ELECTROPHYSIOLOGICAL INVESTIGATION OF BINOCULAR RIVALRY

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When the two eyes view dissimilar, monocular images, stable vision breaks down and one or the other eye dominates perception in alternation. This phenomenon is called binocular rivalry (BR), and it is a good example of how the visual system can constrain its input to obtain meaningful representations. BR is closely linked to fusion and stereopsis; in fact, it demonstrates the existence of important underlying processes that operate constantly to establish unified vision. Furthermore, the inhibitory interactions underlying this phenomenon may represent a general mechanism that encompasses phenomena such as lateral inhibition, nonclassical surround effects, or pathological suppression due to amblyopia or nonamblyopic strabismus. Our goal is to research the neural interactions that instigate this perceptual alteration and their role in binocular fusion and stereoscopic depth perception. Although much psychophysical work has been devoted to BR, the proposed research will provide the first systematic neurophysiological examination of this phenomenon. Experiments will be conducted on monkeys trained to report their perceptions while viewing rivalry-inducing stimuli. Single unit activity in the striate cortex will be recorded to investigate which cells show response modulations during BR. Recording from two cells simultaneously, we will determine which cells might show reciprocal inhibition. The response dynamics of such neurons will be studied to establish whether they are sufficient to explain the perceptual alternations or if dominance is determined either by the number of units active for a period of time or by the degree of correlation in their firing rate. To understand the extent to which cross-inhibition operates during normal binocular vision, the sensitivity of the cells for different stimulus attributes will be tested under fusion, stereopsis, and BR conditions. The activity of disparity-tuned neurons that may also show response modulation during BR will be studied to determine the conditions under which the cells exhibit oscillatory modulations. The responses of such cells will be examined with stereoscopic stimuli of different spatial frequencies and positional or orientational disparities. Of particular interest is the response of disparity-tuned cells to random dot stereograms superimposed on rivalrous stimuli. In addition to providing important information regarding the physiology of binocular vision, these experiments will make a significant contribution by giving insights to a phenomenon that allows clear discrimination between sensory and conscious, perceptual processing.