Context-dependent arm pointing adaptation

We sought to determine the effectiveness of head posture as a contextual cu e to facilitate adaptive transitions in manual control during visuomotor di stortions. Subjects performed arm pointing movements by drawing on a digiti zing tablet, with targets and movement trajectories displayed in real time on a computer monitor. Adaptation was induced by presenting the trajectorie s in an altered gain format on the monitor. The subjects were shown visual displays of their movements that corresponded to either 0.5 or 1.5 scaling of the movements made. Subjects were assigned to three groups: the head ori entation group tilted the head towards the right shoulder when drawing unde r a 0.5 gain of display and towards the left shoulder when drawing under a 1.5 gain of display; the target orientation group had the home and target p ositions rotated counterclockwise when drawing under the 0.5 gain and clock wise for the 1.5 gain; the arm posture group changed the elbow angle of the arm they were not drawing with from full flexion to full extension with 0. 5 and 1.5 gain display changes. To determine if contextual cues were associ ated with display alternations, the gain changes were returned to the stand ard (1.0) display. Aftereffects were assessed to determine the efficacy of the head orientation contextual cue compared to the two control cues. The h ead orientation cue was effectively associated with the multiple gains. The target orientation cue also demonstrated some effectiveness while the arm posture cue did not. The results demonstrate that contextual cues can be us ed to switch between multiple adaptive states. These data provide support f or the idea that static head orientation information is a crucial component to the arm adaptation process. These data further define the functional li nkage between head pasture and arm pointing movements. (C) 2001 Elsevier Sc ience B.V. All rights reserved.