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 – “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 Knee Joint Angle Hip Joint Angle 180 45 -10 85
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?