Auditory Rhythm Biases Visual Speed Perception and Shows Tempo-Dependent Signatures During Motion Extrapolation

Auditory signals can bias visual motion judgements, but how dynamic auditory structure affects variable-speed motion during perception and subsequent extrapolation remains unclear. Across three experiments, we paired changing visual motion with changes in auditory tempo or pitch. In Experiment 1, slow and fast tempi produced robust, opposite shifts in the point of subjective equality for visual speed-change judgements, without reliable evidence for a change in discrimination precision in this paradigm. Experiment 2 revealed a weaker asymmetric pitch effect: Descending pitch shifted judgements toward deceleration, whereas ascending pitch produced no reliable opposite shift. A pooled comparison localized the tempo-pitch difference primarily to the speeding-direction bias rather than psychometric slope. In Experiment 3, the omnibus three-level auditory effect on manual time-to-contact (TTC) was not significant; however, within the two sound-present conditions, accelerating tempo shortened mean manual TTC by approximately 32 ms relative to decelerating tempo. The corresponding primary eye-TTC contrast was small and not significant, although time-resolved eye analyses revealed a transient postocclusion eye-velocity effect together with broader sound-related pupil responses. Leave-one-condition-out model comparison nevertheless showed that the same tempo-by-physical-TTC functional model provided the best held-out prediction for both manual and eye-based estimates. Together, these findings indicate robust auditory-tempo biases in online visual speed judgements and more qualified, tempo-dependent signatures during forward extrapolation after visual information disappears; the absence of a JND effect here should not be generalized to all audiovisual motion tasks.