The role of proprioception and attention in a visuomotor adaptation task

The role of proprioception in the control and adaptation of visuomotor rela tionships is still unclear. We have studied a deafferented subject, IW, and control subjects in a task in which they used single joint elbow extension to move to a visual target, with visual feedback of the terminal position provided by a cursor displayed in the plane of their movements. We report t he differences in movement accuracy between the deafferented subject and co ntrols in the normal task and when challenged with a cognitive load, counti ng backwards. All subjects were less accurate when counting; this was a sma ll effect for the controls (<10% change) but much greater for the deafferen ted subject (>60% change). We also examined changes in movement kinematics when the instructed amplitude was altered via a changed gain between final arm position and presentation of the feedback cursor. The deafferented subj ect maintained temporal movement parameters stable and altered amplitude by scaling force (i.e. changed peak velocity), whereas the controls scaled bo th movement velocity and duration. Finally, we compared the subjects' adapt ation of movement amplitude after a period of exposure to the changed visuo motor gain. The deafferented subject was able to adapt, but his adaptation was severely impaired by the counting task. These results suggest that prop rioception is not an absolute requirement for adaptation to occur. Instead, proprioception has a more subtle role to play in the adjustment to visuomo tor perturbations. It has an important role in the control of reaching move ments, while in the absence of proprioception, attention appears necessary to monitor movements.