Chapter 5Chapter 5

Motor Control TheoriesMotor 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 PracticeTheory and Professional Practice

What is a theory?What is a theory?–Accurately describes a large class of observationsAccurately describes a large class of observations–Make definite predictions about results of future observations Make definite predictions about results of future observations

(Hawking, 1996)(Hawking, 1996)

Theories of motor learning and control focus on:Theories of motor learning and control focus on:–Explaining human movement behaviorExplaining human movement behavior–Providing explanations about why people perform skills as they Providing explanations about why people perform skills as they

dodo

Does a theory have relevance to professional practice?Does a theory have relevance to professional practice?–Provides the “why” basis for what practitioners doProvides the “why” basis for what practitioners do

[[See Figure 5.1See Figure 5.1]]

Motor Control TheoryMotor Control Theory

Describes and explains how the nervous Describes and explains how the nervous system produces coordinated movement system produces coordinated movement of motor skill in a variety of environmentsof motor skill in a variety of environments

Two important terms:Two important terms:–CoordinationCoordination–The degrees of freedom problemThe degrees of freedom problem

CoordinationCoordination

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

Two parts to consider:Two parts to consider:–Movement pattern of a skill in relation to a specific Movement pattern of a skill in relation to a specific

point of timepoint of time–Context of the environment of the head, body, Context of the environment of the head, body,

and/or limb movements so the actions can be and/or limb movements so the actions can be accomplishedaccomplished

Degrees of Freedom ProblemDegrees of Freedom Problem

Degrees of freedom (df) =Degrees of freedom (df) = Number of independent Number of independent elements in a system and the ways each element can elements in a system and the ways each element can actact

Degrees of freedom problem =Degrees of freedom problem = How to control the df to How to control the df to make a complex system act in a specific waymake a complex system act in a specific way

–e.g. The control of a helicopter’s flight (described in e.g. The control of a helicopter’s flight (described in the textbook)the textbook)

Degree of freedom problem for the control of movement:Degree of freedom problem for the control of movement:–How does the nervous system control the many df of muscles, How does the nervous system control the many df of muscles,

limbs, and joints to enable a person to perform an action as limbs, and joints to enable a person to perform an action as intended?intended?

Two General Types of Two General Types of Control SystemsControl Systems

Open- and Closed-Loop Control SystemsOpen- and Closed-Loop Control Systems[[See Figure 5.3See Figure 5.3]]Incorporated into all theories of motor controlIncorporated into all theories of motor controlModels of basic descriptions to show different ways Models of basic descriptions to show different ways the CNS and PNS initiate and control actionthe CNS and PNS initiate and control actionEach has a central control center (executive)Each has a central control center (executive)

–Function to generate and forward movement instructions Function to generate and forward movement instructions to effectors (i.e., muscles)to effectors (i.e., muscles)

Each includes movement instructions from control Each includes movement instructions from control center to effectorscenter to effectors

–Content of the instructions differs between systemsContent of the instructions differs between systems

Differences Between the SystemsDifferences Between the SystemsOpen-LoopOpen-Loop

Does not use feedbackDoes not use feedbackControl center provides all the information for effectors to Control center provides all the information for effectors to carry out movementcarry out movement

–Does not use feedback to continue and terminate movementDoes not use feedback to continue and terminate movement

Closed-LoopClosed-Loop

Uses feedbackUses feedbackControl center issues information to effectors sufficient Control center issues information to effectors sufficient only to initiate movementonly to initiate movement

–Relies on feedback to continue and terminate movementRelies on feedback to continue and terminate movement

Movement control center

Movementeffectors

MovementControl center

Movement effectors

Movement instructions

Movement instructions

Two Theories of Motor ControlTwo Theories of Motor Control

1.1. Motor Program-based theory:Motor Program-based theory: Memory-based Memory-based mechanism that controls coordinated mechanism that controls coordinated movementmovement

2.2. Dynamic Pattern theory (a.k.a. Dynamical Dynamic Pattern theory (a.k.a. Dynamical Systems):Systems): Describes and explains coordinated Describes and explains coordinated movement control by emphasizing the role of movement control by emphasizing the role of information in the environment and information in the environment and mechanical properties of the body and limbsmechanical properties of the body and limbs

Motor Program-Based TheoryMotor Program-Based Theory

Best example comes from “Schema Theory” by Best example comes from “Schema Theory” by Schmidt (1988)Schmidt (1988)

Generalized motor program (GMP):Generalized motor program (GMP): Hypothesized memory-based mechanism Hypothesized memory-based mechanism responsible for adaptive and flexible qualities of responsible for adaptive and flexible qualities of human movementhuman movement

Proposed that each GMP controls a Proposed that each GMP controls a class of class of actionsactions that have common that have common invariantinvariant characteristicscharacteristics

Motor Program-Based Theory, Motor Program-Based Theory, cont’dcont’dGMP FunctionGMP Function

–To serve as the basis for generating movement instructions To serve as the basis for generating movement instructions prior toprior to andand duringduring the performance of an action the performance of an action

