Comparing adaptation of constrained and unconstrained movements in three dimensions

This paper describes targeted reaching exper- iments conducted using a new augmented reality system. Combining a large-workspace immersive virtual environment with physical force feedback, the system distorted subjects' movements using a viscous curl force field Following previous experiments using a different robot, half the subjects were constrained to horizontal, planar movements. The remaining subjects performed unconstrained movements throughout the 3D workspace. Examining after-effects as an indication of learning, we found that constrained subjects learned the force field. However, it was difficult to detect whether the uncon- strained subjects learned forces of identical magnitude. Our results found that force fields strengths eliciting constrained 2D adaptation have difficulty exhibiting after-effects for un- constrained 3D movements. The increased motor variability for 3D reaching movements requires consideration for future experimental design.