(De)Stabilization of Required and Spontaneous Postural Dynamics With Learning

The present research examined how learning a new ankle-hip coordination influenced the preexisting postural repertoire. Standing participants learned a new ankle-hip coordination mode (relative phase of 90°). Before and after practice, postural patterns were evaluated in two different tasks. In the required task, specific ankle-hip patterns were requested (12 relative phases in multiples of 30°). In the spontaneous task, participants performed a tracking task in which no instructions about ankle-hip coordination were given. Learning induced changes in both required and spontaneous coordination dynamics. When ankle-hip patterns were required, learning led to improvement and homogenization in performance over the entire postural repertoire. When ankle-hip patterns emerged spontaneously, in-phase and antiphase preexisting patterns destabilized and changed toward the learned pattern of 90°. These findings demonstrate that learning a new coordination pattern can induce modifications of patterns that have not been practiced. The results also suggest that the consequences of learning do not generalize across different types of tasks, even when similar coordination modes are involved. We discuss implications of these findings for the generality of learning mechanisms.