Fundamental Concepts of Motor Development

1. Fundamental Concepts of Motor Development Developmental Systems Theories

2. History • maturation vs experience •  interaction • Systems theory – influenced PT 1980’s

3. Developmental Systems Theory

4. 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

5. How did we get here • dynamical systems theory • dynamical action theory • neuronal group selection theory

6. 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

7. 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

8. 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

9. Dynamic Systems Theory • Thelen • Used DST to offer “unconventional” explanation of disappearance of primitive walking - more about this later!

10. 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

11. Physical Principles • At critical points in the exchange of energy, the system becomes unstable, and a qualitatively new form of behavior emerges

12. Equilibrium State • Well understood example: • sitting balance • let’s try it!

13. 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

14. PT Perspective • I’ve seen that stable kind of behavior • How do I get the system to change? • Control parameters • Order parameters

15. Learning DST Language • Control Parameters and Order Parameters

16. Control Parameters • Control Parameters are like catalysts they precipitate change in motor behavior

17. 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

18. 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

19. Example of Developmental Control Parameter • Thelen proposed: • ↑ weight of the limb the disappearance of stepping

20. 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!

21. 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!

22. Order Parameters • Order Parameters • “simple” quantitative expressions that capture the complexity of movement coordination • Used to document changes in behavior

23. Measuring the Complexity of Stepping • Dynamical systems theory explains how complex movements change form • Walking to running, etc. • How are complex patterns measured?

24. 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

25. An Order Parameter – The Phase Plane Plot 45 Hip Joint Angle -10 85 180 Knee Joint Angle

26. 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!

27. 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

28. “simple” quantitative expressions that capture the complexity of movement coordination

29. 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”)

30. Why I prefer Variables • Variables can be manipulated in clinical practice – the level of measurement may not always be “quantitative” • The theory still holds!

31. Back to our Example • Control parameter = weight of the limb • Order variable = stepping (a complex behavior measured as present or absent!)

32. 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

33. Terminology: Constraint • 3 types of factors shape or guide motor behavior • attributes of individuals • characteristics of the environment • the goal task

34. Constraint • Attributes of individuals • physical size • flexibility • strength • cognitive capacity • what else?

35. Terminology: Constraint • Characteristics of the environment • physical environment • size, location, stability of objects and surfaces • social environment • support and motivation • audiences? • what else?

36. Terminology: Constraint • Task goal • movement or posture • speed or accuracy • what else?

37. Break!