Phantoms in the Brain: Probing the Mysteries of the Human Mind (40 page)

First, imagine that you are a future superscientist with a complete knowledge of the workings of the human brain. Unfortunately you are also completely color−blind. You don't have any cone receptors (the structures in your retina that allow your eyes to discriminate the different colors), but you do have rods (for seeing black and white), and you also have the correct machinery for processing colors higher up inside your brain. If your eyes could distinguish colors, so could your brain.

Now suppose that you, the superscientist, study my brain. I am a normal color perceiver—I can see that the sky is blue, the grass is green and a banana is yellow—and you want to know what I mean by these color terms. When I look at objects and describe them as turquoise, chartreuse or vermilion, you don't have any idea 156

what I'm talking about. To you, they all look like shades of gray.

But you are intensely curious about the phenomenon, so you point a spectrometer at the surface of a ripe red apple. It indicates that light with a wavelength of six hundred nanometers is emanating from the fruit. But you still have no idea what
color
this might correspond to because you can't experience it. Intrigued, you study the light−sensitive pigments of my eye and the color pathways in my brain until you eventually come up with a complete description of the laws of wavelength processing. Your theory allows you to trace the entire sequence of color perception, starting from the receptors in my eye and passing all the way into my brain, where you monitor the neural activity that generates the word "red." In short, you completely understand the laws of color vision (or more strictly, the laws of wavelength processing), and you can tell me in advance which word I will use to describe the color of an apple, orange or lemon. As a superscientist,
you have no
reason to doubt the completeness of your account.

Satisfied, you approach me with your flow diagram and say, "Rama−chandran, this is what's going on in your brain!"

But I must protest. "Sure, that's what's going on. But I also
see
red. Where is the red in this diagram?"

"What is that?" you ask.

"That's part of the actual, ineffable experience of the color, which I can never seem to convey to you because you're totally color−blind."

This example leads to a definition of "qualia": they are aspects of my brain state that seem to make the scientific description incomplete—from my point of view.

As a second example, imagine a species of Amazonian electric fish that is very intelligent, in fact, as intelligent and sophisticated as you or I. But it has something we lack—namely, the ability to sense electrical fields

using special organs in its skin. Like the superscientist in the previous example, you can study the neurophysiology of this fish and figure out how the electrical organs on the sides of its body transduce electrical current, how this information is conveyed to the brain, what part of the brain analyzes this information and how the fish uses this information to dodge predators, find prey and so on. If the fish could talk, however, it would say, "Fine, but you'll never know what it
feels
like to sense electricity."

These examples clearly state the problem of why qualia are thought to be essentially private. They also illustrate why the problem of qualia is not necessarily a scientific problem. Recall that your
scientific
description is complete. It's just that the your account is incomplete episte−mologically because the actual experience of electric fields or redness is something you never will know. For you, it will forever remain a

"third−person" account.

For centuries philosophers have assumed that this gap between brain and mind poses a deep epistemological problem—a barrier that simply cannot be crossed. But is this really true? I agree that the barrier hasn't yet been crossed, but does it follow that it can
never
be crossed? I'd like to argue that there is in fact no such barrier, no great vertical divide in nature between mind and matter, substance and spirit. Indeed, I believe that this barrier is only apparent and that it arises as a result of language. This sort of obstacle emerges when there is
any translation
from one language to another.2

How does this idea apply to the brain and the study of consciousness? I submit that we are dealing here with two mutually unintelligible languages. One is the language of nerve impulses—the spatial and temporal 157

patterns of neuronal activity that allow us to see red, for example. The second language, the one that allows us to communicate what we are seeing to others, is a natural spoken tongue like English or German or Japanese—rarefied, compressed waves of air traveling between you and the listener. Both are languages in the strict technical sense, that is, they are information−rich messages that are intended to convey meaning, across synapses between different brain parts in one case and across the air between two people in the other.

The problem is that I can tell you, the color−blind superscientist, about my qualia (my experience of seeing red) only by using a spoken language. But the ineffable "experience" itself is lost in the translation. The actual

"redness" of red will remain forever unavailable to you.

But what if I were to skip spoken language as a medium of commu−

nication and instead hook a cable of neural pathways (taken from tissue culture or from another person) from the color−processing areas in my brain directly into the color−processing regions of your brain (remember that your brain has the machinery to see color even though your eyes cannot discriminate wavelengths because they have no color receptors)? The cable allows the color information to go straight from my brain to neurons in your brain without intermediate translation. This is a farfetched scenario, but there is nothing logically impossible about it.

Earlier when I said "red," it didn't make any sense to you because the mere use of the word "red" already involves a translation. But if you skip the translation and use a cable, so that the nerve impulses themselves go directly to the color area, then perhaps you'll say, "Oh, my God, I see exactly what you mean. I'm having this wonderful new experience."3

This scenario demolishes the philosophers' argument that there is an insurmountable logical barrier to understanding qualia. In principle, you
can
experience another creature's qualia, even the electric fish's. If you could find out what the electroceptive part of the fish brain is doing and if you could somehow graft it onto the relevant parts of your brain with all the proper associated connections, then you would start experiencing the fish's electrical qualia. Now, we could get into a philosophical debate over whether you need to be a
fish
to experience it or whether as a human being you could experience it, but the debate is not relevant to my argument. The logical point I am making here pertains only to the electrical qualia—not to the whole experience of being a fish.

