The contribution of vision to asymmetries in manual aiming.

An experiment was conducted to examine the hypothesis that the right hand system is superior in the processing of visual information. A manual aiming task utilizing four visual conditions was employed. In the full-vision (FV) condition subjects were afforded vision of both the hand and the target throughout the course of the movement. In the ambient-illumination-off (AO) condition, the room lights were extinguished at movement initiation, thus preventing vision of the moving limb. The target remained illuminated. In the target-off (TO) condition, the target was extinguished upon initiation of the movement. Ambient illumination and thus vision of the hand remained present. Finally there was a no-vision (NV) condition in which ambient illumination was removed and the target was extinguished upon initiation of the response movement. Although the manipulation of vision had potent effects upon terminal accuracy, and influenced reaction and movement time measures, the hands did not differ in the extent to which these characteristics were expressed. A left hand advantage for reaction time was observed. This may reflect a relative increase in right hemisphere involvement prior to aiming movements which are spatially complex.