Neural Mechanism Of The Flash-induced Bouncing Effect

Two identical visual disks moving towards each other on a two-dimensional display are more likely to be perceived as "streaming through" than "bouncing off" each other after their coincidence.However,either a brief auditory tone or visual flash presented at the coincident moment of the disks can strikingly increase the incidence of the bouncing percept.Despite the neural substrates underlying the sound-induced bouncing effect have been widely investigated,little is known about the neural mechanisms underlying the flash-induced bouncing effect.The Experiment 1 used event-related potential(ERP)recordings to explore the temporal dynamics of the flash-induced bouncing effect.The results showed that the amplitude of the post-coincidence parieto-occipital P2 component(190-230 ms after coincidence)elicited by the visual motion was significantly smaller on bouncing relative to streaming trials only when the flash was presented but not when absent.In addition,the parietal P3 component(330-430 ms)was found to be larger on bouncing than streaming trials when the flash was presented,but the opposite was true when no flash was presented.These electrophysiological findings suggest that the flash-induced bouncing effect may occur at both perceptual and post-perceptual stages of processing.On the basis of the experiment 1,the experiment 2 also used the ERP recordings,and the experimental stimulus were improved.A slow-motion version of the stream/bounce motion display was used to further extract the bouncing percept trials only induced by FBE The within-subject(percept-based)analysis showed that under the FBE condition,the amplitude of parieto-occipital P2 component(190-230ms after coincidence)of the streaming trials was significantly larger than bouncing trials,and the parietal P3 component(330-430ms)of bouncing trials was significantly larger than that of streaming trials.The between-subject analysis indicated that there was no significant difference between the subjects of P2 and P3 components under the FBE condition.The results of Experiment 2 showed that the neural activity of the perceptual and post-perceptual stages of processing underlying the occurrence of flash-induced bouncing effect were necessary but not sufficient for eventually determining the FBE magnitude.