ADAPTATION TO ALTERED VISUAL-VESTIBULAR FEEDBACK - MECHANISMS OF MAINTENANCE AND RECOVERY

Adaptation of perceived movement during head motion (apparent concomit ant motion, ACM) and the subsequent elimination of adaptation were stu died in two experiments. During the adaptation phase of both experimen ts, subjects performed voluntary 1-Hz head oscillations for 6 min whil e fixating a stimulus moving either in the same (with) direction as or the opposite (against) direction of head movements. In Experiment 1, ACM adaptation was measured following either a 1- or a 4-min delay aft er the adaptation phase. Results indicated some loss of adaptation dur ing the additional 3-min delay demonstrating a tendency of the system linking head and image to return to its preadaptation state following removal of an adaptation stimulus. In Experiment 2, subjects viewed a stimulus after adaptation that appeared to move minimally in the same manner as the adaptation stimulus during 3 min of head oscillations. N o loss of adaptation was measured in these subjects between the beginn ing and the end of the 3-min interval. In another condition, subjects viewed a stimulus that appeared to move alternately in the same direct ion as and in the opposite direction of the adaptation stimulus during a similar 3-min interval following adaptation. ACM adaptation was sub stantially reduced during this 3-min interval. These results implicate two mechanisms that: operate to either maintain or eliminate ACM adap tation. One is passive and operates in the absence of visual feedback to eliminate the short-term adapted state, and the other responds to p ostadaptation visual feedback.