Coordination dynamics of learning and transfer across different effector systems.
Résumé
If different effector systems share a common task-specific coordination dynamics, transfer and gener-alization of sensorimotor learning are predicted. Subjects learned a visually specified phase relationship with either the arms or the legs. Coordination tendencies in both effector systems were evaluated before and after practice to detect attractive states of the coordination dynamics. Results indicated that learning a novel relative phase with a single effector system spontaneously transferred to the other, untrained effector system. Transfer was revealed not only as improvements in performance but also as modifica-tions of each system’s initial (prelearning) coordinative landscape. What is learned, appears to be a high-level but neurally instantiated dynamic representation of skilled behavior that proves to be largely effector independent, at least across anatomically symmetric limbs. That animals and humans can achieve the same goal using different effectors (and, conversely, different goals using the same effectors) attests to the generative and multifunctional nature of the central nervous system (CNS). A notable example is human speech: The fixing (Kelso & Tuller, 1983; MacNeilage, 1980) or sudden perturbation (Kelso, Tuller, Vatikiotis-Bateson, & Fowler, 1984) of an articulator normally involved in the production of a sound is rapidly compensated by other, putatively coupled effec-tors in such a way as to preserve the speaker’s intent. This so-called motor equivalence (Hebb, 1949; Lashley, 1930) has led to the idea of a high-level, task- or function-specific structure that deals with action goals, relegating the details of muscle selection and activation to lower levels, such as the spinal interneuronal system (for a review, see Georgopoulos, 1997). Such units or modules are variously referred to as functional synergies or coor-