SourceSparse Feature Circuits: Discovering and Editing Interpretable Causal Graphs in Language Models
The authors discover sparse feature circuits for subject-verb agreement across a relative clause in both models. In both, the circuit first detects the grammatical number of the main subject, then detects the start of a modifying PP or RC, and finally promotes the matching verb inflection at the end of the clause. Gemma-2-2b additionally employs NP number tracker features that remain active on all tokens within a noun phrase of a given number. The circuits for agreement across a relative clause and across a prepositional phrase share over 85% of their features in both models, indicating a largely uniform handling of these syntactically distinct structures.