Change-point oddball elicits pupil-linked signatures of Bayesian belief updating
The auditory oddball protocol is widely used to study neural responses to unexpected events. In conventional designs, however, stimulus statistics are stationary: deviants do not indicate environmental change and therefore should not drive learning. Here, we introduce change-point oddball, a passive, no-report protocol in which the standard-oddball mapping reverses at unpredictable change points, requiring inference over latent environmental states. We measured pupil-linked arousal in three human cohorts. Pupil responses were larger for state-specific oddballs than standards, decayed across newly established standards after state changes, and scaled with model-derived change-point probability. A many-standards control experiment implicated a prediction-based rather than repetition-based mechanism. Finally, within participants, stronger pupil encoding of change-point probability during the passive task was associated with greater change-point-sensitive belief updating in a separate active navigation task. Thus, passive change-point oddball preserves core signatures of adaptive belief updating, enabling cross-species and clinical investigations.