The Geometry of Multilingual Language Model Representations

Tyler Chang, Zhuowen Tu, Benjamin Bergen


Abstract
We assess how multilingual language models maintain a shared multilingual representation space while still encoding language-sensitive information in each language. Using XLM-R as a case study, we show that languages occupy similar linear subspaces after mean-centering, evaluated based on causal effects on language modeling performance and direct comparisons between subspaces for 88 languages. The subspace means differ along language-sensitive axes that are relatively stable throughout middle layers, and these axes encode information such as token vocabularies. Shifting representations by language means is sufficient to induce token predictions in different languages. However, we also identify stable language-neutral axes that encode information such as token positions and part-of-speech. We visualize representations projected onto language-sensitive and language-neutral axes, identifying language family and part-of-speech clusters, along with spirals, toruses, and curves representing token position information. These results demonstrate that multilingual language models encode information along orthogonal language-sensitive and language-neutral axes, allowing the models to extract a variety of features for downstream tasks and cross-lingual transfer learning.
Anthology ID:
2022.emnlp-main.9
Volume:
Proceedings of the 2022 Conference on Empirical Methods in Natural Language Processing
Month:
December
Year:
2022
Address:
Abu Dhabi, United Arab Emirates
Editors:
Yoav Goldberg, Zornitsa Kozareva, Yue Zhang
Venue:
EMNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
119–136
Language:
URL:
https://aclanthology.org/2022.emnlp-main.9
DOI:
10.18653/v1/2022.emnlp-main.9
Bibkey:
Cite (ACL):
Tyler Chang, Zhuowen Tu, and Benjamin Bergen. 2022. The Geometry of Multilingual Language Model Representations. In Proceedings of the 2022 Conference on Empirical Methods in Natural Language Processing, pages 119–136, Abu Dhabi, United Arab Emirates. Association for Computational Linguistics.
Cite (Informal):
The Geometry of Multilingual Language Model Representations (Chang et al., EMNLP 2022)
Copy Citation:
PDF:
https://aclanthology.org/2022.emnlp-main.9.pdf