Transcript Dynamical systems

Dynamic Systems
Theory
What is a dynamic system?
A system of elements that
changes over time
Dynamic Systems:
Background 1

Systems approaches to development
 Developmental
psychobiologists working in
1940’s, 1950’s, 1960’s (Schneirla,
Lehrman, Kuo)
 Response to prevalent learning theory and
ethological perspectives

Goal of systems approach
 Eliminate
question of what is learned vs.
what is innate
 Behavior is complex, variable, and takes
place in continually changing internal and
external environments
 Focus on relationships among components
as source of change
Dynamic Systems:
Background 2

Dynamical systems
a
class of mathematical equations that
describe time-based systems with
particular properties (e.g., complexity,
nonlinearity)
 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….
Who turns on the genes?
 Who decides what the organism
absorbs and retains?
 There must be a causal agent who
evaluates information and makes
decisions.

 Novelty
along.
doesn’t really develop; it’s there all
Dynamic Systems Approach

New forms emerge through processes
of self-organization
 patterns
and order emerge from the
interactions
 of the multiple components of a complex
system
 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
Discovery of invariants (programs,
stages, structures, modules) that
underlie performance at different ages
 Study of “core abilities”

The “Mind-as-Mountain
Stream” Metaphor

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Patterns in a fast-moving mountain stream
are constant and regular
Emerge from immediate factors (e.g., rate of
water flow, configuration of stream bed,
weather, characteristics of water molecules)
And factors operating over different time
scales (e.g., geological history of mountains,
climate, erosion)
The “Mind-as-Mountain
Stream” Metaphor
Behavior is the product of multiple,
contributing influences
 Each of which has a history
 No distinction between real-time
behavior and lifetime processes that
contribute to it
 Behavior is constructed by its own
history and systemwide activity
 Form is a product of process

Two Major Concepts
1.
Behavior is softly assembled.


Behavior is assembled from all of the
interacting parts at the moment
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.

A small change in one subsystem can
lead to big changes in behavior.
Nonlinearity


Pattern coherence in dynamic systems is
maintained despite internal fluctuations and
small external perturbations (e.g., walking in
high heels, while chewing gum)
But as system parameters or external
conditions change (e.g., surface slope):
 The
old pattern loses coherence and stability
 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
Newborns take “steps” when held
upright with feet touching a table.
 Within a few months, the “stepping
reflex” disappears, and later reappears.
 How and why does this happen?

Account #1: Brain Maturity
Maturation of voluntary movement
centers inhibits reflexive stepping.
Thelen and Fisher (1982)
Compared patterns of movement and
muscle activity in babies’ legs as they
stepped and kicked.
 Identical patterns of muscle activity
during kicking and stepping:

 contraction
to flex leg
 relaxation -- leg pulled back down by
gravity and springiness
The Problem:
Kicking and stepping involve the same
muscles, and probably the same brain
areas.
 Babies continue to kick even after they
stop stepping.
 Why would stepping disappear and
kicking remain? It doesn’t make sense!

What else could be going on?
During the period when stepping is
suppressed, infants grow very rapidly.
 Most growth is in subcutaneous fat, not
muscle.
 Babies’ legs get proportionally heavier,
but not stronger.
 More strength is required to lift the legs
when upright than when supine.

Account #2: Dynamic
Systems Theory
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More strength is required to lift the legs when
upright than when supine.
Before babies develop fat legs, they have no
trouble lifting them in either posture.
As legs get fatter and heavier, muscle
strength used to lift the legs isn’t enough to lift
them in upright posture.
 But
kicking when lying down remains.
The Fish Tank Experiment
(Thelen, Fisher, & RidleyJohnson, 1984)
Average Steps per Minute
25
20
15
10
5
0
Out-of-Water
In-Water
Weighting the Legs
(Thelen, Fisher, & RidleyJohnson, 1984)
Average Steps per Minute
25
20
15
10
5
0
Without Weights
Weights Added
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

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Frames developmental questions in terms of
when systems are stable, when they change,
and what makes them change
Views traditionally separate domains as
subsumed under the same dynamic
processes
Captures the richness and complexity of reallife human behavior
Dynamic Systems Theory:
Summary

There is no single element in the childenvironment system that “determines”
behavior or “controls” developmental
change
 Behavior
and development are multiply
determined

Behavior isn’t just in the brain. It’s in the
brain-body-task-environment interaction.
Dynamic Systems Theory:
Summary
Everything matters