Motor Learning: Changes in the Structure of Variability in a Redundant Task

Abstract

Although variability is a fundamental and ubiquitous feature of movement in all biological systems, skilled performance is typically associated with a low level of variability and, implicitly, random noise. Hence, during practice performance variability undergoes changes leading to an overall reduction. However, learning manifests itself through more than just a reduction of random noise. To better understand the processes underlying acquisition and control of movements we show how the examination of variability and its changes with practice provides a suitable window to shed light on this phenomenon. We present one route into this problem that is particularly suited for tasks with redundant degrees of freedom: task performance is parsed into execution and result variables that are related by some function which provides a set of equivalent executions for a given result. Variability over repeated performances is analyzed with a view to this solution manifold. We present a method that parses the structure of variability into four conceptually motivated components and review three methods that are currently used in motor control research. Their advantages and limitations are discussed.

Learning Spinal Manipulation Skills: Assessment of Biomechanical Parameters in a 5-Year Longitudinal Study

“…Therefore, during practice, motor performance undergoes changes that lead to an overall reduction of trial-to-trial variability. 17,18 Although global coordination improved linearly throughout both stages of learning, it was only in the second phase that learners reached values approaching those of experts. 5 These data clearly indicate, however, that global coordination is not totally mastered by the end of the academic training.…”

Reorganization of Finger Coordination Patterns During Adaptation to Rotation and Scaling of a Newly Learned Sensorimotor Transformation

“…Generalization developed along with a reduction of motion in those degrees of freedom not contributing to cursor motion (i.e., the task's null space). As recognized by Todorov and colleagues (Todorov 2004;Todorov and Jordan 2002) and others (Diedrichsen 2007;Latash et al 2007;Müller and Sternad 2009;Scheidt et al 2000;Scholz and Schöner 1999;Smith et al 2006), examining the evolution of behavior within the null space of the task provides insight into how the nervous system organizes and reorganizes patterns of coordination as it learns. In Mosier's study, reduction in the extent and variability of null-space motion may have reflected a minimization of task energetics or an optimization of some other measure of efficiency, an interpretation consistent with the view that motor planning and control can be understood as resulting from an interplay between competing kinematic, energetic, and/or other "costs of control" (Shadmehr and Krakauer 2008).…”

Whole Body Coordination and Knee Movement Control During Five Rehabilitation Exercises

“…It has been suggested that movement of all components in the system to constrain CoM movement [25] is achieved through a whole body synergy whereby movement of all constituent parts are related to each other. Movement variability of the constituent parts to some extent can cancel each other out so that an overall control parameter moves with reduced variability [21]. This co-variation or compensatory variability [26] during whole body movement has been demonstrated in a number of studies involving healthy subjects [25,[27][28].…”

“…Variability is equally considered part of normal movement and is considered to be essential for effective motor control and motor learning [19][20]; for instance better coordination has been associated with reduced magnitudes of movement fluctuations [21]. It is unlikely that minimizing frontal plane knee movement is principally the parameter that is controlled during normal functional movement.…”