Left-hemisphere motor dominance in righthanders.

Left-hemisphere dominance for motor programming was tested in two experiments by measuring acquisition and cross-hand transfer of a complex key-pressing skill in righthanded adults. In the first experiment, visual feedback was excluded to insure unilaterality of motor control. Consistent with left-hemisphere motor dominance, males showed faster acquisition with righthand training than with lefthand training and greater transfer from left to right then vice versa; but females exhibited neither asymmetry. To investigate the possibility that females relied on verbal strategies to remember which keys to press and that this prevented them from showing the predicted asymmetries, the need for such strategies was reduced in a second experiment by allowing visual feedback. Although the provision of visual input may have mitigated against motor asymmetries by directly engaging both hemispheres in the task, results showed more rapid improvement in skills with the right hand than with the left for both sexes, extending evidence for left-hemisphere motor dominance to a population including females as well as males.