Source estimation of contrast-related perception based on frequency-tagged binocular rivalry.

Binocular rivalry is a visual perceptual phenomenon which occurs when two incongruent stimuli are viewed by a subject through each eye, but only one of them is perceived at a time, with a switch in perception every few seconds, which reflects the alternation of perceptual dominance. To investigate the correlation between contrast-related perception and neural activities, the subjects' EEGs were recorded with a 64-channel electroencephalograph while experiencing binocular rivalry. A higher contrast grating flickering at one frequency was presented to one eye while a lower contrast grating flickering at a slightly different frequency was presented to the other eye. Steady-state visual evoked potentials (SSVEP) at the flickering frequencies were used to ;tag' the two stimuli. An improved inverse algorithm termed SSLOFO (standardized shrinking LORETA-FOCUSS) was used to solve this inverse problem, which acquires the spatial distribution of neural active sources from the EEG data. The result shows that activity in primary visual cortex (V1) increased when subjects perceived the higher contrast pattern and decreased when they perceived the lower contrast pattern. This paper presents a method based on EEG to investigate neural correlates of consciousness in real-time, which provides an alternative method to achieve comparable results to those based on fMRI methods.