with moving coloured squares on a computer screen that changed from red to green or vice versa as they changed direction of movement. It was found that subjects seemed to perceive changes in colour some 70-80 msecs before they perceived a change in the direction of motion of the squares. Further work by Arnold *et al.* (2001) and Arnold and Clifford (2001) have confirmed that colour changes seem to be perceived before motion. Arnold and Clifford (2001) also found a quantitative relationship between the colour/motion asynchrony and the direction of change of motion, complete reversals of direction giving rise to the greatest asynchrony between the detection of colour and motion changes. Moutoussis and Zeki (1997) conclude by stating that the asynchrony of neural processes shows that \"..the perception of each attribute is solely the result of the activity in the specialised system involved in its processing..\". It seems more likely that the experiments simply show that slow neural processes are not synchronised before they become percepts (the third option above). The experiments are excellent evidence for the concept of the cortex as a set of specialised processors that deliver their output asynchronously to some other place where the output becomes a percept. These experiments on colour and motion suggest that there is no synchronisation between the processes that deal with these two aspects of vision. Another set of experiments by Clifford *et al.* (2003) supports this idea of processing being asynchronous. They asked subjects to perform a variety of judgements of when visual events occurred and found that the degree of synchrony of one visual event with another depends on the type of judgement. Different judgements probably use processors in different areas of cortex and the output from these arrives asynchronously at the part of the brain that supports the percept. When the percept is formed there must be feedback to the cortical processes that create its content. Otherwise it would not be possible to report about the percept and the cortex would be unable to direct processing to the percept in preference to other, non-conscious cortical data. Although slow processes (20 milliseconds to 1 second) do not seem to be synchronised there is some evidence for very rapid synchronisation. Andrews *et al.* (1996) revisited a problem raised by the famous physiologist Charles Sherrington. Sherrington considered the phenomenon of \'flicker fusion\' in which a flickering light appears to be a continuous steady light if it flashes on and off at frequencies of about 45 Hz or higher. He reasoned that if the images from both eyes are brought together to form a single image then the frequency at which a flickering light appears to be steady should depend on whether one or two eyes are used. Flicker fusion should occur if each eye receives alternate flashes at only half the normal flicker fusion frequency. The flicker should disappear if the left eye receives flashes at 23 pulses per second and the right eye receives alternate flashes at 23 pulses per second. When Sherrington performed the experiment he found that this was not the case, using approximate figures, each eye required 46 pulses per second for fusion to occur. Sherrington proposed that the flicker fusion in alternate binocular presentation was occurring \"psychically\", outside of normal physiological processes. Andrews *et al.* duplicated Sherrington\'s result but investigated it further. They found that when lights were flashed in each eye alternately at low frequences (2 Hz) the experience was the same as a light being flashed in both eyes at this rate. At frequencies of four Hz and higher the subjects began to report that the lights being flashed alternately in both eyes seemed to flicker at the same rate as lights being flashed in both eyes at half the frequency. It seemed as if a flash in one eye followed by a flash in the other eye was being perceived as a single flash or \"conflated\" as the authors put it. The authors explained this effect by suggesting that the brain activity corresponding to the flashes was sampled for a short period and any number of flashes occurring during this period became perceived as a single flash. The maximum rate of sampling would be about 45 Hz. This idea is similar to option (1) above, where the buffer is filled and emptied 40 - 50 times a second. An experience buffer that is refreshed at 40-50 times a second might also explain the results obtained with colour and motion asynchrony because synchronisation between processes may well happen too quickly to affect processes that occur at very slow rates. Singer and Gray (1995), Singer (2001) have proposed that synchronisation between neurones at about 45 Hz is the discriminator between those neurones with activity that contributes to conscious experience and activity in other neurones. A rapid refresh rate in a synchronising buffer agrees with the results found by Fries *et al.* (1997) in which visual cortical neurones that represent a percept underwent synchronous oscillations in the gamma frequency range (39--63 Hz). Tononi *et al.* (1998) have also found synchronisation of neural activity in neurones that represent the percept. The gamma frequency oscillations are intrinsic to the cortex but are triggered by the thalamus and are part of the \'arousal system\'. Readers should be wary of the term \'arousal system\' because it evokes the idea of something waking up a conscious cortex. The cortex can be fully active during sleep and even during pathological unconsciousness such as persistent vegetative state so it is possible that the arousal centres themselves or nearby structures actually host phenomenal consciousness. ## EEG and synchronisation If electrodes are placed on the scalp varying electrical potentials of a few tens of microvolts can be recorded between the electrodes. Recordings of potentials from electrodes on the scalp are known as electroencephalograms (EEGs). The potentials recorded in the EEG are due to postsynaptic potentials in nerve cells. The EEG is insensitive to the activity of single cells and occurs as a result of relatively slow, **synchronised**, changes in large areas of cells. The differences in potential between two scalp electrodes are largely due to depolarisation and hyperpolarisation of the dendritic trees of cortical pyramidal cells. The folding of the cortex (gyri) is problematical for recording and interpreting EEGs because opposing layers of cortex can cancel any net potentials. The EEG shows rhythmic activity. This is conventionally divided into the following frequency bands: Delta waves 0--4 Hz Theta waves 4--8 Hz Alpha waves 8--12 Hz Beta waves \>10 Hz Gamma waves (also called fast beta) 25--100 Hz EEGs also contain short bursts of activity called spindles and very fast oscillations (VFOs). Spindles last for 1--2 seconds and contain rhythmic activity at 7--14 Hz. They are associated with the onset of sleep. The VFOs consist of short bursts at frequencies of over 80 Hz. When the eyes are closed the amplitude of activity from most pairs of electrodes is increased compared with when the eyes are open. When subjects are awake the EEG consists mainly of alpha and beta activity with considerable low amplitude gamma when the eyes are open. In stage 1 sleep the EEG consists of theta waves, in stage 2 sleep of varied activity and spindles, in stage 4 sleep of delta and during REM sleep of beta and theta activity. In epileptic seizures there tends to be high amplitude activity with pronounced synchronisation between many pairs of electrodes. The rhythmic electrical activity is due to cortical feedback loops, cortico-cortical synchronisation, thalamic pacemakers and thalamo-cortical synchronisation. VFOs have been attributed to the activity of electrical connections between cells (dendro-dendritic gap junctions) (Traub (2003)). The gamma activity, centred on a frequency of 40 Hz appears to be related to activity in cortical interneurons that form electrical connections between their dendrites (Tamas *et al.* 2000). These oscillations can be triggered by high frequency stimulation of the posterior intralaminar nuclei of the thalamus (Barth and MacDonald 1996, Sukov and Barth 2001) and as a result of activation of the reticular system (Munk *et al.* 1996). This suggests that stimulation of cortex by thalamic sensory relays triggers gamma band activity in the cortex. A shift from gamma to beta waves can occur in human event related potentials after about 0.2 secs (Pantev 1995, Traub *et al.* 1999). The alpha activity is related to thalamic pacemakers, perhaps as a result of intrinsic oscillatory activity in thalamic sensory relays (see Roy & Prichep 2005 for a brief review). Theta activity, which occurs during some cognitive tasks and mental arithmetic involves a loop from the cortex to the non-specific thalamic nuclei. Delta activity seems to be endogenous to cortex when input is suppressed during sleep. Beta activity is due to cortico-cortical interactions, often after a brief period of gamma activation. It should be noted that gamma and beta activity can be expressed as impulses in cortico-thalamic pathways and that when cortical and thalamic activity is correlated there is a conscious state. In other words gamma or beta waves in the cortex are not correlates of consciousness on their own - see for instance Laureys *et al.* (2002). ## Event related potentials After a sudden event there are a characteristic set of changes in EEG activity known as **event related potentials** or ERPs. The time course of the ERP is shown in the diagram below.  ERPs occur in response to novel stimuli and are also produced by brief transcranial magnetic stimulation (TMS)(Iramina *et al.* 2002). The slow component is known as the P3 or P300 phase of the ERP. It is due to activation of areas of the brain that are relatively remote from the primary sensory areas of brain. Nieuwenhuis *et al.* (2005) have reviewed the origin of the P300 ERP: \"To summarize, convergent evidence suggests that P3-like activity can be recorded in several, widely separated brain areas. These include some medial temporal and subcortical structures (e.g., the hippocampal formation, amygdala, and thalamus), but these structures are unlikely to contribute directly to the scalp-recorded P3.\". According to Nieuwenhuis *et al.* (2005) the recorded P300 may be due to temporo-parietal and prefrontal cortical activity. Linden (2005) has also concluded that widespread, but specific, cortical activation is correlated with the recorded P300 ERP. The generator of the P300 is still obscure. Nieuwenhuis *et al.* (2005) consider that the Locus coeruleus, a nucleus in the pons that regulates task related attention and part of the sleep-wake cycle, may be responsible. In line with this, Mashour *et al.* (2005) have discovered that TMS induced P300 activity is reduced in unconscious states. Whether the P300 is related to Libet\'s 0.5 second delay is still obscure but the discovery that the P300 occurs in association with subliminal stimuli (stimuli that do not enter awareness)(Bernat *et al.* 2001) suggests that it is associated with non-conscious cortical processing. Williams *et al.* (2004), in an investigation of subliminal and supraliminal fear perception, found that \"conscious fear perception was distinguished by a more prominent N4, peaking around 400 msec\"; the N4 component follows the P300 component in the succession of phases of the ERP. Williams *et al.* considered that the earlier phases in the ERP are probably related to non-conscious processing. In contrast Vogel *et al.* (1998) found that suppression of the P300 was associated with suppression of awareness. ## The integration delay Psychological experiments often involve binary decisions where subjects give one of two outputs in response to stimuli. It is found that if the stimuli are made increasingly noisy or complex the response time tends to increase. Psychophyicists have developed various mathematical models to explain the increased response times due to noise such as the Integrator and Accumulator models (cf: Luce(1986)). These models have been fairly successful when explaining experiments such as judging the net direction of movement of sets of dots on a screen when the dots are given semi-random paths and different brightness etc. In these circumstances it can take up to 2 seconds for an accurate decision. There are many tasks however where the accuracy of decision making does not improve after about 300 milliseconds. The accuracy of the performance of rats when choosing between two alternatives when reacting to odours peaks at about 300 ms (Uchida and Mainen(2003), Abraham *et al.* (2004)). The accuracy of humans when performing vernier acuity tasks, line detection, contrast sensitivity, motion velocity discrimination and stereoscopic depth discrimination seems to peak at 300ms (Uchida *et al.* 2006). Uchida, Kepecs and Mainen (2006) suggest that \"rapid and short integration time is a sensible strategy for rapid processing of low-level sensory information in order to form more complex sensory images, both in vision and olfaction.\" Whether these authors regard these derived sensory images as the content of consciousness is not mentioned. The authors propose that the 300ms optimal integration time may be partly due to the mechanics of sniffing (a sniff takes about 125-200ms) and the nature of optical fixation (inter-saccade intervals are typically 200-400 ms ). The authors note that the animal or human could, in principle, choose to integrate over longer intervals but if it is moving this may not lead to information that is current for changed circumstances. An optimal processing time of about 300 ms would be consistent with the delays observed before conscious awareness occurs in response to a stimulus - an interval required to form \"more complex sensory images\". ## Global Workspace Theory Global Workspace Theory is the idea that somewhere in the brain there is a facility that integrates the processes that occur in the various separate areas of the brain. The theory was first proposed by Descartes as the *sensus communis*, the common sense, but the modern form of the theory dispenses with the idea of a point soul looking at the brain. In modern Global Workspace theory it is proposed that an area of brain receives input from most of the cerebral cortex and broadcasts its outputs to all of the unconscious modular information processors in the brain. Modern Global Workspace Theory has been championed by Baars (1983, 1988). There is increasing evidence for a Global Workspace or Global Workspaces in the brain. Much of this evidence comes from fMRI, single unit and magnetoencephalography studies in which it is shown that non-conscious or subliminal processing mainly occupies primary, sensory cortex whereas conscious processing occupies large areas of cerebral cortex. In binocular rivalry the stimulus that is consciously perceived is responsible for relatively intense activation of large areas of brain whereas the non-conscious stimulus is often suppressed (see above and Sheinberg & Logothetis (1997), Tononi *et al.* (1998)). The suppression is likely to occur in the Lateral Geniculate Nuclei which suggests a role for the Thalamic Reticular Nuclei, which modulate LGN activity, in the control of the percept. ### Masking and visual awareness Word masking has also been used to investigate the idea of a Global Workspace. When a word is presented on its own for a few tens of milliseconds it remains readable but if it is immediately succeeded by, or accompanied by, another word it becomes indistinct or invisible. This effect is known as \"word masking\". Vogel *et al.* (1998) have investigated a version of word masking known as the \"attentional blink\". They found that when stimuli became invisible the P3 component of the Event Related Potential, which peaks at around 300-500 millisecs after a stimulus, was completely suppressed. The P3 component of the ERP has been related to the lodging of data in working memory and also to gamma band activity in the EEG. This strongly suggests the involvement of a cortico-thalamic loop in the \"attentional blink\". The delay of 0.3 to 0.5 secs is typical of the time required for conscious awareness (see above). Word masking in conjunction with fMRI and Event Related Potential (ERP) recordings has been used by Dehaene *et al.* (2001) to expose control by a central mechanism. It was found that masked words activate mainly the visual cortex and ventral stream (inferior temporal lobe) whereas visible words also activated distant parietal, prefrontal and cingulate sites. Dehaene *et al.* (2003) and found that the dynamics of the loss of visibility of words in an attentional blink experiment could be modelled by a simulated cortico-thalamic loop. In their simulation a distributed cortical process determined which events would receive attention and the system used the thalamic gating systems to exclude those that did not receive attention. Tse *et al.* (2005) have used purely visual stimuli in masking experiments and concluded that, in the case of purely visual stimuli, the neural correlates of awareness were limited to the occipital cortex: \"We suggest that there are both lower and upper bounds within the visual hierarchy for the processing of visual masking and the maintenance of visual awareness of simple unattended targets; the lower bound is at least as high as the border between V2 and V3, and the upper bound is within the occipital lobe, possibly somewhere downstream of V4.\" This discovery would mean that activation of large areas of cortex are unnecessary for awareness. Melloni *et al.* (2007) compared compared the electrophysiological responses related to the processing of visible and invisible words in a delayed matching to sample task. Both perceived and nonperceived words caused a similar increase of local (gamma) oscillations in the EEG, but only perceived words induced a transient long-distance synchronization of gamma oscillations across widely separated regions of the brain. After this transient period of temporal coordination, the electrographic signatures of conscious and unconscious processes continue to diverge. Only words reported as perceivedinduced (1) enhanced theta oscillations over frontal regions during the maintenance interval, (2) an increase of the P300 component of the event-related potential, and (3) an increase in power and phase synchrony of gamma oscillationsbefore the anticipated presentation of the test word. We propose that the critical process mediating the access to conscious perception is the earlytransient global increase of phase synchrony of oscillatory activity in the gammafrequency. Melloni L, Molina C, Pena M, Torres D, Singer W, Rodriguez E. (2007). Synchronization of neural activity across cortical areas correlates withconscious perception.J Neurosci. 2007 Mar 14;27(11):2858-65. ### Attention and the global workspace Baars (2002) in his review of evidence for the Global Workspace Theory quotes many other experiments that show activation of larger areas of cortex in response to conscious stimuli compared with unconscious or subliminal stimuli.The effect is also seen in change blindness, learning and attention. Newman and Baars (1993) consider that the \"workspace\" is fairly global in the brain: \"This Neural Global Workspace (NGW) model views conscious processes in terms of a globally integrative brain system. The neural circuitry contributing to this system is not only widely distributed across the neocortex, but includes key corticothalamic and midbrain circuits as well. These cortico-subcortical circuits are hypothesized to be critical to understanding the mechanisms of attentional control that provide an essential basis for the conscious processing of information\". However they focus particularly on the role of the thalamic Reticular Nucleus and cortico-thalamic connectivity in the control of attention. Other ideas for the location of the Global Workspace are the idea of Singer et al. that gamma synchrony controls access to the content of consciousness and Llinas et al. (1998) that the thalamus is the hub through which communication occurs between areas of cortex. One of the problems with Global Workspace theory is that it suggests that attention, working memory, cognitive control and consciousness may all be in the same area of the brain. It is likely that the mechanisms of attention, working memory, and cognitive control may involve several, interlinked systems perhaps co-opting the basal ganglia in the process. In view of this Maia and Cleeremans (2005) propose that \".. attention, working memory, cognitive control and consciousness are not distinct functions implemented by separate brain systems. Attempting to find separate neural correlates for each may therefore be the wrong approach. Instead, we suggest that they should be understood in terms of the dynamics of global competition, with biasing from PFC (prefrontal cortex).\". The inclusion by Maia and Cleeremans of consciousness with distributed attention, working memory and cognitive control is reminiscent of Zeki & Bartel\'s idea of microconsciousness. It should be noted that, in common with Libet\'s data, the percept seems to be available to phenomenal consciousness some 0.3 to 0.5 secs after a stimulus; this suggests that whatever determines the content of phenomenal consciousness operates before events become part of phenomenal consciousness. This relegates phenomenal consciousness from being a controller of attention to being the recipient of content that is the subject of attention. This finding is consistent with the philosophical problem of the **apparently** epiphenomenal nature of phenomenal consciousness. Given the data on the timing of conscious awareness it seems that there may be two \"workspaces\", an active workspace that models the world, discarding and suppressing data during rivalry, and a passive workspace that receives the final, edited product. The active workspace would correlate with the cortical systems stressed by Dehaene *et al.* and Maia and Cleermans although, given the results of Tse et al., the workspace would be limited to small zones of cortex. The loading of the passive workspace with the output of the active workspace would correlate with thalamo-cortical activity during component P3 of the ERP in which data is transferred from the cortex to the thalamus. This workspace might constitute the source for reports of the content of phenomenal consciousness. Llinas *et al.* (1998) have proposed two parallel cortico-thalamic attentional systems, one of which is related to the thalamic specific nuclei and the other to the thalamic non-specific nuclei, especially the ILN. The non-specific system would be related to consciousness itself. ## The \"cognitive map\" and the neural basis of perceptual space Our bodies appear to be mobile within a constant space. We walk around a room; the room does not rotate around us. The constancy of the location of things gives us the feeling that we are directly viewing a constant world. But how does the brain provide a constant world rather than a world that rotates with the movement of the sense organs? Why is our view of the world when we move our eyes so different from the disturbing flow of images that occur when a video camera is waved around? Do our brains contain a constant \"cognitive map\" (O\'Keefe and Nadel 1978) of our surroundings? Mittelstaedt & Mittelstaedt (1980, 1982) discovered that female gerbils were able to recover their pups in darkened surroundings by searching in a semi random fashion on the outbound journey and then proceeding directly back to the nest on the inbound journey. The direct journey back to the nest seemed to be due to an integration of the various directions taken on the outward journey (**path integration**). If the equipment being explored by the mother gerbil was rotated very slowly the mother would make an error equivalent to the amount of rotation. More rapid rotations that activated the vestibular system of the rat (acceleration measurement) did not cause errors in navigation. This demonstration that rodents could navigate accurately on the basis of **idiothetic** cues (cues that are due to internal senses) led to research on the neural basis of the navigation. As early as 1971 O\'Keefe and Dostrovsky had discovered that there are particular cells in the hippocampus that fire according to the position of an animal in the environment. This has been complimented by research that showed that changes in visual cues within the environment caused changes in the firing rate of place cells in hippocampal area CA3 (.   !Entorhinal cortex approximately maps to areas 28 and 34{width="500"} F. P. Battaglia and A. Treves. 1998 Attractor neural networks storing multiple space representations: A model for hippocampal place fields. PHYSICAL REVIEW E DECEMBER 1998 VOLUME 58, NUMBER 6 <http://www.sissa.it/~ale/Bat+98b.pdf> Leutgeb, S., Leutgeb, J.K., Moser, M-B, and Moser, E.I. 2005. Place cells, spatial maps and the population code for memory. Current Opinion in Neurobiology 2005, 15:738--746. <http://instruct1.cit.cornell.edu/courses/bionb720nejc/reprints/LeutgebEtAl2005.pdf> Mittelstaedt, H. & Mittelstaedt, M-L. 1982. Avian Navigation. (ed. Papi, F. & Wallraff, H.) 290-297. Springer, Berlin. Mittelstaedt, M-L & Glasauer, S. 1991. Idiothetic Navigation in Gerbils and Humans. Zool. Jb. Physiol. 95 (1991), 427-435 <http://web.archive.org/web/20110125132449/http://www.nefo.med.uni-muenchen.de/~sglasauer/MittelstaedtGlasauer1991.pdf> O\'Keefe, J. & Dostrovsky, J. (1971). The hippocampus as a spatial map: preliminary evidence from unit activity in the freely moving rat. Brain Res. 34, 171-175. O\'Keefe, J. & Nadel, L. (1978). The Hippocampus as a cognitive map. (Oxford) ## Bibliography Defining the States of Consciousness. Tassi, P., Muzet, A. (2001) Neuroscience and Behavioural Reviews 25(2001) 175-191. 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# Consciousness Studies/Neuroscience 2#Binocular Rivalry, Pattern Rivalry and Binocular Fusion *Contributors: please include full data in the references section for all references in the text.* ```{=html} <div class="noprint"> ``` Home ```{=html} </div> ``` ## Perceptual \"filling in\" Perceptual \"filling in\" occurs when visual properties such as textures, colours, brightness or motion are extended in the visual field to areas where they do not have corresponding events in the world. The filling in of the blind spot by the properties of the field in the contralateral eye has already been discussed. The part of the visual field represented by the blind spot is also \"filled in\" in the case of monocular vision.  Shut the right eye and focus on the pink cross with the left eye, if the head is moved towards the pink cross there is a point at which the yellow disk disappears but the white lines are still present. In this \"filling in\" the visual field does not appear to be distorted. Fiorani *et al.* (1992) developed a technique for probing the cortical blind spot using vertical and horizontal bar stimuli. Matsumoto & komatsu (2005) used this technique on macaque monkeys. In the monocular case they found that as a bar was moved across the visual field so that it crossed the blind spot there was a sudden change in neural activity in the deep layers of the neurons in the blind spot area of V1. When the bar was moved across the same part of the visual field of the contralateral eye the neural activity in the blind spot area increased steadily as the bar was moved. The authors found that there were neurons in the deep layers of blind spot cortex that had elongated receptive fields that could respond to stimuli outside the blind spot and transfer this activation into the blind spot cortex. Filling in of a slightly different type occurs in \"scotoma\". In scotoma an area of the retina is damaged and unresonsive to visual stimuli, immediately after the damage patients report an area of visual field that is unresponsive to stimuli. After several months patients report that the area of field represented by the scotoma contains visual properties related to the physical world surrounding the area that would have formed an image on the scotoma. This results in a distortion of the visual field. (see for instance Gilbert(1993)). Direct measurements of activity in cortical area V1 show that the neurons that represented the area of the scotoma become sensitive to activity in the surrounding visual field. At the cortical level the scotoma is literally \"filled in\". There are many stimuli that cause \"filling in\". These stimuli are known as \"illusions\" because they produce phenomenal experience that has no correlate in the world outside the body. In the \"neon colour spreading illusion\" a lightly coloured circle appears where there should be a white background. Sasaki and Watanabe (2004) used fMRI to show that the part of the topographic map in cortical area V1 corresponding to the light coloured circle was activated.  Fiorani, M., Rosa, M.G.P., Gattas, R. & Rocha-Miranda, C.E. (1992). Dynamic surrounds of receptive fields in primate striate cortex: a physiological basis for perceptual completion? Proc. Natl. Acad. Sci. 89, 8547-8551. <http://www.pnas.org/cgi/content/abstract/89/18/8547> Gilbert, C.D. (1993). Circuitry, architecture and functional dynamics of visual cortex. Matsumoto, M & Komatsu, H. (2005). Neural responses in the macaque V1 to bar stimuli with various lengths presented on the blind spot. J neurophysiol. 93. 2374-2387. <http://jn.physiology.org/cgi/content/abstract/93/5/2374> Sasaki, Y & Watanabe, T. The primary visual cortex fills in colour. Proc. Natl. Acad. Sci. USA 101, 18251-18256. (2004). ## Binocular Rivalry, Pattern Rivalry and Binocular Fusion Sir Charles Wheatstone (1838) was the first scientist to systematically investigate binocular rivalry. Binocular rivalry occurs when different images are presented to the left and right eyes. The subject sees successively one image, a combined image and then the other image. The swapping of images can take a second or more. Binocular rivalry is of interest in consciousness research because the parts of the brain that contain the dominant image should also be those parts that are contributing to conscious experience. Binocular rivalry involves at least two components; the first switches from one image to a merged image and then to the other image and the second permits the view to be part of conscious experience.  The switching of one image for another may involve selecting one of the images as the percept or selecting one of the eyes. Blake *et al.* (1979) performed an experiment in which subjects could change the image at a given eye by pressing a button. When a particular image became dominant they pressed a button to change the image at the eye receiving the dominant image for the non-dominant image. They found that the subjects immediately experienced the second image as the dominant image. This suggests that binocular rivalry is selecting between eyes rather than images. Lehky in 1988 proposed that the switching may be occurring as a result of feedback between visual cortical area V1 and the Lateral Geniculate Nucleus (a thalamic relay - see Carandini *et al.* 2002) and Blake in 1989 also proposed that the switching occurred at the level of area V1. (Visual cortical area V1 receives visual input direct from the LGN.) Tong (2001) has argued that, in humans, the switching of images in binocular rivalry may occur at the earliest levels in the visual cortex. In particular, Tong and Engel (2001) used an elegant technique measuring the activity in the visual cortex that represents the blind spot of the eye to show that almost complete switching to the dominant image occurs at the level of visual cortical area V1. In support of this idea of switching at the level of V1 or even before the cortex, Kreimann *et al.* (2001, 2002) used direct electrode recordings in human cortex and found that the activity of most neurons changed with the percept. Other experiments have not shown a single locus in the brain where the suppressed sensory information gets switched out (Blake & Logothetis 2002, Leopold & Logothetis 1996, Gail et al., 2004). Functional MRI has also shown cortical activity outside of sensory visual cortex related to both images in binocular rivalry. Lumer *et al.* (1998) found that only the fronto-parietal areas of cortex switched with the percept, Fang & He (2005) found that activity relating to both suppressed and unsuppressed images were present in the dorsal stream of the visual system. Wunderlich *et al.* (2005) and Haynes *et al.* (2005) have both found suppression at the level of the lateral geniculate nucleus using fMRI in humans. Pasley *et al.* (2004) have shown that, even during suppression, fearful faces can produce activity in the amygdala (see Pessoa (2005) for a review). Rivalry alternations seem to be the result of widespread activity changes that cover large parts of the brain, including but not necessarily originating at the earliest sensory stages of visual processing. Most investigators have found that, once switching has occurred, there are areas of the brain that contain activity that is solely related to the percept but this varies from most of the cortex to largely more frontal regions depending upon the study. The most likely explanation for binocular rivalry is that the switching occurs at the level of the LGN as a result of feedback from the cortex. Pattern Rivalry is also of interest in consciousness research for the same reasons as binocular rivalry. In pattern rivalry a figure may have two or more forms that replace each other. Typical examples of such figures are the Necker cube and Rubin\'s face-vase. The similarity of the time course of the switching between percepts in binocular rivalry and pattern rivalry has led many authors to suggest that these involve the same mechanism. Logothetis *et al.* (1996) used novel dichoptic stimuli (different images to each eyes) to produce a form of rivalry that seems to involve switching at levels in the cerebral cortex that are more distal to the sensory stimulus than V1. Leopold and Logothetis (1999), on the basis of their work with monkeys, state that \"..many neurons throughout the visual system, both monocular and binocular, continue to respond to a stimulus even when it is perceptually suppressed.\". Kleinschmidt *et al.* (1998) investigated pattern rivalry with MRI and found activity in higher order visual areas during change of dominant pattern. Pettigrew (2001) also describes effects on rivalry due to thought and mood that may require involvement of large areas of cortex in the switching operation and stresses the way that V1 represents different visual fields in different hemispheres of the brain so that inter-hemispheric switching must also be considered. It seems likely that the change of dominant pattern or percept is associated with higher level cortical activity but once the dominant percept is established many of the visually responsive neurons in the cortex are switched over to the new percept. This might account for the similarities in timing of binocular and pattern rivalry and the disparate results found by the various groups of authors. In the words of Kleinschmidt *et al.* (1998): \"The transient activity fluctuations we found suggest that perceptual metastability elicited by ambiguous stimuli is associated with rapid redistributions of neural activity between separate specialized cortical and subcortical structures.\" Which permits both the idea of selecting particular eyes or percepts, perhaps by feedback that switches a thalamic relay on the basis of cortical processing of patterns. Once the cortex has switched the thalamic relay most of the neurons in V1 would become exposed to the dominant percept but there would still be a few neurons in the cortical visual system receiving data from the non dominant image. The investigations of binocular and pattern rivalry provide evidence that conscious visual experience is probably distal to V1 (i.e.: cortex or thalamus). Perceptual rivalry may be part of complex decision making rather than being simply a switch to blank out unwelcome input. It is clear from the Rubin face-vase that pattern rivalry is linked to recognition and would involve a complex delineation of forms within cortical processing. This would suggest that many areas of cortex should be involved before a particular percept is made dominant. Pettigrew (2001) argues that rivalry is the result of a complex phenomenon rather than being simply a switching event. Pettigrew\'s discovery that laughter abolishes rivalry also points to a complex cortical system for switching percepts. Pettigrew proposes that complex cortical processes control rivalry and that the actual switching of percepts is performed sub-cortically in the Ventral Tegmental Area. He concludes his review of the problem by noting that \"Rivalry may thus reflect fundamental aspects of perceptual decision making..\" Pettigrew (2001). Another effect, known as \"binocular fusion\", provides further compelling evidence for the non-conscious nature of the cerebral cortex. In binocular fusion images from both eyes are fused together to create a single image in experience. Moutoussis and Zeki (2002) used a form of binocular fusion in which images of faces were flashed at 100ms intervals to both eyes simultaneously. When both eyes received images of the same colour the subject could see the faces but when one eye received a green image on a red background and the other a red image on a green background the subjects reported seeing a uniform yellow field that contained no faces. fMRI scans of the subject\'s brains showed that when both eyes were exposed to images of the same colour the part of the brain that deals with faces was active and when each eye received images of different colours the same areas of brain showed activity. In other words the cortex contained strong activity related to faces whether or not faces were experienced. Moutoussis and Zeki found a similar effect when they used images of houses instead of images of faces. The authors concluded that: \"The present study further suggests that there are no separate processing and perceptual areas but rather that the same cortical regions are involved in both the processing and, when certain levels of activation are reached and probably in combination with the activation of other areas as well, the generation of a conscious visual percept\". This conclusion does not seem to be supported by the data. There is no evidence that any area of cortex contains the percept itself. The experiment shows that the cortex contains data relating to both red and green faces which suggests that the cortex is not the site of the conscious percept. The percept is most likely distal to the cortex perhaps in the thalamus or some other area that receives cortical sensory output. It is interesting that Fries *et al.* (1997) found that neurons that were activated by the dominant image in binocular rivalry fired synchronously whereas those that were activated by the non-dominant image did not. Thalamocorticothalamic oscillations are the most likely source for synchronising neurons over whole areas of cortex, suggesting that the conscious percept is located in the thalamus rather than the cortex. ## Synchronisation of Neural Processes Our experience seems to contain entities with their attributes attached to them at the correct places in space and time. When a dog barks we see its jaws open at the same time as the bark and both jaws and bark are at the same location. We take this for granted but the brain must be engaging in some complex processing to achieve this synchronised and appropriately positioned set of objects and events. The illustration below shows the two basic processes that might be used to synchronise events between the different specialised processors in the cerebral cortex and brain in general.  In the first option a complete model of sensation, dream etc. may be created and then allowed to become part of conscious experience. In the second model events are released into experience as fast as possible but are synchronous when recalled, having been synchronised in a storage buffer. There is a third option in which there is no synchronisation of events so that the output from different processors would occur at different times. The \'experience buffer\' would be a volume of brain in which a succession of events could be recorded. The buffer might either be updated in steps, the previous content being discarded, or continuously updated with the oldest content being lost continuously. In the first option events from different processes would always appear to be simultaneous unless the experience buffer were updated as a series of steps in which case any changes at around the moment of updating might appear in successive buffers. For instance, if change of position were processed before change in colour a circle on a screen that changed from green to red at the start of a motion might seem to be briefly green during the motion and then turn red. In the second model events from different processors might appear asynchronous at the moment of experience but synchronous when recalled. Colour vision and motion vision are processed in different parts of the visual cortex and in distinct parts of visual cortical areas V1 and V2. They are different processes and hence ideal for studying the synchronisation of cortical activity. Moutoussis and Zeki (1997) presented subjects with moving coloured squares on a computer screen that changed from red to green or vice versa as they changed direction of movement. It was found that subjects seemed to perceive changes in colour some 70-80 msecs before they perceived a change in the direction of motion of the squares. Further work by Arnold *et al.* (2001) and Arnold and Clifford (2001) have confirmed that colour changes seem to be perceived before motion. Arnold and Clifford (2001) also found a quantitative relationship between the colour/motion asynchrony and the direction of change of motion, complete reversals of direction giving rise to the greatest asynchrony between the detection of colour and motion changes. Moutoussis and Zeki (1997) conclude by stating that the asynchrony of neural processes shows that \"..the perception of each attribute is solely the result of the activity in the specialised system involved in its processing..\". It seems more likely that the experiments simply show that slow neural processes are not synchronised before they become percepts (the third option above). The experiments are excellent evidence for the concept of the cortex as a set of specialised processors that deliver their output asynchronously to some other place where the output becomes a percept. These experiments on colour and motion suggest that there is no synchronisation between the processes that deal with these two aspects of vision. Another set of experiments by Clifford *et al.* (2003) supports this idea of processing being asynchronous. They asked subjects to perform a variety of judgements of when visual events occurred and found that the degree of synchrony of one visual event with another depends on the type of judgement. Different judgements probably use processors in different areas of cortex and the output from these arrives asynchronously at the part of the brain that supports the percept. When the percept is formed there must be feedback to the cortical processes that create its content. Otherwise it would not be possible to report about the percept and the cortex would be unable to direct processing to the percept in preference to other, non-conscious cortical data. Although slow processes (20 milliseconds to 1 second) do not seem to be synchronised there is some evidence for very rapid synchronisation. Andrews *et al.* (1996) revisited a problem raised by the famous physiologist Charles Sherrington. Sherrington considered the phenomenon of \'flicker fusion\' in which a flickering light appears to be a continuous steady light if it flashes on and off at frequencies of about 45 Hz or higher. He reasoned that if the images from both eyes are brought together to form a single image then the frequency at which a flickering light appears to be steady should depend on whether one or two eyes are used. Flicker fusion should occur if each eye receives alternate flashes at only half the normal flicker fusion frequency. The flicker should disappear if the left eye receives flashes at 23 pulses per second and the right eye receives alternate flashes at 23 pulses per second. When Sherrington performed the experiment he found that this was not the case, using approximate figures, each eye required 46 pulses per second for fusion to occur. Sherrington proposed that the flicker fusion in alternate binocular presentation was occurring \"psychically\", outside of normal physiological processes. Andrews *et al.* duplicated Sherrington\'s result but investigated it further. They found that when lights were flashed in each eye alternately at low frequences (2 Hz) the experience was the same as a light being flashed in both eyes at this rate. At frequencies of four Hz and higher the subjects began to report that the lights being flashed alternately in both eyes seemed to flicker at the same rate as lights being flashed in both eyes at half the frequency. It seemed as if a flash in one eye followed by a flash in the other eye was being perceived as a single flash or \"conflated\" as the authors put it. The authors explained this effect by suggesting that the brain activity corresponding to the flashes was sampled for a short period and any number of flashes occurring during this period became perceived as a single flash. The maximum rate of sampling would be about 45 Hz. This idea is similar to option (1) above, where the buffer is filled and emptied 40 - 50 times a second. An experience buffer that is refreshed at 40-50 times a second might also explain the results obtained with colour and motion asynchrony because synchronisation between processes may well happen too quickly to affect processes that occur at very slow rates. Singer and Gray (1995), Singer (2001) have proposed that synchronisation between neurones at about 45 Hz is the discriminator between those neurones with activity that contributes to conscious experience and activity in other neurones. A rapid refresh rate in a synchronising buffer agrees with the results found by Fries *et al.* (1997) in which visual cortical neurones that represent a percept underwent synchronous oscillations in the gamma frequency range (39--63 Hz). Tononi *et al.* (1998) have also found synchronisation of neural activity in neurones that represent the percept. The gamma frequency oscillations are intrinsic to the cortex but are triggered by the thalamus and are part of the \'arousal system\'. Readers should be wary of the term \'arousal system\' because it evokes the idea of something waking up a conscious cortex. The cortex can be fully active during sleep and even during pathological unconsciousness such as persistent vegetative state so it is possible that the arousal centres themselves or nearby structures actually host phenomenal consciousness. ## EEG and synchronisation If electrodes are placed on the scalp varying electrical potentials of a few tens of microvolts can be recorded between the electrodes. Recordings of potentials from electrodes on the scalp are known as electroencephalograms (EEGs). The potentials recorded in the EEG are due to postsynaptic potentials in nerve cells. The EEG is insensitive to the activity of single cells and occurs as a result of relatively slow, **synchronised**, changes in large areas of cells. The differences in potential between two scalp electrodes are largely due to depolarisation and hyperpolarisation of the dendritic trees of cortical pyramidal cells. The folding of the cortex (gyri) is problematical for recording and interpreting EEGs because opposing layers of cortex can cancel any net potentials. The EEG shows rhythmic activity. This is conventionally divided into the following frequency bands: Delta waves 0--4 Hz Theta waves 4--8 Hz Alpha waves 8--12 Hz Beta waves \>10 Hz Gamma waves (also called fast beta) 25--100 Hz EEGs also contain short bursts of activity called spindles and very fast oscillations (VFOs). Spindles last for 1--2 seconds and contain rhythmic activity at 7--14 Hz. They are associated with the onset of sleep. The VFOs consist of short bursts at frequencies of over 80 Hz. When the eyes are closed the amplitude of activity from most pairs of electrodes is increased compared with when the eyes are open. When subjects are awake the EEG consists mainly of alpha and beta activity with considerable low amplitude gamma when the eyes are open. In stage 1 sleep the EEG consists of theta waves, in stage 2 sleep of varied activity and spindles, in stage 4 sleep of delta and during REM sleep of beta and theta activity. In epileptic seizures there tends to be high amplitude activity with pronounced synchronisation between many pairs of electrodes. The rhythmic electrical activity is due to cortical feedback loops, cortico-cortical synchronisation, thalamic pacemakers and thalamo-cortical synchronisation. VFOs have been attributed to the activity of electrical connections between cells (dendro-dendritic gap junctions) (Traub (2003)). The gamma activity, centred on a frequency of 40 Hz appears to be related to activity in cortical interneurons that form electrical connections between their dendrites (Tamas *et al.* 2000). These oscillations can be triggered by high frequency stimulation of the posterior intralaminar nuclei of the thalamus (Barth and MacDonald 1996, Sukov and Barth 2001) and as a result of activation of the reticular system (Munk *et al.* 1996). This suggests that stimulation of cortex by thalamic sensory relays triggers gamma band activity in the cortex. A shift from gamma to beta waves can occur in human event related potentials after about 0.2 secs (Pantev 1995, Traub *et al.* 1999). The alpha activity is related to thalamic pacemakers, perhaps as a result of intrinsic oscillatory activity in thalamic sensory relays (see Roy & Prichep 2005 for a brief review). Theta activity, which occurs during some cognitive tasks and mental arithmetic involves a loop from the cortex to the non-specific thalamic nuclei. Delta activity seems to be endogenous to cortex when input is suppressed during sleep. Beta activity is due to cortico-cortical interactions, often after a brief period of gamma activation. It should be noted that gamma and beta activity can be expressed as impulses in cortico-thalamic pathways and that when cortical and thalamic activity is correlated there is a conscious state. In other words gamma or beta waves in the cortex are not correlates of consciousness on their own - see for instance Laureys *et al.* (2002). ## Event related potentials After a sudden event there are a characteristic set of changes in EEG activity known as **event related potentials** or ERPs. The time course of the ERP is shown in the diagram below.  ERPs occur in response to novel stimuli and are also produced by brief transcranial magnetic stimulation (TMS)(Iramina *et al.* 2002). The slow component is known as the P3 or P300 phase of the ERP. It is due to activation of areas of the brain that are relatively remote from the primary sensory areas of brain. Nieuwenhuis *et al.* (2005) have reviewed the origin of the P300 ERP: \"To summarize, convergent evidence suggests that P3-like activity can be recorded in several, widely separated brain areas. These include some medial temporal and subcortical structures (e.g., the hippocampal formation, amygdala, and thalamus), but these structures are unlikely to contribute directly to the scalp-recorded P3.\". According to Nieuwenhuis *et al.* (2005) the recorded P300 may be due to temporo-parietal and prefrontal cortical activity. Linden (2005) has also concluded that widespread, but specific, cortical activation is correlated with the recorded P300 ERP. The generator of the P300 is still obscure. Nieuwenhuis *et al.* (2005) consider that the Locus coeruleus, a nucleus in the pons that regulates task related attention and part of the sleep-wake cycle, may be responsible. In line with this, Mashour *et al.* (2005) have discovered that TMS induced P300 activity is reduced in unconscious states. Whether the P300 is related to Libet\'s 0.5 second delay is still obscure but the discovery that the P300 occurs in association with subliminal stimuli (stimuli that do not enter awareness)(Bernat *et al.* 2001) suggests that it is associated with non-conscious cortical processing. Williams *et al.* (2004), in an investigation of subliminal and supraliminal fear perception, found that \"conscious fear perception was distinguished by a more prominent N4, peaking around 400 msec\"; the N4 component follows the P300 component in the succession of phases of the ERP. Williams *et al.* considered that the earlier phases in the ERP are probably related to non-conscious processing. In contrast Vogel *et al.* (1998) found that suppression of the P300 was associated with suppression of awareness. ## The integration delay Psychological experiments often involve binary decisions where subjects give one of two outputs in response to stimuli. It is found that if the stimuli are made increasingly noisy or complex the response time tends to increase. Psychophyicists have developed various mathematical models to explain the increased response times due to noise such as the Integrator and Accumulator models (cf: Luce(1986)). These models have been fairly successful when explaining experiments such as judging the net direction of movement of sets of dots on a screen when the dots are given semi-random paths and different brightness etc. In these circumstances it can take up to 2 seconds for an accurate decision. There are many tasks however where the accuracy of decision making does not improve after about 300 milliseconds. The accuracy of the performance of rats when choosing between two alternatives when reacting to odours peaks at about 300 ms (Uchida and Mainen(2003), Abraham *et al.* (2004)). The accuracy of humans when performing vernier acuity tasks, line detection, contrast sensitivity, motion velocity discrimination and stereoscopic depth discrimination seems to peak at 300ms (Uchida *et al.* 2006). Uchida, Kepecs and Mainen (2006) suggest that \"rapid and short integration time is a sensible strategy for rapid processing of low-level sensory information in order to form more complex sensory images, both in vision and olfaction.\" Whether these authors regard these derived sensory images as the content of consciousness is not mentioned. The authors propose that the 300ms optimal integration time may be partly due to the mechanics of sniffing (a sniff takes about 125-200ms) and the nature of optical fixation (inter-saccade intervals are typically 200-400 ms ). The authors note that the animal or human could, in principle, choose to integrate over longer intervals but if it is moving this may not lead to information that is current for changed circumstances. An optimal processing time of about 300 ms would be consistent with the delays observed before conscious awareness occurs in response to a stimulus - an interval required to form \"more complex sensory images\". ## Global Workspace Theory Global Workspace Theory is the idea that somewhere in the brain there is a facility that integrates the processes that occur in the various separate areas of the brain. The theory was first proposed by Descartes as the *sensus communis*, the common sense, but the modern form of the theory dispenses with the idea of a point soul looking at the brain. In modern Global Workspace theory it is proposed that an area of brain receives input from most of the cerebral cortex and broadcasts its outputs to all of the unconscious modular information processors in the brain. Modern Global Workspace Theory has been championed by Baars (1983, 1988). There is increasing evidence for a Global Workspace or Global Workspaces in the brain. Much of this evidence comes from fMRI, single unit and magnetoencephalography studies in which it is shown that non-conscious or subliminal processing mainly occupies primary, sensory cortex whereas conscious processing occupies large areas of cerebral cortex. In binocular rivalry the stimulus that is consciously perceived is responsible for relatively intense activation of large areas of brain whereas the non-conscious stimulus is often suppressed (see above and Sheinberg & Logothetis (1997), Tononi *et al.* (1998)). The suppression is likely to occur in the Lateral Geniculate Nuclei which suggests a role for the Thalamic Reticular Nuclei, which modulate LGN activity, in the control of the percept. ### Masking and visual awareness Word masking has also been used to investigate the idea of a Global Workspace. When a word is presented on its own for a few tens of milliseconds it remains readable but if it is immediately succeeded by, or accompanied by, another word it becomes indistinct or invisible. This effect is known as \"word masking\". Vogel *et al.* (1998) have investigated a version of word masking known as the \"attentional blink\". They found that when stimuli became invisible the P3 component of the Event Related Potential, which peaks at around 300-500 millisecs after a stimulus, was completely suppressed. The P3 component of the ERP has been related to the lodging of data in working memory and also to gamma band activity in the EEG. This strongly suggests the involvement of a cortico-thalamic loop in the \"attentional blink\". The delay of 0.3 to 0.5 secs is typical of the time required for conscious awareness (see above). Word masking in conjunction with fMRI and Event Related Potential (ERP) recordings has been used by Dehaene *et al.* (2001) to expose control by a central mechanism. It was found that masked words activate mainly the visual cortex and ventral stream (inferior temporal lobe) whereas visible words also activated distant parietal, prefrontal and cingulate sites. Dehaene *et al.* (2003) and found that the dynamics of the loss of visibility of words in an attentional blink experiment could be modelled by a simulated cortico-thalamic loop. In their simulation a distributed cortical process determined which events would receive attention and the system used the thalamic gating systems to exclude those that did not receive attention. Tse *et al.* (2005) have used purely visual stimuli in masking experiments and concluded that, in the case of purely visual stimuli, the neural correlates of awareness were limited to the occipital cortex: \"We suggest that there are both lower and upper bounds within the visual hierarchy for the processing of visual masking and the maintenance of visual awareness of simple unattended targets; the lower bound is at least as high as the border between V2 and V3, and the upper bound is within the occipital lobe, possibly somewhere downstream of V4.\" This discovery would mean that activation of large areas of cortex are unnecessary for awareness. Melloni *et al.* (2007) compared compared the electrophysiological responses related to the processing of visible and invisible words in a delayed matching to sample task. Both perceived and nonperceived words caused a similar increase of local (gamma) oscillations in the EEG, but only perceived words induced a transient long-distance synchronization of gamma oscillations across widely separated regions of the brain. After this transient period of temporal coordination, the electrographic signatures of conscious and unconscious processes continue to diverge. Only words reported as perceivedinduced (1) enhanced theta oscillations over frontal regions during the maintenance interval, (2) an increase of the P300 component of the event-related potential, and (3) an increase in power and phase synchrony of gamma oscillationsbefore the anticipated presentation of the test word. We propose that the critical process mediating the access to conscious perception is the earlytransient global increase of phase synchrony of oscillatory activity in the gammafrequency. Melloni L, Molina C, Pena M, Torres D, Singer W, Rodriguez E. (2007). Synchronization of neural activity across cortical areas correlates withconscious perception.J Neurosci. 2007 Mar 14;27(11):2858-65. ### Attention and the global workspace Baars (2002) in his review of evidence for the Global Workspace Theory quotes many other experiments that show activation of larger areas of cortex in response to conscious stimuli compared with unconscious or subliminal stimuli.The effect is also seen in change blindness, learning and attention. Newman and Baars (1993) consider that the \"workspace\" is fairly global in the brain: \"This Neural Global Workspace (NGW) model views conscious processes in terms of a globally integrative brain system. The neural circuitry contributing to this system is not only widely distributed across the neocortex, but includes key corticothalamic and midbrain circuits as well. These cortico-subcortical circuits are hypothesized to be critical to understanding the mechanisms of attentional control that provide an essential basis for the conscious processing of information\". However they focus particularly on the role of the thalamic Reticular Nucleus and cortico-thalamic connectivity in the control of attention. Other ideas for the location of the Global Workspace are the idea of Singer et al. that gamma synchrony controls access to the content of consciousness and Llinas et al. (1998) that the thalamus is the hub through which communication occurs between areas of cortex. One of the problems with Global Workspace theory is that it suggests that attention, working memory, cognitive control and consciousness may all be in the same area of the brain. It is likely that the mechanisms of attention, working memory, and cognitive control may involve several, interlinked systems perhaps co-opting the basal ganglia in the process. In view of this Maia and Cleeremans (2005) propose that \".. attention, working memory, cognitive control and consciousness are not distinct functions implemented by separate brain systems. Attempting to find separate neural correlates for each may therefore be the wrong approach. Instead, we suggest that they should be understood in terms of the dynamics of global competition, with biasing from PFC (prefrontal cortex).\". The inclusion by Maia and Cleeremans of consciousness with distributed attention, working memory and cognitive control is reminiscent of Zeki & Bartel\'s idea of microconsciousness. It should be noted that, in common with Libet\'s data, the percept seems to be available to phenomenal consciousness some 0.3 to 0.5 secs after a stimulus; this suggests that whatever determines the content of phenomenal consciousness operates before events become part of phenomenal consciousness. This relegates phenomenal consciousness from being a controller of attention to being the recipient of content that is the subject of attention. This finding is consistent with the philosophical problem of the **apparently** epiphenomenal nature of phenomenal consciousness. Given the data on the timing of conscious awareness it seems that there may be two \"workspaces\", an active workspace that models the world, discarding and suppressing data during rivalry, and a passive workspace that receives the final, edited product. The active workspace would correlate with the cortical systems stressed by Dehaene *et al.* and Maia and Cleermans although, given the results of Tse et al., the workspace would be limited to small zones of cortex. The loading of the passive workspace with the output of the active workspace would correlate with thalamo-cortical activity during component P3 of the ERP in which data is transferred from the cortex to the thalamus. This workspace might constitute the source for reports of the content of phenomenal consciousness. Llinas *et al.* (1998) have proposed two parallel cortico-thalamic attentional systems, one of which is related to the thalamic specific nuclei and the other to the thalamic non-specific nuclei, especially the ILN. The non-specific system would be related to consciousness itself. ## The \"cognitive map\" and the neural basis of perceptual space Our bodies appear to be mobile within a constant space. We walk around a room; the room does not rotate around us. The constancy of the location of things gives us the feeling that we are directly viewing a constant world. But how does the brain provide a constant world rather than a world that rotates with the movement of the sense organs? Why is our view of the world when we move our eyes so different from the disturbing flow of images that occur when a video camera is waved around? Do our brains contain a constant \"cognitive map\" (O\'Keefe and Nadel 1978) of our surroundings? Mittelstaedt & Mittelstaedt (1980, 1982) discovered that female gerbils were able to recover their pups in darkened surroundings by searching in a semi random fashion on the outbound journey and then proceeding directly back to the nest on the inbound journey. The direct journey back to the nest seemed to be due to an integration of the various directions taken on the outward journey (**path integration**). If the equipment being explored by the mother gerbil was rotated very slowly the mother would make an error equivalent to the amount of rotation. More rapid rotations that activated the vestibular system of the rat (acceleration measurement) did not cause errors in navigation. This demonstration that rodents could navigate accurately on the basis of **idiothetic** cues (cues that are due to internal senses) led to research on the neural basis of the navigation. 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# Consciousness Studies/Neuroscience 2#Synchronisation of Neural Processes *Contributors: please include full data in the references section for all references in the text.* ```{=html} <div class="noprint"> ``` Home ```{=html} </div> ``` ## Perceptual \"filling in\" Perceptual \"filling in\" occurs when visual properties such as textures, colours, brightness or motion are extended in the visual field to areas where they do not have corresponding events in the world. The filling in of the blind spot by the properties of the field in the contralateral eye has already been discussed. The part of the visual field represented by the blind spot is also \"filled in\" in the case of monocular vision.  Shut the right eye and focus on the pink cross with the left eye, if the head is moved towards the pink cross there is a point at which the yellow disk disappears but the white lines are still present. In this \"filling in\" the visual field does not appear to be distorted. Fiorani *et al.* (1992) developed a technique for probing the cortical blind spot using vertical and horizontal bar stimuli. Matsumoto & komatsu (2005) used this technique on macaque monkeys. In the monocular case they found that as a bar was moved across the visual field so that it crossed the blind spot there was a sudden change in neural activity in the deep layers of the neurons in the blind spot area of V1. When the bar was moved across the same part of the visual field of the contralateral eye the neural activity in the blind spot area increased steadily as the bar was moved. The authors found that there were neurons in the deep layers of blind spot cortex that had elongated receptive fields that could respond to stimuli outside the blind spot and transfer this activation into the blind spot cortex. Filling in of a slightly different type occurs in \"scotoma\". In scotoma an area of the retina is damaged and unresonsive to visual stimuli, immediately after the damage patients report an area of visual field that is unresponsive to stimuli. After several months patients report that the area of field represented by the scotoma contains visual properties related to the physical world surrounding the area that would have formed an image on the scotoma. This results in a distortion of the visual field. (see for instance Gilbert(1993)). Direct measurements of activity in cortical area V1 show that the neurons that represented the area of the scotoma become sensitive to activity in the surrounding visual field. At the cortical level the scotoma is literally \"filled in\". There are many stimuli that cause \"filling in\". These stimuli are known as \"illusions\" because they produce phenomenal experience that has no correlate in the world outside the body. In the \"neon colour spreading illusion\" a lightly coloured circle appears where there should be a white background. Sasaki and Watanabe (2004) used fMRI to show that the part of the topographic map in cortical area V1 corresponding to the light coloured circle was activated.  Fiorani, M., Rosa, M.G.P., Gattas, R. & Rocha-Miranda, C.E. (1992). Dynamic surrounds of receptive fields in primate striate cortex: a physiological basis for perceptual completion? Proc. Natl. Acad. Sci. 89, 8547-8551. <http://www.pnas.org/cgi/content/abstract/89/18/8547> Gilbert, C.D. (1993). Circuitry, architecture and functional dynamics of visual cortex. Matsumoto, M & Komatsu, H. (2005). Neural responses in the macaque V1 to bar stimuli with various lengths presented on the blind spot. J neurophysiol. 93. 2374-2387. <http://jn.physiology.org/cgi/content/abstract/93/5/2374> Sasaki, Y & Watanabe, T. The primary visual cortex fills in colour. Proc. Natl. Acad. Sci. USA 101, 18251-18256. (2004). ## Binocular Rivalry, Pattern Rivalry and Binocular Fusion Sir Charles Wheatstone (1838) was the first scientist to systematically investigate binocular rivalry. Binocular rivalry occurs when different images are presented to the left and right eyes. The subject sees successively one image, a combined image and then the other image. The swapping of images can take a second or more. Binocular rivalry is of interest in consciousness research because the parts of the brain that contain the dominant image should also be those parts that are contributing to conscious experience. Binocular rivalry involves at least two components; the first switches from one image to a merged image and then to the other image and the second permits the view to be part of conscious experience.  The switching of one image for another may involve selecting one of the images as the percept or selecting one of the eyes. Blake *et al.* (1979) performed an experiment in which subjects could change the image at a given eye by pressing a button. When a particular image became dominant they pressed a button to change the image at the eye receiving the dominant image for the non-dominant image. They found that the subjects immediately experienced the second image as the dominant image. This suggests that binocular rivalry is selecting between eyes rather than images. Lehky in 1988 proposed that the switching may be occurring as a result of feedback between visual cortical area V1 and the Lateral Geniculate Nucleus (a thalamic relay - see Carandini *et al.* 2002) and Blake in 1989 also proposed that the switching occurred at the level of area V1. (Visual cortical area V1 receives visual input direct from the LGN.) Tong (2001) has argued that, in humans, the switching of images in binocular rivalry may occur at the earliest levels in the visual cortex. In particular, Tong and Engel (2001) used an elegant technique measuring the activity in the visual cortex that represents the blind spot of the eye to show that almost complete switching to the dominant image occurs at the level of visual cortical area V1. In support of this idea of switching at the level of V1 or even before the cortex, Kreimann *et al.* (2001, 2002) used direct electrode recordings in human cortex and found that the activity of most neurons changed with the percept. Other experiments have not shown a single locus in the brain where the suppressed sensory information gets switched out (Blake & Logothetis 2002, Leopold & Logothetis 1996, Gail et al., 2004). Functional MRI has also shown cortical activity outside of sensory visual cortex related to both images in binocular rivalry. Lumer *et al.* (1998) found that only the fronto-parietal areas of cortex switched with the percept, Fang & He (2005) found that activity relating to both suppressed and unsuppressed images were present in the dorsal stream of the visual system. Wunderlich *et al.* (2005) and Haynes *et al.* (2005) have both found suppression at the level of the lateral geniculate nucleus using fMRI in humans. Pasley *et al.* (2004) have shown that, even during suppression, fearful faces can produce activity in the amygdala (see Pessoa (2005) for a review). Rivalry alternations seem to be the result of widespread activity changes that cover large parts of the brain, including but not necessarily originating at the earliest sensory stages of visual processing. Most investigators have found that, once switching has occurred, there are areas of the brain that contain activity that is solely related to the percept but this varies from most of the cortex to largely more frontal regions depending upon the study. The most likely explanation for binocular rivalry is that the switching occurs at the level of the LGN as a result of feedback from the cortex. Pattern Rivalry is also of interest in consciousness research for the same reasons as binocular rivalry. In pattern rivalry a figure may have two or more forms that replace each other. Typical examples of such figures are the Necker cube and Rubin\'s face-vase. The similarity of the time course of the switching between percepts in binocular rivalry and pattern rivalry has led many authors to suggest that these involve the same mechanism. Logothetis *et al.* (1996) used novel dichoptic stimuli (different images to each eyes) to produce a form of rivalry that seems to involve switching at levels in the cerebral cortex that are more distal to the sensory stimulus than V1. Leopold and Logothetis (1999), on the basis of their work with monkeys, state that \"..many neurons throughout the visual system, both monocular and binocular, continue to respond to a stimulus even when it is perceptually suppressed.\". Kleinschmidt *et al.* (1998) investigated pattern rivalry with MRI and found activity in higher order visual areas during change of dominant pattern. Pettigrew (2001) also describes effects on rivalry due to thought and mood that may require involvement of large areas of cortex in the switching operation and stresses the way that V1 represents different visual fields in different hemispheres of the brain so that inter-hemispheric switching must also be considered. It seems likely that the change of dominant pattern or percept is associated with higher level cortical activity but once the dominant percept is established many of the visually responsive neurons in the cortex are switched over to the new percept. This might account for the similarities in timing of binocular and pattern rivalry and the disparate results found by the various groups of authors. In the words of Kleinschmidt *et al.* (1998): \"The transient activity fluctuations we found suggest that perceptual metastability elicited by ambiguous stimuli is associated with rapid redistributions of neural activity between separate specialized cortical and subcortical structures.\" Which permits both the idea of selecting particular eyes or percepts, perhaps by feedback that switches a thalamic relay on the basis of cortical processing of patterns. Once the cortex has switched the thalamic relay most of the neurons in V1 would become exposed to the dominant percept but there would still be a few neurons in the cortical visual system receiving data from the non dominant image. The investigations of binocular and pattern rivalry provide evidence that conscious visual experience is probably distal to V1 (i.e.: cortex or thalamus). Perceptual rivalry may be part of complex decision making rather than being simply a switch to blank out unwelcome input. It is clear from the Rubin face-vase that pattern rivalry is linked to recognition and would involve a complex delineation of forms within cortical processing. This would suggest that many areas of cortex should be involved before a particular percept is made dominant. Pettigrew (2001) argues that rivalry is the result of a complex phenomenon rather than being simply a switching event. Pettigrew\'s discovery that laughter abolishes rivalry also points to a complex cortical system for switching percepts. Pettigrew proposes that complex cortical processes control rivalry and that the actual switching of percepts is performed sub-cortically in the Ventral Tegmental Area. He concludes his review of the problem by noting that \"Rivalry may thus reflect fundamental aspects of perceptual decision making..\" Pettigrew (2001). Another effect, known as \"binocular fusion\", provides further compelling evidence for the non-conscious nature of the cerebral cortex. In binocular fusion images from both eyes are fused together to create a single image in experience. Moutoussis and Zeki (2002) used a form of binocular fusion in which images of faces were flashed at 100ms intervals to both eyes simultaneously. When both eyes received images of the same colour the subject could see the faces but when one eye received a green image on a red background and the other a red image on a green background the subjects reported seeing a uniform yellow field that contained no faces. fMRI scans of the subject\'s brains showed that when both eyes were exposed to images of the same colour the part of the brain that deals with faces was active and when each eye received images of different colours the same areas of brain showed activity. In other words the cortex contained strong activity related to faces whether or not faces were experienced. Moutoussis and Zeki found a similar effect when they used images of houses instead of images of faces. The authors concluded that: \"The present study further suggests that there are no separate processing and perceptual areas but rather that the same cortical regions are involved in both the processing and, when certain levels of activation are reached and probably in combination with the activation of other areas as well, the generation of a conscious visual percept\". This conclusion does not seem to be supported by the data. There is no evidence that any area of cortex contains the percept itself. The experiment shows that the cortex contains data relating to both red and green faces which suggests that the cortex is not the site of the conscious percept. The percept is most likely distal to the cortex perhaps in the thalamus or some other area that receives cortical sensory output. It is interesting that Fries *et al.* (1997) found that neurons that were activated by the dominant image in binocular rivalry fired synchronously whereas those that were activated by the non-dominant image did not. Thalamocorticothalamic oscillations are the most likely source for synchronising neurons over whole areas of cortex, suggesting that the conscious percept is located in the thalamus rather than the cortex. ## Synchronisation of Neural Processes Our experience seems to contain entities with their attributes attached to them at the correct places in space and time. When a dog barks we see its jaws open at the same time as the bark and both jaws and bark are at the same location. We take this for granted but the brain must be engaging in some complex processing to achieve this synchronised and appropriately positioned set of objects and events. The illustration below shows the two basic processes that might be used to synchronise events between the different specialised processors in the cerebral cortex and brain in general.  In the first option a complete model of sensation, dream etc. may be created and then allowed to become part of conscious experience. In the second model events are released into experience as fast as possible but are synchronous when recalled, having been synchronised in a storage buffer. There is a third option in which there is no synchronisation of events so that the output from different processors would occur at different times. The \'experience buffer\' would be a volume of brain in which a succession of events could be recorded. The buffer might either be updated in steps, the previous content being discarded, or continuously updated with the oldest content being lost continuously. In the first option events from different processes would always appear to be simultaneous unless the experience buffer were updated as a series of steps in which case any changes at around the moment of updating might appear in successive buffers. For instance, if change of position were processed before change in colour a circle on a screen that changed from green to red at the start of a motion might seem to be briefly green during the motion and then turn red. In the second model events from different processors might appear asynchronous at the moment of experience but synchronous when recalled. Colour vision and motion vision are processed in different parts of the visual cortex and in distinct parts of visual cortical areas V1 and V2. They are different processes and hence ideal for studying the synchronisation of cortical activity. Moutoussis and Zeki (1997) presented subjects with moving coloured squares on a computer screen that changed from red to green or vice versa as they changed direction of movement. It was found that subjects seemed to perceive changes in colour some 70-80 msecs before they perceived a change in the direction of motion of the squares. Further work by Arnold *et al.* (2001) and Arnold and Clifford (2001) have confirmed that colour changes seem to be perceived before motion. Arnold and Clifford (2001) also found a quantitative relationship between the colour/motion asynchrony and the direction of change of motion, complete reversals of direction giving rise to the greatest asynchrony between the detection of colour and motion changes. Moutoussis and Zeki (1997) conclude by stating that the asynchrony of neural processes shows that \"..the perception of each attribute is solely the result of the activity in the specialised system involved in its processing..\". It seems more likely that the experiments simply show that slow neural processes are not synchronised before they become percepts (the third option above). The experiments are excellent evidence for the concept of the cortex as a set of specialised processors that deliver their output asynchronously to some other place where the output becomes a percept. These experiments on colour and motion suggest that there is no synchronisation between the processes that deal with these two aspects of vision. Another set of experiments by Clifford *et al.* (2003) supports this idea of processing being asynchronous. They asked subjects to perform a variety of judgements of when visual events occurred and found that the degree of synchrony of one visual event with another depends on the type of judgement. Different judgements probably use processors in different areas of cortex and the output from these arrives asynchronously at the part of the brain that supports the percept. When the percept is formed there must be feedback to the cortical processes that create its content. Otherwise it would not be possible to report about the percept and the cortex would be unable to direct processing to the percept in preference to other, non-conscious cortical data. Although slow processes (20 milliseconds to 1 second) do not seem to be synchronised there is some evidence for very rapid synchronisation. Andrews *et al.* (1996) revisited a problem raised by the famous physiologist Charles Sherrington. Sherrington considered the phenomenon of \'flicker fusion\' in which a flickering light appears to be a continuous steady light if it flashes on and off at frequencies of about 45 Hz or higher. He reasoned that if the images from both eyes are brought together to form a single image then the frequency at which a flickering light appears to be steady should depend on whether one or two eyes are used. Flicker fusion should occur if each eye receives alternate flashes at only half the normal flicker fusion frequency. The flicker should disappear if the left eye receives flashes at 23 pulses per second and the right eye receives alternate flashes at 23 pulses per second. When Sherrington performed the experiment he found that this was not the case, using approximate figures, each eye required 46 pulses per second for fusion to occur. Sherrington proposed that the flicker fusion in alternate binocular presentation was occurring \"psychically\", outside of normal physiological processes. Andrews *et al.* duplicated Sherrington\'s result but investigated it further. They found that when lights were flashed in each eye alternately at low frequences (2 Hz) the experience was the same as a light being flashed in both eyes at this rate. At frequencies of four Hz and higher the subjects began to report that the lights being flashed alternately in both eyes seemed to flicker at the same rate as lights being flashed in both eyes at half the frequency. It seemed as if a flash in one eye followed by a flash in the other eye was being perceived as a single flash or \"conflated\" as the authors put it. The authors explained this effect by suggesting that the brain activity corresponding to the flashes was sampled for a short period and any number of flashes occurring during this period became perceived as a single flash. The maximum rate of sampling would be about 45 Hz. This idea is similar to option (1) above, where the buffer is filled and emptied 40 - 50 times a second. An experience buffer that is refreshed at 40-50 times a second might also explain the results obtained with colour and motion asynchrony because synchronisation between processes may well happen too quickly to affect processes that occur at very slow rates. Singer and Gray (1995), Singer (2001) have proposed that synchronisation between neurones at about 45 Hz is the discriminator between those neurones with activity that contributes to conscious experience and activity in other neurones. A rapid refresh rate in a synchronising buffer agrees with the results found by Fries *et al.* (1997) in which visual cortical neurones that represent a percept underwent synchronous oscillations in the gamma frequency range (39--63 Hz). Tononi *et al.* (1998) have also found synchronisation of neural activity in neurones that represent the percept. The gamma frequency oscillations are intrinsic to the cortex but are triggered by the thalamus and are part of the \'arousal system\'. Readers should be wary of the term \'arousal system\' because it evokes the idea of something waking up a conscious cortex. The cortex can be fully active during sleep and even during pathological unconsciousness such as persistent vegetative state so it is possible that the arousal centres themselves or nearby structures actually host phenomenal consciousness. ## EEG and synchronisation If electrodes are placed on the scalp varying electrical potentials of a few tens of microvolts can be recorded between the electrodes. Recordings of potentials from electrodes on the scalp are known as electroencephalograms (EEGs). The potentials recorded in the EEG are due to postsynaptic potentials in nerve cells. The EEG is insensitive to the activity of single cells and occurs as a result of relatively slow, **synchronised**, changes in large areas of cells. The differences in potential between two scalp electrodes are largely due to depolarisation and hyperpolarisation of the dendritic trees of cortical pyramidal cells. The folding of the cortex (gyri) is problematical for recording and interpreting EEGs because opposing layers of cortex can cancel any net potentials. The EEG shows rhythmic activity. This is conventionally divided into the following frequency bands: Delta waves 0--4 Hz Theta waves 4--8 Hz Alpha waves 8--12 Hz Beta waves \>10 Hz Gamma waves (also called fast beta) 25--100 Hz EEGs also contain short bursts of activity called spindles and very fast oscillations (VFOs). Spindles last for 1--2 seconds and contain rhythmic activity at 7--14 Hz. They are associated with the onset of sleep. The VFOs consist of short bursts at frequencies of over 80 Hz. When the eyes are closed the amplitude of activity from most pairs of electrodes is increased compared with when the eyes are open. When subjects are awake the EEG consists mainly of alpha and beta activity with considerable low amplitude gamma when the eyes are open. In stage 1 sleep the EEG consists of theta waves, in stage 2 sleep of varied activity and spindles, in stage 4 sleep of delta and during REM sleep of beta and theta activity. In epileptic seizures there tends to be high amplitude activity with pronounced synchronisation between many pairs of electrodes. The rhythmic electrical activity is due to cortical feedback loops, cortico-cortical synchronisation, thalamic pacemakers and thalamo-cortical synchronisation. VFOs have been attributed to the activity of electrical connections between cells (dendro-dendritic gap junctions) (Traub (2003)). The gamma activity, centred on a frequency of 40 Hz appears to be related to activity in cortical interneurons that form electrical connections between their dendrites (Tamas *et al.* 2000). These oscillations can be triggered by high frequency stimulation of the posterior intralaminar nuclei of the thalamus (Barth and MacDonald 1996, Sukov and Barth 2001) and as a result of activation of the reticular system (Munk *et al.* 1996). This suggests that stimulation of cortex by thalamic sensory relays triggers gamma band activity in the cortex. A shift from gamma to beta waves can occur in human event related potentials after about 0.2 secs (Pantev 1995, Traub *et al.* 1999). The alpha activity is related to thalamic pacemakers, perhaps as a result of intrinsic oscillatory activity in thalamic sensory relays (see Roy & Prichep 2005 for a brief review). Theta activity, which occurs during some cognitive tasks and mental arithmetic involves a loop from the cortex to the non-specific thalamic nuclei. Delta activity seems to be endogenous to cortex when input is suppressed during sleep. Beta activity is due to cortico-cortical interactions, often after a brief period of gamma activation. It should be noted that gamma and beta activity can be expressed as impulses in cortico-thalamic pathways and that when cortical and thalamic activity is correlated there is a conscious state. In other words gamma or beta waves in the cortex are not correlates of consciousness on their own - see for instance Laureys *et al.* (2002). ## Event related potentials After a sudden event there are a characteristic set of changes in EEG activity known as **event related potentials** or ERPs. The time course of the ERP is shown in the diagram below.  ERPs occur in response to novel stimuli and are also produced by brief transcranial magnetic stimulation (TMS)(Iramina *et al.* 2002). The slow component is known as the P3 or P300 phase of the ERP. It is due to activation of areas of the brain that are relatively remote from the primary sensory areas of brain. Nieuwenhuis *et al.* (2005) have reviewed the origin of the P300 ERP: \"To summarize, convergent evidence suggests that P3-like activity can be recorded in several, widely separated brain areas. These include some medial temporal and subcortical structures (e.g., the hippocampal formation, amygdala, and thalamus), but these structures are unlikely to contribute directly to the scalp-recorded P3.\". According to Nieuwenhuis *et al.* (2005) the recorded P300 may be due to temporo-parietal and prefrontal cortical activity. Linden (2005) has also concluded that widespread, but specific, cortical activation is correlated with the recorded P300 ERP. The generator of the P300 is still obscure. Nieuwenhuis *et al.* (2005) consider that the Locus coeruleus, a nucleus in the pons that regulates task related attention and part of the sleep-wake cycle, may be responsible. In line with this, Mashour *et al.* (2005) have discovered that TMS induced P300 activity is reduced in unconscious states. Whether the P300 is related to Libet\'s 0.5 second delay is still obscure but the discovery that the P300 occurs in association with subliminal stimuli (stimuli that do not enter awareness)(Bernat *et al.* 2001) suggests that it is associated with non-conscious cortical processing. Williams *et al.* (2004), in an investigation of subliminal and supraliminal fear perception, found that \"conscious fear perception was distinguished by a more prominent N4, peaking around 400 msec\"; the N4 component follows the P300 component in the succession of phases of the ERP. Williams *et al.* considered that the earlier phases in the ERP are probably related to non-conscious processing. In contrast Vogel *et al.* (1998) found that suppression of the P300 was associated with suppression of awareness. ## The integration delay Psychological experiments often involve binary decisions where subjects give one of two outputs in response to stimuli. It is found that if the stimuli are made increasingly noisy or complex the response time tends to increase. Psychophyicists have developed various mathematical models to explain the increased response times due to noise such as the Integrator and Accumulator models (cf: Luce(1986)). These models have been fairly successful when explaining experiments such as judging the net direction of movement of sets of dots on a screen when the dots are given semi-random paths and different brightness etc. In these circumstances it can take up to 2 seconds for an accurate decision. There are many tasks however where the accuracy of decision making does not improve after about 300 milliseconds. The accuracy of the performance of rats when choosing between two alternatives when reacting to odours peaks at about 300 ms (Uchida and Mainen(2003), Abraham *et al.* (2004)). The accuracy of humans when performing vernier acuity tasks, line detection, contrast sensitivity, motion velocity discrimination and stereoscopic depth discrimination seems to peak at 300ms (Uchida *et al.* 2006). Uchida, Kepecs and Mainen (2006) suggest that \"rapid and short integration time is a sensible strategy for rapid processing of low-level sensory information in order to form more complex sensory images, both in vision and olfaction.\" Whether these authors regard these derived sensory images as the content of consciousness is not mentioned. The authors propose that the 300ms optimal integration time may be partly due to the mechanics of sniffing (a sniff takes about 125-200ms) and the nature of optical fixation (inter-saccade intervals are typically 200-400 ms ). The authors note that the animal or human could, in principle, choose to integrate over longer intervals but if it is moving this may not lead to information that is current for changed circumstances. An optimal processing time of about 300 ms would be consistent with the delays observed before conscious awareness occurs in response to a stimulus - an interval required to form \"more complex sensory images\". ## Global Workspace Theory Global Workspace Theory is the idea that somewhere in the brain there is a facility that integrates the processes that occur in the various separate areas of the brain. The theory was first proposed by Descartes as the *sensus communis*, the common sense, but the modern form of the theory dispenses with the idea of a point soul looking at the brain. In modern Global Workspace theory it is proposed that an area of brain receives input from most of the cerebral cortex and broadcasts its outputs to all of the unconscious modular information processors in the brain. Modern Global Workspace Theory has been championed by Baars (1983, 1988). There is increasing evidence for a Global Workspace or Global Workspaces in the brain. Much of this evidence comes from fMRI, single unit and magnetoencephalography studies in which it is shown that non-conscious or subliminal processing mainly occupies primary, sensory cortex whereas conscious processing occupies large areas of cerebral cortex. In binocular rivalry the stimulus that is consciously perceived is responsible for relatively intense activation of large areas of brain whereas the non-conscious stimulus is often suppressed (see above and Sheinberg & Logothetis (1997), Tononi *et al.* (1998)). The suppression is likely to occur in the Lateral Geniculate Nuclei which suggests a role for the Thalamic Reticular Nuclei, which modulate LGN activity, in the control of the percept. ### Masking and visual awareness Word masking has also been used to investigate the idea of a Global Workspace. When a word is presented on its own for a few tens of milliseconds it remains readable but if it is immediately succeeded by, or accompanied by, another word it becomes indistinct or invisible. This effect is known as \"word masking\". Vogel *et al.* (1998) have investigated a version of word masking known as the \"attentional blink\". They found that when stimuli became invisible the P3 component of the Event Related Potential, which peaks at around 300-500 millisecs after a stimulus, was completely suppressed. The P3 component of the ERP has been related to the lodging of data in working memory and also to gamma band activity in the EEG. This strongly suggests the involvement of a cortico-thalamic loop in the \"attentional blink\". The delay of 0.3 to 0.5 secs is typical of the time required for conscious awareness (see above). Word masking in conjunction with fMRI and Event Related Potential (ERP) recordings has been used by Dehaene *et al.* (2001) to expose control by a central mechanism. It was found that masked words activate mainly the visual cortex and ventral stream (inferior temporal lobe) whereas visible words also activated distant parietal, prefrontal and cingulate sites. Dehaene *et al.* (2003) and found that the dynamics of the loss of visibility of words in an attentional blink experiment could be modelled by a simulated cortico-thalamic loop. In their simulation a distributed cortical process determined which events would receive attention and the system used the thalamic gating systems to exclude those that did not receive attention. Tse *et al.* (2005) have used purely visual stimuli in masking experiments and concluded that, in the case of purely visual stimuli, the neural correlates of awareness were limited to the occipital cortex: \"We suggest that there are both lower and upper bounds within the visual hierarchy for the processing of visual masking and the maintenance of visual awareness of simple unattended targets; the lower bound is at least as high as the border between V2 and V3, and the upper bound is within the occipital lobe, possibly somewhere downstream of V4.\" This discovery would mean that activation of large areas of cortex are unnecessary for awareness. Melloni *et al.* (2007) compared compared the electrophysiological responses related to the processing of visible and invisible words in a delayed matching to sample task. Both perceived and nonperceived words caused a similar increase of local (gamma) oscillations in the EEG, but only perceived words induced a transient long-distance synchronization of gamma oscillations across widely separated regions of the brain. After this transient period of temporal coordination, the electrographic signatures of conscious and unconscious processes continue to diverge. Only words reported as perceivedinduced (1) enhanced theta oscillations over frontal regions during the maintenance interval, (2) an increase of the P300 component of the event-related potential, and (3) an increase in power and phase synchrony of gamma oscillationsbefore the anticipated presentation of the test word. We propose that the critical process mediating the access to conscious perception is the earlytransient global increase of phase synchrony of oscillatory activity in the gammafrequency. Melloni L, Molina C, Pena M, Torres D, Singer W, Rodriguez E. (2007). Synchronization of neural activity across cortical areas correlates withconscious perception.J Neurosci. 2007 Mar 14;27(11):2858-65. ### Attention and the global workspace Baars (2002) in his review of evidence for the Global Workspace Theory quotes many other experiments that show activation of larger areas of cortex in response to conscious stimuli compared with unconscious or subliminal stimuli.The effect is also seen in change blindness, learning and attention. Newman and Baars (1993) consider that the \"workspace\" is fairly global in the brain: \"This Neural Global Workspace (NGW) model views conscious processes in terms of a globally integrative brain system. The neural circuitry contributing to this system is not only widely distributed across the neocortex, but includes key corticothalamic and midbrain circuits as well. These cortico-subcortical circuits are hypothesized to be critical to understanding the mechanisms of attentional control that provide an essential basis for the conscious processing of information\". However they focus particularly on the role of the thalamic Reticular Nucleus and cortico-thalamic connectivity in the control of attention. Other ideas for the location of the Global Workspace are the idea of Singer et al. that gamma synchrony controls access to the content of consciousness and Llinas et al. (1998) that the thalamus is the hub through which communication occurs between areas of cortex. One of the problems with Global Workspace theory is that it suggests that attention, working memory, cognitive control and consciousness may all be in the same area of the brain. It is likely that the mechanisms of attention, working memory, and cognitive control may involve several, interlinked systems perhaps co-opting the basal ganglia in the process. In view of this Maia and Cleeremans (2005) propose that \".. attention, working memory, cognitive control and consciousness are not distinct functions implemented by separate brain systems. Attempting to find separate neural correlates for each may therefore be the wrong approach. Instead, we suggest that they should be understood in terms of the dynamics of global competition, with biasing from PFC (prefrontal cortex).\". The inclusion by Maia and Cleeremans of consciousness with distributed attention, working memory and cognitive control is reminiscent of Zeki & Bartel\'s idea of microconsciousness. It should be noted that, in common with Libet\'s data, the percept seems to be available to phenomenal consciousness some 0.3 to 0.5 secs after a stimulus; this suggests that whatever determines the content of phenomenal consciousness operates before events become part of phenomenal consciousness. This relegates phenomenal consciousness from being a controller of attention to being the recipient of content that is the subject of attention. This finding is consistent with the philosophical problem of the **apparently** epiphenomenal nature of phenomenal consciousness. Given the data on the timing of conscious awareness it seems that there may be two \"workspaces\", an active workspace that models the world, discarding and suppressing data during rivalry, and a passive workspace that receives the final, edited product. The active workspace would correlate with the cortical systems stressed by Dehaene *et al.* and Maia and Cleermans although, given the results of Tse et al., the workspace would be limited to small zones of cortex. The loading of the passive workspace with the output of the active workspace would correlate with thalamo-cortical activity during component P3 of the ERP in which data is transferred from the cortex to the thalamus. This workspace might constitute the source for reports of the content of phenomenal consciousness. Llinas *et al.