Recent works show that sound can alter the visual perception qualitatively on a large scale. However, it is not clear whether the interaction between two modalities, auditory and visual perception, occurs at the early stage of sensory processing or late stage of perceptual processing, perceptual organization. The purpose of this study was to investigate whether or not sound facilitate the detection of a visual target without auditory perceptual organization, the grouping of parts into larger units. 5 subjects took part in the experiment to detect a visual target in a rapidly changing sequence of visual distracters under three sound conditions (741Hz, 1000Hz, and 1259Hz). Sound was synchronized with visual stimuli involving a target and distracters. In the experimental condition, the visual target stimulus was synchronized with the salient sound of a frequency different from those of other sounds. In the control condition, the visual target was synchronized with the sound of the same frequency as the other sounds. The mean reaction times were significantly shorter under the experimental condition than under the control condition. On the contrary, there were no significant differences in target detection rate between two conditions. These results suggest that sound does not exert any influence on the detection of the visual target without auditory perceptual organization. We conclude cross-modal interaction is related to the higher perceptual processing that may lead to perceptual organization.
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