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A bias generating temporal distortions in serial perception

A precise estimation of event timing is essential for survival.1 Yet, temporal distortions are ubiquitous in our daily sensory experience.2 A specific type of temporal distortion is the time order error (TOE), which occurs when estimating the duration of events organized in a series.3 TOEs shrink or dilate objective event duration. Understanding the mechanics of subjective time distortions is fundamental since we perceive events in a series, not in isolation. In previous work,4 we showed that TOEs appear when discriminating small duration differences (20 or 60 ms) between two short events (Standard, S and Comparison, C), but only if the interval between events is shorter than 1 second. TOEs have been variously attributed to sensory desensitization,5,6 reduced temporal attention,7,4 poor sensory weighting of C relative to S,8 or idiosyncratic response bias.6Surprisingly, the serial dynamics of relative event duration were never considered as a factor generating TOEs. In two experiments we tested them by swapping the order of presentation of S and C. Bayesian hierarchical modelling showed that TOEs emerge when the first event in a series is shorter than the second event, independently of event type (S or C), sensory precision or individual response bias. Participants disproportionately expanded first-position shorter events. Significantly fewer errors were made when the first event was objectively longer, confirming the inference of a strong bias in perceiving ordered event durations. Our finding identifies a hitherto unknown duration-dependent encoding inefficiency in human serial perception.