Manual Localization of Lateralized Visual Targets

The effects of visual field, responding limb and extrapersonal space on the ability to localize visual targets using slow positioning movements of the arm were examined. Special contact lenses were used to lateralize visual information and to make comparisons with localization under monocular control conditions. Subjects made slow positioning movements to place a cursor directly beneath target lights. They saw target lights but not the moving limb during the trial. For directional error, results indicated that subjects were more accurate localizing targets lateralized to the right hemisphere than targets lateralized to the left hemisphere, indicating right hemisphere superiority for localization of visual targets in grasping space. Localization performance was significantly better with the right hand than the left hand. the left hand demonstrated a directional bias to the right of the targets. Responding hand and visual field did not interact. Finally, contrary to subjects' awareness and verbal reports, target localization was not less accurate in lens than in monocular control conditions. This was true for both amplitude and directional error. This is consistent with other studies where visual information about limb position is not available.