A Cognitive Theory of Consciousness.
Bernard J. Baars
The Wright Institute 2728 Durant Ave. Berkeley, Calif. 94704
Published by Cambridge University Press, 1988-1998. Electronic version published by author (@ B.J. Baars, 1998). Individual copies may be made for educational purposes. Please notify author of copies made electronically, bbaars@wrightinst.edu. Republication not permitted without permission.
This book is gratefully dedicated to the pioneers in cognitive science, who made it possible.
We shall not cease from exploration and the end of all our exploring will be to come back to the place from which we came and know it for the first time.
--- T.S. E liot
Table of Contents.
Preface.
Part I. Introduction.
Chapter 1. What is to be explained? Some preliminaries.
We focus on the issue of conscious experience as such by comparing pairs of similar events that seem to differ only in that one event is conscious while the other is not. There are many such îminimally contrastiveï pairs of well- established facts. Different models emerge depending on which set of contrasts we emphasize. Global Workspace (GW) theory captures most of the evidence in a single coherent framework.
Part II. The basic model.
Chapter 2. Model 1: Conscious representations are internally consistent and globally distributed.
In which we develop the basic theoretical metaphor of a îglobal workspaceï (GW) operating in a îdistributed system of specialized processorsï. A first- approximation model based on these ideas fits a sizable subset of the evidence.
Chapter 3. The neural basis of conscious experience.
The Global Workspace metaphor has a natural neural interpretation in the Extended Reticular-Thalamic Activating System (ERTAS) of the brain. Parts of the frontal and parietal cortex seem to control access to this system.
___ Part III. The fundamental role of context.
Chapter 4. Model 2: Unconscious contexts shape conscious experiences.
In which we contrast the îobjectsï of conscious experience with numerous unconscious contextual systems that are needed to shape, define and evoke them.
Chapter 5. Model 3: Conscious experience is îinformativeï --- it always demands some degree of adaptation. Repeated events tend to fade from consciousness, yet they continue to be processed unconsciously. To be conscious an event must be novel or significant; it must apparently trigger widespread adaptive processing in the nervous system. One result of this view is an interpretation of îlearningï as a îchange in the context of experience that alters the way the learned material is experiencedï. Numerous examples are presented.
Part IV. Goals and voluntary control.
Chapter 6. Model 4: Goal contexts, spontaneous problem-solving, and the stream of consciousness.
îIntentionsï can be treated as largely unconscious goal structures which use conscious goal images to recruit effectors and subgoals to accomplish their goals. This suggests ways in which conscious experience works to solve problems in learning, perception, thinking, and action.
Chapter 7. Model 5: Volition as ideomotor control of thought and action.
William James' ideomotor theory can handle a number of puzzling questions about voluntary control. The Global Workspace model can incorporate James' theory very comfortably; it implies that volition always involves conscious goal images that are îtacitly editedï by multiple unconscious criteria. Abstract concepts may be controlled by similar goal images, which may be conscious only fleetingly. ‹j_
Part V. Attention, self, and conscious self-monitoring.
Chapter 8. Model 6: Attention as control of access to consciousness.
Common sense makes a useful distinction between îconscious experienceï as a subjectively passive state, versus îattentionï as the active control of access to consciousness. GW theory easily absorbs this distinction.
Chapter 9. Model 7: Self as the dominant context of experience and action.
We can adapt the method of minimal contrasts from previous chapters to give more clarity and empirical precision to the notion of self. It appears that "self" can be treated as the enduring context of experience, one that serves to organize and stabilize experiences across many different local contexts. The "self-concept" can then be viewed as a control system that makes use of consciousness to monitor, evaluate, and control the self-system.
Part VI. Consciousness is functional.
Chapter 10. The functions of consciousness.
Contrary to some, we find that conscious experience serves a multitude of vital functions in the nervous system.
Part VII. Conclusion.
Chapter 11. A summary and some future directions.
