A preliminary analysis of the coordination of reaching, grasping, and walking

The purpose of this investigation was to describe the strategies used by individuals when motor systems controlling locomotion and prehension must be used simultaneously to perform a task. Subjects were required to perform five tasks: walk normally, walk and pick up a small object, walk and pick up a large object, pick up a small object from a stationary standing position, and pick up a large object while standing. The grasping and walking movements were videotaped and the frequencies of various behaviors were observed (type of grasp, location of contact with the object, support leg during contact with the object, timing of gaze toward object). Characteristics of the grasp were influenced by object size, not by whether the subject was walking. Gaze was shifted to the object before initiation of reach and this pattern was not influenced by size of the object or movement of the subject. Finally, subjects preferred using an ipsilateral support leg while generating the reach, which is a deviation from normal gait patterns. Findings indicate that the motor control system may be hierarchically organized in such a way that stability of the lower limbs supersedes the control of the movement patterns of an upper limb.