WMOM:WU:chap2

# The Mystery of Consciousness

Investigating the nature of consciousness itself—and transforming its contents through deliberate training—is the basis of spiritual life. In
scientific terms, however,
consciousness remains
notoriously difficult to
understand, or even to define.
In fact, many debates about
its character have been waged
without the participants’
finding even a common topic
as common ground. While we
need not recapitulate the
history of our confusion on
this point, it will be useful to
briefly examine why
consciousness still poses a
unique challenge to science.
Having done so, we will see
that spirituality is not just
important for living a good
life; it is actually essential for
understanding the human
mind.

In one of the most
influential essays on
consciousness ever written,
the philosopher Thomas
Nagel asks us to consider
what it is like to be a bat. His
interest isn’t in bats but in
how we define the concept of
“consciousness.” Nagel
argues that an organism is
conscious “if and only if there
is something that it is like to
*be* that organism—something
that it is like *for* the
organism.” Whether you find
that statement brilliant,
trivial, or merely perplexing
probably says a lot about your
appetite for philosophy.
“Brilliant” and “trivial” can
both be defended, but Nagel’s
claim needn’t leave you
confused. He is simply asking
you to imagine trading places
with a bat. If you would be
left with *any* experience,
however indescribable—
some spectrum of sights,
sounds, sensations, feelings
—*that* is what consciousness
is in the case of a bat. If being
transformed into a bat were
tantamount to annihilation,
however, then bats are not
conscious. Nagel’s point is
that whatever else
consciousness may or may
not entail in physical terms,
the difference between it and
unconsciousness is a matter
of subjective experience.
Either the lights are on, or
they are not.

But experience is one
thing, and our growing
scientific picture of reality is
another. At this moment, you
might be vividly aware of
reading this book, but you are
completely unaware of the
electrochemical events
occurring at each of the
trillions of synapses in your
brain. However much you
may know about physics,
chemistry, and biology, you
live elsewhere. As a matter of
your *experience*, you are not
a body of atoms, molecules,
and cells; you are
consciousness and its ever-
changing contents, passing
through various stages of
wakefulness and sleep, from
cradle to grave.

And the question of how
consciousness relates to the
physical world remains
famously unresolved. There
are reasons to believe that it
emerges on the basis of
information processing in
complex systems like a
human brain, because when
we look at the universe, we
find it filled with simpler
structures, like stars, and
processes, like nuclear fusion,
that offer no outward signs of
consciousness. But our
intuitions here may not
amount to much. After all,
how would the sun appear if
it were conscious? Perhaps
exactly as it does now.
(Would you expect it to talk?)
And yet somehow it seems
far less likely that the stars
are conscious and simply
mute than that they lack inner
lives altogether.

Whatever the ultimate
relationship between
consciousness and matter,
almost everyone will agree
that at some point in the
development of complex
organisms like ourselves,
consciousness *seems* to
emerge. This emergence does
not depend on a change of
materials, for you and I are
built of the same atoms as a
fern or a ham sandwich.
Instead, the birth of
consciousness must be the
result of organization:
Arranging atoms in certain
ways appears to bring about
an experience of *being* that
very collection of atoms. This
is undoubtedly one of the
deepest mysteries given to us
to contemplate.

Nevertheless, Nagel was
right to observe that the
reality of consciousness is,
first and foremost, subjective
—for it is simply the fact of
subjectivity itself. And
whether something *seems*
conscious from the outside is
never quite the point. I
happen to know a person who
once woke up during a
surgery for which he had
received a general anesthetic.
Owing to the paralytic
component of the anesthesia,
however, he was unable to
signal to his doctors that he
was awake and feeling rather
more of the procedure than he
liked. This was inconvenient,
to say the least, because they
were in the process of
replacing his liver. If you
think the important part of
consciousness is its link to
speech and behavior, spare a
moment to consider the
problem of “anesthesia
awareness.” It is a cure for
much bad philosophy.

It is surely a sign of
intellectual progress that a
discussion of consciousness
need no longer begin with a
debate about its existence. To
say that consciousness may
only *seem* to exist, from the
inside, is to admit its
existence in full—for if
things seem any way at all,
*that* is consciousness. Even if
I happen to be a brain in a vat
at this moment—and all my
memories are false, and all
my perceptions are of a world
that does not exist—the fact
that I am *having an
experience* is indisputable (to
me, at least). This is all that is
required for me (or any other
sentient being) to fully
establish the reality of
consciousness. Consciousness
is the one thing in this
universe that cannot be an
illusion.

As our understanding of the
physical world has evolved,
our notion of what counts as
“physical” has broadened
considerably. A world
teeming with fields and
forces, vacuum fluctuations,
and the other gossamer spawn
of modern physics is not the
physical world of common
sense. In fact, our common
sense seems to be stuck
somewhere in the sixteenth
century. It has also been
generally forgotten that many
of the patriarchs of physics in
the first half of the twentieth
century regularly impugned
the “physicality” of the
universe and placed mind—or
thoughts, or consciousness
itself—at the very wellspring
of reality. Nonreductive
views like those of Arthur
Eddington, James Jeans,
Wolfgang Pauli, Werner
Heisenberg, and Erwin
Schrödinger seem to have had
no lasting impact.  In some
ways we can be thankful for
this, for a fair amount of
mumbo jumbo was in the air.
Pauli, for instance, was a
devotee of Carl Jung, who
apparently analyzed no fewer
than 1,300 of the great man’s
dreams. Although Pauli was
one of the titans of physics,
his thoughts about the
irreducibility of mind
probably had as much to do
with Jung’s febrile
imagination as they did with
quantum mechanics.

The allure of the numinous
eventually subsided. Once
physicists got down to the
serious business of building
bombs, we were apparently
returned to a universe of
objects—and to a style of
discourse, across all branches
of science and philosophy,
that made the mind seem ripe
for reduction to the
“physical” world.

These developments have
greatly inconvenienced New
Age thinkers—or would
have, had they deigned to
notice them. Authors
struggling to link spirituality
to science generally pin their
hopes on misunderstandings
of the “Copenhagen
interpretation of quantum
mechanics,” which they take
as proof that consciousness
plays a central role in
determining the character of
the physical world. If nothing
is real until it is observed,
consciousness cannot arise
from electrochemical events
in the brains of animals like
ourselves; rather, it must be
part of the very fabric of
reality. But this simply isn’t
the position of mainstream
physics. It is true that,
according to Copenhagen,
quantum mechanical systems
do not behave classically
until they are observed, and
before that they may seem to
exist in many different states
simultaneously. But what
counts as “observation” under
the original Copenhagen view
was never clearly defined.
The notion has been refined
since, and it has nothing to do
with consciousness. It’s not
that the mysteries of quantum
mechanics have been
resolved—the physical
picture is strange however
one looks at it. And the
problem of how an
underlying quantum
mechanical reality becomes
the seemingly classical world
of tables and chairs hasn’t
been completely understood.
However, there is no reason
to think that consciousness is
integral to the process. It
seems certain, therefore, that
anyone who would base his
spirituality on
misinterpretations of 1930s
physics is bound to be
disappointed. As we will see,
the link between spirituality
and science must be found in
another place.

We know, of course, that
human *minds* are the product
of human brains. There is
simply no question that your
ability to decode and
understand this sentence
depends upon
neurophysiological events
taking place inside your head
at this moment. But most of
this mental work occurs
entirely in the dark, and it is a
mystery why any part of the
process should be attended by
consciousness. Nothing about
a brain, when surveyed as a
physical system, suggests that
it is a locus of experience.
Were we not already
brimming with consciousness
ourselves, we would find no
evidence for it in the universe
—nor would we have any
notion of the many
experiential states that it
gives rise to. The only proof
that it is like something to be
you at this moment is the fact
(obvious only to you) that it
is like something to be you.

However we propose to
explain the emergence of
consciousness—be it in
biological, functional,
computational, or any other
terms—we have committed
ourselves to this much: First
there is a physical world,
unconscious and seething
with unperceived events;
then, by virtue of some
physical property or process,
consciousness itself springs,
or staggers, into being. This
idea seems to me not merely
strange but perfectly
mysterious. That doesn’t
mean it isn’t true. When we
linger over the details,
however, this notion of
emergence seems merely a
placeholder for a miracle.

Consciousness—the sheer
fact that this universe is
illuminated by sentience—is
precisely what
unconsciousness is not. And I
believe that no description of
unconscious complexity will
fully account for it. To simply
assert that consciousness
arose at some point in the
evolution of life, and that it
results from a specific
arrangement of neurons firing
in concert within an
individual brain, doesn’t give
us any inkling of *how* it could
emerge from unconscious
processes, even in principle.
However, this is not to say
that some other thesis about
consciousness must be true.
Consciousness may very well
be the lawful product of
unconscious information
processing. But I don’t know
what that sentence actually
means—and I don’t think
anyone else does either.
This situation has been
characterized as an
“explanatory gap” and as
the “hard problem of
consciousness,” and it is
surely both. Some
philosophers have suggested
that the relationship between
mind and body will be
understood only with
reference to concepts that are
neither physical nor mental
but that are in some way
“neutral.” Others claim that
consciousness can be known
to be the product of physical
causes but cannot be
conceptually reduced to such
causes. Still others have
argued that the notion of a
nonreductive physical
account is incoherent.

