The goal of this research is to investigate the neural basis of the spatial visual deficits in amblyopia, a developmental visual disorder of central nervous system origin. Suitably-reared macaque monkeys show a pattern of visual deficits very similar to that found in human amblyopes. We now plan to approach more directly the nature and biological foundations of the spatial deficits in amblyopia, taking advantage of the animal model to allow direct comparison of behavioral, neurophysiological, and anatomical correlates of the condition. We plan a series of psychophysical experiments in experimentally amblyopic monkeys to establish where in the amblyopic visual system, and in what manner, spatial information is lost. There appear to be two different types of amblyopia, one characterized primarily by contrast sensitivity deficits and another characterized by more dramatic deficits in spatial vision. There is an association between the type of amblyopia and the associated condition of strabismus or anisometropia, but the association is imperfect. To evaluate more carefully the origins and characteristics of these two types of amblyopia, we will compare the performance of animals with experimentally-induced strabismus and anisometropia. One series of experiments will explore the peripheral and central components of changes in visual efficiency in amblyopic monkeys. A second series will explore mechanisms of spatial position discrimination, and the way these are altered in amblyopia. Because amblyopia is a disorder of development, it is important to understand the normal developmental process and the limitations on visual performance in infants. Accordingly, we plan two developmental studies of information processing in infants that parallel those planned for adult amblyopes. To test hypotheses about the biological changes underlying amblyopia, we will study neuronal response properties and structural organization in the striate cortex of the behaviorally characterized animals. Our neurophysiological studies are designed to explore the neuronal bases of visual efficiency and of spatial position discrimination, and the way these are affected in amblyopia.
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