Two experiments required right-handed subjects to trace circular trajectories while complying with either a symmetric or asymmetric pattern. In symmetric patterns, circles were traced in a mirror image either inward or outward. In asymmetric patterns, circles were traced in the same direction either clockwise or counterclockwise. Subjects were instructed to trace with spatial accuracy while maintaining a strict temporal relationship to a metronome that scaled movement rates from 1.25 to 3 Hz. The symmetric patterns were more stable than asymmetric patterns; the circularity of trajectories was greater for the dominant side; and there were spontaneous reversals in the direction of circling in the nondominant limb when performing asymmetric patterns. The second experiment examined the same subjects under the instruction of intentionally changing the pattern by reversing the left or right limb circling direction when cued to do so. The degree of interlimb interference was highly asymmetric and contingent on the direction of pattern change. Intentional direction reversals were more expedient and with less disruption to the contralateral limb when asymmetric to symmetric pattern changes were effected through a reversal in the direction of nondominant side. The results are interpreted with reference to evidence that the supplementary motor area mediates descending input to the upper limbs during disparate bimanual actions, but not during symmetric actions.

Item Type:	Refereed Article
Research Division:	Medical and Health Sciences
Research Group:	Human Movement and Sports Science
Research Field:	Motor Control
Objective Division:	Expanding Knowledge
Objective Group:	Expanding Knowledge
Objective Field:	Expanding Knowledge in Psychology and Cognitive Sciences
UTAS Author:	Summers, JJ (Professor Jeffery Summers)
ID Code:	17338
Year Published:	1999
Web of Science® Times Cited:	44
Deposited By:	Psychology
Deposited On:	1999-08-01
Last Modified:	2000-05-13
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