Dynamics of learning new postural patterns: influence on preexisting spontaneous behaviors.

In stance, rotations around the hips and ankles typically exhibit a relative phase close to 20° or 180°. In 2 experiments, the authors studied the reciprocal influence of those coordination tendencies with learning an ankle-hip relative phase of 135°. Before, during, and after learning a new mode of coordination, they assessed participants' (N = 24 in each experiment) spontaneous postural patterns with a tracking task in which no specific coordination was required. Learning the 135° phase relation led to persistent modifications of the spontaneous in-phase and antiphase modes. Contrary to the theoretical predictions of the dynamical approach, the initial stability of the preexisting patterns did not influence the difficulty of producing the new mode or the improvement in performance during learning. Initial stability did, however, influence the rate and type of modification of spontaneous patterns. The authors discuss the results in relation to conclusions drawn from bimanual studies.