Zombies Dolphins and Blindsight
|
Is consciousness the
hardest of hard problems? Is it all down to bits of wiring in the brain
or quantum mechanics? And do animals know more than we think?
Alun Anderson, Bob Holmes and Liz Else.
What's the definition of a scientist? Someone who looks for
a black cat in a dark room. And a philosopher? Someone who looks for a black
cat in a dark room where there is no black cat.
By sheer coincidence, this drollery appeared in the horoscope section of
the Tucson Weekly newspaper just as 800 scientists and philosophers
gathered for the second biennial Tucson conference, "Towards a Science of
Consciousness". The cat the scientists are looking for is an explanation
of how processes in the brain create conscious awareness. They haven't captured
their cat yet but occasional sightings make them believe they will one day.
[I wonder if this elusive cat is the younger cousin of the elusive
lion in physics? -LB]
Whether the cat the philosophers are after-the so-called "hard
problem" of consciousness exists at all is much more in doubt. If it does,
the scientists are in deep trouble. Salvos between them and the believers
in the hard problem dominated the opening day and reverberated throughout
the conference. Whoever is right, one thing is certain - consciousness remains
the first and last of the great human mysteries.
So what kind of problem is it? The philosophers of the hard
school think that consciousness is in a league of its own. Consciousness,
they argue, has absolutely unique properties: it is private, subjective,
peculiar to the individual, and cannot be directly observed by a third person.
As David Chalmers of the University of California, Santa Cruz, and the hardest
of the hard school of philosophers, summed it up after the last Tucson
conference: "When we see, we experience visual sensations-the felt quality
of redness, the experience of dark and light, the quality of depth in a visual
field. Other experiences go along with
perception
in different modalities-the sound of a clarinet, the smell of mothballs...
Then there are bodily sensations from pains to orgasms - mental images that
are conjured up internally, the felt quality of emotion, and the experience
of a stream of conscious thought. What unites all of these states is that
there is something it is to be to be in them. All of them are states of
experience."
The hard school believes that understanding how the brain works
does not automatically mean we will understand consciousness. They accept
that we will be able, for example, to trace the visual processes that help
us to discriminate colour, starting with cells in the retina that respond
to different wavelengths of light. But really explaining consciousness,
explaining why these neural processes should be accompanied by a feeling
of "what it is like to be me", is a completely different kind of problem,
says Chalmers.
Indeed, he has suggested that consciousness might turn out to be an irreducible
property, in the same category as time and space, and understanding it may
force us to rewrite everything we know abut the Universe. Others think that
consciousness can be explained only by turning to a field such as
quantum mechanics, where normal laws of causality
seem not to hold.
This is all nonsense for those on the other side. At Tucson,
Daniel Dennett, from Tufts University, author of Consciousness Explained
was first to attack. Facing an audience mostly sympathetic to the hard problem
stance, Dennett said he felt like "a cop at Woodstock". But this didn't stop
him from absolutely dismissing the hard problem.
For Dennett, there is no mysterious process required for the brain's
information processing capabilities to become "conscious": the brain is a
kind of hypothesis-making machine, constantly throwing up new "drafts" of
what is going on in the world.
"Mental states," explains Dennett, "do not become conscious
by entering some special chamber in the brain, nor by being transduced into
some privileged and mysterious medium but by winning the competition against
other mental states for domination in the control of behaviour." Those who
think that brain processes cannot explain our first-person experience of
consciousness have the question all wrong, according to Dennett. "It presupposes
that what you are is something else-in addition to all of this brain-body
activity. But what you are, however just is the organisation of all this
competitive activity between this host of competencies which your body has
developed. You automatically know about these things going on inside your
body because if you didn't, it wouldn't be your body."
Later in the week, Patricia Churchland from the Institute
for Neural Computation at La Jolla, California, weighed in with Dennett.
Setting conscious experience on a pedestal as the hard problem may be
counterproductive, she said.
"It suggests that we can already see that the hard problem is going to have
to have a real humdinger of a solution-that it's going to have to be really
radical, that it's going to have to come from somewhere really neat like
quantum mechanics, that it can't just be a matter of a complex, dynamical
system doing its thing. Well, I can't actually see that," concluded Churchland.
'Mental states become conscious by winning the competition against other mental states...'
Language gives us our clearest view into the consciousness
of other people through our myriad social dealings.
