Auditory effects to complement the absence of visual information

The majority of research on audio–visual interaction focused on spatio-temporal factors and synesthesia-like phenomena. Especially, research on synesthesia-like phenomena has been advanced by Marks et al., and they found synesthesia-like correlation between brightness and size of visual stimuli and pitch of auditory stimuli (Marks, 1987). It seems that main interest of research on synesthesia-like phenomena is what perceptual similarity/difference between synesthetes and non-synesthetes is. We guessed that cross-modal phenomena of non-synesthetes on perceptual level emerge as a function to complement the absence or ambiguity of a certain stimulus. To verify the hypothesis, we investigated audio–visual interaction using movement (speed) of an object as visual stimuli and sine-waves as auditory stimuli. In this experiment objects (circles) moved at a fixed speed in one trial and the objects were masked in arbitrary positions, and auditory stimuli (high, middle, low pitch) were given simultaneously with the disappearance of objects. Subject reported the expected position of the objects when auditory stimuli stopped. Result showed that correlation between the position, i.e., the movement speed, of the object and pitch of sound was found. We conjecture that cross-modal phenomena on non-synesthetes tend to occur when one of sensory stimuli are absent/ambiguous.