Fine-Tuning Enhances Existing Mechanisms: A Case Study on Entity Tracking
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Abstract (arXiv)
Fine-tuning on generalized tasks such as instruction following, code generation, and mathematics has been shown to enhance language models' performance on a range of tasks. Nevertheless, explanations of how such fine-tuning influences the internal computations in these models remain elusive. We study how fine-tuning affects the internal mechanisms implemented in language models. As a case study, we explore the property of entity tracking, a crucial facet of language comprehension, where models fine-tuned on mathematics have substantial performance gains. We identify the mechanism that enables entity tracking and show that (i) in both the original model and its fine-tuned versions primarily the same circuit implements entity tracking. In fact, the entity tracking circuit of the original model on the fine-tuned versions performs better than the full original model. (ii) The circuits of all the models implement roughly the same functionality: Entity tracking is performed by tracking the position of the correct entity in both the original model and its fine-tuned versions. (iii) Performance boost in the fine-tuned models is primarily attributed to its improved ability to handle the augmented positional information. To uncover these findings, we employ: Patch Patching, DCM, which automatically detects model components responsible for specific semantics, and CMAP, a new approach for patching activations across models to reveal improved mechanisms. Our findings suggest that fine-tuning enhances, rather than fundamentally alters, the mechanistic operation of the model.
Key facts. Cited by 140 papers in the map (data through 7 Oct 2026). Builds on 35 of its 51 references that are in the map. First posted on arXiv 22 Feb 2024.
Builds on
35 of 51 references.
References · 35
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- 2020Similarity Analysis of Contextual Word Representation Modelscited by 54
- 2023Entity Tracking in Language Modelscited by 44
- 2021A Closer Look at How Fine-tuning Changes BERTcited by 42
- 2023Discovering Variable Binding Circuitry with Desideratacited by 32
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Citing papers per year: 2024: 36; 2025: 50; 2026: 54.
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