Changing pitch of sounds alters perceived visual motion trajectory.

Several studies have examined the effects of auditory stimuli on visual perception. In studies of cross-modal correspondences, auditory pitch has been shown to modulate visual motion perception. In particular, low-reliability visual motion stimuli tend to be affected by metaphorically or physically congruent or incongruent sounds. In the present study, we examined the modulatory effects of auditory pitch on visual perception of motion trajectory for visual inputs of varying reliability. Our results indicated that an auditory pitch implying the illusory motion toward the outside of the visual field-modulated perceived motion trajectory. In contrast, auditory pitch implying the illusory motion toward the central visual field did not affect the perception of motion trajectory. This asymmetrical effect of auditory stimuli occurred depending on the reliability of the visual input. Moreover, sounds that corresponded in terms of their pitch-elevation mapping altered the perception of the trajectory of visual motion when apparent motion could be perceived smoothly. Therefore, the present results demonstrate that auditory stimuli modulate visual motion perception especially when smooth motion is perceived in the peripheral visual field.