We review the flow of arguments in this book, and attempt to distill the necessary conditions for conscious experience that have emerged so far. Many phenomena remain to be explained. We sketch some ways in which GW theory may be able to accomodate them.‹
j_ îAppendices.ï
I. Glossary of theoretical terms.
II. Index of tables and figures.
Subject Index.
References and Author Index.
îPrefaceï
Conscious experience is notoriously the great, confusing, and contentious nub of psychological science. We are all con?scious beings, but consciousness is not something we can observe directly, other than in ourselves, and then only in retrospect. Yet as scientists we aim to gather objective knowledge even about subjectivity itself. Can that be done? This book will sketch one approach, and no doubt the reader will come to his or her own judgment of its inadequacies. Of one thing, however, we can be very sure: that we cannot pursue scientific psychology and hope to avoid the problem for very long.
Indeed, historically psychologists have neither addressed nor evaded consciousness successfully, and two major psychologi?cal metatheories, introspectionism and behaviorism, have come to grief on the horns of this dilemma. Having perhaps gained some wisdom from these failures, most scientific psychologists now subscribe to a third metatheory for psychology, the cognitive approach (Baars, 1986a). Whether cognitive psychology will succeed where others have not depends in part on its success in under¨standing conscious experience: not just because "it is there," but because consciousness, if it is of any scientific interest at all, must play a major îfunctionalï role in the human nervous system.
The first obstacle in dealing with consciousness as a serious scientific issue comes in trying to make sense of the tangled thicket of conflicting ideas, opinions, facts, preju?dices, insights, misunderstandings, fundamental truths and fundamental falsehoods that surrounds the topic. Natsoulas (197x) counts at least seven major definitions of the word "conscious?ness" in English. One topic alone, the mind-body issue, has a relevant literature extending from the Upanishads to the latest philosophical journals --- four thousand years of serious thought. We can only nod respectfully to the vast philosophical literature and go our own way. In doing so we do not discount the importance of philosophical questions. But one time-honored strategy in science is to side-step philosophical issues for a time by focusing on empirically decideable ones, in the hope that eventually, new scientific insights may cast some light on the perennial philosophical concerns.
How are we to discover empirical evidence about conscious?ness? What is a theory of consciousness a theory of? Nineteenth-?century psychologists like Wilhelm Wundt and William James believed that consciousness was the fundamental constitutive problem for psychology, but they had remarkably little to say about it îas suchï. Freud and the psychodynamic tradition have much to say about îunïconscious motivation, but conscious experience is taken largely for granted. Behaviorists tended to discourage any serious consideration of consciousness in the first half of this‹h______‹ century; and even cognitive psychologists have studiously avoided it until the last few years.
In truth, the facts of consciousness are all around us, ready to be studied. Practically all psychological findings involve conscious experience. Modern psychologists find them?selves in much the position of Molieô`re's îBourgeois Gentlemanï, who hires a scholar to make him as sophisticated as he is wealthy. Among other absurdities, the scholar tries to teach the bourgeois the difference between îproseï and îpoetryï, pointing out that the gentleman has been speaking îproseï all his life. This unsuspected talent fills the bourgeois gentleman with astonished pride --- speaking îproseï, and without even knowing it! In just this way, some psychologists will be surprised to realize that they have been studying consciousness all of their professional lives. The physicalistic philosophy of most psychologists has tended to disguise this fundamental fact, and our usual emphasis on sober empirical detail makes us feel more secure with less glamorous questions. But a psychologist can no more evade consciousness than a physicist can side-step gravity.
