Motor control is a young and aspiring field of natural science. Over the past 40 years, it has become an established field of study with several important theoretical developments, including the equilibrium-point hypothesis and its more recent version known as the control with referent spatial coordinates, the principle of abundance, the uncontrolled manifold hypothesis, and the concept of dynamic neural field as the means of task formulation. Important experimental advances have included the exploration of the notion of synergies, the links between descending signals from the brain and referent coordinates of the effectors, and applications of motor control principles to analysis of disordered movements. Further maturation of motor control requires focusing on theory-driven studies. It promises fruitful applications to applied fields such as movement disorders and rehabilitation.
Motor Control: Creating a Natural Science of Biological Movement
Mark L. Latash
Abundant Degrees of Freedom Are Not a Problem
Mark L. Latash
The problem of motor redundancy has been one of the fundamental, albeit elusive, problems in motor control. Traditionally, it has been viewed as a computational problem for the brain, solved with either optimization methods or by introducing additional constraints to motor tasks. This review suggests that the problem was wrongly formulated, and that the abundant degrees of freedom are not to be eliminated but used to ensure dynamic stability of motor performance, which is vital given the unpredictable intrinsic states and external forces. The idea of synergies as mechanisms ensuring action stability is introduced based on the uncontrolled manifold hypothesis and the theory of control with spatial referent coordinates. The importance of controlled stability is illustrated with the phenomena of anticipatory synergy adjustments. This approach is productive for both basic and applied fields as illustrated, in particular, by changes in motor synergies with neurological disorder and exercise.
Human Movement: In Search of Borderlands Between Philosophy and Physics
Scott Kretchmar and Mark L. Latash
In this essay, we adopt a theory of behavior developed by the French philosopher Maurice Merleau-Ponty in an attempt to find common ground between philosophy and physics. We look for ways to reconcile matter with meaning, physical motion with the principles of ethics, body with mind. We proceed in three steps, first by providing a review of Merleau-Ponty’s theory; second by showing how ethical behavior is constrained and shaped by factors found in physics, chemistry, and biology; and, finally, by describing how physical motion is affected by factors that transcend the laws of classical physics. For the latter purpose, we accept a theory of parametric control of movements with spatial referent coordinates. Our purpose is not to solve specific problems of motor control or moral decision making but, rather, to test a general theoretical scheme that carries a number of practical implications for both research and education, including the need for collaboration between and among diverse research subdisciplines in kinesiology.