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 its timing should influence its perceived pitch. Previous research has found that higher-pitched sounds tend to be perceived as faster than lower-pitched sounds, and in the present study we investigated whether sounds that arrive earlier or later than expected are similarly perceived as higher or lower in pitch. In Experiment 1, participants heard isochronous, repeating standard tones followed by a pitch-shifted probe, and indicated if the pitch increased or decreased. 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 on-beat probes. In Experiment 2, we used an adaptive difficulty procedure to investigate whether this timing-induced bias strengthens under conditions of low discriminability. We did not find evidence that bias varies with the magnitude of pitch change or with individual differences in pitch sensitivity. In conjunction with past findings of pitch-induced illusory timing changes, our results support the hypothesis that pitch and time are perceptually integrated. We discuss this integration within a Bayesian predictive coding framework, as possibly learned from real-world correlations between pitch and timing that derive from latent properties of sound sources.