Oculo-manual tracking of visual targets: control learning, coordination control and coordination model.

The processes which develop to coordinate eye and hand movements in response to motion of a visual target were studied in young children and adults. We have shown that functional maturation of the coordination control between eye and hand takes place as a result of training. We observed, in the trained child and in the adult, that when the hand is used either as a target or to track a visual target, the dynamic characteristics of the smooth pursuit system are markedly improved: the eye to target delay is decreased from 150 ms in eye alone tracking to 30 ms, and smooth pursuit maximum velocity is increased by 100%. Coordination signals between arm and eye motor systems may be responsible for smooth pursuit eye movements which occur during self-tracking of hand or finger in darkness. These signals may also account for the higher velocity smooth pursuit eye movements and the shortened tracking delay when the hand is used as a target, as well as for the synkinetic eye-arm motions observed at the early stage of oculo-manual tracking training in children. We propose a model to describe the interaction which develops between two systems involved in the execution of a common sensorimotor task. The model applies to the visuo-oculo-manual tracking system, but it may be generalized to other coordinated systems. According to our definition, coordination control results from the reciprocal transfer of sensory and motor information between two or more systems involved in the execution of single, goal-directed or conjugate actions. This control, originating in one or more highly specialized structures of the central nervous system, combines with the control processes normally operating in each system. Our model relies on two essential notions which describe the dynamic and static aspects of coordination control: timing and mutual coupling.