Even if the reader is willing to grant this much, it may still be unclear how to approach and define the issue empirical?ly. Here, as elsewhere, we borrow a leaf from William James' book. In îThe Principles of Psychologyï (1890) James suggests a way of focusing on the issue of consciousness as such, by îcontrastingï comparable conscious and unconscious events. James himself was hindered in carrying out this program because he believed that psychology should not deal with îunïconscious processes as such; unconscious events, he thought, were physiological. In contrast, our current cognitive metatheory suggests that we can indeed talk psychologically about both conscious îandï unconscious processes, îifï we can infer the properties of both on the basis of public evidence. In cognitive psychology, conscious and unconscious events have the same status as any other scientific constructs. A wealth of information has now accumulated based on this reason?ing, clearing the way for us to consider comparable conscious and unconscious events side by side. We call the resulting method îcontrastive analysisï, a term borrowed from linguistics, where it is used to determine the perceived similarities and differences between classes of speech sounds. One can think of contrastive analysis as an experiment with consciousness as the independent variable and everything else held as constant as possible.
The results of this method are very satisfying. Contrastive analysis makes it possible, for example, to take Pavlov's findings about the Orienting Response (OR), the massive wave of activity that affects all parts of the nervous system when we encounter a novel situation. We can contrast our conscious experience of a stimulus that elicits an OR to our unconscious representation of the same stimulus after the OR has become habituated due to repetition of the stimulus (Sokolov, 1963; see Chapters 1 and 5). Now we can ask: what îisï the difference between the conscious and the unconscious representation of this stimulus? After all, the physical stimulus is the same, the inferred stimulus representation is the same, and the organism itself is still much the same: but in the first case the stimulus is conscious, while in the second it is not. In this way we focus on the îdifferential implicationsï of conscious experience in other?wise very similar circumstances. It makes not a bit of difference that Pavlov was a devout physicalist, who felt that a scientific treatment of conscious experience was impossible. In time-honored scientific fashion, good data outlast the orientation of the investigators who collected them.
While a number of investigators have discussed contrasts like this, there has been a very unfortunate tendency to focus on the most difficult and problematic cases, rather than the simplest and most revealing ones. For instance, there has been extensive debate about subliminal perception and "blind sight" the kind of brain damage in which people can identify visual stimuli without a sense of being conscious of them. These are important phenomena, but they are methodologically and concept?ually very difficult and controversial. They are very poor sources of evidence at this stage in our understanding. Trying to tackle the most difficult phenomena first is simply destructive of the normal process of science. It leads to confusion and controversy, rather than clarity. When Newton began the modern study of light, he did not begin with the confusing question of wave-particle duality, but with a simple prism and a ray of sunlight. Only by studying simple clear cases first can we begin to build the solid framework within which more complex and debatable questions can be understood. We will adopt this standard scientific strategy here. First we consider the clear contrasts between comparable conscious and unconscious events. Only then will we use the resulting framework to generate ideas about the very difficult boundary questions.
One could easily generate dozens of tables of contrasts, listing hundreds of facts about comparable conscious and uncon?scious phenomena (see Baars, 1986b). In Chapter 1 we survey some of the contrastive pairs of facts that invite such an analysis. However, in our theoretical development, starting in Chapter 2, we prefer to present only a few simplified tables, summarizing many observations in a few statements. Others might like to arrange the data differently, to suggest different theoretical consequences. The reader may find it interesting to build a model as we go along, based on the contrastive facts laid out through?out the book.
îThe use of cumulative empirical constraints.ï
While a great deal of research must still be done to resolve numerous specific issues, many useful things can already be said about the picture as a whole. Integrative theory can be based on "cumulative constraints." This is rather different from the usual method of inquiry in psychology, which involves a careful investigation of precise îlocalï evidence. Let me illustrate the difference.
Suppose we are given four hints about an unknown word.
1. It is something to eat. 2. One a day keeps the doctor away. 3.It is as American as Mom's unspecified pie. 4. It grows in an orchard.
