Superbizarre Is Not Superb: Derivational Morphology Improves BERT’s Interpretation of Complex Words

Valentin Hofmann, Janet Pierrehumbert, Hinrich Schütze


Abstract
How does the input segmentation of pretrained language models (PLMs) affect their interpretations of complex words? We present the first study investigating this question, taking BERT as the example PLM and focusing on its semantic representations of English derivatives. We show that PLMs can be interpreted as serial dual-route models, i.e., the meanings of complex words are either stored or else need to be computed from the subwords, which implies that maximally meaningful input tokens should allow for the best generalization on new words. This hypothesis is confirmed by a series of semantic probing tasks on which DelBERT (Derivation leveraging BERT), a model with derivational input segmentation, substantially outperforms BERT with WordPiece segmentation. Our results suggest that the generalization capabilities of PLMs could be further improved if a morphologically-informed vocabulary of input tokens were used.
Anthology ID:
2021.acl-long.279
Volume:
Proceedings of the 59th Annual Meeting of the Association for Computational Linguistics and the 11th International Joint Conference on Natural Language Processing (Volume 1: Long Papers)
Month:
August
Year:
2021
Address:
Online
Editors:
Chengqing Zong, Fei Xia, Wenjie Li, Roberto Navigli
Venues:
ACL | IJCNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
3594–3608
Language:
URL:
https://aclanthology.org/2021.acl-long.279
DOI:
10.18653/v1/2021.acl-long.279
Bibkey:
Cite (ACL):
Valentin Hofmann, Janet Pierrehumbert, and Hinrich Schütze. 2021. Superbizarre Is Not Superb: Derivational Morphology Improves BERT’s Interpretation of Complex Words. In Proceedings of the 59th Annual Meeting of the Association for Computational Linguistics and the 11th International Joint Conference on Natural Language Processing (Volume 1: Long Papers), pages 3594–3608, Online. Association for Computational Linguistics.
Cite (Informal):
Superbizarre Is Not Superb: Derivational Morphology Improves BERT’s Interpretation of Complex Words (Hofmann et al., ACL-IJCNLP 2021)
Copy Citation:
PDF:
https://aclanthology.org/2021.acl-long.279.pdf
Video:
 https://aclanthology.org/2021.acl-long.279.mp4
Code
 valentinhofmann/superbizarre