* (1998) have proposed two parallel cortico-thalamic attentional systems, one of which is related to the thalamic specific nuclei and the other to the thalamic non-specific nuclei, especially the ILN. The non-specific system would be related to consciousness itself. ## The \"cognitive map\" and the neural basis of perceptual space Our bodies appear to be mobile within a constant space. We walk around a room; the room does not rotate around us. The constancy of the location of things gives us the feeling that we are directly viewing a constant world. But how does the brain provide a constant world rather than a world that rotates with the movement of the sense organs? Why is our view of the world when we move our eyes so different from the disturbing flow of images that occur when a video camera is waved around? Do our brains contain a constant \"cognitive map\" (O\'Keefe and Nadel 1978) of our surroundings? Mittelstaedt & Mittelstaedt (1980, 1982) discovered that female gerbils were able to recover their pups in darkened surroundings by searching in a semi random fashion on the outbound journey and then proceeding directly back to the nest on the inbound journey. The direct journey back to the nest seemed to be due to an integration of the various directions taken on the outward journey (**path integration**). If the equipment being explored by the mother gerbil was rotated very slowly the mother would make an error equivalent to the amount of rotation. More rapid rotations that activated the vestibular system of the rat (acceleration measurement) did not cause errors in navigation. This demonstration that rodents could navigate accurately on the basis of **idiothetic** cues (cues that are due to internal senses) led to research on the neural basis of the navigation. As early as 1971 O\'Keefe and Dostrovsky had discovered that there are particular cells in the hippocampus that fire according to the position of an animal in the environment. This has been complimented by research that showed that changes in visual cues within the environment caused changes in the firing rate of place cells in hippocampal area CA3 (.   !Entorhinal cortex approximately maps to areas 28 and 34{width="500"} F. P. Battaglia and A. Treves. 1998 Attractor neural networks storing multiple space representations: A model for hippocampal place fields. PHYSICAL REVIEW E DECEMBER 1998 VOLUME 58, NUMBER 6 <http://www.sissa.it/~ale/Bat+98b.pdf> Leutgeb, S., Leutgeb, J.K., Moser, M-B, and Moser, E.I. 2005. Place cells, spatial maps and the population code for memory. Current Opinion in Neurobiology 2005, 15:738--746. <http://instruct1.cit.cornell.edu/courses/bionb720nejc/reprints/LeutgebEtAl2005.pdf> Mittelstaedt, H. & Mittelstaedt, M-L. 1982. Avian Navigation. (ed. Papi, F. & Wallraff, H.) 290-297. Springer, Berlin. Mittelstaedt, M-L & Glasauer, S. 1991. Idiothetic Navigation in Gerbils and Humans. Zool. Jb. Physiol. 95 (1991), 427-435 <http://web.archive.org/web/20110125132449/http://www.nefo.med.uni-muenchen.de/~sglasauer/MittelstaedtGlasauer1991.pdf> O\'Keefe, J. & Dostrovsky, J. (1971). The hippocampus as a spatial map: preliminary evidence from unit activity in the freely moving rat. Brain Res. 34, 171-175. O\'Keefe, J. & Nadel, L. (1978). The Hippocampus as a cognitive map. (Oxford) ## Bibliography Defining the States of Consciousness. Tassi, P., Muzet, A. (2001) Neuroscience and Behavioural Reviews 25(2001) 175-191. 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# Consciousness Studies/Neuroscience 2#EEG and synchronisation *Contributors: please include full data in the references section for all references in the text.* ```{=html} <div class="noprint"> ``` Home ```{=html} </div> ``` ## Perceptual \"filling in\" Perceptual \"filling in\" occurs when visual properties such as textures, colours, brightness or motion are extended in the visual field to areas where they do not have corresponding events in the world. The filling in of the blind spot by the properties of the field in the contralateral eye has already been discussed. The part of the visual field represented by the blind spot is also \"filled in\" in the case of monocular vision.  Shut the right eye and focus on the pink cross with the left eye, if the head is moved towards the pink cross there is a point at which the yellow disk disappears but the white lines are still present. In this \"filling in\" the visual field does not appear to be distorted. Fiorani *et al.* (1992) developed a technique for probing the cortical blind spot using vertical and horizontal bar stimuli. Matsumoto & komatsu (2005) used this technique on macaque monkeys. In the monocular case they found that as a bar was moved across the visual field so that it crossed the blind spot there was a sudden change in neural activity in the deep layers of the neurons in the blind spot area of V1. When the bar was moved across the same part of the visual field of the contralateral eye the neural activity in the blind spot area increased steadily as the bar was moved. The authors found that there were neurons in the deep layers of blind spot cortex that had elongated receptive fields that could respond to stimuli outside the blind spot and transfer this activation into the blind spot cortex. Filling in of a slightly different type occurs in \"scotoma\". In scotoma an area of the retina is damaged and unresonsive to visual stimuli, immediately after the damage patients report an area of visual field that is unresponsive to stimuli. After several months patients report that the area of field represented by the scotoma contains visual properties related to the physical world surrounding the area that would have formed an image on the scotoma. This results in a distortion of the visual field. (see for instance Gilbert(1993)). Direct measurements of activity in cortical area V1 show that the neurons that represented the area of the scotoma become sensitive to activity in the surrounding visual field. At the cortical level the scotoma is literally \"filled in\". There are many stimuli that cause \"filling in\". These stimuli are known as \"illusions\" because they produce phenomenal experience that has no correlate in the world outside the body. In the \"neon colour spreading illusion\" a lightly coloured circle appears where there should be a white background. Sasaki and Watanabe (2004) used fMRI to show that the part of the topographic map in cortical area V1 corresponding to the light coloured circle was activated.  Fiorani, M., Rosa, M.G.P., Gattas, R. & Rocha-Miranda, C.E. (1992). Dynamic surrounds of receptive fields in primate striate cortex: a physiological basis for perceptual completion? Proc. Natl. Acad. Sci. 89, 8547-8551. <http://www.pnas.org/cgi/content/abstract/89/18/8547> Gilbert, C.D. (1993). Circuitry, architecture and functional dynamics of visual cortex. Matsumoto, M & Komatsu, H. (2005). Neural responses in the macaque V1 to bar stimuli with various lengths presented on the blind spot. J neurophysiol. 93. 2374-2387. <http://jn.physiology.org/cgi/content/abstract/93/5/2374> Sasaki, Y & Watanabe, T. The primary visual cortex fills in colour. Proc. Natl. Acad. Sci. USA 101, 18251-18256. (2004). ## Binocular Rivalry, Pattern Rivalry and Binocular Fusion Sir Charles Wheatstone (1838) was the first scientist to systematically investigate binocular rivalry. Binocular rivalry occurs when different images are presented to the left and right eyes. The subject sees successively one image, a combined image and then the other image. The swapping of images can take a second or more. Binocular rivalry is of interest in consciousness research because the parts of the brain that contain the dominant image should also be those parts that are contributing to conscious experience. Binocular rivalry involves at least two components; the first switches from one image to a merged image and then to the other image and the second permits the view to be part of conscious experience.  The switching of one image for another may involve selecting one of the images as the percept or selecting one of the eyes. Blake *et al.* (1979) performed an experiment in which subjects could change the image at a given eye by pressing a button. When a particular image became dominant they pressed a button to change the image at the eye receiving the dominant image for the non-dominant image. They found that the subjects immediately experienced the second image as the dominant image. This suggests that binocular rivalry is selecting between eyes rather than images. Lehky in 1988 proposed that the switching may be occurring as a result of feedback between visual cortical area V1 and the Lateral Geniculate Nucleus (a thalamic relay - see Carandini *et al.* 2002) and Blake in 1989 also proposed that the switching occurred at the level of area V1. (Visual cortical area V1 receives visual input direct from the LGN.) Tong (2001) has argued that, in humans, the switching of images in binocular rivalry may occur at the earliest levels in the visual cortex. In particular, Tong and Engel (2001) used an elegant technique measuring the activity in the visual cortex that represents the blind spot of the eye to show that almost complete switching to the dominant image occurs at the level of visual cortical area V1. In support of this idea of switching at the level of V1 or even before the cortex, Kreimann *et al.* (2001, 2002) used direct electrode recordings in human cortex and found that the activity of most neurons changed with the percept. Other experiments have not shown a single locus in the brain where the suppressed sensory information gets switched out (Blake & Logothetis 2002, Leopold & Logothetis 1996, Gail et al., 2004). Functional MRI has also shown cortical activity outside of sensory visual cortex related to both images in binocular rivalry. Lumer *et al.* (1998) found that only the fronto-parietal areas of cortex switched with the percept, Fang & He (2005) found that activity relating to both suppressed and unsuppressed images were present in the dorsal stream of the visual system. Wunderlich *et al.* (2005) and Haynes *et al.* (2005) have both found suppression at the level of the lateral geniculate nucleus using fMRI in humans. Pasley *et al.* (2004) have shown that, even during suppression, fearful faces can produce activity in the amygdala (see Pessoa (2005) for a review). Rivalry alternations seem to be the result of widespread activity changes that cover large parts of the brain, including but not necessarily originating at the earliest sensory stages of visual processing. Most investigators have found that, once switching has occurred, there are areas of the brain that contain activity that is solely related to the percept but this varies from most of the cortex to largely more frontal regions depending upon the study. The most likely explanation for binocular rivalry is that the switching occurs at the level of the LGN as a result of feedback from the cortex. Pattern Rivalry is also of interest in consciousness research for the same reasons as binocular rivalry. In pattern rivalry a figure may have two or more forms that replace each other. Typical examples of such figures are the Necker cube and Rubin\'s face-vase. The similarity of the time course of the switching between percepts in binocular rivalry and pattern rivalry has led many authors to suggest that these involve the same mechanism. Logothetis *et al.* (1996) used novel dichoptic stimuli (different images to each eyes) to produce a form of rivalry that seems to involve switching at levels in the cerebral cortex that are more distal to the sensory stimulus than V1. Leopold and Logothetis (1999), on the basis of their work with monkeys, state that \"..many neurons throughout the visual system, both monocular and binocular, continue to respond to a stimulus even when it is perceptually suppressed.\". Kleinschmidt *et al.* (1998) investigated pattern rivalry with MRI and found activity in higher order visual areas during change of dominant pattern. Pettigrew (2001) also describes effects on rivalry due to thought and mood that may require involvement of large areas of cortex in the switching operation and stresses the way that V1 represents different visual fields in different hemispheres of the brain so that inter-hemispheric switching must also be considered. It seems likely that the change of dominant pattern or percept is associated with higher level cortical activity but once the dominant percept is established many of the visually responsive neurons in the cortex are switched over to the new percept. This might account for the similarities in timing of binocular and pattern rivalry and the disparate results found by the various groups of authors. In the words of Kleinschmidt *et al.* (1998): \"The transient activity fluctuations we found suggest that perceptual metastability elicited by ambiguous stimuli is associated with rapid redistributions of neural activity between separate specialized cortical and subcortical structures.\" Which permits both the idea of selecting particular eyes or percepts, perhaps by feedback that switches a thalamic relay on the basis of cortical processing of patterns. Once the cortex has switched the thalamic relay most of the neurons in V1 would become exposed to the dominant percept but there would still be a few neurons in the cortical visual system receiving data from the non dominant image. The investigations of binocular and pattern rivalry provide evidence that conscious visual experience is probably distal to V1 (i.e.: cortex or thalamus). Perceptual rivalry may be part of complex decision making rather than being simply a switch to blank out unwelcome input. It is clear from the Rubin face-vase that pattern rivalry is linked to recognition and would involve a complex delineation of forms within cortical processing. This would suggest that many areas of cortex should be involved before a particular percept is made dominant. Pettigrew (2001) argues that rivalry is the result of a complex phenomenon rather than being simply a switching event. Pettigrew\'s discovery that laughter abolishes rivalry also points to a complex cortical system for switching percepts. Pettigrew proposes that complex cortical processes control rivalry and that the actual switching of percepts is performed sub-cortically in the Ventral Tegmental Area. He concludes his review of the problem by noting that \"Rivalry may thus reflect fundamental aspects of perceptual decision making..\" Pettigrew (2001). Another effect, known as \"binocular fusion\", provides further compelling evidence for the non-conscious nature of the cerebral cortex. In binocular fusion images from both eyes are fused together to create a single image in experience. Moutoussis and Zeki (2002) used a form of binocular fusion in which images of faces were flashed at 100ms intervals to both eyes simultaneously. When both eyes received images of the same colour the subject could see the faces but when one eye received a green image on a red background and the other a red image on a green background the subjects reported seeing a uniform yellow field that contained no faces. fMRI scans of the subject\'s brains showed that when both eyes were exposed to images of the same colour the part of the brain that deals with faces was active and when each eye received images of different colours the same areas of brain showed activity. In other words the cortex contained strong activity related to faces whether or not faces were experienced. Moutoussis and Zeki found a similar effect when they used images of houses instead of images of faces. The authors concluded that: \"The present study further suggests that there are no separate processing and perceptual areas but rather that the same cortical regions are involved in both the processing and, when certain levels of activation are reached and probably in combination with the activation of other areas as well, the generation of a conscious visual percept\". This conclusion does not seem to be supported by the data. There is no evidence that any area of cortex contains the percept itself. The experiment shows that the cortex contains data relating to both red and green faces which suggests that the cortex is not the site of the conscious percept. The percept is most likely distal to the cortex perhaps in the thalamus or some other area that receives cortical sensory output. It is interesting that Fries *et al.* (1997) found that neurons that were activated by the dominant image in binocular rivalry fired synchronously whereas those that were activated by the non-dominant image did not. Thalamocorticothalamic oscillations are the most likely source for synchronising neurons over whole areas of cortex, suggesting that the conscious percept is located in the thalamus rather than the cortex. ## Synchronisation of Neural Processes Our experience seems to contain entities with their attributes attached to them at the correct places in space and time. When a dog barks we see its jaws open at the same time as the bark and both jaws and bark are at the same location. We take this for granted but the brain must be engaging in some complex processing to achieve this synchronised and appropriately positioned set of objects and events. The illustration below shows the two basic processes that might be used to synchronise events between the different specialised processors in the cerebral cortex and brain in general.  In the first option a complete model of sensation, dream etc. may be created and then allowed to become part of conscious experience. In the second model events are released into experience as fast as possible but are synchronous when recalled, having been synchronised in a storage buffer. There is a third option in which there is no synchronisation of events so that the output from different processors would occur at different times. The \'experience buffer\' would be a volume of brain in which a succession of events could be recorded. The buffer might either be updated in steps, the previous content being discarded, or continuously updated with the oldest content being lost continuously. In the first option events from different processes would always appear to be simultaneous unless the experience buffer were updated as a series of steps in which case any changes at around the moment of updating might appear in successive buffers. For instance, if change of position were processed before change in colour a circle on a screen that changed from green to red at the start of a motion might seem to be briefly green during the motion and then turn red. In the second model events from different processors might appear asynchronous at the moment of experience but synchronous when recalled. Colour vision and motion vision are processed in different parts of the visual cortex and in distinct parts of visual cortical areas V1 and V2. They are different processes and hence ideal for studying the synchronisation of cortical activity. Moutoussis and Zeki (1997) presented subjects with moving coloured squares on a computer screen that changed from red to green or vice versa as they changed direction of movement. It was found that subjects seemed to perceive changes in colour some 70-80 msecs before they perceived a change in the direction of motion of the squares. Further work by Arnold *et al.* (2001) and Arnold and Clifford (2001) have confirmed that colour changes seem to be perceived before motion. Arnold and Clifford (2001) also found a quantitative relationship between the colour/motion asynchrony and the direction of change of motion, complete reversals of direction giving rise to the greatest asynchrony between the detection of colour and motion changes. Moutoussis and Zeki (1997) conclude by stating that the asynchrony of neural processes shows that \"..the perception of each attribute is solely the result of the activity in the specialised system involved in its processing..\". It seems more likely that the experiments simply show that slow neural processes are not synchronised before they become percepts (the third option above). The experiments are excellent evidence for the concept of the cortex as a set of specialised processors that deliver their output asynchronously to some other place where the output becomes a percept. These experiments on colour and motion suggest that there is no synchronisation between the processes that deal with these two aspects of vision. Another set of experiments by Clifford *et al.* (2003) supports this idea of processing being asynchronous. They asked subjects to perform a variety of judgements of when visual events occurred and found that the degree of synchrony of one visual event with another depends on the type of judgement. Different judgements probably use processors in different areas of cortex and the output from these arrives asynchronously at the part of the brain that supports the percept. When the percept is formed there must be feedback to the cortical processes that create its content. Otherwise it would not be possible to report about the percept and the cortex would be unable to direct processing to the percept in preference to other, non-conscious cortical data. Although slow processes (20 milliseconds to 1 second) do not seem to be synchronised there is some evidence for very rapid synchronisation. Andrews *et al.* (1996) revisited a problem raised by the famous physiologist Charles Sherrington. Sherrington considered the phenomenon of \'flicker fusion\' in which a flickering light appears to be a continuous steady light if it flashes on and off at frequencies of about 45 Hz or higher. He reasoned that if the images from both eyes are brought together to form a single image then the frequency at which a flickering light appears to be steady should depend on whether one or two eyes are used. Flicker fusion should occur if each eye receives alternate flashes at only half the normal flicker fusion frequency. The flicker should disappear if the left eye receives flashes at 23 pulses per second and the right eye receives alternate flashes at 23 pulses per second. When Sherrington performed the experiment he found that this was not the case, using approximate figures, each eye required 46 pulses per second for fusion to occur. Sherrington proposed that the flicker fusion in alternate binocular presentation was occurring \"psychically\", outside of normal physiological processes. Andrews *et al.* duplicated Sherrington\'s result but investigated it further. They found that when lights were flashed in each eye alternately at low frequences (2 Hz) the experience was the same as a light being flashed in both eyes at this rate. At frequencies of four Hz and higher the subjects began to report that the lights being flashed alternately in both eyes seemed to flicker at the same rate as lights being flashed in both eyes at half the frequency. It seemed as if a flash in one eye followed by a flash in the other eye was being perceived as a single flash or \"conflated\" as the authors put it. The authors explained this effect by suggesting that the brain activity corresponding to the flashes was sampled for a short period and any number of flashes occurring during this period became perceived as a single flash. The maximum rate of sampling would be about 45 Hz. This idea is similar to option (1) above, where the buffer is filled and emptied 40 - 50 times a second. An experience buffer that is refreshed at 40-50 times a second might also explain the results obtained with colour and motion asynchrony because synchronisation between processes may well happen too quickly to affect processes that occur at very slow rates. Singer and Gray (1995), Singer (2001) have proposed that synchronisation between neurones at about 45 Hz is the discriminator between those neurones with activity that contributes to conscious experience and activity in other neurones. A rapid refresh rate in a synchronising buffer agrees with the results found by Fries *et al.* (1997) in which visual cortical neurones that represent a percept underwent synchronous oscillations in the gamma frequency range (39--63 Hz). Tononi *et al.* (1998) have also found synchronisation of neural activity in neurones that represent the percept. The gamma frequency oscillations are intrinsic to the cortex but are triggered by the thalamus and are part of the \'arousal system\'. Readers should be wary of the term \'arousal system\' because it evokes the idea of something waking up a conscious cortex. The cortex can be fully active during sleep and even during pathological unconsciousness such as persistent vegetative state so it is possible that the arousal centres themselves or nearby structures actually host phenomenal consciousness. ## EEG and synchronisation If electrodes are placed on the scalp varying electrical potentials of a few tens of microvolts can be recorded between the electrodes. Recordings of potentials from electrodes on the scalp are known as electroencephalograms (EEGs). The potentials recorded in the EEG are due to postsynaptic potentials in nerve cells. The EEG is insensitive to the activity of single cells and occurs as a result of relatively slow, **synchronised**, changes in large areas of cells. The differences in potential between two scalp electrodes are largely due to depolarisation and hyperpolarisation of the dendritic trees of cortical pyramidal cells. The folding of the cortex (gyri) is problematical for recording and interpreting EEGs because opposing layers of cortex can cancel any net potentials. The EEG shows rhythmic activity. This is conventionally divided into the following frequency bands: Delta waves 0--4 Hz Theta waves 4--8 Hz Alpha waves 8--12 Hz Beta waves \>10 Hz Gamma waves (also called fast beta) 25--100 Hz EEGs also contain short bursts of activity called spindles and very fast oscillations (VFOs). Spindles last for 1--2 seconds and contain rhythmic activity at 7--14 Hz. They are associated with the onset of sleep. The VFOs consist of short bursts at frequencies of over 80 Hz. When the eyes are closed the amplitude of activity from most pairs of electrodes is increased compared with when the eyes are open. When subjects are awake the EEG consists mainly of alpha and beta activity with considerable low amplitude gamma when the eyes are open. In stage 1 sleep the EEG consists of theta waves, in stage 2 sleep of varied activity and spindles, in stage 4 sleep of delta and during REM sleep of beta and theta activity. In epileptic seizures there tends to be high amplitude activity with pronounced synchronisation between many pairs of electrodes. The rhythmic electrical activity is due to cortical feedback loops, cortico-cortical synchronisation, thalamic pacemakers and thalamo-cortical synchronisation. VFOs have been attributed to the activity of electrical connections between cells (dendro-dendritic gap junctions) (Traub (2003)). The gamma activity, centred on a frequency of 40 Hz appears to be related to activity in cortical interneurons that form electrical connections between their dendrites (Tamas *et al.* 2000). These oscillations can be triggered by high frequency stimulation of the posterior intralaminar nuclei of the thalamus (Barth and MacDonald 1996, Sukov and Barth 2001) and as a result of activation of the reticular system (Munk *et al.* 1996). This suggests that stimulation of cortex by thalamic sensory relays triggers gamma band activity in the cortex. A shift from gamma to beta waves can occur in human event related potentials after about 0.2 secs (Pantev 1995, Traub *et al.* 1999). The alpha activity is related to thalamic pacemakers, perhaps as a result of intrinsic oscillatory activity in thalamic sensory relays (see Roy & Prichep 2005 for a brief review). Theta activity, which occurs during some cognitive tasks and mental arithmetic involves a loop from the cortex to the non-specific thalamic nuclei. Delta activity seems to be endogenous to cortex when input is suppressed during sleep. Beta activity is due to cortico-cortical interactions, often after a brief period of gamma activation. It should be noted that gamma and beta activity can be expressed as impulses in cortico-thalamic pathways and that when cortical and thalamic activity is correlated there is a conscious state. In other words gamma or beta waves in the cortex are not correlates of consciousness on their own - see for instance Laureys *et al.* (2002). ## Event related potentials After a sudden event there are a characteristic set of changes in EEG activity known as **event related potentials** or ERPs. The time course of the ERP is shown in the diagram below.  ERPs occur in response to novel stimuli and are also produced by brief transcranial magnetic stimulation (TMS)(Iramina *et al.* 2002). The slow component is known as the P3 or P300 phase of the ERP. It is due to activation of areas of the brain that are relatively remote from the primary sensory areas of brain. Nieuwenhuis *et al.* (2005) have reviewed the origin of the P300 ERP: \"To summarize, convergent evidence suggests that P3-like activity can be recorded in several, widely separated brain areas. These include some medial temporal and subcortical structures (e.g., the hippocampal formation, amygdala, and thalamus), but these structures are unlikely to contribute directly to the scalp-recorded P3.\". According to Nieuwenhuis *et al.* (2005) the recorded P300 may be due to temporo-parietal and prefrontal cortical activity. Linden (2005) has also concluded that widespread, but specific, cortical activation is correlated with the recorded P300 ERP. The generator of the P300 is still obscure. Nieuwenhuis *et al.* (2005) consider that the Locus coeruleus, a nucleus in the pons that regulates task related attention and part of the sleep-wake cycle, may be responsible. In line with this, Mashour *et al.* (2005) have discovered that TMS induced P300 activity is reduced in unconscious states. Whether the P300 is related to Libet\'s 0.5 second delay is still obscure but the discovery that the P300 occurs in association with subliminal stimuli (stimuli that do not enter awareness)(Bernat *et al.* 2001) suggests that it is associated with non-conscious cortical processing. Williams *et al.* (2004), in an investigation of subliminal and supraliminal fear perception, found that \"conscious fear perception was distinguished by a more prominent N4, peaking around 400 msec\"; the N4 component follows the P300 component in the succession of phases of the ERP. Williams *et al.* considered that the earlier phases in the ERP are probably related to non-conscious processing. In contrast Vogel *et al.* (1998) found that suppression of the P300 was associated with suppression of awareness. ## The integration delay Psychological experiments often involve binary decisions where subjects give one of two outputs in response to stimuli. It is found that if the stimuli are made increasingly noisy or complex the response time tends to increase. Psychophyicists have developed various mathematical models to explain the increased response times due to noise such as the Integrator and Accumulator models (cf: Luce(1986)). These models have been fairly successful when explaining experiments such as judging the net direction of movement of sets of dots on a screen when the dots are given semi-random paths and different brightness etc. In these circumstances it can take up to 2 seconds for an accurate decision. There are many tasks however where the accuracy of decision making does not improve after about 300 milliseconds. The accuracy of the performance of rats when choosing between two alternatives when reacting to odours peaks at about 300 ms (Uchida and Mainen(2003), Abraham *et al.* (2004)). The accuracy of humans when performing vernier acuity tasks, line detection, contrast sensitivity, motion velocity discrimination and stereoscopic depth discrimination seems to peak at 300ms (Uchida *et al.* 2006). Uchida, Kepecs and Mainen (2006) suggest that \"rapid and short integration time is a sensible strategy for rapid processing of low-level sensory information in order to form more complex sensory images, both in vision and olfaction.\" Whether these authors regard these derived sensory images as the content of consciousness is not mentioned. The authors propose that the 300ms optimal integration time may be partly due to the mechanics of sniffing (a sniff takes about 125-200ms) and the nature of optical fixation (inter-saccade intervals are typically 200-400 ms ). The authors note that the animal or human could, in principle, choose to integrate over longer intervals but if it is moving this may not lead to information that is current for changed circumstances. An optimal processing time of about 300 ms would be consistent with the delays observed before conscious awareness occurs in response to a stimulus - an interval required to form \"more complex sensory images\". ## Global Workspace Theory Global Workspace Theory is the idea that somewhere in the brain there is a facility that integrates the processes that occur in the various separate areas of the brain. The theory was first proposed by Descartes as the *sensus communis*, the common sense, but the modern form of the theory dispenses with the idea of a point soul looking at the brain. In modern Global Workspace theory it is proposed that an area of brain receives input from most of the cerebral cortex and broadcasts its outputs to all of the unconscious modular information processors in the brain. Modern Global Workspace Theory has been championed by Baars (1983, 1988). There is increasing evidence for a Global Workspace or Global Workspaces in the brain. Much of this evidence comes from fMRI, single unit and magnetoencephalography studies in which it is shown that non-conscious or subliminal processing mainly occupies primary, sensory cortex whereas conscious processing occupies large areas of cerebral cortex. In binocular rivalry the stimulus that is consciously perceived is responsible for relatively intense activation of large areas of brain whereas the non-conscious stimulus is often suppressed (see above and Sheinberg & Logothetis (1997), Tononi *et al.* (1998)). The suppression is likely to occur in the Lateral Geniculate Nuclei which suggests a role for the Thalamic Reticular Nuclei, which modulate LGN activity, in the control of the percept. ### Masking and visual awareness Word masking has also been used to investigate the idea of a Global Workspace. When a word is presented on its own for a few tens of milliseconds it remains readable but if it is immediately succeeded by, or accompanied by, another word it becomes indistinct or invisible. This effect is known as \"word masking\". Vogel *et al.* (1998) have investigated a version of word masking known as the \"attentional blink\". They found that when stimuli became invisible the P3 component of the Event Related Potential, which peaks at around 300-500 millisecs after a stimulus, was completely suppressed. The P3 component of the ERP has been related to the lodging of data in working memory and also to gamma band activity in the EEG. This strongly suggests the involvement of a cortico-thalamic loop in the \"attentional blink\". The delay of 0.3 to 0.5 secs is typical of the time required for conscious awareness (see above). Word masking in conjunction with fMRI and Event Related Potential (ERP) recordings has been used by Dehaene *et al.* (2001) to expose control by a central mechanism. It was found that masked words activate mainly the visual cortex and ventral stream (inferior temporal lobe) whereas visible words also activated distant parietal, prefrontal and cingulate sites. Dehaene *et al.* (2003) and found that the dynamics of the loss of visibility of words in an attentional blink experiment could be modelled by a simulated cortico-thalamic loop. In their simulation a distributed cortical process determined which events would receive attention and the system used the thalamic gating systems to exclude those that did not receive attention. Tse *et al.* (2005) have used purely visual stimuli in masking experiments and concluded that, in the case of purely visual stimuli, the neural correlates of awareness were limited to the occipital cortex: \"We suggest that there are both lower and upper bounds within the visual hierarchy for the processing of visual masking and the maintenance of visual awareness of simple unattended targets; the lower bound is at least as high as the border between V2 and V3, and the upper bound is within the occipital lobe, possibly somewhere downstream of V4.\" This discovery would mean that activation of large areas of cortex are unnecessary for awareness. Melloni *et al.* (2007) compared compared the electrophysiological responses related to the processing of visible and invisible words in a delayed matching to sample task. Both perceived and nonperceived words caused a similar increase of local (gamma) oscillations in the EEG, but only perceived words induced a transient long-distance synchronization of gamma oscillations across widely separated regions of the brain. After this transient period of temporal coordination, the electrographic signatures of conscious and unconscious processes continue to diverge. Only words reported as perceivedinduced (1) enhanced theta oscillations over frontal regions during the maintenance interval, (2) an increase of the P300 component of the event-related potential, and (3) an increase in power and phase synchrony of gamma oscillationsbefore the anticipated presentation of the test word. We propose that the critical process mediating the access to conscious perception is the earlytransient global increase of phase synchrony of oscillatory activity in the gammafrequency. Melloni L, Molina C, Pena M, Torres D, Singer W, Rodriguez E. (2007). Synchronization of neural activity across cortical areas correlates withconscious perception.J Neurosci. 2007 Mar 14;27(11):2858-65. ### Attention and the global workspace Baars (2002) in his review of evidence for the Global Workspace Theory quotes many other experiments that show activation of larger areas of cortex in response to conscious stimuli compared with unconscious or subliminal stimuli.The effect is also seen in change blindness, learning and attention. Newman and Baars (1993) consider that the \"workspace\" is fairly global in the brain: \"This Neural Global Workspace (NGW) model views conscious processes in terms of a globally integrative brain system. The neural circuitry contributing to this system is not only widely distributed across the neocortex, but includes key corticothalamic and midbrain circuits as well. These cortico-subcortical circuits are hypothesized to be critical to understanding the mechanisms of attentional control that provide an essential basis for the conscious processing of information\". However they focus particularly on the role of the thalamic Reticular Nucleus and cortico-thalamic connectivity in the control of attention. Other ideas for the location of the Global Workspace are the idea of Singer et al. that gamma synchrony controls access to the content of consciousness and Llinas et al. (1998) that the thalamus is the hub through which communication occurs between areas of cortex. One of the problems with Global Workspace theory is that it suggests that attention, working memory, cognitive control and consciousness may all be in the same area of the brain. It is likely that the mechanisms of attention, working memory, and cognitive control may involve several, interlinked systems perhaps co-opting the basal ganglia in the process. In view of this Maia and Cleeremans (2005) propose that \".. attention, working memory, cognitive control and consciousness are not distinct functions implemented by separate brain systems. Attempting to find separate neural correlates for each may therefore be the wrong approach. Instead, we suggest that they should be understood in terms of the dynamics of global competition, with biasing from PFC (prefrontal cortex).\". The inclusion by Maia and Cleeremans of consciousness with distributed attention, working memory and cognitive control is reminiscent of Zeki & Bartel\'s idea of microconsciousness. It should be noted that, in common with Libet\'s data, the percept seems to be available to phenomenal consciousness some 0.3 to 0.5 secs after a stimulus; this suggests that whatever determines the content of phenomenal consciousness operates before events become part of phenomenal consciousness. This relegates phenomenal consciousness from being a controller of attention to being the recipient of content that is the subject of attention. This finding is consistent with the philosophical problem of the **apparently** epiphenomenal nature of phenomenal consciousness. Given the data on the timing of conscious awareness it seems that there may be two \"workspaces\", an active workspace that models the world, discarding and suppressing data during rivalry, and a passive workspace that receives the final, edited product. The active workspace would correlate with the cortical systems stressed by Dehaene *et al.* and Maia and Cleermans although, given the results of Tse et al., the workspace would be limited to small zones of cortex. The loading of the passive workspace with the output of the active workspace would correlate with thalamo-cortical activity during component P3 of the ERP in which data is transferred from the cortex to the thalamus. This workspace might constitute the source for reports of the content of phenomenal consciousness. Llinas *et al.* (1998) have proposed two parallel cortico-thalamic attentional systems, one of which is related to the thalamic specific nuclei and the other to the thalamic non-specific nuclei, especially the ILN. The non-specific system would be related to consciousness itself. ## The \"cognitive map\" and the neural basis of perceptual space Our bodies appear to be mobile within a constant space. We walk around a room; the room does not rotate around us. The constancy of the location of things gives us the feeling that we are directly viewing a constant world. But how does the brain provide a constant world rather than a world that rotates with the movement of the sense organs? Why is our view of the world when we move our eyes so different from the disturbing flow of images that occur when a video camera is waved around? Do our brains contain a constant \"cognitive map\" (O\'Keefe and Nadel 1978) of our surroundings? Mittelstaedt & Mittelstaedt (1980, 1982) discovered that female gerbils were able to recover their pups in darkened surroundings by searching in a semi random fashion on the outbound journey and then proceeding directly back to the nest on the inbound journey. The direct journey back to the nest seemed to be due to an integration of the various directions taken on the outward journey (**path integration**). If the equipment being explored by the mother gerbil was rotated very slowly the mother would make an error equivalent to the amount of rotation. More rapid rotations that activated the vestibular system of the rat (acceleration measurement) did not cause errors in navigation. This demonstration that rodents could navigate accurately on the basis of **idiothetic** cues (cues that are due to internal senses) led to research on the neural basis of the navigation. 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# Consciousness Studies/Neuroscience 2#Event related potentials *Contributors: please include full data in the references section for all references in the text.* ```{=html} <div class="noprint"> ``` Home ```{=html} </div> ``` ## Perceptual \"filling in\" Perceptual \"filling in\" occurs when visual properties such as textures, colours, brightness or motion are extended in the visual field to areas where they do not have corresponding events in the world. The filling in of the blind spot by the properties of the field in the contralateral eye has already been discussed. The part of the visual field represented by the blind spot is also \"filled in\" in the case of monocular vision.  Shut the right eye and focus on the pink cross with the left eye, if the head is moved towards the pink cross there is a point at which the yellow disk disappears but the white lines are still present. In this \"filling in\" the visual field does not appear to be distorted. Fiorani *et al.* (1992) developed a technique for probing the cortical blind spot using vertical and horizontal bar stimuli. Matsumoto & komatsu (2005) used this technique on macaque monkeys. In the monocular case they found that as a bar was moved across the visual field so that it crossed the blind spot there was a sudden change in neural activity in the deep layers of the neurons in the blind spot area of V1. When the bar was moved across the same part of the visual field of the contralateral eye the neural activity in the blind spot area increased steadily as the bar was moved. The authors found that there were neurons in the deep layers of blind spot cortex that had elongated receptive fields that could respond to stimuli outside the blind spot and transfer this activation into the blind spot cortex. Filling in of a slightly different type occurs in \"scotoma\". In scotoma an area of the retina is damaged and unresonsive to visual stimuli, immediately after the damage patients report an area of visual field that is unresponsive to stimuli. After several months patients report that the area of field represented by the scotoma contains visual properties related to the physical world surrounding the area that would have formed an image on the scotoma. This results in a distortion of the visual field. (see for instance Gilbert(1993)). Direct measurements of activity in cortical area V1 show that the neurons that represented the area of the scotoma become sensitive to activity in the surrounding visual field. At the cortical level the scotoma is literally \"filled in\". There are many stimuli that cause \"filling in\". These stimuli are known as \"illusions\" because they produce phenomenal experience that has no correlate in the world outside the body. In the \"neon colour spreading illusion\" a lightly coloured circle appears where there should be a white background. Sasaki and Watanabe (2004) used fMRI to show that the part of the topographic map in cortical area V1 corresponding to the light coloured circle was activated.  Fiorani, M., Rosa, M.G.P., Gattas, R. & Rocha-Miranda, C.E. (1992). Dynamic surrounds of receptive fields in primate striate cortex: a physiological basis for perceptual completion? Proc. Natl. Acad. Sci. 89, 8547-8551. <http://www.pnas.org/cgi/content/abstract/89/18/8547> Gilbert, C.D. (1993). Circuitry, architecture and functional dynamics of visual cortex. Matsumoto, M & Komatsu, H. (2005). Neural responses in the macaque V1 to bar stimuli with various lengths presented on the blind spot. J neurophysiol. 93. 2374-2387. <http://jn.physiology.org/cgi/content/abstract/93/5/2374> Sasaki, Y & Watanabe, T. The primary visual cortex fills in colour. Proc. Natl. Acad. Sci. USA 101, 18251-18256. (2004). ## Binocular Rivalry, Pattern Rivalry and Binocular Fusion Sir Charles Wheatstone (1838) was the first scientist to systematically investigate binocular rivalry. Binocular rivalry occurs when different images are presented to the left and right eyes. The subject sees successively one image, a combined image and then the other image. The swapping of images can take a second or more. Binocular rivalry is of interest in consciousness research because the parts of the brain that contain the dominant image should also be those parts that are contributing to conscious experience. Binocular rivalry involves at least two components; the first switches from one image to a merged image and then to the other image and the second permits the view to be part of conscious experience.  The switching of one image for another may involve selecting one of the images as the percept or selecting one of the eyes. Blake *et al.* (1979) performed an experiment in which subjects could change the image at a given eye by pressing a button. When a particular image became dominant they pressed a button to change the image at the eye receiving the dominant image for the non-dominant image. They found that the subjects immediately experienced the second image as the dominant image. This suggests that binocular rivalry is selecting between eyes rather than images. Lehky in 1988 proposed that the switching may be occurring as a result of feedback between visual cortical area V1 and the Lateral Geniculate Nucleus (a thalamic relay - see Carandini *et al.* 2002) and Blake in 1989 also proposed that the switching occurred at the level of area V1. (Visual cortical area V1 receives visual input direct from the LGN.) Tong (2001) has argued that, in humans, the switching of images in binocular rivalry may occur at the earliest levels in the visual cortex. In particular, Tong and Engel (2001) used an elegant technique measuring the activity in the visual cortex that represents the blind spot of the eye to show that almost complete switching to the dominant image occurs at the level of visual cortical area V1. In support of this idea of switching at the level of V1 or even before the cortex, Kreimann *et al.* (2001, 2002) used direct electrode recordings in human cortex and found that the activity of most neurons changed with the percept. Other experiments have not shown a single locus in the brain where the suppressed sensory information gets switched out (Blake & Logothetis 2002, Leopold & Logothetis 1996, Gail et al., 2004). Functional MRI has also shown cortical activity outside of sensory visual cortex related to both images in binocular rivalry. Lumer *et al.* (1998) found that only the fronto-parietal areas of cortex switched with the percept, Fang & He (2005) found that activity relating to both suppressed and unsuppressed images were present in the dorsal stream of the visual system. Wunderlich *et al.* (2005) and Haynes *et al.* (2005) have both found suppression at the level of the lateral geniculate nucleus using fMRI in humans. Pasley *et al.* (2004) have shown that, even during suppression, fearful faces can produce activity in the amygdala (see Pessoa (2005) for a review). Rivalry alternations seem to be the result of widespread activity changes that cover large parts of the brain, including but not necessarily originating at the earliest sensory stages of visual processing. Most investigators have found that, once switching has occurred, there are areas of the brain that contain activity that is solely related to the percept but this varies from most of the cortex to largely more frontal regions depending upon the study. The most likely explanation for binocular rivalry is that the switching occurs at the level of the LGN as a result of feedback from the cortex. Pattern Rivalry is also of interest in consciousness research for the same reasons as binocular rivalry. In pattern rivalry a figure may have two or more forms that replace each other. Typical examples of such figures are the Necker cube and Rubin\'s face-vase. The similarity of the time course of the switching between percepts in binocular rivalry and pattern rivalry has led many authors to suggest that these involve the same mechanism. Logothetis *et al.* (1996) used novel dichoptic stimuli (different images to each eyes) to produce a form of rivalry that seems to involve switching at levels in the cerebral cortex that are more distal to the sensory stimulus than V1. Leopold and Logothetis (1999), on the basis of their work with monkeys, state that \"..many neurons throughout the visual system, both monocular and binocular, continue to respond to a stimulus even when it is perceptually suppressed.\". Kleinschmidt *et al.* (1998) investigated pattern rivalry with MRI and found activity in higher order visual areas during change of dominant pattern. Pettigrew (2001) also describes effects on rivalry due to thought and mood that may require involvement of large areas of cortex in the switching operation and stresses the way that V1 represents different visual fields in different hemispheres of the brain so that inter-hemispheric switching must also be considered. It seems likely that the change of dominant pattern or percept is associated with higher level cortical activity but once the dominant percept is established many of the visually responsive neurons in the cortex are switched over to the new percept. This might account for the similarities in timing of binocular and pattern rivalry and the disparate results found by the various groups of authors. In the words of Kleinschmidt *et al.* (1998): \"The transient activity fluctuations we found suggest that perceptual metastability elicited by ambiguous stimuli is associated with rapid redistributions of neural activity between separate specialized cortical and subcortical structures.\" Which permits both the idea of selecting particular eyes or percepts, perhaps by feedback that switches a thalamic relay on the basis of cortical processing of patterns. Once the cortex has switched the thalamic relay most of the neurons in V1 would become exposed to the dominant percept but there would still be a few neurons in the cortical visual system receiving data from the non dominant image. The investigations of binocular and pattern rivalry provide evidence that conscious visual experience is probably distal to V1 (i.e.: cortex or thalamus). Perceptual rivalry may be part of complex decision making rather than being simply a switch to blank out unwelcome input. It is clear from the Rubin face-vase that pattern rivalry is linked to recognition and would involve a complex delineation of forms within cortical processing. This would suggest that many areas of cortex should be involved before a particular percept is made dominant. Pettigrew (2001) argues that rivalry is the result of a complex phenomenon rather than being simply a switching event. Pettigrew\'s discovery that laughter abolishes rivalry also points to a complex cortical system for switching percepts. Pettigrew proposes that complex cortical processes control rivalry and that the actual switching of percepts is performed sub-cortically in the Ventral Tegmental Area. He concludes his review of the problem by noting that \"Rivalry may thus reflect fundamental aspects of perceptual decision making..\" Pettigrew (2001). Another effect, known as \"binocular fusion\", provides further compelling evidence for the non-conscious nature of the cerebral cortex. In binocular fusion images from both eyes are fused together to create a single image in experience. Moutoussis and Zeki (2002) used a form of binocular fusion in which images of faces were flashed at 100ms intervals to both eyes simultaneously. When both eyes received images of the same colour the subject could see the faces but when one eye received a green image on a red background and the other a red image on a green background the subjects reported seeing a uniform yellow field that contained no faces. fMRI scans of the subject\'s brains showed that when both eyes were exposed to images of the same colour the part of the brain that deals with faces was active and when each eye received images of different colours the same areas of brain showed activity. In other words the cortex contained strong activity related to faces whether or not faces were experienced. Moutoussis and Zeki found a similar effect when they used images of houses instead of images of faces. The authors concluded that: \"The present study further suggests that there are no separate processing and perceptual areas but rather that the same cortical regions are involved in both the processing and, when certain levels of activation are reached and probably in combination with the activation of other areas as well, the generation of a conscious visual percept\". This conclusion does not seem to be supported by the data. There is no evidence that any area of cortex contains the percept itself. The experiment shows that the cortex contains data relating to both red and green faces which suggests that the cortex is not the site of the conscious percept. The percept is most likely distal to the cortex perhaps in the thalamus or some other area that receives cortical sensory output. It is interesting that Fries *et al.* (1997) found that neurons that were activated by the dominant image in binocular rivalry fired synchronously whereas those that were activated by the non-dominant image did not. Thalamocorticothalamic oscillations are the most likely source for synchronising neurons over whole areas of cortex, suggesting that the conscious percept is located in the thalamus rather than the cortex. ## Synchronisation of Neural Processes Our experience seems to contain entities with their attributes attached to them at the correct places in space and time. When a dog barks we see its jaws open at the same time as the bark and both jaws and bark are at the same location. We take this for granted but the brain must be engaging in some complex processing to achieve this synchronised and appropriately positioned set of objects and events. The illustration below shows the two basic processes that might be used to synchronise events between the different specialised processors in the cerebral cortex and brain in general.  In the first option a complete model of sensation, dream etc. may be created and then allowed to become part of conscious experience. In the second model events are released into experience as fast as possible but are synchronous when recalled, having been synchronised in a storage buffer. There is a third option in which there is no synchronisation of events so that the output from different processors would occur at different times. The \'experience buffer\' would be a volume of brain in which a succession of events could be recorded. The buffer might either be updated in steps, the previous content being discarded, or continuously updated with the oldest content being lost continuously. In the first option events from different processes would always appear to be simultaneous unless the experience buffer were updated as a series of steps in which case any changes at around the moment of updating might appear in successive buffers. For instance, if change of position were processed before change in colour a circle on a screen that changed from green to red at the start of a motion might seem to be briefly green during the motion and then turn red. In the second model events from different processors might appear asynchronous at the moment of experience but synchronous when recalled. Colour vision and motion vision are processed in different parts of the visual cortex and in distinct parts of visual cortical areas V1 and V2. They are different processes and hence ideal for studying the synchronisation of cortical activity. Moutoussis and Zeki (1997) presented subjects with moving coloured squares on a computer screen that changed from red to green or vice versa as they changed direction of movement. It was found that subjects seemed to perceive changes in colour some 70-80 msecs before they perceived a change in the direction of motion of the squares. Further work by Arnold *et al.* (2001) and Arnold and Clifford (2001) have confirmed that colour changes seem to be perceived before motion. Arnold and Clifford (2001) also found a quantitative relationship between the colour/motion asynchrony and the direction of change of motion, complete reversals of direction giving rise to the greatest asynchrony between the detection of colour and motion changes. Moutoussis and Zeki (1997) conclude by stating that the asynchrony of neural processes shows that \"..the perception of each attribute is solely the result of the activity in the specialised system involved in its processing..\". It seems more likely that the experiments simply show that slow neural processes are not synchronised before they become percepts (the third option above). The experiments are excellent evidence for the concept of the cortex as a set of specialised processors that deliver their output asynchronously to some other place where the output becomes a percept. These experiments on colour and motion suggest that there is no synchronisation between the processes that deal with these two aspects of vision. Another set of experiments by Clifford *et al.* (2003) supports this idea of processing being asynchronous. They asked subjects to perform a variety of judgements of when visual events occurred and found that the degree of synchrony of one visual event with another depends on the type of judgement. Different judgements probably use processors in different areas of cortex and the output from these arrives asynchronously at the part of the brain that supports the percept. When the percept is formed there must be feedback to the cortical processes that create its content. Otherwise it would not be possible to report about the percept and the cortex would be unable to direct processing to the percept in preference to other, non-conscious cortical data. Although slow processes (20 milliseconds to 1 second) do not seem to be synchronised there is some evidence for very rapid synchronisation. Andrews *et al.* (1996) revisited a problem raised by the famous physiologist Charles Sherrington. Sherrington considered the phenomenon of \'flicker fusion\' in which a flickering light appears to be a continuous steady light if it flashes on and off at frequencies of about 45 Hz or higher. He reasoned that if the images from both eyes are brought together to form a single image then the frequency at which a flickering light appears to be steady should depend on whether one or two eyes are used. Flicker fusion should occur if each eye receives alternate flashes at only half the normal flicker fusion frequency. The flicker should disappear if the left eye receives flashes at 23 pulses per second and the right eye receives alternate flashes at 23 pulses per second. When Sherrington performed the experiment he found that this was not the case, using approximate figures, each eye required 46 pulses per second for fusion to occur. Sherrington proposed that the flicker fusion in alternate binocular presentation was occurring \"psychically\", outside of normal physiological processes. Andrews *et al.* duplicated Sherrington\'s result but investigated it further. They found that when lights were flashed in each eye alternately at low frequences (2 Hz) the experience was the same as a light being flashed in both eyes at this rate. At frequencies of four Hz and higher the subjects began to report that the lights being flashed alternately in both eyes seemed to flicker at the same rate as lights being flashed in both eyes at half the frequency. It seemed as if a flash in one eye followed by a flash in the other eye was being perceived as a single flash or \"conflated\" as the authors put it. The authors explained this effect by suggesting that the brain activity corresponding to the flashes was sampled for a short period and any number of flashes occurring during this period became perceived as a single flash. The maximum rate of sampling would be about 45 Hz. This idea is similar to option (1) above, where the buffer is filled and emptied 40 - 50 times a second. An experience buffer that is refreshed at 40-50 times a second might also explain the results obtained with colour and motion asynchrony because synchronisation between processes may well happen too quickly to affect processes that occur at very slow rates. Singer and Gray (1995), Singer (2001) have proposed that synchronisation between neurones at about 45 Hz is the discriminator between those neurones with activity that contributes to conscious experience and activity in other neurones. A rapid refresh rate in a synchronising buffer agrees with the results found by Fries *et al.* (1997) in which visual cortical neurones that represent a percept underwent synchronous oscillations in the gamma frequency range (39--63 Hz). Tononi *et al.* (1998) have also found synchronisation of neural activity in neurones that represent the percept. The gamma frequency oscillations are intrinsic to the cortex but are triggered by the thalamus and are part of the \'arousal system\'. Readers should be wary of the term \'arousal system\' because it evokes the idea of something waking up a conscious cortex. The cortex can be fully active during sleep and even during pathological unconsciousness such as persistent vegetative state so it is possible that the arousal centres themselves or nearby structures actually host phenomenal consciousness. ## EEG and synchronisation If electrodes are placed on the scalp varying electrical potentials of a few tens of microvolts can be recorded between the electrodes. Recordings of potentials from electrodes on the scalp are known as electroencephalograms (EEGs). The potentials recorded in the EEG are due to postsynaptic potentials in nerve cells. The EEG is insensitive to the activity of single cells and occurs as a result of relatively slow, **synchronised**, changes in large areas of cells. The differences in potential between two scalp electrodes are largely due to depolarisation and hyperpolarisation of the dendritic trees of cortical pyramidal cells. The folding of the cortex (gyri) is problematical for recording and interpreting EEGs because opposing layers of cortex can cancel any net potentials. The EEG shows rhythmic activity. This is conventionally divided into the following frequency bands: Delta waves 0--4 Hz Theta waves 4--8 Hz Alpha waves 8--12 Hz Beta waves \>10 Hz Gamma waves (also called fast beta) 25--100 Hz EEGs also contain short bursts of activity called spindles and very fast oscillations (VFOs). Spindles last for 1--2 seconds and contain rhythmic activity at 7--14 Hz. They are associated with the onset of sleep. The VFOs consist of short bursts at frequencies of over 80 Hz. When the eyes are closed the amplitude of activity from most pairs of electrodes is increased compared with when the eyes are open. When subjects are awake the EEG consists mainly of alpha and beta activity with considerable low amplitude gamma when the eyes are open. In stage 1 sleep the EEG consists of theta waves, in stage 2 sleep of varied activity and spindles, in stage 4 sleep of delta and during REM sleep of beta and theta activity. In epileptic seizures there tends to be high amplitude activity with pronounced synchronisation between many pairs of electrodes. The rhythmic electrical activity is due to cortical feedback loops, cortico-cortical synchronisation, thalamic pacemakers and thalamo-cortical synchronisation. VFOs have been attributed to the activity of electrical connections between cells (dendro-dendritic gap junctions) (Traub (2003)). The gamma activity, centred on a frequency of 40 Hz appears to be related to activity in cortical interneurons that form electrical connections between their dendrites (Tamas *et al.* 2000). These oscillations can be triggered by high frequency stimulation of the posterior intralaminar nuclei of the thalamus (Barth and MacDonald 1996, Sukov and Barth 2001) and as a result of activation of the reticular system (Munk *et al.* 1996). This suggests that stimulation of cortex by thalamic sensory relays triggers gamma band activity in the cortex. A shift from gamma to beta waves can occur in human event related potentials after about 0.2 secs (Pantev 1995, Traub *et al.* 1999). The alpha activity is related to thalamic pacemakers, perhaps as a result of intrinsic oscillatory activity in thalamic sensory relays (see Roy & Prichep 2005 for a brief review). Theta activity, which occurs during some cognitive tasks and mental arithmetic involves a loop from the cortex to the non-specific thalamic nuclei. Delta activity seems to be endogenous to cortex when input is suppressed during sleep. Beta activity is due to cortico-cortical interactions, often after a brief period of gamma activation. It should be noted that gamma and beta activity can be expressed as impulses in cortico-thalamic pathways and that when cortical and thalamic activity is correlated there is a conscious state. In other words gamma or beta waves in the cortex are not correlates of consciousness on their own - see for instance Laureys *et al.* (2002). ## Event related potentials After a sudden event there are a characteristic set of changes in EEG activity known as **event related potentials** or ERPs. The time course of the ERP is shown in the diagram below.  ERPs occur in response to novel stimuli and are also produced by brief transcranial magnetic stimulation (TMS)(Iramina *et al.* 2002). The slow component is known as the P3 or P300 phase of the ERP. It is due to activation of areas of the brain that are relatively remote from the primary sensory areas of brain. Nieuwenhuis *et al.* (2005) have reviewed the origin of the P300 ERP: \"To summarize, convergent evidence suggests that P3-like activity can be recorded in several, widely separated brain areas. These include some medial temporal and subcortical structures (e.g., the hippocampal formation, amygdala, and thalamus), but these structures are unlikely to contribute directly to the scalp-recorded P3.\". According to Nieuwenhuis *et al.* (2005) the recorded P300 may be due to temporo-parietal and prefrontal cortical activity. Linden (2005) has also concluded that widespread, but specific, cortical activation is correlated with the recorded P300 ERP. The generator of the P300 is still obscure. Nieuwenhuis *et al.* (2005) consider that the Locus coeruleus, a nucleus in the pons that regulates task related attention and part of the sleep-wake cycle, may be responsible. In line with this, Mashour *et al.* (2005) have discovered that TMS induced P300 activity is reduced in unconscious states. Whether the P300 is related to Libet\'s 0.5 second delay is still obscure but the discovery that the P300 occurs in association with subliminal stimuli (stimuli that do not enter awareness)(Bernat *et al.* 2001) suggests that it is associated with non-conscious cortical processing. Williams *et al.* (2004), in an investigation of subliminal and supraliminal fear perception, found that \"conscious fear perception was distinguished by a more prominent N4, peaking around 400 msec\"; the N4 component follows the P300 component in the succession of phases of the ERP. Williams *et al.* considered that the earlier phases in the ERP are probably related to non-conscious processing. In contrast Vogel *et al.* (1998) found that suppression of the P300 was associated with suppression of awareness. ## The integration delay Psychological experiments often involve binary decisions where subjects give one of two outputs in response to stimuli. It is found that if the stimuli are made increasingly noisy or complex the response time tends to increase. Psychophyicists have developed various mathematical models to explain the increased response times due to noise such as the Integrator and Accumulator models (cf: Luce(1986)). These models have been fairly successful when explaining experiments such as judging the net direction of movement of sets of dots on a screen when the dots are given semi-random paths and different brightness etc. In these circumstances it can take up to 2 seconds for an accurate decision. There are many tasks however where the accuracy of decision making does not improve after about 300 milliseconds. The accuracy of the performance of rats when choosing between two alternatives when reacting to odours peaks at about 300 ms (Uchida and Mainen(2003), Abraham *et al.* (2004)). The accuracy of humans when performing vernier acuity tasks, line detection, contrast sensitivity, motion velocity discrimination and stereoscopic depth discrimination seems to peak at 300ms (Uchida *et al.* 2006). Uchida, Kepecs and Mainen (2006) suggest that \"rapid and short integration time is a sensible strategy for rapid processing of low-level sensory information in order to form more complex sensory images, both in vision and olfaction.\" Whether these authors regard these derived sensory images as the content of consciousness is not mentioned. The authors propose that the 300ms optimal integration time may be partly due to the mechanics of sniffing (a sniff takes about 125-200ms) and the nature of optical fixation (inter-saccade intervals are typically 200-400 ms ). The authors note that the animal or human could, in principle, choose to integrate over longer intervals but if it is moving this may not lead to information that is current for changed circumstances. An optimal processing time of about 300 ms would be consistent with the delays observed before conscious awareness occurs in response to a stimulus - an interval required to form \"more complex sensory images\". ## Global Workspace Theory Global Workspace Theory is the idea that somewhere in the brain there is a facility that integrates the processes that occur in the various separate areas of the brain. The theory was first proposed by Descartes as the *sensus communis*, the common sense, but the modern form of the theory dispenses with the idea of a point soul looking at the brain. In modern Global Workspace theory it is proposed that an area of brain receives input from most of the cerebral cortex and broadcasts its outputs to all of the unconscious modular information processors in the brain. Modern Global Workspace Theory has been championed by Baars (1983, 1988). There is increasing evidence for a Global Workspace or Global Workspaces in the brain. Much of this evidence comes from fMRI, single unit and magnetoencephalography studies in which it is shown that non-conscious or subliminal processing mainly occupies primary, sensory cortex whereas conscious processing occupies large areas of cerebral cortex. In binocular rivalry the stimulus that is consciously perceived is responsible for relatively intense activation of large areas of brain whereas the non-conscious stimulus is often suppressed (see above and Sheinberg & Logothetis (1997), Tononi *et al.* (1998)). The suppression is likely to occur in the Lateral Geniculate Nuclei which suggests a role for the Thalamic Reticular Nuclei, which modulate LGN activity, in the control of the percept. ### Masking and visual awareness Word masking has also been used to investigate the idea of a Global Workspace. When a word is presented on its own for a few tens of milliseconds it remains readable but if it is immediately succeeded by, or accompanied by, another word it becomes indistinct or invisible. This effect is known as \"word masking\". Vogel *et al.* (1998) have investigated a version of word masking known as the \"attentional blink\". They found that when stimuli became invisible the P3 component of the Event Related Potential, which peaks at around 300-500 millisecs after a stimulus, was completely suppressed. The P3 component of the ERP has been related to the lodging of data in working memory and also to gamma band activity in the EEG. This strongly suggests the involvement of a cortico-thalamic loop in the \"attentional blink\". The delay of 0.3 to 0.5 secs is typical of the time required for conscious awareness (see above). Word masking in conjunction with fMRI and Event Related Potential (ERP) recordings has been used by Dehaene *et al.* (2001) to expose control by a central mechanism. It was found that masked words activate mainly the visual cortex and ventral stream (inferior temporal lobe) whereas visible words also activated distant parietal, prefrontal and cingulate sites. Dehaene *et al.* (2003) and found that the dynamics of the loss of visibility of words in an attentional blink experiment could be modelled by a simulated cortico-thalamic loop. In their simulation a distributed cortical process determined which events would receive attention and the system used the thalamic gating systems to exclude those that did not receive attention. Tse *et al.* (2005) have used purely visual stimuli in masking experiments and concluded that, in the case of purely visual stimuli, the neural correlates of awareness were limited to the occipital cortex: \"We suggest that there are both lower and upper bounds within the visual hierarchy for the processing of visual masking and the maintenance of visual awareness of simple unattended targets; the lower bound is at least as high as the border between V2 and V3, and the upper bound is within the occipital lobe, possibly somewhere downstream of V4.\" This discovery would mean that activation of large areas of cortex are unnecessary for awareness. Melloni *et al.* (2007) compared compared the electrophysiological responses related to the processing of visible and invisible words in a delayed matching to sample task. Both perceived and nonperceived words caused a similar increase of local (gamma) oscillations in the EEG, but only perceived words induced a transient long-distance synchronization of gamma oscillations across widely separated regions of the brain. After this transient period of temporal coordination, the electrographic signatures of conscious and unconscious processes continue to diverge. Only words reported as perceivedinduced (1) enhanced theta oscillations over frontal regions during the maintenance interval, (2) an increase of the P300 component of the event-related potential, and (3) an increase in power and phase synchrony of gamma oscillationsbefore the anticipated presentation of the test word. We propose that the critical process mediating the access to conscious perception is the earlytransient global increase of phase synchrony of oscillatory activity in the gammafrequency. Melloni L, Molina C, Pena M, Torres D, Singer W, Rodriguez E. (2007). Synchronization of neural activity across cortical areas correlates withconscious perception.J Neurosci. 2007 Mar 14;27(11):2858-65. ### Attention and the global workspace Baars (2002) in his review of evidence for the Global Workspace Theory quotes many other experiments that show activation of larger areas of cortex in response to conscious stimuli compared with unconscious or subliminal stimuli.The effect is also seen in change blindness, learning and attention. Newman and Baars (1993) consider that the \"workspace\" is fairly global in the brain: \"This Neural Global Workspace (NGW) model views conscious processes in terms of a globally integrative brain system. The neural circuitry contributing to this system is not only widely distributed across the neocortex, but includes key corticothalamic and midbrain circuits as well. These cortico-subcortical circuits are hypothesized to be critical to understanding the mechanisms of attentional control that provide an essential basis for the conscious processing of information\". However they focus particularly on the role of the thalamic Reticular Nucleus and cortico-thalamic connectivity in the control of attention. Other ideas for the location of the Global Workspace are the idea of Singer et al. that gamma synchrony controls access to the content of consciousness and Llinas et al. (1998) that the thalamus is the hub through which communication occurs between areas of cortex. One of the problems with Global Workspace theory is that it suggests that attention, working memory, cognitive control and consciousness may all be in the same area of the brain. It is likely that the mechanisms of attention, working memory, and cognitive control may involve several, interlinked systems perhaps co-opting the basal ganglia in the process. In view of this Maia and Cleeremans (2005) propose that \".. attention, working memory, cognitive control and consciousness are not distinct functions implemented by separate brain systems. Attempting to find separate neural correlates for each may therefore be the wrong approach. Instead, we suggest that they should be understood in terms of the dynamics of global competition, with biasing from PFC (prefrontal cortex).\". The inclusion by Maia and Cleeremans of consciousness with distributed attention, working memory and cognitive control is reminiscent of Zeki & Bartel\'s idea of microconsciousness. It should be noted that, in common with Libet\'s data, the percept seems to be available to phenomenal consciousness some 0.3 to 0.5 secs after a stimulus; this suggests that whatever determines the content of phenomenal consciousness operates before events become part of phenomenal consciousness. This relegates phenomenal consciousness from being a controller of attention to being the recipient of content that is the subject of attention. This finding is consistent with the philosophical problem of the **apparently** epiphenomenal nature of phenomenal consciousness. Given the data on the timing of conscious awareness it seems that there may be two \"workspaces\", an active workspace that models the world, discarding and suppressing data during rivalry, and a passive workspace that receives the final, edited product. The active workspace would correlate with the cortical systems stressed by Dehaene *et al.* and Maia and Cleermans although, given the results of Tse et al., the workspace would be limited to small zones of cortex. The loading of the passive workspace with the output of the active workspace would correlate with thalamo-cortical activity during component P3 of the ERP in which data is transferred from the cortex to the thalamus. This workspace might constitute the source for reports of the content of phenomenal consciousness. Llinas *et al.* (1998) have proposed two parallel cortico-thalamic attentional systems, one of which is related to the thalamic specific nuclei and the other to the thalamic non-specific nuclei, especially the ILN. The non-specific system would be related to consciousness itself. ## The \"cognitive map\" and the neural basis of perceptual space Our bodies appear to be mobile within a constant space. We walk around a room; the room does not rotate around us. The constancy of the location of things gives us the feeling that we are directly viewing a constant world. But how does the brain provide a constant world rather than a world that rotates with the movement of the sense organs? Why is our view of the world when we move our eyes so different from the disturbing flow of images that occur when a video camera is waved around? Do our brains contain a constant \"cognitive map\" (O\'Keefe and Nadel 1978) of our surroundings? Mittelstaedt & Mittelstaedt (1980, 1982) discovered that female gerbils were able to recover their pups in darkened surroundings by searching in a semi random fashion on the outbound journey and then proceeding directly back to the nest on the inbound journey. The direct journey back to the nest seemed to be due to an integration of the various directions taken on the outward journey (**path integration**). If the equipment being explored by the mother gerbil was rotated very slowly the mother would make an error equivalent to the amount of rotation. More rapid rotations that activated the vestibular system of the rat (acceleration measurement) did not cause errors in navigation. This demonstration that rodents could navigate accurately on the basis of **idiothetic** cues (cues that are due to internal senses) led to research on the neural basis of the navigation. As early as 1971 O\'Keefe and Dostrovsky had discovered that there are particular cells in the hippocampus that fire according to the position of an animal in the environment. This has been complimented by research that showed that changes in visual cues within the environment caused changes in the firing rate of place cells in hippocampal area CA3 (.   !Entorhinal cortex approximately maps to areas 28 and 34{width="500"} F. P. Battaglia and A. Treves. 1998 Attractor neural networks storing multiple space representations: A model for hippocampal place fields. PHYSICAL REVIEW E DECEMBER 1998 VOLUME 58, NUMBER 6 <http://www.sissa.it/~ale/Bat+98b.pdf> Leutgeb, S., Leutgeb, J.K., Moser, M-B, and Moser, E.I. 2005. Place cells, spatial maps and the population code for memory. Current Opinion in Neurobiology 2005, 15:738--746. <http://instruct1.cit.cornell.edu/courses/bionb720nejc/reprints/LeutgebEtAl2005.pdf> Mittelstaedt, H. & Mittelstaedt, M-L. 1982. Avian Navigation. (ed. 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# Consciousness Studies/Neuroscience 2#The integration delay *Contributors: please include full data in the references section for all references in the text.* ```{=html} <div class="noprint"> ``` Home ```{=html} </div> ``` ## Perceptual \"filling in\" Perceptual \"filling in\" occurs when visual properties such as textures, colours, brightness or motion are extended in the visual field to areas where they do not have corresponding events in the world. The filling in of the blind spot by the properties of the field in the contralateral eye has already been discussed. The part of the visual field represented by the blind spot is also \"filled in\" in the case of monocular vision.  Shut the right eye and focus on the pink cross with the left eye, if the head is moved towards the pink cross there is a point at which the yellow disk disappears but the white lines are still present. In this \"filling in\" the visual field does not appear to be distorted. Fiorani *et al.* (1992) developed a technique for probing the cortical blind spot using vertical and horizontal bar stimuli. Matsumoto & komatsu (2005) used this technique on macaque monkeys. In the monocular case they found that as a bar was moved across the visual field so that it crossed the blind spot there was a sudden change in neural activity in the deep layers of the neurons in the blind spot area of V1. When the bar was moved across the same part of the visual field of the contralateral eye the neural activity in the blind spot area increased steadily as the bar was moved. The authors found that there were neurons in the deep layers of blind spot cortex that had elongated receptive fields that could respond to stimuli outside the blind spot and transfer this activation into the blind spot cortex. Filling in of a slightly different type occurs in \"scotoma\". In scotoma an area of the retina is damaged and unresonsive to visual stimuli, immediately after the damage patients report an area of visual field that is unresponsive to stimuli. After several months patients report that the area of field represented by the scotoma contains visual properties related to the physical world surrounding the area that would have formed an image on the scotoma. This results in a distortion of the visual field. (see for instance Gilbert(1993)). Direct measurements of activity in cortical area V1 show that the neurons that represented the area of the scotoma become sensitive to activity in the surrounding visual field. At the cortical level the scotoma is literally \"filled in\". There are many stimuli that cause \"filling in\". These stimuli are known as \"illusions\" because they produce phenomenal experience that has no correlate in the world outside the body. In the \"neon colour spreading illusion\" a lightly coloured circle appears where there should be a white background. Sasaki and Watanabe (2004) used fMRI to show that the part of the topographic map in cortical area V1 corresponding to the light coloured circle was activated.  Fiorani, M., Rosa, M.G.P., Gattas, R. & Rocha-Miranda, C.E. (1992). Dynamic surrounds of receptive fields in primate striate cortex: a physiological basis for perceptual completion? Proc. Natl. Acad. Sci. 89, 8547-8551. <http://www.pnas.org/cgi/content/abstract/89/18/8547> Gilbert, C.D. (1993). Circuitry, architecture and functional dynamics of visual cortex. Matsumoto, M & Komatsu, H. (2005). Neural responses in the macaque V1 to bar stimuli with various lengths presented on the blind spot. J neurophysiol. 93. 2374-2387. <http://jn.physiology.org/cgi/content/abstract/93/5/2374> Sasaki, Y & Watanabe, T. The primary visual cortex fills in colour. Proc. Natl. Acad. Sci. USA 101, 18251-18256. (2004). ## Binocular Rivalry, Pattern Rivalry and Binocular Fusion Sir Charles Wheatstone (1838) was the first scientist to systematically investigate binocular rivalry. Binocular rivalry occurs when different images are presented to the left and right eyes. The subject sees successively one image, a combined image and then the other image. The swapping of images can take a second or more. Binocular rivalry is of interest in consciousness research because the parts of the brain that contain the dominant image should also be those parts that are contributing to conscious experience. Binocular rivalry involves at least two components; the first switches from one image to a merged image and then to the other image and the second permits the view to be part of conscious experience.  The switching of one image for another may involve selecting one of the images as the percept or selecting one of the eyes. Blake *et al.* (1979) performed an experiment in which subjects could change the image at a given eye by pressing a button. When a particular image became dominant they pressed a button to change the image at the eye receiving the dominant image for the non-dominant image. They found that the subjects immediately experienced the second image as the dominant image. This suggests that binocular rivalry is selecting between eyes rather than images. Lehky in 1988 proposed that the switching may be occurring as a result of feedback between visual cortical area V1 and the Lateral Geniculate Nucleus (a thalamic relay - see Carandini *et al.* 2002) and Blake in 1989 also proposed that the switching occurred at the level of area V1. (Visual cortical area V1 receives visual input direct from the LGN.) Tong (2001) has argued that, in humans, the switching of images in binocular rivalry may occur at the earliest levels in the visual cortex. In particular, Tong and Engel (2001) used an elegant technique measuring the activity in the visual cortex that represents the blind spot of the eye to show that almost complete switching to the dominant image occurs at the level of visual cortical area V1. In support of this idea of switching at the level of V1 or even before the cortex, Kreimann *et al.* (2001, 2002) used direct electrode recordings in human cortex and found that the activity of most neurons changed with the percept. Other experiments have not shown a single locus in the brain where the suppressed sensory information gets switched out (Blake & Logothetis 2002, Leopold & Logothetis 1996, Gail et al., 2004). Functional MRI has also shown cortical activity outside of sensory visual cortex related to both images in binocular rivalry. Lumer *et al.* (1998) found that only the fronto-parietal areas of cortex switched with the percept, Fang & He (2005) found that activity relating to both suppressed and unsuppressed images were present in the dorsal stream of the visual system. Wunderlich *et al.* (2005) and Haynes *et al.* (2005) have both found suppression at the level of the lateral geniculate nucleus using fMRI in humans. Pasley *et al.* (2004) have shown that, even during suppression, fearful faces can produce activity in the amygdala (see Pessoa (2005) for a review). Rivalry alternations seem to be the result of widespread activity changes that cover large parts of the brain, including but not necessarily originating at the earliest sensory stages of visual processing. Most investigators have found that, once switching has occurred, there are areas of the brain that contain activity that is solely related to the percept but this varies from most of the cortex to largely more frontal regions depending upon the study. The most likely explanation for binocular rivalry is that the switching occurs at the level of the LGN as a result of feedback from the cortex. Pattern Rivalry is also of interest in consciousness research for the same reasons as binocular rivalry. In pattern rivalry a figure may have two or more forms that replace each other. Typical examples of such figures are the Necker cube and Rubin\'s face-vase. The similarity of the time course of the switching between percepts in binocular rivalry and pattern rivalry has led many authors to suggest that these involve the same mechanism. Logothetis *et al.* (1996) used novel dichoptic stimuli (different images to each eyes) to produce a form of rivalry that seems to involve switching at levels in the cerebral cortex that are more distal to the sensory stimulus than V1. Leopold and Logothetis (1999), on the basis of their work with monkeys, state that \"..many neurons throughout the visual system, both monocular and binocular, continue to respond to a stimulus even when it is perceptually suppressed.\". Kleinschmidt *et al.* (1998) investigated pattern rivalry with MRI and found activity in higher order visual areas during change of dominant pattern. Pettigrew (2001) also describes effects on rivalry due to thought and mood that may require involvement of large areas of cortex in the switching operation and stresses the way that V1 represents different visual fields in different hemispheres of the brain so that inter-hemispheric switching must also be considered. It seems likely that the change of dominant pattern or percept is associated with higher level cortical activity but once the dominant percept is established many of the visually responsive neurons in the cortex are switched over to the new percept. This might account for the similarities in timing of binocular and pattern rivalry and the disparate results found by the various groups of authors. In the words of Kleinschmidt *et al.* (1998): \"The transient activity fluctuations we found suggest that perceptual metastability elicited by ambiguous stimuli is associated with rapid redistributions of neural activity between separate specialized cortical and subcortical structures.\" Which permits both the idea of selecting particular eyes or percepts, perhaps by feedback that switches a thalamic relay on the basis of cortical processing of patterns. Once the cortex has switched the thalamic relay most of the neurons in V1 would become exposed to the dominant percept but there would still be a few neurons in the cortical visual system receiving data from the non dominant image. The investigations of binocular and pattern rivalry provide evidence that conscious visual experience is probably distal to V1 (i.e.: cortex or thalamus). Perceptual rivalry may be part of complex decision making rather than being simply a switch to blank out unwelcome input. It is clear from the Rubin face-vase that pattern rivalry is linked to recognition and would involve a complex delineation of forms within cortical processing. This would suggest that many areas of cortex should be involved before a particular percept is made dominant. Pettigrew (2001) argues that rivalry is the result of a complex phenomenon rather than being simply a switching event. Pettigrew\'s discovery that laughter abolishes rivalry also points to a complex cortical system for switching percepts. Pettigrew proposes that complex cortical processes control rivalry and that the actual switching of percepts is performed sub-cortically in the Ventral Tegmental Area. He concludes his review of the problem by noting that \"Rivalry may thus reflect fundamental aspects of perceptual decision making..\" Pettigrew (2001). Another effect, known as \"binocular fusion\", provides further compelling evidence for the non-conscious nature of the cerebral cortex. In binocular fusion images from both eyes are fused together to create a single image in experience. Moutoussis and Zeki (2002) used a form of binocular fusion in which images of faces were flashed at 100ms intervals to both eyes simultaneously. When both eyes received images of the same colour the subject could see the faces but when one eye received a green image on a red background and the other a red image on a green background the subjects reported seeing a uniform yellow field that contained no faces. fMRI scans of the subject\'s brains showed that when both eyes were exposed to images of the same colour the part of the brain that deals with faces was active and when each eye received images of different colours the same areas of brain showed activity. In other words the cortex contained strong activity related to faces whether or not faces were experienced. Moutoussis and Zeki found a similar effect when they used images of houses instead of images of faces. The authors concluded that: \"The present study further suggests that there are no separate processing and perceptual areas but rather that the same cortical regions are involved in both the processing and, when certain levels of activation are reached and probably in combination with the activation of other areas as well, the generation of a conscious visual percept\". This conclusion does not seem to be supported by the data. There is no evidence that any area of cortex contains the percept itself. The experiment shows that the cortex contains data relating to both red and green faces which suggests that the cortex is not the site of the conscious percept. The percept is most likely distal to the cortex perhaps in the thalamus or some other area that receives cortical sensory output. It is interesting that Fries *et al.* (1997) found that neurons that were activated by the dominant image in binocular rivalry fired synchronously whereas those that were activated by the non-dominant image did not. Thalamocorticothalamic oscillations are the most likely source for synchronising neurons over whole areas of cortex, suggesting that the conscious percept is located in the thalamus rather than the cortex. ## Synchronisation of Neural Processes Our experience seems to contain entities with their attributes attached to them at the correct places in space and time. When a dog barks we see its jaws open at the same time as the bark and both jaws and bark are at the same location. We take this for granted but the brain must be engaging in some complex processing to achieve this synchronised and appropriately positioned set of objects and events. The illustration below shows the two basic processes that might be used to synchronise events between the different specialised processors in the cerebral cortex and brain in general.  In the first option a complete model of sensation, dream etc. may be created and then allowed to become part of conscious experience. In the second model events are released into experience as fast as possible but are synchronous when recalled, having been synchronised in a storage buffer. There is a third option in which there is no synchronisation of events so that the output from different processors would occur at different times. The \'experience buffer\' would be a volume of brain in which a succession of events could be recorded. The buffer might either be updated in steps, the previous content being discarded, or continuously updated with the oldest content being lost continuously. In the first option events from different processes would always appear to be simultaneous unless the experience buffer were updated as a series of steps in which case any changes at around the moment of updating might appear in successive buffers. For instance, if change of position were processed before change in colour a circle on a screen that changed from green to red at the start of a motion might seem to be briefly green during the motion and then turn red. In the second model events from different processors might appear asynchronous at the moment of experience but synchronous when recalled. Colour vision and motion vision are processed in different parts of the visual cortex and in distinct parts of visual cortical areas V1 and V2. They are different processes and hence ideal for studying the synchronisation of cortical activity. Moutoussis and Zeki (1997) presented subjects with moving coloured squares on a computer screen that changed from red to green or vice versa as they changed direction of movement. It was found that subjects seemed to perceive changes in colour some 70-80 msecs before they perceived a change in the direction of motion of the squares. Further work by Arnold *et al.* (2001) and Arnold and Clifford (2001) have confirmed that colour changes seem to be perceived before motion. Arnold and Clifford (2001) also found a quantitative relationship between the colour/motion asynchrony and the direction of change of motion, complete reversals of direction giving rise to the greatest asynchrony between the detection of colour and motion changes. Moutoussis and Zeki (1997) conclude by stating that the asynchrony of neural processes shows that \"..the perception of each attribute is solely the result of the activity in the specialised system involved in its processing..\". It seems more likely that the experiments simply show that slow neural processes are not synchronised before they become percepts (the third option above). The experiments are excellent evidence for the concept of the cortex as a set of specialised processors that deliver their output asynchronously to some other place where the output becomes a percept. These experiments on colour and motion suggest that there is no synchronisation between the processes that deal with these two aspects of vision. Another set of experiments by Clifford *et al.* (2003) supports this idea of processing being asynchronous. They asked subjects to perform a variety of judgements of when visual events occurred and found that the degree of synchrony of one visual event with another depends on the type of judgement. Different judgements probably use processors in different areas of cortex and the output from these arrives asynchronously at the part of the brain that supports the percept. When the percept is formed there must be feedback to the cortical processes that create its content. Otherwise it would not be possible to report about the percept and the cortex would be unable to direct processing to the percept in preference to other, non-conscious cortical data. Although slow processes (20 milliseconds to 1 second) do not seem to be synchronised there is some evidence for very rapid synchronisation. Andrews *et al.* (1996) revisited a problem raised by the famous physiologist Charles Sherrington. Sherrington considered the phenomenon of \'flicker fusion\' in which a flickering light appears to be a continuous steady light if it flashes on and off at frequencies of about 45 Hz or higher. He reasoned that if the images from both eyes are brought together to form a single image then the frequency at which a flickering light appears to be steady should depend on whether one or two eyes are used. Flicker fusion should occur if each eye receives alternate flashes at only half the normal flicker fusion frequency. The flicker should disappear if the left eye receives flashes at 23 pulses per second and the right eye receives alternate flashes at 23 pulses per second. When Sherrington performed the experiment he found that this was not the case, using approximate figures, each eye required 46 pulses per second for fusion to occur. Sherrington proposed that the flicker fusion in alternate binocular presentation was occurring \"psychically\", outside of normal physiological processes. Andrews *et al.* duplicated Sherrington\'s result but investigated it further. They found that when lights were flashed in each eye alternately at low frequences (2 Hz) the experience was the same as a light being flashed in both eyes at this rate. At frequencies of four Hz and higher the subjects began to report that the lights being flashed alternately in both eyes seemed to flicker at the same rate as lights being flashed in both eyes at half the frequency. It seemed as if a flash in one eye followed by a flash in the other eye was being perceived as a single flash or \"conflated\" as the authors put it. The authors explained this effect by suggesting that the brain activity corresponding to the flashes was sampled for a short period and any number of flashes occurring during this period became perceived as a single flash. The maximum rate of sampling would be about 45 Hz. This idea is similar to option (1) above, where the buffer is filled and emptied 40 - 50 times a second. An experience buffer that is refreshed at 40-50 times a second might also explain the results obtained with colour and motion asynchrony because synchronisation between processes may well happen too quickly to affect processes that occur at very slow rates. Singer and Gray (1995), Singer (2001) have proposed that synchronisation between neurones at about 45 Hz is the discriminator between those neurones with activity that contributes to conscious experience and activity in other neurones. A rapid refresh rate in a synchronising buffer agrees with the results found by Fries *et al.