1. Motor Control Theories
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 and Professional Practice
What is a theory?
Accurately describes a large class of observations
Make definite predictions about results of future observations (Hawking, 1996)
Theories of motor learning and control focus on:
Explaining human movement behavior
Providing explanations about why people perform skills as they do
Does a theory have relevance to professional practice?
Provides the “why” basis for what practitioners do
[See Figure 5.1]

3. Motor Control Theory
Describes and explains how the nervous system produces coordinated movement of motor skill in a variety of environments
Two important terms:
Coordination
The degrees of freedom problem

4. 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 relation to a specific point of time
Context of the environment of the head, body, and/or limb movements so the actions can be accomplished

5. Degrees of Freedom Problem
Degrees of freedom (df) = Number of independent elements in a system and the ways each element can act
Degrees of freedom problem = How to control the df to make a complex system act in a specific way
e.g. The control of a helicopter’s flight (described in the textbook)
Degree of freedom problem for the control of movement:
How does the nervous system control the many df of muscles, limbs, and joints to enable a person to perform an action as intended?

6. Two General Types of Control Systems
Open- and Closed-Loop Control Systems
[See Figure 5.3]
Incorporated into all theories of motor control
Models of basic descriptions to show different ways the CNS and PNS initiate and control action
Each has a central control center (executive)
Function to generate and forward movement instructions to effectors (i.e., muscles)
Each includes movement instructions from control center to effectors
Content of the instructions differs between systems

7. Differences Between the Systems
Open-Loop
Does not use feedback
Control center provides all the information for effectors to carry out movement
Does not use feedback to continue and terminate movement
Movement instructions
Movement
control center
Movement
effectors
Closed-Loop
Uses feedback
Control center issues information to effectors sufficient only to initiate movement
Relies on feedback to continue and terminate movement
Movement instructions
Movement
Control center
Movement
effectors

8. Two Theories of Motor Control
Motor Program-based theory: Memory-based mechanism that controls coordinated movement
Dynamic Pattern theory (a.k.a. Dynamical Systems): Describes and explains coordinated movement control by emphasizing the role of information in the environment and mechanical properties of the body and limbs

9. Motor Program-Based Theory
Best example comes from “Schema Theory” by Schmidt (1988)
Generalized motor program (GMP): Hypothesized memory-based mechanism responsible for adaptive and flexible qualities of human movement
Proposed that each GMP controls a class of actions that have common invariant characteristics

10. Motor Program-Based Theory, cont’d
GMP Function
To serve as the basis for generating movement instructions prior to and during the performance of an action
GMP Characteristics
Invariant features
Characteristics of the GMP that do not vary across performances of a skill within class of actions
The identifying signature of a GMP
Parameters
Specific movement features added to the invariant features to enable the performance of a skill in a specific situation
Characteristics can vary from one performance of a skill to another

11. Motor Program-Based Theory, cont’d
Invariant features and parameters
Example of an invariant feature
Relative time of the components of an action (i.e. % of total time each component uses during performance)
Example of a parameter
Overall time (i.e.) for performing a skill
An Analogy from Music and Dance
Relative time = Rhythm (beat) of the music, e.g. The 3 beats to a measure for a waltz
Overall time = Tempo (The speed at which you waltz)
Regardless of how fast or slow you waltz, the rhythm remains the same (i.e. invariant)

12. GMP for Walking Invariant Parameter
Relative time for gait cycle phases -
Parameter
Walking speed

13. Motor Program-Based Theory: Testing Relative Time Invariance
Experiment by Shapiro et al. (1981)
Used gait characteristics to test prediction of relative time invariance for a class of actions controlled by a GMP:
Are walking and running one or two classes of action?
Assessed 4 components of 1 step cycle
Calculated relative time for each component at 9 different speeds (3 – 12 km/hr)
Relative time = % of total time each component required for 1 step cycle
Results: Relative time similar within speeds when walking but different from speeds when running (similar within speeds when running) [See Figure 5.5]

14. 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
Began to influence views about motor control in early 1980’s
Views the process of human motor control as a complex system that behaves like any complex biological or physical system
Concerned with identifying laws (natural and physical) that govern changes in human coordination patterns

15. Dynamic Pattern Theory Concepts
Motor control system operates on the basis of non-linear dynamics:
Behavioral changes are not always continuous, linear progressions but often make sudden and abrupt changes
Behaviors specified by environmental and task characteristics/conditions
Behaviors are self-organized

16. Dynamic Pattern Theory Concepts: Attractors
Attractor – A stable state of the motor control system that leads to behavior according to preferred coordination patterns (e.g. walking)
Characteristics of an attractor:
Identified by order parameters (e.g., relative phase)
Control parameters (e.g., speed) influence order parameters
Minimum trial-to-trial performance variability
Stability – Retains present state despite perturbation
Energy efficient

17. Dynamic Pattern Theory Concepts: Order and Control Parameters
Order parameters
Also called collective variables
Functionally 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
Relative phase is the most prominent of order parameters which represents the movement relationship between two movement segments (see chapter 2)

18. Order and Control Parameters, cont’d
A 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

19. Dynamic Pattern Theory Concepts: 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

20. Attractors and Self-Organization for Movement Coordination
Gait Transitions
Research (to be discussed more in ch. 7) shows that if a person begins walking on treadmill at slow speed
Treadmill speed increases every few minutes
Person begins to run at a certain speed [not same speed for all people]
Same effect if person begins running on treadmill - Begins to walk at certain speed
Swim Stroke Transitions
Research in France (2004)
14 elite male swimmers
Each trial involved a swim velocity increase [began at preferred velocity]
Arm-stroke analysis showed 2 distinct arm movement coordination modes
Began in one mode but abruptly began 2nd mode at a specific swim velocity

21. Attractors and Self-Organization for Movement Coordination, cont’d
Discuss how the two research examples on the previous slide demonstrate the dynamic pattern theory concepts of:
Self-organization
Control parameter
Attractors (i.e., stable coordination states)
Non-linear behavior change

22. Dynamic Pattern Theory Concepts: Coordinative Structures
Functional synergies (i.e. cooperative groups) of muscles and joints that act cooperatively to produce an action
If a perturbation stops one set of muscles from working, another works in its place
e.g. walking with a leg cast
Develop through practice, experience, or naturally

23. Dynamic Pattern Theory Concepts: Perception and Action Coupling
The linking together (i.e. coupling) of movement to environmental information
The perception part
The detection of critical invariant information in the environment
The action part
The movement that becomes associated with what is specified by the environmental information
An example
When walking, the time to contact an object in your pathway (specified by the perception of the changing size of the object) determines when you initiate stepping over the object
i.e. Your stepping action is “coupled” with your visual perception of the object

24. Present State of the Control Theory Issue
Currently, both the motor program-based theory and dynamic pattern theory predominate
Research investigating each has shown that a theory of motor control cannot focus exclusively on movement information specified by the CNS
Task and environmental characteristics must be also be taken into account
Speculation exists that a hybrid of the two theories as a compromise theory could emerge to explain the control of coordinated movement