Many studies have now demonstrated that subjective synchrony between two events, such as an auditory (A) or visual event (V), can change following adaptation. For example, after repeated presentations of A leading V, observers report A leading V as more synchronous. Proposed explanations of this phenomenon include a change in unisensory neural latency, adaptation of temporally tuned channels, or a change in decisional criteria. To clarify the underlying mechanisms we measured, for the first time, whether adaptation could change sensitivity for perceived synchrony. Observers decided which of three intervals was different—one interval contained a synchronous A-V pair and the other two intervals contained identical asynchronous pairs—under four adaptation conditions: A leads V, V leads A, A-V synchrony, and no adaptation. We found that adaptation changed sensitivity. In comparison with no adaptation, adaptation to A leads V impaired the discrimination of A leads V asynchronies from synchrony, but improved the discrimination of V leads A asynchronies. The opposite pattern of results was obtained when adapting to V leads A. Finally, adaptation to A-V synchrony improved the discrimination of both A leads V and V leads A asynchronies. These selective changes are specifically inconsistent with any of the previously proposed explanations, though are consistent with certain variations of temporal channel models. In such models the effect of adaptation on perception has been related to efficient computation of the statistics of the environment in order to enhance the sensory representation of relationships that were experienced often in the recent past, as well as those that are novel.
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