Some researchers have tried to peek through the same window into the minds
of other species, and many have come away with the distinct feeling that
these other animals may also be conscious. This viewpoint used to attract
scorn, but recently the evidence has become
much stronger that humans are not alone in using language and in forming
abstract concepts.
"The mind of the ape cannot be that much different from our
own," says Sue
Savage- Rumbaugh from Georgia State University, who is one of the most
passionate believers that apes, at least, have a well-developed consciousness.
The first attempts to teach an ape to "speak"-in sign language, since apes
lack the vocal apparatus to speak aloud-proved disappointing, she admits.
A female chimp named Washoe was never good enough
at communicating to convince sceptics that she was actively using language.
But Washoe was only taught to speak, not to listen-a crucial
omission, says Savage- Rumbaugh. She taught a pair of chimps called Sherman
and Austin together and their language abilities burgeoned as they learnt
to listen to one another and used language to cooperate to their mutual
benefit.
More recently, Savage-Rumbaugh reared a pair of bonobos, or pygmy chimpanzees,
in the company of humans who spoke English to them and pointed to symbols
on a board. While the bonobos, Kanzi,and Panbanisha, never received any explicit
training in language, they picked it up anyway.
"These conditions are all that is needed for apes to acquire
understanding of language at least equal to a three-year-old child," says
Savage-Rumbaugh. For example, the bonobos can respond correctly, even on
first hearing, to new sentences such as "Can you find the pine needles in
the refrigerator?"
Kanzi and Panbanisha clearly understand even more complex concepts, says
Savage- Rumbaugh, for example, Panbanisha watched as a human secretly substituted
a bug for some sweets in a box. When a second human tried to open the box,
the first human asked the bonobo "What is she looking for?" Panbanisha replied
that the human was looking for the sweets. "To answer a question as sophisticated
as this, Panbanisha needs a concept of what thinking is, and that other people's
thinking is different from her own, says Savage-Rumbaugh.
[Psychological experiments with children show that they don't have a concept
of what is in the mind of someone else until about the age of three.These
animals then, are out-thinking a three year old human -LB]
Even more strikingly, Panbanisha added that the first person
was being "bad" to play such a trick-the same comment that the researcher's
four-year-old daughter made.
[Oddly showing moral judgement,this may come as a surprise to those that
do not credit animals with intelligence -LB]
Wild bonobos that have never been exposed to human language may also use
language of a sort to communicate with one another. Bonobos hang out in the
treetops in large groups of between 60 and 100 individuals, but when they
move from roost to roost they travel across the ground in smaller groups.
On a recent trip to Zaire, Savage-Rumbaugh noticed that bonobos
had carefully broken off plants of the same species just before and after
two trails crossed,apparently as a way of marking which fork to take for
the groups following them. Intrigued, she began to search the forest for
more markings. She found 96 places where plants had clearly been broken off
by bonobos. All but a handful served as some sort of trail-marking.
Apes undoubtedly show the clearest evidence of conscious thought among nonhuman
animals. Similar intelligence might be much harder to recognise in, say,
dolphins, simply because they are so different
from us. Humans and some apes use their hands to fashion tools, a sign of
intelligence. "How do we look for intelligence in a non-handed animal?" asks
Diana Reiss of Rutgers University in New Jersey.
On land, humans know that trail-marking is clever, but what
takes its place in the ocean? Humans can talk to apes, and the apes can sign
back, but how could we communicate with a dolphin?
Despite these difficulties, Reiss sees clear glimpses of an active intelligence.
"I often walk away thinking there's somebody in there - or maybe I should
say, there's some mind in there," says Reiss.
For example, the dolphins she studies at Marine World Africa in Vallejo,
California, blow bubble rings, just as humans blow smoke rings from cigarettes,
and then play with the rings as they rise to the surface.
She has even seen them drop various items, such as bits of
fish or seaweed, into the centre of a bubble ring and watch how the turbulence
buffets them. "It looks like intelligent, goal-directed behaviour," she says.
"I felt like I was watching a bunch of scientists testing contingencies."
If researchers have a hard time measuring intelligence in a dolphin, they
find it still harder to crawl inside the brain of a
bird. Yet here, too, at least one researcher sees
glimmerings of what may be consciousness. For twenty years,
Irene Pepperberg
of the University of Arizona has studied the mental capacities of a grey
parrot called Alex , who listens to questions in English and responds aloud
with English words.
| ** BLOG - SCIAM OBSERVATIONS ** An interview with Alex, the African grey parrot |
| As you may have heard, Alex, the celebrated African Grey
parrot, died recently. In 1996, former Scientific American editor Madhusree
Mukerjee paid Alex a visit at Pepperberg's lab, then at the University of
Arizona. [Scientific American 2007] |
'I often walk away thinking there's somebody in there' or maybe I should say, there's some mind in there'
"Alex
is no Einstein. We think he's an average parrot," says
Pepperberg.
