The benefit of multisensory integration with biological motion signals

Assessing intentions, direction, and velocity of others is necessary for most daily tasks, and such information is often made available by both visual and auditory motion cues. Therefore, it is not surprising our great ability to perceive human motion. Here, we explore the multisensory integration of cues of biological motion walking speed. After testing for audiovisual asynchronies (visual signals led auditory ones by 30 ms in simultaneity temporal windows of 76.4 ms), in the main experiment, visual, auditory, and bimodal stimuli were compared to a standard audiovisual walker in a velocity discrimination task. Results in variance reduction conformed to optimal integration of congruent bimodal stimuli across all subjects. Interestingly, the perceptual judgements were still close to optimal for stimuli at the smallest level of incongruence. Comparison of slopes allows us to estimate an integration window of about 60 ms, which is smaller than that reported in audiovisual speech.