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W. David Hairston, Mark T. Wallace, Barry E. Stein, J. William Vaughan, James A. Schirillo; Cross modal bias occurs with perceptual unity of spatially disparate signals. Journal of Vision 2001;1(3):251. doi: 10.1167/1.3.251.
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© ARVO (1962-2015); The Authors (2016-present)
The ventriloquist effect occurs when an auditory signal's perceptual location is biased in the direction of a spatially disparate visual signal. The present experiments explore the characteristics and impact of this cross-modal bias on the perceptual unification of signals. Subjects used a laser pointer to indicate the location of a broadband noise burst presented out to +/−30 degrees from midline. On most trials this sound was accompanied by an irrelevant LED light that was spatially disparate from the sound by 2.5 – 20 degrees. In experiment I, subjects made localization judgements. In experiment II, subjects also reported whether or not they perceived the two signals to be spatially coincident. In experiment III, subjects provided only judgements of visual-auditory spatial unity. In some cases the visual bias of an auditory signal equaled all the disparities between the signals. The extent of bias was less in peripheral than in central space, and least when the visual signals were lateral to the auditory signals in the periphery. There were, however, large interindividual variations in the amount of bias. Reports of spatial unity decreased with increasing visual-auditory disparity. Once again, there were large interindividual variations in the effect. In general, bias occurred when subjects reported spatial unity, and little bias occurred when spatial unity was not reported. The exact relationship between the perception of spatial unity and bias depended on the degree of spatial disparity. We hypothesize that visual-auditory bias decreased in peripheral space due to a decrease in the salience of visual signals. This is consistent with having found an increase in the variance and a decrease in the detection of peripheral visual signals. At modest spatial disparities, cross-modal signals are perceived as originating from a single location. The consequence of this perceptual unification is a biasing toward the visual signal.
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