HAND PREFERENCE, PRACTICE ORDER, AND SPATIAL ASSIMILATIONS IN RAPID BIMANUAL MOVEMENT

When subjects make rapid bimanual aiming movements over different dist ances, spatial assimilations are shown; the shorter distance limb over shoots when paired with a longer distance limb. Recent research has al so shown spatial assimilations to be greater in the nonpreferred left limb of fight-handed subjects, but it is not known whether the increas ed spatial assimilations represent a handedness effect or one of hemis pheric lateralization of motor control. To determine the nature of the asymmetric effect, left- (n = 32) and fight- (n = 60) handed subjects part practiced, then whole practiced short (20-degrees) and long (60- degrees) reversal movements. During whole practice, both groups showed spatial assimilations in the shorter distance limb, particularly when the left limb performed the short movement. This asymmetry was greate st for fight-handed subjects, but left-handed subjects showed smaller, but systematic effects, providing moderate support for the hypothesis that the asymmetric effect is due to hemispheric lateralization of mo tor control. All interlimb differences in spatial accuracy for the sho rt and long movements were eliminated with practice, however, suggesti ng the asymmetric effect was temporary as well. In addition, subjects who part practiced the long movement just prior to whole practice show ed greater overshooting in the short distance limb compared with subje cts who followed the other practice order throughout whole practice an d the no-KR retention trials. Such findings suggest that the part-prac tice order of bimanual tasks can directionally bias whole-task perform ance.