Two different motor learning mechanisms contribute to learning reaching movements in a rotated visual environment

Virginia Way Tong Chu; Terence David Sanger

doi:10.12688/f1000research.3676.2

Two different motor learning mechanisms contribute to learning reaching movements in a rotated visual environment

F1000Res. 2014 Mar 17:3:72. doi: 10.12688/f1000research.3676.2. eCollection 2014.

Authors

Virginia Way Tong Chu¹, Terence David Sanger²

Affiliations

¹ Department of Occupational Therapy, University of Illinois at Chicago, Chicago, IL 60612, USA.
² Departments of Biomedical Engineering, Neurology, and Biokinesiology, University of Southern California, Los Angeles, CA 90089-1111, USA.

Abstract

Practice of movement in virtual-reality and other artificially altered environments has been proposed as a method for rehabilitation following neurological injury and for training new skills in healthy humans. For such training to be useful, there must be transfer of learning from the artificial environment to the performance of desired skills in the natural environment. Therefore an important assumption of such methods is that practice in the altered environment engages the same learning and plasticity mechanisms that are required for skill performance in the natural environment. We test the hypothesis that transfer of learning may fail because the learning and plasticity mechanism that adapts to the altered environment is different from the learning mechanism required for improvement of motor skill. In this paper, we propose that a model that separates skill learning and environmental adaptation is necessary to explain the learning and aftereffects that are observed in virtual reality experiments. In particular, we studied the condition where practice in the altered environment should lead to correct skill performance in the original environment. Our 2-mechanism model predicts that aftereffects will still be observed when returning to the original environment, indicating a lack of skill transfer from the artificial environment to the original environment. To illustrate the model prediction, we tested 10 healthy participants on the interaction between a simple overlearned motor skill (straight hand movements to targets in different directions) and an artificially altered visuomotor environment (rotation of visual feedback of the results of movement). As predicted by the models, participants show adaptation to the altered environment and after-effects on return to the baseline environment even when practice in the altered environment should have led to correct skill performance. The presence of aftereffect under all conditions that involved changes in environment demonstrates separation of environmental adaptation and skill learning. Our results support the existence of two distinct learning modules with different adaptation properties. Therefore we suggest that adaptation to an altered environment may not be useful for training new skills.

Keywords: motor learning, adaptation, visual rotation, reaching.

Grants and funding

This study was conducted as part of a graduate research work at Stanford University, supported by grant 1103725-100-PAAWK from the National Institute of Health to Dr. Sanger, as well as by the Stanford University BIOX bioengineering graduate student fellowship. We acknowledge additional funding from the Crowley-Carter Foundation and the Don and Linda Carter Foundation.