I am sympathetic with
those who, like the
philosopher Colin McGinn
and the psychologist Steven
Pinker, have suggested that
perhaps the emergence of
consciousness is simply
incomprehensible in human
terms Every chain of
explanation must end
somewhere—generally with a
brute fact that neglects to
explain itself. Perhaps
consciousness presents an
impasse of this sort.

In any case, the task of
explaining consciousness in
physical terms bears little
resemblance to other
successful explanations in the
history of science. The
analogies that scientists and
philosophers marshal here are
invariably misleading. The
fact, for instance, that we can
now describe the properties
of matter, such as fluidity, in
terms of microscopic events
that are not themselves
“fluid” does not suggest a
way to understand
consciousness as an emergent
property of the unconscious
world. It is easy to see that no
single water molecule can be
“fluid,” and it is easy to see
that billions of such
molecules, freely sliding past
one another, would appear as
“fluidity” on the scale of a
human hand. What is not easy
to see is how analogies of this
kind have persuaded so many
people that consciousness can
be readily explained in terms
of information processing.

For an explanation of a
phenomenon to be satisfying,
it must first be, at a
minimum, *intelligible*. In this
regard, the emergence of
fluidity poses no problems:
The free sliding of molecules
seems exactly the sort of
thing that should be true of a
substance to ensure its
fluidity. Why can I pass my
hand through liquid water and
not through rock? Because
the molecules of water are not
bound so tightly as to resist
my motion. Notice that this
explanation of fluidity is
perfectly reductive: Fluidity
really is “nothing but” the
free motion of molecules. For
this explanation to be
sufficient, we must admit that
molecules exist, of course,
but once we do, the problem
is solved. No one has
described a set of
unconscious events whose
sufficiency as a cause of
consciousness would make
sense in this way. Any
attempt to understand
consciousness in terms of
brain activity merely
correlates a person’s ability to
report an experience
(demonstrating that he was
aware of it) with specific
states of his brain. While such
correlations can amount to
fascinating neuroscience, they
bring us no closer to
explaining the emergence of
consciousness itself.

There will almost certainly
come a time when we will
build a robot whose facial
expressiveness, tone of voice,
and flexibility of thought will
cause us to wonder whether
or not it is conscious. This
robot might even claim to be
conscious and be eager to
participate in the kinds of
experiments we now perform
on human beings, allowing us
to correlate its responses to
stimuli with changes in its
“brain.” It seems clear,
however, that unless we can
do more than this, we will
never know whether there is
“something that it is like” to
be such a machine.

Some readers may think
that I’ve stacked the deck
against the sciences of the
mind by comparing
consciousness to a
phenomenon as easily
understood as fluidity. Surely
science has dispelled far
greater mysteries. What, for
instance, is the difference
between a living system and a
dead one? Insofar as
questions about
consciousness itself can be
kept off the table, it seems
that the difference is now
reasonably clear to us. And
yet, as late as 1932, the
Scottish physiologist J. S.
Haldane (father of J. B. S.
Haldane) wrote:

What intelligible account can the mechanistic theory of life give of the . . . recovery from disease and injuries? Simply none at all, except that these phenomena are so complex and strange that as yet we cannot understand them. It is exactly the same with the closely related phenomena of reproduction. We cannot by any stretch of the imagination conceive a delicate and complex mechanism which is capable, like a living organism, of reproducing itself
indefinitely often.

Scarcely twenty years passed
before our imaginations were
duly stretched. Much work in
biology remains to be done,
but anyone who entertains
*vitalism* at this point is
simply ignorant about the
nature of living systems. The
jury is no longer out on
questions of this kind, and
more than half a century has
passed since the earth’s
creatures required an *élan
vital* to propagate themselves
or to recover from injury. Is
my skepticism that we will
arrive at a physical
explanation of consciousness
analogous to Haldane’s doubt
about the feasibility of
explaining life in terms of
processes that are not
themselves alive?

It wouldn’t seem so. To
say that a system is alive is
very much like saying that it
is fluid, because life is a
matter of what systems do
with respect to their
environment. Like fluidity,
life is defined according to
external criteria.
Consciousness is not (and, I
think, cannot be). We would
never have occasion to say of
something that does not eat,
excrete, grow, or reproduce
that it might be “alive.” It
might, however, be
conscious.

Might a mature
neuroscience nevertheless
offer a proper explanation of
consciousness in terms of its
underlying brain processes?
Again, there is nothing about
a brain, studied at any scale,
that even suggests that it
might harbor consciousness
—apart from the fact that we
experience consciousness
directly and have correlated
many of its contents, or lack
thereof, with processes in our
brains. Nothing about human
behavior or language or
culture demonstrates that it is
mediated by consciousness,
apart from the fact that we
simply know that it is—a
truth that someone can
appreciate in himself directly
and in others by analogy.

Here is where the
distinction between studying
consciousness itself and
studying its *contents* becomes
paramount. It is easy to see
how the contents of
consciousness might be
understood in
neurophysiological terms.
Consider, for instance, our
experience of seeing an
object: Its color, contours,
apparent motion, and location
in space arise in
consciousness as a seamless
unity, even though this
information is processed by
many separate systems in the
brain. Thus, when a golfer
prepares to hit a shot, he does
not first see the ball’s
roundness, then its whiteness,
and only then its position on
the tee. Rather, he enjoys a
unified perception of the ball.
Many neuroscientists believe
that this phenomenon of
“binding” can be explained
by disparate groups of
neurons firing in synchrony.
Whether or not this theory is
true, it is at least intelligible—because synchronous
activity seems just the sort of
thing that could explain the
unity of a percept.

This work suggests, as
many other findings in
neuroscience do, that the
*contents* of consciousness can
often be made sense of in
terms of their underlying
neurophysiology. However,
when we ask why such
phenomena should be
experienced in the first place,
we are returned to the
mystery of consciousness in
full.

Unfortunately, efforts to
locate consciousness in the
brain generally fail to
distinguish between
consciousness and its
contents. As a result, many
researchers have taken one
form of consciousness (or one
class of its contents) as a
sufficient view of the whole.
For instance, Christof Koch
and others have done some
very clever work on vision,
looking for which regions of
the brain encode conscious
visual perception. The
phenomenon of *binocular
rivalry* has provided an
especially useful foothold
here: It just so happens that
when each eye is presented
with a different visual
stimulus, a person’s
conscious experience is not a
blending of the two images
but, rather, a series of
apparently random transitions
between them. If, for
instance, you are shown a
picture of a house in one eye
and a human face in the other,
you will not see the two
images competing with each
other or otherwise
superimposed. You will see
the house for a few seconds,
and then the face, and then
the house again, switching at
random intervals. This
phenomenon has allowed
experimenters to look for
those regions of the brain (in
both humans and monkeys)
that respond to a change in
conscious perception. The
psychophysical situation
seems tailor-made to
distinguish the frontier
between the conscious and
unconscious components of
vision, because the input
remains constant—each eye
receives the continuous
impression of a single image
—while somewhere in the
brain a wholesale change in
the contents of consciousness
occurs every few seconds.
This is very interesting—and
yet subjects experiencing
binocular rivalry are
*conscious* throughout the
experiment; only the contents
of visual awareness have
been modulated by the task.
If you shut your eyes at this
moment, the contents of your
consciousness change quite
drastically, but your
consciousness (arguably)
does not.

This is not to say that our
understanding of the mind
won’t change in surprising
ways through our study of the
brain. There may be no limit
to how a maturing
neuroscience might reshape
our beliefs about the nature of
conscious experience. Are we
unconscious during sleep or
merely unable to remember
what sleep is like? Can
human minds be duplicated?
Neuroscience may one day
answer such questions—and
the answers might well
surprise us.

But the reality of
consciousness appears
irreducible. Only
consciousness can know itself
—and directly, through first-
person experience. It follows,
therefore, that rigorous
introspection—“spirituality”
in the widest sense of the
term—is an indispensable
part of understanding the
nature of the mind.

## THE MIND DIVIDED

If spirituality is to become
part of science, however, it
must integrate with the rest of
what we know about the
world. It has long been
obvious that traditional
approaches to spirituality
cannot do this—being based,
to one or another degree, on
religious myths and
superstitions. Consider the
idea that human beings, alone
among Nature’s animals,
have been installed with
immortal souls. This dogma
came under pressure the
moment Darwin published
*On the Origin of Species* in
1859, but it is now truly dead.
By sequencing a wide variety
of genomes, we have finally
rendered our continuity with
the rest of life undeniable.
We are such stuff as yeasts
are made of. Of course, only
25 percent of Americans
believe in evolution (while 68
percent believe in the literal
existence of Satan). But we
can now say that any
conception of our place in the
universe that denies we
evolved from more primitive
life forms is pure delusion.

Neuroscience has also
produced results that are
equally hostile to the
traditional idea of souls—
and, therefore, to any
approach to spirituality that
presupposes their existence.
One such finding,
conclusively demonstrated in
humans and animals since the
1950s, is widely known as the
“split brain”—a phenomenon
so at odds with common
sense that, even within the
culture of science, it has
defied integration into our
thoughts.
The human brain is divided at
the level of the cerebrum
(everything above the brain
stem) into right and left
hemispheres. The reason for
this is still unclear, but it does
not seem altogether strange
that the left-right symmetry
of our bodies would be
reflected in our central
nervous system. This
structure turns out to have
surprising consequences.

