Intermanual transfer of learning reveals representations in simultaneous extrinsic and intrinsic coordinate systems

Recent research on learning and recovery in rehabilitation has raised questions about the manner in which the nervous system stores and recalls memories of skills learned. This is functionally important when an individual is asked to generalize what was learned to a different movement direction, another part of the workspace, or with the opposite hand. Subjects underwent training in Cartesian force field (Saddle type field) in a training workspace. This experiment built upon other approaches by testing before and after training in a new workspace and with the opposite hand in the presence of both extrinsic (Cartesian-based) and intrinsic (joint-based) force fields. Results show that training led to clearly better performance improvements in the extrinsic coordinate system, and also suggest that subjects are influenced by a joint based force field when they are asked to transfer their knowledge their opposite arm. These results suggest that there are multiple simultaneous representations of the training experience in the nervous system that subjects can recall when asked to generalize. These results may be important to the design of future rehabilitation regimens that optimize the training coordinate systems for the best chances of restoration of function.