* (1997) in which visual cortical neurones that represent a percept underwent synchronous oscillations in the gamma frequency range (39--63 Hz). Tononi *et al.* (1998) have also found synchronisation of neural activity in neurones that represent the percept. The gamma frequency oscillations are intrinsic to the cortex but are triggered by the thalamus and are part of the \'arousal system\'. Readers should be wary of the term \'arousal system\' because it evokes the idea of something waking up a conscious cortex. The cortex can be fully active during sleep and even during pathological unconsciousness such as persistent vegetative state so it is possible that the arousal centres themselves or nearby structures actually host phenomenal consciousness. ## EEG and synchronisation If electrodes are placed on the scalp varying electrical potentials of a few tens of microvolts can be recorded between the electrodes. Recordings of potentials from electrodes on the scalp are known as electroencephalograms (EEGs). The potentials recorded in the EEG are due to postsynaptic potentials in nerve cells. The EEG is insensitive to the activity of single cells and occurs as a result of relatively slow, **synchronised**, changes in large areas of cells. The differences in potential between two scalp electrodes are largely due to depolarisation and hyperpolarisation of the dendritic trees of cortical pyramidal cells. The folding of the cortex (gyri) is problematical for recording and interpreting EEGs because opposing layers of cortex can cancel any net potentials. The EEG shows rhythmic activity. This is conventionally divided into the following frequency bands: Delta waves 0--4 Hz Theta waves 4--8 Hz Alpha waves 8--12 Hz Beta waves \>10 Hz Gamma waves (also called fast beta) 25--100 Hz EEGs also contain short bursts of activity called spindles and very fast oscillations (VFOs). Spindles last for 1--2 seconds and contain rhythmic activity at 7--14 Hz. They are associated with the onset of sleep. The VFOs consist of short bursts at frequencies of over 80 Hz. When the eyes are closed the amplitude of activity from most pairs of electrodes is increased compared with when the eyes are open. When subjects are awake the EEG consists mainly of alpha and beta activity with considerable low amplitude gamma when the eyes are open. In stage 1 sleep the EEG consists of theta waves, in stage 2 sleep of varied activity and spindles, in stage 4 sleep of delta and during REM sleep of beta and theta activity. In epileptic seizures there tends to be high amplitude activity with pronounced synchronisation between many pairs of electrodes. The rhythmic electrical activity is due to cortical feedback loops, cortico-cortical synchronisation, thalamic pacemakers and thalamo-cortical synchronisation. VFOs have been attributed to the activity of electrical connections between cells (dendro-dendritic gap junctions) (Traub (2003)). The gamma activity, centred on a frequency of 40 Hz appears to be related to activity in cortical interneurons that form electrical connections between their dendrites (Tamas *et al.* 2000). These oscillations can be triggered by high frequency stimulation of the posterior intralaminar nuclei of the thalamus (Barth and MacDonald 1996, Sukov and Barth 2001) and as a result of activation of the reticular system (Munk *et al.* 1996). This suggests that stimulation of cortex by thalamic sensory relays triggers gamma band activity in the cortex. A shift from gamma to beta waves can occur in human event related potentials after about 0.2 secs (Pantev 1995, Traub *et al.* 1999). The alpha activity is related to thalamic pacemakers, perhaps as a result of intrinsic oscillatory activity in thalamic sensory relays (see Roy & Prichep 2005 for a brief review). Theta activity, which occurs during some cognitive tasks and mental arithmetic involves a loop from the cortex to the non-specific thalamic nuclei. Delta activity seems to be endogenous to cortex when input is suppressed during sleep. Beta activity is due to cortico-cortical interactions, often after a brief period of gamma activation. It should be noted that gamma and beta activity can be expressed as impulses in cortico-thalamic pathways and that when cortical and thalamic activity is correlated there is a conscious state. In other words gamma or beta waves in the cortex are not correlates of consciousness on their own - see for instance Laureys *et al.* (2002). ## Event related potentials After a sudden event there are a characteristic set of changes in EEG activity known as **event related potentials** or ERPs. The time course of the ERP is shown in the diagram below.  ERPs occur in response to novel stimuli and are also produced by brief transcranial magnetic stimulation (TMS)(Iramina *et al.* 2002). The slow component is known as the P3 or P300 phase of the ERP. It is due to activation of areas of the brain that are relatively remote from the primary sensory areas of brain. Nieuwenhuis *et al.* (2005) have reviewed the origin of the P300 ERP: \"To summarize, convergent evidence suggests that P3-like activity can be recorded in several, widely separated brain areas. These include some medial temporal and subcortical structures (e.g., the hippocampal formation, amygdala, and thalamus), but these structures are unlikely to contribute directly to the scalp-recorded P3.\". According to Nieuwenhuis *et al.* (2005) the recorded P300 may be due to temporo-parietal and prefrontal cortical activity. Linden (2005) has also concluded that widespread, but specific, cortical activation is correlated with the recorded P300 ERP. The generator of the P300 is still obscure. Nieuwenhuis *et al.* (2005) consider that the Locus coeruleus, a nucleus in the pons that regulates task related attention and part of the sleep-wake cycle, may be responsible. In line with this, Mashour *et al.* (2005) have discovered that TMS induced P300 activity is reduced in unconscious states. Whether the P300 is related to Libet\'s 0.5 second delay is still obscure but the discovery that the P300 occurs in association with subliminal stimuli (stimuli that do not enter awareness)(Bernat *et al.* 2001) suggests that it is associated with non-conscious cortical processing. Williams *et al.* (2004), in an investigation of subliminal and supraliminal fear perception, found that \"conscious fear perception was distinguished by a more prominent N4, peaking around 400 msec\"; the N4 component follows the P300 component in the succession of phases of the ERP. Williams *et al.* considered that the earlier phases in the ERP are probably related to non-conscious processing. In contrast Vogel *et al.* (1998) found that suppression of the P300 was associated with suppression of awareness. ## The integration delay Psychological experiments often involve binary decisions where subjects give one of two outputs in response to stimuli. It is found that if the stimuli are made increasingly noisy or complex the response time tends to increase. Psychophyicists have developed various mathematical models to explain the increased response times due to noise such as the Integrator and Accumulator models (cf: Luce(1986)). These models have been fairly successful when explaining experiments such as judging the net direction of movement of sets of dots on a screen when the dots are given semi-random paths and different brightness etc. In these circumstances it can take up to 2 seconds for an accurate decision. There are many tasks however where the accuracy of decision making does not improve after about 300 milliseconds. The accuracy of the performance of rats when choosing between two alternatives when reacting to odours peaks at about 300 ms (Uchida and Mainen(2003), Abraham *et al.* (2004)). The accuracy of humans when performing vernier acuity tasks, line detection, contrast sensitivity, motion velocity discrimination and stereoscopic depth discrimination seems to peak at 300ms (Uchida *et al.* 2006). Uchida, Kepecs and Mainen (2006) suggest that \"rapid and short integration time is a sensible strategy for rapid processing of low-level sensory information in order to form more complex sensory images, both in vision and olfaction.\" Whether these authors regard these derived sensory images as the content of consciousness is not mentioned. The authors propose that the 300ms optimal integration time may be partly due to the mechanics of sniffing (a sniff takes about 125-200ms) and the nature of optical fixation (inter-saccade intervals are typically 200-400 ms ). The authors note that the animal or human could, in principle, choose to integrate over longer intervals but if it is moving this may not lead to information that is current for changed circumstances. An optimal processing time of about 300 ms would be consistent with the delays observed before conscious awareness occurs in response to a stimulus - an interval required to form \"more complex sensory images\". ## Global Workspace Theory Global Workspace Theory is the idea that somewhere in the brain there is a facility that integrates the processes that occur in the various separate areas of the brain. The theory was first proposed by Descartes as the *sensus communis*, the common sense, but the modern form of the theory dispenses with the idea of a point soul looking at the brain. In modern Global Workspace theory it is proposed that an area of brain receives input from most of the cerebral cortex and broadcasts its outputs to all of the unconscious modular information processors in the brain. Modern Global Workspace Theory has been championed by Baars (1983, 1988). There is increasing evidence for a Global Workspace or Global Workspaces in the brain. Much of this evidence comes from fMRI, single unit and magnetoencephalography studies in which it is shown that non-conscious or subliminal processing mainly occupies primary, sensory cortex whereas conscious processing occupies large areas of cerebral cortex. In binocular rivalry the stimulus that is consciously perceived is responsible for relatively intense activation of large areas of brain whereas the non-conscious stimulus is often suppressed (see above and Sheinberg & Logothetis (1997), Tononi *et al.* (1998)). The suppression is likely to occur in the Lateral Geniculate Nuclei which suggests a role for the Thalamic Reticular Nuclei, which modulate LGN activity, in the control of the percept. ### Masking and visual awareness Word masking has also been used to investigate the idea of a Global Workspace. When a word is presented on its own for a few tens of milliseconds it remains readable but if it is immediately succeeded by, or accompanied by, another word it becomes indistinct or invisible. This effect is known as \"word masking\". Vogel *et al.* (1998) have investigated a version of word masking known as the \"attentional blink\". They found that when stimuli became invisible the P3 component of the Event Related Potential, which peaks at around 300-500 millisecs after a stimulus, was completely suppressed. The P3 component of the ERP has been related to the lodging of data in working memory and also to gamma band activity in the EEG. This strongly suggests the involvement of a cortico-thalamic loop in the \"attentional blink\". The delay of 0.3 to 0.5 secs is typical of the time required for conscious awareness (see above). Word masking in conjunction with fMRI and Event Related Potential (ERP) recordings has been used by Dehaene *et al.* (2001) to expose control by a central mechanism. It was found that masked words activate mainly the visual cortex and ventral stream (inferior temporal lobe) whereas visible words also activated distant parietal, prefrontal and cingulate sites. Dehaene *et al.* (2003) and found that the dynamics of the loss of visibility of words in an attentional blink experiment could be modelled by a simulated cortico-thalamic loop. In their simulation a distributed cortical process determined which events would receive attention and the system used the thalamic gating systems to exclude those that did not receive attention. Tse *et al.* (2005) have used purely visual stimuli in masking experiments and concluded that, in the case of purely visual stimuli, the neural correlates of awareness were limited to the occipital cortex: \"We suggest that there are both lower and upper bounds within the visual hierarchy for the processing of visual masking and the maintenance of visual awareness of simple unattended targets; the lower bound is at least as high as the border between V2 and V3, and the upper bound is within the occipital lobe, possibly somewhere downstream of V4.\" This discovery would mean that activation of large areas of cortex are unnecessary for awareness. Melloni *et al.* (2007) compared compared the electrophysiological responses related to the processing of visible and invisible words in a delayed matching to sample task. Both perceived and nonperceived words caused a similar increase of local (gamma) oscillations in the EEG, but only perceived words induced a transient long-distance synchronization of gamma oscillations across widely separated regions of the brain. After this transient period of temporal coordination, the electrographic signatures of conscious and unconscious processes continue to diverge. Only words reported as perceivedinduced (1) enhanced theta oscillations over frontal regions during the maintenance interval, (2) an increase of the P300 component of the event-related potential, and (3) an increase in power and phase synchrony of gamma oscillationsbefore the anticipated presentation of the test word. We propose that the critical process mediating the access to conscious perception is the earlytransient global increase of phase synchrony of oscillatory activity in the gammafrequency. Melloni L, Molina C, Pena M, Torres D, Singer W, Rodriguez E. (2007). Synchronization of neural activity across cortical areas correlates withconscious perception.J Neurosci. 2007 Mar 14;27(11):2858-65. ### Attention and the global workspace Baars (2002) in his review of evidence for the Global Workspace Theory quotes many other experiments that show activation of larger areas of cortex in response to conscious stimuli compared with unconscious or subliminal stimuli.The effect is also seen in change blindness, learning and attention. Newman and Baars (1993) consider that the \"workspace\" is fairly global in the brain: \"This Neural Global Workspace (NGW) model views conscious processes in terms of a globally integrative brain system. The neural circuitry contributing to this system is not only widely distributed across the neocortex, but includes key corticothalamic and midbrain circuits as well. These cortico-subcortical circuits are hypothesized to be critical to understanding the mechanisms of attentional control that provide an essential basis for the conscious processing of information\". However they focus particularly on the role of the thalamic Reticular Nucleus and cortico-thalamic connectivity in the control of attention. Other ideas for the location of the Global Workspace are the idea of Singer et al. that gamma synchrony controls access to the content of consciousness and Llinas et al. (1998) that the thalamus is the hub through which communication occurs between areas of cortex. One of the problems with Global Workspace theory is that it suggests that attention, working memory, cognitive control and consciousness may all be in the same area of the brain. It is likely that the mechanisms of attention, working memory, and cognitive control may involve several, interlinked systems perhaps co-opting the basal ganglia in the process. In view of this Maia and Cleeremans (2005) propose that \".. attention, working memory, cognitive control and consciousness are not distinct functions implemented by separate brain systems. Attempting to find separate neural correlates for each may therefore be the wrong approach. Instead, we suggest that they should be understood in terms of the dynamics of global competition, with biasing from PFC (prefrontal cortex).\". The inclusion by Maia and Cleeremans of consciousness with distributed attention, working memory and cognitive control is reminiscent of Zeki & Bartel\'s idea of microconsciousness. It should be noted that, in common with Libet\'s data, the percept seems to be available to phenomenal consciousness some 0.3 to 0.5 secs after a stimulus; this suggests that whatever determines the content of phenomenal consciousness operates before events become part of phenomenal consciousness. This relegates phenomenal consciousness from being a controller of attention to being the recipient of content that is the subject of attention. This finding is consistent with the philosophical problem of the **apparently** epiphenomenal nature of phenomenal consciousness. Given the data on the timing of conscious awareness it seems that there may be two \"workspaces\", an active workspace that models the world, discarding and suppressing data during rivalry, and a passive workspace that receives the final, edited product. The active workspace would correlate with the cortical systems stressed by Dehaene *et al.* and Maia and Cleermans although, given the results of Tse et al., the workspace would be limited to small zones of cortex. The loading of the passive workspace with the output of the active workspace would correlate with thalamo-cortical activity during component P3 of the ERP in which data is transferred from the cortex to the thalamus. This workspace might constitute the source for reports of the content of phenomenal consciousness. Llinas *et al.* (1998) have proposed two parallel cortico-thalamic attentional systems, one of which is related to the thalamic specific nuclei and the other to the thalamic non-specific nuclei, especially the ILN. The non-specific system would be related to consciousness itself. ## The \"cognitive map\" and the neural basis of perceptual space Our bodies appear to be mobile within a constant space. We walk around a room; the room does not rotate around us. The constancy of the location of things gives us the feeling that we are directly viewing a constant world. But how does the brain provide a constant world rather than a world that rotates with the movement of the sense organs? Why is our view of the world when we move our eyes so different from the disturbing flow of images that occur when a video camera is waved around? Do our brains contain a constant \"cognitive map\" (O\'Keefe and Nadel 1978) of our surroundings? Mittelstaedt & Mittelstaedt (1980, 1982) discovered that female gerbils were able to recover their pups in darkened surroundings by searching in a semi random fashion on the outbound journey and then proceeding directly back to the nest on the inbound journey. The direct journey back to the nest seemed to be due to an integration of the various directions taken on the outward journey (**path integration**). If the equipment being explored by the mother gerbil was rotated very slowly the mother would make an error equivalent to the amount of rotation. More rapid rotations that activated the vestibular system of the rat (acceleration measurement) did not cause errors in navigation. This demonstration that rodents could navigate accurately on the basis of **idiothetic** cues (cues that are due to internal senses) led to research on the neural basis of the navigation. As early as 1971 O\'Keefe and Dostrovsky had discovered that there are particular cells in the hippocampus that fire according to the position of an animal in the environment. This has been complimented by research that showed that changes in visual cues within the environment caused changes in the firing rate of place cells in hippocampal area CA3 (.   !Entorhinal cortex approximately maps to areas 28 and 34{width="500"} F. P. Battaglia and A. Treves. 1998 Attractor neural networks storing multiple space representations: A model for hippocampal place fields. PHYSICAL REVIEW E DECEMBER 1998 VOLUME 58, NUMBER 6 <http://www.sissa.it/~ale/Bat+98b.pdf> Leutgeb, S., Leutgeb, J.K., Moser, M-B, and Moser, E.I. 2005. Place cells, spatial maps and the population code for memory. Current Opinion in Neurobiology 2005, 15:738--746. <http://instruct1.cit.cornell.edu/courses/bionb720nejc/reprints/LeutgebEtAl2005.pdf> Mittelstaedt, H. & Mittelstaedt, M-L. 1982. Avian Navigation. (ed. Papi, F. & Wallraff, H.) 290-297. Springer, Berlin. Mittelstaedt, M-L & Glasauer, S. 1991. Idiothetic Navigation in Gerbils and Humans. Zool. Jb. Physiol. 95 (1991), 427-435 <http://web.archive.org/web/20110125132449/http://www.nefo.med.uni-muenchen.de/~sglasauer/MittelstaedtGlasauer1991.pdf> O\'Keefe, J. & Dostrovsky, J. (1971). The hippocampus as a spatial map: preliminary evidence from unit activity in the freely moving rat. Brain Res. 34, 171-175. O\'Keefe, J. & Nadel, L. (1978). The Hippocampus as a cognitive map. (Oxford) ## Bibliography Defining the States of Consciousness. Tassi, P., Muzet, A. (2001) Neuroscience and Behavioural Reviews 25(2001) 175-191. 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# Consciousness Studies/Neuroscience 2#Global Workspace Theory *Contributors: please include full data in the references section for all references in the text.* ```{=html} <div class="noprint"> ``` Home ```{=html} </div> ``` ## Perceptual \"filling in\" Perceptual \"filling in\" occurs when visual properties such as textures, colours, brightness or motion are extended in the visual field to areas where they do not have corresponding events in the world. The filling in of the blind spot by the properties of the field in the contralateral eye has already been discussed. The part of the visual field represented by the blind spot is also \"filled in\" in the case of monocular vision.  Shut the right eye and focus on the pink cross with the left eye, if the head is moved towards the pink cross there is a point at which the yellow disk disappears but the white lines are still present. In this \"filling in\" the visual field does not appear to be distorted. Fiorani *et al.* (1992) developed a technique for probing the cortical blind spot using vertical and horizontal bar stimuli. Matsumoto & komatsu (2005) used this technique on macaque monkeys. In the monocular case they found that as a bar was moved across the visual field so that it crossed the blind spot there was a sudden change in neural activity in the deep layers of the neurons in the blind spot area of V1. When the bar was moved across the same part of the visual field of the contralateral eye the neural activity in the blind spot area increased steadily as the bar was moved. The authors found that there were neurons in the deep layers of blind spot cortex that had elongated receptive fields that could respond to stimuli outside the blind spot and transfer this activation into the blind spot cortex. Filling in of a slightly different type occurs in \"scotoma\". In scotoma an area of the retina is damaged and unresonsive to visual stimuli, immediately after the damage patients report an area of visual field that is unresponsive to stimuli. After several months patients report that the area of field represented by the scotoma contains visual properties related to the physical world surrounding the area that would have formed an image on the scotoma. This results in a distortion of the visual field. (see for instance Gilbert(1993)). Direct measurements of activity in cortical area V1 show that the neurons that represented the area of the scotoma become sensitive to activity in the surrounding visual field. At the cortical level the scotoma is literally \"filled in\". There are many stimuli that cause \"filling in\". These stimuli are known as \"illusions\" because they produce phenomenal experience that has no correlate in the world outside the body. In the \"neon colour spreading illusion\" a lightly coloured circle appears where there should be a white background. Sasaki and Watanabe (2004) used fMRI to show that the part of the topographic map in cortical area V1 corresponding to the light coloured circle was activated.  Fiorani, M., Rosa, M.G.P., Gattas, R. & Rocha-Miranda, C.E. (1992). Dynamic surrounds of receptive fields in primate striate cortex: a physiological basis for perceptual completion? Proc. Natl. Acad. Sci. 89, 8547-8551. <http://www.pnas.org/cgi/content/abstract/89/18/8547> Gilbert, C.D. (1993). Circuitry, architecture and functional dynamics of visual cortex. Matsumoto, M & Komatsu, H. (2005). Neural responses in the macaque V1 to bar stimuli with various lengths presented on the blind spot. J neurophysiol. 93. 2374-2387. <http://jn.physiology.org/cgi/content/abstract/93/5/2374> Sasaki, Y & Watanabe, T. The primary visual cortex fills in colour. Proc. Natl. Acad. Sci. USA 101, 18251-18256. (2004). ## Binocular Rivalry, Pattern Rivalry and Binocular Fusion Sir Charles Wheatstone (1838) was the first scientist to systematically investigate binocular rivalry. Binocular rivalry occurs when different images are presented to the left and right eyes. The subject sees successively one image, a combined image and then the other image. The swapping of images can take a second or more. Binocular rivalry is of interest in consciousness research because the parts of the brain that contain the dominant image should also be those parts that are contributing to conscious experience. Binocular rivalry involves at least two components; the first switches from one image to a merged image and then to the other image and the second permits the view to be part of conscious experience.  The switching of one image for another may involve selecting one of the images as the percept or selecting one of the eyes. Blake *et al.* (1979) performed an experiment in which subjects could change the image at a given eye by pressing a button. When a particular image became dominant they pressed a button to change the image at the eye receiving the dominant image for the non-dominant image. They found that the subjects immediately experienced the second image as the dominant image. This suggests that binocular rivalry is selecting between eyes rather than images. Lehky in 1988 proposed that the switching may be occurring as a result of feedback between visual cortical area V1 and the Lateral Geniculate Nucleus (a thalamic relay - see Carandini *et al.* 2002) and Blake in 1989 also proposed that the switching occurred at the level of area V1. (Visual cortical area V1 receives visual input direct from the LGN.) Tong (2001) has argued that, in humans, the switching of images in binocular rivalry may occur at the earliest levels in the visual cortex. In particular, Tong and Engel (2001) used an elegant technique measuring the activity in the visual cortex that represents the blind spot of the eye to show that almost complete switching to the dominant image occurs at the level of visual cortical area V1. In support of this idea of switching at the level of V1 or even before the cortex, Kreimann *et al.* (2001, 2002) used direct electrode recordings in human cortex and found that the activity of most neurons changed with the percept. Other experiments have not shown a single locus in the brain where the suppressed sensory information gets switched out (Blake & Logothetis 2002, Leopold & Logothetis 1996, Gail et al., 2004). Functional MRI has also shown cortical activity outside of sensory visual cortex related to both images in binocular rivalry. Lumer *et al.* (1998) found that only the fronto-parietal areas of cortex switched with the percept, Fang & He (2005) found that activity relating to both suppressed and unsuppressed images were present in the dorsal stream of the visual system. Wunderlich *et al.* (2005) and Haynes *et al.* (2005) have both found suppression at the level of the lateral geniculate nucleus using fMRI in humans. Pasley *et al.* (2004) have shown that, even during suppression, fearful faces can produce activity in the amygdala (see Pessoa (2005) for a review). Rivalry alternations seem to be the result of widespread activity changes that cover large parts of the brain, including but not necessarily originating at the earliest sensory stages of visual processing. Most investigators have found that, once switching has occurred, there are areas of the brain that contain activity that is solely related to the percept but this varies from most of the cortex to largely more frontal regions depending upon the study. The most likely explanation for binocular rivalry is that the switching occurs at the level of the LGN as a result of feedback from the cortex. Pattern Rivalry is also of interest in consciousness research for the same reasons as binocular rivalry. In pattern rivalry a figure may have two or more forms that replace each other. Typical examples of such figures are the Necker cube and Rubin\'s face-vase. The similarity of the time course of the switching between percepts in binocular rivalry and pattern rivalry has led many authors to suggest that these involve the same mechanism. Logothetis *et al.* (1996) used novel dichoptic stimuli (different images to each eyes) to produce a form of rivalry that seems to involve switching at levels in the cerebral cortex that are more distal to the sensory stimulus than V1. Leopold and Logothetis (1999), on the basis of their work with monkeys, state that \"..many neurons throughout the visual system, both monocular and binocular, continue to respond to a stimulus even when it is perceptually suppressed.\". Kleinschmidt *et al.* (1998) investigated pattern rivalry with MRI and found activity in higher order visual areas during change of dominant pattern. Pettigrew (2001) also describes effects on rivalry due to thought and mood that may require involvement of large areas of cortex in the switching operation and stresses the way that V1 represents different visual fields in different hemispheres of the brain so that inter-hemispheric switching must also be considered. It seems likely that the change of dominant pattern or percept is associated with higher level cortical activity but once the dominant percept is established many of the visually responsive neurons in the cortex are switched over to the new percept. This might account for the similarities in timing of binocular and pattern rivalry and the disparate results found by the various groups of authors. In the words of Kleinschmidt *et al.* (1998): \"The transient activity fluctuations we found suggest that perceptual metastability elicited by ambiguous stimuli is associated with rapid redistributions of neural activity between separate specialized cortical and subcortical structures.\" Which permits both the idea of selecting particular eyes or percepts, perhaps by feedback that switches a thalamic relay on the basis of cortical processing of patterns. Once the cortex has switched the thalamic relay most of the neurons in V1 would become exposed to the dominant percept but there would still be a few neurons in the cortical visual system receiving data from the non dominant image. The investigations of binocular and pattern rivalry provide evidence that conscious visual experience is probably distal to V1 (i.e.: cortex or thalamus). Perceptual rivalry may be part of complex decision making rather than being simply a switch to blank out unwelcome input. It is clear from the Rubin face-vase that pattern rivalry is linked to recognition and would involve a complex delineation of forms within cortical processing. This would suggest that many areas of cortex should be involved before a particular percept is made dominant. Pettigrew (2001) argues that rivalry is the result of a complex phenomenon rather than being simply a switching event. Pettigrew\'s discovery that laughter abolishes rivalry also points to a complex cortical system for switching percepts. Pettigrew proposes that complex cortical processes control rivalry and that the actual switching of percepts is performed sub-cortically in the Ventral Tegmental Area. He concludes his review of the problem by noting that \"Rivalry may thus reflect fundamental aspects of perceptual decision making..\" Pettigrew (2001). Another effect, known as \"binocular fusion\", provides further compelling evidence for the non-conscious nature of the cerebral cortex. In binocular fusion images from both eyes are fused together to create a single image in experience. Moutoussis and Zeki (2002) used a form of binocular fusion in which images of faces were flashed at 100ms intervals to both eyes simultaneously. When both eyes received images of the same colour the subject could see the faces but when one eye received a green image on a red background and the other a red image on a green background the subjects reported seeing a uniform yellow field that contained no faces. fMRI scans of the subject\'s brains showed that when both eyes were exposed to images of the same colour the part of the brain that deals with faces was active and when each eye received images of different colours the same areas of brain showed activity. In other words the cortex contained strong activity related to faces whether or not faces were experienced. Moutoussis and Zeki found a similar effect when they used images of houses instead of images of faces. The authors concluded that: \"The present study further suggests that there are no separate processing and perceptual areas but rather that the same cortical regions are involved in both the processing and, when certain levels of activation are reached and probably in combination with the activation of other areas as well, the generation of a conscious visual percept\". This conclusion does not seem to be supported by the data. There is no evidence that any area of cortex contains the percept itself. The experiment shows that the cortex contains data relating to both red and green faces which suggests that the cortex is not the site of the conscious percept. The percept is most likely distal to the cortex perhaps in the thalamus or some other area that receives cortical sensory output. It is interesting that Fries *et al.* (1997) found that neurons that were activated by the dominant image in binocular rivalry fired synchronously whereas those that were activated by the non-dominant image did not. Thalamocorticothalamic oscillations are the most likely source for synchronising neurons over whole areas of cortex, suggesting that the conscious percept is located in the thalamus rather than the cortex. ## Synchronisation of Neural Processes Our experience seems to contain entities with their attributes attached to them at the correct places in space and time. When a dog barks we see its jaws open at the same time as the bark and both jaws and bark are at the same location. We take this for granted but the brain must be engaging in some complex processing to achieve this synchronised and appropriately positioned set of objects and events. The illustration below shows the two basic processes that might be used to synchronise events between the different specialised processors in the cerebral cortex and brain in general.  In the first option a complete model of sensation, dream etc. may be created and then allowed to become part of conscious experience. In the second model events are released into experience as fast as possible but are synchronous when recalled, having been synchronised in a storage buffer. There is a third option in which there is no synchronisation of events so that the output from different processors would occur at different times. The \'experience buffer\' would be a volume of brain in which a succession of events could be recorded. The buffer might either be updated in steps, the previous content being discarded, or continuously updated with the oldest content being lost continuously. In the first option events from different processes would always appear to be simultaneous unless the experience buffer were updated as a series of steps in which case any changes at around the moment of updating might appear in successive buffers. For instance, if change of position were processed before change in colour a circle on a screen that changed from green to red at the start of a motion might seem to be briefly green during the motion and then turn red. In the second model events from different processors might appear asynchronous at the moment of experience but synchronous when recalled. Colour vision and motion vision are processed in different parts of the visual cortex and in distinct parts of visual cortical areas V1 and V2. They are different processes and hence ideal for studying the synchronisation of cortical activity. Moutoussis and Zeki (1997) presented subjects with moving coloured squares on a computer screen that changed from red to green or vice versa as they changed direction of movement. It was found that subjects seemed to perceive changes in colour some 70-80 msecs before they perceived a change in the direction of motion of the squares. Further work by Arnold *et al.* (2001) and Arnold and Clifford (2001) have confirmed that colour changes seem to be perceived before motion. Arnold and Clifford (2001) also found a quantitative relationship between the colour/motion asynchrony and the direction of change of motion, complete reversals of direction giving rise to the greatest asynchrony between the detection of colour and motion changes. Moutoussis and Zeki (1997) conclude by stating that the asynchrony of neural processes shows that \"..the perception of each attribute is solely the result of the activity in the specialised system involved in its processing..\". It seems more likely that the experiments simply show that slow neural processes are not synchronised before they become percepts (the third option above). The experiments are excellent evidence for the concept of the cortex as a set of specialised processors that deliver their output asynchronously to some other place where the output becomes a percept. These experiments on colour and motion suggest that there is no synchronisation between the processes that deal with these two aspects of vision. Another set of experiments by Clifford *et al.* (2003) supports this idea of processing being asynchronous. They asked subjects to perform a variety of judgements of when visual events occurred and found that the degree of synchrony of one visual event with another depends on the type of judgement. Different judgements probably use processors in different areas of cortex and the output from these arrives asynchronously at the part of the brain that supports the percept. When the percept is formed there must be feedback to the cortical processes that create its content. Otherwise it would not be possible to report about the percept and the cortex would be unable to direct processing to the percept in preference to other, non-conscious cortical data. Although slow processes (20 milliseconds to 1 second) do not seem to be synchronised there is some evidence for very rapid synchronisation. Andrews *et al.* (1996) revisited a problem raised by the famous physiologist Charles Sherrington. Sherrington considered the phenomenon of \'flicker fusion\' in which a flickering light appears to be a continuous steady light if it flashes on and off at frequencies of about 45 Hz or higher. He reasoned that if the images from both eyes are brought together to form a single image then the frequency at which a flickering light appears to be steady should depend on whether one or two eyes are used. Flicker fusion should occur if each eye receives alternate flashes at only half the normal flicker fusion frequency. The flicker should disappear if the left eye receives flashes at 23 pulses per second and the right eye receives alternate flashes at 23 pulses per second. When Sherrington performed the experiment he found that this was not the case, using approximate figures, each eye required 46 pulses per second for fusion to occur. Sherrington proposed that the flicker fusion in alternate binocular presentation was occurring \"psychically\", outside of normal physiological processes. Andrews *et al.* duplicated Sherrington\'s result but investigated it further. They found that when lights were flashed in each eye alternately at low frequences (2 Hz) the experience was the same as a light being flashed in both eyes at this rate. At frequencies of four Hz and higher the subjects began to report that the lights being flashed alternately in both eyes seemed to flicker at the same rate as lights being flashed in both eyes at half the frequency. It seemed as if a flash in one eye followed by a flash in the other eye was being perceived as a single flash or \"conflated\" as the authors put it. The authors explained this effect by suggesting that the brain activity corresponding to the flashes was sampled for a short period and any number of flashes occurring during this period became perceived as a single flash. The maximum rate of sampling would be about 45 Hz. This idea is similar to option (1) above, where the buffer is filled and emptied 40 - 50 times a second. An experience buffer that is refreshed at 40-50 times a second might also explain the results obtained with colour and motion asynchrony because synchronisation between processes may well happen too quickly to affect processes that occur at very slow rates. Singer and Gray (1995), Singer (2001) have proposed that synchronisation between neurones at about 45 Hz is the discriminator between those neurones with activity that contributes to conscious experience and activity in other neurones. A rapid refresh rate in a synchronising buffer agrees with the results found by Fries *et al.* (1997) in which visual cortical neurones that represent a percept underwent synchronous oscillations in the gamma frequency range (39--63 Hz). Tononi *et al.* (1998) have also found synchronisation of neural activity in neurones that represent the percept. The gamma frequency oscillations are intrinsic to the cortex but are triggered by the thalamus and are part of the \'arousal system\'. Readers should be wary of the term \'arousal system\' because it evokes the idea of something waking up a conscious cortex. The cortex can be fully active during sleep and even during pathological unconsciousness such as persistent vegetative state so it is possible that the arousal centres themselves or nearby structures actually host phenomenal consciousness. ## EEG and synchronisation If electrodes are placed on the scalp varying electrical potentials of a few tens of microvolts can be recorded between the electrodes. Recordings of potentials from electrodes on the scalp are known as electroencephalograms (EEGs). The potentials recorded in the EEG are due to postsynaptic potentials in nerve cells. The EEG is insensitive to the activity of single cells and occurs as a result of relatively slow, **synchronised**, changes in large areas of cells. The differences in potential between two scalp electrodes are largely due to depolarisation and hyperpolarisation of the dendritic trees of cortical pyramidal cells. The folding of the cortex (gyri) is problematical for recording and interpreting EEGs because opposing layers of cortex can cancel any net potentials. The EEG shows rhythmic activity. This is conventionally divided into the following frequency bands: Delta waves 0--4 Hz Theta waves 4--8 Hz Alpha waves 8--12 Hz Beta waves \>10 Hz Gamma waves (also called fast beta) 25--100 Hz EEGs also contain short bursts of activity called spindles and very fast oscillations (VFOs). Spindles last for 1--2 seconds and contain rhythmic activity at 7--14 Hz. They are associated with the onset of sleep. The VFOs consist of short bursts at frequencies of over 80 Hz. When the eyes are closed the amplitude of activity from most pairs of electrodes is increased compared with when the eyes are open. When subjects are awake the EEG consists mainly of alpha and beta activity with considerable low amplitude gamma when the eyes are open. In stage 1 sleep the EEG consists of theta waves, in stage 2 sleep of varied activity and spindles, in stage 4 sleep of delta and during REM sleep of beta and theta activity. In epileptic seizures there tends to be high amplitude activity with pronounced synchronisation between many pairs of electrodes. The rhythmic electrical activity is due to cortical feedback loops, cortico-cortical synchronisation, thalamic pacemakers and thalamo-cortical synchronisation. VFOs have been attributed to the activity of electrical connections between cells (dendro-dendritic gap junctions) (Traub (2003)). The gamma activity, centred on a frequency of 40 Hz appears to be related to activity in cortical interneurons that form electrical connections between their dendrites (Tamas *et al.* 2000). These oscillations can be triggered by high frequency stimulation of the posterior intralaminar nuclei of the thalamus (Barth and MacDonald 1996, Sukov and Barth 2001) and as a result of activation of the reticular system (Munk *et al.* 1996). This suggests that stimulation of cortex by thalamic sensory relays triggers gamma band activity in the cortex. A shift from gamma to beta waves can occur in human event related potentials after about 0.2 secs (Pantev 1995, Traub *et al.* 1999). The alpha activity is related to thalamic pacemakers, perhaps as a result of intrinsic oscillatory activity in thalamic sensory relays (see Roy & Prichep 2005 for a brief review). Theta activity, which occurs during some cognitive tasks and mental arithmetic involves a loop from the cortex to the non-specific thalamic nuclei. Delta activity seems to be endogenous to cortex when input is suppressed during sleep. Beta activity is due to cortico-cortical interactions, often after a brief period of gamma activation. It should be noted that gamma and beta activity can be expressed as impulses in cortico-thalamic pathways and that when cortical and thalamic activity is correlated there is a conscious state. In other words gamma or beta waves in the cortex are not correlates of consciousness on their own - see for instance Laureys *et al.* (2002). ## Event related potentials After a sudden event there are a characteristic set of changes in EEG activity known as **event related potentials** or ERPs. The time course of the ERP is shown in the diagram below.  ERPs occur in response to novel stimuli and are also produced by brief transcranial magnetic stimulation (TMS)(Iramina *et al.* 2002). The slow component is known as the P3 or P300 phase of the ERP. It is due to activation of areas of the brain that are relatively remote from the primary sensory areas of brain. Nieuwenhuis *et al.* (2005) have reviewed the origin of the P300 ERP: \"To summarize, convergent evidence suggests that P3-like activity can be recorded in several, widely separated brain areas. These include some medial temporal and subcortical structures (e.g., the hippocampal formation, amygdala, and thalamus), but these structures are unlikely to contribute directly to the scalp-recorded P3.\". According to Nieuwenhuis *et al.* (2005) the recorded P300 may be due to temporo-parietal and prefrontal cortical activity. Linden (2005) has also concluded that widespread, but specific, cortical activation is correlated with the recorded P300 ERP. The generator of the P300 is still obscure. Nieuwenhuis *et al.* (2005) consider that the Locus coeruleus, a nucleus in the pons that regulates task related attention and part of the sleep-wake cycle, may be responsible. In line with this, Mashour *et al.* (2005) have discovered that TMS induced P300 activity is reduced in unconscious states. Whether the P300 is related to Libet\'s 0.5 second delay is still obscure but the discovery that the P300 occurs in association with subliminal stimuli (stimuli that do not enter awareness)(Bernat *et al.* 2001) suggests that it is associated with non-conscious cortical processing. Williams *et al.* (2004), in an investigation of subliminal and supraliminal fear perception, found that \"conscious fear perception was distinguished by a more prominent N4, peaking around 400 msec\"; the N4 component follows the P300 component in the succession of phases of the ERP. Williams *et al.* considered that the earlier phases in the ERP are probably related to non-conscious processing. In contrast Vogel *et al.* (1998) found that suppression of the P300 was associated with suppression of awareness. ## The integration delay Psychological experiments often involve binary decisions where subjects give one of two outputs in response to stimuli. It is found that if the stimuli are made increasingly noisy or complex the response time tends to increase. Psychophyicists have developed various mathematical models to explain the increased response times due to noise such as the Integrator and Accumulator models (cf: Luce(1986)). These models have been fairly successful when explaining experiments such as judging the net direction of movement of sets of dots on a screen when the dots are given semi-random paths and different brightness etc. In these circumstances it can take up to 2 seconds for an accurate decision. There are many tasks however where the accuracy of decision making does not improve after about 300 milliseconds. The accuracy of the performance of rats when choosing between two alternatives when reacting to odours peaks at about 300 ms (Uchida and Mainen(2003), Abraham *et al.* (2004)). The accuracy of humans when performing vernier acuity tasks, line detection, contrast sensitivity, motion velocity discrimination and stereoscopic depth discrimination seems to peak at 300ms (Uchida *et al.* 2006). Uchida, Kepecs and Mainen (2006) suggest that \"rapid and short integration time is a sensible strategy for rapid processing of low-level sensory information in order to form more complex sensory images, both in vision and olfaction.\" Whether these authors regard these derived sensory images as the content of consciousness is not mentioned. The authors propose that the 300ms optimal integration time may be partly due to the mechanics of sniffing (a sniff takes about 125-200ms) and the nature of optical fixation (inter-saccade intervals are typically 200-400 ms ). The authors note that the animal or human could, in principle, choose to integrate over longer intervals but if it is moving this may not lead to information that is current for changed circumstances. An optimal processing time of about 300 ms would be consistent with the delays observed before conscious awareness occurs in response to a stimulus - an interval required to form \"more complex sensory images\". ## Global Workspace Theory Global Workspace Theory is the idea that somewhere in the brain there is a facility that integrates the processes that occur in the various separate areas of the brain. The theory was first proposed by Descartes as the *sensus communis*, the common sense, but the modern form of the theory dispenses with the idea of a point soul looking at the brain. In modern Global Workspace theory it is proposed that an area of brain receives input from most of the cerebral cortex and broadcasts its outputs to all of the unconscious modular information processors in the brain. Modern Global Workspace Theory has been championed by Baars (1983, 1988). There is increasing evidence for a Global Workspace or Global Workspaces in the brain. Much of this evidence comes from fMRI, single unit and magnetoencephalography studies in which it is shown that non-conscious or subliminal processing mainly occupies primary, sensory cortex whereas conscious processing occupies large areas of cerebral cortex. In binocular rivalry the stimulus that is consciously perceived is responsible for relatively intense activation of large areas of brain whereas the non-conscious stimulus is often suppressed (see above and Sheinberg & Logothetis (1997), Tononi *et al.* (1998)). The suppression is likely to occur in the Lateral Geniculate Nuclei which suggests a role for the Thalamic Reticular Nuclei, which modulate LGN activity, in the control of the percept. ### Masking and visual awareness Word masking has also been used to investigate the idea of a Global Workspace. When a word is presented on its own for a few tens of milliseconds it remains readable but if it is immediately succeeded by, or accompanied by, another word it becomes indistinct or invisible. This effect is known as \"word masking\". Vogel *et al.* (1998) have investigated a version of word masking known as the \"attentional blink\". They found that when stimuli became invisible the P3 component of the Event Related Potential, which peaks at around 300-500 millisecs after a stimulus, was completely suppressed. The P3 component of the ERP has been related to the lodging of data in working memory and also to gamma band activity in the EEG. This strongly suggests the involvement of a cortico-thalamic loop in the \"attentional blink\". The delay of 0.3 to 0.5 secs is typical of the time required for conscious awareness (see above). Word masking in conjunction with fMRI and Event Related Potential (ERP) recordings has been used by Dehaene *et al.* (2001) to expose control by a central mechanism. It was found that masked words activate mainly the visual cortex and ventral stream (inferior temporal lobe) whereas visible words also activated distant parietal, prefrontal and cingulate sites. Dehaene *et al.* (2003) and found that the dynamics of the loss of visibility of words in an attentional blink experiment could be modelled by a simulated cortico-thalamic loop. In their simulation a distributed cortical process determined which events would receive attention and the system used the thalamic gating systems to exclude those that did not receive attention. Tse *et al.* (2005) have used purely visual stimuli in masking experiments and concluded that, in the case of purely visual stimuli, the neural correlates of awareness were limited to the occipital cortex: \"We suggest that there are both lower and upper bounds within the visual hierarchy for the processing of visual masking and the maintenance of visual awareness of simple unattended targets; the lower bound is at least as high as the border between V2 and V3, and the upper bound is within the occipital lobe, possibly somewhere downstream of V4.\" This discovery would mean that activation of large areas of cortex are unnecessary for awareness. Melloni *et al.* (2007) compared compared the electrophysiological responses related to the processing of visible and invisible words in a delayed matching to sample task. Both perceived and nonperceived words caused a similar increase of local (gamma) oscillations in the EEG, but only perceived words induced a transient long-distance synchronization of gamma oscillations across widely separated regions of the brain. After this transient period of temporal coordination, the electrographic signatures of conscious and unconscious processes continue to diverge. Only words reported as perceivedinduced (1) enhanced theta oscillations over frontal regions during the maintenance interval, (2) an increase of the P300 component of the event-related potential, and (3) an increase in power and phase synchrony of gamma oscillationsbefore the anticipated presentation of the test word. We propose that the critical process mediating the access to conscious perception is the earlytransient global increase of phase synchrony of oscillatory activity in the gammafrequency. Melloni L, Molina C, Pena M, Torres D, Singer W, Rodriguez E. (2007). Synchronization of neural activity across cortical areas correlates withconscious perception.J Neurosci. 2007 Mar 14;27(11):2858-65. ### Attention and the global workspace Baars (2002) in his review of evidence for the Global Workspace Theory quotes many other experiments that show activation of larger areas of cortex in response to conscious stimuli compared with unconscious or subliminal stimuli.The effect is also seen in change blindness, learning and attention. Newman and Baars (1993) consider that the \"workspace\" is fairly global in the brain: \"This Neural Global Workspace (NGW) model views conscious processes in terms of a globally integrative brain system. The neural circuitry contributing to this system is not only widely distributed across the neocortex, but includes key corticothalamic and midbrain circuits as well. These cortico-subcortical circuits are hypothesized to be critical to understanding the mechanisms of attentional control that provide an essential basis for the conscious processing of information\". However they focus particularly on the role of the thalamic Reticular Nucleus and cortico-thalamic connectivity in the control of attention. Other ideas for the location of the Global Workspace are the idea of Singer et al. that gamma synchrony controls access to the content of consciousness and Llinas et al. (1998) that the thalamus is the hub through which communication occurs between areas of cortex. One of the problems with Global Workspace theory is that it suggests that attention, working memory, cognitive control and consciousness may all be in the same area of the brain. It is likely that the mechanisms of attention, working memory, and cognitive control may involve several, interlinked systems perhaps co-opting the basal ganglia in the process. In view of this Maia and Cleeremans (2005) propose that \".. attention, working memory, cognitive control and consciousness are not distinct functions implemented by separate brain systems. Attempting to find separate neural correlates for each may therefore be the wrong approach. Instead, we suggest that they should be understood in terms of the dynamics of global competition, with biasing from PFC (prefrontal cortex).\". The inclusion by Maia and Cleeremans of consciousness with distributed attention, working memory and cognitive control is reminiscent of Zeki & Bartel\'s idea of microconsciousness. It should be noted that, in common with Libet\'s data, the percept seems to be available to phenomenal consciousness some 0.3 to 0.5 secs after a stimulus; this suggests that whatever determines the content of phenomenal consciousness operates before events become part of phenomenal consciousness. This relegates phenomenal consciousness from being a controller of attention to being the recipient of content that is the subject of attention. This finding is consistent with the philosophical problem of the **apparently** epiphenomenal nature of phenomenal consciousness. Given the data on the timing of conscious awareness it seems that there may be two \"workspaces\", an active workspace that models the world, discarding and suppressing data during rivalry, and a passive workspace that receives the final, edited product. The active workspace would correlate with the cortical systems stressed by Dehaene *et al.* and Maia and Cleermans although, given the results of Tse et al., the workspace would be limited to small zones of cortex. The loading of the passive workspace with the output of the active workspace would correlate with thalamo-cortical activity during component P3 of the ERP in which data is transferred from the cortex to the thalamus. This workspace might constitute the source for reports of the content of phenomenal consciousness. Llinas *et al.* (1998) have proposed two parallel cortico-thalamic attentional systems, one of which is related to the thalamic specific nuclei and the other to the thalamic non-specific nuclei, especially the ILN. The non-specific system would be related to consciousness itself. ## The \"cognitive map\" and the neural basis of perceptual space Our bodies appear to be mobile within a constant space. We walk around a room; the room does not rotate around us. The constancy of the location of things gives us the feeling that we are directly viewing a constant world. But how does the brain provide a constant world rather than a world that rotates with the movement of the sense organs? Why is our view of the world when we move our eyes so different from the disturbing flow of images that occur when a video camera is waved around? Do our brains contain a constant \"cognitive map\" (O\'Keefe and Nadel 1978) of our surroundings? Mittelstaedt & Mittelstaedt (1980, 1982) discovered that female gerbils were able to recover their pups in darkened surroundings by searching in a semi random fashion on the outbound journey and then proceeding directly back to the nest on the inbound journey. The direct journey back to the nest seemed to be due to an integration of the various directions taken on the outward journey (**path integration**). If the equipment being explored by the mother gerbil was rotated very slowly the mother would make an error equivalent to the amount of rotation. More rapid rotations that activated the vestibular system of the rat (acceleration measurement) did not cause errors in navigation. This demonstration that rodents could navigate accurately on the basis of **idiothetic** cues (cues that are due to internal senses) led to research on the neural basis of the navigation. As early as 1971 O\'Keefe and Dostrovsky had discovered that there are particular cells in the hippocampus that fire according to the position of an animal in the environment. This has been complimented by research that showed that changes in visual cues within the environment caused changes in the firing rate of place cells in hippocampal area CA3 (.   !Entorhinal cortex approximately maps to areas 28 and 34{width="500"} F. P. Battaglia and A. Treves. 1998 Attractor neural networks storing multiple space representations: A model for hippocampal place fields. PHYSICAL REVIEW E DECEMBER 1998 VOLUME 58, NUMBER 6 <http://www.sissa.it/~ale/Bat+98b.pdf> Leutgeb, S., Leutgeb, J.K., Moser, M-B, and Moser, E.I. 2005. Place cells, spatial maps and the population code for memory. Current Opinion in Neurobiology 2005, 15:738--746. <http://instruct1.cit.cornell.edu/courses/bionb720nejc/reprints/LeutgebEtAl2005.pdf> Mittelstaedt, H. & Mittelstaedt, M-L. 1982. Avian Navigation. (ed. 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# Consciousness Studies/Neuroscience 2#The "cognitive map" and the neural basis of perceptual space *Contributors: please include full data in the references section for all references in the text.* ```{=html} <div class="noprint"> ``` Home ```{=html} </div> ``` ## Perceptual \"filling in\" Perceptual \"filling in\" occurs when visual properties such as textures, colours, brightness or motion are extended in the visual field to areas where they do not have corresponding events in the world. The filling in of the blind spot by the properties of the field in the contralateral eye has already been discussed. The part of the visual field represented by the blind spot is also \"filled in\" in the case of monocular vision.  Shut the right eye and focus on the pink cross with the left eye, if the head is moved towards the pink cross there is a point at which the yellow disk disappears but the white lines are still present. In this \"filling in\" the visual field does not appear to be distorted. Fiorani *et al.* (1992) developed a technique for probing the cortical blind spot using vertical and horizontal bar stimuli. Matsumoto & komatsu (2005) used this technique on macaque monkeys. In the monocular case they found that as a bar was moved across the visual field so that it crossed the blind spot there was a sudden change in neural activity in the deep layers of the neurons in the blind spot area of V1. When the bar was moved across the same part of the visual field of the contralateral eye the neural activity in the blind spot area increased steadily as the bar was moved. The authors found that there were neurons in the deep layers of blind spot cortex that had elongated receptive fields that could respond to stimuli outside the blind spot and transfer this activation into the blind spot cortex. Filling in of a slightly different type occurs in \"scotoma\". In scotoma an area of the retina is damaged and unresonsive to visual stimuli, immediately after the damage patients report an area of visual field that is unresponsive to stimuli. After several months patients report that the area of field represented by the scotoma contains visual properties related to the physical world surrounding the area that would have formed an image on the scotoma. This results in a distortion of the visual field. (see for instance Gilbert(1993)). Direct measurements of activity in cortical area V1 show that the neurons that represented the area of the scotoma become sensitive to activity in the surrounding visual field. At the cortical level the scotoma is literally \"filled in\". There are many stimuli that cause \"filling in\". These stimuli are known as \"illusions\" because they produce phenomenal experience that has no correlate in the world outside the body. In the \"neon colour spreading illusion\" a lightly coloured circle appears where there should be a white background. Sasaki and Watanabe (2004) used fMRI to show that the part of the topographic map in cortical area V1 corresponding to the light coloured circle was activated.  Fiorani, M., Rosa, M.G.P., Gattas, R. & Rocha-Miranda, C.E. (1992). Dynamic surrounds of receptive fields in primate striate cortex: a physiological basis for perceptual completion? Proc. Natl. Acad. Sci. 89, 8547-8551. <http://www.pnas.org/cgi/content/abstract/89/18/8547> Gilbert, C.D. (1993). Circuitry, architecture and functional dynamics of visual cortex. Matsumoto, M & Komatsu, H. (2005). Neural responses in the macaque V1 to bar stimuli with various lengths presented on the blind spot. J neurophysiol. 93. 2374-2387. <http://jn.physiology.org/cgi/content/abstract/93/5/2374> Sasaki, Y & Watanabe, T. The primary visual cortex fills in colour. Proc. Natl. Acad. Sci. USA 101, 18251-18256. (2004). ## Binocular Rivalry, Pattern Rivalry and Binocular Fusion Sir Charles Wheatstone (1838) was the first scientist to systematically investigate binocular rivalry. Binocular rivalry occurs when different images are presented to the left and right eyes. The subject sees successively one image, a combined image and then the other image. The swapping of images can take a second or more. Binocular rivalry is of interest in consciousness research because the parts of the brain that contain the dominant image should also be those parts that are contributing to conscious experience. Binocular rivalry involves at least two components; the first switches from one image to a merged image and then to the other image and the second permits the view to be part of conscious experience.  The switching of one image for another may involve selecting one of the images as the percept or selecting one of the eyes. Blake *et al.* (1979) performed an experiment in which subjects could change the image at a given eye by pressing a button. When a particular image became dominant they pressed a button to change the image at the eye receiving the dominant image for the non-dominant image. They found that the subjects immediately experienced the second image as the dominant image. This suggests that binocular rivalry is selecting between eyes rather than images. Lehky in 1988 proposed that the switching may be occurring as a result of feedback between visual cortical area V1 and the Lateral Geniculate Nucleus (a thalamic relay - see Carandini *et al.* 2002) and Blake in 1989 also proposed that the switching occurred at the level of area V1. (Visual cortical area V1 receives visual input direct from the LGN.) Tong (2001) has argued that, in humans, the switching of images in binocular rivalry may occur at the earliest levels in the visual cortex. In particular, Tong and Engel (2001) used an elegant technique measuring the activity in the visual cortex that represents the blind spot of the eye to show that almost complete switching to the dominant image occurs at the level of visual cortical area V1. In support of this idea of switching at the level of V1 or even before the cortex, Kreimann *et al.* (2001, 2002) used direct electrode recordings in human cortex and found that the activity of most neurons changed with the percept. Other experiments have not shown a single locus in the brain where the suppressed sensory information gets switched out (Blake & Logothetis 2002, Leopold & Logothetis 1996, Gail et al., 2004). Functional MRI has also shown cortical activity outside of sensory visual cortex related to both images in binocular rivalry. Lumer *et al.* (1998) found that only the fronto-parietal areas of cortex switched with the percept, Fang & He (2005) found that activity relating to both suppressed and unsuppressed images were present in the dorsal stream of the visual system. Wunderlich *et al.* (2005) and Haynes *et al.* (2005) have both found suppression at the level of the lateral geniculate nucleus using fMRI in humans. Pasley *et al.* (2004) have shown that, even during suppression, fearful faces can produce activity in the amygdala (see Pessoa (2005) for a review). Rivalry alternations seem to be the result of widespread activity changes that cover large parts of the brain, including but not necessarily originating at the earliest sensory stages of visual processing. Most investigators have found that, once switching has occurred, there are areas of the brain that contain activity that is solely related to the percept but this varies from most of the cortex to largely more frontal regions depending upon the study. The most likely explanation for binocular rivalry is that the switching occurs at the level of the LGN as a result of feedback from the cortex. Pattern Rivalry is also of interest in consciousness research for the same reasons as binocular rivalry. In pattern rivalry a figure may have two or more forms that replace each other. Typical examples of such figures are the Necker cube and Rubin\'s face-vase. The similarity of the time course of the switching between percepts in binocular rivalry and pattern rivalry has led many authors to suggest that these involve the same mechanism. Logothetis *et al.* (1996) used novel dichoptic stimuli (different images to each eyes) to produce a form of rivalry that seems to involve switching at levels in the cerebral cortex that are more distal to the sensory stimulus than V1. Leopold and Logothetis (1999), on the basis of their work with monkeys, state that \"..many neurons throughout the visual system, both monocular and binocular, continue to respond to a stimulus even when it is perceptually suppressed.\". Kleinschmidt *et al.* (1998) investigated pattern rivalry with MRI and found activity in higher order visual areas during change of dominant pattern. Pettigrew (2001) also describes effects on rivalry due to thought and mood that may require involvement of large areas of cortex in the switching operation and stresses the way that V1 represents different visual fields in different hemispheres of the brain so that inter-hemispheric switching must also be considered. It seems likely that the change of dominant pattern or percept is associated with higher level cortical activity but once the dominant percept is established many of the visually responsive neurons in the cortex are switched over to the new percept. This might account for the similarities in timing of binocular and pattern rivalry and the disparate results found by the various groups of authors. In the words of Kleinschmidt *et al.* (1998): \"The transient activity fluctuations we found suggest that perceptual metastability elicited by ambiguous stimuli is associated with rapid redistributions of neural activity between separate specialized cortical and subcortical structures.\" Which permits both the idea of selecting particular eyes or percepts, perhaps by feedback that switches a thalamic relay on the basis of cortical processing of patterns. Once the cortex has switched the thalamic relay most of the neurons in V1 would become exposed to the dominant percept but there would still be a few neurons in the cortical visual system receiving data from the non dominant image. The investigations of binocular and pattern rivalry provide evidence that conscious visual experience is probably distal to V1 (i.e.: cortex or thalamus). Perceptual rivalry may be part of complex decision making rather than being simply a switch to blank out unwelcome input. It is clear from the Rubin face-vase that pattern rivalry is linked to recognition and would involve a complex delineation of forms within cortical processing. This would suggest that many areas of cortex should be involved before a particular percept is made dominant. Pettigrew (2001) argues that rivalry is the result of a complex phenomenon rather than being simply a switching event. Pettigrew\'s discovery that laughter abolishes rivalry also points to a complex cortical system for switching percepts. Pettigrew proposes that complex cortical processes control rivalry and that the actual switching of percepts is performed sub-cortically in the Ventral Tegmental Area. He concludes his review of the problem by noting that \"Rivalry may thus reflect fundamental aspects of perceptual decision making..\" Pettigrew (2001). Another effect, known as \"binocular fusion\", provides further compelling evidence for the non-conscious nature of the cerebral cortex. In binocular fusion images from both eyes are fused together to create a single image in experience. Moutoussis and Zeki (2002) used a form of binocular fusion in which images of faces were flashed at 100ms intervals to both eyes simultaneously. When both eyes received images of the same colour the subject could see the faces but when one eye received a green image on a red background and the other a red image on a green background the subjects reported seeing a uniform yellow field that contained no faces. fMRI scans of the subject\'s brains showed that when both eyes were exposed to images of the same colour the part of the brain that deals with faces was active and when each eye received images of different colours the same areas of brain showed activity. In other words the cortex contained strong activity related to faces whether or not faces were experienced. Moutoussis and Zeki found a similar effect when they used images of houses instead of images of faces. The authors concluded that: \"The present study further suggests that there are no separate processing and perceptual areas but rather that the same cortical regions are involved in both the processing and, when certain levels of activation are reached and probably in combination with the activation of other areas as well, the generation of a conscious visual percept\". This conclusion does not seem to be supported by the data. There is no evidence that any area of cortex contains the percept itself. The experiment shows that the cortex contains data relating to both red and green faces which suggests that the cortex is not the site of the conscious percept. The percept is most likely distal to the cortex perhaps in the thalamus or some other area that receives cortical sensory output. It is interesting that Fries *et al.* (1997) found that neurons that were activated by the dominant image in binocular rivalry fired synchronously whereas those that were activated by the non-dominant image did not. Thalamocorticothalamic oscillations are the most likely source for synchronising neurons over whole areas of cortex, suggesting that the conscious percept is located in the thalamus rather than the cortex. ## Synchronisation of Neural Processes Our experience seems to contain entities with their attributes attached to them at the correct places in space and time. When a dog barks we see its jaws open at the same time as the bark and both jaws and bark are at the same location. We take this for granted but the brain must be engaging in some complex processing to achieve this synchronised and appropriately positioned set of objects and events. The illustration below shows the two basic processes that might be used to synchronise events between the different specialised processors in the cerebral cortex and brain in general.  In the first option a complete model of sensation, dream etc. may be created and then allowed to become part of conscious experience. In the second model events are released into experience as fast as possible but are synchronous when recalled, having been synchronised in a storage buffer. There is a third option in which there is no synchronisation of events so that the output from different processors would occur at different times. The \'experience buffer\' would be a volume of brain in which a succession of events could be recorded. The buffer might either be updated in steps, the previous content being discarded, or continuously updated with the oldest content being lost continuously. In the first option events from different processes would always appear to be simultaneous unless the experience buffer were updated as a series of steps in which case any changes at around the moment of updating might appear in successive buffers. For instance, if change of position were processed before change in colour a circle on a screen that changed from green to red at the start of a motion might seem to be briefly green during the motion and then turn red. In the second model events from different processors might appear asynchronous at the moment of experience but synchronous when recalled. Colour vision and motion vision are processed in different parts of the visual cortex and in distinct parts of visual cortical areas V1 and V2. They are different processes and hence ideal for studying the synchronisation of cortical activity. Moutoussis and Zeki (1997) presented subjects with moving coloured squares on a computer screen that changed from red to green or vice versa as they changed direction of movement. It was found that subjects seemed to perceive changes in colour some 70-80 msecs before they perceived a change in the direction of motion of the squares. Further work by Arnold *et al.* (2001) and Arnold and Clifford (2001) have confirmed that colour changes seem to be perceived before motion. Arnold and Clifford (2001) also found a quantitative relationship between the colour/motion asynchrony and the direction of change of motion, complete reversals of direction giving rise to the greatest asynchrony between the detection of colour and motion changes. Moutoussis and Zeki (1997) conclude by stating that the asynchrony of neural processes shows that \"..the perception of each attribute is solely the result of the activity in the specialised system involved in its processing..\". It seems more likely that the experiments simply show that slow neural processes are not synchronised before they become percepts (the third option above). The experiments are excellent evidence for the concept of the cortex as a set of specialised processors that deliver their output asynchronously to some other place where the output becomes a percept. These experiments on colour and motion suggest that there is no synchronisation between the processes that deal with these two aspects of vision. Another set of experiments by Clifford *et al.* (2003) supports this idea of processing being asynchronous. They asked subjects to perform a variety of judgements of when visual events occurred and found that the degree of synchrony of one visual event with another depends on the type of judgement. Different judgements probably use processors in different areas of cortex and the output from these arrives asynchronously at the part of the brain that supports the percept. When the percept is formed there must be feedback to the cortical processes that create its content. Otherwise it would not be possible to report about the percept and the cortex would be unable to direct processing to the percept in preference to other, non-conscious cortical data. Although slow processes (20 milliseconds to 1 second) do not seem to be synchronised there is some evidence for very rapid synchronisation. Andrews *et al.* (1996) revisited a problem raised by the famous physiologist Charles Sherrington. Sherrington considered the phenomenon of \'flicker fusion\' in which a flickering light appears to be a continuous steady light if it flashes on and off at frequencies of about 45 Hz or higher. He reasoned that if the images from both eyes are brought together to form a single image then the frequency at which a flickering light appears to be steady should depend on whether one or two eyes are used. Flicker fusion should occur if each eye receives alternate flashes at only half the normal flicker fusion frequency. The flicker should disappear if the left eye receives flashes at 23 pulses per second and the right eye receives alternate flashes at 23 pulses per second. When Sherrington performed the experiment he found that this was not the case, using approximate figures, each eye required 46 pulses per second for fusion to occur. Sherrington proposed that the flicker fusion in alternate binocular presentation was occurring \"psychically\", outside of normal physiological processes. Andrews *et al.* duplicated Sherrington\'s result but investigated it further. They found that when lights were flashed in each eye alternately at low frequences (2 Hz) the experience was the same as a light being flashed in both eyes at this rate. At frequencies of four Hz and higher the subjects began to report that the lights being flashed alternately in both eyes seemed to flicker at the same rate as lights being flashed in both eyes at half the frequency. It seemed as if a flash in one eye followed by a flash in the other eye was being perceived as a single flash or \"conflated\" as the authors put it. The authors explained this effect by suggesting that the brain activity corresponding to the flashes was sampled for a short period and any number of flashes occurring during this period became perceived as a single flash. The maximum rate of sampling would be about 45 Hz. This idea is similar to option (1) above, where the buffer is filled and emptied 40 - 50 times a second. An experience buffer that is refreshed at 40-50 times a second might also explain the results obtained with colour and motion asynchrony because synchronisation between processes may well happen too quickly to affect processes that occur at very slow rates. Singer and Gray (1995), Singer (2001) have proposed that synchronisation between neurones at about 45 Hz is the discriminator between those neurones with activity that contributes to conscious experience and activity in other neurones. A rapid refresh rate in a synchronising buffer agrees with the results found by Fries *et al.* (1997) in which visual cortical neurones that represent a percept underwent synchronous oscillations in the gamma frequency range (39--63 Hz). Tononi *et al.* (1998) have also found synchronisation of neural activity in neurones that represent the percept. The gamma frequency oscillations are intrinsic to the cortex but are triggered by the thalamus and are part of the \'arousal system\'. Readers should be wary of the term \'arousal system\' because it evokes the idea of something waking up a conscious cortex. The cortex can be fully active during sleep and even during pathological unconsciousness such as persistent vegetative state so it is possible that the arousal centres themselves or nearby structures actually host phenomenal consciousness. ## EEG and synchronisation If electrodes are placed on the scalp varying electrical potentials of a few tens of microvolts can be recorded between the electrodes. Recordings of potentials from electrodes on the scalp are known as electroencephalograms (EEGs). The potentials recorded in the EEG are due to postsynaptic potentials in nerve cells. The EEG is insensitive to the activity of single cells and occurs as a result of relatively slow, **synchronised**, changes in large areas of cells. The differences in potential between two scalp electrodes are largely due to depolarisation and hyperpolarisation of the dendritic trees of cortical pyramidal cells. The folding of the cortex (gyri) is problematical for recording and interpreting EEGs because opposing layers of cortex can cancel any net potentials. The EEG shows rhythmic activity. This is conventionally divided into the following frequency bands: Delta waves 0--4 Hz Theta waves 4--8 Hz Alpha waves 8--12 Hz Beta waves \>10 Hz Gamma waves (also called fast beta) 25--100 Hz EEGs also contain short bursts of activity called spindles and very fast oscillations (VFOs). Spindles last for 1--2 seconds and contain rhythmic activity at 7--14 Hz. They are associated with the onset of sleep. The VFOs consist of short bursts at frequencies of over 80 Hz. When the eyes are closed the amplitude of activity from most pairs of electrodes is increased compared with when the eyes are open. When subjects are awake the EEG consists mainly of alpha and beta activity with considerable low amplitude gamma when the eyes are open. In stage 1 sleep the EEG consists of theta waves, in stage 2 sleep of varied activity and spindles, in stage 4 sleep of delta and during REM sleep of beta and theta activity. In epileptic seizures there tends to be high amplitude activity with pronounced synchronisation between many pairs of electrodes. The rhythmic electrical activity is due to cortical feedback loops, cortico-cortical synchronisation, thalamic pacemakers and thalamo-cortical synchronisation. VFOs have been attributed to the activity of electrical connections between cells (dendro-dendritic gap junctions) (Traub (2003)). The gamma activity, centred on a frequency of 40 Hz appears to be related to activity in cortical interneurons that form electrical connections between their dendrites (Tamas *et al.* 2000). These oscillations can be triggered by high frequency stimulation of the posterior intralaminar nuclei of the thalamus (Barth and MacDonald 1996, Sukov and Barth 2001) and as a result of activation of the reticular system (Munk *et al.* 1996). This suggests that stimulation of cortex by thalamic sensory relays triggers gamma band activity in the cortex. A shift from gamma to beta waves can occur in human event related potentials after about 0.2 secs (Pantev 1995, Traub *et al.* 1999). The alpha activity is related to thalamic pacemakers, perhaps as a result of intrinsic oscillatory activity in thalamic sensory relays (see Roy & Prichep 2005 for a brief review). Theta activity, which occurs during some cognitive tasks and mental arithmetic involves a loop from the cortex to the non-specific thalamic nuclei. Delta activity seems to be endogenous to cortex when input is suppressed during sleep. Beta activity is due to cortico-cortical interactions, often after a brief period of gamma activation. It should be noted that gamma and beta activity can be expressed as impulses in cortico-thalamic pathways and that when cortical and thalamic activity is correlated there is a conscious state. In other words gamma or beta waves in the cortex are not correlates of consciousness on their own - see for instance Laureys *et al.* (2002). ## Event related potentials After a sudden event there are a characteristic set of changes in EEG activity known as **event related potentials** or ERPs. The time course of the ERP is shown in the diagram below.  ERPs occur in response to novel stimuli and are also produced by brief transcranial magnetic stimulation (TMS)(Iramina *et al.* 2002). The slow component is known as the P3 or P300 phase of the ERP. It is due to activation of areas of the brain that are relatively remote from the primary sensory areas of brain. Nieuwenhuis *et al.* (2005) have reviewed the origin of the P300 ERP: \"To summarize, convergent evidence suggests that P3-like activity can be recorded in several, widely separated brain areas. These include some medial temporal and subcortical structures (e.g., the hippocampal formation, amygdala, and thalamus), but these structures are unlikely to contribute directly to the scalp-recorded P3.\". According to Nieuwenhuis *et al.* (2005) the recorded P300 may be due to temporo-parietal and prefrontal cortical activity. Linden (2005) has also concluded that widespread, but specific, cortical activation is correlated with the recorded P300 ERP. The generator of the P300 is still obscure. Nieuwenhuis *et al.* (2005) consider that the Locus coeruleus, a nucleus in the pons that regulates task related attention and part of the sleep-wake cycle, may be responsible. In line with this, Mashour *et al.* (2005) have discovered that TMS induced P300 activity is reduced in unconscious states. Whether the P300 is related to Libet\'s 0.5 second delay is still obscure but the discovery that the P300 occurs in association with subliminal stimuli (stimuli that do not enter awareness)(Bernat *et al.* 2001) suggests that it is associated with non-conscious cortical processing. Williams *et al.* (2004), in an investigation of subliminal and supraliminal fear perception, found that \"conscious fear perception was distinguished by a more prominent N4, peaking around 400 msec\"; the N4 component follows the P300 component in the succession of phases of the ERP. Williams *et al.* considered that the earlier phases in the ERP are probably related to non-conscious processing. In contrast Vogel *et al.* (1998) found that suppression of the P300 was associated with suppression of awareness. ## The integration delay Psychological experiments often involve binary decisions where subjects give one of two outputs in response to stimuli. It is found that if the stimuli are made increasingly noisy or complex the response time tends to increase. Psychophyicists have developed various mathematical models to explain the increased response times due to noise such as the Integrator and Accumulator models (cf: Luce(1986)). These models have been fairly successful when explaining experiments such as judging the net direction of movement of sets of dots on a screen when the dots are given semi-random paths and different brightness etc. In these circumstances it can take up to 2 seconds for an accurate decision. There are many tasks however where the accuracy of decision making does not improve after about 300 milliseconds. The accuracy of the performance of rats when choosing between two alternatives when reacting to odours peaks at about 300 ms (Uchida and Mainen(2003), Abraham *et al.* (2004)). The accuracy of humans when performing vernier acuity tasks, line detection, contrast sensitivity, motion velocity discrimination and stereoscopic depth discrimination seems to peak at 300ms (Uchida *et al.* 2006). Uchida, Kepecs and Mainen (2006) suggest that \"rapid and short integration time is a sensible strategy for rapid processing of low-level sensory information in order to form more complex sensory images, both in vision and olfaction.\" Whether these authors regard these derived sensory images as the content of consciousness is not mentioned. The authors propose that the 300ms optimal integration time may be partly due to the mechanics of sniffing (a sniff takes about 125-200ms) and the nature of optical fixation (inter-saccade intervals are typically 200-400 ms ). The authors note that the animal or human could, in principle, choose to integrate over longer intervals but if it is moving this may not lead to information that is current for changed circumstances. An optimal processing time of about 300 ms would be consistent with the delays observed before conscious awareness occurs in response to a stimulus - an interval required to form \"more complex sensory images\". ## Global Workspace Theory Global Workspace Theory is the idea that somewhere in the brain there is a facility that integrates the processes that occur in the various separate areas of the brain. The theory was first proposed by Descartes as the *sensus communis*, the common sense, but the modern form of the theory dispenses with the idea of a point soul looking at the brain. In modern Global Workspace theory it is proposed that an area of brain receives input from most of the cerebral cortex and broadcasts its outputs to all of the unconscious modular information processors in the brain. Modern Global Workspace Theory has been championed by Baars (1983, 1988). There is increasing evidence for a Global Workspace or Global Workspaces in the brain. Much of this evidence comes from fMRI, single unit and magnetoencephalography studies in which it is shown that non-conscious or subliminal processing mainly occupies primary, sensory cortex whereas conscious processing occupies large areas of cerebral cortex. In binocular rivalry the stimulus that is consciously perceived is responsible for relatively intense activation of large areas of brain whereas the non-conscious stimulus is often suppressed (see above and Sheinberg & Logothetis (1997), Tononi *et al.* (1998)). The suppression is likely to occur in the Lateral Geniculate Nuclei which suggests a role for the Thalamic Reticular Nuclei, which modulate LGN activity, in the control of the percept. ### Masking and visual awareness Word masking has also been used to investigate the idea of a Global Workspace. When a word is presented on its own for a few tens of milliseconds it remains readable but if it is immediately succeeded by, or accompanied by, another word it becomes indistinct or invisible. This effect is known as \"word masking\". Vogel *et al.* (1998) have investigated a version of word masking known as the \"attentional blink\". They found that when stimuli became invisible the P3 component of the Event Related Potential, which peaks at around 300-500 millisecs after a stimulus, was completely suppressed. The P3 component of the ERP has been related to the lodging of data in working memory and also to gamma band activity in the EEG. This strongly suggests the involvement of a cortico-thalamic loop in the \"attentional blink\". The delay of 0.3 to 0.5 secs is typical of the time required for conscious awareness (see above). Word masking in conjunction with fMRI and Event Related Potential (ERP) recordings has been used by Dehaene *et al.* (2001) to expose control by a central mechanism. It was found that masked words activate mainly the visual cortex and ventral stream (inferior temporal lobe) whereas visible words also activated distant parietal, prefrontal and cingulate sites. Dehaene *et al.* (2003) and found that the dynamics of the loss of visibility of words in an attentional blink experiment could be modelled by a simulated cortico-thalamic loop. In their simulation a distributed cortical process determined which events would receive attention and the system used the thalamic gating systems to exclude those that did not receive attention. Tse *et al.* (2005) have used purely visual stimuli in masking experiments and concluded that, in the case of purely visual stimuli, the neural correlates of awareness were limited to the occipital cortex: \"We suggest that there are both lower and upper bounds within the visual hierarchy for the processing of visual masking and the maintenance of visual awareness of simple unattended targets; the lower bound is at least as high as the border between V2 and V3, and the upper bound is within the occipital lobe, possibly somewhere downstream of V4.\" This discovery would mean that activation of large areas of cortex are unnecessary for awareness. Melloni *et al.* (2007) compared compared the electrophysiological responses related to the processing of visible and invisible words in a delayed matching to sample task. Both perceived and nonperceived words caused a similar increase of local (gamma) oscillations in the EEG, but only perceived words induced a transient long-distance synchronization of gamma oscillations across widely separated regions of the brain. After this transient period of temporal coordination, the electrographic signatures of conscious and unconscious processes continue to diverge. Only words reported as perceivedinduced (1) enhanced theta oscillations over frontal regions during the maintenance interval, (2) an increase of the P300 component of the event-related potential, and (3) an increase in power and phase synchrony of gamma oscillationsbefore the anticipated presentation of the test word. We propose that the critical process mediating the access to conscious perception is the earlytransient global increase of phase synchrony of oscillatory activity in the gammafrequency. Melloni L, Molina C, Pena M, Torres D, Singer W, Rodriguez E. (2007). Synchronization of neural activity across cortical areas correlates withconscious perception.J Neurosci. 2007 Mar 14;27(11):2858-65. ### Attention and the global workspace Baars (2002) in his review of evidence for the Global Workspace Theory quotes many other experiments that show activation of larger areas of cortex in response to conscious stimuli compared with unconscious or subliminal stimuli.The effect is also seen in change blindness, learning and attention. Newman and Baars (1993) consider that the \"workspace\" is fairly global in the brain: \"This Neural Global Workspace (NGW) model views conscious processes in terms of a globally integrative brain system. The neural circuitry contributing to this system is not only widely distributed across the neocortex, but includes key corticothalamic and midbrain circuits as well. These cortico-subcortical circuits are hypothesized to be critical to understanding the mechanisms of attentional control that provide an essential basis for the conscious processing of information\". However they focus particularly on the role of the thalamic Reticular Nucleus and cortico-thalamic connectivity in the control of attention. Other ideas for the location of the Global Workspace are the idea of Singer et al. that gamma synchrony controls access to the content of consciousness and Llinas et al. (1998) that the thalamus is the hub through which communication occurs between areas of cortex. One of the problems with Global Workspace theory is that it suggests that attention, working memory, cognitive control and consciousness may all be in the same area of the brain. It is likely that the mechanisms of attention, working memory, and cognitive control may involve several, interlinked systems perhaps co-opting the basal ganglia in the process. In view of this Maia and Cleeremans (2005) propose that \".. attention, working memory, cognitive control and consciousness are not distinct functions implemented by separate brain systems. Attempting to find separate neural correlates for each may therefore be the wrong approach. Instead, we suggest that they should be understood in terms of the dynamics of global competition, with biasing from PFC (prefrontal cortex).\". The inclusion by Maia and Cleeremans of consciousness with distributed attention, working memory and cognitive control is reminiscent of Zeki & Bartel\'s idea of microconsciousness. It should be noted that, in common with Libet\'s data, the percept seems to be available to phenomenal consciousness some 0.3 to 0.5 secs after a stimulus; this suggests that whatever determines the content of phenomenal consciousness operates before events become part of phenomenal consciousness. This relegates phenomenal consciousness from being a controller of attention to being the recipient of content that is the subject of attention. This finding is consistent with the philosophical problem of the **apparently** epiphenomenal nature of phenomenal consciousness. Given the data on the timing of conscious awareness it seems that there may be two \"workspaces\", an active workspace that models the world, discarding and suppressing data during rivalry, and a passive workspace that receives the final, edited product. The active workspace would correlate with the cortical systems stressed by Dehaene *et al.* and Maia and Cleermans although, given the results of Tse et al., the workspace would be limited to small zones of cortex. The loading of the passive workspace with the output of the active workspace would correlate with thalamo-cortical activity during component P3 of the ERP in which data is transferred from the cortex to the thalamus. This workspace might constitute the source for reports of the content of phenomenal consciousness. Llinas *et al.* (1998) have proposed two parallel cortico-thalamic attentional systems, one of which is related to the thalamic specific nuclei and the other to the thalamic non-specific nuclei, especially the ILN. The non-specific system would be related to consciousness itself. ## The \"cognitive map\" and the neural basis of perceptual space Our bodies appear to be mobile within a constant space. We walk around a room; the room does not rotate around us. The constancy of the location of things gives us the feeling that we are directly viewing a constant world. But how does the brain provide a constant world rather than a world that rotates with the movement of the sense organs? Why is our view of the world when we move our eyes so different from the disturbing flow of images that occur when a video camera is waved around? Do our brains contain a constant \"cognitive map\" (O\'Keefe and Nadel 1978) of our surroundings? Mittelstaedt & Mittelstaedt (1980, 1982) discovered that female gerbils were able to recover their pups in darkened surroundings by searching in a semi random fashion on the outbound journey and then proceeding directly back to the nest on the inbound journey. The direct journey back to the nest seemed to be due to an integration of the various directions taken on the outward journey (**path integration**). If the equipment being explored by the mother gerbil was rotated very slowly the mother would make an error equivalent to the amount of rotation. More rapid rotations that activated the vestibular system of the rat (acceleration measurement) did not cause errors in navigation. This demonstration that rodents could navigate accurately on the basis of **idiothetic** cues (cues that are due to internal senses) led to research on the neural basis of the navigation. As early as 1971 O\'Keefe and Dostrovsky had discovered that there are particular cells in the hippocampus that fire according to the position of an animal in the environment. This has been complimented by research that showed that changes in visual cues within the environment caused changes in the firing rate of place cells in hippocampal area CA3 (.   !Entorhinal cortex approximately maps to areas 28 and 34{width="500"} F. P. Battaglia and A. Treves. 1998 Attractor neural networks storing multiple space representations: A model for hippocampal place fields. PHYSICAL REVIEW E DECEMBER 1998 VOLUME 58, NUMBER 6 <http://www.sissa.it/~ale/Bat+98b.pdf> Leutgeb, S., Leutgeb, J.K., Moser, M-B, and Moser, E.I. 2005. Place cells, spatial maps and the population code for memory. Current Opinion in Neurobiology 2005, 15:738--746. <http://instruct1.cit.cornell.edu/courses/bionb720nejc/reprints/LeutgebEtAl2005.pdf> Mittelstaedt, H. & Mittelstaedt, M-L. 1982. Avian Navigation. (ed. Papi, F. & Wallraff, H.) 290-297. Springer, Berlin. Mittelstaedt, M-L & Glasauer, S. 1991. Idiothetic Navigation in Gerbils and Humans. Zool. Jb. Physiol. 95 (1991), 427-435 <http://web.archive.org/web/20110125132449/http://www.nefo.med.uni-muenchen.de/~sglasauer/MittelstaedtGlasauer1991.pdf> O\'Keefe, J. & Dostrovsky, J. (1971). The hippocampus as a spatial map: preliminary evidence from unit activity in the freely moving rat. Brain Res. 34, 171-175. O\'Keefe, J. & Nadel, L. (1978). The Hippocampus as a cognitive map. (Oxford) ## Bibliography Defining the States of Consciousness. Tassi, P., Muzet, A. (2001) Neuroscience and Behavioural Reviews 25(2001) 175-191. 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# Consciousness Studies/Behaviourism And Consciousness References - Behaviourism. Graham, G. (2002) Stanford Encyclopedia of Philosophy - Watson, J.B. (1907) Studying the Mind of Animals The World Today, 12, 421-426. - Watson, J.B. (1913) Psychology as the Behaviorist Views it. Psychological Review, 20, 158-177 - Lektorsky, V.A. (1980)Subject Object Cognition. - Vygotsky L.S. (1925) "Consciousness as a problem in the psychology of behavior" Undiscovered Vygotsky: Etudes on the pre-history of cultural-historical psychology (European Studies in the History of Science and Ideas. Vol. 8), pp. 251-281 - Gibson, J. J. (1950). The perception of the visual world. Boston: Houghton-Mifflin - Gibson, J. J.(1979). The ecological approach to visual perception. Boston: Houghton-Mifflin - Ryle, G. (1949). The concept of mind. Harmondsworth, Middlesex: Penguin.

