Abstract
Vision is considered the dominant modality particularly in the domain of spatial perception. Thus, judgments on the spatial aspects of a visual stimulus are expected not to be significantly affected by characteristics of accompanying sounds etc. We provide evidence to the contrary. Methods: A red uniform disk was briefly flashed either in the fovea or in periphery. The flash was accompanied with a brief binaural tone which simulated a sound a) stationary in space, b) moving horizontally to the left, or c) to the right. Participants were asked to judge in each trial whether the disk was stationary, or moving horizontally. Eye movements were monitored throughout the experiment. Although the visual stimulus was stationary in all trials, observers perceived the disk (only when in periphery) as moving in the majority of trials when it was accompanied by auditory motion. We refer to this phenomenon as sound-induced illusory visual motion. In a second experiment, we added conditions in which the disk was physically moving to the left or right. As before, observers reported perceiving motion when the stationary disk was accompanied by moving sound. In addition, we found a reverse effect: some of the moving flashes which were accompanied by stationary sound were perceived as stationary. This effect was significantly smaller than the illusory motion effect, however. In a third experiment, in which the continuously moving sound was replaced by discrete sounds, we found that illusory visual motion can also be induced by apparent auditory motion. Conclusion: Various control conditions indicated that the illusory motion is a perceptual illusion and is not due to a cognitive bias derived from knowledge of the sound. The results altogether demonstrate that a moving sound (real or apparent) can induce perception of motion for a temporally coincident visual stimulus in the periphery. These findings counter the general belief that vision is unconditionally the dominant modality in spatial perception. Support: NIH grant HD08506.