Depth cues and perceived audiovisual synchrony of biological motion.

Background: Due to their different propagation times, visual and auditory signals from external events arrive at the human sensory receptors with a disparate delay. This delay consistently varies with distance, but, despite such variability, most events are perceived as synchronic. There is, however, contradictory data and claims regarding the existence of compensatory mechanisms for distance in simultaneity judgments.

Principal Findings: In this paper we have used familiar audiovisual events--a visual walker and footstep sounds--and manipulated the number of depth cues. In a simultaneity judgment task we presented a large range of stimulus onset asynchronies corresponding to distances of up to 35 meters. We found an effect of distance over the simultaneity estimates, with greater distances requiring larger stimulus onset asynchronies, and vision always leading. This effect was stronger when both visual and auditory cues were present but was interestingly not found when depth cues were impoverished.

Significance: These findings reveal that there should be an internal mechanism to compensate for audiovisual delays, which critically depends on the depth information available.