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
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]
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
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
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?
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
Differences Between the Systems
Open-Loop
Movement
control center
Movement instructions
Movement
effectors
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
Closed-Loop
Movement
Control center
Movement instructions
Movement
effectors
Uses feedback
Control center issues information to effectors sufficient
only to initiate movement
– Relies on feedback to continue and terminate movement
Two Theories of Motor Control
1.
2.
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
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
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
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)
GMP for Walking
Invariant
– Relative time for gait cycle phases -
Parameter
– Walking speed
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]
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
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
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
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)
Order and Control Parameters,
cont’d
Control parameter
– 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
Dynamic Pattern Theory Concepts:
Self-Organization
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
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
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
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
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
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