A dynamical systems approach to skill acquisition.

This paper argues that the answer to the question, what has to be learned, needs to be established before the question, how is it learned, can be meaningfully addressed. Based on this conviction, some of the limitations of current and past research on skill acquisition are discussed. Motivated by the dynamical systems approach, the question of "what has to be learned" was tackled by setting up a non-linear mathematical model of the task (i.e. learning to make sideways movements on a ski apparatus). On the basis of this model, the phase lag between movements of the platform of the apparatus and the actions of the subject was isolated as an ensemble variable reflecting the timing of the subject in relation to the dynamics of the apparatus. This variable was subsequently used to study "how" the task was learned in a discovery learning experiment, in which predictions stemming from the model were tested and confirmed. Overall, these findings provided support for the hypothesis, formulated by Bernstein (1967), that one of the important effects of practice is learning to make use of reactive forces, thereby reducing the need for active muscular forces. In addition, the data from a previous learning experiment on the ski apparatus--the results of which had been equivocal--were reconsidered. The use of phase lag as a dependent variable provided a resolution of those findings. On the basis of the confirmatory testing of predictions stemming from the model and the clarification of findings from a previous experiment, it is argued that the dynamical systems approach put forward here provides a powerful method for pursuing issues in skill acquisition. Suggestions are made as to how this approach can be used to systematically pursue the questions that arise as a natural outcome of the experimental evidence presented here.