Normal stereopsis provides visual information about spatial relationships that is necessary for efficient performance in many normal activities and occupations. This form of depth-distance information is unavailable to the 3 to 4 percent of the population who have deficient stereopsis or are stereoblind from strabismus during childhood. However, in a real-world environment the perception of depth and distance involves information derived from both binocular and monocular cues, and the perceptual impact of stereodeficiencies will depend on whether or not an individual can compensate for his/her reduced stereopsis by an increased sensitivity to non-stereoscopic depth cues. The long-term objective of the proposed research is to gain a better understanding of the functional significance of stereodeficiencies caused by a period of abnormal binocular vision during infancy. The principal investigations will examine two alternatives for the development of depth perception in the absence of the primary binocular depth cue: 1) subjects with deficient stereopsis may utilize monocular depth cues more precisely than subjects with normal stereopsis (compensation hypothesis), or 2) normal stereopsis may be required to learn the precise use of non-stereoscopic cues and, thus, stereodeficient subjects also are less sensitive to monocular (empirical) depth information (Calibration hypothesis). The proposed experiments involve psychophysical investigations of monkeys and humans with reduced stereoacuities. Depth discrimination functions for combinations of binocular (stereopsis) and monocular (perspective cues and motion parallax) depth cues will determine the relative sensitivities of the separate cues and the modes of interaction between cues. The overall results of the proposed studies should provide information that is important for establishing treatment protocols for infantile strabismus. If children can compensate for a loss of stereopsis by more efficient use of empirical depth cues, then early treatment to preserve stereopsis is not imperative. On the other hand, if normal stereopsis is necessary for the development of normal sensitivities to all depth cues, then the early treatment of binocular vision anomalies is paramount.
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