chapter 5

theories of motor control
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Terms in this set (...)

theory
framework that helps understand phenomena and explain why phenomena exist or behave as they do
who defined good theory
Stephen Hawking
define good theory
accurately describe large class of observations
make definite predictions about the results of future observations
relevance of Motor ctrl theories for the practioner
foundation for developing effective preactice environments for skill instruction or intervention strategies for rehabilitation
5 things theories enable practitioners to do and example of stroke pt
1. identify performance problems
WHAT IS THE PROBLEM?
2. develop intervention strategies
WHAT INTERVENTIONS MAY HELP?
3. develop systematic approaches to increase ability
WHAT IS THE BEST APPROACH?
4. predict effectiveness of intervention strategies
HOW MUCH IMPROVEMENT WILL OCCUR?
5.create new intervention strategies
ARE NOVEL INTERVENTIONS NEEDED?
MCT on behavioral level
explain observed behavior w/o attempting to specify neural-level ft of control

propose laws and principles that govern coordinated human motor behavior

*good theory should address biomechanics and neurophysiology
Key issues of importance to theories of motor control
coordination

degrees of freedom
coordination
patterning of head, body, and/or limb motions relative to the patterning of environmental objects and events
Key aspects in the definition of coordination
Patterns of head, body and limb movements
- ex: angles/relationship btwn limbs, pattern of displacement

Organization



Relative to pattern of environmental objects and events
Nicolai Bernstein
Russian physiologist

nervous system had to solve what he termed the "degrees of freedom"
Degrees of Freedom
-helicopter pedal, propeller example

-number of independent elements and components in a control system and the number of ways each component can act

-each element is free to vary in a specific way
ex: the elbow joint can flex and extend

Involves controlling a complex system made up of many joints and muscles

Problem involves determining how to constrain the degrees of free to produce the specific behavior
Open loop control system
all information needed to initiate and execute and action is contained in the initial instruction
ex: videocassete recorder, throwing a dart at a dartboard
Closed loop control system
during movement execution, feedback is compared with a standard reference to enable movement
ex: thermostat in a house, driving a car
Difference Between Closed-Loop and Open-Loop Control Systems
Feedback
-closed-loop feedback permits the CNS to make corrections to ongoing movements

Movement Instructions
-open-loop controls system issues all necessary info for movement execution
-closed-loop control system initially issue incomplete movement instructions
Motor Program-Based Theory
movement instructions are specified by the CNS
Dynamic Pattern Theory
movement instructions are specified by dynamic interactions of the environment with the musculoskeletal and nervous systems
motor program
memory representation that stores the info needed to perform an action

solves the DOF problem
Richard Schmidt
proposed generalized motor program

recognized that previous views limited the motor program to controlling specific movements or sequences of movements
Generalized motor program
Control mechanism repsonsible for controlling the general characteristics of classes of action

ex: throwing, kicking, walking, running

Memory representation of a class of actions that have a common set of invariant features

Controlling the class of actions provides the basis for controlling a specific action
Invariant features
Attributes that do not vary from one performance of the action to another

Fundamental pattern of the class of actions
**ex: relative timing, relative force
Parameters
Features that can be varied from one performance of a skill to another

Allow the performer to meet the specific movement demands of the situation
**ex: overall duration, overall force
Schmidt as Schema Theory
Formalized theory of how the GMP operates

Schema is a rule or set of rules that serves to provide the basis for a motor decision

Schema provides an abstract representation of rules governing movement

Used schema concept to describe GMP and motor response schema, control components involved in the learning and control of skills, the motor response schema provides parameters to the GMP

Adaptation occurs by updating schema when motor actions occur in new situations or environmental contexts

Executive control operations organize generalized motor programs and schemas to solve the degrees of freedom problem
Motor response schema
provides specific rules governing an action in a given situation

provides parameters to the generalized motor program
Dynamic Pattern Theory
Variant of dynamical systems theory

Emphasis on role of info in environment and dynamic properties of the musculoskeletal system

Movement patterns emerge as a function of the constraints placed on them

Views human movement control as a complex system that behaves in ways similar to any complex bio or physical system

Views human motor control from perspective of nonlinear dynamics
Non linear dynamics
Properties or behaviors that change in abrupt, non linear ways in response to systematic changes of a specific variable

Ex: boiling water, finger tapping, walk-to-run
Key features of dynamic pattern theory
attractors
self organization
order parameters
control parameters
coordinative structure
perception-action coupling
Attractors
stable behavioral steady states of systems

characterize preferred behavioral states
ex: in-phase and anti-phase finger movements

minimal behavioral variability and optimal energy efficiency
self organization
emergence of stable patterns due to the presence of certain conditions rather than specific control mechanisms

ex: jogging emerges as a walk faster, in-phase finger movements emerge during rapid finger tapping
Order parameters
collective variable

functionally specific variable that define the overall behavior of a system

enable a coordinated pattern of movement to be reproduced and distinguished from other patterns

ex: relative phase(in-phase out of phase- 180 deg/360 deg)
Control parameters
variables that can freely change across different action situation, move performer into a new attractor state(ie direction, speed, perceptual info)

changing a control parameter can alter the stability of an order parameter

provide the basis for defining attractor states

ex: changing movement speed can create transitions between attractor
Coordinative structures
muscle synergies

functionally specific collectives of muscles and joints that act cooperatively during actions

may exist naturally or occur through practice
Intrinsic coordinative structures
muscles and joints of the limbs have natural tendency to demo coordination patterns early in life

ex: involved in actions such as walking, running, bimanual coordination
Learned coordinative structures
develop through practice

new combos of muscles and joints that act together to produce a coordination patttern that allows the achievement of a action goal

ex: tennis serve, swim stroke
Perception-action coupling
permit interactions between performer and environment during movement

spatial and temporal coordination of vision with hands or feet
Present State of Control Theory Issue
Control theories cannot focus exclusively on movement information specified by CNS

Environmental characteristics must be taken into account

Some would like to see compromise between the two theories
Modern Control Theories
Forward control models(Miall, Wolpert)
Bayesian Decision Theory(Wolpert, Kording)
Optimal Control Theory (Wolpert, Shadmehr)
Optimal
Q's about dynamic
...
PT relearning to walk in relation to dynamic pattern theory
After an injury the patient will display a given gait pattern as
result of the constraints imposed on the system.
Patients leg strength serves as a control parameter.
As the patient's legs become stronger it leads to changes in
the walk (coordinative structures).
Walking improves through practice involving walking in all
different situational constraints (perceptual action
coupling)
In other words, increases in leg strength could cause a
phase shift and a new gait (attractor state) could selforganize.