The right and left
hemispheres of all vertebrate
brains are connected by
several nerve tracts called
*commissures*, the function of
which, we now know, is to
pass information back and
forth between them. The main
commissure in the brains of
placental mammals like
ourselves is the *corpus
callosum*, the fibers of which
link similar regions of the
cortex across the
hemispheres. The
evolutionary history of this
structure is still a matter of
dispute, but in human beings
it represents a larger system
of connectivity than the sum
of all the fibers linking the
cortex to the rest of the
nervous system As we are
about to see, the unity of
every human mind depends
on the normal functioning of
these connections. Without
them, our brains—and minds
—are divided.

Certain people have had
their forebrain commissures
surgically severed. This is
generally undertaken as a
treatment for severe epilepsy,
though other surgeries
occasionally require that
some of these fibers be cut.
As a treatment for epilepsy,
patients usually receive a
*callosotomy*, a procedure
whereby most or all of the
corpus callosum is severed to
prevent local storms of
unregulated activity from
spreading throughout the
brain and producing a
seizure.

The split brain was
brought to the world’s
attention half a century ago
by Roger W. Sperry and
colleagues. Sperry was
awarded a Nobel Prize in
1981 for this work, which
inspired a literature that now
spans neuroscience,
psychology, linguistics,
psychiatry, and philosophy.
Before Sperry began his
research, it appeared that
dividing the brains of these
patients simply mitigated
their seizures (which was,
after all, the point) without
producing any changes in
their behavior. This seemed
to lend credence to the
ancient notion that the corpus
callosum does nothing more
than hold the two
hemispheres of the brain
together.

Once patients recover
from this surgery, they
generally appear quite
normal, even on neurological
exam. Under the
experimental conditions that
Sperry and his colleagues
devised, however—first in
cats and monkeys, and then
in humans—two principal
findings emerged. First, the
left and right hemispheres of
the brain display a high
degree of *functional
specialization*. This discovery
was not entirely new, because
it had been known for at least
a century that damage to the
left hemisphere could impair
the use of language. But the
split-brain procedure allowed
scientists to test each
hemisphere independently on
a variety of tasks, revealing a
range of segregated abilities.
The second finding was that
when the forebrain
commissures are cut, the
hemispheres display an
altogether astonishing
*functional independence*,
including separate memories,
learning processes, behavioral
intentions, and—it seems all
but certain—centers of
conscious experience.

The independence of the
hemispheres in a split-brain
patient comes about because
most nerve tracts running to
and from the cortex are
segregated, left and right.
Everything that falls in the
left visual field of each eye,
for instance, is projected to
the right hemisphere of the
brain, and everything in the
right visual field is projected
to the left hemisphere. The
same pattern holds for both
sensation and fine motor
control in our extremities.
Thus, each hemisphere relies
on intact commissures to
receive information from its
own side of the world. While
it can rarely speak, because
speech is usually confined to
the left hemisphere, the right
hemisphere can respond to
questions by pointing to
written words and objects
with the left hand.

The classic demonstration
of hemispheric independence
in a split-brain patient runs as
follows: Show the right
hemisphere a word—egg, say
—by briefly flashing it in the
left half of the visual field,
and the subject (speaking
from his language-dominant
left hemisphere) will claim to
have seen nothing at all. Ask
him to reach behind a
partition and select with his
left hand (which is
predominantly controlled by
the right hemisphere) the
thing that he “did not see,”
and he will succeed in
picking out an egg from
among a multitude of objects.
Ask him to name the item he
now holds in his left hand
without allowing the left
hemisphere to get a look at it,
and he will be unable to
reply. If shown the egg and
asked why he selected it from
among the available
materials, he will probably
confabulate an answer (again,
with his language-dominant
left hemisphere), saying
something like “Oh, I picked
it because I had eggs for
breakfast yesterday.” This is a
peculiar state of affairs.

When the lateralization of
inputs to the brain is
exploited in this way, it
becomes difficult to say that
the person whose brain has
been split is a single subject,
for everything about his
behavior suggests that a silent
intelligence lurks in his right
hemisphere, about which the
articulate left hemisphere
knows nothing. The duality of
mind is further demonstrated
by the fact that these patients
can simultaneously perform
separate manual tasks. For
instance, a person whose
brain is functioning normally
will find it impossible to draw
incompatible figures
simultaneously with the right
and left hands; divided brains
accomplish this task easily,
like two artists working in
parallel. In the acute phase
after surgery, patients’ left
and right hands sometimes
engage in a tug-of-war over
an object or sabotage each
other’s work. The left
hemisphere can speak about
its condition and may even
understand the anatomical
details of the procedure that
has brought it about, yet it
remains remarkably naïve
about the experience of its
neighbor on the right. Even
many years after surgery, the
left hemispheres of these
subjects express surprise or
irritation when their right
hemispheres respond to an
experimenter’s instructions.
To ask the left hemisphere
what it is like to not know
what the right hemisphere is
thinking is rather like asking
a normal subject what it is
like to not know what another
person is thinking: He simply
*does not know* what the other
person is thinking (or even,
perhaps, that he or she exists).

What is most startling
about the split-brain
phenomenon is that we have
every reason to believe that
the isolated right hemisphere
is independently conscious. It
is true that some scientists
and philosophers have
resisted this conclusion, but
none have done so credibly.
If complex language were
necessary for consciousness,
then all nonhuman animals
and human infants would be
devoid of consciousness in
principle. If those whose left
hemispheres have been
surgically removed are still
believed to be conscious—
and they are—how could the
mere presence of a
functioning left hemisphere
rob the right one of its
subjectivity in the case of a
split-brain patient?

The consciousness of the
right hemisphere is especially
difficult to deny whenever a
subject possesses linguistic
ability on both sides of the
brain, because in such cases
the divided hemispheres often
express different intentions.
In a famous example, a young
patient was asked what he
wanted to be when he grew
up: His left brain replied, “A
draftsman,” while his right
brain used letter cards to spell
out “racing driver.” In fact,
the divided hemispheres
sometimes seem to address
each other directly, in the
form of a verbalized,
interhemispheric argument.

In such cases, each
hemisphere might well have
its own beliefs. Consider
what this says about the
dogma—widely held under
Christianity and Islam—that a
person’s salvation depends
upon her believing the right
doctrine about God. If a split-
brain patient’s left
hemisphere accepts the
divinity of Jesus, but the right
doesn’t, are we to imagine
that she now harbors two
immortal souls, one destined
for the company of angels
and the other for an eternity
in hellfire?

The question of whether
there is “something that it is
like” to be the right
hemisphere of a split-brain
patient must be answered in
the only way that it is ever
answered in science: We can
merely observe that its
behavior and underlying
neurology are sufficiently
similar to that which we
know to be correlated with
consciousness in our own
case. There is no difficulty in
doing this for a normal split-
brain patient who retains the
use of her left hand. In fact,
the consciousness of the
disconnected right
hemisphere is easier to
establish than that of most
toddlers. The question of
whether the right hemisphere
is conscious is really a
pseudo-mystery used to bar
the door to a great one: the
uncanny fact that the human
mind can be divided with a
knife.

## STRUCTURE AND FUNCTION

The right and left
hemispheres of our brain
show differences in their
gross anatomy, many of
which are also found in the
brains of other animals. In
humans, the left hemisphere
generally makes a unique
contribution to language and
to the performance of
complex movements.
Consequently, damage on this
side tends to be accompanied
by *aphasia* (impairment of
spoken or written language)
and *apraxia* (impairment of
coordinated movement).

People usually show a
right-ear (left-hemisphere)
advantage for words, digits,
nonsense syllables, Morse
code, difficult rhythms, and
the ordering of temporal
information, whereas they
show a left-ear (right-
hemisphere) advantage for
melodies, musical chords,
environmental sounds, and
tones of voice. Similar
differences have been found
for other senses as well. We
know, for instance, that the
right hand (sensation from
which projects almost entirely
to the left hemisphere) is
better able to discriminate the
order of stimuli, while the left
hand is more sensitive to their
spatial characteristics.

However, the right
hemisphere is dominant for
many higher cognitive
abilities, both in normal
brains and in those that have
been surgically divided. It
tends to have an advantage
when reading faces, intuiting
geometrical principles and
spatial relationships,
perceiving wholes from a
collection of parts, and
judging musical chords.
The right hemisphere is also
better at displaying emotion
(with the left side of the face)
and at detecting emotions in
others.  Interestingly, this
obliges us to view one
another’s least expressive
side of the face (the right)
with our most emotionally
astute hemisphere (the right),
and vice versa. Psychopaths
generally do not show this
right-hemisphere advantage
for the perception of emotion;
perhaps this is one reason
why they are bad at detecting
emotional distress in others.

Most evidence suggests
that the two hemispheres
differ in temperament, and it
now seems uncontroversial to
say that they can make
different (and even opposing)
contributions to a person’s
emotional life. In a divided
brain, the hemispheres are
unlikely to perceive self and
world in the same way, nor
are they likely to feel the
same about them.

Much of what makes us
human is generally
accomplished by the right
side of the brain.
Consequently, we have every
reason to believe that the
disconnected right
hemisphere is independently
conscious and that the
divided brain harbors two
distinct points of view. This
fact poses an insurmountable
problem for the notion that
each of us has a single,
indivisible self—much less an
immortal soul. The idea of a
soul arises from the feeling
that our subjectivity has a
unity, simplicity, and
integrity that must somehow
transcend the biochemical
wheelworks of the body. But
the split-brain phenomenon
proves that our subjectivity
can quite literally be sliced in
two. (This is why Sir John
Eccles, a neuroscientist and a
committed Christian,
declared, against all evidence,
that the right hemisphere of
the divided brain must be
unconscious.) This fact has
interesting ethical
repercussions. For instance,
the biologist Lee Silver
wonders what we should do if
a person with a split brain
wanted to have her right
hemisphere removed because
she could no longer endure
the conflict with her “other
self.” Would this be a
therapeutic intervention or a
murder? However, the most
important implications are for
our view of consciousness: It
is divisible—and, therefore,
more fundamental than any
apparent self.

