Adaptation to displaced and delayed visual feedback from the hand.

S viewed an oscilloscope trace of a short bar which appeared at the position of his nonvisible right hand. The motion of the trace was equivalent to the movements of the hand, which were restricted to a frontal plane. The bar could be optically displaced by 20 diopter prisms, either to the left or right, and its motion could be made to lag behind that of the hand by 1 of 6 delay intervals ranging from 0.0 to 3.0 sec. Results show that the adaptation to displacement found with no delay is completely eliminated under all delay intervals, including the minimum of 0.3 sec. In recent years investigators have experimented with devices which introduce a time delay between the occurrence of an event and its registration at the eye. Normally, as 6 moves his hand, motion of its retinal image follows with a negligible lag caused by the transmission time of light. However, the new devices have been used to introduce delays in visual feedback ranging from a fraction of a second up to several seconds. A few authors have reported severe loss of control in self-paced, visually guided movements