Thinking about the Conscious Mind.

By: Christof Koch

W HETHER WE SCIENTISTS ARE INSPIRED, BORED, OR INFURIATED BY PHILOSOPHY, all our theorizing and experimentation depends on particular philosophical background assumptions. This hidden influence is an acute embarrassment to many researchers, and it is therefore not often acknowledged. Such fundamental notions as reality, space, time, and causality—notions found at the core of the scientific enterprise all rely on particular metaphysical assumptions about the world. The situation for brain scientists is no different. The thinking of psychologists, neuroscientists, clinicians, and others who care about the subjective mind and how it relates to the objective brain is constrained, by and large, by terms René Descartes introduced in the mid- 17th century. Everything under the sun consists of one of two substances (hence this sort of philosophy is termed dualism): it is either physical stuff that has extension (res extensa) or mental stuff, thinking substance (res cogitans; by this he meant consciousness).

HUMANS ARE UNIQUE in that they are made up of both substances (for Descartes took the position that animals are not conscious). Of course, classical dualism is vehemently rejected by the large majority of today’s scientists. Nonetheless, these Cartesian terms remain immensely influential; they continue to frame the modern mind-body debate, making a resolution unlikely. So argues John Searle the University of California, Berkeley philosopher who put forth the Chinese room argument against the notion that computers can understand anything—in his latest book, Mind: A Brief Introduction.

In this short book that can easily be read on a transatlantic flight, Searle succinctly outlines the confusing variety of -isms that seek to explain the relationship between mind and brain. These include property and substance dualism, idealism, and materialism and its offspring (logical and methodological behaviorism, physicalism, epiphenomenalism, functionalism, and eliminative reductionism). Over the past 100 years, there have been three successive dominant scientific approaches to problems of the mind: behaviorism (which denied the existence of consciousness), computational functionalism (which asserted that consciousness is to the brain what a program is to a computer), and the contemporary focus on brain regions and neurons involved in the genesis of specific conscious percepts.

Philosophers have no such unifying framework. Some respond to the existence of conscious percepts, feelings, and thoughts (sometimes referred to as qualia) that constitute experienced life by denying their existence. Others accept them as given but declare that they are forever beyond the pale of a reductionistic, scientific explanation. Still others try to understand them as part of the natural order of things. Searle falls within the latter camp. To him, “Consciousness is a system- level, biological feature in much the same way that digestion, or growth, or the secretion of bile are system-level, biological features.” The crucial problem in understanding the mind is to cxplain how mental phenomena relate to the material substrate of the brain. In particular, what is the causal relationship between the mental and the physical? Refuting the entire Cartesian framework, Searle argues that (I) consciousness is causally reducible to the relevant micro variables (that is, to its neurobiological substrate), yet (ii) consciousness is not ontologically reducible to these brain processes. The implications of this syncretistic dualistic-materialistic account are profound.

The first statement avers that the causal powers of consciousness are exactly the same as the causal powers of the neuronal correlates of consciousness (the NCC); neither more nor less. Consciousness is part of the ordinary physical world; it is not something over and above it (res cogitans or the mind cannot act on its own, without the brain). The second one implies that the first-person perspective of the experiencing subject is real and is not identical to the objective description of the underlying neuronal processes that are sufficient for the conscious experiences (the third- person perspective of an external observer). Even though feelings are caused by brain processes, they have their own existence. (As anybody who has ever suffered from a tooth pain knows only too well; the sodium, potassium, calcium, and other ions sloshing around the brain that are sufficient for the pain are not the same as the awful feeling itself.) Searle argues in line with what Francis Crick and I have been advocating—that the inchoate science of consciousness needs to move from a research program that characterizes the NCC, through tests of their causal powers, to an ultimate theory of consciousness. It is difficult to convey in a few sentences the forcefulness and common sense of Searle’s position, which he labels biological naturalism. A believer in the scientific method, he accepts no mysticism or denial of the obvious. Whether Searle has truly untangled the Gordian knot of the mind-body problem remains to be seen. But his views are compatible with everything we know about the world and consciousness.

The book also covers related topics, in particular intentionality (another age-old philosophical conundrum concerned with meaning), causation, the unconscious, and the self As a proper understanding of mental causation may radically contradict the traditional image that people have formed of themselves throughout the ages and across cultures, Searle spends two fascinating chapters on this problem. It is easy enough to state. The universe is casually closed: that is, anything that happened, happened because it was caused by something else. Given the causes, the effect had to occur. There is no choice. When I climb and my feet slip, I fall if the force of gravity on my body exceeds the force that my hands exert on the rock. It is as simple as that. On the other hand, there is the profound experience of freedom of will. Except when drunk, hypnotized, under some powerful emotion (such as rage), or in a similar condition, I am free at the psychological level. Nobody compelled me to go climbing, to pick this particular route, or to make this sequence of moves.

Now these are obviously absolutely irreconcilable convictions. Can both be true? Many have argued that there is no freedom. To this Searle retorts, “If.. .1 am in a restaurant and I am confronted with a menu and the waiter asks me what I would like, I cannot say ‘I’m a determinist, I’ll just wait and see what happens,’ because even that utterance is only intelligible to me as an exercise of my free will.” Yet where does freedom come in? Refreshingly, Searle admits to puzzlement. (In my experience, it is rare for a philosopher to admit not understanding something.)

Why should primates have evolved a large decision-making apparatus (most of the prefrontal cortex is concerned with making decisions of various kinds) and the perception of freedom of action if it is all a big illusion? Searle does propose that quantum indeterminacy may be important here. However at this point it is mysterious how an injection of randomness at the subneuronal level should lead to indeterminacy of a useful kind at the behavioral level. We will have to see how this plays out over the years.

Mind finishes with a chapter whose title says it all, ~PhiIosophy and the Scientific World-View.” That masterful, three-page essay should top the required-reading list in every high school and college around the world. Although I have a few disagreements with Searle, I believe that every thinking person concerned about the mind and its place in the world should own a copy. Easy to read, the book keeps philosophical jargon to a minimum. Pound per pound, you don’t get much better value.

The reviewer is in the

Computation and Neural Systems Program,

Division of Biology, California Institute of Technology (CIT)

Pasadena, California 91125, U.S.A.


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