Imagine undergoing a
complete callosotomy. Like
most such surgeries, you
could be kept awake, because
there are no pain receptors in
the brain. There is also no
reason to think that you
would lose consciousness
during the procedure, because
a person can have an entire
hemisphere removed
(*hemispherectomy*) without
loss of consciousness. Nor
would you suffer a lapse in
memory. After surgery, you
would tend to speak in a way
characteristic of *alexithymia*
(the inability to describe your
emotional life), and you
might also demonstrate an
inappropriate degree of
politeness.  Whether or not
you had occasion to notice
these changes in yourself, it
seems all but certain that you
would retain your sense of
being a “self” throughout the
experience.

Given that each
hemisphere in your divided
brain would have its own
point of view, whereas now
you appear to have only one,
it is natural to wonder which
side of the longitudinal
fissure “you” would find
yourself on once the corpus
callosum was cut. Would you
land on the right or on the
left? It is hard to resist the
uncanny demands of
arithmetic here. Assuming
that you were not simply
extinguished and replaced by
two new subjects—which
seems ruled out by the fact
that you would probably
remain conscious throughout
the procedure and retain your
memories—it is tempting to
conclude that your
subjectivity must collapse to
a single hemisphere. Once the
surgery was over, it would be
obvious that you can’t be on
both sides of the great divide.
Perhaps it is reasonable to
believe that you would find
yourself in the left
hemisphere, retaining the
reins of speech, since speech
and discursive thinking do
much to define your
experience in the present. But
consider some of the other
cognitive abilities you now
consciously enjoy, which we
know are governed primarily
by your right hemisphere.
Who, for instance, would
greet your loved ones with
your left hand and effortlessly
recognize their faces, their
facial expressions, and their
tones of voice?

I think this riddle admits
of a rather straightforward
solution. Consciousness—
whatever its relation to neural
events—is divisible. And just
as it isn’t shared between the
brains of separate individuals,
it need not be shared between
the hemispheres of a single
brain once the structures that
facilitate such sharing have
been cut. If some way of
linking two brains with an
artificial commissure were
ever devised, we should
expect that what had been
two distinct persons would be
unified in the only sense that
*consciousness* is ever unified,
as a single point of view, and
unified in the only sense that
*minds* are ever unified, by
virtue of common contents
and functional abilities.

The experience of
dreaming is instructive here.
Each night, we lie down to
sleep, only to be stolen from
our beds and plunged into a
realm where our personal
histories and the laws of
nature no longer apply.
Generally, we do not retain
enough of a purchase on
reality to even notice that
anything out of the ordinary
has happened. The most
astonishing quality of dreams
is surely our *lack* of
astonishment when they arise.
The sleeping brain seems to
have no expectation of
continuity from one moment
to the next. (This is probably
owing to the diminished
activity in the frontal lobes
that occurs during REM
sleep.) Thus, sweeping
changes in our experience do
not, in principle, detract from
the unity of consciousness.
Left to its own devices,
consciousness seems happy to
just experience one thing
after the next.

If my brain harbors only
one conscious point of view
—if all that is remembered,
intended, and perceived is
known by a single
“subject”—then I enjoy unity
of mind. The evidence is
overwhelming, however, that
such unity, if it ever exists in
a human being, depends upon
some humble tracts of white
matter crossing the midline of
the brain.

## ARE OUR MINDS ALREADY SPLIT?

Roger Sperry and his
colleagues demonstrated in
the 1950s that the corpus
callosum cannot facilitate a
complete transfer of learning
between the cerebral
hemispheres.  After cutting
the optic chiasma in cats (and
thereby confining the inputs
from each eye to a single
hemisphere), they discovered
that only simple learning
acquired through one eye
could transfer to the other
side of the brain. Given the
immense amount of
information processing that
takes place in each
hemisphere, it seems certain
that even a normal human
brain will be functionally
split to one or another degree.
Two hundred million nerve
fibers seem insufficient to
integrate the simultaneous
activity of 20 billion neurons
in the cerebral cortex, each of
which makes hundreds or
thousands (sometimes tens of
thousands) of connections to
its neighbors. Given this partitioning of information,
how can our brains not harbor
multiple centers of
consciousness even now?

The philosopher Roland
Puccetti once observed that
the existence of separate
spheres of consciousness in
the normal brain would
explain one of the most
perplexing features of split-
brain research: Why is it that
the right hemisphere is
generally willing to bear
silent witness to the errors
and confabulations of the
left? Could it be that the right
hemisphere is used to it?

An answer consistent with the hypothesis of mental duality in the normal human brain suggests itself. The non-speaking hemisphere has known the true state of affairs from a very tender age. It has known this because beginning at age two or three it heard speech emanating from the common body that, as language development on the left proceeded, became too complex grammatically and syntactically for it to believe it was generating; the same, of course, for what it observed the preferred hand writing down in school through the years. Postsurgically, little has changed for the mute hemisphere (other than loss of sensory information about the ipsilateral half of bodily space). . . . Being inured to this status of cerebral helot, it goes along. Thankless cooperation can become a way of life.
Take a moment to absorb
how bizarre this possibility is.
The point of view from which
you are consciously reading
these words may not be the
only *conscious* point of view
to be found in your brain. It is
one thing to say that you are
unaware of a vast amount of
activity in your brain. It is
quite another to say that some
of this activity is aware of
itself and is watching your
every move.

There must be a reason
why the structural integrity of
the corpus callosum creates a
functional unity of mind
(insofar as it does), and
perhaps it is only the division
of the corpus callosum that
makes for separated regions
of consciousness in the
human brain. But whatever
the final lesson of the split
brain is, it thoroughly violates
our commonsense intuitions
about the nature of our
subjectivity.

A person’s experience of
the world, while apparently
unified in a normal brain, can
be physically divided. The
problem this poses for the
study of consciousness may
be insurmountable. If I were
to interrogate my brain with
the help of a colleague—one
who was willing to expose
my cortex and begin probing
with a microelectrode—
neither of us would know
what to make of a region that
failed to influence the
contents of “my”
consciousness. The split-brain
phenomenon suggests that all
that I would be able to say is
whether I (as perhaps only
one among many centers of
consciousness to be found in
my brain) felt anything when
my friend applied the current.
Feeling nothing, I wouldn’t
know whether the neurons in
question constituted a region
of consciousness in their own
right—for the simple reason
that I might be just like a
split-brain patient given to
wonder, with his articulate
left hemisphere, whether or
not his right hemisphere is
conscious. It surely is, and yet
no amount of experimental
probing on his part will drive
the relevant facts into view.
As long as we must correlate
changes in the brain—or any
other physical system—with
first-person reports, any
physical systems that are
functionally mute may
nevertheless prove to be
conscious, and our attempt to
understand the causes of
consciousness will fail to take
them into account.

All brains—and persons—may be split to one or another
degree. Each of us may live,
even now, in a fluid state of
split and overlapping
subjectivity. Whether or not
this seems plausible to you
may not be the point. Another
part of your brain may see the
matter differently.

## CONSCIOUS AND UNCONSCIOUS PROCESSING IN THE BRAIN

The frontier between
conscious and unconscious
mental processes has
fascinated psychologists and
neuroscientists for more than
a century. The realization that
the unconscious mind must
have some cognitive and
emotional structure was the
foundation of Freud’s work
and also the stage upon which
he erected an impressively
unscientific mythology. The
connection between
conscious thoughts and
unconscious processes was
also present in the work of
William James, whose views
on this topic, and on the mind
in general, still deserve our
attention:

Suppose we try to recall a forgotten name. The state of our consciousness is peculiar. There is a gap therein; but no mere gap. It is a gap that is intensely active. A sort of wraith of the name is in it, beckoning us in a given direction, making us at moments tingle with the sense of our closeness, and then letting us sink back without the longed-for term. If wrong names are proposed to us, this singularly definite gap acts immediately so as to negate them. They do not fit into its mould. And the gap of one word does not feel like the gap of another, all empty of content as both might seem necessarily to be when described as gaps. . . . The rhythm of a lost word may be there without a sound to clothe it; or the evanescent sense of something which is the initial vowel or consonant may mock us fitfully, without growing more distinct.
In other words, the
unconscious mind exists, and
our conscious experience
gives some indication of its
structure. Recent advances in
experimental psychology and
neuroimaging have allowed
us to study the boundary
between conscious and
unconscious mental processes
with increasing precision. We
now know that at least two
systems in the brain—often
referred to as “dual
processes”—govern human
cognition, emotion, and
behavior. One is
evolutionarily older,
unconscious, and automatic;
the other evolved more
recently and is both conscious
and deliberative. When you
find another person annoying,
sexually attractive, or
inadvertently funny, you are
experiencing the percolations
of System 1. The heroic
efforts you make to conceal
these feelings out of
politeness are the work of
System 2.

