Composition and decomposition of internal models in motor learning under altered kinematic and dynamic environments

The learning process of reaching movements was examined under novel environ ments whose kinematic and dynamic properties were altered. We used a kinema tic transformation (visuomotor rotation), a dynamic transformation (viscous curl field), and a combination of these transformations. When the subjects learned the combined transformation, reaching errors were smaller if the s ubject first learned the separate kinematic and dynamic transformations. Re aching errors under the kinematic (but not the dynamic) transformation were smaller if subjects first learned the combined transformation. These resul ts suggest that the brain learns multiple internal models to compensate for each transformation and has some ability to combine and decompose these in ternal models as called for by the occasion.