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Friday, Jan. 19, 2007

The Mystery of Consciousness

By Steven Pinker

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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