Scientists have learned
how to target System 1
through the phenomenon of
“priming,” revealing that
complex mental processes
lurk beneath the level of
conscious awareness.  The
experimental technique of
“backward masking” has
been at the center of this
research: Human beings can
consciously perceive very
brief visual stimuli (down to
about 1/30 of a second), but
we can no longer see these
images if they are
immediately followed by a
dissimilar pattern (a “mask”).
This fact allows for words
and pictures to be delivered to
the mind subliminally, and
these stimuli have subsequent
effects on a person’s
cognition and behavior. For
instance, you will be faster to
recognize that *ocean* is a
word if it follows a related
prime, like *wave*, than if it
follows an unrelated one, like
*hammer*. And emotionally
charged terms are more easily
recognized than neutral ones
(*sex* can be presented more
briefly than *car*), which
further demonstrates that the
meanings of words must be
gleaned prior to
consciousness. Subliminally
promised rewards drive
activity in the brain’s reward
centers, and masked fearful
faces and emotional words
increase activity in the
amygdala. Clearly, we are
not aware of all the
information that influences
our thoughts, feelings, and
actions.

Many other findings attest
to the importance of our
unconscious mental lives.
Amnesiacs, who can no
longer form conscious
memories, can still improve
their performance on a wide
variety of tasks through
practice. For instance, a
person can learn to play golf
with increasing proficiency,
all the while believing that
whenever she picks up a club
it is for the first time. The
acquisition of such motor
skills occurs outside of
consciousness in normal
people as well. Your
conscious memories of
practicing a musical
instrument, driving a car, or
tying your shoelaces are
neurologically distinct from
your *learning* how to do these
things and from your *knowing*
how to do them now. People
with amnesia can even learn
new facts and have their
ability to recognize names
and generate concepts
improve in response to prior
exposure, without having any
memory of acquiring such
knowledge. In fact, we are all
in this position with respect to
most of our semantic
knowledge of the world. Do
you remember learning the
meaning of the word door?
Probably not. How do you
recognize it and bring its
meaning to mind? You have
no idea. These processes
occur outside
consciousness.

## CONSCIOUSNESS IS WHAT MATTERS

Despite the obvious
importance of the
unconscious mind,
consciousness is what matters
to us—not just for the
purpose of spiritual practice
but in every aspect of our
lives. Consciousness is the
substance of any experience
we can have or hope for, now
or in the future. If God spoke
to Moses out of a burning
bush, the bush would have
been a visual percept
(whether veridical or not) of
which Moses was consciously
aware. It should be clear that
if a person begins to suffer
from intractable pain or
depression, if he experiences
a continuous ringing in his
ears or the consequences of
having acquired a bad
reputation among his
colleagues, these
developments are matters of
consciousness and its
contents, whatever the nature
of the unconscious processes
that give rise to them.

Consciousness is also what
gives our lives a moral
dimension. Without
consciousness, we would
have no cause to wonder how
we should behave toward
other human beings, nor
could we care how we were
treated in return. Granted,
many moral emotions and
intuitions operate
unconsciously, but it is
because they influence the
contents of consciousness that
they matter to us. I have
argued elsewhere, and at
length in *The Moral Landscape*, that we have
ethical responsibilities toward
other creatures precisely to
the degree that our actions
can affect their conscious
experience for better or
worse. We don’t have
ethical obligations toward
rocks (on the assumption that
they are not conscious), but
we do have such obligations
toward any creature that can
suffer or be deprived of
happiness. Of course, it can
be wrong to destroy rocks if
they happen to be valuable to
other conscious creatures.
The Taliban’s destruction of
the 1,500-year-old standing
Buddhas of Bamiyan was
wrong not from the
perspective of the statues
themselves but from that of
all the people who cared
about them (and the future
people who might have
cared).

I have never come across a
coherent notion of bad or
good, right or wrong,
desirable or undesirable that
did not depend upon some
change in the experience of
conscious creatures. It is not
always easy to nail down
what we mean by “good” and
“bad”—and their definitions
may remain perpetually open
to revision—but such
judgments seem to require, in
every instance, that some
difference register at the level
of experience. Why would it
be wrong to murder a billion
human beings? Because so
much pain and suffering
would result. Why would it
be wrong to painlessly kill
every man, woman, and child
in their sleep? Because of all
the possibilities for future
happiness that would be
foreclosed. If you think such
actions are wrong primarily
because they would anger
God or would lead to your
punishment after death, you
are still worried about
perturbations of
consciousness—albeit ones
that stand a good chance of
being wholly imaginary.

I take it to be axiomatic,
therefore, that our notions of
meaning, morality, and value
presuppose the actuality of
consciousness (or its loss)
*somewhere*. If anyone has a
conception of meaning,
morality, and value that has
nothing to do with the
experience of conscious
beings, in this world or in a
world to come, I have yet to
hear of it. And it would seem
that such a conception of
value could hold no interest
for anyone, by definition,
because it would be
guaranteed to be outside the
experience of every conscious
being, now and in the future.

The fact that the universe
is illuminated where you
stand—that your thoughts and
moods and sensations have a
qualitative character in this
moment—is a mystery,
exceeded only by the mystery
that there should be
something rather than nothing
in the first place. Although
science may ultimately show
us how to truly maximize
human well-being, it may still
fail to dispel the fundamental
mystery of our being itself.
That doesn’t leave much
scope for conventional
religious beliefs, but it does
offer a deep foundation for a
contemplative life. Many
truths about ourselves will be
discovered in consciousness
directly or not discovered at
all.

1. ↑ T. Nagel. 1974. “What Is It Like to Be a Bat?” *Philosophical Review* 83.
2. ↑ One could argue that this notion of “trading places” is fraught with confusion, but Nagel’s notion of consciousness being identical to subjective experience isn’t.
3. ↑ It’s true that some philosophers and neuroscientists will want to pull the brakes right here. Daniel Dennett, with whom I agree about many things, tells me that if I can’t imagine the falsehood of a statement like “Either the lights are on, or they are not,” I’m not trying hard enough. However, on a question as rudimentary as the ontology of consciousness, the debate often comes down to irreconcilable intuitions. While I will try my best to unpack my intuition that the above statement cannot be false, at a certain point a person has to admit that he can’t understand what his opponents are talking about.
4. ↑ The picture does not change (much) if you are a dualist who believes that brains are conscious only because consciousness is somehow inserted into them. There are many problems with dualism, but even a dualist should agree that consciousness appears to be associated only with organisms of sufficient complexity. Whether or not one is a dualist, one has no compelling reason to believe that there is something that it is like to be a tomato.
5. ↑ Saying that a creature is conscious, therefore, is not to make a claim about its behavior or its use of language, because we can find examples of both behavior and language without consciousness (a primitive robot) and consciousness without either (a person suffering “locked-in syndrome”). Of course, it is possible that some robots are conscious—and if consciousness is the sort of thing that comes into being purely by virtue of information processing, then our cell phones and coffeemakers may be conscious. But few of us imagine that there is something that it is like to be even the most advanced computer. Whatever its relationship to information processing, consciousness is an internal reality that cannot necessarily be appreciated from the outside and need not be associated with behavior or responsiveness to stimuli. If you doubt this, read *The Diving Bell and the Butterfly* (1997), Jean Dominique-Bauby’s astonishing and heartbreaking account of his own “locked-in syndrome,” which he dictated by signing to a nurse with his left eyelid. Then try to imagine his predicament if even this degree of motor control had been denied him.
6. ↑ Descartes is probably the first
Western philosopher to make
this point, but others have
continued to emphasize it,
notably the philosophers John
Searle and David Chalmers. I
do not agree with Descartes’s
dualism or with some of what
Searle and Chalmers have said
about the nature of
consciousness, but I agree that
its subjective reality is both
primary and indisputable. This
does not rule out the possibility
that consciousness is, in fact,
identical to certain brain
processes.

Again, I should say that
some philosophers, such as
Daniel Dennett and Paul
Churchland, just don’t buy this.
But I do not understand why.
My not seeing how
consciousness can possibly be
an illusion entails my not
understanding how they (or
anyone else) can think that it
might be one. I agree that we
may be profoundly mistaken
about consciousness—about
how it arises, about its
connection to the brain, about
precisely what we are
conscious of and when. But
this is not the same as saying
that consciousness itself may
be illusory. The state of being
completely confused about the
nature of consciousness is itself
a demonstration of
consciousness.
7. ↑ “The stuff of the world is
mind-stuff.” A. S. Eddington.
1928. *The Nature of the Physical World*. Cambridge,
UK: Cambridge University
Press, p. 276.

“The old dualism of mind
and matter . . . seems likely to
disappear . . . through
substantial matter resolving
itself into a creation and
manifestation of mind.” J.
Jeans. 1930. *The Mysterious Universe*. Cambridge, UK:
Cambridge University Press, p. 158.

“The only acceptable point
of view appears to be the one
that recognizes both sides of
reality—the quantitative and
the qualitative, the physical and
the psychical—as compatible
with each other, and can
embrace them simultaneously.”
W. Pauli, C. P. Enz, and K. v.
Meyenn. [1955] 1994. *Writings on Physics and Philosophy*.
New York: Springer-Verlag, p. 259.

“The conception of the
objective reality of the
elementary particles has thus
evaporated not into the cloud of
some obscure new reality
concept, but into the
transparent clarity of a
mathematics that represents no
longer the behavior of the
particle but rather our
knowledge of this behavior.”
W. Heisenberg. 1958. “The
Representation of Nature in
Contemporary Physics.”
*Daedalus* 87 (Summer): 100.

