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Lynne Kiorpes, J. A. Movshon; Extended developmental time course for global visual functions in primates. Journal of Vision 2002;2(10):47. doi: 10.1167/2.10.47.
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The critical period for visual development is typically considered to coincide with the time period over which visual acuity develops. Recent studies in monkeys and humans have shown that some visual functions have different critical periods and some, such as Vernier acuity and contour integration, develop more slowly and over a much longer period of time than simple grating acuity. We studied visual functions that require integration of information over space and time and compared their development to that for basic spatial vision tasks in Macaca nemestrina. The results show that visual development continues over a longer period of time than was previously thought.
We studied three types of global visual functions: contour integration, motion discrimination, and form discrimination. Contour integration was measured by detection of the location of a coherent ring of Gabor patches in a field of randomly-arrayed and oriented Gabors. Motion discrimination was tested by detection, and discrimination of the direction, of motion in random dot kinematograms. Form discrimination was tested by detection of linear, concentric, or radial organization in Glass patterns. Contrast sensitivity functions were measured for comparison. The animals were tested at ages ranging from 3 weeks to adult.
Contour integration ability develops late and over a longer period of time compared to contrast sensitivity. While contrast sensitivity is adult-like by 9–12 months, contour integration develops beginning around 4 months and continues over 1.5–2 years. Motion discrimination ability is apparent within the first 3 postnatal weeks, but develops over a long time course up to about 3 years of age. Form discrimination is relatively difficult for the animals. This ability, like contour integration, develops late, but continues to improve over several years. The data show that complex visual functions develop over a much longer period of time than the classical critical period.
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