Motor Skill Learning
MOTOR SKILL LEARNING
A variety of motor skills occur in various forms of movement: work, play, sport, communication, dance, and so on. Psychophysical studies of the learning and retention of motor skills date from the 1890s, with neurophysiological studies coming later. Attempts to combine cognitive and neural approaches flourished in the twentieth century (Bernstein, 1967) and persist unabated, capitalizing on advances in technology.
The theoretical and operational emphases of this field parallel those in other subdomains of learning, in part because motor, perceptual, and cognitive skills are not mutually exclusive and in part because of anatomical advances that show the underlying modular architecture of the brain (Houk, 2001). Definitions of motor skills typically pertain to the movements of the limbs and torso as opposed to those of perceptions and the formulation of ideas, but the conceptual boundaries blur in the face of the planning that precedes elaborate motor acts.
How do people learn and remember how to dance, type, hop, play the piano, and tie their shoelaces? Bartlett (1932) said of the skilled tennis player, "When I make the stroke I do not, as a matter of fact, produce something absolutely new, and I never merely repeat something old." A central issue in the learning of motor skills is how the movement form is acquired through practice and retained over time. A related issue is the role that variations of movement form play in realizing the goal of the act. These two issues, movement invariance and motor equivalence, have been the focus of the theorizing about the acquisition and retention of motor skills.
Motor skills involve two distinctive operations: One is to select, recall, and initiate the movement segment required at each stage in a task; the other is to guide the trajectories of the movement segments so that they achieve the subgoals required to complete the task. Much of the work on skill learning and retention has emphasized the second operation, the refinement of trajectories based on the experience gained through the sensory consequences of the movement (Adams, 1971).
The emerging conceptions of cognitive psychology challenged the one-to-one memory accounts of movement representation. An outgrowth of this trend was Schmidt's (1975) schema theory of motor learning, which promoted a one-to-many representational construct for both recall and recognition processes of movement control. The representation for each memory state consisted of the relations between task, organism, and environmental variables rather than the absolute levels of the variables themselves. The schema was a generic rule for a given class of movements that allowed the generalization of movement outcome to a variety of task and environmental circumstances. Schema theory proposed that the more variable the practice within the potential class of movements (e.g., variations in the length, velocity, and/or angle of a forehand drive in tennis), the more general the schema rule would become for that activity. Neurobiologically based theories of movement control seem to be able to account for most of this framework (Bertier et al., 1993).
The schema theory seemed to provide a solution to two enduring problems in motor-skill acquisition and retention: novelty and the limited storage capacity. The novelty problem addresses the question of how the performer accommodates to novel tasks and environmental circumstances. The limited storage capacity of the CNS arises as a consequence of the many one-to-one representations that would be generated from an individual's lifetime movement experience, especially in the absence of schema theory. The Schmidt schema theory could not resolve the novelty problem because it did not explain the initial establishment of the movement class; it accounted only for changes in the scaling of force, velocity, or position of a given action pattern (such as a tennis forehand drive) rather than the generation of pattern of the forehand drive movement—perhaps because it did not interface with the emerging knowledge about the basal ganglia (Houk and Wise, 1995).
During the 1980s one-to-one and one-to-many prescriptive accounts of motor-skill learning were challenged by the tenets of the ecological approach to perception and action (Kugler and Turvey, 1987). The ecological approach seeks the solution to motor learning through the mapping of perception and action with minimal appeal to the representational processes typically posited by cognitive psychologists. A central concern has been the appropriateness of cognitive strategies proposed to map the emergent movement dynamics into a rule-based symbolic representation.
The emergent structure and variability of the movement sequence was subsequently analyzed in terms of physical-systems solutions to the mapping of the gradient and equilibrium regions of the perceptual and motor processes (Kugler and Turvey, 1987; Schoner and Kelso, 1988). A physical approach to the study of the learning and retention of motor skills must contend with the question of how information and dynamics relate to the intention of the performer. Learning can be viewed as an exploratory activity, with the performer searching for stable regions of the perceptual and motor dynamics that realize the goal of the act (Newell et al., 1989).
The 1990s saw a rising interest in understanding how the networks of the brain might learn to generate motor command signals capable of controlling skilled movements. Neural-network models of the cerebellum based on the anatomy and physiology of these circuits helped to relate skill acquisition and performance to many fundamental features of motor performance, such as the one-to-many representational construct for motor programs (Berthier et al., 1993) and the predictive capacity required to prevent instability caused by closed-loop control (Barto et al., 1999). Models of the interaction between the cerebellum and the cerebral cortex suggested the manner in which memories might be translocated to improve the speed and automaticity of practiced skills. New techniques such as transcranial magnetic stimulation are shedding light on the changes in the motor cortex that occur with practice (Classen et al., 1998). Functional imaging of the brain is helping to define the networks that participate in motor programming (van Mier et al., 1998).
Traditional theories of motor learning and retention fail to capture many of the qualities of the progression from novice to expert in skill acquisition. The development of a skill is a continuous exploratory activity, not a replica of a static representation of action. Neurobiological cognitive models, based on new techniques for studying brain activation, combined with the ecological approach to perception and action, are beginning to capture some of the important qualities, both invariant and changing, of the dynamics of motorskill acquisition and retention.
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Revised byJames C.Houk