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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
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Fundamental Concepts of Motor Development Developmental Systems Theories
History • maturation vs experience • interaction • Systems theory – influenced PT 1980’s
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 catalystto 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 85 180 Knee Joint Angle
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?