Fundamental Concepts of Motor Development

January 17, 2018 | Author: Anonymous | Category: Science, Health Science, Neurology
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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 • 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!

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