Differential performance over a wide range of possible postural coordination modes was investigated using 16 ankle-hip relative phase patterns from 0° to 337.5°. Participants were instructed to produce each coordination mode with and without real time visual feedback. Feedback consisted of a Lissajous figure indicating the discrepancy between actual and requested ankle-hip relative phase. The results showed: (1) the presence of a unique attractor around the anti-phase pattern (relative phase ≈ 180°); (2) performance was similar with and without visual feedback; (3) the absence of an attractor for the in-phase pattern (relative phase ≈ 20°). The third result is not consistent with previous research in which both in-phase and anti-phase patterns emerged when they were not imposed [B.G. Bardy, L. Martin, T.A. Stoffregen, R.J. Bootsma, Postural coordination modes considered as emergent phenomena, J. Exp. Psychol. Hum. Percept. Perform. 25 (1999) 1284-1301; B.G. Bardy, O. Oullier, R.J. Bootsma, T.A. Stoffregen, Dynamics of human postural transitions, J. Exp. Psychol. Hum. Percept. Perform. 28 (1999) 499-514]. This finding indicates the strong dependency to task variation and instructions of postural pattern formation.
Bibliographical noteFunding Information:
Research supported by Enactive Interfaces, (EU IST contract #002114) and by the National Science Foundation (BCS-0236627).
- Ankle-hip relative phase
- Closed-loop feedback system
- Coordination dynamics
- Standing posture