Hypotheses of learning and generalization of a visuomotor rotation – the case of orientation-matching.

(a)-(b) Extrinsic learning hypothesis—transfer of learning of an extrinsically represented axis. (c)-(d) Intrinsic learning hypothesis—transfer of learning of an intrinsically represented axis. The dark and light hands represent the expected initial and final orientations of the hand, respectively. The black rotation axes are drawn with respect to an extrinsic reference frame. The colors are as in Fig 3. If participants adapt to the visuomotor rotation while training, their aim is expected to gradually deviate from the ideal BL1 axis in the direction opposite to that of the perturbation. If participants transfer the perturbation across orthogonal initial orientations, their aim is expected to deviate in the same direction from the ideal BL2 axis in the early transfer trials. The spheres present the hypotheses regarding the hand rotation axis in an intrinsic reference frame at each key trial. The early TRN axis may deviate from the ideal BL1 axis due to corrections. Axes which are ideally equal, such as the ideal BL1 and ideal BL2 axes in (d), were separated for better visualization.