Subword models struggle with word learning, but surprisal hides it

Bastian Bunzeck, Sina Zarrieß


Abstract
We study word learning in subword and character language models with the psycholinguistic lexical decision task. While subword LMs struggle to discern words and non-words with high accuracy, character LMs solve this task easily and consistently. Only when supplied with further contexts do subword LMs perform similarly to character models. Additionally, when looking at word-level and syntactic learning trajectories, we find that both processes are separable in character LMs. Word learning happens before syntactic learning, whereas both occur simultaneously in subword LMs. This raises questions about the adequacy of subword LMs for modeling language acquisition and positions character LMs as a viable alternative to study processes below the syntactic level.
Anthology ID:
2025.acl-short.24
Volume:
Proceedings of the 63rd Annual Meeting of the Association for Computational Linguistics (Volume 2: Short Papers)
Month:
July
Year:
2025
Address:
Vienna, Austria
Editors:
Wanxiang Che, Joyce Nabende, Ekaterina Shutova, Mohammad Taher Pilehvar
Venue:
ACL
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
286–300
Language:
URL:
https://preview.aclanthology.org/acl25-workshop-ingestion/2025.acl-short.24/
DOI:
Bibkey:
Cite (ACL):
Bastian Bunzeck and Sina Zarrieß. 2025. Subword models struggle with word learning, but surprisal hides it. In Proceedings of the 63rd Annual Meeting of the Association for Computational Linguistics (Volume 2: Short Papers), pages 286–300, Vienna, Austria. Association for Computational Linguistics.
Cite (Informal):
Subword models struggle with word learning, but surprisal hides it (Bunzeck & Zarrieß, ACL 2025)
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PDF:
https://preview.aclanthology.org/acl25-workshop-ingestion/2025.acl-short.24.pdf