Sounds modulate the perceived duration of visual stimuli via crossmodal integration

Previous studies have shown that the perceived duration of visual stimuli can be strongly distorted by auditory stimuli presented simultaneously. In this study, we examine whether sounds presented separately from target visual stimuli alter the perceived duration of the target's presentation. The participants' task was to classify the duration of the target visual stimuli as perceived by them into four categories. Our results demonstrate that a sound presented before and after a visual target increases or decreases the perceived visual duration depending on the inter-stimulus interval between the sounds and the visual stimulus. In addition, three tones presented before and after a visual target did not increase or decrease the perceived visual duration. This indicates that auditory perceptual grouping prevents intermodal perceptual grouping, and eliminates crossmodal effects. These findings suggest that the auditory-visual integration, rather than a high arousal state caused by the presentation of the preceding sound, can induce distortions of perceived visual duration, and that inter- and intramodal perceptual grouping plays an important role in crossmodal time perception. These findings are discussed with reference to the Scalar Expectancy Theory.