“We simply cannot see how
material events can be
transformed into sensation and
thought, however many
textbooks . . . go on talking
nonsense on the subject.” E.
Schrödinger. 1964. *My View of the World*, trans. C. Hastings.
Cambridge, UK: Cambridge
University Press, pp. 61–62.
8. ↑ F. Dyson. 2002. “The
Conscience of Physics.” *Nature*
420 (December 12): 607–8
9. ↑ I am grateful to my friend, physicist Lawrence Krauss, for clarifying several of these points.
10. ↑ If we look for consciousness in
the physical world, we find
only complex systems giving
rise to complex behavior—
which may or may not be
attended by consciousness. The
fact that the behavior of our
fellow human beings persuades
us that they are conscious
(more or less) does not get us
any closer to linking
consciousness to physical
events. Is a starfish conscious?
It seems clear that we will not
make any progress on this
question by drawing analogies
between starfish behavior and
our own. Only in the presence
of animals sufficiently like
ourselves do our intuitions
about (and attributions of)
consciousness begin to
crystallize. Is there something
that it is like to be a cocker
spaniel? Does it feel its pains
and pleasures? Surely it must.
How do we know? Behavior
and analogy.

Some scientists and
philosophers have formed the
mistaken impression that it is
always more parsimonious to
deny consciousness in lower
animals than to attribute it to
them. I have argued elsewhere
that this is not the case (S.
Harris. 2004. *The End of Faith: Religion, Terror, and the Future of Reason*. New York:
Norton, pp. 276–77). To deny
consciousness in chimpanzees,
for instance, is to assume the
burden of explaining *why* their
genetic, neuroanatomical, and
behavioral similarity to us is an
insufficient basis for it. (Good
luck.)
11. ↑ The idea that consciousness is
identical to (or emerged from)
a certain class of unconscious
physical events seems
impossible to properly
conceive—which is to say that
we can think we are thinking it,
but we are probably mistaken.
We can say the right words:
”Consciousness emerges from
unconscious information
processing.” We can also say
“Some squares are as round as
circles” and “2 plus 2 equals
7.” But are we really thinking
these things all the way
through? I don’t think so.
12. ↑ J. Levine. 1983. “Materialism
and Qualia: The Explanatory
Gap.” *Pacific Philosophical
Quarterly* 64.
13. ↑ D. J. Chalmers. 1996. *The Conscious Mind: In Search of a Fundamental Theory*. New York: Oxford University Press.
14. ↑ This maneuver has its
antecedents in the “neutral
monism” (so dubbed by
Russell) of James and Mach. It
is a view I substantially agree
with. Here is Nagel on the
subject:
"What will be the point of view, so to speak, of such a theory? If we could arrive at it, it would render transparent the relation between mental and physical, not directly, but through the transparency of their common relation to something that is not merely either of them. Neither the mental nor the physical point of view will do for this purpose. The mental will not do because it simply leaves out the physiology, and has no room for it. The physical will not do because while it includes the behavioral and functional manifestations of the mental, this doesn’t, in view of the falsity of conceptual reductionism, enable it to reach to the mental concepts themselves. . . . The difficulty is that such a viewpoint cannot be constructed by the mere conjunction of the mental and the physical. It has to be something genuinely new, otherwise it will not possess the necessary unity. . . . Such a conception will have to be created; we won’t just find it lying around. All the great reductive successes in the history of science have depended on theoretical concepts, not natural ones—concepts whose whole justification is that they permit us to replace brute correlations with reductive explanations. At present such a solution to the mind-body problem is literally unimaginable, but it may not be impossible.”
(T. Nagel. 1998.
“Conceiving the Impossible and the Mind-Body Problem.” *Philosophy* 73[285]: pp. 337–52.)
15. ↑ J. R. Searle. 1992. *The Rediscovery of the Mind*.
Cambridge, MA: MIT Press,
1992; J. R. Searle. 2007.
“Dualism Revisited.” *J Physiol
Paris* 101 (4–6); J. R. Searle.
1998. “How to Study
Consciousness Scientifically.”
*Philos Trans R Soc Lond B
Biol Sci* 353 (1377).
16. ↑ J. Kim. 1993. “The Myth of Nonreductive Materialism.” *In Supervenience and Mind*.
Cambridge, UK: Cambridge University Press.
17. ↑ C. McGinn. 1989. “Can We Solve the Mind-Body Problem?” *Mind* 98; C. McGinn. 1999.
*The Mysterious Flame: Conscious Minds in a Material World*. New York: Basic Books. Steven Pinker also throws his lot in with McGinn: S. Pinker. 1997. *How the Mind Works*. New York: Norton, pp. 558–65. This is more or less where Thomas Nagel comes out, though he
considers himself less pessimistic than McGinn: Nagel, “Conceiving the Impossible and the Mind-Body Problem.”
18. ↑ Whatever its relation to the
physical world, consciousness
seems to be conceptually
irreducible, because any
attempt to define *consciousness*
or its surrogates (*sentience*,
*awareness*, *subjectivity*) leads
us in a lexical circle. One of the
great obstacles to
understanding consciousness
probably lurks here: If an
adequate, noncircular definition
of consciousness exists, no one
has found it. The same can be
said about any idea that is truly
basic to our thinking. The
reader is invited to try to define
the word *causation* in
noncircular terms.
Consequently, many
philosophers and scientists
change the subject whenever
the discussion turns to matters
of consciousness—conflating it
with attention, self-awareness,
wakefulness, responsiveness to
stimuli, or some other, more
tractable and less fundamental
aspect of cognition. These
digressions are often
inadvertent and rarely aim at a
reductive definition of
“consciousness.” Where they
do, as in the case of (analytical)
behaviorism, they invariably
seem false and question-
begging.
19. ↑ Be it “40-Hz coherent activity
in thalamocortical pathways”
(R. Llinas. 2001. *I of the Vortex: From Neurons to Self*.
Cambridge, MA: MIT Press; R.
Llinas et al. 1998. “The Neuronal Basis for Consciousness.” *Philos Trans R Soc Lond B Biol Sci*353[1377]); “cross-regional
integrations of neural activity”
involving the brain-stem
reticular formation, the
thalamus, and somatosensory
and cingulate cortices (A.
Damasio. 1999. *The Feeling of
What Happens: Body and
Emotion in the Making of
Consciousness*. New York:
Harcourt Brace); “selectional
reentrant activity of groups of
neurons in the
[thalamocortical] core” (G. M.
Edelman. 2006. *Second
Nature: Brain Science and
Human Knowledge*. New
Haven, CT: Yale University
Press); “quantum-coherent
oscillations within
microtubules” (R. Penrose.
1994. *Shadows of the Mind*.
Oxford: Oxford University
Press); “the interactions of
specialized, modular
components in a distributed
neural network” (J. W. Cooney
and M. S. Gazzaniga. 2003.
“Neurological Disorders and
the Structure of Human
Consciousness.” *Trends Cogn
Sci* 7[4]); or some other
physical or functional state.
20. ↑ To see the impasse more
clearly, it might be useful to
consider a neuroscientific
account of consciousness that
proceeds with the usual
buoyant disregard for this
philosophical terrain. The
neuroscientists Gerald Edelman
and Giulio Tononi claim that it
is the intrinsic “integration,” or
unity, of consciousness that
provides the best clue to its
physical character. In their
view, consciousness is a
“unified neural process” born
of “ongoing, recursive, highly
parallel signaling within and
among brain areas.” (Gerald M.
Edelman and Giulio Tononi.
2002. *A Universe of Consciousness: How Matter Becomes Imagination*. New
York: Basic Books; G. Tononi
and G. M. Edelman. 1998.
“Consciousness and Complexity.” *Science*
282[5395].) Accounting for
why the highly synchronous
activities of generalized
seizures and slow-wave sleep
do not suffice for
consciousness, the authors
provide another criterion: The
“repertoire of differentiated
neural states” must be large
rather than small.
Consciousness, therefore, is
intrinsically “integrated” and
“differentiated.” The fact that
over a long enough time scale,
the entire brain may be said to
display such characteristics
demands another caveat—
because the entire brain cannot
be the locus of consciousness.
Thus, the authors declare that
such integration and
differentiation must occur
within a window of a few
hundred milliseconds. These
criteria together constitute their
“dynamic core hypothesis.”

Tononi and Edelman have
done some fascinating
neuroscience, but their research
demonstrates how forlorn any
empirical results seem when
hurled against the mystery of
consciousness. The problem is
that such work does nothing to
render the emergence of
consciousness comprehensible.
While Tononi and Edelman are
probably aware of this fact,
they nevertheless announce,
arms akimbo, that “a scientific
explanation of consciousness is
becoming increasingly
feasible.” (G. Tononi and G.
M. Edelman. 1998. p. 1850.)

