Amblyopic Deficits in Contrast Sensitivity Do Not Predict Deficits in Global Perception

Abstract

Abstract: : Purpose: Amblyopic deficits are typically characterized by losses in such basic spatial visual functions as acuity and contrast sensitivity. However, it is well known that the extent of the amblyopic deficit can differ depending on the type of function measured. For example, in many amblyopes, the loss in sensitivity to spatial position is greater than that for grating acuity. To explore this problem further, I studied the ability of amblyopic monkeys to perform global perceptual tasks and compared the deficits exhibited to those in contrast sensitivity in the same monkeys. Methods: Ten amblyopic monkeys (Macaca nemestrina) were subjects for this study. Amblyopia developed following experimentally-induced esotropia (surgical) or anisometropia (lens-rearing). Esotropia and anisometropia were imposed at 3-4 weeks postnatal. All subjects were adult at the time of test. Global perception was assessed by three tasks: detection of coherent motion in random dot displays, detection of structure in Glass patterns, and contour integration ability. For the detection tasks, the animals chose between two dot fields to indicate which field contained coherent motion or coherent structure. For the contour integration task, they indicated the location of a coherent ring of Gabor patches in a field of randomly arrayed patches. Full contrast sensitivity functions were measured for comparison. In each case, monocular thresholds were based on 2AFC data collected according to the method of constant stimuli. Results: The results show that basic deficits in acuity and contrast sensitivity do not predict "perceptual" losses. Individual animals showed qualitatively similar deficits for perceptual organization and form perception. That is, the extent of impairment was similar for contour integration and for the detection of Glass patterns. Losses in sensitivity to coherent motion were not related to losses in contrast sensitivity, although the range of sensitivity to spatial displacement in the motion displays was consistent with the deficit in acuity. Conclusion: These results suggest that amblyopia reflects a far more complicated perceptual change than is implied by the simple loss in acuity.

Keywords: animal model • spatial vision • perceptual organization