It has recently been shown that aspects of visual perception can be significantly altered by auditory stimuli. We asked whether the perceived direction of visual motion could be affected by auditory signals. The visual stimulus was a spatiotemporally vignetted sinewave grating (0.5 cpd, 5% contrast). Multiple frames of this stimulus were combined into short movies. Each frame lasted 125 ms, and each movie consisted of 3 frames. Between successive frames the spatial phase of the grating was altered, with nine phases sampled, ranging from 90 deg to 270 deg in increments of 18 deg. To investigate the influence of auditory signals on visual motion we paired the presentation of the movies with auditory stimuli. The auditory stimulus was a binaural amplitude-gated burst of pink noise. The total duration of the noisebursts coincided with the duration of the motion movie. The relative onset, temporal phase and amplitude of the noisebursts were controlled to create a virtual soundsource whose location and motion in 3D auditory space could be manipulated. In the rightward sound condition soundsource onset occurred at a point 2 virtual meters to the left of the head and moved at a constant velocity to a location 2 virtual meters to the right of the head. The opposite occurred in the leftward sound condition. In the no motion control condition the two ears received the same toneburst, and the sound appeared stationary and centered within the head. There was also a no sound control condition. On each trial observers were instructed to ignore the auditory stimulus and to judge the direction of visual motion. The perceived direction of visual motion was strongly influenced by the direction of concurrent auditory motion. Auditory motion not only captured ambiguous visual motion, but could even reverse the perceived direction of unambiguous visual motion. These results suggest that visual motion, a dynamic and spatiotemporal aspect of visual perception, can be altered by sound.
ASJC Scopus subject areas
- Sensory Systems