Nevertheless, Alex can count objects up to six, recognise shapes and colours,
and perform simple comparisons such as same/different and larger/smaller.
Alex can also ask for objects, and he will correct his trainer if she
gives the wrong response. If Alex says "wanna grape", for example, and
is given a piece of banana instead, about three times out of four he will
say "no", then repeat his request. Pepperberg won't go so far as to claim
that this behaviour shows that Alex can consciously compare his expectations
to reality, but she does believe that "there's certainly a 'there' there".
What kind of a "there" might it be? It's tempting to see
consciousness as an all or nothing phenomenon but that's a mistake. A parrot
may be conscious of what is going on around it but, to paraphrase Dennett,
it probably can't wonder whether it's Friday and even whether it's a parrot.
If anyone can be considered the grandfather of the hard problem school of
consciousness it is Rene Descartes, born 400 years ago this year. His meditations
on the unique unity of consciousness, which convinced him that "mind" and
"body" were separate, were quoted at length at Tucson by Michael Lockwood,
from Green College, Oxford.
"When I consider the mind," wrote Descartes, "that is myself
in so far as am merely a conscious being. I can distinguish no part within
myself. I understand myself to be a single and complete thing. Nor can the
faculties of feeling, will, understanding and so on be called its parts,
for it is one and the same mind that wills, feels and understands."
Descartes may have thought his consciousness was a unity,
but neurologists today would not agree. There is, they say, no more graphic
evidence of the way consciousness is "assembled" from different neuronal
processes than the bizarre way that brain injuries can tear them apart.
Perhaps most startling of all is "blindsight",which
violates our common-sense view of consciousness. Here, damage to areas of
the primary visual cortex removes all sensation of light or colour from
corresponding areas of the visual field. Patients with this damage appear
totally blind in one part of the visual field. If asked whether they can
see an object in this area, the answer obviously enough, is no.
But, astonishingly, if the patients are forced to guess where
this object they cannot see is located, they often point at it quite accurately.
Although they have lost all conscious sensation of "seeing", at some level
they are still able to see. "Consciousness" and the brain's information
processing thus appear split.
What can it be like to have blindsight? Most patients simply say they are
totally blind and cannot understand why experimenters ask them to "guess"
where objects are when it is obviously pointless. But Larry Weiskrantz from
the University of Oxford, who coined the term blindsight, has described how
a few can have a mysterious feeling of awareness under the right circumstances.
"It's a sense that I haven't got, if that makes sense," was how one patient
explained it.
Blindsight is possible, the neurologists assume, because the
visual pathway splits into many parallel streams as it approaches the cortex
and some streams go on to different parts of the brain, bypassing the primary
visual cortex. Although these parts of the brain cannot create visual
consciousness, they can provide some unconscious information to guide behaviour.
Blindsight can thus give clues as to which parts of the brain are essential
to generate consciousness.
Damage even higher in the visual system or in the prefrontal cortex - where
the planning of behaviour takes place and links to motor output are made
- creates even more bizarre problems. Lesions may not so much remove
consciousness as strip away some of its attributes.
The conscious vision of patients with damage in the extrastriate
cortex may lack one or more qualities: the patients can "see" but they may
not be able to detect colour or movement. In philosophers' jargon, they have
lost one or more of the "qualia" which populate the conscious sensory
world.
Some damage within the extrastriate cortex may leave the patient able to
sense a full repertoire of qualia but destroy the ability to bind them together
to perceive a whole object. This is called aperceptive agnosia.
"Such patients," says Petra Stoerig from the Institute of
Medical Psychology in Munich, "may have normal visual fields, normal acuity,
normal brightness discrimination, normal colour vision, normal motion processing,
but still they are unable to form an object out of these impressions." If
they are shown a triangle, for example, they can see it but they cannot connect
it with other geometric objects such as a circle or a square. If they try
to make drawings of objects, they can produce only meaningless scribbles.
