The effect of visuomotor displacements on arm movement paths

The gently curved paths evident in point-to-point arm movements have been a ttributed to both an imperfect execution of a planned straight-hand path or as an emergent property of a control strategy in which an intrinsic cost, dependent on arm dynamics, is minimised. We used a virtual visual feedback system to test whether path curvature was mainly determined by the visually perceived or actual location of the moving limb. Hand paths were measured for movements between three pairs of targets under both veridical and unifo rmly translated visual feedback. This allowed us to decouple the actual and perceived hand location during movement. Under different conditions of vis ual feedback the curvature of the hand paths did not correlate with either the visually perceived location of the limb or the actual location but rath er with the relative displacement between the actual and visually perceived limb locations. The results are consistent with the hypothesis that in pla nning a movement the internal estimate of intrinsic coordinates, such as jo int angles, is at least partially derived from visual information.