[Facilitation effects of an auditory accessory stimulus on visual reaction time]

Visual reaction time (RT) is reduced when the visual stimulus is paired with an auditory stimulus. This auditory stimulus is accessory in the sense that subjects need not to pay attention to it in the visual RT task. This study examined how the facilitation effect of the auditory accessory stimulus changes with varying the stimulus onset asynchrony (SOA) between the two stimuli, and their intensities. The results showed that RTs are reduced as the visual stimulus is preceded by the auditory stimulus. Furthermore, RTs are transiently reduced when the two stimuli are presented at the same time. The magnitude of this facilitation is directly proportional to the intensity of the auditory stimulus and is inversely proportional to that of the visual stimulus. These findings suggest that there are two different kinds of facilitation effects on visual RTs made by the auditory accessory stimulus.