Design for a Brain: The origin of adaptive behaviour

294 Pages·1960·11.06 MB·English

by  W. Ross Ashby M.A.

DESIGN FOR A BRAIN
BY THE SAME AUTHOR
An Introduction to Cybernetics
Design for a Brain
The origin of adaptive hehaviour
w. ROSS ASHBY
M.A., M.D.(Cantah), D.P.M.
SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.
© w. ROSS ASHBY 1960
ORIGINALLY PUBLISHED BY CHAPMAN & HALL IN 1960
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dition that it shall not, by way of trade or otherwise, be lent,
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subsequent purchaser.
ISBN 978-0-412-20090-8 ISBN 978-94-015-1320-3 (eBook)
DOI 10.1007/978-94-015-1320-3
Preface
THE book is not a treatise on aIl cerebral mechanisms but a pro
poscd solution of a specific problem: the origin of the nervous
system's unique ability to produce adaptive behaviour. The
work has as basis the fact that the nervous system behaves adap
tively and the hypothesis that it is essentiaIly mechanistic; it
proceeds on the assumption that these two data are not irrecon
cilable. It attempts to deduce from the observed facts what sort
of a mechanism it must be that behaves so differently from any
machinc made so far. Other proposed solutions have usuaIly left
open the question whether so me different theory might not fit the
facts equaIly weIl: I have attempted to deduce what is necessary,
what properties the nervous system must have if it is to behave
at once mechanisticaIly and adaptively.
For the deduction to be rigorous, an adequately developed logic
of mechanism is essential. Until recently, discussions of mechan
ism were carried on almost entirely in terms of so me particular
embodiment-the mechanical, the electronic, the neuronie, and so
on. Those days are past. There now exists a weIl-developed
logic of pure mechanism, rigorous as geometry, and likely to play
the same fundamental part, in our understanding of the complex
systems of biology, that geometry does in astronomy. Only by
the dcvelopment of this basic logic has thc work in this book been
made possible.
The conclusions reached are summarised at the end of Chapter
18, but they are likely to be unintelligible or misleading if taken
by themselves; for they are intended only to make prominent the
key points along a road that the reader has already traversed.
They may, however, be useful as he proceeds, by helping hirn to
distinguish the major features from the minor.
Having experienced the confusion that tends to arise whenever
wc try to relate cerebral mechanisms to observed behaviour, I
made it my aim to accept nothing that could not be stated in
mathematical form, for only in this language can one be sure,
during one's progress, that one is not unconsciously changing the
v
PREFACE
meaning of terms, or adding assumptions, or otherwise drifting
towards confusion. The aim proved achievable. The concepts
of organisation, behaviour, change of behaviour, part, whole,
dynamic system, co-ordination, etc.-notoriously elusive hut
essential-were successfully given rigorous definition and welded
into a coherent whole. But the rigour and coherence depended
on the mathematical form, which is not read with ease by every
body. As the basic thesis, however, rests on essentially common
sense reasoning, I have been able to divide the account into two
parts. The main account (Chapters 1-18) is non-mathematical
and is coniplete in itself. The Appendix (Chapters 19-22) contains
the mathematical matter.
Since the reader will probably need cross-reference frequently,
the chapters have been divided into sections. These are indicated
thus: S. 4/5, which means Chapter 4's fifth section. Each figure
and table is numbered within its own scction: Figure 4/5/2 is the
second figure in S. 4/5. Section-numbers are given at the top of
every page, so finding a seetion or a figure should be as simple
and direct as finding a page.
It is a pleasure to be able to express my indebtedness to the
Govemors of Bamwood Rouse and to Dr. G. W. T. R. Fleming
for their generous support during the prosecution of the work, and
to Professor F. L. Golla and Dr. W. Grey Waltcr for mueh help
ful criticism.
vi
Preface to the Second Edition
AT the time when this book was first written, information theory
was just beginning to be known. Since then its contribution to
our understanding of the logic of mechanism has been so great
that a separate treatment of these aspects has been given in my
Introduction to Cybernetics * (which will be referred to in this book
as I. to C.). Its outlook and methods are fundamental to the
present work.
The overlap is smalI. I. to C. is concerned with first principles,
as they concern the topics of mechanism, communication, and
regulation; but it is concerned with the principles and does not
appreciably develop their applications. It considers mechanisms
as if they go in small discrete steps, a supposition that makes their
logical properties very easy to understand. Design JOT a Brain,
while based on the same principles, mentions them only so far as
is necessary for their application to the particular problem of the
origin of adaptive behaviour. It considers mechanisms that
change continuously (i.e. as the steps shrink to zero), for this
