Résumé
Analyses of postural states (and changes between them) have been a major focus of research in the neuro-muscular approach to postural coordination pioneered by Nashner (e.g., Nashner & McCollum, 1985). In a somewhat different context, we have recently focused our attention on the emergence of these postural states as well as on the constraints that shape their dynamics (Bardy, Marin, Stoffregen, & Bootsma, in press; Marin, Bardy, Stoffregen, Baumberger, & Flückiger, in press; Marin, Bardy, & Bootsma, in press). In this series of studies, standing participants who were asked to follow with their head the displacement of a target oscillating along the line of sight exhibited two preferred coordination modes for movements of the ankles and hips: An in-phase mode, with the two joints moving simultaneously in the same direction (
r close to 0°), and an anti-phase mode with the two joints oscillating simultaneously in opposite directions (ør close to 180°). The emergence of either one of these two phase relations depended on the interaction between environmental, intrinsic, and intentional constraints. In the present experiment, we focus on the (non-linear) properties of transitions between these postural states.