Abstract
C. Gabbard and C. Helbig (2004) found, when examining seated participants' limb selection for reaching and grasping in hemispace, that right-handers preferred to switch to the nondominant left arm for objects located approximately 20° horizontally from body midline (90°) in left hemispace. In the present study, the authors examined 13 strongly lateralized seated right-handers' kinematics of reaching to object positions ranging from body midline to 40° horizontally in left hemispace. Participants executed faster reaches with the left arm than with the right arm to objects placed 20°-40° from midline, whereas they did not change the proportion of time they spent accelerating the hands when the position of the object changed. A 2nd main finding was an increase in the left hand's trajectory curvature as object position moved farther from midline, with a corresponding decrease in the contribution of upper-arm motion to the reach. Those observations suggest that the switch from dominant right-arm reaching to nondominant left-arm reaching in left hemispace reported in the aforementioned study may have emerged from a shift from a shoulder-driven reach to an elbow-driven action.