The effect of postural stability and spatial orientation of the upper limbs on interlimb coordination.

It has recently been reported that the spatial orientation of two moving limbs has a determining influence on the relative accuracy and stability of coordination patterns. The purpose of the present experiments was to test perceptual and neuromuscular explanations of these spatial orientation effects. Experiment 1 was an initial test of the hypotheses and an extension of a previous study [Lee et al. (2002) Exp Brain Res 146:205-212] that required participants to coordinate inphase and antiphase movement patterns in four spatial orientations: two symmetric orientations (90 degrees and 180 degrees separation between the limbs) and two asymmetric orientations (90 degrees and 135 degrees separation between the limbs). Results of Experiment 1 suggest that the symmetry of movement may be a key factor influencing spatial orientation effects observed during interlimb coordination. In Experiment 2, participants again performed inphase and antiphase movement patterns in symmetric and asymmetric spatial orientations. However, one-half of the participants in Experiment 2 were provided with mechanical constraints during the performance of the desired coordination patterns. The mechanical constraints provided postural support but did not influence the visual experience. Results showed that the addition of the postural support improved performance. These findings suggest that neuromuscular, and perhaps biomechanical, constraints contribute more to the influence of spatial orientation than visual-perceptual constraints.