Friday, February 02, 2007

 

The Mystery of Consciousness







The young women had survived the car crash, after a fashion. In
the five months since parts of her brain had been crushed, she could
open her eyes but didn't respond to sights, sounds or jabs. In the
jargon of neurology, she was judged to be in a persistent vegetative
state. In crueler everyday language, she was a vegetable.

So
picture the astonishment of British and Belgian scientists as they
scanned her brain using a kind of MRI that detects blood flow to active
parts of the brain. When they recited sentences, the parts involved in
language lit up. When they asked her to imagine visiting the rooms of
her house, the parts involved in navigating space and recognizing
places ramped up. And when they asked her to imagine playing tennis,
the regions that trigger motion joined in. Indeed, her scans were
barely different from those of healthy volunteers. The woman, it
appears, had glimmerings of consciousness.

Try to comprehend
what it is like to be that woman. Do you appreciate the words and
caresses of your distraught family while racked with frustration at
your inability to reassure them that they are getting through? Or do
you drift in a haze, springing to life with a concrete thought when a
voice prods you, only to slip back into blankness? If we could
experience this existence, would we prefer it to death? And if these
questions have answers, would they change our policies toward
unresponsive patients--making the Terri Schiavo case look like child's
play?

The report of this unusual case last September was just
the latest shock from a bracing new field, the science of
consciousness. Questions once confined to theological speculations and
late-night dorm-room bull sessions are now at the forefront of
cognitive neuroscience. With some problems, a modicum of consensus has
taken shape. With others, the puzzlement is so deep that they may never
be resolved. Some of our deepest convictions about what it means to be
human have been shaken.

It shouldn't be surprising that research
on consciousness is alternately exhilarating and disturbing. No other
topic is like it. As René Descartes noted, our own consciousness is the
most indubitable thing there is. The major religions locate it in a
soul that survives the body's death to receive its just deserts or to
meld into a global mind. For each of us, consciousness is life itself,
the reason Woody Allen said, "I don't want to achieve immortality
through my work. I want to achieve it by not dying." And the conviction
that other people can suffer and flourish as each of us does is the
essence of empathy and the foundation of morality.

To make
scientific headway in a topic as tangled as consciousness, it helps to
clear away some red herrings. Consciousness surely does not depend on
language. Babies, many animals and patients robbed of speech by brain
damage are not insensate robots; they have reactions like ours that
indicate that someone's home. Nor can consciousness be equated with
self-awareness. At times we have all lost ourselves in music, exercise
or sensual pleasure, but that is different from being knocked out cold.

THE "EASY" AND "HARD" PROBLEMS

WHAT
REMAINS IS NOT ONE PROBLEM ABOUT CONSCIOUSNESS BUT two, which the
philosopher David Chalmers has dubbed the Easy Problem and the Hard
Problem. Calling the first one easy is an in-joke: it is easy in the
sense that curing cancer or sending someone to Mars is easy. That is,
scientists more or less know what to look for, and with enough
brainpower and funding, they would probably crack it in this century.

What
exactly is the Easy Problem? It's the one that Freud made famous, the
difference between conscious and unconscious thoughts. Some kinds of
information in the brain--such as the surfaces in front of you, your
daydreams, your plans for the day, your pleasures and peeves--are
conscious. You can ponder them, discuss them and let them guide your
behavior. Other kinds, like the control of your heart rate, the rules
that order the words as you speak and the sequence of muscle
contractions that allow you to hold a pencil, are unconscious. They
must be in the brain somewhere because you couldn't walk and talk and
see without them, but they are sealed off from your planning and
reasoning circuits, and you can't say a thing about them.

The
Easy Problem, then, is to distinguish conscious from unconscious mental
computation, identify its correlates in the brain and explain why it
evolved.

The Hard Problem, on the other hand, is why it feels
like something to have a conscious process going on in one's head--why
there is first-person, subjective experience. Not only does a green
thing look different from a red thing, remind us of other green things
and inspire us to say, "That's green" (the Easy Problem), but it also
actually looks green: it produces an experience of sheer greenness that
isn't reducible to anything else. As Louis Armstrong said in response
to a request to define jazz, "When you got to ask what it is, you never
get to know."

The Hard Problem is explaining how subjective
experience arises from neural computation. The problem is hard because
no one knows what a solution might look like or even whether it is a
genuine scientific problem in the first place. And not surprisingly,
everyone agrees that the hard problem (if it is a problem) remains a
mystery.

