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Yee Joon Kim, Robert Shapley, Nava Rubin; Coherent global percepts increase steady-state visual evoked potential (SSVEP). Journal of Vision 2010;10(7):334. doi: 10.1167/10.7.334.
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One way to study the neural basis of perception is to measure the effects of the different perceptual states induced by bi-stable visual stimuli on brain responses. Previously, we reported that the steady-state visual evoked potentials (SSVEP) to a bi-stable counter-phase flickering 8-arm radial pattern was modulated according to perceptual state, yielding higher power during perception of rotational apparent motion than during flicker perception. The current study investigated whether this dependence of SSVEP on the perceptual interpretation of an ambiguous display can be generalized to other bi-stable phenomena. We used a plaid pattern undergoing apparent motion in steps of 1/8 cycle every 50 msec, to generate 20 Hz local flicker. Similarly to continuously moving plaids, the stimulus appeared to either move as a whole in one direction (Coherency) or as two gratings sliding over each other (Transparency). The angle between the superimposed gratings was adjusted for each observer, so that the proportion of coherency percept was approximately 50%. During each 1-minute trial, observers indicated their perception continuously (coherency or transparency) by holding one of two buttons while their EEGs were recorded with 64 scalp electrodes. Coherency percept enhanced the SSVEP response at 20 Hz in the posterior (occipital) scalp region compared to the transparency percept. The results of the current study and our previous findings suggest that perceiving coherent global motion (global plaid motion or global rotation) in a dynamic bi-stable display could cause an increased phase-coherence of stimulus-driven neural activity.
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