Motor Control Theory
Chapter 5 – slide set 4
The crucial relationship is:

From the last slide set…
• Between the order parameter(s), control
parameter(s) and stability…
• For the baby stepping:
•Order parameter = step reflex; control parameters
= fat weight, muscle strength, environment
• Energy efficiency is the overall guide to the
circumstances under which the step is more
or less stable
The crucial relationship is:

So where does the step part of the
movement come from?
• Remember the idea of interacting parts of a
system (from the water example)?
• Here the interacting parts are muscles, and
their connections
• When innervated as a whole, the babies
muscles resolve themselves into a kick
The crucial relationship is:
• …and the dynamics of the CNS adapting to
the most energy efficient solution to the
problem (given enough time and experience)
•Leads to many “local solutions”
•Learning progresses by de-stabilizing these
in favor of more effective solutions
• Think of developing bad habits in sport, and trying
to get out of them – the longer they have persisted,
the more stable they are and the harder they are
to break
Relating to humans – another example –
running and walking (see link below)
1. Order
Parameter
2. Control
parameter
3. Attractor
state
A
B
C
http://perso.wanadoo.fr/l.d.v.dujardin/ct/cusp.html#applet2
But really – how does it apply to
humans??? Another example:
In-phase:
Faster and faster…
Kelso & Scholtz, 1985
But really – how does it apply to
humans??? Another example:
In-phase:
Faster and faster…
& Scholtz,
KelsoKelso
& Scholtz,
19851985
But really – how does it apply to
humans??? Another example:
Anti-phase:
Faster and faster…
& Scholtz,
KelsoKelso
& Scholtz,
19851985
But really – how does it apply to
humans??? Another example:
Anti-phase:
Faster and faster…
& Scholtz,
KelsoKelso
& Scholtz,
19851985
But really – how does it apply to
humans???

Coordination
Stability
Stability and attractors
• The in-phase and out-of-
Variation in jt. Angles
(arbitrary units)
Difference between
jt. Angles
180
160
140
120
100
80
60
40
20
0
Anti-phase
In-phase
•
phase states in the Kelso
example are attractor
states for the movement
Perturbing the
movement when it is in
a stable attractor region
will result in a quick
return to stability (inphase)
But really – how does it apply to
humans???

Coordination
Stability and attractors
•
Stability
Variation in jt. Angles
(arbitrary units)
Difference between
jt. Angles
180
160
140
120
100
80
60
40
20
0
Anti-phase
In-phase
•
Perturbing the movement
when it is close to a region
of instability will result in
either a longer period of
instability followed by a
resumption of the original
state, or a new attractor
state
When close to a period of
transition, the movement
will exhibit critical
fluctuations
• the movement will be
more ‘wobbly,’ less stable
Exploring the coordination of movement
using synergetics
1.
2.
3.
4.
5.
6.
7.
8.
Define system and joint motions used to perform task
Scale a parameter within the task and identify the
slowest “moving” relationships of joint motions (order
parameter)
Scan the dynamics of the slow moving relationships
Identify the preferred and non-preferred patterns
Choose a potential control parameter
Determine the relative stability of the patterns within
a phase transition experiment
Mathematically model your system
Test the model
Properties of DST

Attractor states are characterized by

Self-organization
• optimal energy efficiency
• Stability
• Motor development example:
• The emergence of the shape of the step
wasn’t dictated by the brain, but emerged as
a consequence of the interplay amongst a
whole range of variables.
Properties of DST

Coordinative structures
• Partial solution to the degrees of freedom problem
• joint or limb components ‘linked’ to each other
during movement
• become sensitive to the movements of other parts
• they become one structure for the purposes of
coordination
•Kelso et al. (1984) – jaw movements
•Arytunyen et al. (1980) – pistol shooting
Properties of DST

Perception-action coupling
• Rather than the brain specifying behavior, the
environment specifies behavior (such as timing) –
that is it constrains the movement in an important
way
• There are many examples of this:
• Long-jump (Lee, Lishman & Thomson, 1982)
• Control of braking (Lee, 1976)
• Catching (Savelsburgh, Whiting & Bootsma, 1992)
Perception-action coupling - examples
Perception-action coupling - examples
Other thoughts...
“Embodied
cognition” in
artificial
intelligence
Other thoughts...
Pictures from Thelen’s (and
Ulrich’s) early research –
stepping and kicking
Other thoughts...
Pictures from Thelen’s (and
Ulrich’s) early research –
“walking” on a treadmill
Other thoughts...
Data from Thelen et al. 1993:
two children showing very
different approaches to reaching
for an object. However...
...by the end
of the first
year, the
movements
are very
similar.
What does
that say
about the
search for
coordination
?
Other thoughts...
Schematic from Thelen et al. 2001: the
“A not B” problem. A truly complex and
adaptive case of modeling order and
control parameters...see next slide
Other thoughts...
Excerpt from Spencer et al (2006): the
“A not B” problem. A list of control
parameters in the task. And another
comment on embodied cognition. DST
doesn't only deal with movement.