Washington DC
Consciousness Lost and Found by Lawrence Weiskrantz, Oxford
University Press, 拢19.99, ISBN 0198523017
SOME brain-damaged patients retain capacities of which they are oblivious.
Neologisms such as 鈥渂lindsight鈥� or 鈥渘umbsense鈥� convey how people who are
conventionally blind or insensible can nonetheless discriminate visual or
tactile test stimuli with near-perfect accuracy. These patients insist that they
can鈥檛 鈥渟ee鈥� or 鈥渇eel鈥� anything, despite objective evidence to the contrary.
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This leads Lawrence Weiskrantz to use their condition to investigate
awareness (consciousness) itself in Consciousness Lost and Found. The
title confuses, however. By 鈥渓ost鈥� he means missing awareness, and by 鈥渇ound鈥� he
means retained perceptual capacity. The field he reviews鈥攚hich has no
accepted name鈥攃entres on the distinction between 鈥渁wareness of鈥� and
鈥渁wareness that鈥�. Put differently, he considers discrimination per se versus the
awareness that one鈥檚 sensual discrimination is accurate.
Arguing that patients with blindsight, numbsense, amnesia, prosopagnosia,
unilateral neglect, aphasia and anosognosia can no longer 鈥渃omment鈥� on whatever
know-how remains amid their defective skill, Weiskrantz surmises that such
commentary is key to the experience of awareness. Setting aside whether his
formulation furthers our understanding of consciousness, I am unconvinced that
the clinical examples he gathers actually share any one quality that unifies
them into a conceptual whole.
Weiskrantz held the chair of psychology at Oxford for 26 years and
scrutinised blindsight for roughly as long. Yet Consciousness Lost and
Found reads like the close of an era, rather than a summary of one that
promises to explain brain function afresh. It has the flavour of an old book
informed by earlier theories that have not held up. He says nothing about how
concepts have changed historically, and accepted facts appear as new
discoveries. For example: 鈥淚t is becoming widely appreciated that much of our
behaviour is not accessible to conscious control or awareness . . .鈥�
Odd statements pepper the text. Comparing the amnesiac syndrome to the memory
loss of Alzheimer鈥檚, for example, Weiskrantz marvels that 鈥渢he striking aspect鈥�
of the former 鈥渋s its relative purity and its isolation from other cognitive,
motor, and perceptual difficulties鈥�. The evident reason they differ is the
selectiveness of the lesions that cause amnesia compared with the diffuseness of
the pathology of Alzheimer鈥檚. I find nothing striking in two disparate
pathologies leading to dissimilar clinical manifestations.
Though Weiskrantz鈥檚 review aims to include a nonspecialist audience as well
as academics, his style is too dry and technical. Even some explanations of
simple concepts are disorganised: I had to reread a fundamental premise of
blindsight, namely that in the absence of vision鈥檚 well-known striate cortex,
there are a number of parallel routes from the retina to various brain
structures that might explain why patients retain some visual abilities.
He poses as a critical question whether the absence of striate cortex
eliminates visual awareness, then announces that 鈥渟triate cortex is essential鈥�
for any `seen鈥� perception whatsoever鈥�. He appears unaware of synaesthesia
research in humans from Britain鈥檚 Institute of Neurology, which used functional
imaging to show that it is possible to have a conscious visual experience
without activation of striate cortex.
In a misleading analysis, Weiskrantz confuses wavelength 鈥渟ensitivity鈥� and
鈥減rocessing鈥� with colour perception. Perhaps he still clings to the Helmholtz
theory that associates different colours with different wavelengths, but he
should know that brains do not perceive wavelengths. Colours are perceived
through physical characteristics completely independent of wavelength, as Edwin
Land first demonstrated in 1959. Samir Zeki of University College London has
repeated Land鈥檚 classic experiments during the past decade.
Reading this book taught me little about either consciousness or residual
capacity without awareness. Chapter titles that posed questions such as, 鈥淗ow
does the brain generate consciousness awareness?鈥� went unanswered.