Synchronized sound bursts disrupt visual apparent motion

Abstract

Identical discs moving in opposite trajectories generate perception of an event that is bistable between a passing and a bouncing percept. This bistability can be biased toward bouncing when a burst of sound is presented at the time of trajectory contact. This cross- modal effect is considered to involve arousal and/or an event-based interpretation that a burst of sound implies collision. Alternatively, a synchronized sound burst may facilitate a bouncing percept by disrupting continuous motion perception. We employed a motion-aftereffect paradigm to test this possibility because the strength of motion processing can be inferred from the duration of the motion aftereffect without asking observers to introspect about the quality of perceived motion. This paradigm also allowed us to evaluate effects of sound on motion adaptation (by presenting sound bursts during adaptation) as well as on motion perception (by presenting sound bursts during perception of the motion aftereffect). We used a flicker motion aftereffect so that we could present brief (10 ms) bursts of white noise either synchronously or asynchronously with the visual stimuli. The adaptor stimulus displayed rotational apparent motion and the test stimulus displayed rotationally ambiguous flicker, which appeared to rotate in the direction opposite to adaptation until the adaptation wore off. The frame rate was always 4 Hz (producing robust apparent motion). The synchronized sound bursts reduced the duration of the motion aftereffect whether they were presented during adaptation or test. These effects were not due to increased arousal or cross-modal distraction because the sound bursts produced no effects when they were presented in anti-phase with the visual display. Synchronized sound bursts thus interfere with visual apparent motion processing both in terms of reducing motion adaptation and disrupting motion perception. This cross-modal effect may originate from the experience that sound bursts frequently accompany changes in motion direction.