The key idea here is that the qualia problem is not unique to the mind−body problem. It is no different in kind from problems that arise from
any
translation, and thus there is no need to invoke a great division in nature between the world of qualia and the material world. There is only one world with lots of translation barriers. If you can overcome them, the problems vanish.

This may sound like an esoteric, theoretical debate, but let me give you a more realistic example—an experiment we are actually planning to do. In the seventeenth century the English astronomer William Molyneux posed a challenge (another thought experiment). What would happen, he asked, if a child were raised in complete darkness from birth to age twenty−one and were then suddenly allowed to see a cube?

Would he recognize the cube? Indeed, what would happen if the child were suddenly allowed to see ordinary daylight? Would he experience the light,

saying, "Aha! I now see what people mean by light!" or would he act utterly bewildered and continue to be blind? (For the sake of argument, the philosopher assumes that the child's visual pathways have not degenerated from the deprivation and that he has an intellectual concept of seeing, just as our superscientist had an intellectual concept of color before we used the cable.)

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This turns out to be a thought experiment that can actually be answered empirically. Some unfortunate individuals are born with such serious damage to their eyes that they have never seen the world and are curious about what "seeing" really is: To them it's as puzzling as the fish's electroception is to you. It's now possible to stimulate small parts of their brains directly with a device called a transcranial magnetic stimulator—an extremely powerful, fluctuating magnet that activates neural tissue with some degree of precision. What if one were to stimulate the visual cortex of such a person with magnetic pulses, thereby bypassing the nonfunctional optics of the eye? I can imagine two possible outcomes. He might say, "Hey, I feel something funny zapping the back of my head," but nothing else. Or he might say, "Oh, my God, this is extraordinary! I now understand what all of you folks are talking about. I am finally experiencing this abstract thing called vision. So this is light, this is color, this is seeing!"

This experiment is logically equivalent to the neuron cable experiment we did on the superscientist because we are bypassing spoken language and directly hitting the blind person's brain. Now you may ask, If he does experience totally novel sensations (what you and I call seeing), how can we be sure that it is in fact true vision? One way would be to look for evidence of topography in his brain. I could stimulate different parts of his visual cortex and ask him to point to various regions of the outside world where he experiences these strange new sensations. This is akin to the way you might see stars "out there" in the world when I hit you on the head with a hammer; you don't experience the stars as being inside your skull. This exercise would provide convincing evidence that he was indeed experiencing for the first time something very close to our experience of seeing, although it might not be as discriminating or sophisticated as normal seeing.4

Why did qualia—subjective sensation—emerge in evolution? Why did some brain events come to have qualia? Is there a particular
style
of

information processing that produces qualia, or are there some
types
of neurons exclusively associated with qualia? (The Spanish neurologist Ramón y Cajal calls these neurons the "psychic neurons.") Just as we know that only a tiny part of the cell, namely, the deoxyribonucleic acid (DNA) molecule, is directly involved in heredity and other parts such as proteins are not, could it be that only some neural circuits are involved in qualia and others aren't? Francis Crick and Christof Koch have made the ingenious suggestion that qualia arise from a set of neurons in the lower layers of the primary sensory areas, because these are the ones that project to the frontal lobes where many so−called higher functions are carried out. Their theory has galvanized the entire scientific community and served as a catalyst for those seeking biological explanations for qualia.

Others have suggested that the actual patterns of nerve impulses (spikes) from widely separated brain regions become "synchronized" when you pay attention to something and become aware of it.5 In other words, it is the synchronization itself that leads to conscious awareness. There's no direct evidence for this yet, but it's encouraging to see that people are at least trying to explore the question experimentally.

These approaches are attractive for one main reason, namely, the fact that reductionism has been the single most successful strategy in science. As the English biologist Peter Medawar defines it, "Reductionism is the belief that a whole may be represented as a function (in the mathematical sense) of its constituent parts, the functions having to do with the spatial and temporal ordering of the parts and with the precise way in which they interact." Unfortunately, as I stated at the beginning of this book, it's not always easy to know a priori what the appropriate level of reductionism is for any given scientific problem. For understanding consciousness and qualia there wouldn't be much point in looking at ion channels that conduct nerve impulses, at the brain stem reflex that mediates sneezing or at the spinal cord reflex arc that controls the bladder, even though these are interesting problems in themselves (at least to some people). They would be no more useful in understanding higher brain functions like qualia than looking at silicon chips in a microscope in an attempt to understand the logic of a computer program. And yet this is precisely the strategy most neuroscientists use in trying to understand the higher functions of the brain. They argue either that the problem doesn't exist or that it will be solved some fine day as we plod along looking at the activity of individual neurons.6

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Philosophers offer another solution to this dilemma when they say that consciousness and qualia are "epiphenomena." According to this view, consciousness is like the whistling sound that a train makes or the shadow of a horse as it runs: It plays no causal role in the real work done by the brain. After all, you can imagine a "zombie" unconsciously doing everything in exactly the same manner that a conscious being does. A sharp tap on the tendon near your knee joint sets in motion a cascade of neural and chemical events that causes a reflex knee jerk (stretch receptors in the knee connect to nerves in the spinal cord, which in turn send messages to the muscles). Consciousness doesn't enter into this picture; a paraplegic has an excellent knee jerk even though he can't feel the tap. Now imagine a much more complex cascade of events starting with long−wavelength light striking your retina and various relays, leading to your saying