GMP CharacteristicsGMP CharacteristicsInvariant featuresInvariant features

–Characteristics of the GMP that do not vary across performances of Characteristics of the GMP that do not vary across performances of a skill within class of actionsa skill within class of actions

–The identifying signature of a GMPThe identifying signature of a GMP

ParametersParameters –Specific movement features added to the invariant features to Specific movement features added to the invariant features to

enable the performance of a skill in a specific situationenable the performance of a skill in a specific situation

–Characteristics can vary from one performance of a skill to anotherCharacteristics can vary from one performance of a skill to another

Motor Program-Based Theory, Motor Program-Based Theory, cont’dcont’d

Invariant features and parametersInvariant features and parametersExample of an invariant featureExample of an invariant feature

–Relative time of the components of an action (i.e. % of Relative time of the components of an action (i.e. % of total time each component uses during performance)total time each component uses during performance)

Example of a parameterExample of a parameter–Overall time (i.e.) for performing a skillOverall time (i.e.) for performing a skill

An Analogy from Music and DanceRelative time = Rhythm (beat) of the music, e.g. The 3 beats to a measure for a waltzOverall time = Tempo (The speed at which you waltz) Regardless of how fast or slow you waltz, the rhythm remains the same (i.e. invariant)

GMP for WalkingGMP for WalkingInvariantInvariant– Relative time for gait cycle phases - Relative time for gait cycle phases -

ParameterParameter– Walking speedWalking speed

Motor Program-Based Theory: Motor Program-Based Theory: Testing Relative Time InvarianceTesting Relative Time InvarianceExperiment by Shapiro et al. (1981)Experiment by Shapiro et al. (1981)Used gait characteristics to test prediction of Used gait characteristics to test prediction of relative time relative time invarianceinvariance for a class of actions controlled by a GMP: for a class of actions controlled by a GMP:Are walking and running one or two classes of Are walking and running one or two classes of action?action?Assessed 4 components of 1 step cycleAssessed 4 components of 1 step cycleCalculated Calculated relative timerelative time for each component at 9 for each component at 9 different speeds (3 – 12 different speeds (3 – 12 km/hrkm/hr))

– Relative timeRelative time = % of total time each component required = % of total time each component required for 1 step cyclefor 1 step cycle

Results:Results: Relative time similar within speeds when walking Relative time similar within speeds when walking but different from speeds when running (similar within but different from speeds when running (similar within speeds when running)speeds when running) [[See Figure 5.5See Figure 5.5]]

Dynamic Pattern Theory Dynamic Pattern Theory (a.k.a., Dynamical Systems)(a.k.a., Dynamical Systems)

Describes the control of coordinated movement that Describes the control of coordinated movement that emphasizes the role of information in the environment emphasizes the role of information in the environment and dynamic properties of the body/limbsand dynamic properties of the body/limbs

Began to influence views about motor control in early Began to influence views about motor control in early 1980’s1980’s

Views the process of human motor control as a Views the process of human motor control as a complex systemcomplex system that behaves like any complex that behaves like any complex biological or physical systembiological or physical system

Concerned with identifying Concerned with identifying lawslaws (natural and physical) (natural and physical) that govern changes in human coordination patternsthat govern changes in human coordination patterns

Dynamic Pattern Theory ConceptsDynamic Pattern Theory Concepts

Motor control system operates on the basis Motor control system operates on the basis of non-linear dynamics:of non-linear dynamics:Behavioral changesBehavioral changes are not always continuous, are not always continuous, linear progressions butlinear progressions but often make sudden and often make sudden and abrupt changes abrupt changes

Behaviors specified by environmental and task Behaviors specified by environmental and task characteristics/conditionscharacteristics/conditions

Behaviors are self-organizedBehaviors are self-organized

Dynamic Pattern Theory Concepts: Dynamic Pattern Theory Concepts: AttractorsAttractors

Attractor – Attractor – A stable state of the motor control A stable state of the motor control system that leads to behavior according to system that leads to behavior according to preferred coordination patterns (preferred coordination patterns (e.g. walkinge.g. walking))

Characteristics of an attractorCharacteristics of an attractor::Identified by order parametersIdentified by order parameters ( (e.ge.g., relative phase)., relative phase)

Control parameters (Control parameters (e.ge.g., speed) influence order ., speed) influence order parameters parameters

Minimum trial-to-trial performance variabilityMinimum trial-to-trial performance variability

Stability – Stability – Retains present state despite perturbationRetains present state despite perturbation

Energy efficientEnergy efficient

Dynamic Pattern Theory Concepts: Dynamic Pattern Theory Concepts: Order and Control ParametersOrder and Control Parameters

Order parametersOrder parameters–Also called collective variablesAlso called collective variables–Functionally specific and abstract variables Functionally specific and abstract variables

that define the overall behavior of the systemthat define the overall behavior of the system–Enable a coordinated pattern of movement Enable a coordinated pattern of movement

that can be reproduced and distinguished from that can be reproduced and distinguished from other patternsother patterns

