The aim of the present study was to determine whether normal subjects with one eye covered and patients in whom one eye had been enucleated generate more head movements than subjects using binocular vision during the performance of a visually guided grasping movement. In experiment 1, 14 right-handed normal subjects were tested binocularly and monocularly in a task in which they were required to reach out and grasp oblong blocks of different sizes at different distances. Although the typical binocular advantage in reaching and grasping was observed, the overall head movement scores did not differ between these testing conditions. In experiment 2, seven right-handed enucleated patients were compared to seven age and sex-matched control subjects (tested under binocular and monocular viewing conditions), on the same task as used in experiment 1. While no differences were found in the kinematics of reaches produced by the enucleated patients and the control subjects, the patients did produce larger and faster resultant head movements, composed mainly of lateral and vertical movements. This suggests that enucleated patients may be generating more head movements in order to better utilize retinal motion cues to aid in manual prehension.

SUMMARYRecent work in onr laboratory has revealed that enucleated patients produce large lateral and vertical head movements during visually guided grasping.These movements may allow them to maximise the use of retinal motion cues in planning and controlling their grasp. The aim of the present study was to determine whether the tendency to produce these adaptive head movements increases as a function of time since enucleation. We tested a group of 12 enucleated patients in whom the time between surgery and testing varied from 2 weeks to 35 years (mean = 11.2 years). These patients were required to reach out and grasp oblong blocks of different sizes at different distances. Correlational tests revealed an increase in the proportion of self-generated lateral and vertical head movements versus forward head movements as a function of post-enucleation time (r(s)(12) = 0.68, p<0.025 and r(S)(12) = 0.65, p<0.025, respectively).This suggests that enucleated patients may be adapting to living with one eye by learning to increase the proportion of their lateral and vertical head movements during the performance of skilled motor acts.It has been suggested that enucleated patients undergo some form of adaptation since patients who still have good vision in their remaining eye typically report no permanent visual difficulty following enucleation and return to normal activities within a year, often making the adjustment in less than 1 month.1 , 2 Previous research has highlighted the strength and effectiveness of the use of visual motion depth cues (generated by translational and rotational movements of the head) by enucleated patients when trying to resolve small depth differ ences. 3 , 4 A recent study. in our laboratory was performed to determine whether or not enucleated patients (who were tested more than 1 year after surgery) generate more head movements than control subjects, who either wore an eye-patch or used binocular vision, during the performance of a visually guided grasping movement. s The study clearly revealed that enucleated patients produced larger and faster resultant head movements, com posed mainly of lateral and vertical movements, while control subjects under the monocular viewing condition generated larger forward head movements. This result suggested that the enucleated patients may have been exaggerating the natural head (and torso) movements that occur during a reach in order to better utilise retinal motion cues to aid in manual prehension. It is possible that these patients may have, over time, learned that horizontal head movements are the most effective form of head motion for the production of motion depth cues 4 , 6 , 7 which can assist them in calibrating the distance (and size) of objects that they might wish to grasp.T his paper describes an examination of head movements produced by a group of enucleated patients, in whom the post-enucleation time varied from 2 weeks to 35 years, during the performance of a visually guided grasping movement. The aim of this study was to determine whether t...