Why would the difference
between consciousness and
unconsciousness be a matter of
“a distributed neural process
that is both highly integrated
and highly differentiated”? And
why should the time course of
such integration be a few
hundred milliseconds? What if
it were a few hundred years?
What if distributed geological
processes gave rise to
consciousness? Let’s just say,
for the sake of argument, that
they do. This would not explain
how consciousness emerges. It
would be nothing short of a
miracle if mere integration and
differentiation among processes
in the earth sufficed to make
the planet conscious. Is the
linkage between neural
synchrony and consciousness
any more intelligible? No—
apart from the fact that we
already know that we are
conscious.
Consider some other
possibilities for emergence: Let
us say that there is something
that it is like to be a coral reef
battered by waves of precisely
0.5 hertz; there is something
that it is like to be a 150-mile-per-hour wind gust laying
waste to a trailer park (but only
if the trailers are made entirely
of aluminum); there is
something that it is like to be
the sum total of New Year’s
resolutions left unfulfilled.
How could such diverse
“brains” possibly give rise to
consciousness? We have no
idea. And yet, if we stipulate
that they do, their powers are
no less comprehensible than
those of the brains we have in
our heads. But they are not
comprehensible at all, of course
—and that is the problem of
consciousness.
21. ↑ Cited in C. Sagan. 1995. *The Demon-Haunted World: Science as a Candle in the Dark*. New York: Random
House, p. 272.
22. ↑ *Vitalism* is the now discredited
doctrine that living systems require
some nonphysical principle to
explain their organization and
behavior.
23. ↑ This distinction was obvious to
many thinkers even before
vitalism was discredited. C. D.
Broad (1925) summed it up
with admirable precision:
The one and only kind of evidence that we ever have for believing that a thing is alive is that it behaves in certain characteristic ways. E.g., it moves spontaneously, eats, drinks, digests, grows, reproduces, and so on. Now all these are just actions of one body on other bodies. There seems to be no reason whatever to suppose that “being alive” means any more than exhibiting these various forms of bodily behaviour. . . . But the position about consciousness, certainly seems to be very different. It is perfectly true that an essential part of our evidence for believing that anything but ourselves has a mind and is having such and such experiences is that it performs certain characteristic bodily movements in certain situations. . . . But it is plain that our observation of the behavior of external bodies is not our only or our primary ground for asserting the existence of minds and mental processes. And it seems to me equally plain that by “having a mind” we do not mean simply “behaving in such and such ways.”
(Cited in A. Beckermann. 2000. “The Reductive Explainability of Phenomenal Consciousness.” In *Neural Correlates of Consciousness: Empirical and Conceptual Questions*, ed. T. Metzinger. Cambridge, MA: MIT Press, p. 49).
24. ↑ Another way of stating the
matter is that if, as all
physicalists believe, there is a
necessary connection between
the physical and the
phenomenal, we would not
expect to see evidence for it—
apart from the reliability of
correlation itself. If we are told
that phenomenal state X is
really brain state Y, we must
ask, “By virtue of what is this
identity true?” The answer
must be that one cannot find X
without Y or Y without X. But
this disgorges two further facts:
Such an identity can be
established only by virtue of
empirical correlations, and the
phenomenal term is in no way
subordinate, with respect to
defining what a state is, to its
physical correlate. As Donald
Davidson said, “If some mental
events are physical events, this
makes them no more physical
than mental. Identity is a
symmetrical relation.” (D.
Davidson. 1987. “Knowing
One’s Own Mind.”
*Proceedings and Addresses of
the American Philosophical
Association* 61.) Brain state Y
is identifiable as phenomenal
state X only by virtue of its X-
ness.

The problem is further
complicated by the fact that the
neural correlates of conscious
states seem liable to be a far
more heterogeneous class of
events than I have indicated.
This raises the issue of *multiple
realizability*: the possibility that
different physical states may be
capable of producing
consciousness. Finding one
such state (or class of states) to
be reliably correlated with
consciousness would not
necessarily reveal anything
about the possibilities of
consciousness in other physical
systems. Multiple realizability
is especially problematic for
any theory that seeks to reduce
consciousness to a specific type
of brain state (i.e., any “type-
type identity” theory of
consciousness). In
neuroanatomical terms, we
know that a limited form of
multiple realizability must be
true, because different species
of birds and mammals perform
many of the same cognitive
operations with importantly
different neuronal
architectures. Of course, it is
conceivable that only human
beings are conscious, or that
consciousness may be
instantiated in precisely the
same neural circuits in
dissimilar brains—but both
these propositions strike me as
extremely doubtful.

Whatever one’s ontological
bias, the meaningfulness of
correlation depends on the
belief that a causal linkage (if
not identity) exists between
physical states and subjective
experience. And yet,
correlation is itself the only
basis for establishing this
linkage. This is not merely a
case of Humean angst with
respect to causation: We are
blind to the physical causes of
phenomenal events to a much
greater degree than we are to
the physical causes of physical
events. In fact, Hume’s
skepticism about our
knowledge of causation has not
aged very well. Even rats
appear to intuit causal
connections beyond mere
correlations. One can also
argue that our ability to pick
out individual events in a
temporal sequence, or to group
events into categories, is the
product of causal reasoning.
(See M. R. Waldmann, Y.
Hagmayer, and A. P. Blaisdell.
2006. “Beyond the Information
Given: Causal Models in
Learning and Reasoning.”
*Current Directions in
Psychological Science* 15[6];
M. J. Buehner and P. W.
Cheng. 2005. “Causal
Learning.” In *The Cambridge
Handbook of Thinking and
Reasoning*, ed. K. J. Holyoak
and R. G. Morrison. New
York: Cambridge University
Press.) When I break a pencil,
the force applied to it by my
hands and its subsequent
breaking are correlated, but not
merely so. There is much to be
said about the microstructure of
pencils that makes their
brittleness, and hence the
observed correlation,
intelligible. With
consciousness, however, the
link appears to be brute. As
Chalmers and others have
noted, the question remains:
Why should such events in the
brain be *experienced* at all? (D.
J. Chalmers. 1995. “The Puzzle
of Conscious Experience.” *Sci
Am* 273[6]; Chalmers, *The Conscious Mind*; D. J.
Chalmers. 1997. “Moving Forward on the Problem of
Consciousness.” *Journal of Consciousness Studies* 4[1].)
But this does not stop
neuroscientists and
philosophers from trying to
simply ram through
explanatory analogies that
don’t quite fit.
25. ↑ W. Singer. 1999. “Neuronal
Synchrony: A Versatile Code
for the Definition of
Relations?” *Neuron* 24(1).
26. ↑ For doubts on this point, see M.
N. Shadlen and J. A. Movshon.
1999. “Synchrony Unbound: A
Critical Evaluation of the
Temporal Binding
Hypothesis.” *Neuron* 24(1).
27. ↑ Prinz also observes that
binding and consciousness are
fully dissociable. J. Prinz.
2001. “Functionalism, Dualism
and Consciousness.” In
*Philosophy and the
Neurosciences*, ed. W. Bechtel
et al. Oxford: Blackwell.
28. ↑ A. Polonsky et al. 2000.
“Neuronal Activity in Human
Primary Visual Cortex
Correlates with Perception
During Binocular Rivalry.” *Nat
Neurosci* 3(11); G. Rees, G.
Kreiman, and C. Koch. 2002.
“Neural Correlates of
Consciousness in Humans.”
*Nat Rev Neurosci* 3(4); F.
Crick and C. Koch. 1998.
“Consciousness and
Neuroscience.” *Cerebral*
Cortex 8; F. Crick and C.
Koch. 1999. “The Unconscious
Humunculus.” In *The Neural
Correlates of Consciousness*,
ed. T. Metzinger. Cambridge,
MA: MIT Press; F. Crick and
C. Koch. 2003. “A Framework
for Consciousness.” *Nat
Neurosci* 6(2); J. D. Haynes.
2009. “Decoding Visual
Consciousness from Human
Brain Signals.” *Trends Cogn Sci* 13(5).
29. ↑ Statistics available at
www.gallup.com.
30. ↑ G. M. Bogen and J. E. Bogen.
1986. “On the Relationship of
Cerebral Duality to Creativity.”
*Bull Clin Neurosci* 51.
31. ↑  J. E. Bogen, R. W. Sperry, and
P. J. Vogel. 1969. “Addendum:
Commissural Section and
Propagation of Seizures.” In
*Basic Mechanisms of the
Epilepsies*, ed. Jasper et al.
Boston: Little, Brown; E.
Zaidel, M. Iacoboni, D. Zaidel,
and J. E. Bogen. 2003. “The
Callosal Syndromes.” In
*Clinical Neuropsychology*.
Oxford: Oxford University
Press; E. Zaidel, D. W. Zaidel,
and J. Bogen. Undated. “The
Split Brain.”
www.its.caltech.edu/~jbogen/text/ref130.htm
32. ↑ M. S. Gazzaniga, J. E. Bogen,
and R. W. Sperry. 1965.
“Observations on Visual
Perception after Disconnexion
of the Cerebral Hemispheres in
Man.” *Brain* 88(2); R. W.
Sperry. 1961. “Cerebral
Organization and Behavior:
The Split Brain Behaves in
Many Respects Like Two
Separate Brains, Providing
New Research Possibilities.”
*Science* 133(3466); R. W.
Sperry. 1968. “Hemisphere
Deconnection and Unity in
Conscious Awareness.” *Am
Psychol* 23(10); R. W. Sperry,
E. Zaidel, and D. Zaidel. 1979.
“Self Recognition and Social
Awareness in the Deconnected
Minor Hemisphere.”
*Neuropsychologia* 17(2).
33. ↑ R. Sperry. 1982. “Some Effects
of Disconnecting the Cerebral
Hemispheres. Nobel Lecture, 8
December 1981.” *Biosci Rep*
2(5).
34. ↑ R. E. Myers and R. W. Sperry.
1958. “Interhemispheric
Communication through the
Corpus Callosum: Mnemonic
Carry-over between the
Hemispheres.” *AMA Arch
Neurol Psychiatry* 80(3);
Sperry, “Cerebral Organization
and Behavior.”
35. ↑ M. S. Gazzaniga, J. E. Bogen,
and R. W. Sperry. 1962. “Some
Functional Effects of
Sectioning the Cerebral
Commissures in Man.” *Proc
Natl Acad Sci USA* 48.
36. ↑  Zaidel et al., “The Callosal
Syndromes”; Zaidel, Zaidel,
and Bogen, “The Split Brain.”
37. ↑ K. R. Popper and J. C. Eccles.
[1977] 1993. *The Self and Its Brain*. London: Routledge.
38. ↑ See C. E. Marks. 1980.
*Commissurotomy, Consciousness, and the Unity
of Mind*. Montgomery, VT:
Bradford Books; J. E. Bogen.
1997. “Does Cognition in the
Disconnected Right
Hemisphere Require Right
Hemisphere Possession of
Language?” *Brain Lang* 57(1).
39. ↑ T. Nørretranders. 1998. *The
User Illusion: Cutting
Consciousness Down to Size*.
New York: Viking.
40. ↑ V. Mark. 1996. “Conflicting
Communicative Behavior in a
Split-Brain Patient: Support for
Dual Consciousness.” In
*Toward a Science of
Consciousness: The First
Tucson Discussions and
Debates*, ed. S. Hameroff, A.
W. Kaszniak, and A. C. Scott.
Cambridge, MA: MIT Press.
41. ↑ Sperry, “Some Effects of
Disconnecting the Cerebral
Hemispheres.”
42. ↑ J. J. Schmitt, W. Hartje, and K.
Willmes. 1997. “Hemispheric
Asymmetry in the Recognition
of Emotional Attitude
Conveyed by Facial
Expression, Prosody and
Propositional Speech.” *Cortex*
33(1).
43. ↑ J. Blair, D. R. Mitchell, and K.
Blair. 2005. *The Psychopath:
Emotion and the Brain*.
Malden, MA: Blackwell.
44. ↑ Most of the studies involved
have relied on the Wada test, in
which sodium amobarbital is
injected into the left or right
carotid artery, temporarily
anesthetizing the hemisphere
on the same side. Researchers
have found that anesthesia of
the left hemisphere is often
associated with depression,
whereas anesthesia of the right
can lead to euphoria. The
literature on stroke has tended
to support this lateralization of
mood, correlating left-
hemisphere strokes with
depression, but some studies
have put this interpretation in
question. See A. J. Carson et al.
2000. “Depression after Stroke
and Lesion Location: A
Systematic Review.” *Lancet*
356(9224); D. W. Desmond et
al. 2003. “Ischemic Stroke and
Depression.” *J Int
Neuropsychol Soc* 9(3).