–Relative phaseRelative phase is the most prominent of is the most prominent of order parameters which represents the order parameters which represents the movement relationship between two movement relationship between two movement segments (see chapter 2)movement segments (see chapter 2)

Order and Control Parameters, Order and Control Parameters, cont’d cont’d

Control parameterControl parameter–A variable, when increased or decreased, A variable, when increased or decreased,

will influence the stability and character of the will influence the stability and character of the order parameterorder parameter

–Is important to identify since it becomes Is important to identify since it becomes the variable to manipulate in order to assess the variable to manipulate in order to assess the stability of the order parameterthe stability of the order parameter

–Provides the basis for determining Provides the basis for determining attractor states for patterns of limb movementattractor states for patterns of limb movement

Dynamic Pattern Theory Concepts: Dynamic Pattern Theory Concepts: Self-OrganizationSelf-Organization

Self-OrganizationSelf-Organization–When certain conditions characterize a When certain conditions characterize a

situation, a specific pattern of limb movement situation, a specific pattern of limb movement emergesemerges

–This pattern of movement self-organizes This pattern of movement self-organizes within the characteristic of environmental within the characteristic of environmental conditions and limb dynamicsconditions and limb dynamics

Attractors and Self-Organization for Attractors and Self-Organization for Movement CoordinationMovement Coordination

Gait TransitionsGait TransitionsResearch (Research (to be discussed to be discussed more in ch. 7more in ch. 7) shows that if ) shows that if a person begins walking on a person begins walking on treadmill at slow speedtreadmill at slow speedTreadmill speed increases Treadmill speed increases every few minutes every few minutes Person begins to run at a Person begins to run at a certain speed [certain speed [not same not same speed for all peoplespeed for all people]]Same effect if person begins Same effect if person begins running on treadmill - running on treadmill - Begins to walk at certain Begins to walk at certain speedspeed

Swim Stroke TransitionsSwim Stroke TransitionsResearch in France (2004)Research in France (2004)14 elite male swimmers14 elite male swimmersEach trial involved a swim Each trial involved a swim velocity increase [began at velocity increase [began at preferred velocity]preferred velocity]Arm-stroke analysis showed 2 Arm-stroke analysis showed 2 distinct arm movement distinct arm movement coordination modescoordination modesBegan in one mode but abruptly Began in one mode but abruptly began 2began 2ndnd mode at a specific mode at a specific swim velocityswim velocity

Attractors and Self-Organization for Attractors and Self-Organization for Movement Coordination, cont’dMovement Coordination, cont’d

Discuss how the two research examples on the Discuss how the two research examples on the previous slide demonstrate the dynamic previous slide demonstrate the dynamic pattern theory concepts of:pattern theory concepts of:

Self-organizationSelf-organization Control parameterControl parameter Attractors Attractors ((i.e., stable coordination statesi.e., stable coordination states)) Non-linear behavior changeNon-linear behavior change

Dynamic Pattern Theory Concepts: Dynamic Pattern Theory Concepts: Coordinative StructuresCoordinative Structures

Functional synergies (Functional synergies (i.ei.e. cooperative groups) . cooperative groups) of muscles and joints that act cooperatively to of muscles and joints that act cooperatively to produce an actionproduce an action

–If a perturbation stops one set of muscles from If a perturbation stops one set of muscles from working, another works in its place working, another works in its place

e.g. walking with a leg caste.g. walking with a leg cast

Develop through practice, experience, or Develop through practice, experience, or naturallynaturally

Dynamic Pattern Theory Concepts: Dynamic Pattern Theory Concepts: Perception and Action CouplingPerception and Action Coupling

The linking together (The linking together (i.ei.e. coupling) of movement to . coupling) of movement to environmental informationenvironmental information

The perception part The perception part –The detection of critical invariant information in the environmentThe detection of critical invariant information in the environment

The action part The action part –The movement that becomes associated with what is specified The movement that becomes associated with what is specified

by the environmental informationby the environmental information

An exampleAn example–When walking, the time to contact an object in your pathway When walking, the time to contact an object in your pathway

(specified by the perception of the changing size of the object) (specified by the perception of the changing size of the object) determines when you initiate stepping over the object determines when you initiate stepping over the object

i.e. Your stepping action is “coupled” with your visual perception i.e. Your stepping action is “coupled” with your visual perception of the objectof the object

Present State of the Control Present State of the Control Theory IssueTheory Issue

Currently, both the motor program-based theory Currently, both the motor program-based theory and dynamic pattern theory predominateand dynamic pattern theory predominateResearch investigating each has shown that a Research investigating each has shown that a theory of motor control cannot focus exclusively theory of motor control cannot focus exclusively on movement information specified by the CNSon movement information specified by the CNS

–Task and environmental characteristics must be also Task and environmental characteristics must be also be taken into accountbe taken into account

Speculation exists that a hybrid of the two Speculation exists that a hybrid of the two theories as a compromise theory could emerge theories as a compromise theory could emerge to explain the control of coordinated movementto explain the control of coordinated movement