Timing-induced illusory percepts of pitch

It has long been proposed that the brain integrates pitch and timing cues during auditory perception. If true, the pitch of a sound should influence its perceived timing, and the timing of a sound should similarly influence its perceived pitch. Previous research suggests that changes in the pitch of speech and music can induce illusory changes in their perceived tempo. We conducted two experiments to test the opposite effect: whether deviations from rhythmic timing can also influence the perceived pitch of a sound. In Experiment 1, participants heard an isochronous, repeating standard tone followed by a potentially mistimed, pitch-shifted probe tone, and were asked to discriminate between pitch increases and decreases. We observed a strong biasing effect of the probe's timing on its perceived pitch, such that later probes were more likely to be perceived as lower than the standard. Correct, bias-conforming responses to mistimed probes were also significantly faster than responses to probe tones played on the beat. In Experiment 2, we used an adaptive-difficulty version of Experiment 1 to investigate whether this timing-induced bias strengthens under conditions of low discriminability. We found that the biasing effects of probe timing were similarly strong regardless of how large the to-be-judged pitch difference was, and regardless of individual differences in pitch sensitivity. Alongside previous literature on pitch-induced illusory tempo changes, our present observation of timing-induced illusory pitch changes support the hypothesis that pitch and time are perceptually integrated. We discuss pitch-time integration within a Bayesian framework, as a possible result of a learned prior reflecting real-world correlations between changes in pitch and timing.