The long-term goal of this psychophysical research project is to understand human spatial perception. Thus, two general objectives are (a) to identify the spatio-temporal relationships that provide information about the geometrical structure of environmental scenes, objects, and motions, and (b) to quantify human abilities for discriminating this optical information. By improving descriptions of the optical information acquired by vision, the results of this project should lead to an improved understanding of the physiological and anatomical mechanisms that underlie spatial vision, aid comparative evaluations of visual function in various human populations, and facilitate the engineering design of artificial systems for acquiring and displaying optical information. Experiments are designed to evaluate two related aspects of early visual sensitivity to spatial and temporal relations in optical patterns: (a) the coherence of spatio-temporal phase relations among local retinal responses to global optical patterns, and (b) the perception of surface structure. The proposed experiments evaluate acuities for discriminating spatial relations in moving, stereoscopic, and stationary luminance patterns. Studies of the coherence of vision will evaluate the detectabilities of global geometric relations among local moving stimuli at separate retinal locations. Experimental variables include the geometrical transformations that describe the relative motions, retinal separation and eccentricity, spatial and temporal resolution, temporal phase lags, and background surface structure. Experiments on the coherence of binocular vision aim to determine the spatio-temporal bandwidth of the monocular signals underlying stereopsis and to quantify the binocular coherence of these signals. Studies of the perception of surface structure will (a) evaluate the role of smooth surface structure as a basic determinant of perceived spatial relations, (b) evaluate the detectability of discontinuities in surface gradients, and (c) test hypotheses concerning the perception of geometric structure from motion.