Fundamental Concepts of Motor
Development
Developmental Systems Theories
History
• maturation vs experience
•  interaction
• Systems theory – influenced PT 1980’s
Developmental Systems
Theory
Developmental System
• Any system that changes over time
• Developmental researchers are interested in
change across months, years, decades…
• Therefore developmental systemtheory is
attractive to motor development researchers
How did we get here
• dynamical systems theory
• dynamical action theory
• neuronal group selection theory
Dynamical System
• Any system that changes over time
• Specifically, an “open system”
– One that exchanges energy with the environment
• Change in the system explained using
principles of non-equilibrium thermodynamics
Dynamical System
– Non-Equilibrium Thermodynamics
• A system that through “open energy exchange” can
move between steady states and has the capacity to
create increasingly complex order
Dynamic Systems
• Open Systems
– free exchange of energy
from the outside
– living systems are “open”...
exchanging food, air, etc.
– information is also
considered a form of
“energy”
• think of a sensory receptor
picking up energy from the
environment)
• Closed Systems
– limited exchange of energy
from the outside
– an atom is a relatively
closed system
– no system is completely
closed
Dynamic Systems Theory
• Thelen
• Used DST to offer “unconventional”
explanation of disappearance of primitive
walking - more about this later!
Physical Principles
• Living organisms are subject to the laws of
physics (thermodynamics)
– Systems close to an equilibrium state return to
equilibrium when perturbed
– Open systems can exist in a state removed from
equilibrium and given sufficient energy can
reorganize into a new (or different) behavior
Physical Principles
– At critical points in the exchange of energy, the
system becomes unstable, and a qualitatively new
form of behavior emerges
Equilibrium State
• Well understood example:
– sitting balance
– let’s try it!
Physical Principles
– Systems exhibit 1 of 2 possible phases
• A creative phase (a developmental phase)
– when the system is unstable
• A stable phase
– when the system maintains a specific form of behavior
PT Perspective
• I’ve seen that stable kind of behavior
• How do I get the system to change?
• Control parameters
• Order parameters
Learning DST Language
• Control Parameters and Order Parameters
Control Parameters
• Control Parameters are like catalysts they
precipitate change in motor behavior
Control Parameter
• A factor that shifts behavior from one form to
another.
• A control parameter must be scalar... allowing
study of varying magnitudes of the variable
• A control parameter does not control the
change in behavior but rather acts as a
catalyst for reorganization of the behavior
Disappearance of Early Stepping
• Newborns have the capacity to perform
stepping movements when held erect
– Maturational theory proposed:
• newborn stepping is a “primitive reflex” one that is
present early in infancy and later disappears –
• Stepping reflex as a result of neural maturation
– brain stem structures (tonic reflexes) begin to dominate
behavior
–  positive supporting reactions
Example of Developmental Control
Parameter
• Thelen proposed:
– ↑ weight of the limb
the disappearance of
stepping
Test of Dynamic Systems Theory
• Put babies who had stopped stepping into a
water bath (effectively reducing the relative
weight of the limb through buoyancy)
– Stepping reappeared!
• Back on dry land
– Stepping disappeared!
Control Parameter
• a variable that can be “scaled” to act as a
catalyst to change behavior
– hard to change the weight of the limb
– but easier to strengthen the limb!
Order Parameters
• Order Parameters
– “simple” quantitative expressions that capture the
complexity of movement coordination
– Used to document changes in behavior
Measuring the Complexity of Stepping
• Dynamical systems theory explains how
complex movements change form
– Walking to running, etc.
• How are complex patterns measured?
Order Parameter
• A collective variable... a graphic or
mathematical representation of complex
movement that is a “simple” quantitative
expression that captures the complexity of
movement coordination
An Order Parameter –
The Phase Plane Plot
45
Hip Joint
Angle
-10
85
Knee Joint Angle
180
Order Parameters
• Order Parameters
– “simple” quantitative expressions that capture the
complexity of movement coordination
– Used to document changes in behavior
– Yeah, right… I am going to document the change
using phase plane plots!
Dynamical Systems Theory
• Researchers test theory using “Parameters”
thus suggest “quantitative measures” of
control and order variables
– making it difficult for clinicians to document
outcomes
“simple” quantitative expressions that capture the complexity of
movement coordination
Parameters versus Variables
• Parameter
– a factor that changes and the change can be
measured quantitatively
• Variable
– a factor that varies
• variation can be measured numerically
(“quantitatively”)
• or…variation can be measured by description
(“qualitatively”)
Why I prefer Variables
• Variables can be manipulated in clinical
practice – the level of measurement may not
always be “quantitative”
• The theory still holds!
Back to our Example
• Control parameter = weight of the limb
• Order variable = stepping (a complex behavior
measured as present or absent!)
Order Parameters
• Variables used to document a system’s
behavior:
– Determine effects of different factors on pattern
stability
– Discover variables that could precipitate pattern
change
– Scale the variable to test Dynamical Systems
Theory
Terminology: Constraint
• 3 types of factors shape or guide motor
behavior
– attributes of individuals
– characteristics of the environment
– the goal task
Constraint
– Attributes of individuals
•
•
•
•
physical size
flexibility
strength
cognitive capacity
• what else?
Terminology: Constraint
– Characteristics of the environment
• physical environment
– size, location, stability of objects and surfaces
• social environment
– support and motivation
– audiences?
• what else?
Terminology: Constraint
– Task goal
• movement or posture
• speed or accuracy
• what else?
BREAK!