Shifts in the eye-centered frame of reference may underlie saccades, visual perception, and eye-hand coordination

Conventional, computational theories limit the understanding of how action and perception are controlled. In an alternative scheme, the nervous system controls the values of physical and neurophysiological parameters that predetermine the choice of the spatial frames of reference (FRs) for action and perception. For example, all possible eye positions, Q, can be considered as comprising a spatial FR in which extraocular muscles (EOMs) stabilize gaze directions. The origin or referent point of this FR is a specific, threshold eye position, R, at which EOMs can be quiescent but activated depending on the difference between Q and R. Starting before eye motion, shifts in R cause displacement of the FR and resetting of the stable equilibrium position to which the eyes are forced to move. Rather than corollary discharge, the depiction of visual images integrated across the entire retina in the shifted spatial FR is responsible for remapping visual receptive fields and visual constancy. These suggestions are illustrated in computer models of saccades in the referent control framework in humans and monkeys. The existence of three types of visual RF remapping during saccades is suggested. Properly scaled, shifts in the R underlying a saccade are transmitted to motoneurons of arm muscles to guide reach-to-grasp motion in the same, eye-centered FR. Some predictions of the proposed control scheme have been verified and new tests are suggested. The scheme is applicable to several eye-hand coordination deficits including micrography in Parkinson's disease and explains why vision helps deafferented subjects diminish movement deficits.