Defects elsewhere in the extrastriate cortex can rob consciousness
of more of its normal qualities. To recognise, as well as see, an object,
you must be able to create a web of associations around it by naming it and
recalling things about it. These processes are destroyed in patients suffering
from associative agnosia. They can see objects and make drawings of them
perfectly well, but they cannot recognise the objects, nor say what they
do, explains Stoerig.
Even stranger is the world of people suffering from anosognosia.
The condition occasionally occurs after stroke damage to the right side of
the brain which leaves the patient paralysed on the left side of the body.
Despite their obvious paralysis, however, anosognosics claim that their useless
limbs work perfectly well.
"This has got to be the most peculiar thing I've ever seen in all of neurology,"
says Vilayanur Ramachandran [Ref: Iotm11], of the
University of California, San Diego who described his work with such patients
to the conference. "Here is somebody perfectly sane and rational, who watches
her arm not performing and yet claims she is not paralysed."
When Ramachandran asked one patient to touch him on the nose,
for example, she insisted that she was doing so, even though her arm remained
limp at her side. When he asked her to clap, she beat the air with her good
arm but said she was clapping normally.
Another after failing repeatedly to tie her shoe, insisted she had in fact
tied it "with both hands" - a point that normal individuals rarely bother
to mention. This is evidence that deep down, anosognosics may know the
truth.
If this were a purely psychological delusion, it should apply equally to
left and right-side paralysis. But anosognosia shows up almost exclusively
in people with paralysis on the left side. This suggests that there must
be specific neurological damage to the right side of the brain, says
Ramachandran.
Anosognosia is a problem of the mind's belief system,
not its perceptual system, Ramachandran thinks.The mind needs a theory of
the world in order to organise and make sense of the constant stream of sensory
inputs. But the theory - making part of the brain must also be able to ignore
inputs that don't fit with its world view, lest every mistaken perception
shake us to our roots. In Ramachandran's hypothesis, this bull-headed theorist
resides in the left half of the brain.
The right half of the brain, he thinks, acts as devil's advocate. When too
much conflicting data accumulates-for example, repeated awareness that the
left arm cannot move-the devil's advocate overcomes the left brain's defence
mechanisms and forces it to restructure its world view to fit the new
information.
He thinks that in people with anosognosia "that mechanism -
your devil's advocate - is damaged, and the left brain is free to pursue
a strategy of denial and confabulation. There is no limit to the
delusion."
'Their first goal, hard problem or no hard problem, is to find a neural correlate of consciousness'
No longer need one spend time attempting to understand the
far-fetched speculations of physicists, nor endure the tedium of philosophers
perpetually disagreeing with each other. Consciousness is now largely a
scientific problem."
For those who think that neurobiology will provide the answers and the hard
problem is a philosopher's delusion, this fighting talk from Nobel laureate
Francis Crick is just what is needed. His words, taken from an article published
two months earlier in Nature, were quoted
approvingly by the neurobiologists at Tucson. And although Crick was not
at the conference, his long-term collaborator, Christof Koch, of the California
Institute of Technology, was there to lay out the game plan.
Their first goal, hard problem or no hard problem, is to find
a "neural correlate of consciousness"-activities in the brain that correspond
specifically to the workings of conscious awareness.
The search begins by locating areas where changing neural activity can be
specifically linked to changing awareness of phenomena. To find these areas,
neurobiologists are making use of cunning experiments in which stimuli from
the external world hold constant while awareness changes - either spontaneously
or as a result of conscious activity.
 |
Long-established work on illusions provides the most fertile
hunting ground for such effects. When we look at the famous "vase" illusion,
after a little while, we alternately see the vase and two faces. The stimulus
does not change but what we see in mind's eye does.
The most complete experiments of this sort came from Nikos Logothetis of
Baylor College of Medicine at Houston. "Like Crick and Koch, we wondered
if there were any neurons that are specifically related to the act of
perceiving," said Logothetis. His experiments on monkeys used visual illusions
that can be generated by a phenomenon called binocular rivalry.
In Logothetis's first experiments, a set of stripes slanting
one way was shown to one eye and an identical set slanting in the opposite
direction was shown to the other eye. After a short while, the two alternate
irregularly -just like the vase and the two faces-as the incompatible inputs
from the two eyes battle with each other: the stimuli do not change but what
the monkey "sees" does.
Logothetis trained his monkeys to press a bar according to which way the
stripes appeared to be oriented. At the same time, he made electrical recordings
from numerous places at different levels along the visual pathways. The firing
pattern of many cells remained constant whatever the monkey reported seeing-
the neurons were locked into the unchanging stimuli presented to each eye.
