DISTORTED VISUAL FEEDBACK EFFECTS ON DRAWING IN PARKINSONS-DISEASE

We investigated the effects of distorted visual feedback on the drawin g performance of a group with Parkinson's disease (PD) and a control g roup. Twenty older healthy adults and 20 PD patients copied figures on to a digitizer tablet with a pen under normal and distorted visual fee dback conditions. PD patients were less able than controls to adjust t he size of their drawing to compensate for distortions in visual feedb ack. The effect was particularly pronounced when patients were require d to draw smaller than normal. Nevertheless, with practice, PD patient s showed a similar degree of improvement in size as controls, although they did not match the control group's level of performance. Overall, these findings support the notion that PD may have specific difficult y adjusting to a change in gain (or discrepancy) between visual and ki nesthetic feedback when they must alter the size of their drawing. The se findings point to the putative role of the basal ganglia in adjusti ng for the intermodal discrepancy between sensory feedback, and re-sca ling the size of movements.