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by John Searle

Can consciousness be measured scientifically? What exactly is consciousness? John Searle approaches the scientific investigation of consciousness and its possible neurobiological roots from a philosophical perspective.


Originally published October 8, 1999 as an academic paper, University of California at Berkeley. Posted on August 13, 2001. Article on John Searle's home page can be read here.

Until very recently, most neurobiologists did not regard consciousness as a suitable topic for scientific investigation. This reluctance was based on certain philosophical mistakes, primarily the mistake of supposing that the subjectivity of consciousness made it beyond the reach of an objective science. Once we see that consciousness is a biological phenomenon like any other, then it can be investigated neurobiologically. Consciousness is entirely caused by neurobiological processes and is realized in brain structures. The essential trait of consciousness that we need to explain is unified qualitative subjectivity. Consciousness thus differs from other biological phenomena in that it has a subjective or first-person ontology, but this subjective ontology does not prevent us from having an epistemically objective science of consciousness. We need to overcome the philosophical tradition that treats the mental and the physical as two distinct metaphysical realms. Two common approaches to consciousness are those that adopt the building block model, according to which any conscious field is made of its various parts, and the unified field model, according to which we should try to explain the unified character of subjective states of consciousness. These two approaches are discussed and reasons are given for preferring the unified field theory to the building block model. Some relevant research on consciousness involves the subjects of blindsight, the split-brain experiments, binocular rivalry, and gestalt switching.

I. Resistance to the Problem

As recently as two decades ago there was little interest among neuroscientists, philosophers, psychologists and cognitive scientists generally in the problem of consciousness. Reasons for the resistance to the problem varied from discipline to discipline. Philosophers had turned to the analysis of language, psychologists had become convinced that a scientific psychology must be a science of behavior, and cognitive scientists took their research program to be the discovery of the computer programs in the brain that, they thought, would explain cognition. It seemed especially puzzling that neuroscientists should be reluctant to deal with the problem of consciousness, because one of the chief functions of the brain is to cause and sustain conscious states. Studying the brain without studying consciousness would be like studying the stomach without studying digestion, or studying genetics without studying the inheritance of traits. When I first got interested in this problem seriously and tried to discuss it with brain scientists, I found that most of them were not interested in the question.

The reasons for this resistance were various but they mostly boiled down to two. First, many neuroscientists felt--and some still do--that consciousness is not a suitable subject for neuroscientific investigation. A legitimate brain science can study the microanatomy of the Purkinje cell, or attempt to discover new neurotransmitters, but consciousness seems too airy-fairy and touchy-feely to be a real scientific subject. Others did not exclude consciousness from scientific investigation, but they had a second reason: "We are not ready" to tackle the problem of consciousness. They may be right about that, but my guess is that a lot of people in the early 1950s thought we were not ready to tackle the problem of the molecular basis of life and heredity. They were wrong; and I suggest for the current question, the best way to get ready to deal with a research problem may be to try to solve it.

There were, of course, famous earlier twentieth century exceptions to the general reluctance to deal with consciousness, and their work has been valuable. I am thinking in particular of the work of Sir Arthur Sherrington, Roger Sperry, and Sir John Eccles.

Whatever was the case 20 years ago, today many serious researchers are attempting to tackle the problem. Among neuroscientists who have written recent books about consciousness are Cotterill (1998), Crick (1994), Damasio (1999), Edelman (1989, 1992), Freeman (1995), Gazzaniga (1988), Greenfield (1995), Hobson (1999), Libet (1993), and Weiskrantz (1997). As far as I can tell, the race to solve the problem of consciousness is already on. My aim here is not to try to survey this literature but to characterize some of the neurobiological problems of consciousness from a philosophical point of view.

II. Consciousness as a Biological Problem

What exactly is the neurobiological problem of consciousness? The problem, in its crudest terms, is this: How exactly do brain processes cause conscious states and how exactly are those states realized in brain structures? So stated, this problem naturally breaks down into a number of smaller but still large problems: What exactly are the neurobiological correlates of conscious states (NCC), and which of those correlates are actually causally responsible for the production of consciousness? What are the principles according to which biological phenomena such as neuron firings can bring about subjective states of sentience or awareness? How do those principles relate to the already well understood principles of biology? Can we explain consciousness with the existing theoretical apparatus or do we need some revolutionary new theoretical concepts to explain it? Is consciousness localized in certain regions of the brain or is it a global phenomenon? If it is confined to certain regions, which ones? Is it correlated with specific anatomical features, such as specific types of neurons, or is it to be explained functionally with a variety of anatomical correlates? What is the right level for explaining consciousness? Is it the level of neurons and synapses, as most researchers seem to think, or do we have to go to higher functional levels such as neuronal maps (Edelman 1989, 1992), or whole clouds of neurons (Freeman 1995), or are all of these levels much too high and we have to go below the level of neurons and synapses to the level of the microtubules (Penrose 1994 and Hameroff 1998a, 1998b)? Or do we have to think much more globally in terms of Fourier transforms and holography (Pribram 1976, 1991, 1999)?

As stated, this cluster of problems sounds similar to



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