THE INTERACTION OF VISUAL AND PROPRIOCEPTIVE INPUTS IN POINTING TO ACTUAL AND REMEMBERED TARGETS

Errors in pointing to actual and remembered targets presented in three -dimensional (3D) space in a dark room were studied under various cond itions of visual feedback. During their movements, subjects either had no vision of their arms or of the target vision of the target but not of their arms, vision of a light-emitting diode (LED) on their moving index fingertip but not of the target, or vision of an LED on their m oving index fingertip and of the target. Errors depended critically up on feedback condition. 3D errors were largest for movements to remembe red target without Visual feedback diminished with vision of the movin g fingertip, and diminished further with vision of the target and visi on of the finger and the target. Moreover, the different conditions di fferentially influenced the radial distance, azimuth, and elevation er rors, indicating that subjects control motion along all three axes rel atively independently. The pattern of errors suggest that the neural s ystems that mediate processing of actual versus remembered targets may have different capacities for integrating visual and proprioceptive i nformation in order to program spatially directed arm movements.