Hand And Hemispace Differences In The Visual Control Of Aiming Movements

The purpose of this thesis was to examine left and right hand performance in three aiming movement experiments, designed to identify differences in movement kinematics when task demands were varied along dimensions thought to differ between the hemispheres. In Experiment 1, fourteen subjects were required to make aiming movements with the index finger to single light emitting diodes (LEDs) or to the midpoints of two simultaneously illuminated LEDs. Movements were recorded using a WATSMART system (Northern Digital, Inc.). Contrary to previous claims, no evidence was found for left hand advantages in accuracy in hand-invisible conditions. The large advantage in accuracy shown by the right hand in single target pointing was attenuated in bisecting. This attenuation may have been related to increased right hemispheric participation in the bisection task. In Experiment 2, the number of trials in which 11 subjects reached for in hand-invisible conditions was increased to over 800 trials. It was hypothesized that longer periods without the opportunity to recalibrate aiming movements with vision would result in a gradual increase in directional endpoint errors in both hands. Contrary to expectations, endpoint errors did not shift over the course of the sessions. Many of the changes in kinematic variables which occurred did so in the first 100-200 trials of the session and tended to remain stable for the remaining trials. Differences were found for movements made to the same vs. the opposite side of the reaching limb (i.e., hemispatial effects) in both hands, and tended to remain stable over the course of the sessions.;In the final experiment, the nature of these hemispatial effects in movement in kinematics were examined by dissociating the side of stimulus presentation from the side of motor response. Twenty-six subjects were required to reach to the mirror symmetric position on the side opposite to the target. For movement duration, peak velocity and the percentage of the movement spent in deceleration, ipsilateral advantages were consistently seen for side of motor response, rather than side of stimulus presentation