The interplay between motion perception and perceptual completion

Effective visual perception surmounts noise, partial information and dynamic changes in stimuli, resulting in perceptual completion that is often studied using illusory contour (IC) stimuli. Visual evoked potentials (VEPs) from humans yield a characteristic response - the IC_effect - the VEP difference between responses to the presence vs. absence of ICs with multiple phases at ∼150-200 ms and ∼240-400 ms post-stimulus onset. To address how motion signals and an individual's capability to discriminate motion may contribute to perceptual completion as indexed by the IC_effect, we recorded 128-channel VEPs from 20 healthy adults. On each trial, they indicated which of two stimulus arrays was perceived to move (through linear changes in stimulus size), independently of the presence/absence of ICs. Participants were sub-divided based on a median split in task performance: those "adept" and "non-adept" at detecting moving stimuli. Over the 240-329 ms post-stimulus period, responses from "adept" individuals were characterized by distinct topographies depending on whether stimuli were moving, whereas for "non-adept" individuals the same topography characterized responses to both moving and static stimuli (p = 0.048; η²ₚ=0.300). Furthermore, the VEP topography characterizing responses to moving ICs positively correlated with an individual's motion discrimination accuracy (Spearman's rho₍₁₈₎= 0.467; p = 0.038). Source modelling of this IC_effect included regions of the lateral inferior occipital cortices, parahippocampal cortices extending into the insula, the precentral cortex, and middle frontal cortex and underscores the role of both low-level and high-level cortices in IC perception. Collectively, these data highlight the interplay between motion discrimination and perceptual completion processes.