But the behaviour of some neurons correlated very closely with the monkey's
awareness. Their firing pattern changed dramatically just before the monkey
switched bars to report that the lines were changing from one orientation
to another.
Many of these neurons were found in an area known as V4, at
the top of the hierarchy of the visual cortex. This location fits well with
the view of consciousness put forward by Crick and Koch. They believe that
you cannot be consciously aware of the information processing that goes on
in the lower parts of the visual system, from the retina up to the primary
visual cortex called V1. Consciousness is related to the high-level, "explicit",
representations generated at the top of the visual cortex.
An explicit representation is seen in cells that respond only to a complex
property of an object, rather than to dots or lines or patches of brightness.
The best known of the "explicit" neurons are those found in the mid-temporal
cortex that respond only to faces seen from a particular angle. Damage to
this area causes prosopagnosia, an inability to recognise familiar faces.
To generate a full conscious experience, Crick and Koch postulate
that cells which code explicitly for a face, for example, must somehow link
up to many other neurons that relate to them-perhaps to the name of the person,
memories involving the person and so on. They must also link to the motor
cortex so that the experience can generate a response.
How all this happens is anyone's guess right now, but we would expect
consciousness to arise in neurons linking the highest parts of the visual
system with the prefrontal cortex which contains the language centres and
areas involved in planning action.
 |
Not everyone wants to see the
"hard problem" solved. Unlike the so-called "easy problems" - explaining
how the brain carries out its various information processing tasks from analysing
the colour of objects to processing a stream of words-solving the hard problem
means understanding phenomenal consciousness. |
| Susan Greenfield
of the University of Oxford [Ref:
Iotm11] described a theory by which the fleeting
recruitment of populations of neurons could be linked to the level of
consciousness. But the theory would not necessarily grasp how it feels to
be a specific individual with a unique, private view of the world. All anyone
would be able to point to, she said, was an increasingly refined correlation
between the behaviour of a group of neurons and some measure of consciousness.
That would not solve the hard problem. Greenfield was happy with that. "If we really and deeply knew how groups of neurons generated consciousness, then we couldn't exclude the possibility that we could hack into each other's consciousness," she said."If we did that, then we'd annihilate the individual, and I for one would not want to see that day." |
|
As Koch explains: "Naively put, neurons in the visual part
of the brain project forwards to the prefrontal [cortex], and the prefrontal
looks back at the high-level visual output. That interaction is where we
believe the neural correlate of consciousness arises."
At Tucson, Logothetis reported new binocular rivalry experiments with monkeys
pitting pictures of faces against pictures of objects while recording from
face recognition neurons. Once again, he found some cells that started firing
just before the monkey pulled a lever to say it was now seeing a face.
But when he was asked if he thought he had found possible candidates for
the neural correlate of consciousness, Logothetis was cautious: "When there
is a pattern that is consistently happening somewhere, you still don't know
if it is a cause or an effect."
Finding neurons that appear to track visual awareness is still just the first
step to pinning down the neural correlate of consciousness. The key step
now is to find out what these neurons are connected to and how they respond.
At least the hunt has begun and more results can be expected
as researchers turn to humans. Excitement was high at the possibilities offered
by functional magnetic resonance imaging -the most sophisticated of
all of the new brain scanners.
Roger Tootell of the Massachusetts General Hospital's Nuclear Magnetic Resonance
Center is one of the pioneers with his work using the waterfall illusion:
if you stare at a waterfall or anything moving continuously and then look
away, stationary objects seem to stream by in the opposite direction. Using
a brain scanner to study subjects while they experienced the illusion, Tootell
was able to map the parts of the brain that changed as the perception faded
away. Once again, parts of the mid-temporal cortex appeared critical.
The real fun will come when these imaging techniques are applied
in cases where visual awareness has been split off from information processing
in the brain. Weiskrantz has already experimented with one of his blindsight
subjects who develops some degree of "awareness" of the stimulus if it has
enough contrast. His experiments were designed to see what changes in the
brain as the subject shifts between the "aware" state and the "unaware" state.
Results are expected any day.
"As far as consciousness is concerned, one is in a powerful position if one
can compare aware and unaware modes," says Weiskrantz. "We may be able to
sneak up on the process of the neural basis of awareness."
