Going around in circles: The dynamics of bimanual circling

In the study of the dynamics of motor control, tasks requiring multijoint intralimb coordination have been rare and considerations of multijoint bimanual coordination almost completely absent. This chapter reviews some recent research we have conducted using a bimanual circle drawing task to elucidate the dynamics of intralimb and interlimb coordination. Right-handed and left-handed subjects were required to produce circles in the horizontal plane with both hands simultaneously in either a symmetrical mode (i.e., one hand moving clockwise, the other counter-clockwise) or in an asymmetrical mode (i.e., both hands moving clockwise or counter-clockwise). These movements were performed at various frequencies. The main findings from the studies were: (1) symmetrical cirling was a much easier task than asymmetrical circling; (2) in the asymmetrical mode, distortions of movement trajectories, suggestive of loss of stability, and phase transitions, were evident as movement frequency was increased; and (3) distortions of circular trajectories were most prominent for movements of the nondominant hand and appeared to precipitate movement reversals. The results are discussed in terms of manual asymmetries and the putative neural mechanisms underlying the bimanual circling effects