CONTROL OF HUMAN ARM MOVEMENTS IN 2 DIMENSIONS - INFLUENCE OF POINTERLENGTH ON OBSTACLE AVOIDANCE

Human subjects (N = 13) made arm movements in a horizontal plane by us ing the shoulder, elbow, and wrist to move a pointer to a target while avoiding simple obstacles. Movements with no pointer and with pointer s of three different lengths were tested so that the lever arm of the wrist could be changed and its effective redundancy altered. With incr easing pointer length, movement durations decreased, wrist movement us ed in avoiding obstacles increased, and variability in proximal joint angles increased. Most characteristics of paths and joint movements pr eviously described for movements with the long pointer were found to g eneralize to movements with shorter pointers or with no pointer-the co ndition used in several previous comparisons of 2- and 3-joint movemen ts. Both joint angles and path parameters changed in accommodating to the constraints added by obstacles and by increasing pointer length, i mplying that criteria defined in workspace and in joint space together influence paths in workspace and joint movement, as postulated by bid irectional models. increased wrist extension and flexion during moveme nt, compared with static pointing, indicate that dynamic factors are a lso important.