Chapter 5

1. Chapter 5 Motor Control Theories Concept: Theories about how we control coordinated movement differ in terms of the roles of central and environmental features of a control system

2. Theory andProfessional Practice • What is theory? • Accurately describes a large class of observations • Make definite predictions about results of future observations (Hawking, 1996) • With motor learning and control, theories focus on: • Explaining human behavior • Providing explanations about why people perform skills as they do • Identifying variables through observations of these performances

3. THEORY (Miller, 1983) • A theory is a set of interconnected statements that describe UNOBSERVABLE structures or processes and relate them to each other and to unobservable invents. Theory gives meaning to facts, just as a blueprint provides the structure that transforms stones into a house

4. Motor Control Theory • Describes and explains how the nervous system produces coordinated movement of motor skill in a variety of environments • Two issues of importance: • Coordination • Degrees of freedom

5. Coordination • Patterning of body and limb motions relative to the patterning of environmental objects and events (Turvey, 1990) • Two parts to consider: • Movement pattern of a skill in relationship at a specific point of time • Context of the environment of the head, body, and/or limb movements so the actions can be accomplished

6. Degrees of Freedom • Number of independent elements in a central system and the ways each component can act • Degree of Freedom problem: • Control problem • Occurs in the designing of a complex system that produces a specific result • Involves determining how many degrees of freedom is required to produce the result

7. DF definition • Latitude of variation a statistical system has Two numbers have to add to 100 and one number is known = one DF DF the number of separate, independent dimension of movement in a system that has to be controlled

8. Nicolai Bernstein • 100 joints and 792 muscles • System has to act in a specific way • Large number od DF if different positions and speeds are needed for specific movement execution

9. Theory of Motor Control • FLEXIBILITY • UNIQUENESS • CONSISTENCY • MODIFIABILITY

10. FLEXIBILTY - Many ways to achieve the movement goal. - Using variety of muscular resourses

11. UNIQUENESS • A LARGE NUMBER OF VARIABLES INFLUENCE EACH MOVEMENT • MAKING IDENTICAL MOVEMENT IS IMPOSSIBLE

12. MODIFIABILITY • ABILITY TO ALTER A MOVEMENT DURING ITS PERFORMANCE • SAFETY • CREATIVITY

13. CONSISTENCY • ABILITY TO PERFORM THE TASK AS CLOSE TO THE TARGET AS POSSIBLE • TASK REPRODUCTION

14. Theories in Clinical Practice • Theory helps to interpret the behavior and allows the therapist to go beyond one patient • Framework for Behavioral Interpretation

15. Case study • Case: After a cerebral-vascular accident, a patient has flexed left arm at the elbow and uses toe-heel gate pattern • Theory: Reflex theory: abnormal reflexes (spasticity) are a major reason for patient’s dysfunction

16. Case study - Assumptions • Normal movement emerges as an interaction among many control systems • Movement is organized around a behavioral goal and in constrained by the environment • Interaction with environment leads to predictive and adaptive behavior

17. Guide for Clinical Action • Malfunction is a result of compensation for a deficiency of control systems • CNS causes a release of abnormal reflexes, normally organized at lower level of CNS

18. Cont… • Lesions in Motor cortex result in dysfunction • Lesions may release control of lower control centers – primitive pathological behavior may emerge

19. Motor Control Theories • Reflex theory • Hierarchical theories • Dynamic systems theories

20. Reflex Theories • Behaviour is explained by stereotype, involuntary responses to stimuli • Habits are developed through conditioning • A stimulus elicits the response as a result of practice

21. Hierarchical Theories • Brain orchestrates lower levels of CNS • Executive level • Effector level • Open loop • Closed loop • Generalized Motor Program

22. Open Loop andClosed Loop Systems • Models of basic descriptions that show the CNS and PNS initiate and control action • Each has a central executive • Executive generates and issues movement instructions to effectors (muscles/joints) • Both also contain movement instructions from control center to effectors

23. Open Loop Does not use feedback Control center provides all the information for effectors to carry out movement Closed Loop Uses feedback Control center issues information to effectors sufficient only to initiate movement Differences Betweenthe Systems • Two differences

24. Adams’ Closed Loop Theory • Memory Trace -produces movement -modest MP -selects action -shove towards the target • Perceptual trace -reference mechanism of correctness -memory of past movements -responsible for movement in progress -PT is developed by practice

25. Adams’ predictions • Interference with KR degrades learning • Errors decrease with KR • Degrading quality of perceptual feedback retards development of PT • Errors are damaging to PT

26. Two Theories ofMotor Control • Motor Program-based theory: memory-based construct that controls coordinated movement • Dynamic Pattern theory, a.k.a. Dynamic Systems: approach to describing and explaining the control of coordinated movement that emphasize the role of information in the environment and properties of the body/limbs

27. MP Definitions • 1890, William James: idea of motor action, clear image of the action • 1960, Franklin Henry: neural pattern of movement is controlled by a stored program, which is used to direct the motoneuron detail of motor performance

28. MP • 1968, Steven Keele: MP is a set of commands that are structured before a movement sequence begins and that allow the entire sequence to be carried out without influence of peripheral feedback.

