Spatiotemporal Coordination Between Transport and Grasp Components during Prehension Movements

Abstract

Human prehensile movements consist of two motor components: a transport component and a grasp component. The purpose of this study was to determine how the transport component is related to the grasp component in terms of spatiotemporal aspects such as the time series of a hand transport trajectory.
Seven subjects were asked to point to a target (a circle of 2 cm in diameter) by using the right index finger or to grasp a disc (2, 4, 6, or 8 cm in diameter and 2 cm in length) between the thumb and index finger of the right hand. Both the target and disk were placed 30 cm directly in front of the starting position of the right hand.
The results showed that: (1) As the size of the disk increased, the inclination of the hand in its final shape became larger; (2) As the inclination of the hand when grasping the disk became larger, both the peak and final heights of the wrist position during the hand transport movement increased; and (3) the hand aperture was related spatiotemporally to the change in the hand transport trajectory. These results suggest that transport and grasp components are coordinated spatiotemporally during human prehension movements.