Manual asymmetries in visually directed aiming.

Abstract

Several authors (e.g., Flowers, 1975; Roy, 1983) have suggested that manual asymmetries in visual aiming stem from differences in the ability of the hand-hemisphere systems to use visual feedback. Specifically, it has been proposed that the right-hand system is faster at processing visual feedback. The two experiments reported here were designed to examine this hypothesis directly by manipulating visual feedback. In the first study subjects pointed at a target using a range of movement times (100-400 msec) under two illumination conditions: lights-on and lights-off in which only the target light diode remained visible following initiation of the aiming movement. While the results confirmed that movement accuracy deteriorates less with increased speed for the right hand, the feedback interpretation for hand differences in speed-accuracy tradeoff was not supported, since both hands evidenced similar lights-on benefits. The second experiment focused on aiming movements performed in less than 200 msec. No effect of illumination was apparent, suggesting that visual information available during the course of the movement was not useful. The right-hand advantage in pointing accuracy remained, however. These findings indicate that hand differences in visual aiming are not the result of right-hand advantages in visual feedback utilization. Several other possibilities are discussed.