Kinematics of Goal-Directed Arm Movements in Neglect: Control of Hand Velocity

Abstract

Do patients with unilateral neglect exhibit direction-specific deficits in the control of movement velocity when performing goal-directed arm movements? Five patients with left-sided neglect performed unrestrained three-dimensional pointing movements to visual targets presented at body midline, the left and right hemispace. A group of healthy adults and a group of patients with right-hemispheric brain damage but no neglect served as controls. Pointing was performed under normal room light or in darkness. Time-position data of the hand were recorded with an opto-electronic camera system. We found that compared to healthy controls, movement times were longer in both patient groups due to prolonged acceleration and deceleration phases. Tangential peak hand velocity was lower in both patient groups, but not significantly different from controls. Single peak, bell-shaped velocity profiles of the hand were preserved in all right hemispheric patients and in three out of five neglect patients. Most important, the velocity profiles of neglect patients to leftward targets did not differ significantly from those to targets in the right hemispace. In summary, we found evidence for general bradykinesia in neglect patients, but not for a direction-specific deficit in the control of hand velocity. We conclude that visual neglect induces characteristic changes in exploratory behavior, but not in the kinematics of goal-directed movements to objects in peripersonal space.