Lexical surprisal drives pupil dilation during continuous story listening

Lexical surprisal during naturalistic story listening is selectively tracked by pupil dilation in a 1,700–2,350 ms window after word onset for forward speech, not reversed control speech.

• Why it matters: Pupil dynamics are linked to internal arousal and mental effort, but it is unclear which cognitive computations drive them in naturalistic settings beyond tightly controlled visual tasks.
• What they did: Volunteers listened to spoken stories in darkness with either intact (forward) or unintelligible reversed speech while pupil responses were recorded, testing whether dilation tracks lexical surprisal.
• The result: Pupil-linked arousal is tuned to global, context-dependent processing, indexing the cognitive cost of updating predictive models during naturalistic listening.

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