Perceptual-Motor Coordination: Control of Eye and Hand in Space and Time (Coordination, Motor Control, Movement).

The processes of perceiving and acting form the basis of a broad range of human behaviors. Psychologists have studied perception and movement separately for some time, and have recently begun to discover close links between the mechanisms that underlie these systems. The dissertation explores one aspect of the relationship between perception and action: the role of eye movements in the coordination and control of movements of the limbs. Three experiments are reported in which subjects performed discrete, rapid, wrist-rotation movements toward a visible target region. During the movements, the position of the subject's eyes was monitored. In Experiment 1 subjects spontaneously executed a saccadic eye movement to the target for the limb movement. The saccade was closely time-locked to the onset of limb movement, although the precise serial order of eye and limb movement varied, and was not critical for accurate limb performance. In Experiments 2 and 3 subjects produced rapid limb movements, either with or without visual feedback from the moving limb, while they were (i) not permitted to move their eyes to the target, (ii) allowed to make a saccade to the target, or (iii) required to move their eyes to the target with a smooth-pursuit movement. Limb movement endpoints were equally accurate when subjects fixated the target after either saccade or pursuit movements, but were less accurate when subjects could not look at the target. This occurred even when vision of the movement was unavailable. When subjects could look at the target, overall temporal and spatial features of the limb movements did not depend on the type of eye movements used. However, analysis of detailed kinematic features of the wrist-rotations revealed systematic differences in component phases of the movements that did depend on the type of eye movement. The results are interpreted in the context of a model in which (1) the initial distance-covering phase of a rapid limb movement is prepared on the basis of the perceived distance to move, and (2) the final homing-in phase of movement is programmed to arrive at a specific location. The assessment of distance appears to depend upon both the position of the eye and the type of eye-movement, whereas the specification of location depends only on the position of the eye. The results have implications for the perception of visual direction, the control of aimed movement, and the link between perceptual and motor systems.