The Bernstein Perspective: I. The Problems of Degrees of Freedom and Context-Conditioned Variability
M. T. Turvey, Hollis L. Fitch, Betty Tuller University of Connecticut and Haskins Laboratories
The perspective to be developed in this chapter and the two that follow might be termed the Bernstein perspective after the Soviet physiologist Nicolai Aleksandrovitch Bernstein ( 1896-1966). In other perspectives, both traditional and contemporary, the contribution of the kinematic and dynamic aspects of movement to its control and coordination are either simply ignored or terribly underestimated. For Bernstein, the obvious fundamentality of these aspects led him to characterize the study of movements in terms of the problems of coordinating and controlling a complex system of biokinematic links. He recognized that the focus of analysis could not simply be the muscular forces provided by the animal but must necessarily include inertia and reactive forces. In a nutshell, Bernstein recognized that any theory that ignores the totality of forces and considers only those contributed by muscles in its functional description of movements would be a theory of the miming of movements rather than a theory of movements themselves, for the very simple reason that any coordinated activity requires an environment of forces for its proper expression ( Fowler & Turvey, 1978). The purpose of this first chapter is to identify the two major problems that shape the analysis of movement in the Bernstein perspective.
We begin with a view of motor control that was popular in the 19th century and that is depicted in Fig. 10.1. This view assumes an "executive" responsible for the control of movement, whose capabilities are not unlike those of a human being. To put it bluntly, the executive is a scaled-down version of a human being, and traditionally this "little man inside the head" is referred to as the "homunculus." At the disposal of this little man, or homunculus, is a memory bank containing programs for movement, where those programs can be likened to musical scores. To perform a movement the homunculus retrieves a score from