supposition makes their practical properties more evident. It has
been written to be complete in itself, but the reader may find
I. to C. helpful in regard to the foundations.
In the eight years that have elapsed between the preparations
of the two editions, our understanding of brain-like mechanisms
has improved immeasurably. For this reason the book has been
re-arranged, and the latter two-thirds completely re-written.
The new version, I am satisfied, presents the material in an alto
gether clearer, simpler, and more cogent form than the earlier.
The change of lay-out has unfortunately made a retention of
the previous section-numberings impossible, so there is no cor
respondence between the numberings in the two editions. I
would have avoided this source of confusion if I could, but feIt
that the claims of clarity and simplicity must be given precedence
over all else.
~ Chapman & Hall, London: 4th imp. 1961, reprinted 1964. Also trans
lations in Czech, French, Polish, Russian and Spanish.
vii
Contents
CHAPTER PAGE
Preface v
Preface to the Second Edition Vll
1 The Problem 1
Behaviour, reflex and learned. Relation of part to part.
Genetic contro!. Restrietions on the concepts. Conscious
ness. The problem.
2 Dynamic Systems 13
Variable and system. The operational method. Phase-
space and field. The natural system. Strategy for the com-
plex system.
3 The Organism as Machine 30
oe
The specification behaviour. Organism and environment.
Essential variables.
4. Stability 44.
Diagram of immediate effects. Feedback. Goal-sccking.
Stability and the whole.
5 Adaptation as Stability 58
Homeostasis. Generalised homeostasis. Surviva!. Stability
and co-ordination.
6 Parameters 71
Parameter and field. Stimuli. Joining systems. Para-
meter and stability. Equilibria oC part and whole.
7 The Ultrastable System 80
The implications of adaptation. The implications of double
feedback. Step-functions. Systems containing step
mechanisffiS. The ultrastable system.
8 The Homeostat 100
The Homeostat as adapter. Training. So me apparent
faults.
9 Ultrastability in the Organism 122
Step-mechanisms in the organism. A molecular basis for
memory? Are step-mechanisms necessary? Levels of feed-
oe
back. Control aim. Gene-pattern and ultrastability.
Summary.
viii
CONTENTS
CHAPTER PAGE
10 The Recurrent Situation 138
Accumulation of adaptations.
11 The Fully-joined System 148
Adaptation-time. Cumulative adaptation.
12 Temporary Independence 158
Independence. The effects of constancy. The effects of
local stabilities.
13 The System with Local Stabilities 171
Progression to equilibrium. Dispersion. Localisation in the
polystable system.
14 Repetitive Stimuli and Habituation 184
Habituation. Minor disturbances.
15 Adaptation in Iterated and Serial Systems 192
Iterated systems. Serial adaptation.
16 Adaptation in the Multistable System 205
The richly-joined environment. Thc poorly-joined environ
ment. Retroactive inhibition.
17 Ancillary Regulations 218
Communication within the brain. Ancillary regulations.
Distribution of feedback.
18 Amplifying Adaptation 231
Selection in the state-determinerl system. AI11Jllifying
adaptation. The origin of adaptive behaviour.
APPENDIX
19 The State-determined System 241
The logie of mechanism. Canonical representation. Trans
formations.
20 Stability 253
Probability of stability.
21 Parameters 262
Joining systems. The state-detcrminerl system.
22 The Effects of Constancy 272
Ultrastability. Tcmporary independence. Diagrams of
effects.
References 281
Index 283
ix
CHAPTER 1
The Problem
I/I. How does the brain produee adaptive behaviour? In
attempting to answer the question, seientists have diseovered two
sets of faets and have had some diffieulty in reeoneiling them.
On the one hand the physiologists have shown in a variety of ways
how closely the brain resembles a maehine: in its dependenee on
ehemieal reaetions, in its dependenee on thc integrity of anatomieal
paths, and in the precision and determinateness with whieh its
eomponent parts aet on one another. On the other hand, the
psyehologists and biologists have eonfirmed with fuH objeetivity
the layman's eonvietion that the living organism behaves typieally
in a purposeful and adaptive way. These two eharaeteristies of
the brain's behaviour have proved diffieult to reeoneile, and some
workers have gone so far as to declare them ineompatible.
Sueh a point of view will not be taken here. I hope to show
that a system ean be both meehanistie in nature and yet produee
behaviour that is adaptive. I hope to show that the essential
differenee between the brain and any maehine yet made is that
the brain makes extensive use of a method hitherto little used in
maehines. I hope to show that by the use of this method a
maehine's behaviour may be made as adaptive as we please, and
that the method may be eapable of explaining even the adaptive
ness of Man.
But first we must examinc more closely the nature of the
problem, and this will be eommeneed in this ehapter. The suc
ceeding chapters will develop more aceurate eoncepts, and when
we ean state the problem with preeision we shall not be far from
its solution.
Behaviour, reflex and learned
1/2. Thf: aetivities of the nervous system may be divided more
or less distinctly into two types. Thc diehotomy is probably an
1