Time and time again: isochronous sequences create temporal expectations D Rhodes, M Di Luca |
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School of Psychology, University of Birmingham, United Kingdom
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| Isochronous sequences can create expectations about future stimuli. Here we investigate how expectations can affect the perception of anisochronous stimuli. We presented a sequence of unimodal stimuli (either sounds or lights) with a final stimulus either isochronous or anisochronous. When participants judged whether the sequence appeared regular, anisochronies were detected more readily with longer sequences. In another experiment participants judged whether the last stimulus in the sequence appeared before or after a temporal probe in another modality. Perceived timing of anisochronous stimuli shifts towards the expected time based on the previous sequence. Overall, regular sequences affect individual stimuli so that as the number of prior stimuli increases the perceived time of the last stimulus is shifted towards isochrony while any presented anisochrony become more detectable. We modeled these seemingly irreconcilable effects using a Bayesian framework: the expectation of when a stimulus is to occur (prior distribution) is combined with sensory evidence (likelihood function) to give rise to perception (posterior distribution). If a stimulus is not presented when expected, its perceived timing is drawn towards isochrony by the effect of the prior probability and the difference between prior and posterior becomes more noticeable as the prior shapes up with longer sequences. |
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