There's just one small snag, however: blindsight patients
are hard to find. Instead, researchers may be able to turn to "induced
blindsight". Late last year, Christopher Kolb and Jochen Braun from Koch's
group at Caltech reported an experiment like that described in the figure
below. Such displays, "too terrible to behold" as Braun described them, leaves
people able to use vision while removing conscious awareness of what they
are "seeing".
 |
| Roger Penrose: toiling at the quantum face |
The patterns appear to interfere with visual processing in
the primary visual cortex in much the same way at lesions in this region
interfere with processing in people with true blindsight. These experiments
will make it possible to use MRI to study neural changes as the brain shifts
between consciously "aware" and "unaware" states.
Even "hard man" Chalmers was impressed by the new possibilities. Induced
blindsight work is most promising since it deals with normal subjects. That's
going to explode in the next few years," he predicts.
Koch's own vision of the future of neurobiology was even more
euphoric. If, as he thinks, there are very specific neurons that have to
be activated to encode the specific content of visual awareness, then they
must have something unique about them.
"If that is true, then by definition there has to be a set of genes that
codes for them and that means that at some point you'll be able to get an
antibody or set of antibodies for the neurons that are your correlate of
visual awareness. This will then let you use the power of molecular biology
to make incredible progress. You can then stain these neurons, you can maybe
transiently inactivate them and see what happens." It might even be possible
to create a "zombie", a creature that has everything but awareness, thereby
showing by default just what consciousness gives us.
Two big ideas emerged at the first Tucson conference in 1994
that have caused a stir in the consciousness community ever since: one was
the "hard problem". as championed by Chalmers, which is very much alive.
The other is the brainchild of Roger
Penrose, a mathematician from Oxford
University [Ref: Iotm49], and anaesthesiologist
Stuart Hameroff of the university of Arizona. Consciousness, they claim,
arises from quantum-mechanical processes taking place within tubes of protein
inside nerve cells (see "Quantum states of mind", New Scientist, 20 August
1994, p35).
|
| It's easy to see in each of these two images that there is a small square (here towards the upper left corner) which stands out because it contains short lines running at right angles to those in the surroundings. But if the two images are shown simultaneously to the right and left eye for a very short time the square vanishes. The images appear to fuse in the brain: adding them together will obviously superimpose a line slanting to the left on every line slanting to the right so that no overall area of discrepancy remains. The square cannot now be seen but if it is moved from one corner of the figure to another,subjects can still reliably report where it is. They can thus "see" the square but cannot consciously perceive it-the phenomenon of induced blindsight. |
On the face of it, quantum mechanics is
tremendously seductive. Quantum processes operate without
cause and effect, a very appealing notion since
it leaves room for free will and spontaneity.
Penrose also argues that human minds do things that networks of nerve cells
and the computers modelled on them can never do: "understanding is a quality,
I claim, that cannot be captured in any form of computation whatever." The
unpredictability of quantum events provides a noncomputable way for understanding
to arise in the brain, he argues.
Despite their appeal, however, quantum processes take place at atomic or
subatomic scales and in the merest whisper of a microsecond-far too small
and fast, seemingly, to affect nerve cells.
But at the first Tucson conference, Penrose and Hameroff proposed
that microtubules- cylindrical tubes of protein
molecules called tubulin, which form the internal skeleton of cells- might
provide a safe haven in which quantum events could multiply until they became
powerful enough to make a difference.
What are these events? Quantum theory maintains that an electron, for example,
has no location at any particular time until some later event requires it
to have one. Until then, the electron could be anywhere, and its position
is described by a probability function.
Similarly, the outcome of any event at the quantum level is
not determined until some later event demands it. In a new twist, Penrose
and Hameroff suggested that vast armies of tubulin molecules may suddenly
and spontaneously resolve their quantum uncertainties. Each time this
happens, we have an experience, they said.
The audience was somewhat less than overwhelmed, however, and a show of hands
indicated that most of them remained sceptical, in large part, because no
one has found any experimental evidence that anything like this is actually
going on.
"If we're going to see the quantum approach flower, what we
need is not just a matching of equations. What we need is some good experimental
evidence." says Churchland, who is one of the tartest critics of what she
calls "Penrose's
toilings".
Moreover. says Churchland, "even if the theory is true, how does that explain
the phenomenon at issue? I haven't seen the slightest explanation of what
all that might have to do with consciousness."
Of course, that's pretty much what Chalmers says about the neuroscientists...
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