Variability and Determinism in Motor Behavior

TLDR

Variability in motor behavior can be viewed as interfering, neutral, or essential, and recent work favors treating it as a key factor for studying motor actions. The authors review how variability and determinism manifest in postural and rhythmic movements. Analysis shows that motor variability reflects a mix of noise and deterministic structure, and that higher variability does not imply randomness while greater controllability does not equate to determinism.

Abstract

In investigations into perception-action systems, variability of observable behavior may be considered to (a) interfere with inquiry, (b) be neither detrimental nor particularly useful to inquiry, or (c) play a crucial role in inquiry. The authors underscore recent suggestions that alternative (c) is a preferred strategy for the study of many motor behaviors. In tutorial fashion, the authors review the concepts of variability and determinism with respect to postural and rhythmic movements. Study of the variability of those behaviors has revealed crucial features suggestive of underlying mechanisms and control, such as particular blends of noise and determinism (piecewise determinism). It has also revealed general lessons (for example, more variable does not mean more random and more controllable does not mean more deterministic) that may extend to other classes of perceptual behavior.