What is a dynamic system? A system of elements that changes over time
Dynamic Systems: Background 1 n Systems approaches to development u Developmental psychobiologists working in 1940’s, 1950’s, 1960’s (Schneirla, Lehrman, Kuo) u Response to prevalent learning theory and ethological perspectives
n Goal of systems approach u Eliminate question of what is learned vs. what is innate u Behavior is complex, variable, and takes place in continually changing internal and external environments u Focus on relationships among components as source of change
Dynamic Systems: Background 2 n Dynamical systems u a class of mathematical equations that describe time-based systems with particular properties (e.g., complexity, nonlinearity) u examples: chemical reactions, global weather changes, dripping faucets, developing humans
Intellectual Goal of Dynamic Systems Theory What are the origins of novel forms of behavior? How can developing systems create something from nothing?
Traditional Approach Look for sources of new forms in either the organism or the environment (or both)
But…. n Who turns on the genes? n Who decides what the organism absorbs and retains? n There must be a causal agent who evaluates information and makes decisions. u Novelty doesn’t really develop; it’s there all along.
Dynamic Systems Approach n New forms emerge through processes of self-organization u patterns and order emerge from the interactions u of the multiple components of a complex system u without explicit instructions from organism or environment
Extraordinarily complex structural patterns can emerge from very simple initial conditions in dynamic systems During development, living things with particular properties spontaneously organize themselves into patterns
The question isn’t “What causes what to happen?” But rather “How does change happen?”
Not programs, structures, modules, and schemas But complexity, stability, and change
Little attention has been paid to the process of change in contemporary developmental psychology n Discovery of invariants (programs, stages, structures, modules) that underlie performance at different ages n Study of “core abilities”
The “Mind-as-Mountain Stream” Metaphor n Patterns in a fast-moving mountain stream are constant and regular n Emerge from immediate factors (e.g., rate of water flow, configuration of stream bed, weather, characteristics of water molecules) n And factors operating over different time scales (e.g., geological history of mountains, climate, erosion)
The “Mind-as-Mountain Stream” Metaphor n Behavior is the product of multiple, contributing influences n Each of which has a history n No distinction between real-time behavior and lifetime processes that contribute to it n Behavior is constructed by its own history and systemwide activity n Form is a product of process
Two Major Concepts 1. Behavior is softly assembled. u Behavior is assembled from all of the interacting parts at the moment u Assembly is flexible, not prescribed by a program
Development is a series of patterns evolving and dissolving over time and, at any point in time, possessing particular degrees of stability.
Two Major Concepts 2. Interaction between behavior and subsystems is non-linear. u A small change in one subsystem can lead to big changes in behavior.
Nonlinearity n Pattern coherence in dynamic systems is maintained despite internal fluctuations and small external perturbations (e.g., walking in high heels, while chewing gum) n But as system parameters or external conditions change (e.g., surface slope): u The old pattern loses coherence and stability u The system finds a qualitatively new pattern
This is a nonlinear phase shift Gradual changes in a slope steepness lead to gradual changes in walking, until a small change in slope causes a large change in gait style.
An Example: The Case of the Disappearing Reflex
The Disappearing Reflex n Newborns take “steps” when held upright with feet touching a table. n Within a few months, the “stepping reflex” disappears, and later reappears. n How and why does this happen?
Account #1: Brain Maturity Maturation of voluntary movement centers inhibits reflexive stepping.
Thelen and Fisher (1982) n Compared patterns of movement and muscle activity in babies’ legs as they stepped and kicked. n Identical patterns of muscle activity during kicking and stepping: u contraction to flex leg u relaxation -- leg pulled back down by gravity and springiness
The Problem: n Kicking and stepping involve the same muscles, and probably the same brain areas. n Babies continue to kick even after they stop stepping. n Why would stepping disappear and kicking remain? It doesn’t make sense!
What else could be going on? n During the period when stepping is suppressed, infants grow very rapidly. n Most growth is in subcutaneous fat, not muscle. n Babies’ legs get proportionally heavier, but not stronger. n More strength is required to lift the legs when upright than when supine.
Account #2: Dynamic Systems Theory n More strength is required to lift the legs when upright than when supine. n Before babies develop fat legs, they have no trouble lifting them in either posture. n As legs get fatter and heavier, muscle strength used to lift the legs isn’t enough to lift them in upright posture. u But kicking when lying down remains.
The Fish Tank Experiment (Thelen, Fisher, & Ridley- Johnson, 1984)
Weighting the Legs (Thelen, Fisher, & Ridley- Johnson, 1984)
Body fat deposition is a growth change that is not specific to leg movements. Yet it results in a qualitative shift in behavior.
Dynamic Systems Theory: Summary n Frames developmental questions in terms of when systems are stable, when they change, and what makes them change n Views traditionally separate domains as subsumed under the same dynamic processes n Captures the richness and complexity of real- life human behavior
Dynamic Systems Theory: Summary n There is no single element in the child- environment system that “determines” behavior or “controls” developmental change u Behavior and development are multiply determined n Behavior isn’t just in the brain. It’s in the brain-body-task-environment interaction.
Dynamic Systems Theory: Summary Everything matters