Although neither problem has been solved,
neuroscientists agree on many features of both of them, and the feature
they find least controversial is the one that many people outside the
field find the most shocking. Francis Crick called it "the astonishing
hypothesis"--the idea that our thoughts, sensations, joys and aches
consist entirely of physiological activity in the tissues of the brain.
Consciousness does not reside in an ethereal soul that uses the brain
like a PDA; consciousness is the activity of the brain.

THE BRAIN AS MACHINE

SCIENTISTS
HAVE EXORCISED THE GHOST FROM THE MACHINE NOT because they are
mechanistic killjoys but because they have amassed evidence that every
aspect of consciousness can be tied to the brain. Using functional MRI,
cognitive neuroscientists can almost read people's thoughts from the
blood flow in their brains. They can tell, for instance, whether a
person is thinking about a face or a place or whether a picture the
person is looking at is of a bottle or a shoe.

And
consciousness can be pushed around by physical manipulations.
Electrical stimulation of the brain during surgery can cause a person
to have hallucinations that are indistinguishable from reality, such as
a song playing in the room or a childhood birthday party. Chemicals
that affect the brain, from caffeine and alcohol to Prozac and LSD, can
profoundly alter how people think, feel and see. Surgery that severs
the corpus callosum, separating the two hemispheres (a treatment for
epilepsy), spawns two consciousnesses within the same skull, as if the
soul could be cleaved in two with a knife.

And when the
physiological activity of the brain ceases, as far as anyone can tell
the person's consciousness goes out of existence. Attempts to contact
the souls of the dead (a pursuit of serious scientists a century ago)
turned up only cheap magic tricks, and near death experiences are not
the eyewitness reports of a soul parting company from the body but
symptoms of oxygen starvation in the eyes and brain. In September, a
team of Swiss neuroscientists reported that they could turn out-of-body
experiences on and off by stimulating the part of the brain in which
vision and bodily sensations converge.

THE ILLUSION OF CONTROL

ANOTHER
STARTLING CONCLUSION FROM the science of consciousness is that the
intuitive feeling we have that there's an executive "I" that sits in a
control room of our brain, scanning the screens of the senses and
pushing the buttons of the muscles, is an illusion. Consciousness turns
out to consist of a maelstrom of events distributed across the brain.
These events compete for attention, and as one process outshouts the
others, the brain rationalizes the outcome after the fact and concocts
the impression that a single self was in charge all along.

Take
the famous cognitive-dissonance experiments. When an experimenter got
people to endure electric shocks in a sham experiment on learning,
those who were given a good rationale ("It will help scientists
understand learning") rated the shocks as more painful than the ones
given a feeble rationale ("We're curious.") Presumably, it's because
the second group would have felt foolish to have suffered for no good
reason. Yet when these people were asked why they agreed to be shocked,
they offered bogus reasons of their own in all sincerity, like "I used
to mess around with radios and got used to electric shocks."

It's
not only decisions in sketchy circumstances that get rationalized but
also the texture of our immediate experience. We all feel we are
conscious of a rich and detailed world in front of our eyes. Yet
outside the dead center of our gaze, vision is amazingly coarse. Just
try holding your hand a few inches from your line of sight and counting
your fingers. And if someone removed and reinserted an object every
time you blinked (which experimenters can simulate by flashing two
pictures in rapid sequence), you would be hard pressed to notice the
change. Ordinarily, our eyes flit from place to place, alighting on
whichever object needs our attention on a need-to-know basis. This
fools us into thinking that wall-to-wall detail was there all along--an
example of how we overestimate the scope and power of our own
consciousness.

Our authorship of voluntary
actions can also be an illusion, the result of noticing a correlation
between what we decide and how our bodies move. The psychologist Dan
Wegner studied the party game in which a subject is seated in front of
a mirror while someone behind him extends his arms under the subject's
armpits and moves his arms around, making it look as if the subject is
moving his own arms. If the subject hears a tape telling the person
behind him how to move (wave, touch the subject's nose and so on), he
feels as if he is actually in command of the arms.

The brain's
spin doctoring is displayed even more dramatically in neurological
conditions in which the healthy parts of the brain explain away the
foibles of the damaged parts (which are invisible to the self because
they are part of the self). A patient who fails to experience a
visceral click of recognition when he sees his wife but who
acknowledges that she looks and acts just like her deduces that she is
an amazingly well-trained impostor. A patient who believes he is at
home and is shown the hospital elevator says without missing a beat,
"You wouldn't believe what it cost us to have that installed."

