Task complexity and limb selection in reaching.

Research examining limb selection for reaching and grasping an object in various positions of hemispace has noted a strong ipsilateral bias for using the hand on the same side as the stimulus, an observation that to some extent questions the traditional notion of handedness. The present study examined the effects of task complexity in regard to such actions. Forty-four right-handed, blindfolded subjects were required to grasp a small cube at one location and release it at another site, with movement initiated only after the second cue was presented. In condition A, the first tone identified the location where the subject was to grasp the cube (the second tone, the release point), while in condition B the order was reversed. A view of both conditions revealed a similar trend. As expected, the vast majority (average 96%) used their dominant (right) hand to reach into right hemispace and release in the left field. However, when the reach cue was presented in left hemispace, only 40% of subjects selected their nondominant (ipsilateral) limb to complete the action. Since this value is substantially less than reported previously with a less complex task (70%), we speculate that when deeper processing is required there is a tendency to revert to the dominant limb, even when it necesssitates reaching contralaterally. Additional discussion focuses on programming selection for reach and release.