The long-term objective of this research is to determine how central visual pathways in the brain encode and transmit spatial and temporal information. The proposed project utilizes neurophysiological methods to record from single neurons or from small groups of cells in striate and parastriate visual cortex. (1) Intercellular connections: (a) A hypothesis will be tested that simple-to-simple cell communication underlies direction selectivity. (b) Predictions of a disparity energy model will be explored by recording simultaneously from binocular simple and complex cells. (c) Different processing levels will be investigated for members of complex-to-complex cell pairs. (d) A conjecture will be addressed that phase disparity tuning of neighboring complex cells involves quadrature encoding. (2) Functional properties of area 18: (a) Contrast sensitivities and dynamic ranges will be compared in areas 17 and 18. (b) A hypothesis will be examined that near and far cell function in area 18 may be accounted for by a disparity energy model. (c) the joint processing of motion and depth will be investigated. (d) Temporal tuning, timing, and filtering characteristics will be determined. (e) An analysis of nonlinear function will be made by using white noise stimuli. (3) Center-surround receptive field organization: (a) Surround characteristics will be examined to determine spatial distributions and properties. (b) Timing characteristics between center and surround will be explored to examine the hypothesis that surround inhibition arises from local intracortical connections. (c) A hypothesis will be tested that surround suppression participates in contrast normalization. (d) A possibility will be explored that surround suppression is part of the near and far disparity encoding process. These investigations will provide fundamental insights into receptive field organization and neural circuitry in the visual system. This basic information about normal visual function will help form a framework for the diagnosis and treatment of visual disorders.
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