A Mechanistic Analysis of a Transformer Trained on a Symbolic Multi-Step Reasoning Task

Jannik Brinkmann, Abhay Sheshadri, Victor Levoso, Paul Swoboda, Christian Bartelt


Abstract
Transformers demonstrate impressive performance on a range of reasoning benchmarks. To evaluate the degree to which these abilities are a result of actual reasoning, existing work has focused on developing sophisticated benchmarks for behavioral studies. However, these studies do not provide insights into the internal mechanisms driving the observed capabilities. To improve our understanding of the internal mechanisms of transformers, we present a comprehensive mechanistic analysis of a transformer trained on a synthetic reasoning task. We identify a set of interpretable mechanisms the model uses to solve the task, and validate our findings using correlational and causal evidence. Our results suggest that it implements a depth-bounded recurrent mechanisms that operates in parallel and stores intermediate results in selected token positions. We anticipate that the motifs we identified in our synthetic setting can provide valuable insights into the broader operating principles of transformers and thus provide a basis for understanding more complex models.
Anthology ID:
2024.findings-acl.242
Volume:
Findings of the Association for Computational Linguistics ACL 2024
Month:
August
Year:
2024
Address:
Bangkok, Thailand and virtual meeting
Editors:
Lun-Wei Ku, Andre Martins, Vivek Srikumar
Venue:
Findings
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
4082–4102
Language:
URL:
https://aclanthology.org/2024.findings-acl.242
DOI:
Bibkey:
Cite (ACL):
Jannik Brinkmann, Abhay Sheshadri, Victor Levoso, Paul Swoboda, and Christian Bartelt. 2024. A Mechanistic Analysis of a Transformer Trained on a Symbolic Multi-Step Reasoning Task. In Findings of the Association for Computational Linguistics ACL 2024, pages 4082–4102, Bangkok, Thailand and virtual meeting. Association for Computational Linguistics.
Cite (Informal):
A Mechanistic Analysis of a Transformer Trained on a Symbolic Multi-Step Reasoning Task (Brinkmann et al., Findings 2024)
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PDF:
https://aclanthology.org/2024.findings-acl.242.pdf