Trends in Motor Control

1. Trends in Motor Control Spring 2010

2. Study of Motor Behavior in the 20th Century • S-R approaches (Black Box) • Hierarchical models (Active Processor) • Dynamic systems (Dynamic interplay among systems)

3. Prior to the 1900’s – introspection and self report measures • Turn of the century – observable only • S-R tradition • Bernstein’s work • Interactions of brain, body, and movement • World War II – Profound effects of motor control work

4. After World War II • Emphasis shifted to teaching, transfer, and retention • Late 40’s • Craik – Information Processing • Brain – computer relationship • Welford • Single Channel Processing • Psychological Refractoriness

5. Poulton’s work on anticipation and prediction in the 1950’s • Effector • Receptor • Perceptual • Fitts’ Law • Speed Accuracy Tradeoff (Length and width) • Movement time • Movement extent • Movement accuracy

6. S-R Theory • In stimulus response models the stimulus triggers a chain of individual reflex circuits that create a response. In this view the performer is a passive recipient responding to the stimuli present in the environment and to which he or she is confronted • Goal directed????

7. Hierarchical models • Motor programs began with the definition of a fixed set of commands that could be structured prior to movement initiation. Schmidt (1975, 1991) provided the concept of a generalized motor program (GMP). “…existence of parameters, some variant, some invariant, that are applied to the GMP in order to specify how a particular movement pattern is to be expressed. These parameters specify overall duration of a movement, the overall force need to accomplish the movement, the temporal phasing of the movement pattern and, the spatial and temporal order in which the components of the movement are to be executed” (Schmdt, p. 5)

8. Henry Adams Schmidt Bernstein Turvey Kelso Thelen Hierarchical control mechanisms Dynamic control mechanisms

9. How is the motor program defined? • A fixed program that can be run off uninterrupted by peripheral feedback. • “The little man inside the head”

10. Henry and Rogers (1960) • Memory drum theory • “This is because a more comprehensive program i.e., a larger amount of stored information, will be needed, and thus the neural impulses will require more time for coordination and diretion into the eventual motor neurons and muscles” (Henry & Rogers, 1960, p. 450). • Henry and Rogers (1960) would have argued that a more complicated movement is dependent on the complex search and ordering of the subroutines thereby affecting the reaction time to a stimulus.

11. Chaos Theory • Complexity Theory • Coordinative Structure Theory • Dynamic Pattern Theory

12. Dynamic Systems Approach • Perception/action model • Invariant motor behavior • Coordinative structures and dissipative structures • Ecological approach • Perturbation • Attractor state

13. Dynamic Systems • Dynamic systems models focus on the interaction between the performer and the environment. • Dynamic systems models differ from information processing models by the way the action is produced. In a dynamic system motor behavior results from the interaction of many systems: neurological, biological, musculoskeletal. These constantly change. • Dynamic systems are emergent.

14. A Dynamic System is Self-organizing • In a self-organizing system no subsystem has high order control. The model is not a hierarchical one.

15. Coordination • “… The process by which an individual constrains or, condenses his or her available degrees of freedom into the smallest number possible to achieve the goal… (Rose, 1996; P11).

16. Coordinative Structures or Synergies • Synergies result from the organizational structures that coordinate the degrees of freedom for a particular movement. Some are ready-built and available at birth but the majority are developed throughout the lifespan and learned. • Muscles are not controlled individually but are functionally linked with other muscles so as to form autonomous systems.

17. Movements Emerge from Constraints Organism Movement Environment Task

18. Context specific variables (Bernstein) • Anatomical • E.g., pectoralis major adducts the arm except when the angle of the arm is above the shoulder then contraction of the pectoralis major abducts the arm • Mechanical • Relationship between the state of the muscle and the movement sequence • Gravity • Inertia • Physiological • The motoneuron responds to signals from the brain and the spinal cord (which work together).