# Consciousness Studies/Models Of Access Consciousness There have been numerous attempts to model reflex and access consciousness. These models, being connectionist and information systems based, do not model phenomenal consciousness but are essential steps in understanding global brain function. ## Neural networks Neural networks achieve information processing by establishing connections between processing units in a system of processors that have similar characteristics. Neural networks are used for classifying data. The processing units serve the function of both filtering and storing information. *This is a stub and requires expansion* ### Classification of sensory stimuli *The path from transducers to a single neuron that responds to a single complex stimulus.* *This is a stub and requires expansion* ### Classification of motor control *From premotor activity to skilled behaviour.* *This is a stub and requires expansion* ### Olfaction: classification out of chaos? *This is a stub and requires expansion* ## Quantum information processing *This is a **stub** and needs expanding*

# Consciousness Studies/Models Of Access Consciousness#Neural networks There have been numerous attempts to model reflex and access consciousness. These models, being connectionist and information systems based, do not model phenomenal consciousness but are essential steps in understanding global brain function. ## Neural networks Neural networks achieve information processing by establishing connections between processing units in a system of processors that have similar characteristics. Neural networks are used for classifying data. The processing units serve the function of both filtering and storing information. *This is a stub and requires expansion* ### Classification of sensory stimuli *The path from transducers to a single neuron that responds to a single complex stimulus.* *This is a stub and requires expansion* ### Classification of motor control *From premotor activity to skilled behaviour.* *This is a stub and requires expansion* ### Olfaction: classification out of chaos? *This is a stub and requires expansion* ## Quantum information processing *This is a **stub** and needs expanding*

