@victor unprompted feature request: I'd love to have a toggle for a HF collection to control whether new items are added to the top or to the bottom. At the moment everything gets added at the bottom, but it would be great to have newer elements on top to make fresh content easily accessible without having to scroll all the way!
This primer can serve as a comprehensive introduction to recent advances in interpretability for Transformer-based LMs for a technical audience, employing a unified notation to introduce network modules and present state-of-the-art interpretability methods.
Interpretability methods are presented with detailed formulations and categorized as either localizing the inputs or model components responsible for a particular prediction or decoding information stored in learned representations. Then, various insights on the role of specific model components are summarized alongside recent work using model internals to direct editing and mitigate hallucinations.
Finally, the paper provides a detailed picture of the open-source interpretability tools landscape, supporting the need for open-access models to advance interpretability research.
๐ Today's pick in Interpretability & Analysis of LMs: by @aadityasingh T. Moskovitz, F. Hill, S. C. Y. Chan, A. M. Saxe (@gatsbyunit)
This work proposes a new methodology inspired by optogenetics (dubbed "clamping") to perform targeted ablations during training to estimate the causal effect of specific interventions on mechanism formation.
Authors use this approach to study the formation of induction heads training a 2L attention-only transformer to label examples via context information.
Notable findings:
- The effects of induction heads are additive and redundant, with weaker heads compensating well for the ablation of a strong induction head in case the latter is ablated. - Competition between induction heads might emerge as a product of optimization pressure to converge faster, but it is not strictly necessary as all heads eventually learn to solve the task. - Previous token heads (PTH) influence induction heads in a many-to-many fashion, with any PTH eliciting above-chance prediction from a subsequent induction head - Three subcircuits for induction are identified, respectively mixing token-label information (1 + 2), matching the previous occurrence of the current class in the context (3qk + 4), and copying the label of the matched class (3v + 5). - The formation of induction heads is slowed down by a larger number of classes & labels, with more classes and more labels slowing down the formation of the matching and copying mechanisms, respectively. This may have implications when selecting a vocabulary size for LLMs: larger vocabularies lead to an increased compression ratio and longer contexts, but they might make copying more challenging by delaying the formation of induction heads.
The tool enables fine-grained customization, highlighting the importance of individual FFN neurons and attention heads. Moreover, vocabulary projections computed using the logit lens approach are provided to examine intermediate predictions of the residual stream, and tokens promoted by specific component updates.
๐ Today's pick in Interpretability & Analysis of LMs: x2 edition!
Today's highlighted works aim reproduce findings from Transformer-centric interpretability literature on new RNN-based architectures such as Mamba and RWKV:
The first paper applies contrastive activation addition, the tuned lens and probing for eliciting latent knowledge in quirky models to Mamba and RWKV LMs, finding these Transformer-specific methods can be applied with slight adaptation to these architectures, obtaining similar results.
The second work applies the ROME method to Mamba, finding weights playing the role of MLPs in encoding factual relations across several Mamba layers, and can be patched to perform model editing. A new SSM-specific technique is also introduced to emulate attention knockout (value zeroing) revealing information flows similar to the ones in Transformers when processing factual statements.