On the Proper Treatment of Tokenization in Psycholinguistics

Mario Giulianelli, Luca Malagutti, Juan Luis Gastaldi, Brian DuSell, Tim Vieira, Ryan Cotterell


Abstract
Language models are widely used in computational psycholinguistics to test theories that relate the negative log probability (the surprisal) of a region of interest (a substring of characters) under a language model to its cognitive cost experienced by readers, as operationalized, for example, by gaze duration on the region. However, the application of modern language models to psycholinguistic studies is complicated by the practice of using tokenization as an intermediate step in training a model. Doing so results in a language model over *token* strings rather than one over character strings. Vexingly, regions of interest are generally misaligned with these token strings. The paper argues that token-level language models should be (approximately) marginalized into character-level language models before they are used in psycholinguistic studies to compute the surprisal of a region of interest; then, the marginalized character-level language model can be used to compute the surprisal of an arbitrary character substring, which we term a focal area, that the experimenter may wish to use as a predictor. Our proposal of marginalizing a token-level model into a character-level one solves this misalignment issue independently of the tokenization scheme. Empirically, we discover various focal areas whose surprisal is a better psychometric predictor than the surprisal of the region of interest itself.
Anthology ID:
2024.emnlp-main.1032
Volume:
Proceedings of the 2024 Conference on Empirical Methods in Natural Language Processing
Month:
November
Year:
2024
Address:
Miami, Florida, USA
Editors:
Yaser Al-Onaizan, Mohit Bansal, Yun-Nung Chen
Venue:
EMNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
18556–18572
Language:
URL:
https://aclanthology.org/2024.emnlp-main.1032
DOI:
10.18653/v1/2024.emnlp-main.1032
Bibkey:
Cite (ACL):
Mario Giulianelli, Luca Malagutti, Juan Luis Gastaldi, Brian DuSell, Tim Vieira, and Ryan Cotterell. 2024. On the Proper Treatment of Tokenization in Psycholinguistics. In Proceedings of the 2024 Conference on Empirical Methods in Natural Language Processing, pages 18556–18572, Miami, Florida, USA. Association for Computational Linguistics.
Cite (Informal):
On the Proper Treatment of Tokenization in Psycholinguistics (Giulianelli et al., EMNLP 2024)
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PDF:
https://aclanthology.org/2024.emnlp-main.1032.pdf