Right-handers' reaching in contralateral hemispace: a kinematic observation

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 degrees horizontally from body midline (90 degrees) 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 degrees horizontally in left hemispace. Participants executed faster reaches with the left arm than with the right arm to objects placed 20 degrees-40 degrees 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.