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Abstract:
In binocular rivalry, the observer views two incongruent
images, one through each eye, but is conscious of only one image at
a time. In this study, human subjects experienced binocular rivalry
between two stimuli, and continuously reported which stimulus was
consciously perceived. A red vertical grating and a blue horizontal
grating were presented one to each eye and frequency tagged by
flickering each grating at a different frequency. Stimulus-evoked
steady-state magnetic fields at each stimulus frequency were
simultaneously recorded with a MEG sensor array covering the whole
head. These signals were used to study stimulus-related brain
activity when a human subject is conscious of the visual stimulus
and when he is not. The power of the steady-state response at the
frequency associated with a grating typically increased at multiple
sensors when the grating was perceived, presumably reflecting local
neural synchronization. Power modulation reached statistical
significance at sensors positioned over occipital, temporal, and
frontal cortices. To identify changes in synchronization between
distinct brain areas, coherence between pairs of widely separated
sensors was analyzed. The results showed that there was a robust
increase in both interhemispheric and intrahemispheric coherence at
the stimulus frequency when the stimulus was perceived. This study
demonstrated a direct correlation between the conscious perception
of a visual image and the synchronous activity of large populations
of neocortical neurons.
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