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No ghost in the machine

Consciousness: A User's Guide; Adam Zeman; Yale University Press: 404 pp., $29.95

October 12, 2003|John R. Searle | John R. Searle is Mills professor of the philosophy of mind and language at UC Berkeley. He is the author of many books, including "The Mystery of Consciousness" and, most recently, "Consciousness and Language."

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.

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