Blindsight and the Nature of Consciousness

154 Pages·2003·0.842 MB·English

by  Jason Holt

Blindsight_front_toc.qxd 1/10/03 1:33 PM Page 1
This electronic material is under
copyright protection and is
provided to a single recipient
for review purposes only.
BLINDSIGHT
AND THE NATURE OF
CONSCIOUSNESS
Blindsight_front_toc.qxd 1/10/03 1:33 PM Page 2
Review Copy
Blindsight_front_toc.qxd 1/10/03 1:33 PM Page 3
Review Copy
BLINDSIGHT
AND THE NATURE OF
CONSCIOUSNESS
JASON HOLT
broadview press
Blindsight_front_toc.qxd 1/10/03 1:33 PM Page 4
Review Copy
2003
© Jason Holt
All rights reserved. The use of any part of this publication reproduced, transmit-
ted in any form or by any means, electronic, mechanical, photocopying, recording,
or otherwise, or stored in a retrieval system, without prior written consent of the
publisher—or in the case of photocopying, a licence from Access Copyright
1900
(Canadian Copyright Licensing Agency), One Yonge Street, Suite , Toronto,
m5e1e5
ON —is an infringement of the copyright law.
National Library of Canada Cataloguing in Publication
Holt, Jason, 1971-
Blindsight and the nature of consciousness / Jason Holt.
Includes bibliographical references.
ISBN 1-55111-351-1
1. Visual perception—Philosophy. 2. Consciousness. I. Title.
BF311.H65 2003 126 C2002-904608-4
Broadview Press Ltd. is an independent, international publishing house, incorpo-
1985
rated in . Broadview believes in shared ownership, both with its employees
2000
and with the general public; since the year Broadview shares have traded
bdp
publicly on the Toronto Venture Exchange under the symbol .
We welcome comments and suggestions regarding any aspect of our
publications—please feel free to contact us at the addresses below or at broad-
[email protected].
North America
1243 k9j 7h5
PO Box , Peterborough, Ontario, Canada
3576 14127
California Road, Orchard Park, NY, USA
705 743-8990 705 743-8353
Tel: ( ) ; Fax: ( )
email: [email protected]
UK, Ireland, and continental Europe
3 4
Thomas Lyster Ltd., Units & a, Old Boundary Way
Burscough Road, Ormskirk
l39 2yw
Lancashire,
01695 575112 01695 570120
Tel: ( ) ; Fax: ( )
email: [email protected]
Australia and New Zealand
UNIREPS, University of New South Wales
2052
Sydney, NSW,
61 2 9664 0999 61 2 9664 5420
Tel: ; Fax:
email: [email protected]
www.broadviewpress.com
Broadview Press Ltd. gratefully acknowledges the financial support of the
Government of Canada through the Book Publishing Industry Development
Program for our publishing activities.
This book is printed on acid-free paper containing
30% post-consumer fibre.
printed in canada
Blindsight_front_toc.qxd 1/10/03 1:33 PM Page 5
Review Copy
CONTENTS
Introduction • 7
chapter 1 A Brief History of Blindsight • 19
chapter 2 Dissociation Cases • 31
chapter 3 Consciousness Lost? • 43
chapter 4 Super Blindsight and Other Disqualifications • 57
chapter 5 Conscious Realism • 69
chapter 6
Access Denied, Zombiehead Revisited,
and What Mary Didn’t Think She Knew • 81
chapter 7 Stereotypes and Token Efforts • 93
chapter 8 The Hard Gap and Had Perspectives • 105
chapter 9 Not Seeing Is Believing • 117
chapter 10 Split Vision • 129
Notes • 137
References • 147
Blindsight_front_toc.qxd 1/10/03 1:33 PM Page 6
Review Copy
Blindsight_intro.qxd 1/9/03 6:14 PM Page 7
Review Copy
INTRODUCTION
his book is about consciousness
T and a phenomenon
that conspicuously lacks it. The phenomenon is blindsight,
one of the most controversial and important scientific dis-
coveries in recent decades. Blindsight is the surprising ability of
people with a certain kind of brain damage to perceive things visually
even though they lack visual experience completely.1They “see” with-
out seeing. The word itself sounds like an oxymoron, and yet it is quite
apt, not despite this fact, but rather because of it. For the lack of visual
consciousness, it is blind, and for the ability of the visual system, so
handicapped, to take in and deploy information about the world, it is
a kind of sight. People with blindsight are unaware of the information
they possess, even when they use it, and so their judgments seem to
them haphazard, mere guesswork. But their judgments are too reli-
able for this to be the case. It is not mere guesswork. It cannotbe. Their
shots in the dark betray excellent marksmanship.