# Consciousness Studies/Models Of Access Consciousness#Quantum information processing There have been numerous attempts to model reflex and access consciousness. These models, being connectionist and information systems based, do not model phenomenal consciousness but are essential steps in understanding global brain function. ## Neural networks Neural networks achieve information processing by establishing connections between processing units in a system of processors that have similar characteristics. Neural networks are used for classifying data. The processing units serve the function of both filtering and storing information. *This is a stub and requires expansion* ### Classification of sensory stimuli *The path from transducers to a single neuron that responds to a single complex stimulus.* *This is a stub and requires expansion* ### Classification of motor control *From premotor activity to skilled behaviour.* *This is a stub and requires expansion* ### Olfaction: classification out of chaos? *This is a stub and requires expansion* ## Quantum information processing *This is a **stub** and needs expanding*

# Consciousness Studies/Contemporary Explanations *This section is about the types of theory that have been advanced to explain consciousness. Specific explanations should be entered as separate pages.* ## Introduction Explanations of consciousness fall into three broad categories, those that attempt to explain the empirical experience called consciousness with scientific theories, those that seek to find some way in which consciousness could be explained by digital computers or nineteenth century materialism by redefining or eliminating experience and those that regard consciousness as inexplicable or supernatural. ## Identity theory of mind The identity theory of mind, or type physicalism, holds that the mind is identical to the brain. Type physicalists identify qualia and the form of experience with brain activity. They argue that \"mind states\" have physical causes and physical effects - thus the mind states themselves must be physical; a non-physical \"middle step\" is superfluous. Type physicalism has not yet gained widespread support because although brain activity that correlates with experience has been found everywhere in the brain, no set of brain activity that is phenomenal consciousness itself has yet been found - although this is not surprising because neuronal spike activity is unlikely to host phenomenal consciousness - see scientific theories of consciousness. ## Functionalism Functionalism was developed as a theory of the mind-body problem because of objections to identity theory and logical behaviourism. Its core idea is that the mental states can be accounted for without taking into account the underlying physical medium (the neurons), instead attending to higher-level functions such as beliefs, desires, and emotions. It is a theory of behaviour and access consciousness and so from the outset avoids any explanation of phenomenal consciousness, substituting beliefs and judgements (functions) for entities such as qualia. According to functionalism, the mental states that make up consciousness can essentially be defined as complex interactions between different functional processes. Because these processes are not limited to a particular physical state or physical medium, they can be realized in multiple ways, including, theoretically, within non-biological systems.This affords consciousness the opportunity to exist in non-human minds that are based on algorithmic processors such as digital computers. This is a highly contentious conjecture although non-functionalist physicalists might agree that machines that are not digital computers could possess consciousness through an identity theory of mind - see The problem of machine and digital consciousness. Functionalism\'s explanation of consciousness, or the mental, is best understood when considering the analogy made by functionalists between the mind and the modern digital computer. More specifically, the analogy is made to a \"machine\" capable of computing any given algorithm (i.e. a Turing machine). This machine would involve: Data input (the senses in humans), data output (both behaviour and memory), functional states (mental states), the ability to move from one functional state into another, and the definition of functional states with reference to the part they play in the operation of the entire entity - i.e. in reference to the other functional states. So long as the same process was achieved, the \"physical stuff\" \-- that being computer hardware or biological structure \-- could achieve consciousness. This variety of functionalism was developed by Hilary Putnam. One of the major proponents of functionalism is Jerry Fodor. Further reading: Block, N. (1996). The Encyclopedia of Philosophy Supplement, Macmillan, 1996 <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/functionalism.pdf> ## Dualism ### Substance dualism This theory proposes that phenomenal experience occurs in a non-physical place. In Cartesian Dualism the non-physical place is an unextended soul that looks out at the brain. In Reid\'s Natural Dualism the non-physical place is a point-soul that looks out at the world. ### Property dualism Property dualism asserts that when matter is organized in the appropriate way (i.e., organized in the way that living human bodies are organized), mental properties emerge. Property dualism is a branch of emergent materialism. The appeal to emergentism deserves closer attention. Scientific theories often deal with emergent phenomena, for instance an enzyme consists of carbon, hydrogen, nitrogen, manganese and oxygen and from this catalytic action emerges. The theory of enzyme structure and the action of this structure on the substrate explains how this emergence occurs. Notice that the theory of enzymes explains the emergence of catalytic activity; emergence does not explain the theory. In science the statement that some property will \'emerge\' means that there will be a theory that accounts for this property. Property dualism, by appealing to emergence, is stating that some theory of consciousness will be possible. In other words it is an explanation that proposes that the explanation is yet to be known. ## Intentionalism ## Higher order thought *This section is a stub and needs expansion* ## Eliminativism Eliminative materialism is the school of thought that argues for an absolute version of materialism with respect to mental entities and mental vocabulary. It principally argues that our common-sense understanding of the mind (often called \'folk psychology\') is not a viable theory on which to base scientific investigation, and therefore no coherent neural basis will be found for many such everyday psychological concepts (such as belief or intention) and that behaviour and experience can only be adequately explained on the biological level. Eliminative materialists therefore believe that consciousness does not exist and that the concept will eventually be eliminated as neuroscience progresses. Similarly, they argue that folk psychological concepts such as belief, desire and intention do not have any consistent neurological substrate. Proponents of this view often make parallels to previous scientific theories which have been eliminated, such as the four humours theory of medicine, the phlogiston theory of combustion and \'vital force\' theory of life. In these cases, science has not produced more detailed versions of these theories, but rejected them as obsolete. Eliminative materialists argue that folk psychology is headed the same way. According to W.V. Quine it will take tens of years before folk psychology will be replaced with real science. (see Phenomenal consciousness and access consciousness). Eliminative materialism was first defended by W.V. Quine, Paul Feyerabend, and Richard Rorty. This view is most associated with philosophers Paul and Patricia Churchland although philosophers such as Daniel Dennett would also consider themselves eliminativists for many aspects of psychology. Philosopher Dale Jacquette has claimed that Occam\'s Razor is the rationale behind eliminativism and reductionism. The most common argument against eliminative materialism is the argument from qualia, which is deployed in various forms by Thomas Nagel, Frank Jackson, and many others. Perhaps the most powerful argument against eliminativism is that experience itself is many things simultaneously; it is, as Aristotle points out, immediate and hence is not composed of judgements. ## Mysterianism New Mysterianism is a philosophy proposing that certain problems (in particular, consciousness) will never be explained. Owen Flanagan noted in his 1991 book \"Science of the Mind\" that some modern thinkers have suggested that consciousness might never be completely explained. Flanagan called them \"the new mysterians\" after the rock group ? and the Mysterians. The term originated with the Japanese alien-invasion film The Mysterians. The \"old mysterians\" are thinkers throughout history who have put forward a similar position. They include Leibniz, Dr Johnson, and Thomas Huxley. The latter said, \"How is it that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, when Aladdin rubbed his lamp.\" \[6, p. 229, quote\] Noam Chomsky distinguishes between problems, which seem solvable, at least in principle, through scientific methods, and mysteries which do not, even in principle. He notes that the cognitive capabilities of all organisms are limited by biology, e.g. a mouse will never speak. In the same way, certain problems may be beyond our understanding. The term New Mysterianism has been extended by some writers to encompass the wider philosophical position that humans don\'t have the intellectual ability to understand many hard problems, not just the problem of consciousness, at a scientific level. This position is also known as Anti-Constructive Naturalism. For example, in the mind-body problem, emergent materialism claims that humans aren\'t smart enough to determine \"the relationship between mind and matter.\" \[4\] Strong agnosticism is a religious application of this position. Colin McGinn is the leading proponent of the New Mysterian position. Critics argue this philosophy isn\'t useful and encourages capitulation. One critic noted: the extreme \"Mysterian\" position, that there are vital issues forever beyond our reach, is in many ways deeply unsatisfying. \[7\] References \[1\] McGinn, Colin - The Problem of Consciousness \[2\] McGinn, Colin - Problems in Philosophy: the limits of enquiry \[3\] McGinn, Colin - The Mysterious Flame \[4\] Blackburn, Simon - Think: A compelling introduction to philosophy, chapter two \[5\] Flanagan, Owen - The Science of the Mind (1991) 2ed MIT Press, Cambridge \[6\] Horgan, John - The Undiscovered Mind (1999), Phoenix, ## Idealism and panpsychism ### Idealism

