ABSTRACT
It is argued that both spontaneous movements and movements under continuous visual monitoring share more common factors than hitherto acknowledged. A brief review is presented of some behavioral data supporting the notion that human gestures have unique features that set them apart from artificial movements. I try to show that these features correspond to specific rules that are obeyed in the planning and execution phases of the movements. Three experiments on visuo-manual pursuit are presented to demonstrate that, even when the geometry and kinematics of the motor response are in principle dictated from without, these rules cannot be waived. A compatibility problem may then arise whenever the input in a visuo-manual coordination task does not comply with the intrinsic properties of the human motor control system. The traditional linear-system approach to the study of pursuit tracking seems insufficient to deal with this issue.