This is all very interesting, perhaps, but why write a book about it?
There are a number of reasons, actually. The notion that one can “see”
without seeingmay strike one as odd, if not absurd. The phenomenon
itself is intriguing, and more than passing reference to it can be found
in works of both high and popular culture, including novels, plays, tel-
evision programs, music, and books of wide appeal despite their tech-
nical orientation. Trying to explain blindsight is no less challenging.
Early experiments sparked heated debates in the psychology litera-
ture, some of which are still ongoing. Philosophers were among the
first to be intrigued. They began discussing blindsight in the late
1970
s, almost a decade before the first detailed case-study was pub-
lished.2The phenomenon has since gained much greater currency, to
the point where it is now standard issue subject matter not only in
psychology and the neurosciences, but in philosophy of mind. Indeed,
blindsight is at the forefront of a new wave of scientific studies and
7
Blindsight_intro.qxd 1/9/03 6:14 PM Page 8
Review Copy
BLINDSIGHT AND THE NATURE OF CONSCIOUSNESS
philosophical investigations of consciousness. It promises to help us
discover important facts about not only the functional architecture of
the brain, but also the neurological basis and—perhaps—even the
true nature of consciousness.
I first became interested in blindsight while doing graduate work
at the University of Western Ontario.3 I was not surprised that
philosophers were discussing blindsight, nor that they seemed to
attach such importance to it that it made a well-known list of the top
ten problems of consciousness.4Nor was I surprised that a number of
clever arguments, based on blindsight, had been constructed to sup-
port a wide variety of philosophical views. The phenomenon itself is
something of a shocker, so it is only natural to expect that it has
telling, if not shocking, implications. The way most of us think about
the mind is fine for practical purposes. However, common sense does
not anticipate such phenomena as blindsight, and, since a refined
understanding of the mind will be sensitive to such phenomena,
common sense will have to give way at some point, although where it
will have to give way is not altogether clear. There are huge differences
of opinion as to what blindsight implies about the nature of con-
sciousness. The surprising thing is that there has been little effort to
settle these disputes. In fact, despite the perceived importance of
blindsight, there has been no extended treatment of it from a philo-
sophical perspective.
It was with an eye to filling this gap that I wrote my doctoral thesis
on blindsight and its philosophical applications. It is from that thesis
that this little book has been cultivated. There has been some new
growth since then, as well as some pruning. Up till now, philosophers
have discussed blindsight primarily in connection with consciousness.
This is not surprising; the connection is obvious. What is odd, I think,
is that philosophers have discussed blindsight almost exclusivelyin con-
nection with consciousness. Other areas of philosophical concern, the-
ories of knowledge and perception in particular, on which blindsight
is likely to bear, have been largely ignored. Much of the new growth I
speak of lies in exploring such neglected applications. As for the prun-
ing, some of the drier, more technical bits of the thesis have been rele-
gated to endnotes or else omitted entirely. My intent is to maintain
8
Blindsight_intro.qxd 1/9/03 6:14 PM Page 9
Review Copy
INTRODUCTION
enough conceptual rigour to satisfy those of my ilk, while presenting a
book that is accessible to non-philosophers—including specialists in
psychology, the neurosciences, and other cognate disciplines—as well
as students and non-academics interested in the subject.
