BRIEF HISTORY OF THE STUDY OF CONSCIOUSNESS 4 WHAT WE HAVE LEARNED FROM MEASURES OF COGNITIVE FUNCTIONING 5 Unconscious Perception 7 Acquiring Tacit Knowledge 9 Perceptual Construction 9 Subliminal Priming and Negative Priming 11 Implicit Memory 12
Nonconscious Basis of Conscious Content 13 Consciousness, Will, and Action 13 Attentional Selection 14
Dissociation Accounts of Some Unusual and Abnormal
Conditions 14 What Is Consciousness For? Why Aren't We Zombies? 16 Conclusions 17
NEUROSCIENTIFIC APPROACHES TO CONSCIOUSNESS 17 Data from Single-Cell Studies 17 Data from Human Pathology 18 An Introduction to Current Theories 20 Dynamic Activity Clusters 20 Sensory Imagery and Binding 21 Thalamocortical Loops 22 Self and Consciousness 24 A Word on Theories at the Subneural Level 25 CONCLUSION: THE FUTURE OF CONSCIOUSNESS 25 REFERENCES 26
Consciousness is an inclusive term for a number of central aspects of our personal existence. It is the arena of self-knowledge, the ground of our individual perspective, the realm of our private thoughts and emotions. It could be argued that these aspects of mental life are more direct and immediate than any perception of the physical world; indeed, according to Descartes, the fact of our own thinking is the only empirical thing we know with mathematical certainty. Nevertheless, the study of consciousness within science has proven both challenging and controversial, so much so that some have doubted the appropriateness of addressing it within the tradition of scientific psychology.
In recent years, however, new methods and technologies have yielded striking insights into the nature of consciousness. Neuroscience in particular has begun to reveal detailed connections between brain events, subjective experiences, and cognitive processes. The effect of these advances has been to give consciousness a central role both in integrating the diverse areas of psychology and in relating them to developments in neuroscience. In this chapter we survey what has been discovered about consciousness; but because of the unique chal lenges that the subject poses, we also devote a fair amount of discussion to methodological and theoretical issues and consider the ways in which prescientific models of consciousness exert a lingering (and potentially harmful) influence.
Two features of consciousness pose special methodological challenges for scientific investigation. First, and best known, is its inaccessibility. A conscious experience is directly accessible only to the one person who has it, and even for that person it is often not possible to express precisely and reliably what has been experienced. As an alternative, psychology has developed indirect measures (such as physiological measurements and reaction time) that permit reliable and quantitative measurement, but at the cost of raising new methodological questions about the relationship between these measures and consciousness itself.
The second challenging feature is that the single word consciousness is used to refer to a broad range of related but distinct phenomena (Farber & Churchland, 1995). Consciousness can mean not being knocked out or asleep; it can mean awareness of a particular stimulus, as opposed to unawareness or implicit processing; it can mean the basic functional state that is modulated by drugs, depression, schizophrenia, or REM sleep. It is the higher order self-awareness that some species have and others lack; it is the understanding of one's own motivations that is gained only after careful reflection; it is the inner voice that expresses some small fraction of what is actually going on below the surface of the mind. On one very old interpretation, it is a transcendent form of unmediated presence in the world; on another, perhaps just as old, it is the inner stage on which ideas and images present themselves in quick succession.
Where scientists are not careful to focus their inquiry or to be explicit about what aspect of consciousness they are studying, this diversity can lead to confusion and talking at cross-purposes. On the other hand, careful decomposition of the concept can point the way to a variety of solutions to the first problem, the problem of access. As it has turned out, the philosophical problems of remoteness and subjectivity need not always intrude in the study of more specific forms of consciousness such as those just mentioned; some of the more prosaic senses of consciousness have turned out to be quite amenable to scientific analysis. Indeed, a few of these—such as "awareness of stimuli" and "ability to remember and report experiences"—have become quite central to the domain of psychology and must now by any measure be considered well studied.
In what follows we provide a brief history of the early development of scientific approaches to consciousness, followed by more in-depth examinations of the two major strands in twentieth century research: the cognitive and the neuroscientific. In this latter area especially, the pace of progress has accelerated quite rapidly in the last decade; though no single model has yet won broad acceptance, it has become possible for theorists to advance hypotheses with a degree of empirical support and fine-grained explanatory power that was undreamed-of 20 years ago. In the concluding section we offer some thoughts about the relationship between scientific progress and everyday understanding.
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