One way to proceed is to take each hint in isolation, and investigate it carefully. For "growing in an orchard," we may survey orchards to define the probability of peaches, pears, plums, cherries and apples. That is a îlocal, increasingly preciseï approach. Another approach is to accept that by itself each hint may only partly constrain the answer, and to use the set of hints as a whole to support the best guess. After all, there are many things to eat. The doctor could be kept away by a daily aspirin,‹h______‹ or by bubonic plague, or by regular exercise. Mom îcouldï bake blueberry pie. And many fruits grow in an orchard. But "growing in an orchard" îplusï "one a day keeps the doctor a way" eliminates bubonic plague and regular exercise. Each hint is locally incomplete. But taken together, the combination of locally incomplete facts help to support a single, highly probable answer for the whole puzzle.
Scientific psychologists are trained to perform local, increasingly precise investigations. This has the advantage of producing more and more accurate information, though sometimes about smaller and smaller pieces of the puzzle. Alternatively, we could use all the local sources of evidence îtogetherï, to constrain global hypotheses. Of course, global models should make novel local predictions. But sometimes we can develop a compel?ling global picture, even if some of the local evidence is still missing.
The two methods are complementary. In this book we will largely pursue the second, global method.
îA suggestion to the reader.ï
This book is in the nature of a scouting expedition, exploring a territory that is not exactly unknown, but at least uncharted by modern psychologists. After a self-imposed absence of many decades the psychological community seems poised to explore this territory once again. In that process it will no doubt probe both the evidence and the theoretical issues in great detail. This work aims to produce a preliminary map to the territory. We try here to cover as much ground as possible, in reasonable detail, to make explicit our current knowledge, and to define gaps therein.
There are two ways to read this book. First, you can take it at face value, as a theory of conscious experience. This entails some work. Though I have tried very hard to make the theory as clear and understandable as possible, the job of understanding each hypothesis, the evidence îproï and îconï, and its relation to the rest of the theory will take some effort. An easier way is to take the theory as one way of organizing what we know today about conscious experience --- a vast amount of evidence. (I believe this book considers nearly all the major cognitive and neuroscientific findings about conscious and unconscious process?es.) Rather than testing each hypothesis, the theory can be taken as a convenient "as if" framework for understanding this great literature. ‹h______‹å The second approach is easier than the first, and may be better for students or for the general reader. Graduate students, professional psychologists, and others with a deeper commitment to the issues will no doubt wish to scrutinize the theory with greater care. The Glossary and Guide to Theoretical Claims at the end of the book defines each major concept formally and relates it to the theory as a whole; this may be helpful to those who wish to examine the theory in more detail.
îA brief guide to the book.ï
This book sketches the outlines of a theory of conscious experience. Although it may seem complicated in detail, the basic ideas are very simple and can be stated in a paragraph or two. In essence, we develop only a single theoretical metaphor: a îpublicity metaphorï of consciousness, suggesting that there is a "global workspace" system underlying conscious experience. The global workspace is the publicity organ of the nervous system; its contents, which correspond roughly to conscious experience, are distributed widely throughout the system. This makes sense if we think of the brain as a vast collection of specialized automatic processors, some of them nested and organized within other processors. Processors can compete or cooperate to gain access to the global workspace underlying consciousness, enabling‹h______‹ them to send global messages to any other interested systems. Any conscious experience emerges from cooperation and competition between many different input processors. One consequence of this is that a global message must be îinternally consistentï, or else it would degrade very rapidly due to internal competition between its components (2.0). Further, conscious experience requires that the îreceiving systemsï be adapting to, matching, or acting to achieve whatever is conveyed in the conscious global message (5.0). Another way of stating this is to say that any conscious message must be globally îinformativeï. But any adaptation to an informative message takes place within a stable but unconscious îcontextï.
