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Towards A Scanpath-Conditioned Surprisal Theory: Modeling Reader Information States

Paper · 2026 · Michael Mooney and Edmond S. L. Ho

Summary

Surprisal theory usually measures how predictable a word is from the full written prefix. That choice assumes a reader who sees every word in order and remembers all of it. Real readers skip words, go back, and forget. Mooney and Ho keep the outcome space and change the conditioning context instead: predictability is computed from what a particular reader has actually fixated, according to their scanpath, and from what memory still makes accessible.

They define two families of variants:

  • Deterministic: a dense context up to the furthest word reached, or a sparse context containing only fixated words.
  • Stochastic: a random accessibility mask over past fixations models forgetting, and surprisal is estimated by Monte Carlo averaging of language-model probabilities.

On the OneStop and CELER eye-tracking corpora, scanpath-conditioned surprisal achieves better held-out log-likelihood on duration-based reading measures than standard surprisal. The authors take this as evidence that surprisal's weak account of non-linear reading stems partly from how the context is defined, not from the theory itself.

Key points

  • Model suite:
    • M0;dense and M0;sparse assume perfect memory.
    • M1 uses kernelized, recency-based forgetting.
    • M2 uses retrieval-based accessibility that is sensitive to how often a word was fixated.
    • Belief-update (BU) and information-gain (IG) extensions are added on top.
  • Base models and data: ModernBERT (masked) and Pythia-70m (autoregressive) were tested on OneStop and CELER across four reading regimes, including ordinary and repeated reading. Parameters were tuned on OneStop and held fixed for all evaluations.
  • Main ranking: M1 and M2 consistently beat M0, and M2 beats M1. BU/IG add further gains, with IG helping proportionally more under M2. Gains are much larger with ModernBERT, although M0;dense does best under the autoregressive model in ordinary reading.
  • Where it helps and where it does not: gains appear in measures such as GD, FRT and RGD. FFD and RGo-Past barely improve, which suggests that the cost of reintegration after a regression lies outside expectation-based accounts.
  • Limitations: results on CELER are volatile, which the authors attribute to its sentence-level stimuli producing denser scanpaths. The BU/IG extension is expensive, needing tens of GB of GPU memory per batch.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Institutions

 Fields, topics and concepts

Cite

Cite as Michael Mooney and Edmond S. L. Ho. 2026. Towards A Scanpath-Conditioned Surprisal Theory: Modeling Reader Information States. Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers).

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.18653/v1/2026.acl-long.1919

@inproceedings{mooney2026scanpath,
  title = {{Towards A Scanpath-Conditioned Surprisal Theory: Modeling Reader Information States}},
  author = {Michael Mooney and Edmond S. L. Ho},
  booktitle = {Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)},
  year = {2026},
  doi = {10.18653/v1/2026.acl-long.1919},
  url = {https://doi.org/10.18653/v1/2026.acl-long.1919}
}

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