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Dennis M. Levi, Stanley A. Klein; Noise provides new signals about the spatial vision of amblyopes. Journal of Vision 2002;2(7):284. doi: 10.1167/2.7.284.
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© ARVO (1962-2015); The Authors (2016-present)
Amblyopia results in a loss of contrast sensitivity, and position acuity. However, the nature of the neural losses is not yet fully understood. Here we report the results of experiments using noise to try to better understand the losses in amblyopia. In the first experiment, we used noise to measure efficiency for detecting a target and for discriminating its position in normal and amblyopic observers. Our results show a loss of efficiency for both detection and position in observers with amblyopia. To determine whether the loss of efficiency was a consequence of a mismatched template, we derived classification images for both tasks. We found that some amblyopic observers show markedly abnormal classification images for the position task, and moderately abnormal classification images for the detection task. The amblyopic position template, like that of the normal parafovea, is a low spatial frequency template, reflecting a shift in the spatial scale of analysis. Reduced efficiency in the amblyopic visual system may reflect a high level of intrinsic noise, a poorly matched position template, or both. To assess the level of internal noise we used a “double pass” technique, in which observers performed the identical experiment twice. The amount of disagreement between the two provides an assay of the observer's intrinsic noise, since the signals and the external noise are identical. Simulations enable us to parse the intrinsic noise into random noise and consistent noise, due to a poorly matched template. For normal observers, for both tasks, about 30% of the noise was random, and 70% consistent noise. Amblyopes show a much higher proportion of random intrinsic noise noise. We conclude that the loss of efficiency in amblyopia is due in part to a poorly matched template, but to a greater degree, to high levels of random intrinsic noise.
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