# Consciousness Studies/Contemporary Explanations#The identity theory of mind *This section is about the types of theory that have been advanced to explain consciousness. Specific explanations should be entered as separate pages.* ## Introduction Explanations of consciousness fall into three broad categories, those that attempt to explain the empirical experience called consciousness with scientific theories, those that seek to find some way in which consciousness could be explained by digital computers or nineteenth century materialism by redefining or eliminating experience and those that regard consciousness as inexplicable or supernatural. ## Identity theory of mind The identity theory of mind, or type physicalism, holds that the mind is identical to the brain. Type physicalists identify qualia and the form of experience with brain activity. They argue that \"mind states\" have physical causes and physical effects - thus the mind states themselves must be physical; a non-physical \"middle step\" is superfluous. Type physicalism has not yet gained widespread support because although brain activity that correlates with experience has been found everywhere in the brain, no set of brain activity that is phenomenal consciousness itself has yet been found - although this is not surprising because neuronal spike activity is unlikely to host phenomenal consciousness - see scientific theories of consciousness. ## Functionalism Functionalism was developed as a theory of the mind-body problem because of objections to identity theory and logical behaviourism. Its core idea is that the mental states can be accounted for without taking into account the underlying physical medium (the neurons), instead attending to higher-level functions such as beliefs, desires, and emotions. It is a theory of behaviour and access consciousness and so from the outset avoids any explanation of phenomenal consciousness, substituting beliefs and judgements (functions) for entities such as qualia. According to functionalism, the mental states that make up consciousness can essentially be defined as complex interactions between different functional processes. Because these processes are not limited to a particular physical state or physical medium, they can be realized in multiple ways, including, theoretically, within non-biological systems.This affords consciousness the opportunity to exist in non-human minds that are based on algorithmic processors such as digital computers. This is a highly contentious conjecture although non-functionalist physicalists might agree that machines that are not digital computers could possess consciousness through an identity theory of mind - see The problem of machine and digital consciousness. Functionalism\'s explanation of consciousness, or the mental, is best understood when considering the analogy made by functionalists between the mind and the modern digital computer. More specifically, the analogy is made to a \"machine\" capable of computing any given algorithm (i.e. a Turing machine). This machine would involve: Data input (the senses in humans), data output (both behaviour and memory), functional states (mental states), the ability to move from one functional state into another, and the definition of functional states with reference to the part they play in the operation of the entire entity - i.e. in reference to the other functional states. So long as the same process was achieved, the \"physical stuff\" \-- that being computer hardware or biological structure \-- could achieve consciousness. This variety of functionalism was developed by Hilary Putnam. One of the major proponents of functionalism is Jerry Fodor. Further reading: Block, N. (1996). The Encyclopedia of Philosophy Supplement, Macmillan, 1996 <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/functionalism.pdf> ## Dualism ### Substance dualism This theory proposes that phenomenal experience occurs in a non-physical place. In Cartesian Dualism the non-physical place is an unextended soul that looks out at the brain. In Reid\'s Natural Dualism the non-physical place is a point-soul that looks out at the world. ### Property dualism Property dualism asserts that when matter is organized in the appropriate way (i.e., organized in the way that living human bodies are organized), mental properties emerge. Property dualism is a branch of emergent materialism. The appeal to emergentism deserves closer attention. Scientific theories often deal with emergent phenomena, for instance an enzyme consists of carbon, hydrogen, nitrogen, manganese and oxygen and from this catalytic action emerges. The theory of enzyme structure and the action of this structure on the substrate explains how this emergence occurs. Notice that the theory of enzymes explains the emergence of catalytic activity; emergence does not explain the theory. In science the statement that some property will \'emerge\' means that there will be a theory that accounts for this property. Property dualism, by appealing to emergence, is stating that some theory of consciousness will be possible. In other words it is an explanation that proposes that the explanation is yet to be known. ## Intentionalism ## Higher order thought *This section is a stub and needs expansion* ## Eliminativism Eliminative materialism is the school of thought that argues for an absolute version of materialism with respect to mental entities and mental vocabulary. It principally argues that our common-sense understanding of the mind (often called \'folk psychology\') is not a viable theory on which to base scientific investigation, and therefore no coherent neural basis will be found for many such everyday psychological concepts (such as belief or intention) and that behaviour and experience can only be adequately explained on the biological level. Eliminative materialists therefore believe that consciousness does not exist and that the concept will eventually be eliminated as neuroscience progresses. Similarly, they argue that folk psychological concepts such as belief, desire and intention do not have any consistent neurological substrate. Proponents of this view often make parallels to previous scientific theories which have been eliminated, such as the four humours theory of medicine, the phlogiston theory of combustion and \'vital force\' theory of life. In these cases, science has not produced more detailed versions of these theories, but rejected them as obsolete. Eliminative materialists argue that folk psychology is headed the same way. According to W.V. Quine it will take tens of years before folk psychology will be replaced with real science. (see Phenomenal consciousness and access consciousness). Eliminative materialism was first defended by W.V. Quine, Paul Feyerabend, and Richard Rorty. This view is most associated with philosophers Paul and Patricia Churchland although philosophers such as Daniel Dennett would also consider themselves eliminativists for many aspects of psychology. Philosopher Dale Jacquette has claimed that Occam\'s Razor is the rationale behind eliminativism and reductionism. The most common argument against eliminative materialism is the argument from qualia, which is deployed in various forms by Thomas Nagel, Frank Jackson, and many others. Perhaps the most powerful argument against eliminativism is that experience itself is many things simultaneously; it is, as Aristotle points out, immediate and hence is not composed of judgements. ## Mysterianism New Mysterianism is a philosophy proposing that certain problems (in particular, consciousness) will never be explained. Owen Flanagan noted in his 1991 book \"Science of the Mind\" that some modern thinkers have suggested that consciousness might never be completely explained. Flanagan called them \"the new mysterians\" after the rock group ? and the Mysterians. The term originated with the Japanese alien-invasion film The Mysterians. The \"old mysterians\" are thinkers throughout history who have put forward a similar position. They include Leibniz, Dr Johnson, and Thomas Huxley. The latter said, \"How is it that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, when Aladdin rubbed his lamp.\" \[6, p. 229, quote\] Noam Chomsky distinguishes between problems, which seem solvable, at least in principle, through scientific methods, and mysteries which do not, even in principle. He notes that the cognitive capabilities of all organisms are limited by biology, e.g. a mouse will never speak. In the same way, certain problems may be beyond our understanding. The term New Mysterianism has been extended by some writers to encompass the wider philosophical position that humans don\'t have the intellectual ability to understand many hard problems, not just the problem of consciousness, at a scientific level. This position is also known as Anti-Constructive Naturalism. For example, in the mind-body problem, emergent materialism claims that humans aren\'t smart enough to determine \"the relationship between mind and matter.\" \[4\] Strong agnosticism is a religious application of this position. Colin McGinn is the leading proponent of the New Mysterian position. Critics argue this philosophy isn\'t useful and encourages capitulation. One critic noted: the extreme \"Mysterian\" position, that there are vital issues forever beyond our reach, is in many ways deeply unsatisfying. \[7\] References \[1\] McGinn, Colin - The Problem of Consciousness \[2\] McGinn, Colin - Problems in Philosophy: the limits of enquiry \[3\] McGinn, Colin - The Mysterious Flame \[4\] Blackburn, Simon - Think: A compelling introduction to philosophy, chapter two \[5\] Flanagan, Owen - The Science of the Mind (1991) 2ed MIT Press, Cambridge \[6\] Horgan, John - The Undiscovered Mind (1999), Phoenix, ## Idealism and panpsychism ### Idealism

# Consciousness Studies/Table Of Theories ## Theories of Consciousness Some recent scientific theories of consciousness are tabulated below. The extent to which they account for the phenomenon of consciousness is shown. It is remarkable that many of the theories are consistent with one another. As in the tale of the \'blind men and the elephant\' some of the theories seem to describe the trunk, some the tail etc. but they all seem to be part of the same elephant! The convergence of the theories is shown in the illustration below:  ## Table of theories ```{=html} <TABLE CELLSPACING=0 BORDER=0 CELLPADDING=7 WIDTH=829> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="31%" VALIGN="TOP"> ``` `<B>`{=html}A = Model of observer\'s view B = Model of Anaesthetic Action in thalamus C = Explanation of Libet\'s data`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="33%" VALIGN="TOP"> ``` `<B>`{=html} D = Explanation of unconscious but active cerebral cortex E = Explanation of knowing you know F = Explanation of non-computability`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="36%" VALIGN="TOP"> ``` `<B>`{=html} G = Binding (simultaneous processing of relevant data) H = Extended present I = Quantum state vector reduction`</B>`{=html} ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} </TABLE> ``` ```{=html} <TABLE BORDER CELLSPACING=1 CELLPADDING=7 WIDTH=607> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` `<B>`{=html}Name`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` `<B>`{=html} Author/Ref`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` `<B>`{=html} A`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} B`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} C`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} D`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} E`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} F`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} G`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} H`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} I`</B>`{=html} ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` Microconsciousness ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` Zeki, S., & Bartel, A. (1999) Toward a Theory of Visual Consciousness. Consciousness & Cognition, 8, 225-259. ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` Geometrical Phenomenalism ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` Green, A. (2003) Geometrical phenomenalism ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` ? ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` ORCH-R ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` Hameroff, S & Penrose, R. 1989 ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` Quantum Brain Model ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` Ricciardi, L. M. and H. Umezawa, 1967. Brain physics and many-body problems, Kibernetik 4, 44-48. <http://arXiv.org/abs/q-bio/0309009> ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ```  N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` ? ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` Many Minds ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` Donald, M. 1990. Quantum Theory and the Brain. Proc R Soc Lond. 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Physics Essays 2/2 128-151. <http://www.math.auckland.ac.nz/~king/Preprints/Transup.htm> ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` ? ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` Spin Mediated Consciousness ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` Hu, H. & Wu, M. 2002. Spin-Mediated Consciousness Theory: An Approach Based On Pan-Protopsychism. <http://cogprints.ecs.soton.ac.uk/archive/00002579/> ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` ? ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` Quantum Theory of Consciousness (synaptic cleft) ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` Walker, E.W. 1998. the `<I>`{=html}Noetic Journal`</I>`{=html}, `<I>`{=html}1`</I>`{=html}, 100-107, 1998 <http://users.erols.com/wcri/CONSCIOUSNESS.html> ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} </TABLE> ```   ```{=html} <TABLE CELLSPACING=0 BORDER=0 CELLPADDING=7 WIDTH=829> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="31%" VALIGN="TOP"> ``` `<B>`{=html}A = Model of observer\'s view B = Model of Anaesthetic Action in thalamus C = Explanation of Libet\'s data`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="33%" VALIGN="TOP"> ``` `<B>`{=html} D = Explanation of unconscious but active cerebral cortex E = Explanation of knowing you know F = Explanation of non-computability`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="36%" VALIGN="TOP"> ``` `<B>`{=html} G = Binding (simultaneous processing of relevant data) H = Extended present I = Quantum state vector reduction`</B>`{=html} ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} </TABLE> ```   ```{=html} <TABLE BORDER CELLSPACING=1 CELLPADDING=7 WIDTH=607> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` `<B>`{=html}Name`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` `<B>`{=html} Author/Ref`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` `<B>`{=html} A`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} B`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} C`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} D`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} E`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} F`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} G`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} H`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} I`</B>`{=html} ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` Global Workspace Theory ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` Baars, B. 1988. A cognitive theory of consciousness. Cambridge University Press, New York <http://www.ceptualinstitute.com/genre/baars/baarsBrain.htm> ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` `<B>`{=html} Y`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} Y`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} Y`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} Y`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} Y`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` Topological Geometrodynamics (TGD) Inspired Theory of Consciousness ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` Pitkänen, M. 199?. Topological Geometrodynamics <http://www.physics.helsinki.fi/~matpitka/mainpage.html> ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` ? ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} Y`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} Y`</B>`{=html} ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` The Conscious Electromagnetic Field Theory ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` McFadden, J.J. 2002 <http://www.surrey.ac.uk/qe/cemi.htm> ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` ? ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` Y ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` N ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` ? ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} </TABLE> ```   ```{=html} <TABLE CELLSPACING=0 BORDER=0 CELLPADDING=7 WIDTH=829> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="31%" VALIGN="TOP"> ``` `<B>`{=html}A = Model of observer\'s view B = Model of Anaesthetic Action in thalamus C = Explanation of Libet\'s data`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="33%" VALIGN="TOP"> ``` `<B>`{=html} D = Explanation of unconscious but active cerebral cortex E = Explanation of knowing you know F = Explanation of non-computability`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="36%" VALIGN="TOP"> ``` `<B>`{=html} G = Binding (simultaneous processing of relevant data) H = Extended present I = Quantum state vector reduction`</B>`{=html} ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} </TABLE> ```   ```{=html} <TABLE BORDER CELLSPACING=1 CELLPADDING=7 WIDTH=612> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` `<B>`{=html}Name`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` `<B>`{=html} Author/Ref`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} A`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="4%" VALIGN="TOP"> ``` `<B>`{=html} B`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} C`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} D`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} E`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} F`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} G`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} H`</B>`{=html} ```{=html} </TD> ``` ```{=html} <TD WIDTH="5%" VALIGN="TOP"> ``` `<B>`{=html} I`</B>`{=html} ```{=html} </TD> ``` ```{=html} </TR> ``` ```{=html} <TR> ``` ```{=html} <TD WIDTH="29%" VALIGN="TOP"> ``` Real Time Consciousness ```{=html} </TD> ``` ```{=html} <TD WIDTH="28%" VALIGN="TOP"> ``` Smythies, J. 2003. 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# Consciousness Studies/Contemporary Explanations#Functionalism *This section is about the types of theory that have been advanced to explain consciousness. Specific explanations should be entered as separate pages.* ## Introduction Explanations of consciousness fall into three broad categories, those that attempt to explain the empirical experience called consciousness with scientific theories, those that seek to find some way in which consciousness could be explained by digital computers or nineteenth century materialism by redefining or eliminating experience and those that regard consciousness as inexplicable or supernatural. ## Identity theory of mind The identity theory of mind, or type physicalism, holds that the mind is identical to the brain. Type physicalists identify qualia and the form of experience with brain activity. They argue that \"mind states\" have physical causes and physical effects - thus the mind states themselves must be physical; a non-physical \"middle step\" is superfluous. Type physicalism has not yet gained widespread support because although brain activity that correlates with experience has been found everywhere in the brain, no set of brain activity that is phenomenal consciousness itself has yet been found - although this is not surprising because neuronal spike activity is unlikely to host phenomenal consciousness - see scientific theories of consciousness. ## Functionalism Functionalism was developed as a theory of the mind-body problem because of objections to identity theory and logical behaviourism. Its core idea is that the mental states can be accounted for without taking into account the underlying physical medium (the neurons), instead attending to higher-level functions such as beliefs, desires, and emotions. It is a theory of behaviour and access consciousness and so from the outset avoids any explanation of phenomenal consciousness, substituting beliefs and judgements (functions) for entities such as qualia. According to functionalism, the mental states that make up consciousness can essentially be defined as complex interactions between different functional processes. Because these processes are not limited to a particular physical state or physical medium, they can be realized in multiple ways, including, theoretically, within non-biological systems.This affords consciousness the opportunity to exist in non-human minds that are based on algorithmic processors such as digital computers. This is a highly contentious conjecture although non-functionalist physicalists might agree that machines that are not digital computers could possess consciousness through an identity theory of mind - see The problem of machine and digital consciousness. Functionalism\'s explanation of consciousness, or the mental, is best understood when considering the analogy made by functionalists between the mind and the modern digital computer. More specifically, the analogy is made to a \"machine\" capable of computing any given algorithm (i.e. a Turing machine). This machine would involve: Data input (the senses in humans), data output (both behaviour and memory), functional states (mental states), the ability to move from one functional state into another, and the definition of functional states with reference to the part they play in the operation of the entire entity - i.e. in reference to the other functional states. So long as the same process was achieved, the \"physical stuff\" \-- that being computer hardware or biological structure \-- could achieve consciousness. This variety of functionalism was developed by Hilary Putnam. One of the major proponents of functionalism is Jerry Fodor. Further reading: Block, N. (1996). The Encyclopedia of Philosophy Supplement, Macmillan, 1996 <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/functionalism.pdf> ## Dualism ### Substance dualism This theory proposes that phenomenal experience occurs in a non-physical place. In Cartesian Dualism the non-physical place is an unextended soul that looks out at the brain. In Reid\'s Natural Dualism the non-physical place is a point-soul that looks out at the world. ### Property dualism Property dualism asserts that when matter is organized in the appropriate way (i.e., organized in the way that living human bodies are organized), mental properties emerge. Property dualism is a branch of emergent materialism. The appeal to emergentism deserves closer attention. Scientific theories often deal with emergent phenomena, for instance an enzyme consists of carbon, hydrogen, nitrogen, manganese and oxygen and from this catalytic action emerges. The theory of enzyme structure and the action of this structure on the substrate explains how this emergence occurs. Notice that the theory of enzymes explains the emergence of catalytic activity; emergence does not explain the theory. In science the statement that some property will \'emerge\' means that there will be a theory that accounts for this property. Property dualism, by appealing to emergence, is stating that some theory of consciousness will be possible. In other words it is an explanation that proposes that the explanation is yet to be known. ## Intentionalism ## Higher order thought *This section is a stub and needs expansion* ## Eliminativism Eliminative materialism is the school of thought that argues for an absolute version of materialism with respect to mental entities and mental vocabulary. It principally argues that our common-sense understanding of the mind (often called \'folk psychology\') is not a viable theory on which to base scientific investigation, and therefore no coherent neural basis will be found for many such everyday psychological concepts (such as belief or intention) and that behaviour and experience can only be adequately explained on the biological level. Eliminative materialists therefore believe that consciousness does not exist and that the concept will eventually be eliminated as neuroscience progresses. Similarly, they argue that folk psychological concepts such as belief, desire and intention do not have any consistent neurological substrate. Proponents of this view often make parallels to previous scientific theories which have been eliminated, such as the four humours theory of medicine, the phlogiston theory of combustion and \'vital force\' theory of life. In these cases, science has not produced more detailed versions of these theories, but rejected them as obsolete. Eliminative materialists argue that folk psychology is headed the same way. According to W.V. Quine it will take tens of years before folk psychology will be replaced with real science. (see Phenomenal consciousness and access consciousness). Eliminative materialism was first defended by W.V. Quine, Paul Feyerabend, and Richard Rorty. This view is most associated with philosophers Paul and Patricia Churchland although philosophers such as Daniel Dennett would also consider themselves eliminativists for many aspects of psychology. Philosopher Dale Jacquette has claimed that Occam\'s Razor is the rationale behind eliminativism and reductionism. The most common argument against eliminative materialism is the argument from qualia, which is deployed in various forms by Thomas Nagel, Frank Jackson, and many others. Perhaps the most powerful argument against eliminativism is that experience itself is many things simultaneously; it is, as Aristotle points out, immediate and hence is not composed of judgements. ## Mysterianism New Mysterianism is a philosophy proposing that certain problems (in particular, consciousness) will never be explained. Owen Flanagan noted in his 1991 book \"Science of the Mind\" that some modern thinkers have suggested that consciousness might never be completely explained. Flanagan called them \"the new mysterians\" after the rock group ? and the Mysterians. The term originated with the Japanese alien-invasion film The Mysterians. The \"old mysterians\" are thinkers throughout history who have put forward a similar position. They include Leibniz, Dr Johnson, and Thomas Huxley. The latter said, \"How is it that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, when Aladdin rubbed his lamp.\" \[6, p. 229, quote\] Noam Chomsky distinguishes between problems, which seem solvable, at least in principle, through scientific methods, and mysteries which do not, even in principle. He notes that the cognitive capabilities of all organisms are limited by biology, e.g. a mouse will never speak. In the same way, certain problems may be beyond our understanding. The term New Mysterianism has been extended by some writers to encompass the wider philosophical position that humans don\'t have the intellectual ability to understand many hard problems, not just the problem of consciousness, at a scientific level. This position is also known as Anti-Constructive Naturalism. For example, in the mind-body problem, emergent materialism claims that humans aren\'t smart enough to determine \"the relationship between mind and matter.\" \[4\] Strong agnosticism is a religious application of this position. Colin McGinn is the leading proponent of the New Mysterian position. Critics argue this philosophy isn\'t useful and encourages capitulation. One critic noted: the extreme \"Mysterian\" position, that there are vital issues forever beyond our reach, is in many ways deeply unsatisfying. \[7\] References \[1\] McGinn, Colin - The Problem of Consciousness \[2\] McGinn, Colin - Problems in Philosophy: the limits of enquiry \[3\] McGinn, Colin - The Mysterious Flame \[4\] Blackburn, Simon - Think: A compelling introduction to philosophy, chapter two \[5\] Flanagan, Owen - The Science of the Mind (1991) 2ed MIT Press, Cambridge \[6\] Horgan, John - The Undiscovered Mind (1999), Phoenix, ## Idealism and panpsychism ### Idealism

# Consciousness Studies/Contemporary Explanations#Property dualism *This section is about the types of theory that have been advanced to explain consciousness. Specific explanations should be entered as separate pages.* ## Introduction Explanations of consciousness fall into three broad categories, those that attempt to explain the empirical experience called consciousness with scientific theories, those that seek to find some way in which consciousness could be explained by digital computers or nineteenth century materialism by redefining or eliminating experience and those that regard consciousness as inexplicable or supernatural. ## Identity theory of mind The identity theory of mind, or type physicalism, holds that the mind is identical to the brain. Type physicalists identify qualia and the form of experience with brain activity. They argue that \"mind states\" have physical causes and physical effects - thus the mind states themselves must be physical; a non-physical \"middle step\" is superfluous. Type physicalism has not yet gained widespread support because although brain activity that correlates with experience has been found everywhere in the brain, no set of brain activity that is phenomenal consciousness itself has yet been found - although this is not surprising because neuronal spike activity is unlikely to host phenomenal consciousness - see scientific theories of consciousness. ## Functionalism Functionalism was developed as a theory of the mind-body problem because of objections to identity theory and logical behaviourism. Its core idea is that the mental states can be accounted for without taking into account the underlying physical medium (the neurons), instead attending to higher-level functions such as beliefs, desires, and emotions. It is a theory of behaviour and access consciousness and so from the outset avoids any explanation of phenomenal consciousness, substituting beliefs and judgements (functions) for entities such as qualia. According to functionalism, the mental states that make up consciousness can essentially be defined as complex interactions between different functional processes. Because these processes are not limited to a particular physical state or physical medium, they can be realized in multiple ways, including, theoretically, within non-biological systems.This affords consciousness the opportunity to exist in non-human minds that are based on algorithmic processors such as digital computers. This is a highly contentious conjecture although non-functionalist physicalists might agree that machines that are not digital computers could possess consciousness through an identity theory of mind - see The problem of machine and digital consciousness. Functionalism\'s explanation of consciousness, or the mental, is best understood when considering the analogy made by functionalists between the mind and the modern digital computer. More specifically, the analogy is made to a \"machine\" capable of computing any given algorithm (i.e. a Turing machine). This machine would involve: Data input (the senses in humans), data output (both behaviour and memory), functional states (mental states), the ability to move from one functional state into another, and the definition of functional states with reference to the part they play in the operation of the entire entity - i.e. in reference to the other functional states. So long as the same process was achieved, the \"physical stuff\" \-- that being computer hardware or biological structure \-- could achieve consciousness. This variety of functionalism was developed by Hilary Putnam. One of the major proponents of functionalism is Jerry Fodor. Further reading: Block, N. (1996). The Encyclopedia of Philosophy Supplement, Macmillan, 1996 <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/functionalism.pdf> ## Dualism ### Substance dualism This theory proposes that phenomenal experience occurs in a non-physical place. In Cartesian Dualism the non-physical place is an unextended soul that looks out at the brain. In Reid\'s Natural Dualism the non-physical place is a point-soul that looks out at the world. ### Property dualism Property dualism asserts that when matter is organized in the appropriate way (i.e., organized in the way that living human bodies are organized), mental properties emerge. Property dualism is a branch of emergent materialism. The appeal to emergentism deserves closer attention. Scientific theories often deal with emergent phenomena, for instance an enzyme consists of carbon, hydrogen, nitrogen, manganese and oxygen and from this catalytic action emerges. The theory of enzyme structure and the action of this structure on the substrate explains how this emergence occurs. Notice that the theory of enzymes explains the emergence of catalytic activity; emergence does not explain the theory. In science the statement that some property will \'emerge\' means that there will be a theory that accounts for this property. Property dualism, by appealing to emergence, is stating that some theory of consciousness will be possible. In other words it is an explanation that proposes that the explanation is yet to be known. ## Intentionalism ## Higher order thought *This section is a stub and needs expansion* ## Eliminativism Eliminative materialism is the school of thought that argues for an absolute version of materialism with respect to mental entities and mental vocabulary. It principally argues that our common-sense understanding of the mind (often called \'folk psychology\') is not a viable theory on which to base scientific investigation, and therefore no coherent neural basis will be found for many such everyday psychological concepts (such as belief or intention) and that behaviour and experience can only be adequately explained on the biological level. Eliminative materialists therefore believe that consciousness does not exist and that the concept will eventually be eliminated as neuroscience progresses. Similarly, they argue that folk psychological concepts such as belief, desire and intention do not have any consistent neurological substrate. Proponents of this view often make parallels to previous scientific theories which have been eliminated, such as the four humours theory of medicine, the phlogiston theory of combustion and \'vital force\' theory of life. In these cases, science has not produced more detailed versions of these theories, but rejected them as obsolete. Eliminative materialists argue that folk psychology is headed the same way. According to W.V. Quine it will take tens of years before folk psychology will be replaced with real science. (see Phenomenal consciousness and access consciousness). Eliminative materialism was first defended by W.V. Quine, Paul Feyerabend, and Richard Rorty. This view is most associated with philosophers Paul and Patricia Churchland although philosophers such as Daniel Dennett would also consider themselves eliminativists for many aspects of psychology. Philosopher Dale Jacquette has claimed that Occam\'s Razor is the rationale behind eliminativism and reductionism. The most common argument against eliminative materialism is the argument from qualia, which is deployed in various forms by Thomas Nagel, Frank Jackson, and many others. Perhaps the most powerful argument against eliminativism is that experience itself is many things simultaneously; it is, as Aristotle points out, immediate and hence is not composed of judgements. ## Mysterianism New Mysterianism is a philosophy proposing that certain problems (in particular, consciousness) will never be explained. Owen Flanagan noted in his 1991 book \"Science of the Mind\" that some modern thinkers have suggested that consciousness might never be completely explained. Flanagan called them \"the new mysterians\" after the rock group ? and the Mysterians. The term originated with the Japanese alien-invasion film The Mysterians. The \"old mysterians\" are thinkers throughout history who have put forward a similar position. They include Leibniz, Dr Johnson, and Thomas Huxley. The latter said, \"How is it that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, when Aladdin rubbed his lamp.\" \[6, p. 229, quote\] Noam Chomsky distinguishes between problems, which seem solvable, at least in principle, through scientific methods, and mysteries which do not, even in principle. He notes that the cognitive capabilities of all organisms are limited by biology, e.g. a mouse will never speak. In the same way, certain problems may be beyond our understanding. The term New Mysterianism has been extended by some writers to encompass the wider philosophical position that humans don\'t have the intellectual ability to understand many hard problems, not just the problem of consciousness, at a scientific level. This position is also known as Anti-Constructive Naturalism. For example, in the mind-body problem, emergent materialism claims that humans aren\'t smart enough to determine \"the relationship between mind and matter.\" \[4\] Strong agnosticism is a religious application of this position. Colin McGinn is the leading proponent of the New Mysterian position. Critics argue this philosophy isn\'t useful and encourages capitulation. One critic noted: the extreme \"Mysterian\" position, that there are vital issues forever beyond our reach, is in many ways deeply unsatisfying. \[7\] References \[1\] McGinn, Colin - The Problem of Consciousness \[2\] McGinn, Colin - Problems in Philosophy: the limits of enquiry \[3\] McGinn, Colin - The Mysterious Flame \[4\] Blackburn, Simon - Think: A compelling introduction to philosophy, chapter two \[5\] Flanagan, Owen - The Science of the Mind (1991) 2ed MIT Press, Cambridge \[6\] Horgan, John - The Undiscovered Mind (1999), Phoenix, ## Idealism and panpsychism ### Idealism

