ABSTRACT
The role of visumotor mechanisms is to match the final position of a moving segment with a target located within extrapersonal space. This critical function involves additive components that can be classified tentatively under two main headings. Directional mechanisms would first determine the spatial pattern of the movement, by generating motor commands according to spatial coordinates of the target, as detected by visual "maps" in different brain areas. Gain-control mechanisms would account for the precision of the movement, by braking and stopping the trajectory at the proper location. Visual images remain stabilized on the retina during head rotation. This effect is achieved at least in part through the vestibulo-ocular responses (VOR), which compensate for head movements by rotating the eyeballs in the opposite direction. The respective contribution of vestibulo-ocular and visual factors in optimal development of VOR gain can be drawn from visual deprivation experiments.
