Inducing Character-level Structure in Subword-based Language Models with Type-level Interchange Intervention Training

Jing Huang, Zhengxuan Wu, Kyle Mahowald, Christopher Potts


Abstract
Language tasks involving character-level manipulations (e.g., spelling corrections, arithmetic operations, word games) are challenging for models operating on subword units. To address this, we develop a causal intervention framework to learn robust and interpretable character representations inside subword-based language models. Our method treats each character as a typed variable in a causal model and learns such causal structures by adapting the interchange intervention training method of Geiger et al. (2021). We additionally introduce a suite of character-level tasks that systematically vary in their dependence on meaning and sequence-level context. While character-level models still perform best on purely form-based tasks like string reversal, our method outperforms character-level models on more complex tasks that blend form, meaning, and context, such as spelling correction in context and word search games. Compared with standard subword-based models, our approach also significantly improves robustness on unseen token sequences and leads to human-interpretable internal representations of characters.
Anthology ID:
2023.findings-acl.770
Volume:
Findings of the Association for Computational Linguistics: ACL 2023
Month:
July
Year:
2023
Address:
Toronto, Canada
Editors:
Anna Rogers, Jordan Boyd-Graber, Naoaki Okazaki
Venue:
Findings
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
12163–12180
Language:
URL:
https://aclanthology.org/2023.findings-acl.770
DOI:
10.18653/v1/2023.findings-acl.770
Bibkey:
Cite (ACL):
Jing Huang, Zhengxuan Wu, Kyle Mahowald, and Christopher Potts. 2023. Inducing Character-level Structure in Subword-based Language Models with Type-level Interchange Intervention Training. In Findings of the Association for Computational Linguistics: ACL 2023, pages 12163–12180, Toronto, Canada. Association for Computational Linguistics.
Cite (Informal):
Inducing Character-level Structure in Subword-based Language Models with Type-level Interchange Intervention Training (Huang et al., Findings 2023)
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PDF:
https://aclanthology.org/2023.findings-acl.770.pdf
Video:
 https://aclanthology.org/2023.findings-acl.770.mp4