# Consciousness Studies/Contemporary Explanations#Intentionalism *This section is about the types of theory that have been advanced to explain consciousness. Specific explanations should be entered as separate pages.* ## Introduction Explanations of consciousness fall into three broad categories, those that attempt to explain the empirical experience called consciousness with scientific theories, those that seek to find some way in which consciousness could be explained by digital computers or nineteenth century materialism by redefining or eliminating experience and those that regard consciousness as inexplicable or supernatural. ## Identity theory of mind The identity theory of mind, or type physicalism, holds that the mind is identical to the brain. Type physicalists identify qualia and the form of experience with brain activity. They argue that \"mind states\" have physical causes and physical effects - thus the mind states themselves must be physical; a non-physical \"middle step\" is superfluous. Type physicalism has not yet gained widespread support because although brain activity that correlates with experience has been found everywhere in the brain, no set of brain activity that is phenomenal consciousness itself has yet been found - although this is not surprising because neuronal spike activity is unlikely to host phenomenal consciousness - see scientific theories of consciousness. ## Functionalism Functionalism was developed as a theory of the mind-body problem because of objections to identity theory and logical behaviourism. Its core idea is that the mental states can be accounted for without taking into account the underlying physical medium (the neurons), instead attending to higher-level functions such as beliefs, desires, and emotions. It is a theory of behaviour and access consciousness and so from the outset avoids any explanation of phenomenal consciousness, substituting beliefs and judgements (functions) for entities such as qualia. According to functionalism, the mental states that make up consciousness can essentially be defined as complex interactions between different functional processes. Because these processes are not limited to a particular physical state or physical medium, they can be realized in multiple ways, including, theoretically, within non-biological systems.This affords consciousness the opportunity to exist in non-human minds that are based on algorithmic processors such as digital computers. This is a highly contentious conjecture although non-functionalist physicalists might agree that machines that are not digital computers could possess consciousness through an identity theory of mind - see The problem of machine and digital consciousness. Functionalism\'s explanation of consciousness, or the mental, is best understood when considering the analogy made by functionalists between the mind and the modern digital computer. More specifically, the analogy is made to a \"machine\" capable of computing any given algorithm (i.e. a Turing machine). This machine would involve: Data input (the senses in humans), data output (both behaviour and memory), functional states (mental states), the ability to move from one functional state into another, and the definition of functional states with reference to the part they play in the operation of the entire entity - i.e. in reference to the other functional states. So long as the same process was achieved, the \"physical stuff\" \-- that being computer hardware or biological structure \-- could achieve consciousness. This variety of functionalism was developed by Hilary Putnam. One of the major proponents of functionalism is Jerry Fodor. Further reading: Block, N. (1996). The Encyclopedia of Philosophy Supplement, Macmillan, 1996 <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/functionalism.pdf> ## Dualism ### Substance dualism This theory proposes that phenomenal experience occurs in a non-physical place. In Cartesian Dualism the non-physical place is an unextended soul that looks out at the brain. In Reid\'s Natural Dualism the non-physical place is a point-soul that looks out at the world. ### Property dualism Property dualism asserts that when matter is organized in the appropriate way (i.e., organized in the way that living human bodies are organized), mental properties emerge. Property dualism is a branch of emergent materialism. The appeal to emergentism deserves closer attention. Scientific theories often deal with emergent phenomena, for instance an enzyme consists of carbon, hydrogen, nitrogen, manganese and oxygen and from this catalytic action emerges. The theory of enzyme structure and the action of this structure on the substrate explains how this emergence occurs. Notice that the theory of enzymes explains the emergence of catalytic activity; emergence does not explain the theory. In science the statement that some property will \'emerge\' means that there will be a theory that accounts for this property. Property dualism, by appealing to emergence, is stating that some theory of consciousness will be possible. In other words it is an explanation that proposes that the explanation is yet to be known. ## Intentionalism ## Higher order thought *This section is a stub and needs expansion* ## Eliminativism Eliminative materialism is the school of thought that argues for an absolute version of materialism with respect to mental entities and mental vocabulary. It principally argues that our common-sense understanding of the mind (often called \'folk psychology\') is not a viable theory on which to base scientific investigation, and therefore no coherent neural basis will be found for many such everyday psychological concepts (such as belief or intention) and that behaviour and experience can only be adequately explained on the biological level. Eliminative materialists therefore believe that consciousness does not exist and that the concept will eventually be eliminated as neuroscience progresses. Similarly, they argue that folk psychological concepts such as belief, desire and intention do not have any consistent neurological substrate. Proponents of this view often make parallels to previous scientific theories which have been eliminated, such as the four humours theory of medicine, the phlogiston theory of combustion and \'vital force\' theory of life. In these cases, science has not produced more detailed versions of these theories, but rejected them as obsolete. Eliminative materialists argue that folk psychology is headed the same way. According to W.V. Quine it will take tens of years before folk psychology will be replaced with real science. (see Phenomenal consciousness and access consciousness). Eliminative materialism was first defended by W.V. Quine, Paul Feyerabend, and Richard Rorty. This view is most associated with philosophers Paul and Patricia Churchland although philosophers such as Daniel Dennett would also consider themselves eliminativists for many aspects of psychology. Philosopher Dale Jacquette has claimed that Occam\'s Razor is the rationale behind eliminativism and reductionism. The most common argument against eliminative materialism is the argument from qualia, which is deployed in various forms by Thomas Nagel, Frank Jackson, and many others. Perhaps the most powerful argument against eliminativism is that experience itself is many things simultaneously; it is, as Aristotle points out, immediate and hence is not composed of judgements. ## Mysterianism New Mysterianism is a philosophy proposing that certain problems (in particular, consciousness) will never be explained. Owen Flanagan noted in his 1991 book \"Science of the Mind\" that some modern thinkers have suggested that consciousness might never be completely explained. Flanagan called them \"the new mysterians\" after the rock group ? and the Mysterians. The term originated with the Japanese alien-invasion film The Mysterians. The \"old mysterians\" are thinkers throughout history who have put forward a similar position. They include Leibniz, Dr Johnson, and Thomas Huxley. The latter said, \"How is it that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, when Aladdin rubbed his lamp.\" \[6, p. 229, quote\] Noam Chomsky distinguishes between problems, which seem solvable, at least in principle, through scientific methods, and mysteries which do not, even in principle. He notes that the cognitive capabilities of all organisms are limited by biology, e.g. a mouse will never speak. In the same way, certain problems may be beyond our understanding. The term New Mysterianism has been extended by some writers to encompass the wider philosophical position that humans don\'t have the intellectual ability to understand many hard problems, not just the problem of consciousness, at a scientific level. This position is also known as Anti-Constructive Naturalism. For example, in the mind-body problem, emergent materialism claims that humans aren\'t smart enough to determine \"the relationship between mind and matter.\" \[4\] Strong agnosticism is a religious application of this position. Colin McGinn is the leading proponent of the New Mysterian position. Critics argue this philosophy isn\'t useful and encourages capitulation. One critic noted: the extreme \"Mysterian\" position, that there are vital issues forever beyond our reach, is in many ways deeply unsatisfying. \[7\] References \[1\] McGinn, Colin - The Problem of Consciousness \[2\] McGinn, Colin - Problems in Philosophy: the limits of enquiry \[3\] McGinn, Colin - The Mysterious Flame \[4\] Blackburn, Simon - Think: A compelling introduction to philosophy, chapter two \[5\] Flanagan, Owen - The Science of the Mind (1991) 2ed MIT Press, Cambridge \[6\] Horgan, John - The Undiscovered Mind (1999), Phoenix, ## Idealism and panpsychism ### Idealism

# Consciousness Studies/Contemporary Explanations#Higher order thought *This section is about the types of theory that have been advanced to explain consciousness. Specific explanations should be entered as separate pages.* ## Introduction Explanations of consciousness fall into three broad categories, those that attempt to explain the empirical experience called consciousness with scientific theories, those that seek to find some way in which consciousness could be explained by digital computers or nineteenth century materialism by redefining or eliminating experience and those that regard consciousness as inexplicable or supernatural. ## Identity theory of mind The identity theory of mind, or type physicalism, holds that the mind is identical to the brain. Type physicalists identify qualia and the form of experience with brain activity. They argue that \"mind states\" have physical causes and physical effects - thus the mind states themselves must be physical; a non-physical \"middle step\" is superfluous. Type physicalism has not yet gained widespread support because although brain activity that correlates with experience has been found everywhere in the brain, no set of brain activity that is phenomenal consciousness itself has yet been found - although this is not surprising because neuronal spike activity is unlikely to host phenomenal consciousness - see scientific theories of consciousness. ## Functionalism Functionalism was developed as a theory of the mind-body problem because of objections to identity theory and logical behaviourism. Its core idea is that the mental states can be accounted for without taking into account the underlying physical medium (the neurons), instead attending to higher-level functions such as beliefs, desires, and emotions. It is a theory of behaviour and access consciousness and so from the outset avoids any explanation of phenomenal consciousness, substituting beliefs and judgements (functions) for entities such as qualia. According to functionalism, the mental states that make up consciousness can essentially be defined as complex interactions between different functional processes. Because these processes are not limited to a particular physical state or physical medium, they can be realized in multiple ways, including, theoretically, within non-biological systems.This affords consciousness the opportunity to exist in non-human minds that are based on algorithmic processors such as digital computers. This is a highly contentious conjecture although non-functionalist physicalists might agree that machines that are not digital computers could possess consciousness through an identity theory of mind - see The problem of machine and digital consciousness. Functionalism\'s explanation of consciousness, or the mental, is best understood when considering the analogy made by functionalists between the mind and the modern digital computer. More specifically, the analogy is made to a \"machine\" capable of computing any given algorithm (i.e. a Turing machine). This machine would involve: Data input (the senses in humans), data output (both behaviour and memory), functional states (mental states), the ability to move from one functional state into another, and the definition of functional states with reference to the part they play in the operation of the entire entity - i.e. in reference to the other functional states. So long as the same process was achieved, the \"physical stuff\" \-- that being computer hardware or biological structure \-- could achieve consciousness. This variety of functionalism was developed by Hilary Putnam. One of the major proponents of functionalism is Jerry Fodor. Further reading: Block, N. (1996). The Encyclopedia of Philosophy Supplement, Macmillan, 1996 <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/functionalism.pdf> ## Dualism ### Substance dualism This theory proposes that phenomenal experience occurs in a non-physical place. In Cartesian Dualism the non-physical place is an unextended soul that looks out at the brain. In Reid\'s Natural Dualism the non-physical place is a point-soul that looks out at the world. ### Property dualism Property dualism asserts that when matter is organized in the appropriate way (i.e., organized in the way that living human bodies are organized), mental properties emerge. Property dualism is a branch of emergent materialism. The appeal to emergentism deserves closer attention. Scientific theories often deal with emergent phenomena, for instance an enzyme consists of carbon, hydrogen, nitrogen, manganese and oxygen and from this catalytic action emerges. The theory of enzyme structure and the action of this structure on the substrate explains how this emergence occurs. Notice that the theory of enzymes explains the emergence of catalytic activity; emergence does not explain the theory. In science the statement that some property will \'emerge\' means that there will be a theory that accounts for this property. Property dualism, by appealing to emergence, is stating that some theory of consciousness will be possible. In other words it is an explanation that proposes that the explanation is yet to be known. ## Intentionalism ## Higher order thought *This section is a stub and needs expansion* ## Eliminativism Eliminative materialism is the school of thought that argues for an absolute version of materialism with respect to mental entities and mental vocabulary. It principally argues that our common-sense understanding of the mind (often called \'folk psychology\') is not a viable theory on which to base scientific investigation, and therefore no coherent neural basis will be found for many such everyday psychological concepts (such as belief or intention) and that behaviour and experience can only be adequately explained on the biological level. Eliminative materialists therefore believe that consciousness does not exist and that the concept will eventually be eliminated as neuroscience progresses. Similarly, they argue that folk psychological concepts such as belief, desire and intention do not have any consistent neurological substrate. Proponents of this view often make parallels to previous scientific theories which have been eliminated, such as the four humours theory of medicine, the phlogiston theory of combustion and \'vital force\' theory of life. In these cases, science has not produced more detailed versions of these theories, but rejected them as obsolete. Eliminative materialists argue that folk psychology is headed the same way. According to W.V. Quine it will take tens of years before folk psychology will be replaced with real science. (see Phenomenal consciousness and access consciousness). Eliminative materialism was first defended by W.V. Quine, Paul Feyerabend, and Richard Rorty. This view is most associated with philosophers Paul and Patricia Churchland although philosophers such as Daniel Dennett would also consider themselves eliminativists for many aspects of psychology. Philosopher Dale Jacquette has claimed that Occam\'s Razor is the rationale behind eliminativism and reductionism. The most common argument against eliminative materialism is the argument from qualia, which is deployed in various forms by Thomas Nagel, Frank Jackson, and many others. Perhaps the most powerful argument against eliminativism is that experience itself is many things simultaneously; it is, as Aristotle points out, immediate and hence is not composed of judgements. ## Mysterianism New Mysterianism is a philosophy proposing that certain problems (in particular, consciousness) will never be explained. Owen Flanagan noted in his 1991 book \"Science of the Mind\" that some modern thinkers have suggested that consciousness might never be completely explained. Flanagan called them \"the new mysterians\" after the rock group ? and the Mysterians. The term originated with the Japanese alien-invasion film The Mysterians. The \"old mysterians\" are thinkers throughout history who have put forward a similar position. They include Leibniz, Dr Johnson, and Thomas Huxley. The latter said, \"How is it that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, when Aladdin rubbed his lamp.\" \[6, p. 229, quote\] Noam Chomsky distinguishes between problems, which seem solvable, at least in principle, through scientific methods, and mysteries which do not, even in principle. He notes that the cognitive capabilities of all organisms are limited by biology, e.g. a mouse will never speak. In the same way, certain problems may be beyond our understanding. The term New Mysterianism has been extended by some writers to encompass the wider philosophical position that humans don\'t have the intellectual ability to understand many hard problems, not just the problem of consciousness, at a scientific level. This position is also known as Anti-Constructive Naturalism. For example, in the mind-body problem, emergent materialism claims that humans aren\'t smart enough to determine \"the relationship between mind and matter.\" \[4\] Strong agnosticism is a religious application of this position. Colin McGinn is the leading proponent of the New Mysterian position. Critics argue this philosophy isn\'t useful and encourages capitulation. One critic noted: the extreme \"Mysterian\" position, that there are vital issues forever beyond our reach, is in many ways deeply unsatisfying. \[7\] References \[1\] McGinn, Colin - The Problem of Consciousness \[2\] McGinn, Colin - Problems in Philosophy: the limits of enquiry \[3\] McGinn, Colin - The Mysterious Flame \[4\] Blackburn, Simon - Think: A compelling introduction to philosophy, chapter two \[5\] Flanagan, Owen - The Science of the Mind (1991) 2ed MIT Press, Cambridge \[6\] Horgan, John - The Undiscovered Mind (1999), Phoenix, ## Idealism and panpsychism ### Idealism

# Consciousness Studies/Contemporary Explanations#Eliminativism *This section is about the types of theory that have been advanced to explain consciousness. Specific explanations should be entered as separate pages.* ## Introduction Explanations of consciousness fall into three broad categories, those that attempt to explain the empirical experience called consciousness with scientific theories, those that seek to find some way in which consciousness could be explained by digital computers or nineteenth century materialism by redefining or eliminating experience and those that regard consciousness as inexplicable or supernatural. ## Identity theory of mind The identity theory of mind, or type physicalism, holds that the mind is identical to the brain. Type physicalists identify qualia and the form of experience with brain activity. They argue that \"mind states\" have physical causes and physical effects - thus the mind states themselves must be physical; a non-physical \"middle step\" is superfluous. Type physicalism has not yet gained widespread support because although brain activity that correlates with experience has been found everywhere in the brain, no set of brain activity that is phenomenal consciousness itself has yet been found - although this is not surprising because neuronal spike activity is unlikely to host phenomenal consciousness - see scientific theories of consciousness. ## Functionalism Functionalism was developed as a theory of the mind-body problem because of objections to identity theory and logical behaviourism. Its core idea is that the mental states can be accounted for without taking into account the underlying physical medium (the neurons), instead attending to higher-level functions such as beliefs, desires, and emotions. It is a theory of behaviour and access consciousness and so from the outset avoids any explanation of phenomenal consciousness, substituting beliefs and judgements (functions) for entities such as qualia. According to functionalism, the mental states that make up consciousness can essentially be defined as complex interactions between different functional processes. Because these processes are not limited to a particular physical state or physical medium, they can be realized in multiple ways, including, theoretically, within non-biological systems.This affords consciousness the opportunity to exist in non-human minds that are based on algorithmic processors such as digital computers. This is a highly contentious conjecture although non-functionalist physicalists might agree that machines that are not digital computers could possess consciousness through an identity theory of mind - see The problem of machine and digital consciousness. Functionalism\'s explanation of consciousness, or the mental, is best understood when considering the analogy made by functionalists between the mind and the modern digital computer. More specifically, the analogy is made to a \"machine\" capable of computing any given algorithm (i.e. a Turing machine). This machine would involve: Data input (the senses in humans), data output (both behaviour and memory), functional states (mental states), the ability to move from one functional state into another, and the definition of functional states with reference to the part they play in the operation of the entire entity - i.e. in reference to the other functional states. So long as the same process was achieved, the \"physical stuff\" \-- that being computer hardware or biological structure \-- could achieve consciousness. This variety of functionalism was developed by Hilary Putnam. One of the major proponents of functionalism is Jerry Fodor. Further reading: Block, N. (1996). The Encyclopedia of Philosophy Supplement, Macmillan, 1996 <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/functionalism.pdf> ## Dualism ### Substance dualism This theory proposes that phenomenal experience occurs in a non-physical place. In Cartesian Dualism the non-physical place is an unextended soul that looks out at the brain. In Reid\'s Natural Dualism the non-physical place is a point-soul that looks out at the world. ### Property dualism Property dualism asserts that when matter is organized in the appropriate way (i.e., organized in the way that living human bodies are organized), mental properties emerge. Property dualism is a branch of emergent materialism. The appeal to emergentism deserves closer attention. Scientific theories often deal with emergent phenomena, for instance an enzyme consists of carbon, hydrogen, nitrogen, manganese and oxygen and from this catalytic action emerges. The theory of enzyme structure and the action of this structure on the substrate explains how this emergence occurs. Notice that the theory of enzymes explains the emergence of catalytic activity; emergence does not explain the theory. In science the statement that some property will \'emerge\' means that there will be a theory that accounts for this property. Property dualism, by appealing to emergence, is stating that some theory of consciousness will be possible. In other words it is an explanation that proposes that the explanation is yet to be known. ## Intentionalism ## Higher order thought *This section is a stub and needs expansion* ## Eliminativism Eliminative materialism is the school of thought that argues for an absolute version of materialism with respect to mental entities and mental vocabulary. It principally argues that our common-sense understanding of the mind (often called \'folk psychology\') is not a viable theory on which to base scientific investigation, and therefore no coherent neural basis will be found for many such everyday psychological concepts (such as belief or intention) and that behaviour and experience can only be adequately explained on the biological level. Eliminative materialists therefore believe that consciousness does not exist and that the concept will eventually be eliminated as neuroscience progresses. Similarly, they argue that folk psychological concepts such as belief, desire and intention do not have any consistent neurological substrate. Proponents of this view often make parallels to previous scientific theories which have been eliminated, such as the four humours theory of medicine, the phlogiston theory of combustion and \'vital force\' theory of life. In these cases, science has not produced more detailed versions of these theories, but rejected them as obsolete. Eliminative materialists argue that folk psychology is headed the same way. According to W.V. Quine it will take tens of years before folk psychology will be replaced with real science. (see Phenomenal consciousness and access consciousness). Eliminative materialism was first defended by W.V. Quine, Paul Feyerabend, and Richard Rorty. This view is most associated with philosophers Paul and Patricia Churchland although philosophers such as Daniel Dennett would also consider themselves eliminativists for many aspects of psychology. Philosopher Dale Jacquette has claimed that Occam\'s Razor is the rationale behind eliminativism and reductionism. The most common argument against eliminative materialism is the argument from qualia, which is deployed in various forms by Thomas Nagel, Frank Jackson, and many others. Perhaps the most powerful argument against eliminativism is that experience itself is many things simultaneously; it is, as Aristotle points out, immediate and hence is not composed of judgements. ## Mysterianism New Mysterianism is a philosophy proposing that certain problems (in particular, consciousness) will never be explained. Owen Flanagan noted in his 1991 book \"Science of the Mind\" that some modern thinkers have suggested that consciousness might never be completely explained. Flanagan called them \"the new mysterians\" after the rock group ? and the Mysterians. The term originated with the Japanese alien-invasion film The Mysterians. The \"old mysterians\" are thinkers throughout history who have put forward a similar position. They include Leibniz, Dr Johnson, and Thomas Huxley. The latter said, \"How is it that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, when Aladdin rubbed his lamp.\" \[6, p. 229, quote\] Noam Chomsky distinguishes between problems, which seem solvable, at least in principle, through scientific methods, and mysteries which do not, even in principle. He notes that the cognitive capabilities of all organisms are limited by biology, e.g. a mouse will never speak. In the same way, certain problems may be beyond our understanding. The term New Mysterianism has been extended by some writers to encompass the wider philosophical position that humans don\'t have the intellectual ability to understand many hard problems, not just the problem of consciousness, at a scientific level. This position is also known as Anti-Constructive Naturalism. For example, in the mind-body problem, emergent materialism claims that humans aren\'t smart enough to determine \"the relationship between mind and matter.\" \[4\] Strong agnosticism is a religious application of this position. Colin McGinn is the leading proponent of the New Mysterian position. Critics argue this philosophy isn\'t useful and encourages capitulation. One critic noted: the extreme \"Mysterian\" position, that there are vital issues forever beyond our reach, is in many ways deeply unsatisfying. \[7\] References \[1\] McGinn, Colin - The Problem of Consciousness \[2\] McGinn, Colin - Problems in Philosophy: the limits of enquiry \[3\] McGinn, Colin - The Mysterious Flame \[4\] Blackburn, Simon - Think: A compelling introduction to philosophy, chapter two \[5\] Flanagan, Owen - The Science of the Mind (1991) 2ed MIT Press, Cambridge \[6\] Horgan, John - The Undiscovered Mind (1999), Phoenix, ## Idealism and panpsychism ### Idealism

# Consciousness Studies/Contemporary Explanations#Mysterianism *This section is about the types of theory that have been advanced to explain consciousness. Specific explanations should be entered as separate pages.* ## Introduction Explanations of consciousness fall into three broad categories, those that attempt to explain the empirical experience called consciousness with scientific theories, those that seek to find some way in which consciousness could be explained by digital computers or nineteenth century materialism by redefining or eliminating experience and those that regard consciousness as inexplicable or supernatural. ## Identity theory of mind The identity theory of mind, or type physicalism, holds that the mind is identical to the brain. Type physicalists identify qualia and the form of experience with brain activity. They argue that \"mind states\" have physical causes and physical effects - thus the mind states themselves must be physical; a non-physical \"middle step\" is superfluous. Type physicalism has not yet gained widespread support because although brain activity that correlates with experience has been found everywhere in the brain, no set of brain activity that is phenomenal consciousness itself has yet been found - although this is not surprising because neuronal spike activity is unlikely to host phenomenal consciousness - see scientific theories of consciousness. ## Functionalism Functionalism was developed as a theory of the mind-body problem because of objections to identity theory and logical behaviourism. Its core idea is that the mental states can be accounted for without taking into account the underlying physical medium (the neurons), instead attending to higher-level functions such as beliefs, desires, and emotions. It is a theory of behaviour and access consciousness and so from the outset avoids any explanation of phenomenal consciousness, substituting beliefs and judgements (functions) for entities such as qualia. According to functionalism, the mental states that make up consciousness can essentially be defined as complex interactions between different functional processes. Because these processes are not limited to a particular physical state or physical medium, they can be realized in multiple ways, including, theoretically, within non-biological systems.This affords consciousness the opportunity to exist in non-human minds that are based on algorithmic processors such as digital computers. This is a highly contentious conjecture although non-functionalist physicalists might agree that machines that are not digital computers could possess consciousness through an identity theory of mind - see The problem of machine and digital consciousness. Functionalism\'s explanation of consciousness, or the mental, is best understood when considering the analogy made by functionalists between the mind and the modern digital computer. More specifically, the analogy is made to a \"machine\" capable of computing any given algorithm (i.e. a Turing machine). This machine would involve: Data input (the senses in humans), data output (both behaviour and memory), functional states (mental states), the ability to move from one functional state into another, and the definition of functional states with reference to the part they play in the operation of the entire entity - i.e. in reference to the other functional states. So long as the same process was achieved, the \"physical stuff\" \-- that being computer hardware or biological structure \-- could achieve consciousness. This variety of functionalism was developed by Hilary Putnam. One of the major proponents of functionalism is Jerry Fodor. Further reading: Block, N. (1996). The Encyclopedia of Philosophy Supplement, Macmillan, 1996 <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/functionalism.pdf> ## Dualism ### Substance dualism This theory proposes that phenomenal experience occurs in a non-physical place. In Cartesian Dualism the non-physical place is an unextended soul that looks out at the brain. In Reid\'s Natural Dualism the non-physical place is a point-soul that looks out at the world. ### Property dualism Property dualism asserts that when matter is organized in the appropriate way (i.e., organized in the way that living human bodies are organized), mental properties emerge. Property dualism is a branch of emergent materialism. The appeal to emergentism deserves closer attention. Scientific theories often deal with emergent phenomena, for instance an enzyme consists of carbon, hydrogen, nitrogen, manganese and oxygen and from this catalytic action emerges. The theory of enzyme structure and the action of this structure on the substrate explains how this emergence occurs. Notice that the theory of enzymes explains the emergence of catalytic activity; emergence does not explain the theory. In science the statement that some property will \'emerge\' means that there will be a theory that accounts for this property. Property dualism, by appealing to emergence, is stating that some theory of consciousness will be possible. In other words it is an explanation that proposes that the explanation is yet to be known. ## Intentionalism ## Higher order thought *This section is a stub and needs expansion* ## Eliminativism Eliminative materialism is the school of thought that argues for an absolute version of materialism with respect to mental entities and mental vocabulary. It principally argues that our common-sense understanding of the mind (often called \'folk psychology\') is not a viable theory on which to base scientific investigation, and therefore no coherent neural basis will be found for many such everyday psychological concepts (such as belief or intention) and that behaviour and experience can only be adequately explained on the biological level. Eliminative materialists therefore believe that consciousness does not exist and that the concept will eventually be eliminated as neuroscience progresses. Similarly, they argue that folk psychological concepts such as belief, desire and intention do not have any consistent neurological substrate. Proponents of this view often make parallels to previous scientific theories which have been eliminated, such as the four humours theory of medicine, the phlogiston theory of combustion and \'vital force\' theory of life. In these cases, science has not produced more detailed versions of these theories, but rejected them as obsolete. Eliminative materialists argue that folk psychology is headed the same way. According to W.V. Quine it will take tens of years before folk psychology will be replaced with real science. (see Phenomenal consciousness and access consciousness). Eliminative materialism was first defended by W.V. Quine, Paul Feyerabend, and Richard Rorty. This view is most associated with philosophers Paul and Patricia Churchland although philosophers such as Daniel Dennett would also consider themselves eliminativists for many aspects of psychology. Philosopher Dale Jacquette has claimed that Occam\'s Razor is the rationale behind eliminativism and reductionism. The most common argument against eliminative materialism is the argument from qualia, which is deployed in various forms by Thomas Nagel, Frank Jackson, and many others. Perhaps the most powerful argument against eliminativism is that experience itself is many things simultaneously; it is, as Aristotle points out, immediate and hence is not composed of judgements. ## Mysterianism New Mysterianism is a philosophy proposing that certain problems (in particular, consciousness) will never be explained. Owen Flanagan noted in his 1991 book \"Science of the Mind\" that some modern thinkers have suggested that consciousness might never be completely explained. Flanagan called them \"the new mysterians\" after the rock group ? and the Mysterians. The term originated with the Japanese alien-invasion film The Mysterians. The \"old mysterians\" are thinkers throughout history who have put forward a similar position. They include Leibniz, Dr Johnson, and Thomas Huxley. The latter said, \"How is it that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, when Aladdin rubbed his lamp.\" \[6, p. 229, quote\] Noam Chomsky distinguishes between problems, which seem solvable, at least in principle, through scientific methods, and mysteries which do not, even in principle. He notes that the cognitive capabilities of all organisms are limited by biology, e.g. a mouse will never speak. In the same way, certain problems may be beyond our understanding. The term New Mysterianism has been extended by some writers to encompass the wider philosophical position that humans don\'t have the intellectual ability to understand many hard problems, not just the problem of consciousness, at a scientific level. This position is also known as Anti-Constructive Naturalism. For example, in the mind-body problem, emergent materialism claims that humans aren\'t smart enough to determine \"the relationship between mind and matter.\" \[4\] Strong agnosticism is a religious application of this position. Colin McGinn is the leading proponent of the New Mysterian position. Critics argue this philosophy isn\'t useful and encourages capitulation. One critic noted: the extreme \"Mysterian\" position, that there are vital issues forever beyond our reach, is in many ways deeply unsatisfying. \[7\] References \[1\] McGinn, Colin - The Problem of Consciousness \[2\] McGinn, Colin - Problems in Philosophy: the limits of enquiry \[3\] McGinn, Colin - The Mysterious Flame \[4\] Blackburn, Simon - Think: A compelling introduction to philosophy, chapter two \[5\] Flanagan, Owen - The Science of the Mind (1991) 2ed MIT Press, Cambridge \[6\] Horgan, John - The Undiscovered Mind (1999), Phoenix, ## Idealism and panpsychism ### Idealism

# Consciousness Studies/Contemporary Explanations#Idealism and panpsychism *This section is about the types of theory that have been advanced to explain consciousness. Specific explanations should be entered as separate pages.* ## Introduction Explanations of consciousness fall into three broad categories, those that attempt to explain the empirical experience called consciousness with scientific theories, those that seek to find some way in which consciousness could be explained by digital computers or nineteenth century materialism by redefining or eliminating experience and those that regard consciousness as inexplicable or supernatural. ## Identity theory of mind The identity theory of mind, or type physicalism, holds that the mind is identical to the brain. Type physicalists identify qualia and the form of experience with brain activity. They argue that \"mind states\" have physical causes and physical effects - thus the mind states themselves must be physical; a non-physical \"middle step\" is superfluous. Type physicalism has not yet gained widespread support because although brain activity that correlates with experience has been found everywhere in the brain, no set of brain activity that is phenomenal consciousness itself has yet been found - although this is not surprising because neuronal spike activity is unlikely to host phenomenal consciousness - see scientific theories of consciousness. ## Functionalism Functionalism was developed as a theory of the mind-body problem because of objections to identity theory and logical behaviourism. Its core idea is that the mental states can be accounted for without taking into account the underlying physical medium (the neurons), instead attending to higher-level functions such as beliefs, desires, and emotions. It is a theory of behaviour and access consciousness and so from the outset avoids any explanation of phenomenal consciousness, substituting beliefs and judgements (functions) for entities such as qualia. According to functionalism, the mental states that make up consciousness can essentially be defined as complex interactions between different functional processes. Because these processes are not limited to a particular physical state or physical medium, they can be realized in multiple ways, including, theoretically, within non-biological systems.This affords consciousness the opportunity to exist in non-human minds that are based on algorithmic processors such as digital computers. This is a highly contentious conjecture although non-functionalist physicalists might agree that machines that are not digital computers could possess consciousness through an identity theory of mind - see The problem of machine and digital consciousness. Functionalism\'s explanation of consciousness, or the mental, is best understood when considering the analogy made by functionalists between the mind and the modern digital computer. More specifically, the analogy is made to a \"machine\" capable of computing any given algorithm (i.e. a Turing machine). This machine would involve: Data input (the senses in humans), data output (both behaviour and memory), functional states (mental states), the ability to move from one functional state into another, and the definition of functional states with reference to the part they play in the operation of the entire entity - i.e. in reference to the other functional states. So long as the same process was achieved, the \"physical stuff\" \-- that being computer hardware or biological structure \-- could achieve consciousness. This variety of functionalism was developed by Hilary Putnam. One of the major proponents of functionalism is Jerry Fodor. Further reading: Block, N. (1996). The Encyclopedia of Philosophy Supplement, Macmillan, 1996 <http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/functionalism.pdf> ## Dualism ### Substance dualism This theory proposes that phenomenal experience occurs in a non-physical place. In Cartesian Dualism the non-physical place is an unextended soul that looks out at the brain. In Reid\'s Natural Dualism the non-physical place is a point-soul that looks out at the world. ### Property dualism Property dualism asserts that when matter is organized in the appropriate way (i.e., organized in the way that living human bodies are organized), mental properties emerge. Property dualism is a branch of emergent materialism. The appeal to emergentism deserves closer attention. Scientific theories often deal with emergent phenomena, for instance an enzyme consists of carbon, hydrogen, nitrogen, manganese and oxygen and from this catalytic action emerges. The theory of enzyme structure and the action of this structure on the substrate explains how this emergence occurs. Notice that the theory of enzymes explains the emergence of catalytic activity; emergence does not explain the theory. In science the statement that some property will \'emerge\' means that there will be a theory that accounts for this property. Property dualism, by appealing to emergence, is stating that some theory of consciousness will be possible. In other words it is an explanation that proposes that the explanation is yet to be known. ## Intentionalism ## Higher order thought *This section is a stub and needs expansion* ## Eliminativism Eliminative materialism is the school of thought that argues for an absolute version of materialism with respect to mental entities and mental vocabulary. It principally argues that our common-sense understanding of the mind (often called \'folk psychology\') is not a viable theory on which to base scientific investigation, and therefore no coherent neural basis will be found for many such everyday psychological concepts (such as belief or intention) and that behaviour and experience can only be adequately explained on the biological level. Eliminative materialists therefore believe that consciousness does not exist and that the concept will eventually be eliminated as neuroscience progresses. Similarly, they argue that folk psychological concepts such as belief, desire and intention do not have any consistent neurological substrate. Proponents of this view often make parallels to previous scientific theories which have been eliminated, such as the four humours theory of medicine, the phlogiston theory of combustion and \'vital force\' theory of life. In these cases, science has not produced more detailed versions of these theories, but rejected them as obsolete. Eliminative materialists argue that folk psychology is headed the same way. According to W.V. Quine it will take tens of years before folk psychology will be replaced with real science. (see Phenomenal consciousness and access consciousness). Eliminative materialism was first defended by W.V. Quine, Paul Feyerabend, and Richard Rorty. This view is most associated with philosophers Paul and Patricia Churchland although philosophers such as Daniel Dennett would also consider themselves eliminativists for many aspects of psychology. Philosopher Dale Jacquette has claimed that Occam\'s Razor is the rationale behind eliminativism and reductionism. The most common argument against eliminative materialism is the argument from qualia, which is deployed in various forms by Thomas Nagel, Frank Jackson, and many others. Perhaps the most powerful argument against eliminativism is that experience itself is many things simultaneously; it is, as Aristotle points out, immediate and hence is not composed of judgements. ## Mysterianism New Mysterianism is a philosophy proposing that certain problems (in particular, consciousness) will never be explained. Owen Flanagan noted in his 1991 book \"Science of the Mind\" that some modern thinkers have suggested that consciousness might never be completely explained. Flanagan called them \"the new mysterians\" after the rock group ? and the Mysterians. The term originated with the Japanese alien-invasion film The Mysterians. The \"old mysterians\" are thinkers throughout history who have put forward a similar position. They include Leibniz, Dr Johnson, and Thomas Huxley. The latter said, \"How is it that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, when Aladdin rubbed his lamp.\" \[6, p. 229, quote\] Noam Chomsky distinguishes between problems, which seem solvable, at least in principle, through scientific methods, and mysteries which do not, even in principle. He notes that the cognitive capabilities of all organisms are limited by biology, e.g. a mouse will never speak. In the same way, certain problems may be beyond our understanding. The term New Mysterianism has been extended by some writers to encompass the wider philosophical position that humans don\'t have the intellectual ability to understand many hard problems, not just the problem of consciousness, at a scientific level. This position is also known as Anti-Constructive Naturalism. For example, in the mind-body problem, emergent materialism claims that humans aren\'t smart enough to determine \"the relationship between mind and matter.\" \[4\] Strong agnosticism is a religious application of this position. Colin McGinn is the leading proponent of the New Mysterian position. Critics argue this philosophy isn\'t useful and encourages capitulation. One critic noted: the extreme \"Mysterian\" position, that there are vital issues forever beyond our reach, is in many ways deeply unsatisfying. \[7\] References \[1\] McGinn, Colin - The Problem of Consciousness \[2\] McGinn, Colin - Problems in Philosophy: the limits of enquiry \[3\] McGinn, Colin - The Mysterious Flame \[4\] Blackburn, Simon - Think: A compelling introduction to philosophy, chapter two \[5\] Flanagan, Owen - The Science of the Mind (1991) 2ed MIT Press, Cambridge \[6\] Horgan, John - The Undiscovered Mind (1999), Phoenix, ## Idealism and panpsychism ### Idealism

# Consciousness Studies/Other Explanations Consciousness-only is the foundation of a buddhist theory known as vijnanavada. Proponents, notably the Yogacara school, suggest that the sum of experience exists only in our minds. Philosophers recognition of this view as subjective idealism is a matter of discussion because these traditions often deny the existence of ontological subject. These views are rooted in the denial of existence of any kind of ontological substance (as Matter, Soul, God, etc.). Consciousness-only views can also be found in taoist philosophy, notably Lao Tzu and Chuang Tzu.

# Consciousness Studies/Other Explanations#Consciousness-only Consciousness-only is the foundation of a buddhist theory known as vijnanavada. Proponents, notably the Yogacara school, suggest that the sum of experience exists only in our minds. Philosophers recognition of this view as subjective idealism is a matter of discussion because these traditions often deny the existence of ontological subject. These views are rooted in the denial of existence of any kind of ontological substance (as Matter, Soul, God, etc.). Consciousness-only views can also be found in taoist philosophy, notably Lao Tzu and Chuang Tzu.

