Amblyopia is a major cause of vision loss in young children (Sachsenweger, 1968). Previous work by the principal investigator and others suggests that three main factors contribute to the loss of spatial vision in amblyopia: i) alterations in the size and sensitivity of cortical receptive fields, ii) reduced density of cortical receptive fields (undersampling), and iii) added noise (jitter) in the topographical positions of cortical receptive fields. This proposal seeks to build on this work in order to learn how each of these factors contributes to limit spatial vision in amblyopic, peripheral, and normal vision, and to assess neural plasticity in amblyopia. A major goal of this project is concerned with the mechanisms which constrain performance in these visual systems. Masking will be used to estimate the orientation and spatial frequency selectivity of the spatial filters underlying position and contrast discrimination. The principal investigator believes that reduced spatial precision in amblyopic and peripheral vision can, at least in large part, be attributed to the use of larger filters by these """"""""degraded"""""""" visual systems. He hypothesizes that there is a cascade of deficits in the visual system of strabismic amblyopes, which escalates at higher levels of processing. He proposes to test this hypothesis by comparing performance with stimuli which are detected by second-order mechanisms. He proposes to test the hypothesis that 2-dimensional spatial interactions in anisometropic amblyopes are scaled versions of those found in the normal fovea, while in strabismic amblyopes, he predicts (based on pilot experiments) that these interactions are qualitatively different, reflecting alterations in both long-range lateral interactions and end-stopping. Both contrast sensitivity and positional acuity are degraded in amblyopic and peripheral vision. The principal investigator proposes to learn about the factors which constrain contrast sensitivity and positional acuity in these visual systems by: i) adding contrast noise, ii) adding positional jitter, and iii) sparse sampling. He will used methods and models developed during the current grant period to learn about """"""""intrinsic"""""""" constraints. He proposes to test a number of specific hypotheses and models with carefully chosen psychophysical methods and stimuli. Pilot data from the principal investigator's laboratory suggest a high degree of neural plasticity in some adults with amblyopia. He proposes to assess the time course and limits of this plasticity in both adults and young children with amblyopia in order to: i) compare losses of adults with amblyopia to those of children, and ii) assess the limits, time course and mechanisms of neural plasticity.
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