The coupling matrix.

The coupling matrix for model M8 is shown for selected trials during the Training phase experienced by G1 to G4 (Training phase was identical for these groups). Before experiencing any errors, all elements of the matrix are zero (Trial 1). The force field is then experienced on both Out and Return movements, resulting in the development of coupling between the corresponding errors (both positive errors). Early in Training phase (trials 10 and 20), there are large errors and the coupling matrix accumulates a weighting away from the origin. As adaptation progresses (trials 30 to 50) the errors reduce. As a result, the coupling shifts towards the origin and increases. The coupling matrix for G5 (not shown) remains unchanged (as in Trial 1) throughout the Training phase as errors are only experienced on the Out movements.