An investigator requests 5 years of support to continue psychophysical and eye movement experiments on human observers. The proposed research focuses on the functional properties of the mechanisms that mediate stereopsis and initiate vergence eye movements for large binocular retinal image disparities that are normally perceived as diplopic. The proposed studies will directly test several key features of current models of sensory and motor binocular vision and provide descriptive data that are needed to further develop these models. In addition, the results may provide insight into how unilateral defocus associated with an anisometropia initiates interocular inhibitory processes that could potential disrupt binocular vision.