Low-Level Visual Processing Speed Modulates Judgment of Audio-Visual Simultaneity

Abstract

Temporal consistency between visual and auditory presentations is necessary for integration of visual and auditory information. Subjective simultaneity perception is more important than the synchrony of physical inputs for temporal consistency. Our previous studies have shown that audio-visual integration is difficult even if the visual and auditory inputs are physically synchronous when visual processing is slow. In the present study, we examined the effects of visual processing speed on audio-visual integration using a simultaneity judgment task. Visual processing speed was manipulated by varying the spatial frequency of visual stimuli. High spatial frequency stimuli require a longer processing time because visual responses to high spatial frequencies are slow. The results indicated that the difference between subjective and physical synchrony was larger in high spatial frequency than in low spatial frequency. Thus, the spatial frequency of the visual stimulus affected the judgments of simultaneity for visual and auditory stimuli. The effects of visual processing speed on audio-visual integration are believed to occur at a lower-order stage of sensory processing.