Meaningful sounds enhance visual sensitivity to human gait regardless of synchrony

Previous research demonstrates that meaningfully related sounds enhance visual sensitivity to point-light displays of human movement. Here we report two psychophysical studies that investigated whether, and if so when, this facilitation is modulated by the temporal relationship between auditory and visual stimuli. In Experiment 1, participants detected point-light walkers in masks while listening to footsteps that were either synchronous or out-of-phase with point-light footfalls. The relative timing of auditory and visual walking did not impact performance. Experiment 2 further tested the importance of multisensory timing by disrupting the rhythm of the auditory and visual streams. Participants detected point-light walkers while listening to footstep or tone sounds that were either synchronous or temporally random with regards to point-light footfalls. Heard footsteps improved visual sensitivity over heard tones regardless of timing. Taken together, these results suggest that during the detection of others' actions, the perceptual system makes use of meaningfully related sounds whether or not they are synchronous. These results are discussed in relation to the unity assumption theory as well as recent empirical data that suggest that temporal correspondence is not always a critical factor in multisensory perception and integration.