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David McCormick, Pascal Mamassian; Audio-visual synchrony in an Apparent-motion discrimination task. Journal of Vision 2007;7(9):871. doi: 10.1167/7.9.871.
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We present a new method designed to study the effect of audio-visual synchrony on visual contrast sensitivity. We displayed a two-frame apparent-motion stimulus composed of square-wave bar trains. The bars in a given frame spanned 30 arcmin and were separated by 6 degrees of arc. They were shifted by 90 arcmin left or right between frames. The first frame contained a suprathreshold bar train while the second comprised a low contrast bar train. Each set of bars was displayed for 33.3ms with four stimulus onset asynchronies (SOAs) varying between 100 and 300ms. Each trial contained an auditory beep of 33.3ms duration, temporally concomitant with either the first or second set of bars. When the second frame was visible, apparent-motion was seen. Observers were required to indicate the direction of the motion on each trial; data were analysed according to the temporal location of the beep, at each of the low contrast values. The data show a trend toward improved performance when beeps were synchronous with the low contrast frames. The efficacy of this method is that the required response (left/right motion) is on a dimension orthogonal to the point of interest (contrast sensitivity). We are therefore able to reject cueing and attentional based accounts and we discuss the attribution of this effect to a cross-modal integration of the visual and auditory systems.
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