Audiovisual influences on the perception of visual apparent motion: exploring the effect of a single sound

Previous research has shown that irrelevant sounds can facilitate the perception of visual apparent motion. Here the effectiveness of a single sound to facilitate motion perception was investigated in three experiments. Observers were presented with two discrete lights temporally separated by stimulus onset asynchronies from 0 to 350 ms. After each trial, observers classified their impression of the stimuli using a categorisation system. A short sound presented temporally (and spatially) midway between the lights facilitated the impression of motion relative to baseline (lights without sound), whereas a sound presented either before the first or after the second light or simultaneously with the lights did not affect motion impression. The facilitation effect also occurred with sound presented far from the visual display, as well as with continuous-sound that was started with the first light and terminated with the second light. No facilitation of visual motion perception occurred if the sound was part of a tone sequence that allowed for intramodal perceptual grouping of the auditory stimuli prior to the critical audiovisual stimuli. Taken together, the findings are consistent with a low-level audiovisual integration approach in which the perceptual system merges temporally proximate sound and light stimuli, thereby provoking the impression of a single multimodal moving object.