Why
does consciousness exist at all, at least in the Easy Problem sense in
which some kinds of information are accessible and others hidden? One
reason is information overload. Just as a person can be overwhelmed
today by the gusher of data coming in from electronic media, decision
circuits inside the brain would be swamped if every curlicue and muscle
twitch that was registered somewhere in the brain were constantly being
delivered to them. Instead, our working memory and spotlight of
attention receive executive summaries of the events and states that are
most relevant to updating an understanding of the world and figuring
out what to do next. The cognitive psychologist Bernard Baars likens
consciousness to a global blackboard on which brain processes post
their results and monitor the results of the others.

BELIEVING OUR OWN LIES

A
SECOND REASON THAT INFORMATION MAY BE SEALED OFF FROM consciousness is
strategic. Evolutionary biologist Robert Trivers has noted that people
have a motive to sell themselves as beneficent, rational, competent
agents. The best propagandist is the one who believes his own lies,
ensuring that he can't leak his deceit through nervous twitches or
self-contradictions. So the brain might have been shaped to keep
compromising data away from the conscious processes that govern our
interaction with other people. At the same time, it keeps the data
around in unconscious processes to prevent the person from getting too
far out of touch with reality.

What about the brain itself? You
might wonder how scientists could even begin to find the seat of
awareness in the cacophony of a hundred billion jabbering neurons. The
trick is to see what parts of the brain change when a person's
consciousness flips from one experience to another. In one technique,
called binocular rivalry, vertical stripes are presented to the left
eye, horizontal stripes to the right. The eyes compete for
consciousness, and the person sees vertical stripes for a few seconds,
then horizontal stripes, and so on.

A low-tech
way to experience the effect yourself is to look through a paper tube
at a white wall with your right eye and hold your left hand in front of
your left eye. After a few seconds, a white hole in your hand should
appear, then disappear, then reappear.

Monkeys experience
binocular rivalry. They can learn to press a button every time their
perception flips, while their brains are impaled with electrodes that
record any change in activity. Neuroscientist Nikos Logothetis found
that the earliest way stations for visual input in the back of the
brain barely budged as the monkeys' consciousness flipped from one
state to another. Instead, it was a region that sits further down the
information stream and that registers coherent shapes and objects that
tracks the monkeys' awareness. Now this doesn't mean that this place on
the underside of the brain is the TV screen of consciousness. What it
means, according to a theory by Crick and his collaborator Christof
Koch, is that consciousness resides only in the "higher" parts of the
brain that are connected to circuits for emotion and decision making,
just what one would expect from the blackboard metaphor.

WAVES OF BRAIN

CONSCIOUSNESS
IN THE BRAIN CAN BE TRACKED NOT JUST IN SPACE but also in time.
Neuroscientists have long known that consciousness depends on certain
frequencies of oscillation in the electroencephalograph (EEG). These
brain waves consist of loops of activation between the cortex (the
wrinkled surface of the brain) and the thalamus (the cluster of hubs at
the center that serve as input-output relay stations). Large, slow,
regular waves signal a coma, anesthesia or a dreamless sleep; smaller,
faster, spikier ones correspond to being awake and alert. These waves
are not like the useless hum from a noisy appliance but may allow
consciousness to do its job in the brain. They may bind the activity in
far-flung regions (one for color, another for shape, a third for
motion) into a coherent conscious experience, a bit like radio
transmitters and receivers tuned to the same frequency. Sure enough,
when two patterns compete for awareness in a binocular-rivalry display,
the neurons representing the eye that is "winning" the competition
oscillate in synchrony, while the ones representing the eye that is
suppressed fall out of synch.

So neuroscientists are well on the
way to identifying the neural correlates of consciousness, a part of
the Easy Problem. But what about explaining how these events actually
cause consciousness in the sense of inner experience--the Hard Problem?

TACKLING THE HARD PROBLEM

TO
APPRECIATE THE HARDNESS OF THE HARD PROBLEM, CONSIDER how you could
ever know whether you see colors the same way that I do. Sure, you and
I both call grass green, but perhaps you see grass as having the color
that I would describe, if I were in your shoes, as purple. Or ponder
whether there could be a true zombie--a being who acts just like you or
me but in whom there is no self actually feeling anything. This was the
crux of a Star Trek plot in which officials wanted to reverse-engineer
Lieut. Commander Data, and a furious debate erupted as to whether this
was merely dismantling a machine or snuffing out a sentient life.

