Participants stood in a moving room and looked at a target that was attached to the front wall of the room. They were instructed either to look at the target or to track it, that is, to move so as to maintain a constant distance between the target and their head. Previous research (e.g. Bardy, Oullier, Bootsma, & Stoffregen, Journal of Experimental Psychology: Human Perception and Performance, 2002) has documented stable modes of coordination of the hip and ankle joints that emerge during the tracking task. In the present study our main goal was to determine the effects of task variation (tracking versus looking) on these postural coordination modes. Within trials, we varied the frequency of room motion between 0.10 and 0.75 Hz. The results revealed that in both the tracking and looking tasks, posture was characterized by the emergence of in-phase and anti-phase modes, although the modes were more prominent in the tracking task. For both tasks the coordination mode adopted depended on the frequency of motion of the moving room. Coupling between motion of the room and motion of the head was stronger in the tracking task than in the looking task. Overall, the dynamics of hip-ankle coordination were qualitatively similar during the looking and tracking tasks. This similarity has consequences for the development of a general theory of the visual regulation of stance.
Bibliographical noteFunding Information:
The research reported in this article was supported by a grant from the Ministère de l'Education Nationale, de la Recherche et de la Technologie. Portions of the data were presented at the XIth International Conference on Perception and Action, Storrs, Connecticut, USA. The authors would like to thank Didier Casalta, Thelma Coyle and Denis Mottet for their help in data processing; Tjeerd Dijkstra for critical discussion and for providing his Relative Phase Toolbox; Mei Si, Randy Paguyellow, and Greg Nelson for helping with data collection; Nat Hemasilpin for programming the moving room; Thierry Ferrand for help in designing Fig. 1 A and B; and Ludovic Marin for helpful comments.