Research on normal brains
has shown that negative
emotions such as disgust,
anxiety, and sadness tend to be
associated with right-
hemisphere activity, whereas
happiness is associated with
activity on the left. However, it
might be better to think about
these emotional asymmetries in
terms of “approach” and
“withdrawal,” because anger, a
classically negative emotion, is
also correlated with activity in
the left hemisphere. (E.
Harmon-Jones, P. A. Gable,
and C. K. Peterson. 2010. “The
Role of Asymmetric Frontal
Cortical Activity in Emotion-
Related Phenomena: A Review
and Update.” *Biol Psychol*
84[3]: 451–62.)

The lateralized presentation
of films suggests that the right
hemisphere is more responsive
to their emotional content,
particularly if it is negative.
(W. Wittling and R.
Roschmann. 1993. “Emotion-
Related Hemisphere
Asymmetry: Subjective
Emotional Responses to
Laterally Presented Films.”
Cortex 29[3].) It is also faster
than the left to recognize the
emotional charge of individual
words (*stupid*, *beautiful*), and
in people suffering from
depression, it shows a
performance bias for negative
words. (R. A. Atchley, S. S.
Ilardi, and A. Enloe. 2003.
“Hemispheric Asymmetry in
the Processing of Emotional
Content in Word Meanings:
The Effect of Current and Past
Depression.” *Brain Lang*
84[1].) The fact that primates
lack direct connections
between the right and left
amygdalae (regions in the
temporal lobes that are
especially sensitive to
emotionally significant events)
suggests an anatomical basis
for lateral differences in mood.
(R. W. Doty. 1998. “The Five
Mysteries of the Mind, and
Their Consequences.”
*Neuropsychologia* 36[10].) The
role of the amygdala in our
emotional lives, particularly
with respect to fear, is very
well established. (Joseph E.
LeDoux. 2002. *Synaptic Self:
How Our Brains Become Who
We Are*. New York: Viking.)
45. ↑ Popper and Eccles, *The Self
and Its Brain*.
46. ↑ Zaidel, Zaidel, and Bogen,
“The Split Brain.”
47. ↑ Myers and Sperry,
“Interhemispheric Communication through the Corpus Callosum.”
48. ↑  Bogen, “On the Relationship of Cerebral Duality to Creativity.”
49. ↑ R. Puccetti. 1981. “The Case
for Mental Duality: Evidence
from Split-Brain Data and
Other Considerations.”
*Behavioral and Brain Sciences*
4: 93–123.
50. ↑ W. James. 1950 [1890]. *The Principles of Psychology* (Vol. I). Dover Publications, p. 251.
51. ↑ However, as Dennett points
out, it can be difficult (or
impossible) to distinguish what
was experienced and then
forgotten from what was never
experienced in the first place.
See his insightful discussion of
Orwellian versus Stalinesque
processes in cognition: D. C.
Dennett. 1991. *Consciousness
Explained*. Boston: Little,
Brown, pp. 116–25. This
ambiguity is largely
attributable to the fact that the
contents of consciousness must
be integrated over time—
around 100–200ms. (Crick and
Koch, “A Framework for
Consciousness.”) This period
of integration allows the
sensation of touching an object
and the associated visual
perception of doing so—which
objectively arrive at the cortex
at different times—to be
experienced as though they
were simultaneous.
Consciousness, therefore, is
dependent upon what is
generally known as “working
memory.”
Many researchers have
drawn this connection: J. M.
Fuster. 2003. *Cortex and Mind:
Unifying Cognition*. Oxford:
Oxford University Press; P.
Thagard and B. Aubie. 2008.
“Emotional Consciousness: A
Neural Model of How
Cognitive Appraisal and
Somatic Perception Interact to
Produce Qualitative
Experience.” *Conscious Cogn*
17(3); B. J. Baars and S.
Franklin. 2003. “How
Conscious Experience and
Working Memory Interact.”
*Trends Cogn Sci* 7(4). And the
principle is somewhat more
loosely captured by Edelman’s
notion of consciousness as “the
remembered present”: G. M.
Edelman. 1989. *The Remembered Present: A Biological Theory of Consciousness*. New York:
Basic Books.
52. ↑ L. Naccache and S. Dehaene.
2001. “Unconscious Semantic
Priming Extends to Novel
Unseen Stimuli.” *Cognition*
80(3). Though several studies
indicate that the priming
stimulus must at least be
attended to: M. Finkbeiner and
K. I. Forster. 2008. “Attention,
Intention and Domain-Specific
Processing.” *Trends Cogn Sci* 12(2).
53. ↑ M. Pessiglione et al. 2007.
“How the Brain Translates
Money into Force: A
Neuroimaging Study of
Subliminal Motivation.”
*Science* 316(5826).
54. ↑ P. J. Whalen et al. 1998.
“Masked Presentations of
Emotional Facial Expressions
Modulate Amygdala Activity
without Explicit Knowledge.” *J
Neurosci* 18(1); L. Naccache et
al. 2005. “A Direct Intracranial
Record of Emotions Evoked by
Subliminal Words.” *Proc Natl
Acad Sci USA* 102(21).
55. ↑ D. L. Schacter. 1987. “Implicit
Expressions of Memory in
Organic Amnesia: Learning of
New Facts and Associations.”
*Hum Neurobiol* 6(2).
56. ↑ L. R. Squire and R. McKee.
1992. “Influence of Prior
Events on Cognitive Judgments
in Amnesia.” *J Exp Psychol
Learn Mem Cogn* 18(1).
57. ↑ M. M. Keane et al. 1997.
“Intact and Impaired
Conceptual Memory Processes
in Amnesia.” *Neuropsychology*
11(1).
58. ↑ Other phenomena distinguish
consciousness from our
unconscious mental lives. For
instance, certain people suffer a
condition called “blindsight,”
which results from damage to
their primary visual cortex. As
a matter of conscious
experience, they are blind (or
blind within a region of their
visual field), and yet they can
accurately describe the visual
properties of objects. They
experience this as purely a
matter of guessing—after all,
they have no experience of
seeing—but they manage to
“guess” with near perfect
accuracy. They are seeing
without knowing that they are
seeing. (L. Weiskrantz. 1996.
“Blindsight Revisited.” *Curr
Opin Neurobiol* 6[2]; L.
Weiskrantz. 2002. “Prime-
Sight and Blindsight.”
*Conscious Cogn* 11[4]; L.
Weiskrantz. 2008. “Is
Blindsight Just Degraded
Normal Vision?” *Exp Brain
Res* 192[3].)
59. ↑ S. Harris. 2004. The End of
Faith, New York: Norton, pp.
173–75, 275–77; S. Harris.
2010. *The Moral Landscape*.
New York: Free Press.