Amblyopia, a reduction in visual acuity produced by abnormal visual experience early in life, affects up to five percent of the population. Although all forms of amblyopia are characterized by reduced visual acuity, functional differences in the visual capabilities of strabismic and anisometropic amblyopes indicate that these two common forms of amblyopia are associated with different neural abnormalities. Knowledge of the neural basis for each form of amblyopia, much of which can only be gained from experiments conducted with appropriate animal models, is required to develop the optimal treatment and management strategies for this common disorder. The long-term objective of the proposed research is to provide insight into human amblyopia through psychophysical investigations of monkey models. Optical and surgical rearing strategies that simulate anisometropia and strabismus, respectively, will be employed to produce a representative range of amblyopias in developing rhesus monkeys. In the proposed investigations, psychophysical procedures will be used to study monocular and binocular visual functions that distinguish anisometropic from strabismic amblyopia and that are thought to reflect fundamental differences in the neural basis for these two forms of amblyopia. Specifically, behavioral procedures will be employed to characterize monocular spatial vision deficits (contrast sensitivity and vernier acuity), binocular interactions (binocular summation and stereopsis), and the prevalence of anomalous adaptive conditions that are commonly observed in humans with abnormal binocular vision (suppression, anomalous retinal correspondence, and eccentric fixation). These experiments will 1) increase our understanding of how anomalous visual experience disrupts normal visual system development and leads to vision disability and 2) determine if, and to what extent, data obtained from monkey models of amblyopia can be extrapolated to human amblyopia.