Chapter 5 Motor Control Theories Concept Theories about

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

Theory and Professional Practice n What is theory? • Accurately describes a large class of observations • Make definite predictions about results of future observations (Hawking, 1996) n 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

THEORY (Miller, 1983) n 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

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

Coordination n Patterning of body and limb motions relative to the patterning of environmental objects and events (Turvey, 1990) n 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

Degrees of Freedom n Number of independent elements in a central system and the ways each component can act n 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

DF definition n 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

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

Theory of Motor Control n FLEXIBILITY n UNIQUENESS n CONSISTENCY n MODIFIABILITY

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

UNIQUENESS - A LARGE NUMBER OF VARIABLES INFLUENCE EACH MOVEMENT - MAKING IDENTICAL MOVEMENT IS IMPOSSIBLE

MODIFIABILITY n ABILITY TO ALTER A MOVEMENT DURING ITS PERFORMANCE n SAFETY n CREATIVITY

CONSISTENCY n ABILITY TO PERFORM THE TASK AS CLOSE TO THE TARGET AS POSSIBLE n TASK REPRODUCTION

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

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

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

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

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

Motor Control Theories n Reflex theory n Hierarchical theories n Dynamic systems theories

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

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

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

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

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

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

Two Theories of Motor Control 1. 2. 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

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

MP n 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.

MP, cont… n 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

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

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

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

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

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

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

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

Schmidt’s Schema Theory n Schema: rules that serve to provide the basis for a decision based from related experiences n 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

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

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

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

Order and Control Parameters n 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

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

Order and Control Parameters, cont’d n 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

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

Order and Control Parameters, cont’d n Self-Organization • When certain conditions characterize a situation, a specific pattern of limb movement emerges • This pattern of movement selforganizes within the characteristic of environmental conditions and limb dynamics

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

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

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

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

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

Chapter 5 Motor Control Theories