Sound alters tactile motion perception

Recently Sekuler et al. (Nature, 1997) investigated the motion-bounce illusion and found that sound can influence ambiguous visual motion perception. Here we investigated the motion-bounce illusion in the tactile-auditory domain. Using a vibro-tactile belt consisting of 7 vibrators we generated tactile apparent motion stimuli by sequentially activating neighboring motors with an onset of 200ms between the motors. Starting at the left and the right hip, two tactile motion stimuli run towards each other. On the body midline an ambiguous event was perceived: either the transition of both stimuli with continuing motion trajectories or a bounce event followed by the reversal of the movement direction. Presenting just the tactile motion stimulus resulted in an ambiguous percept. The presentation of an auditory beep at the time of the collision was sufficient to disambiguate the percept such that a significantly higher proportion of bounces was reported. The presentation of the sound 200ms or 400ms before the tactile collision event reduced the proportion bounces reported and became indistinguishable from the uni-modal baseline condition. This indicates that the temporal window of audio-tactile integration is comparable to that found in the visual-auditory domain. These results suggest that similar supramodal mechanisms exist for apparent motion perception.