No ghost in the machine
In the recent glut of books on consciousness, is there any excuse for another? For Adam Zeman’s “Consciousness: A User’s Guide,” I think there is. Zeman is a practicing neurologist in Edinburgh and a senior lecturer at Edinburgh University. Before he went into medicine, he was trained in philosophy and psychology. He is uniquely qualified to write this particular book, whose chief merit is that it provides a summary of the current state of play in neurobiology, psychology and philosophy.
Because Zeman is a neurologist, you get from his book a concrete sense of patients with real brain problems. He begins by dividing consciousness into three different definitions: consciousness as wakefulness, consciousness as perception, and consciousness as the mind in general. At first I was exasperated by the artificiality of this division. These are, after all, not three different definitions but three different ways of studying consciousness, different aspects of consciousness. But artificial as it is, the division gives him a way of organizing a lot of information, especially a lot of clinical and experimental data.
Few authors would have the nerve to try to explain so much in so little space. In one chapter Zeman tries to explain the anatomy and physiology of the human nervous system in fewer than 40 pages. There is even a chapter titled “The History of Everything,” in which he traces the path that led from the big bang 13 billion years ago to the recent emergence of consciousness. The danger in having such ambitions is that he may give his readers the impression that they understand something that they do not really understand. To his credit, Zeman is aware of this danger and is constantly reminding the reader of both how much he is leaving out and, more important, how little we know about some crucial areas of human experience. “No one knows why we sleep,” he remarks, for example, and, “We do not know the minimal conditions” that will produce consciousness in an organism.
The book’s best feature is its summary of what is known about the brain processes that cause and realize consciousness in its various forms. Even if you don’t learn why we are conscious, you will still learn a lot about such things as epilepsy, anesthetics, sleep, drugs and visual perception. You will learn about the famous case of D.B., who has blind sight: He is blind in a certain area of his visual field, but he can nonetheless, to his amazement, report events occurring in that area. You will also learn about the tragic case of H.M., who, because of the removal of his hippocampus, cannot lay down new long-term memories. He can remember his childhood, but if a doctor to whom he has just been introduced leaves the room for a few minutes and returns, H.M. does not recognize him. He has no recollection. And the famous Phineas Gage is also explained. A 19th century railway worker, Gage had an iron bar pierce his skull. Miraculously he survived, but his personality was totally changed: Previously he had been conscientious, reliable and industrious; he became “fitful, irreverent ... capricious.”
Zeman’s otherwise commendable caution and modesty prevent him from really dealing with a hard set of crucial questions about consciousness, in both philosophy and neuroscience. Though Zeman summarizes the competing views, he is reluctant to get into the fray. Before we reach a solution to these problems we need to understand much better how the brain works; in order to do that, we have to remove a lot of philosophical confusions that afflict brain scientists as much as they do philosophers. He does not do much to help us get out of our confusions. In his crucial chapter, the last, titled “The Nature of Consciousness,” he tries to face the issue head-on, telling us (correctly, in my view) that there are three intuitions about consciousness we should try to respect: First, that “experience is rich and real”; second, that “every distinction drawn in experience will be reflected in a distinctive pattern of neural activity”; and third, that “experience is an evolved capacity which governs our behaviour.” I agree with all of these, but it is much too weak and bashful to describe them as mere intuitions. As far as we know anything about how the world works, they are plain facts. Here is how I would state these facts, and this is what I think he really means.
1. Consciousness is a real part of the real world. It is not an illusion.
2. Consciousness is entirely caused by brain processes. (Don’t say “brain processes give rise to consciousness.” That’s too mealy-mouthed.)
3. Consciousness functions causally in our behavior.
Zeman points out correctly that it is hard to see how, in our philosophical tradition, we can hold all of these propositions, together with what we know about the rest of the universe from science. Dualism is happy with 1 but has trouble acknowledging 2 and 3. Materialism (nowadays called “physicalism”) ends up denying 1 and thus denying what we all know from our own experiences.
The obvious way out is to scrap the traditional philosophical categories, with all their accumulated barnacles of theological and metaphysical confusion, and just state the facts. We know for a fact that brain processes cause consciousness. We know from our own experience that consciousness is a real part of the real world, and if you have any doubts that it functions causally, just raise your arm or scratch your head. The appearance of some hard metaphysical difficulty comes from supposing that if consciousness, with all its privacy and touchy-feely qualities, really exists, as it plainly does, then it can’t be an ordinary part of the real physical, biological world, like digestion or photosynthesis.
But why not? I suggest that it is simply our acceptance of the traditional metaphysical categories, which treat the mind as something separate and distinct from the body, that gives us the illusion that privacy, subjectivity and all the rest of it prevent consciousness from being a real part of the real world like anything else. It seems to me quite obvious that if we scrap the traditional metaphysical dichotomy of mental and physical, then we can state all facts about consciousness without difficulty.
There is a really hard problem left over about how the brain does it, and, as Zeman points out in an entire chapter, brain research so far has not solved this problem. But the philosophical problem -- how such a thing as consciousness can exist -- is an illusion engendered by taking seriously an obsolete vocabulary. Zeman takes me to task in the book because I use the expression “emergent property” in describing consciousness. Well, if that expression engenders confusion, then let’s get rid of it. The substantive point can be stated without it: All of our conscious states are caused by brain processes, and they are realized in the brain as features of the brain.
The weakest passage in the book is Zeman’s discussion of computational theories of consciousness. He confuses the question “Can computation constitute consciousness?” with the question “Can a complex machine made of silicon be conscious?” He apparently thinks that computation has some essential connection with existing computer technologies. That is a mistake. We happen to use silicon-based systems for computing, but that is an incidental fact about a certain stage of technology, not part of the definition of computation. These are the points to keep in mind: We know that the brain is a machine that causes consciousness. So we should hear the question “Can you build an artificial machine that causes consciousness?” the way we hear the question “Can you build an artificial machine that causes the pumping of blood?” There is no obstacle, in principle, to building a conscious machine. But none of this has anything to do with the computational theory of consciousness. For the computational theory, the crucial question is one he does not face: What is the definition of “computation”? If computation just means figuring things out, consciously or not, then we are all conscious computers. The important change in the definition was due to British mathematician Alan Turing, who defined computation in terms of the manipulation of binary symbols, usually given as zeros and ones. The objection to the computational theory is that the zeros and ones, by themselves, do not constitute consciousness -- or, indeed, any other mental phenomena. They are just zeros and ones, nothing more.
So there are two questions: First, is it possible in principle to build a conscious machine? Answer, yes (though silicon is an unlikely building material, for boring biochemical reasons). Second, is computation as currently defined, in terms of the manipulation of binary symbols, sufficient to constitute consciousness? Answer, no. The symbolic objects in the computation -- zeros and ones, or whatever -- are, by themselves, sufficient neither to constitute consciousness nor to cause consciousness.
On balance, I think Zeman has produced a very useful book, and I look forward to the second edition, which will undoubtedly be even better.
