A Mechanistic Interpretation of Arithmetic Reasoning in Language Models using Causal Mediation Analysis

Alessandro Stolfo, Yonatan Belinkov, Mrinmaya Sachan


Abstract
Mathematical reasoning in large language models (LMs) has garnered significant attention in recent work, but there is a limited understanding of how these models process and store information related to arithmetic tasks within their architecture. In order to improve our understanding of this aspect of language models, we present a mechanistic interpretation of Transformer-based LMs on arithmetic questions using a causal mediation analysis framework. By intervening on the activations of specific model components and measuring the resulting changes in predicted probabilities, we identify the subset of parameters responsible for specific predictions. This provides insights into how information related to arithmetic is processed by LMs. Our experimental results indicate that LMs process the input by transmitting the information relevant to the query from mid-sequence early layers to the final token using the attention mechanism. Then, this information is processed by a set of MLP modules, which generate result-related information that is incorporated into the residual stream. To assess the specificity of the observed activation dynamics, we compare the effects of different model components on arithmetic queries with other tasks, including number retrieval from prompts and factual knowledge questions.
Anthology ID:
2023.emnlp-main.435
Volume:
Proceedings of the 2023 Conference on Empirical Methods in Natural Language Processing
Month:
December
Year:
2023
Address:
Singapore
Editors:
Houda Bouamor, Juan Pino, Kalika Bali
Venue:
EMNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
7035–7052
Language:
URL:
https://aclanthology.org/2023.emnlp-main.435
DOI:
10.18653/v1/2023.emnlp-main.435
Bibkey:
Cite (ACL):
Alessandro Stolfo, Yonatan Belinkov, and Mrinmaya Sachan. 2023. A Mechanistic Interpretation of Arithmetic Reasoning in Language Models using Causal Mediation Analysis. In Proceedings of the 2023 Conference on Empirical Methods in Natural Language Processing, pages 7035–7052, Singapore. Association for Computational Linguistics.
Cite (Informal):
A Mechanistic Interpretation of Arithmetic Reasoning in Language Models using Causal Mediation Analysis (Stolfo et al., EMNLP 2023)
Copy Citation:
PDF:
https://aclanthology.org/2023.emnlp-main.435.pdf
Video:
 https://aclanthology.org/2023.emnlp-main.435.mp4