Chapter 15 Basic concepts of motor control: Cognitive science perspectives.

Chapter 15

Basic concepts of motor control: Cognitive

science perspectives

Cognitive science perspectives Objective from syllabus

•To understand how models of motor control can be used to explain how we move

•The general notion is that the brain & CNS is rather too complex to fully understand at this time, so we need a level of analysis once removed

Using Models to Study Motor Control

The role of models in scientific study

Key properties to be explained by models of control•Degrees of freedom

•Motor equivalence

•Serial order

•Perceptual-motor integration

•Skill acquisition (ch. 17)

Information-Processing Models of Motor Control

The human motor system as computer-like•Hardware (brain, receptors, effectors) and

software (computational capabilities of these)

•Processing stages•See next 5 slides for examples (a model, followed

by some movements that it might help explain)

Executive (conscious)

Executive (unconscious)

Central Pattern

Generator

Movement

Conscious intentions

Environment

Sets up the intended movement, with

reference to current body state and

environmental cues

Signal diversifies, with detail added at this

level including necessary

communication between muscles

systems

Collections of motor units innervated,

leading to contractions of

various strengths

Body movement affects environmental goals,

and always changes our orientation with respect

to the environment

Feedback Loops

1. A model

Note many levels of control



Central Pattern

Generator

Movement


Environment



environmental cues




systems



various strengths



to the environment

Feedback Loops

2. A knee-jerk (stretch, myotatic, monosynaptic) reflex

So it’s fast, but doesn’t do much in terms of coordination



Central Pattern

Generator

Movement


Environment



environmental cues




systems



various strengths



to the environment

Feedback Loops

3. Balance (swinging room and normal)

Fast, due to lack of conscious mediation, and complex



Central Pattern

Generator

Movement


Environment



environmental cues




systems



various strengths



to the environment

Feedback Loops

4. Poorly learned skill

Conscious deliberation makes performance jerky, stiff, awkward



Central Pattern

Generator

Movement


Environment



environmental cues




systems



various strengths



to the environment

Feedback Loops

5. Expertly learned skill

Lengthy practice “automates” performance – think of tying your shoelaces as an example

Used just to get things started – will perhaps

monitor for errors, but that’s perhaps not a good thing

(self-talk)

An Alternative Model of Motor Control Problems with information processing

accounts•Homunculi - Infinite regress (why do we walk

the way we do?)

•Context-conditioned variability•anatomical (muscles used to produce a given

movement change with regard to current body ‘context’)

•mechanical (action of a fixed degree of contraction of a muscle changes with respect to current body position)

•Distributed, not central control

An Alternative Model of Motor Control A group of related theories

•Complex systems theory

•Dynamic pattern perspective & synergetics

•Ecological psychology All have in common the tendency to ask

why rather than how•The study of relationships among things, rather

than the things themselves Leads to the study of...

Dynamic Pattern Theory

Shaping movement via:•Constraints...

•Things which limit our range of movements – thus “shaping” them

• ...and affordances•Things which permit (or even suggest) certain

methods of movement or interaction with an object


Surface type

Lighting

Visual flow

Speed/accuracy requirements

Number of tasks

standing

seated

moving

Sensory loss

Cognition

FlexibilityStrength/power

Cardiovascular

Environmental

Constraints

Individual Capabiliti

es

Task Demands

3 categories of constraint (+ examples)

Motor abilities

Environmental stability

From Newell (1986)


Processes in coordination dynamics

Dynamics of CNS

(neural level)

Dynamics of action system

(effector level)

Dynamics of environment(environmental

level)

Connectionism

Action system theory

Laws of perceiving and acting (ecological psychology)

Coordination dynamicsFrom Schmidt & Fitzpatrick (1993)


Constraints and affordances lead to pattern formation•Remember, this is a theory about

shaping of movement

•Why do we walk the way we do?


An example of emergent patterns from motor development •Stepping/Walking

•0-2 months•Stepping a stable behavior

•3-4 months•Stepping disappears

•Why? Where might you look if you believed in constraints and affordances?

•How might you examine this?


An example of emergent patterns from motor development

What causes this

loss of stability?

How might you regain

it?

1 month 3 months

And how else might you lose it?


See anything that changes?

New born

3 months


An example of emergent patterns from motor development

What causes this

loss of stability?

How might you regain

it?

1 month 3 months

And how else might you lose it?


In complex systems terms, there are several aspects to this relationship: •Self-organization

•Attractor

•Order parameter

•Control Parameter

•Stability

•Energy efficiency

•Critical fluctuation

•Critical slowing down

•Hysteresis

An example from adult movement

Kelso & Scholtz, 1985

In-phase:

Faster and faster…



In-phase:





Anti-phase:




0

20

40

60

80

100

120

140

160

180

1.25

1.75

2.25

2.75 1.

5 2 2.5 3

Anti-phase In-phase

Diff

ere

nce

b

etw

een

jt.

An

gle

s

Coordination

Stability

Vari

ati

on

in

jt.

A

ng

les

(arb

itra

ry

un

its)

Stability and attractors• The in-phase and out-

of-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 (in-phase)

An example from adult movement Stability and attractors

• 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

0

20

40

60

80

100

120

140

160

180

1.25

1.75

2.25

2.75 1.

5 2 2.5 3

Anti-phase In-phase

Diff

ere

nce

b

etw

een

jt.

An

gle

s

Coordination

Stability

Vari

ati

on

in

jt.

A

ng

les

(arb

itra

ry

un

its)

Aspects of dynamic systems

1 2

3

5 4

Listen to this first! Then proceed with the others, going

from 1 to 5

Hysteresis in gait

Aspects of dynamic systems

Walk

Run

Speed (control parameter)

Order parameters The difference in the speed (at which the person is running/walking) when the

transition is made from walking to running, compared to when the switch is made from running to walking, signifies the presence of hysteresis – further definition in audio

Hysteresis in gait

Aspects of dynamic systems As it turns out, much the same

relationship exists in many other systems:•Other examples of human coordination

•Human cortical activity

•Cardiac rhythms

•Water flowing from a tap

•Water being heated

•Horses (& other quadrupeds) changing gait

•Stock market, weather patterns, emotional fluctuations, etc.

Chapter 15 Basic concepts of motor control: Cognitive science perspectives.

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Transcript of Chapter 15 Basic concepts of motor control: Cognitive science perspectives.