# Consciousness Studies/BioPsychoSociology This brief summary is an illustration of an attempt to model a multidisciplinary biopsychosocial (bps) understanding of self-consciousness seen from the perspective of both scientific methodology and metaphysical logic where the empirical and the inferential provide a seamless blend of the ontological brain with the epistemological mind. The achievement of self consciousness is the crucial mental state allowing the human species to monitor the equilibrium state of biopsychosocial ongoing contingencies especially when confronting life-threatening circumstances. The inherited proto-semantics and acquired language guide the required recursive co-generation of the appropriate language and thought to meet the contingency. Thus informed, it allows humans to elaborate effective adaptive short and long range responses. ## Definition of terms Bps model uses some unusual definitions of terms. These are explained below. \"Sense-phenomenal awareness\" is defined as an unconscious, life-preserving, adaptive reflex response which may occur without qualia. It originates at a sensory receptor, wherever located in the body economy, and ends at an effector organ, glandular or muscular. - Phenomenal consciousness/awareness is a term normally reserved for experience containing qualia in other analyses. System/network \"awareness\" is defined in the bps model as that unconscious processing occurring during the integration of the participating neural network modules leading to a stereotyped adaptive response. - normally awareness is defined as knowledge that a conscious state is present. Sense-phenomenal awareness may become a conscious experience when relevant inferential networks (e.g., memory, emotions, etc.)are subsequently accessed, including inner-language processors. When experiences are recalled the qualia that arise are called \"conceptual qualia\". \"Access consciousness\" is described as being initially an unconscious process that makes it possible for a life-preserving, reflex-driven and \'unconscious\' sense-phenomenal state of mind to become conscious by making use of available, pertinent and concurrent mental states to interact with the novel sense-phenomenal input, a potentially life-threatening event. \"Proto-linguistic organ\" or \'plo\' is described as the first line of defense to guard against life-threatening stimuli arising from sense-phenomenal inputs (external, visceral or proprioceptive). Housed in the amygdaloidal complex, it represents the inherited proto-semantic (primitive \'meanings\') database responsible for activating the corresponding unconscious fight/flight adaptive Cannon effector response. \"Proto-semantic\" input from plo is described as a required initial participant in the subsequent recursive co-generation of inner language and thought as may be required in the eventual elaboration of \"conceptual consciousness\". ## Higher order consciousness theory The \'bps\' model of \'consciousness\' is a high order consciousness theory in which an unconscious, non inferential phenomenal state (established from either online sensory receptor input or offline memory input), when confronting a novel life-threatening event, triggers an initially unconscious access intermediate stage where relevant modular networks are incorporated including Broca\'s language processor recursively co-generating in the process the \'inner language\' narrative state and accompanying thought, a conscious high order mental state, all of which causally precedes (or is simultaneous with) the adaptive response (if any, as we see in dreams). Notice that bps considers phenomenal states to be non-conscious, this would confuse the ordinary reader who expects the Kantian term \"phenomenal\" to be equivalent to the term \"conscious experience\". Only the higher order mental state is regarded as \"conscious\". The \'bps\' model basically describes two co-existing, ongoing mental states, one non-inferential subconscious \'gut feeling\' inner sense (BOP, a variant of Lycan\'s 1996 HOP) and an initially non-inferential unconscious accessing of narrative pathways leading to (recursive co-generation of \'inner language\' and thought is an open option) the eventual production of higher order thought (HOT) whose content is the feeling that oneself is the subject of self-consciousness. In other words, according to the \'bps\' theory, feelings are not part of consciousness until higher order thought occurs, i.e., qualia needs a context. In \'bps\' theory not even self-consciousness, of which \'qualia\' may arguably be considered a subset of, has revealed its constitutive secrets. This means that bps is a theory of brain processing rather than a theory of the content of consciousness (qualia) or consciousness itself except when it ventures into the postulate that language and self-consciousness are recursively co-generated or co-causal. More controversial is the mediation of the amygdaloid complex (plo) in providing inherited primitive \'meanings\' (protosemantic codelets) to initiate Chomskian language processing and thought co-generation, i.e., protosemantics precedes syntax structuring. For a more complete exposition see: Further Reading: <http://delaSierra-Sheffer.net> For a quantum field perspective see also: <http://www.biopsychosociology.org> <http://spaces.msn.com/angelldls/>

# Miskito/Introduction ## Welcome to *Miskitu Aisas!* !Flag of the Miskito Nation{width="250"} *Miskitu Aisas!* (\"Speak Miskito!\"), a language course in Wikibooks, is an elementary introduction to the Miskito language, spoken in parts of Nicaragua and Honduras. The course focuses primarily on presenting the grammar basics through carefully graded and didactically presented lessons. *Miskitu Aisas!* assumes no prior knowledge of the language and no specialised knowledge of linguistics, although at least a general background in \"school grammar\" will no doubt be helpful, as will any previous experience at learning foreign languages. As well as an understanding of the language\'s overall structure, *Miskitu Aisas!* will also provide you with a knowledge of some basic vocabulary, and will give you the essential preparation needed to continue studying Miskito by other means, if you should wish to do so. A variety of exercises at every step in the learning path will help you gradually to assimilate both grammar and vocabulary, and to check your progress through comparison of the answers provided. A handy feature that makes this on-line course more interactive is found in the Show/Hide toggle switches that accompany model sentences, exercises and vocabularies. These allow you to customise each page and adapt it to your progress and learning pace by either displaying or concealing translations, answers and meanings. In the rest of this introduction you can read about who the Miskito people are and what their language is, and how to use this course, as well as quick links to some key pages in the course. ## The Miskito people and their language !Location of Central America and the Caribbean{width="250"} !Map of Central America and the Caribbean{width="220"} The Miskito people inhabit an area along the Caribbean (Atlantic) coast of Central America. This area, known as the Mosquito Coast, is mostly within the state of Nicaragua, with a northern section in a neighbouring region of Honduras. The territory extends from Cape Cameron in the north to Río Grande in the south. In origin the Miskitos were a local indigenous people, but in the post-colonial era a great deal of racial mixing occurred. A major component of the present population is descended from escaped slaves from other areas who sought refuge among the Miskito people. Because of the inaccessibility of the Miskitos\' territory, Spanish settlers did not begin to arrive until 1787 and even after this the Miskitos, who already had an experienced army and an established political structure, continued to dominate the land, which consequently suffered only limited influence from the Spanish conquest. The Miskitos remained independent until 1894 when their land became part of Nicaragua, but the Nicaraguans, like the Spanish before them, exercised little control and many Miskitos, even today, do not consider themselves Nicaraguan. !Former British Protectorate{width="415" height="415"} On the other hand, the Miskito people entered into contact with British colonists as early as the beginning of the seventeenth century, and during the eighteenth and nineteenth centuries they continued to be influenced by the British, who had economic interests in the area, particularly in the territory of Belize to the northwest (the colonial name for which was British Honduras). As allies of the British the Miskitos were sucked into the slave trade, often being involved in raids against Spanish settlements in Honduras. Such activities brought the Miskitos into contact with other indigenous groups, to whom the Miskitos tended to consider themselves culturally superior. The Miskitos were ruled by their own kings who took on English names (the earliest recorded king, named Oldman, received an audience with king Charles I), and emulated European dress. Following a formal Treaty of Friendship and Alliance between the Miskitos and Britain in 1740, the Miskito Nation was formally a British protectorate until 1787, and British interest in the region continued until the mid-nineteenth century. In addition to the Miskitos\' native language, Miskito, large numbers of Miskitos speak other languages, particularly Miskito Creole English (which arose through contact with the British), neighbouring indigenous languages such as Rama, and Spanish. ```{=html} <table cellspacing=0 cellpadding=6 style="background:#ecf3f7; float:left; width:331px; margin:2px; clear:both;"> ``` ```{=html} <tr> ``` ```{=html} <td width=28% bgcolor="#ffffff"> ``` `<big>`{=html}`<b>`{=html}Miskito word:`</b>`{=html}`</big>`{=html} ```{=html} </td> ``` ```{=html} <td width=40% bgcolor="#ffffff"> ``` `<big>`{=html}`<b>`{=html}Meaning:`</b>`{=html}`</big>`{=html} ```{=html} </td> ``` ```{=html} <td bgcolor="#ffffff"> ``` `<b>`{=html}English source:`</b>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **buk** ```{=html} </td> ``` ```{=html} <td> ``` *book* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}book`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **dur** ```{=html} </td> ``` ```{=html} <td> ``` *door* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}door`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **hilp** ```{=html} </td> ``` ```{=html} <td> ``` *help* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}help`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **kî** ```{=html} </td> ``` ```{=html} <td> ``` *key* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}key`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **laik** ```{=html} </td> ``` ```{=html} <td> ``` *like* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}like`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **lalah** ```{=html} </td> ``` ```{=html} <td> ``` *money* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}dollar`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **lan** ```{=html} </td> ``` ```{=html} <td> ``` *learn* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}learn`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **nu** ```{=html} </td> ``` ```{=html} <td> ``` *know* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}know`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **pain** ```{=html} </td> ``` ```{=html} <td> ``` *well* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}fine`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **prias** ```{=html} </td> ``` ```{=html} <td> ``` *religious observance* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}prayers`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **sap** ```{=html} </td> ``` ```{=html} <td> ``` *shop, store* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}shop`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **skul** ```{=html} </td> ``` ```{=html} <td> ``` *school* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}school`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **tibil** ```{=html} </td> ``` ```{=html} <td> ``` *table* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}table`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **truk** ```{=html} </td> ``` ```{=html} <td> ``` *car, vehicle* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}truck`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **want** ```{=html} </td> ``` ```{=html} <td> ``` *want* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}want`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **wark** ```{=html} </td> ``` ```{=html} <td> ``` *work* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}work`</small>`{=html} ```{=html} </td> ``` ```{=html} </tr> ``` ```{=html} <tr> ``` ```{=html} <td> ``` **windar** ```{=html} </td> ``` ```{=html} <td> ``` *window* ```{=html} </td> ``` ```{=html} <td> ``` `<small>`{=html}window`</small>`{=html} ```{=html} </td> ``` ```{=html} </table> ``` With nearly 200,000 speakers, Miskito is the most widely spoken of a family of languages of Nicaragua and Honduras that has come to be known as Misumalpan. This name is formed from parts of the names of the family\'s subgroups: MIskito, SUmo, MAtagaLPAN. Although some aspects of the internal family tree within this family are uncertain, it is clear that Miskito stands apart from Sumo and Matagalpan, which seem to share a common lower node, and that in the past Miskito was heavily influenced by other Misumalpan languages. Sumo is thought to have been dominant in the area before the period of Miskito ascendancy. Today the relationship has been reversed: many former Sumo speakers have shifted to Miskito, which has in turn heavily influenced the Sumo dialects. Several of these (Tawahka, Panamahka and Tuahka) constitute the Mayangna sub-branch of Sumo, while the Ulwa language is in another sub-branch. The Matagalpan branch of Misumalpan contains two languages that are now extinct: Matagalpa and Cacaopera. The latter was formerly spoken in parts of eastern El Salvador. In addition to many elements borrowed from other Misumalpan languages, Miskito has a large number of loanwords from English via Creole, such as those in the table on the left. All the above words occur in the first ten lessons of *Miskitu Aisas!* Notice how their sounds are adapted to the Miskito language, which only has three vowels: *a, i, u*. Even though Spanish is the official language of Nicaragua and Honduras, its influence on Miskito is much more recent and hence more superficial.\ \ \ \ ## How to use the course ### Contents and navigation There are basically two ways to move around inside this course: (1) use the Table of Contents, or (2) move from page to page using the navigation links. #### The table of contents You can get to the table of contents from the course\'s front page, and also from any other page in the course through a navigation link (see below). You can look at the table of contents right now, if you wish. You are recommended to open it up in a separate browser window so that you can continue reading this page while you inspect the table of contents. Every page that you need to see as part of the course has a link from the table of contents. Notice how the table of contents page is organised. On the right-hand side there is a list with a darker background, with the heading **\"The project\"** at the top. This section has information about the project of creating this course which may or may not interest you as a user (rather than an author) of the course. A little lower down you see another section, **\"Author\'s workbench\"**, which contains more technical information that is important for people working on development of the course, but probably unnecessary for other readers. The rest of the table of contents, with a paler blue background, includes everything that people using the course to learn (or learn about) Miskito will need. This is also divided into several sections which will now be mentioned. The **\"Getting started\"** section is where you are now, and as well as this introduction it also includes a guide to pronouncing and spelling the language. These are the pages you will probably want to have at least a quick look at before starting on the lessons. You can always come back to them later on for more detailed study whenever you feel the need. Next comes the biggest and most important section, **\"The lessons\"**. The links to the first ten lessons are placed where you can\'t miss them: in the middle of the screen, immediately after the \"Getting started\" section. When you get through those, you can scroll down a little to see the rest of the lessons currently available. Near the bottom of the table of contents there are two more sections: **\"Reference section\"** (with vocabularies, appendices, a list of abbreviations and a subject index) and **\"More about Miskito\"** (an external links page and a discussion page). #### Page-to-page navigation At the top of every page in the course you will see the flag of the historical Miskito Nation, which is the logo of the course, together with the title of the page or lesson. Notice the three links to the left of the flag logo: - a \"backwards\" link which will usually take you to the previous page (assuming you are following the pages of the course in order) - a \"forwards\" link (marked **\>Next**) which takes you to the next page in order - a \"Contents\" link, which takes you back to the table of contents from any page in the course You can use these to get around the course. If the \"backwards\" or \"forwards\" link takes you where you want to go, you are there with one click. If not, you can go to the table of contents and from there to wherever you want (two clicks away!). Notice too that there are some links over the vocabulary lists in each lesson providing short cuts to the general vocabularies, the list of abbreviations and the subject index. These will often help you to look up things that you can\'t remember and are not in the lesson\'s vocabulary list. ### Structure of the course If you are a new user of this course, it would be a good idea to open up **Lesson 1** (or any other lesson, if you prefer) in a separate browser window so that you can examine it while reading the following description. Each lesson consists of several learning points, which form the main part of the lesson. At the end of the lesson there is a final section containing a list of the new words in the lesson (the Vocabulary) and a practice activity (a review exercise or a reading). At the beginning of the lesson the table of contents lists the learning points. Each learning point consists of three components: (1) model sentences, (2) comments and (3) a short practice activity or exercise. Different people learn in different ways, so it is up to each learner to decide exactly how to use these. If we think of the comments as \"rules\", then the model sentences act as \"examples\" to illustrate them. Some people like to study the examples first and read the rules afterwards. If you are able to infer the rule from the model sentences, then the comment will serve to confirm your hypothesis, if it was right, or correct it, if it wasn\'t. If you follow this procedure, you will probably want to look at the translations of the model sentences, unless you can guess them, by clicking on the \"Show\" switch on the right. If, on the other hand, you prefer to work from rules to examples, then leave the translations hidden at first. After reading the comments, see if you can work out what the examples mean before looking up their meanings. You may like to consult the vocabulary at the end of the lesson as you do this; it will give you a better chance of getting them right. Don\'t skip the practice activity. You can use it to check whether you understand the point, to test yourself, or to get accustomed to the mechanisms of the language. The exercises will also help you to acquire the vocabulary. Always try the exercise with the answers hidden first before clicking on \"Show\" to see if you were right. When you come to the vocabulary list, if you have already worked through the preceding points and gone through the model sentences and exercises you should already know most of the words on the list by now. In fact, you can easily give yourself a vocabulary test, since the meaning of each word will not be visible until you click on the corresponding \"Show\" button. The exercise or reading that follows the vocabulary will touch on several of the points you have studied in the lesson and also reviews both old and new vocabulary items. Once again, hide or display the answers as it suits you. ## Where to next?

# Japanese/Introduction Japanese is spoken by 130 million people. This makes it the ninth most spoken language by native speakers. Linguists debate over the classification of the Japanese language, and one general theory asserts that Japanese is an isolated language and thus a language family of its own, known as Japonic languages. Another major theory includes Japanese as part of a hypothetical Altaic language family which spans most of Central Asia and would also include Turkic, Mongolic, Tungusic, and Korean languages. Neither of these theories has yet been generally accepted. Japan is the only country where Japanese is the sole official language (though the island of Angaur has Japanese as one of three official languages). There are, however, numerous speakers in other countries. These are largely due to emigration, most notably to the United States of America (California and Hawaii, in particular), Brazil and the Philippines. Furthermore, when Japan occupied and colonized much of East Asia, Southeast Asia, and the Pacific, the locals were educated in the Japanese language. Many elderly locals in Korea, Taiwan, and parts of China still speak Japanese. Japan has steadily developed for many centuries and, unlike many other cultures, has not been seriously affected by any major invasions until recent times. A substantial part of the vocabulary, though, has been borrowed over the years from Chinese, Portuguese, Dutch, German, French, and most recently English. ## Grammar While Japanese grammar is very regular, it is markedly different from English. Japanese has been deemed a subject--object--verb (SOV) and topic-prominent language, whereas English is a subject--verb--object (SVO) and subject-prominent language. To illustrate, the English sentence "Cats eat mice" contains a subject (cats), a verb (eat), and an object (mice), in an SVO order, where the "-s" is a *plural marker*, and "mouse" → "mice" is a plural marker by ablaut, but only the word order indicates which is the subject and the object---i.e. which is dining and which is the meal. +-------------------+----+---------------------+----+-------------------+ | Japanese culture and society is based on a hierarchy of higher status (目上 *meue*) and lower status (目下 *meshita*). As such, there are three varying levels of politeness. Because Japanese is primarily a \"vertical\" society, all relationships contain an element of relative station. For example, a student is a lower station than a teacher, and therefore a student would use polite language when speaking to a teacher, but the teacher would use plain language when speaking to a student. A salesperson talking to a customer would place himself/herself far below the customer, and would therefore use honorific language, whereas the customer would use either plain or polite language. Honorific language is not a separate category from plain and polite language, but a separate concept that uses different rules. When using honorific language, a Japanese speaker modifies nouns, verbs, and adjectives to either lower himself/herself and their associates, or exalt someone else and that individual\'s associates. Whereas the use of plain or polite language is determined by the relative station of the person *to* whom you are speaking, the use of honorific language is determined by the relative station of the person *about* whom you are speaking. Exalted language is applied when you are speaking about someone who is due respect, such as a professor, an executive, a political official, or a customer. Exalted language is only applied to other people, never to oneself. Humble language, however, is *only* applied to oneself and people associated with oneself. It would be inappropriate, for example, to use humble language to describe a beggar, even though they would be extremely low on the social ladder. ## The Japanese writing system Japanese is written mostly using three writing scripts, *kanji*, *hiragana* and *katakana*. Kanji are Chinese characters that were first introduced to Japan in the 4th century. Unlike Chinese, Japanese is a highly inflected language with words changing their ending depending on case, number, etc. For this reason, the hiragana and katakana syllabaries were created. The hiragana serve largely to show the inflection of words, as conjunctions and such. The katakana are mainly used for loan-words from other languages. ### Kanji The Japanese writing system is derived from the Chinese ideographic character set (Japanese: 漢字 *kanji*, Mandarin: 汉字 *hanzi*). They are usually very similar to Traditional Chinese characters. Though kanji are Chinese in origin their use is dictated by Japanese grammar. Each character may be read in different ways depending on the context it is in. The number of existing Chinese characters has been variously estimated at between 40,000 and 80,000; however, only a small subset is commonly used in modern Japanese. An educated Japanese person will generally be able to read between 2,000 and 4,000 characters. In order to be literate in the Japanese language, the student should strive to master at least the 2,136 general-use characters (常用漢字 -- *jōyō kanji*) established by the Ministry of Education. ### Hiragana and katakana The syllabaries, known as *kana* (), were developed around 900 AD by simplifying kanji to form the *hiragana* (ひらがな, or 平仮名) and the more angular *katakana* (カタカナ, or 片仮名). Hiragana can be recognized by the characteristic curved shapes, while katakana are identifiable by their sharp edges and straight lines. The creation of one of the scripts has been attributed to Kūkai (774-835, alias Kōbō Daishi) the famous monk who introduced Shingon Buddhism to Japan. Hiragana and katakana are almost completely phonetic---much more so than the English alphabet. Each set, however, is referred to as a *syllabary* rather than an alphabet because each character represents an entire syllable with only a single consonant (which is a more recent addition) (see ../Pronunciation/ for more). The syllabary charts in Japanese are referred to as the *gojūon* (), meaning \"fifty sounds\" because they are written in a five by ten chart. However, there are a few gaps in the table where certain sounds have fallen out of use. Modern Japanese can be written using 46 kana. In practical use, hiragana is used to write, for example, inflectional endings for adjectives and verbs (送り仮名 *okurigana*), grammatical particles (助詞 *joshi*) and auxiliaries (助動詞 *jodōshi*), Japanese words that have no kanji (or not commonly known kanji), and annotations to kanji to indicate pronunciation (振り仮名 *furigana*). Katakana is used to write, for example, foreign words and names, onomatopoeia, emphasized words (somewhat like italicized words in English text), and technical and scientific words, such as plant, animal, and mineral names. Contents ## References [^1]: 「食べる」

# Japanese/Study methods As with the study of any subject, you need to have self-discipline. Set a certain amount of time that will be devoted to the study of Japanese, and try to make a regular schedule. Don\'t rush yourself and set yourself achievable goals. The ideal method to study a language is to be exposed to the native environment with access to native speakers and have your own personal tutor. These are, however, not necessary and self-study can be rewarding in itself. ## Setting Goals Setting goals is vital. ## Kana If you are serious about learning to read and write Japanese, you must first master kana (hiragana & katakana). These are the two syllabaries, and are phonetic just like the English alphabet. Unlike English, however, Japanese pronunciation is almost perfectly regular, meaning that for the most part, one symbol stands for one sound, and there are very few pronunciation rules to learn. As a result, hiragana and katakana can easily be mastered, though fluency in reading will take longer. The kana are few enough that one can learn them by rote. To reach fluency, one eventually has to drop mnemonic devices anyway. For that transition period, or even for the few that prove difficult to memorise, mnemonics can come in handy. Once you have mastered the kana, you will be able to pronounce all the kana characters you come across, even if you don\'t know the meaning. Not to worry, though, once you build up your vocabulary, you\'ll be amazed how much more you can comprehend. ## Kanji You should begin to learn kanji immediately, as it is very time-consuming. The sooner you start, the sooner you will become proficient. There are a number of ways to learn the kanji. - In Japanese skills, they are taught by **rote.** - One can learn the **radicals**. - There are **etymology-based** mnemonics, and - **pictorial-based** mnemonics. - Calligraphy (書道 shodō) can be a mnemonic and pleasurable way to practice kanji. To learn via *radicals* (the pieces that make them up), you only need to learn the relatively few components (approximately 200), and pretty soon you will be able to guess the meaning and pronunciation of a new character with some accuracy just by looking at it. Writing kanji is an entirely different business; think of kanji as something elegant, an art. Calligraphy is commonly studied and a highly revered art in Japan. Skillfully written characters and proverbs are often hung on walls or displayed in museums, and sell for as much as paintings do in the West. A good strategy to learning all of these characters is to realize that it isn\'t anything like English, Spanish, or other European languages. When memorizing the sounds of a character, try to forget your native language, and think phonetically, rather than in your native alphabet. **Note:** As mentioned earlier, it is important not to rush yourself. The more you try to learn in one go, the easier it is for you to forget. ## See also - How to Learn a Language - Lang Infinity; Write in Japanese, or any language, and get your entries critiqued by natives.

# Japanese/Practical Lessons ## Lesson Plan A Syllabus exists for this lesson plan. ### Lesson Structure Each lesson *should* have the following sections specified: 1. **Lesson:** Lesson name. 1. **Function:** One or more functions, appropriate to the stage of learning, chosen from the Syllabus. 2. **Topic:** A topic, appropriate to the stage of learning, chosen from the Syllabus. 3. **Vocabulary:** Number of new words covered in the lesson, chosen from the Syllabus. 4. **Kanji:** Number of new Kanji covered in the lesson, chosen from the Syllabus. 5. **Grammar:** One or more grammar topics covered in lesson, chosen from the Syllabus. ### Stage I Lessons #### Reading and Writing Hiragana 1. **Lesson:** Hiragana overview 1. Voiced Consonants 2. Long vowel sounds 3. Consonant doubling: small つ 4. small や、ゆ、よ 2. **Lesson:** Hiragana vowels 1. あいうえお 2. Long vowel sounds 3. **Lesson:** Hiragana k row 1. かきくけこ 2. Voiced Consonants 3. がぎぐげご 4. **Lesson:** Hiragana s row 1. さしすせそ 2. ざじずぜぞ 5. **Lesson:** Hiragana t row 1. たちつてと 2. だぢづでど 3. Consonant doubling: small つ 6. **Lesson:** Hiragana n row 1. なにぬねの 7. **Lesson:** Hiragana h row 1. はひふへほ 2. ばびぶべぼ 3. ぱぴぷぺぽ 8. **Lesson:** Hiragana m row 1. まみむめも 9. **Lesson:** Hiragana y row 1. や、ゆ、よ 2. small や、ゆ、よ 10. **Lesson:** Hiragana r row 1. らりるれろ 11. **Lesson:** Hiragana wa, wo, n 1. わをん 12. **Lesson:** Historical Hiragana 1. ゐゑ #### Reading and Writing Katakana 1. **Lesson:** Katakana overview 1. Voiced Consonants 2. Long vowel sounds 3. Consonant doubling: small つ 4. small ヤユヨ 2. **Lesson:** Katakana vowels 1. アイウエオ 2. Long vowel sounds 3. small アイウエオ 3. **Lesson:** Katakana k row 1. カキクケコ 2. ガギグゲゴ 4. **Lesson:** Katakana s row 1. サシスセソ 2. ザジズゼゾ 5. **Lesson:** Katakana t row 1. タチツテト 2. ダヂヅデド 6. **Lesson:** Katakana n row 1. ナニヌネノ 7. **Lesson:** Katakana h row 1. ハヒフヘホ 2. バビブベボ 3. パピプペポ 8. **Lesson:** Katakana m row 1. マミムメモ 9. **Lesson:** Katakana y row 1. ヤユヨ 2. small ヤユヨ 10. **Lesson:** Katakana r row 1. ラリルレロ 11. **Lesson:** Katakana wa, wo, n 1. ワヲン 12. **Lesson:** Historical Katakana 1. ヰヱ 13. **Lesson:** Differences between Katakana and English #### Dialogue Lessons 1. **Lesson:** Will you be my friend? 1. **Topic:** Friends 2. **Function:** Greet and respond to greetings 1. \"Good morning/afternoon/evening.\" (Goodstuff: Unnecessary?) 2. \"How are you?\" (Goodstuff: Unnecessary?) 3. **Function:** Introduce and respond to introductions 1. \"Nice to meet you.\" (Goodstuff: Unnecessary?) 4. **Vocabulary:** 20 Words 5. **Kanji:** 10 Kanji 6. **Grammar:** (Goodstuff: grammar topic chosen from syllabus, need help here!) 1. The declarative 「だ」 2. The copula 「です」 1. Negative Tense 3. The question marker 「か」 4. Introduction to particles 1. Topic Particle 「は」 2. Inclusive Topic Particle 「は」 2. **Lesson:** Hobbies 1. **Topic:** Hobbies 2. **Function:** Express like and dislike 1. \"What are your hobbies?\" 2. \"What kind of \[noun\] do you like?\" 3. **Vocabulary:** 25 Words 4. **Kanji:** 10 Kanji 5. **Grammar:** (Goodstuff: grammar topic chosen from syllabus, need help here!) 1. Na-adjectives and i-adjectives 1. Negative Tense 2. Identifier Particle 「が」 3. **Lesson:** Sports 1. **Topic:** sport 2. **Function:** expressing action 3. **Vocabulary:** 20 Words 4. **Kanji:** 10 Kanji 1. 音読み and 訓読み 2. Stroke Orders 5. **Grammar** 1. Ru-verbs（一段動詞）/u-verbs（五段動詞）/exception verbs 1. Negative Verbs Tenses 2. Polite conjugations （～ます） 2. Object Particle 「を」 3. Target Particle 「に」 4. Directional Particle 「へ」 5. Context Particle 「で」 6. Specifying Time and Date 1. Numbers and Counters 7. Using 「から」 and 「まで」 4. **Lesson:** I\'m a Cat Person 1. **Topic:** Pets and Animals 2. **Function:** Expressing Ownership 1. \"Whose cat is this?\" 2. \"This is my cat\" 3. **Grammar** 1. The 「の」 particle 1. Nominalizing subordinate clauses （のが／のは） 2. Numbers and Counters 5. **Lesson:** Not Today 1. **Topic:** health 2. **Function:** obtain information, begin to provide information 1. \"What did you do yesterday?\" 2. \"I didn\'t feel good last night.\" 3. **Grammar** 1. Past tense conjugations 1. Nouns/Adjectives 2. Verbs

# Japanese/Pronunciation Japanese is characterised largely by its small number of vowels and consonants (five and fourteen, respectively). Pronunciation of each syllable is highly regular with the written system and there are only a few exceptions such as vowel devoicing. This is in stark contrast to English where the written and spoken language can differ a great deal (e.g. the vowel digraph \"ou\" in \"noun\" and \"cough\" and the consonant \"g\" in \"goat\" and \"giraffe\"). Apart from a single isolated consonant (the moraic nasal, \"n\") and double consonants (e.g. \"i**tt**e\" and \"ke**kk**on\") all consonants must be followed by a vowel to form syllables. Double consonants are always a pair of the same consonant, though vowel devoicing sometimes makes different consonants sound one after the other (e.g. \"**s**u**ki**\" and \"**s**u**teki**\"). Japanese has a great deal of homophones that make correct pronunciation quite important. While language learners may have difficulty hearing the difference between nuances like long and short vowels, native speakers are used to these and might not understand incorrectly pronounced words. ## The syllabary There are five vowels in Japanese, normally transcribed into the English alphabet as: \"a\", \"i\", \"u\", \"e\" and \"o\". +----------+----------+----------+----------+----------+----------+ | Vowel | **a** | **i** | ```{=me | **e** | ```{=me | | | | | diawiki} | | diawiki} | | | | | {{ | | {{ | | | | | Audio|Ja | | Audio|Ja | | | | | -U.oga|' | | -O.oga|' | | | | | ''u'''|h | | ''o'''|h | | | | | elp=no}} | | elp=no}} | | | | | ``` | | ``` | | | | | \* | | | +==========+==========+==========+==========+==========+==========+ | App | f | meat`<u> | f`<u> | `<u>`{ | `<u>`{ | | roximate | `<u>`{=h | `{=html} | `{=html} | =html}*e | =html}*o | | sound | tml}*a*` | *y*`</u> | oo`</u>` | *`</u>`{ | *`</u>`{ | | | </u>`{=h | `{=html} | {=html}d | =html}gg | =html}ld | | | tml}ther | | | | | +----------+----------+----------+----------+----------+----------+ \*This sound is pronounced compressed, for which there is no approximation in English. See: <http://en.wikipedia.org/wiki/Close_back_rounded_vowel#Close_back_compressed_vowel> Spanish and Italian speakers may note that Japanese vowels produce the same sounds as their Spanish and Italian equivalents. Japanese vowels always represent distinct phonemes and don\'t form digraphs --- i.e. they don\'t blend together or sound differently when joined. When one vowel follows another they are pronounced separately. Examples are the names *Sae* (sa.e) and *Aoi* (a.o.i) The rest of the syllabary is formed by combining the above vowels with a consonant. <table> <thead> <tr class="header"> <th><p>Clear</p></th> <th><p> </p></th> <th><p>Voiced</p></th> <th><p> </p></th> <th><p>Plosive</p></th> <th><p> </p></th> <th><p>Clear medial y</p></th> <th><p> </p></th> <th><p>Voiced medial y</p></th> <th><p> </p></th> <th><p>Plosive medial y</p></th> </tr> </thead> <tbody> <tr class="odd"> <td><p> </p></td> <td><p>a</p></td> <td><p>i</p></td> <td><p>u</p></td> <td><p>e</p></td> <td><p>o</p></td> <td><p> </p></td> <td><p>a</p></td> <td><p>i</p></td> <td><p>u</p></td> <td><p>e</p></td> </tr> <tr class="even"> <td><p>k</p></td> <td><p>ka</p></td> <td><p>ki</p></td> <td><p>ku</p></td> <td><p>ke</p></td> <td><p>ko</p></td> <td><p>g</p></td> <td><p>ga</p></td> <td><p>gi</p></td> <td><p>gu</p></td> <td><p>ge</p></td> </tr> <tr class="odd"> <td><p>s</p></td> <td><p>sa</p></td> <td></td> <td><p>su</p></td> <td><p>se</p></td> <td><p>so</p></td> <td><p>z</p></td> <td><p>za</p></td> <td><p><strong>ji</strong></p></td> <td><p>zu</p></td> <td><p>ze</p></td> </tr> <tr class="even"> <td><p>t</p></td> <td><p>ta</p></td> <td></td> <td></td> <td><p>te</p></td> <td><p>to</p></td> <td><p>d</p></td> <td><p>da</p></td> <td><p><strong>ji</strong></p></td> <td><p><strong>zu</strong></p></td> <td><p>de</p></td> </tr> <tr class="odd"> <td><p>n</p></td> <td><p>na</p></td> <td></td> <td><p>nu</p></td> <td><p>ne</p></td> <td><p>no</p></td> <td><p> </p></td> <td><p>ni</p></td> <td><p>nya</p></td> <td><p>nyu</p></td> <td><p>nyo</p></td> </tr> <tr class="even"> <td><p>h</p></td> <td><p>ha</p></td> <td></td> <td></td> <td><p>he</p></td> <td><p>ho</p></td> <td><p>b</p></td> <td><p>ba</p></td> <td><p>bi</p></td> <td><p>bu</p></td> <td><p>be</p></td> </tr> <tr class="odd"> <td><p>m</p></td> <td><p>ma</p></td> <td><p>mi</p></td> <td><p>mu</p></td> <td><p>me</p></td> <td><p>mo</p></td> <td><p> </p></td> <td><p> </p></td> <td><p>mi</p></td> <td><p>mya</p></td> <td><p>myu</p></td> </tr> <tr class="even"> <td><p>y</p></td> <td><p>ya</p></td> <td></td> <td><p>yu</p></td> <td></td> <td><p>yo</p></td> <td></td> <td></td> <td></td> <td></td> <td></td> </tr> <tr class="odd"> <td><p>r</p></td> <td></td> <td></td> <td></td> <td></td> <td></td> <td><p>ri</p></td> <td><p>rya</p></td> <td><p>ryu</p></td> <td><p>ryo</p></td> <td></td> </tr> <tr class="even"> <td><p>w</p></td> <td><p>wa</p></td> <td></td> <td><p><strong>o</strong></p></td> <td></td> <td></td> <td></td> <td></td> <td></td> <td></td> <td></td> </tr> </tbody> </table> Note that the sound which is written with a \"y\" is not considered a vowel, but a consonant. This will come as little surprise to German speakers where the same sound is written with a \"j\". The -i line (ki, gi, shi, ji, chi, ni, hi, bi, pi, mi, ri) can be combined with the y- line (ya, yu, yo) to create the *medial y* combinations. These are just like regular consonant + vowel syllables, in that they should be pronounced as one mora (syllabic sound). ```{=html} <div style="border: 2px solid #fd9;"> ``` From this table one can see that the Japanese syllabary is highly systematic. There are a few exceptions, though, and these have been bolded in the table: - \"si\" becomes \"**shi**\" - \"ti\" becomes \"**chi**\" and \"tu\" becomes \"**tsu**\" - \"zi\" and \"di\" become \"**ji**\", and \"du\" becomes \"**zu**\" - \"hu\" becomes \"**fu**\" - \"wo\" becomes \"**o**\" ```{=html} </div> ``` ## Mora Japanese is quite regular in the timing and stress of its syllables. The basic timing unit is called mora. Each mora is pronounced with equal stress and should take about the same amount of time. Two morae should sound twice as long as a single one. The following take up one mora: - a short vowel - a consonant followed by a short vowel - a medial y - a moraic nasal Whereas these take up two morae: - a long vowel - a double consonant ### Examples - *a-o-i* / あおい (*e.* blue): three morae, each vowel is short - *mi-do-ri* / みどり (*e.* green): three morae. - *sha-shu* / しゃしゅ (*e.* car model): two morae. - *ni-n-ji-n* / にんじん (*e.* a carrot): four morae. - *ī-e* / いいえ (*e.* no): three morae (note the long vowel \"i\", denoted by a macron) - *a-k-ka* / あっか (*e.* to worsen): three morae (note that the double consonant isn\'t pronounced twice, just twice as long). The medial y often takes a long vowel. - *gyūnyū* / ぎゅうにゅう (*e.* milk): four morae. ## Long vowels A long vowel takes two morae. In rōmaji it\'s written with a macron: *ā, ī, ū, ē and ō*. In hiragana, it\'s written with an extra \"あ\" (a), \"い\" (i) or \"う\" (u) depending on the vowel. In katakana, it\'s marked by appending a dash-like symbol \"ー\". +----------+----------+------------+--------------------------------+ | Word | Japanese | Meaning | Soundbyte | +==========+==========+============+================================+ | *Ōsaka* | 大阪 | Osaka city | There are a couple of consonants that are pronounced differently from English: Consonant Approximate sound Notes ----------- -------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- g _*g*_ive or si_*ng*_ approximately halfway between these sounds, it is made almost like *ng* depending on the age of the speaker and, in certain cases, dialect. Nowadays, it is beginning to sound more like our guttural g, but the older folks may still say *ng*, which was also taught in many Japanese grammar classes. sh, ch, j   sound is made further back along the tongue than in English ts ba_*ts*_ try saying \"fatso\" without the \"fa\" f _*wh*_o (in British English) blown between the lips, not between the lips and teeth; as if it were a combination of both H+F r   similar to a rolling *r*, but only trilled once making it sound deceptively like a *D* to untrained listeners. The sound is often described as being between \"r\" and \"l\". Except for the doubled consonants and the *n* (which we will cover later), consonants can never end a syllable. They can only begin it. ## Moraic nasal Normally, Japanese consonants must be followed by a vowel except where they double. There is an exception to this: the *moraic nasal* which is transliterated as n. It is usually found at the end of words, but can be found in the middle of composite words. The difference between the moraic nasal and the syllables \"na\", \"ni\", \"nu\", \"ne\" and \"no\" can be difficult for language learners to spot, while native speakers may have difficulty understanding incorrect pronunciation. - *kin\'en* (*ki-n-e-n*) no smoking vs. *kinen* (*ki-ne-n*) commemoration. - *hon\'ya* (*ho-n-ya-*) bookstore (not *ho-nya*) The pronunciation of the moraic nasal changes depending on what sound follows it. This is not so much an irregularity as a shortcut to bridge the sounds between the two morae. When followed by the bilabial plosives, \"b\" and \"p\", the moraic nasal is pronounced like an \"m\". An example: - \"shinbun\" is read as: *shi**m**bun* (OggVorbis, 151 KB) 1. At the end of a word: - *dan* 段 \"level\" - *kin* 金 \"gold\" - *fun* 糞 \"dung\" - *zen* 善 \"goodness\" - *hon* 本 \"book\" 2. Directly before a consonant: - *banzai* 万歳 \"hurrah\", \"long live (the Emperor)\" - *kingyo* 金魚 \"goldfish\" (pronounced like \"ng\") - *kunrei* 訓令 \"directive\" - *zenchi* 全知 \"omniscience\" (pronounced like \"n\") - *honten* 本店 \"main office\" (pronounced like \"n\") 3. Before *m*, *b*, *p* - *genmai* 玄米 \"unmilled rice\" - *honbu* 本部 \"headquarters\" - *tenpura* 天ぷら (battered and fried vegetables or fish) 4. Before *a*, *i*, *e*, *y* - *zen\'aku* 善悪 \"good and evil\" - *ken\'i* 権威 \"authority\" - *han\'ei* 反映 \"reflection\" - *sen\'you* 専用 \"exclusive use\" 5. Note that before *a*, *i*, *e*, and *y*, moraic n is written *n*\' (with an apostrophe). This is to distinguish it from the regular consonant *n*, which is pronounced differently and can produce different words. Some examples of cases where this becomes important are: - *kani* 蟹 \"crab\" **vs.** *kan\'i* 簡易 \"simplicity\" - *kinyuu* 記入 \"fill in\" **vs.** *kin\'yuu* 金融 \"finances\" - *konyakku* コニャック \"cognac\" **vs.** *kon\'yaku* 婚約 \"engagement (to be married)\" ## Consonant doubling (gemination) There are four consonants that can become geminates (get doubled) in native Japanese words: /p/, /t/, /k/, and /s/. The geminate (represented linguistically as \"Q\") takes up an extra mora, with the general effect being to insert a pause that sounds as long as a regular syllable with a short vowel. The geminate is /t/ before ch and ts, /s/ before sh. +--------------+---------------------+---------------------------------------+ | Word | Meaning | Soundbyte | +==============+=====================+=======================================+ | ta**kk**yū | table tennis | (OggVorbis, 75 KB) Word Japanese Meaning ------------- ---------- ------------------------------------------------ akai 赤 red *iro* 色 color *egaku* 描く draw (a picture) *utsu* 打つ hit, beat *osameru* 治める govern *oya* 親 parent(s) *wabi* 侘び (the Japanese aesthetic of subdued refinement) *pari* パリ Paris (France) *tomodach*i 友達 friend *hana* 花 flower *shiji* 指示 instruction *hiza* 膝 knee *tsumori* 積もり intention ### Long and double vowels (OggVorbis, 125 KB) Note in particular that \"deiri\" and \"koushi\" are not long vowels since the vowels are split between composite words. Word Japanese Meaning ------------------------ ---------- ------------------ *sā* さあ come now *ai* 愛 love *au* 会う meet *hae* 蠅 fly (insect) *aoi* 青い blue, green *ī* いい good *iu* 言う say *ie* 家 house *shio* 塩 salt *shurui* 種類 type, kind *nū* 縫う sew *ue* 上 above *uo* 魚 fish *rē* 例 example *supein* スペイン Spain *urei* 憂い grief *deiri* (*de* + *iri*) 出入り coming and going *dēta* データ data *oi* 甥 nephew *sō* そう that way, so *omou* 思う think *koushi* 仔牛 calf (baby cow) *moeru* 燃える burn *hō* 頬 cheek (facial) ### Compound consonants Audio missing Word Japanese Meaning ------------ ---------- ---------------------------------- *toukyou* 東京 Tokyo *gyouza* 餃子 pot-stickers (Chinese dumplings) *gyuunyuu* 牛乳 milk (from a cow) *hyou* 表 chart *byouin* 病院 hospital *denpyou* 伝票 voucher *myou* 妙 strange *muryou* 無料 free (as in beer) *ryuu* 龍 dragon *takkyuu* 卓球 table tennis *happyou* 発表 announcement ### Moraic nasal - (OggVorbis, 91 KB) Word Japanese Meaning ------------ ---------- ------------------------------ *tenki* 天気 weather *renshuu* 練習 practice *zangyou* 残業 overtime (work) *anshin* 安心 relief *sunnari* すんなり slender *denpa* 電波 reception (cell phone, etc.) *senbei* 煎餅 Japanese hard rice cake *genmai* 玄米 unprocessed rice *sen* 千 thousand *hon* 本 book *sen\'you* 専用 exclusive use *hon\'ya* 本屋 bookstore *san\'en* 三円 three yen *tan\'i* 単位 unit, (course) credit ### Comparisons of similarly pronounced words (OggVorbis, 190 KB) 1. *yuki* 雪 \"snow\" and *yuuki* 勇気 \"courage\" 2. *soto* 外 \"outside\" and *souto* 僧徒 \"Buddhist disciple\" 3. *soto* 外 \"outside\" and *sotou* 粗糖 \"unrefined sugar\" 4. *soto* 外 \"outside\" and *soutou* 相当 \"suitable\" 5. *soto* 外 \"outside\" and *sotto* そっと \"softly\" 6. *sotto* そっと \"softly\" and *sottou* 卒倒 \"fainting\" 7. *maki* 巻 \"scroll\" and *makki* 末期 \"last period\" 8. *hako* 箱 \"box\" and *hakkou* 発行 \"publish\" 9. *issei* 一斉 \"all at once\" and *isei* 異性 \"opposite sex\" 10. *tani* 谷 \"valley\" and *tan\'i* 単位 \"unit\", \"(course) credit\" 11. *san\'en* 三円 \"three yen\" and *sannen* 三年 \"three years\" 12. *kinyuu* 記入 \"fill out\" and *kin\'yuu* 金融 \"finances\" 13. *kinen* 記念 \"commemoration\" and *kin\'en* 禁煙 \"no smoking\" ### Normal speech The narration of the following excerpt of Natsume Soseki\'s classic novel *Botchan* is spoken at a natural pace which may be difficult to follow for unaccustomed listeners. - (OggVorbis, 674KB) : *Oyayuzuri no muteppou de kodomo no toki kara son bakari shite iru. Shougakkou ni iru jibun gakkou no nikai kara tobiorite isshuukan hodo koshi o nukashita koto ga aru. Naze sonna muyami o shita to kiku hito ga aru kamoshirenu. Betsudan fukai riyuu demo nai. Shinchiku no nikai kara kubi o dashite itara, doukyuusei no hitori ga joudan ni, \"Ikura ibatte mo, soko kara tobioriru koto wa dekimai. Yowamushi yaai,\" to hayakashita kara de aru. Kozukai ni obusatte kaette kita toki, oyaji ga ookina me o shite \"Nikai gurai kara tobiorite koshi o nukasu yatsu ga aru ka,\" to itta kara, \"Kono tsugi wa nukasazu ni tonde misemasu,\" to kotaeta.* ```{=html} <!-- --> ``` : *Shinrui no mono kara seiyousei no naifu o moratte kirei na ha o hi ni kazashite, tomodachi ni misete itara, hitori ga \"Hikaru koto wa hikaru ga, kiresou mo nai,\" to itta. \"Kirenu koto ga aru ka, nandemo kitte miseru,\" to ukeatta. \"Sonnara, kimi no yubi o kitte miro,\" to chuumon shita kara, \"Nan da yubi gurai kono toori da,\" to migi no te no oyayubi no kou o hasu ni kirikonda. Saiwai naifu ga chiisai no to, oyayubi no hone ga katakatta node, imadani oyayubi wa te ni tsuite iru. Shikashi kizuato wa shinu made kienu.*

# Japanese/Pitch accent Japanese uses **pitch accent**, where every mora can either be pronounced with a high or low pitch. Not all dictionaries will indicate this, but pitch accent is certainly important, because it can make the difference between different words. For example, using **bold** for high pitches: **い**ま (今) - \"now\"\ い**ま** (居間) - \"living room\" Pitch is, however, to some extent a characteristic of regional accents, so a Kanto speaker may be using the opposite pitches to a Kansai speaker. Where pitch is taught, it will be standard Japanese (essentially the Tokyo dialect). Pitchless Japanese is easily understood by native speakers and incorrect pitch will at most sound somewhat odd. Studying pitch, therefore, isn\'t essential to the learning Japanese and is perhaps best picked up by conversing with native speakers. Linguists, however, tend to classify Japanese as having a falling pitch following what is considered the stressed vowel. ## Mora Counting A common misconception is that moras in Japanese are the same as syllables in English. Moras differ from syllables because of how they are counted. Consonant-Vowel Combinations written as Digraphs count as 1 mora. These are cases where you have き、ぎ、し、じ、ち、に、ひ、び、ぴ、み、り combined with や、ゆ、and よ to form Digraphs like きゃ, しゅ, ちょ, etc. So, the **ちゅ** in 中国\[**ちゅ**うごく\] accounts for **1 mora**. The whole word is 4 moras. A vowel combination counts as 2 moras. Combinations like おう、えい are 2 moras. This also includes a vowel being written or said twice, like おお、いい, etc. Ex. the **せい** in the word 人生\[じん**せい**\] or the おう in だろう would count as **2 moras**. The mora **ん** counts as **1 mora** Ex. The **ん** in 先生\[せんせい\] is the 2nd mora in the word, and the whole word has 4 moras. The small tsu (**っ**) which doubles a consonant adds **1 mora**. Ex. the word 学校(がっこう) has 4 moras. There is a unique set of mora known as \"special mora\" (特殊拍) which consist of small tsu \"っ\", the kana \"ん\" and long vowel symbol \"ー\", the last high pitch can not occur on any of these \"special mora\". This is all important information to know when reading pitch accent, and counting Japanese moras. ## Pitch classification When dictionaries give pitch accent, they\'ll usually indicate it with a number. The number tells you the mora where the **last high pitch** is. To figure out the pitch pattern, put a low onto the first mora (unless the last high pitch is on that mora), put high pitches onto all the mora that follows, until you hit the last high pitch. After that, put low pitches. Even more helpful dictionaries will do all of this work for you, by telling you exactly where all the pitches rise or fall. So, to give some examples. +----------------------------------------------------------------------+ | `<span style="font-weight: normal">`{=html}low`</span>`{=html} | | **HIGH HIGH\...** | | | | ```{=html} | | <div style="float: left"> | | ``` | | \(0\) | | | | ```{=html} | | </div> | | ``` | +======================================================================+ | こ**ども** | +----------------------------------------------------------------------+ | わ**たし** | +----------------------------------------------------------------------+ | と**もだち** | +----------------------------------------------------------------------+ | ざ**っし** | +----------------------------------------------------------------------+ | あ**かい** | +----------------------------------------------------------------------+ | が**っこう** | +----------------------------------------------------------------------+ | **HIGH** `<span style="font-weight: normal">`{=html}low | | low\...`</span>`{=html} | | | | ```{=html} | | <div style="float: left"> | | ``` | | \(1\) | | | | ```{=html} | | </div> | | ``` | +----------------------------------------------------------------------+ | **ちゅ**うごく | +----------------------------------------------------------------------+ | **じ**しょ | +----------------------------------------------------------------------+ | **な**に | +----------------------------------------------------------------------+ | **は**し | +----------------------------------------------------------------------+ | **パン**フレット | +----------------------------------------------------------------------+ | `<span style="font-weight: normal">`{=html}low`</span>`{=html} | | **HIGH** `<span style="font-weight: normal">`{=html}low | | low\...`</span>`{=html} | | | | ```{=html} | | <div style="float: left"> | | ``` | | \(2\) | | | | ```{=html} | | </div> | | ``` | +----------------------------------------------------------------------+ | こ**こ**ろ | +----------------------------------------------------------------------+ | じ**て**んしゃ | +----------------------------------------------------------------------+ | プ**レ**ゼント | +----------------------------------------------------------------------+ | `<span style="font-weight: normal">`{=html}low`</span>`{=html} | | **HIGH HIGH** `<span style="font-weight: normal">`{=html}low | | low\...`</span>`{=html} | | | | ```{=html} | | <div style="float: left"> | | ``` | | \(3\) | | | | ```{=html} | | </div> | | ``` | +----------------------------------------------------------------------+ | せ**んせ**い | +----------------------------------------------------------------------+ | お**おき**い | +----------------------------------------------------------------------+ | た**くさ**ん | +----------------------------------------------------------------------+ | `<span style="font-weight: normal">`{=html}low`</span>`{=html} | | **HIGH HIGH HIGH** `<span style="font-weight: normal">`{=html}low | | low\...`</span>`{=html} | | | | ```{=html} | | <div style="float: left"> | | ``` | | \(4\) | | | | ```{=html} | | </div> | | ``` | +----------------------------------------------------------------------+ | あ**たらし**い | +----------------------------------------------------------------------+ | う**つくし**い | +----------------------------------------------------------------------+ | お**とうと** | +----------------------------------------------------------------------+ | | +----------------------------------------------------------------------+ Notice how と**もだち** (0) and お**とうと** (4) look as though they have the same pitch pattern despite the different numbers. The difference is based on the grammatical pattern like -は added afterward. Therefore, the continuation of both pitch pattern becomes と**もだちは** and お**とうと**は.