The study of consciousness has
truly become an interdisciplinary endeavor.  In perhaps no other domain of
study is the theoretician and philosopher so informed by the empirical
sciences.  This is evidenced by Adam Zeman’s Consciousness: A User’s Guide. 
Written from the perspective of a neurologist, this book is both accessible to,
and of interest for, the theoretician and philosopher of consciousness as well
as the more empirically minded scientist.

Zeman begins with an interesting
analysis of a number of closely related consciousness concepts, including
various senses of "self-consciousness."  While some readers might
complain that Zeman focuses too much on "cognitive" or "doxastic"
senses of "consciousness," and does not say enough about conscious
experience, the so-called hard problem of conscious is addressed in some detail
in later chapters, especially chapter nine.  The second chapter provides a
useful primer for those unfamiliar with the basic biology of the human central
nervous system.  The third chapter explores the biology that underpins one of
our most basic senses of "consciousness," wakefulness.  The arousal
of the waking state, Zeman contends, is a precondition for conscious experience. 
Continuing on from chapter three, the fourth chapter considers a variety of
neuropsychological syndromes that diminish or obliterate arousal and
wakefulness.  Consciousness, Zeman concludes, is a fully physical affair that
is both fragile and open to fragmentation under stress.  The fifth chapter
takes up a discussion of the neurophysiological basis of vision, and also
considers various visual phenomena including binding and constancy.  Zeman
emphasizes two important themes here: perception is an activity that always
involves a search for meaning and perception is shaped by our past
experiences.  The sixth chapter considers a number blindness related phenomena
including blindsight and various agnosias, with the aim of uncovering the
neural basis of conscious sight.  The seventh chapter considers some of the
issues surrounding the evolution of conscious organisms.  Of particular
interest in this chapter is Zeman’s discussion of the vexed issue of the
possible uses or functions of consciousness; some of these issues are
considered again in the Epilogue.   In the penultimate chapter, Zeman considers
in some detail the neural correlates of consciousness.  Outlining some of the
approaches for determining the neural correlates of consciousness, Zeman
considers a number of theories noting some of their shared assumptions.  But
can any theory of consciousness tell us that certain sorts of neural activity
should feel as the do, or indeed, that they should feel like anything at all? 
This question brings us to the final chapter which focuses squarely on the
philosophical issues surrounding the nature of conscious experience. 
Specifically, Zeman seeks answers to the following sorts of questions: what is
the relationship between conscious experiences and the neurological activity
with which they are associated?  Is it, in principle, possible to build a
conscious machine?  What are the implications of the close relationship between
consciousness and activity and the brain for the notions of free will and
responsibility?  The first query, of course, concerns the metaphysical status
of consciousness.  Although Zeman is uncertain as to the ultimate answer to
this question, he is, not surprisingly, attracted to views that emphasizes the
inseparability of conscious experiences and the neurophysiological properties
and processes with which they are associated.  On the other hand, Zeman, like
many, worries that the consciousness-mind identity thesis "leaves out the
mind," that is, leaves out the subjective, personal, and qualitative
aspects of one’s own conscious life.  And, like many, Zeman is impressed by the
seemingly important differences between standard examples of empirical
identities like water = H₂O and the identity of conscious
experiences with certain neurophysiological properties of the central nervous
system.  For one thing, while the chemical theory of H₂O provides
insights into the macro properties of water — it explains why, for example,
water is colourless — there is not the same epistemic ascent from the neurophysiology
of the brain to the qualitative aspects of a given conscious experience. 

I believe these are interesting and
compelling problems for the identity theorist, and I will briefly outline one
avenue of response.  We should accept that the identification of consciousness
with certain sorts of neural activity is not analogous to the water/H₂O
identity.  Instead, the identification of conscious experiences with
neurophysiological properties should be construed as perspectival identity,
as when one discovers that two things are really one thing perceived or
accessed from two different perspectives.  The objects of neuroscientist’s
study — the neural correlates of consciousness — are, in fact, experiences
for their owners.  In other words, certain sorts of neural activity are
conscious experiences for the subjects of that activity.  I, as the owner of my
brain, am the subject of my brain’s neural activity.  My neuroscientist’s
access to that same neural activity is less direct; it is mediated by her sense
organs and her instruments, and indeed, her own conscious experiences. And
while she cannot have my experiences, in so far as she can’t be the
subject of my neural activities, she can still observe, study, and refer to
them.  In this case, I believe, the demand for the sort of epistemic ascent had
in the case of water/H₂O — where one can appeal to the chemical
theory H₂O to explain the macro features of water — is misplaced,
and thus, this particular "explanatory gap" is resolved.  What’s
more, on such an account the subjective and experiential aspects of
consciousness are preserved as irreducible components of the explanandum.

Adam Zeman’s Consciousness: A
User’s Guide provides an excellent introduction to many of the scientific
and philosophical issues surrounding the study of consciousness.  As such, Consciousness:
A User’s Guide is an important resource for anyone interested in
consciousness and related issues.

© 2003 Liam Dempsey

Liam
Dempsey is an Assistant Professor in Dalhousie University‘s
Department of Philosophy.