No
one knows what to do with the Hard Problem. Some people may see it as
an opening to sneak the soul back in, but this just relabels the
mystery of "consciousness" as the mystery of "the soul"--a word game
that provides no insight.

Many philosophers, like Daniel
Dennett, deny that the Hard Problem exists at all. Speculating about
zombies and inverted colors is a waste of time, they say, because
nothing could ever settle the issue one way or another. Anything you
could do to understand consciousness--like finding out what wavelengths
make people see green or how similar they say it is to blue, or what
emotions they associate with it--boils down to information processing
in the brain and thus gets sucked back into the Easy Problem, leaving
nothing else to explain. Most people react to this argument with
incredulity because it seems to deny the ultimate undeniable fact: our
own experience.

The most popular attitude to the Hard Problem
among neuroscientists is that it remains unsolved for now but will
eventually succumb to research that chips away at the Easy Problem.
Others are skeptical about this cheery optimism because none of the
inroads into the Easy Problem brings a solution to the Hard Problem
even a bit closer. Identifying awareness with brain physiology, they
say, is a kind of "meat chauvinism" that would dogmatically deny
consciousness to Lieut. Commander Data just because he doesn't have the
soft tissue of a human brain. Identifying it with information
processing would go too far in the other direction and grant a simple
consciousness to thermostats and calculators--a leap that most people
find hard to stomach. Some mavericks, like the mathematician Roger
Penrose, suggest the answer might someday be found in quantum
mechanics. But to my ear, this amounts to the feeling that quantum
mechanics sure is weird, and consciousness sure is weird, so maybe
quantum mechanics can explain consciousness.

And then there is
the theory put forward by philosopher Colin McGinn that our vertigo
when pondering the Hard Problem is itself a quirk of our brains. The
brain is a product of evolution, and just as animal brains have their
limitations, we have ours. Our brains can't hold a hundred numbers in
memory, can't visualize seven-dimensional space and perhaps can't
intuitively grasp why neural information processing observed from the
outside should give rise to subjective experience on the inside. This
is where I place my bet, though I admit that the theory could be
demolished when an unborn genius--a Darwin or Einstein of
consciousness--comes up with a flabbergasting new idea that suddenly
makes it all clear to us.

Whatever the solutions to the Easy and
Hard problems turn out to be, few scientists doubt that they will
locate consciousness in the activity of the brain. For many
nonscientists, this is a terrifying prospect. Not only does it strangle
the hope that we might survive the death of our bodies, but it also
seems to undermine the notion that we are free agents responsible for
our choices--not just in this lifetime but also in a life to come. In
his millennial essay "Sorry, but Your Soul Just Died," Tom Wolfe
worried that when science has killed the soul, "the lurid carnival that
will ensue may make the phrase 'the total eclipse of all values' seem
tame."

TOWARD A NEW MORALITY

MY OWN VIEW
IS THAT THIS IS backward: the biology of consciousness offers a sounder
basis for morality than the unprovable dogma of an immortal soul. It's
not just that an understanding of the physiology of consciousness will
reduce human suffering through new treatments for pain and depression.
That understanding can also force us to recognize the interests of
other beings--the core of morality.

As every student in
Philosophy 101 learns, nothing can force me to believe that anyone
except me is conscious. This power to deny that other people have
feelings is not just an academic exercise but an all-too-common vice,
as we see in the long history of human cruelty. Yet once we realize
that our own consciousness is a product of our brains and that other
people have brains like ours, a denial of other people's sentience
becomes ludicrous. "Hath not a Jew eyes?" asked Shylock. Today the
question is more pointed: Hath not a Jew--or an Arab, or an African, or
a baby, or a dog--a cerebral cortex and a thalamus? The undeniable fact
that we are all made of the same neural flesh makes it impossible to
deny our common capacity to suffer.

And when you think about it,
the doctrine of a life-to-come is not such an uplifting idea after all
because it necessarily devalues life on earth. Just remember the most
famous people in recent memory who acted in expectation of a reward in
the hereafter: the conspirators who hijacked the airliners on 9/11.

Think,
too, about why we sometimes remind ourselves that "life is short." It
is an impetus to extend a gesture of affection to a loved one, to bury
the hatchet in a pointless dispute, to use time productively rather
than squander it. I would argue that nothing gives life more purpose
than the realization that every moment of consciousness is a precious
and fragile gift.

Steven Pinker is Johnstone Professor of
Psychology at Harvard and the author of The Language Instinct, How the
Mind Works and The Blank Slate





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