Trends in Motor Control
Fall 2010
Study of Motor Behavior in the 20th
Century
S-R approaches (Black Box)
 Hierarchical models (Active Processor)
 Dynamic systems (Dynamic interplay
among systems)

Prior to the 1900’s – introspection and
self report measures
 Turn of the century – observable only

◦ S-R tradition

Bernstein’s work
◦ Interactions of brain, body, and movement

World War II – Profound effects of motor
control work

After World War II
◦ Emphasis shifted to teaching, transfer, and
retention

Late 40’s
◦ Craik – Information Processing
◦ Brain – computer relationship
 Welford
 Single Channel Processing
 Psychological Refractoriness

Poulton’s work on anticipation and prediction in
the 1950’s
◦ Effector
◦ Receptor
◦ Perceptual

Fitts’ Law
◦ Speed Accuracy Tradeoff (Length and width)
 Movement time
 Movement extent
 Movement accuracy
S-R Theory
In stimulus response models the stimulus
triggers a chain of individual reflex circuits
that create a response. In this view the
performer is a passive recipient
responding to the stimuli present in the
environment and to which he or she is
confronted
 Goal directed????

Hierarchical models
Motor programs began with the definition of a fixed set
of commands that could be structured prior to
movement initiation. Schmidt (1975, 1991) provided the
concept of a generalized motor program (GMP).
“…existence of parameters, some variant, some invariant,
that are applied to the GMP in order to specify how a
particular movement pattern is to be expressed. These
parameters specify overall duration of a movement, the
overall force need to accomplish the movement, the
temporal phasing of the movement pattern and, the
spatial and temporal order in which the components of
the movement are to be executed” (Schmdt, p. 5)

Henry
Adams
Schmidt
Bernstein
Turvey
Kelso
Thelen
Hierarchical control
mechanisms
Dynamic control
mechanisms
How is the motor program
defined?

A fixed program that can be run off
uninterrupted by peripheral feedback.

“The little man inside the head”
Henry and Rogers (1960)

Memory drum theory
◦ “This is because a more comprehensive program i.e.,
a larger amount of stored information, will be needed,
and thus the neural impulses will require more time
for coordination and diretion into the eventual motor
neurons and muscles” (Henry & Rogers, 1960, p.
450).
◦ Henry and Rogers (1960) would have argued that a
more complicated movement is dependent on the
complex search and ordering of the subroutines
thereby affecting the reaction time to a stimulus.
Chaos Theory
 Complexity Theory
 Coordinative Structure Theory
 Dynamic Pattern Theory

Dynamic Systems Approach
Perception/action model
 Invariant motor behavior
 Coordinative structures D
 Dissipative structures
 Ecological approach
 Perturbation
 Attractor state

Dynamic Systems
Dynamic systems models focus on the interaction
between the performer and the environment.
 Dynamic systems models differ from information
processing models by the way the action is
produced. In a dynamic system motor behavior
results from the interaction of many systems:
neurological, biological, musculoskeletal. These
constantly change.
 Dynamic systems are emergent.

A Dynamic System is Self-organizing

In a self-organizing system no subsystem
has high order control. The model is not
a hierarchical one.
Coordination

“… The process by which an individual
constrains or, condenses his or her
available degrees of freedom into the
smallest number possible to achieve the
goal… (Rose, 1996; P11).
Coordinative Structures or Synergies
Synergies result from the organizational
structures that coordinate the degrees of
freedom for a particular movement. Some are
ready-built and available at birth but the
majority are developed throughout the lifespan
and learned.
 Muscles are not controlled individually but are
functionally linked with other muscles so as to
form autonomous systems.

Movements Emerge from Constraints
Organism
Movement
Environment
Task
Context specific variables
(Bernstein)

Anatomical
◦ E.g., pectoralis major adducts the arm except when the angle of
the arm is above the shoulder then contraction of the pectoralis
major abducts the arm

Mechanical
◦ Relationship between the state of the muscle and the movement
sequence
 Gravity
 Inertia

Physiological
◦ The motoneuron responds to signals from the brain and the
spinal cord (which work together).