Quantitative Studies of Visual Pathways

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DESCRIPTION (provided by applicant): The overall aim is to understand how mechanisms in the lateral geniculate nucleus (LGN) and visual cortex analyze information about the chromatic properties of objects, and how these mechanisms determine human perceptual capabilities. Three closely connected groups of physiological studies are proposed. The first group will establish, through experiment and modeling, the underlying organization of chromatic selectivity in the receptive fields of neurons in LGN and cortex. The studies will answer the following questions: to what extent do the chromatic properties of a receptive field result from selection of inputs from cones of particular classes vs. selection of inputs from cones in particular positions; how does the silent region surrounding the receptive field shape a neuron's chromatic selectivity; do variations in contrast alter the chromatic selectivity of neurons? The second group of studies will characterize in cortical neurons the relationship between the chromatic properties and the binocular properties of receptive fields. One study will reveal whether and how neurons reconcile the conflicting demands that their two receptive fields have matched spatial properties and also matched chromatic properties; another will reveal how binocularly driven neurons combine different color signals arising in the two eyes. These studies are central to understanding binocular color mixture. The third group of studies will characterize mechanisms of chromatic adaptation that profoundly influence color sensitivity and appearance. One study will analyze the early signal transformations, expressed in LGN neurons, that are brought about by adaptation to mean chromaticity; another will analyze the subsequent transformations that occur in cortex--both those brought about by adaptation to the mean chromaticity, and those brought about by adaptation to chromatic contrast.