That said, I want to take the rest of this introduction to paint a
backdrop against which an encounter with blindsight will stand in
appropriate relief. The backdrop, suitably enough, looms large. It is
the problem of consciousness. Beginning here, we will eventually
come to see how something so rare and peculiar as blindsight can illu-
minate something so commonplace as consciousness. If you do not
need a crash-course in the mind/body problem, and you do not want
a refresher, feel free to skip ahead.
Consciousness is exotic. It is also mundane. Funny that. Consider,
right now, the panoply of your present experiences, of the world
around you, the things in it, your place among them, your body’s ori-
entation, various thoughts, various feelings. Now recall some past
event. Imagine a scenario. Form an intention. Act on it. Infer some-
thing trivial about the author of this book. Note the colour of the
book’s cover, the thickness, the texture, the sound of pages flipped
under your thumb. Focus your attention on each word in this sen-
tence, the shape of the letters, the style of font. Mark your sense of the
passage of time, your sense of self, of how it all seems to come together
in each moment and flow smoothly, coherently to the next. So much
awareness!—and all the waking live-long day. Such is the mundanity
of consciousness. It almost goes without saying. But that is yourcon-
sciousness. To others your consciousness is something exotic, closed
off, available at best to imperfect imagination and felicitous inference.
Why, then, is it so unavoidably easy to think of others as conscious?
Part of the reason is that others behave with intelligence and cog-
nizance more or less as you do, and you know—or think you know—
that in your own case consciousness helps produce such actions.
Without evidence that you are an anomaly, a lone consciousness in a
sea of biological automata, the only sane default is that other homines
sapientes are conscious, just like you. The evidence for commonality,
here, outweighs that for anomaly by an appreciable margin.
9
Blindsight_intro.qxd 1/9/03 6:14 PM Page 10
Review Copy
BLINDSIGHT AND THE NATURE OF CONSCIOUSNESS
Although exotic in one sense, other people’s consciousness is, prac-
tically speaking, mundane. We are a sentient species. We should be
able to account for this fact scientifically, if, that is, science offers the
sort of “theory of everything” we think it does. But consciousness
seems especially exotic to worldviews that would have everything in
the universe accounted for by the physical and biological sciences. The
progress of these sciences is so rapid, the achievements so compre-
hensively impressive, that there appears little need for consciousness
and even less room for it. Even in those sciences aimed at modelling
the human mind, most theories get on fine without considering con-
sciousness and fail to catch it besides. Building such models does not
have to involve much consideration of where consciousness fits in the
overall scheme of things. Such consideration seems anathema to
machine-building and response-measuring, even where the machines
are meant to model sentience and even where the responses measured
are those of conscious human subjects. Cognitive flowcharts omitting
consciousness do not seem incomplete, and those including it appear
suspect. Yet consciousness remains irreplaceably our vantage on our-
selves and the world around us, without which it would be impossi-
ble to have the very sciences that seem to threaten it. Despite much
renewed interest in the scientific study of consciousness, the old
habits die hard, and no one knows exactly what new procedures
should replace them.
From a certain point of view, it seems that consciousness cannot be
bothexotic and mundane. One of these two perspectives must be priv-
ileged, the other dismissed. Tough-minded souls may say—some
have—“So much the worse for consciousness!” By the same token,
tender-minded friends of the ethereal, poets and the like, may counter
with equal conviction, if not cachet, “So much the worse for science!”
Here is a more diplomatic suggestion: “Let scientists speak of quarks
and biological imperatives and computational processes—and noth-
ing besides—and let ordinary folk speak of consciousness.”
Unfortunately, such diplomatic suggestions are based on a misunder-
standing of the scope of science and the limits of common sense. They
do not resolve the tension, they dissolve it. Dissolving the tension, in
10