Elicitation and control of movement by the sensed properties of the world are determined by remarkably complex mechanisms of the central nervous system. They can be at least partially understood by relevant behavioral research. The interaction between movement and sensory reception works in both directions and each of them raises problems. On one hand, the mechanism by means of which the several parts of the body- -limbs, head, and eyes--orient towards visible targets is being analyzed in terms of the spatial and temporal properties of these responses. In addition, we are also analyzing this system by studying alterations produced by rearrangement. We are also studying alterations produced by rearrangement affected spatially by prisms and temporally by time delay in the motor-visual feedback loop. On the other hand, we are testing the limits over which the internal signals that produce movement of a limb influence its sensed position and serve to recalibrate the system for visual control of movement. Abnormal sensory stimulation, such as is produced by rearrangement, alters vision in both reversible and permanent ways. We are examining this modification by studying the earliest development of visually guided behavior in infant monkeys. Evidence implies that conditions of vision in infancy and early childhood influence the development of the neuroretina which limits sensitivity throughout life. In order to assess this influence we test the developing acuity of human infants along varied meridians in the field of vision. The distinction we have made between analyzing and orienting modes of vision continues to be a useful guide in separating the visual mechanisms traditionally studied psycho-physically from those more intimately related to spatial orientation and the control of movement. This distinction runs through much of the research of this laboratory.