29. MP, cont… • 1971, R. Schmidt: A motor program whose expression can be varied depending in the choice of certain parameters. -contains advanced instruction - sequence and timing -no capacity to correct errors MP is effective in the stable, predictable conditions

30. Schema theory • Schema is a set of rules that guide production of goal oriented movement • After movement is performed, the info about the movement is abstracted in four general areas

31. General memory areas • Environmental condition at the beginning of the movement • The specific requirement of the movement speed, force..) • The outcome of the movement and KR (comparison of the actual and intended outcome) • Sensory consequences

32. Schema theory predictions • Performer can perform a new movement of learned skill in novel situation • Practice improves ability to make new movements • Increase variety of practice contributes to a better experience with parameters

33. Motor Program-BasedTheory • Based on the work of Richard Schmidt (1988) • Hypothesized generalized motor program: mechanism accounting for adaptive and flexible qualities of human movement • Proposed that generalized motor program controls class of actions vs. specific movement

34. Motor Program-BasedTheory, cont’d • These “invariant factors” are the signatures of the generalized motor program (does not vary from one performance to another) • Parameters are specific movement features that can vary from one performance of a skill to another

35. Class of actions • Class of actions is controlled by “Invariant characteristics”: Relative timing and relative force. • Variant characteristics, Parameters: muscle involved, overall force, and duration are added to movement

36. Steps in movement organization • Response selection • Retrieve MP form LTM • In the response programing stage add parameters • Temporal pattern and relative force stay the same

37. Schmidt’s Schema Theory • Schema: rules that serve to provide the basis for a decision based from related experiences • Described two control components: • Generalized motor program – control mechanism responsible for controlling a class of actions, i.e., kicking • Motor response schema – responsible for providing the specific rules governing an action in a given situation

38. Schmidt’s Schema Theory, cont’d • This theory explains how a person can adapt to new situations or environmental contexts • Solves the degree of freedom problem

39. Dynamic Pattern Theory (a.k.a., Dynamical Systems) • Describes the control of coordinated movement that emphasizes the role of information in the environment and dynamic properties of the body/limbs • Seen from the perspective of nonlinear dynamics (behavioral changes are abrupt)

40. Stability and Attractors • Stability: behavioral steady state of a system • Attractors: stable behavioral steady states of systems • Preferred behavioral states • Energy efficient states

41. Order andControl Parameters • Order parameters, called collective variables • Functional specific and abstract variables that define the overall behavior of the system • Enable a coordinated pattern of movement that can be reproduced and distinguished from other patterns

42. Collective Variables Rhythmic Movements: Relative phase is the most prominent of order parameters which represents the movement relationship between two movement segments Aiming Movements: Equilibrium Point

43. Order andControl Parameters, cont’d • Control parameter • Variable, when increased or decreased, will influence the stability and character of the order parameter • Is important to identify since it becomes the variable to manipulate in order to assess the stability of the order parameter • Provides the basis for determining attractor states for patterns of limb movement

44. Control parameters • Control parameters (speed and force) change freely according to situation. • In research, the Control parameters are systematically changed and Collective variables are measured

45. Order andControl Parameters, cont’d • Self-Organization • When certain conditions characterize a situation, a specific pattern of limb movement emerges • This pattern of movement self-organizes within the characteristic of environmental conditions and limb dynamics

46. Coordinated Structures • Functional synergies of muscles and joints of a person’s nervous system which act cooperatively to produce an action • Develops through practice, experience, or naturally • Can be intrinsic (walking) or developed through practice

47. Perception andAction Coupling • Dynamic pattern theory • Essential element in accounting for skillful performance of open skills • The perception part of the interaction detects and uses critical invariant information in the environment

48. Perception andAction Coupling, cont’d • The action part involves the setting and regulating of movement control features that enable action goal achievement • For example, Greek letter “tau” () • Perceptual variable “tau” couples with dynamic movement

49. Present State of theControl Theory Issue • Motor program-based theory and dynamic pattern theory are the predominant behavioral theories addressing how the nervous system produces coordinated movement • Theory of control cannot focus exclusively on the movement information that is specified by the CNS

50. Present State of theControl Theory Issue, cont’d • Task and environmental characteristics must be taken into account (Newell, 1986) • Speculation of hybrid on a compromise theory could emerge, to explain the control of coordinated movement