ABSTRACT
Prehension movements directed at visual objects were studied by means of a film technique in normal subjects and in a patient with a lesion in her left parietal lobe, which had resulted in disrupting proprioceptive control of her right arm. In the normal subjects, prehension was broken down into two segmental components dealing respectively with approaching the hand from the target (transportation component), and posturing the fingers in anticipation of the grasp (manipulation component). It was found that the two components had remarkably stable temporal patterns. The transportation component had an invariant duration when the distance of the target-object was changed. A secondary acceleration of this component was consistently observed in the late part of its trajectory. The time of occurence of this acceleration corresponded to about 75% of total movement duration. The manipulation component was marked by an anticipatory closure of the fingers which began also within 75% to 80% of total movement duration. The time occurrences of reacceleration of transportation and onset of finger closure for each movement were found to be linearly correlated. Prehension movements were unaffected by whether visual feedback from the moving limb was available or not. In the patient, however, the pattern of prehension was found to depend on the possibility to control the movement directly by vision. When visual control was possible, the patient succeeded in grasping the object though total movement duration was increased and fingers were uncompletely postured. When visual control was prevented, only the initial part of the transportation component was normal. Reacceleration was also present but its coordination with finger closure was lacking. Instead the hand remained widely open and no grasp occurred. It was concluded that proprioceptive feedback generated by movement is necessary for achieving coordination in plurisegmental movements like prehension. Vision is not needed as an ongoing feedback 324when proprioception is present, but becomes the only possible cue in its absence.
