Comparing inter-ocular switch and classical binocular rivalry in the human brain using eeg

When disparate visual stimuli are presented to corresponding retinal locations in the two eyes, perception fluctuates between the presented stimuli. This phenomenon, called binocular rivalry, is an exquisite tool to dissociate sensory stimulation from visual perception. It has therefore been extensively used for studying the neural correlates of visual awareness. Initial theories have tried to explain binocular rivalry by hypothesizing the resolution of competition in V1 through inhibitory interactions between monocular neurons. However, inter-ocular switch rivalry, a paradigm where the rivaling stimuli are rapidly exchanged between the eyes also results in stable percepts that span several swaps of the visual stimuli. This has demonstrated that competition also involves higher level stimulus representations, and not just eye based sensory information. In this study, we compared the electrophysiological correlates underlying stable visual percepts during inter-ocular switch and classical binocular rivalry. Delineating the differences and similarities between the two paradigms of rivalry will provide us with valuable information on the nature of competition during incongruent visual stimulation. We recorded EEGs while human subjects experienced inter-ocular switch and classical binocular rivalry elicited with dichoptic presentation of orthogonally oriented sinusoidal gratings. The subjects reported their percepts via button presses. We extracted and analyzed trials, where subjects reported at least one second long stable percepts. During this time window, we assessed the normalized spectrogram to visualize mean event-related changes in spectral power across a broad frequency range (1-45 Hz). We observed a strong and sustained increase in spectral power between 12-30 Hz across the two conditions approximately 300 ms following the reported perceptual switch. Low Resolution Brain Electromagnetic Tomography (LORETA) was used to localize the cortical sources of the observed changes. The maps of the localized cortical sources of this increase in the spectral power during inter-ocular switch and binocular rivalry were remarkably similar and showed no significant differences. We therefore propose that both types of rivalry have similar EEG correlates in the 12-30 Hz frequency band during a stable visual percept