Our goal is to characterize the biological basis of the visual deficits in amblyopia, a developmental disorder of CNS origin. Human amblyopes have many visual abnormalities, ranging from local spatial interactions to deficits in global form and motion perception. We will measure these deficits psychophysically in macaque monkeys made amblyopic by artificial strabismus or anisometropia in early life, and then study these monkeys in neurophysiological and neuroanatomical experiments to establish the basis of their altered vision. To explore local spatial interactions, we will study the effects of flanking targets on contrast detection and alignment thresholds for well-localized stimuli, and compare the range of spatial interaction for normal observers and amblyopes. To explore longer-range perceptual effects, we will study the ability of normal and amblyopic monkeys to extract coherent features and forms from fields of randomly arrayed targets, and measure large-scale alignment acuity using collinear targets. To understand the development of pattern vision, we will also study the performance of normal infant monkeys on these feature detection tasks. To probe mechanisms of global visual integration, we will study the ability of amblyopic monkeys to utilize global form and motion cues in random-dot motion discrimination, and in Glass pattern discrimination. Some spatial localization and feature integration deficits in amblyopes may depend on the disruption of local and long-range horizontal connections in primary visual cortex, VI, while others may reflect changes in neural organization in extrastriate areas. We will conduct initial neurophysiological and neuroanatomical experiments in areas V1 and V2 of the amblyopic monkeys to explore these changes; later work may involve higher cortical areas. Physiological measurements will determine the range and scope of lateral spatial interactions in cortical receptive fields, and will explore the sensitivity of cortical neurons to long-range form and motion cues. Anatomical studies will visualize and analyze the structure of intra- and inter-areal connections thought to underlie lateral interaction and integration. The results should clarify the nature and basis of the visual abnormalities in amblyopia, and also illuminate higher-level visual processing in normal individuals.
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