Syntactic Belief Update as the Driver of Garden Path Processing Difficulty

Alan Zhou, Miloš Stanojević, John T. Hale


Abstract
Garden path sentences present a processing difficulty for humans— the sentence prefix leads the listener towards one interpretation, until the listener hears a critical word that shows that the initial interpretation was wrong. Lexical surprisal, a measure that usually predicts sentence processing difficulty quite well, fails to provide good predictions for garden path sentences.

We propose an alternative that actively predicts a distribution over syntactic trees (its syntactic belief) and updates that distribution after each new word. If a processor is led down a garden path, syntactic beliefs will be wrong, requiring a large update at the critical word. The magnitude of the update is measured with a Rényi divergence. Crucially, this metric is dependent on lexical items, but is distinct from lexical probability and measures a degree of belief update over non-lexical syntactic structure only. This Syntactic Belief Update provides a better fit to human reading time data on garden path sentences, suggesting a new research direction examining non-lexical alternatives to surprisal for psycholinguistics.
Anthology ID:
2026.emnlp-main.1805
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
41137–41156
Language:
URL:
https://aclanthology.org/2026.emnlp-main.1805/
DOI:
Bibkey:
Cite (ACL):
Alan Zhou, Miloš Stanojević, and John T. Hale. 2026. Syntactic Belief Update as the Driver of Garden Path Processing Difficulty. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 41137–41156, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Syntactic Belief Update as the Driver of Garden Path Processing Difficulty (Zhou et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.1805.pdf