A theory on the control of arbitrary movements.

A theory dealing with the control of human, arbitrary movements is proposed. A schema is set up to suggest how the relevant information flows and what kind of operations affect it. A number of successive steps are distinguished in the production of a movement. It is assumed that the intended movement is carried out in the imagination, and that this imaginary movement is composed of a spatial trajectory and an intensity course, which are considered to be independent features of the intended movement. The spatial trajectory will be encoded in a special coding, which is related to the lengths of the muscles that effect the movement. From this special coding of the intended movement static and dynamic control signals can be derived. Because afferent and efferent signals are encoded in the same way in this schema, the evaluation and correction of the performed movement is quite simple. The higher levels in the control schema may function in an abstract way, i.e. the signals at these levels are barely concerned with details of the peripheral motor system. This abstract functioning of the higher levels is based on the numerous feedback mechanisms involved at all levels of control and in the peripheral motor system. Nevertheless, it is possible to incorporate specific peripheral properties in the generation of the control signals. The assumptions in this theory will be discussed and aspects of the proposed control schema will be compared with general control principles.