Hearing the speed: visual motion biases the perception of auditory tempo.

The coupling between sensory and motor processes has been established in various scenarios: for example, the perception of auditory rhythm entails an audiomotor representation of the sounds. Similarly, visual action patterns can also be represented via a visuomotor transformation. In this study, we tested the hypothesis that the visual motor information, such as embedded in a coherent motion flow, can interact with the perception of a motor-related aspect in auditory rhythm: the tempo. In the first two experiments, we employed an auditory tempo judgment task where participants listened to a standard auditory sequence while concurrently watching visual stimuli of different motion information, after which they judged the tempo of a comparison sequence related to the standard. In Experiment 1, we found that the same auditory tempo was perceived as faster when it was accompanied by accelerating visual motion than by non-motion luminance change. In Experiment 2, we compared the perceived auditory tempo among three visual motion conditions, increase in speed, decrease in speed, and no speed change, and found the corresponding bias in judgment of auditory tempo: faster than it was, slower than it was, and no bias. In Experiment 3, the perceptual bias induced by the change in motion speed was consistently reflected in the tempo reproduction task. Taken together, these results indicate that between a visual spatiotemporal and an auditory temporal stimulation, the embedded motor representations from each can interact across modalities, leading to a spatial-to-temporal bias. This suggests that the perceptual process in one modality can incorporate concurrent motor information from cross-modal sensory inputs to form a coherent experience.