Contexts are relatively enduring structures that are unconscious, but that can evoke and be evoked by conscious events (4.0). Conscious contents and unconscious contexts interweave to create a "stream of consciousness" (6.0). The interplay between them is useful in solving a great variety of problems, in which the conscious component is used to access novel sources of information, while unconscious contexts and processors deal with routine details that need not be conscious. Voluntary control of action can be treated as a special kind of problem-solving, with both conscious and unconscious components (7.0). And if we take one plausible meaning of "self" as the îdominant, enduring context of many conscious experiencesï, we may also say that conscious experience provides information to the self-as-context (9.0). This framework seems to unify the great bulk of empirical‹h______‹ evidence in a reasonable way.
There are other ways to think about conscious experience, but these can be seen to follow from the extended publicity metaphor. Properties like selectivity, limited capacity, self- conscious?ness, the ability to report conscious contents, knowledge of the world, reflective consciousness; consciousness as the domain of rationality; consciousness as the "glue" for combining different perceptual features, as the domain of error- correction and trouble-shooting, as a tool for learning; and the relationship between consciousness and novelty, voluntary control, and self ---- all these points are consistent with, and appear to follow from the present framework. The reader can do a quick preview of the entire theory by perusing all the theoretical figures listed in the Index of Tables and Figures.
The global workspace metaphor results in a remarkable simplification of the evidence presented in the conscious- unconscious contrasts. This great simplification provides one cause for confidence in the theory. Further, a number of specif?ic, testable predictions are generated throughout the book. The ultimate fate of the theory depends of course on the success or failure of those predictions.
Where we cannot suggest plausible answers, we will try at least to ask the right questions. We do this throughout by marking îtheoretical choice-pointsï whenever we are forced to choose between equally plausible hypotheses. At these points reasonable people may well disagree. In each case we state arguments for and against the course we ultimately take, with some ideas for testing the alternatives. For example, in Chapter 2 we suggest that perception and imagery --- so-called "qualita?tive" conscious contents --- play a special role as global input that is broadcast very widely. While there is evidence consistent with this proposal, it is not conclusive; therefore we mark a "theoretical choice-point," to indicate a special need for further evidence. It is still useful to explore the implications of this idea, and we do so with the proviso that further facts may force a retreat to a previous decision point.
No theory at this stage can expect to be definitive. But we do not treat theory here as a once-and-for-all description of reality. Theories are tools for thinking, and like other tools, they tend sooner or later to be surpassed.
îThe need to understand conscious experience.ï
Imagine the enterprise of scientific psychology as a great effort to solve a jig-saw puzzle as big as a football field. Several communities of researchers have been working for decades on the job of finding the missing pieces in the puzzle, and in‹h______‹ recent years many gaps have been filled. However, one central missing piece --- the issue of conscious experience --- has been thought to be so difficult that many researchers have sensibly avoided that part of the puzzle. Yet the gap left by this great central piece has not gone away, and surrounding it are numerous issues that cannot be solved until it is addressed. If that is a reasonable analogy, it follows that the more pieces of the jig-saw puzzle we discover, the more the remaining uncertainties will tend to cluster about the great central gap where the missing piece must fit. The more we learn while continuing to circumvent conscious experience, the more it will be true that the remaining unanswered questions require an understanding of consciousness for their solution.
Certainly not everyone will agree with our method, conclu?sions, theoretical metaphor, or ways of stating the evidence. Good theory thrives on reasoned dissent, and the ideas developed in this book will no doubt change in the face of new evidence and further thought. We can hope to focus and define the issues in a way that is empirically responsible, and to help scotch the notion that conscious experience is something psychology can safely avoid or disregard. No scientific effort comes with a guarantee of success. But if, as the history suggests, we must choose in psychology between trying to understand conscious experience and trying to avoid it, we can in our view but try to understand.
îAcknowledgementsï
Explicit development of this theory began in 1978. Since then a number of psychologists and neuroscientists have provided valuable input, both encouraging and critical. Among these are Donald A. Norman, David Galin, George Mandler, Michael Wapner, Benjamin Libet, Anthony Marcel, James Reason, Donald G. MacKay, Donald E. Broadbent, Paul Rozin, Richard Davidson, Ray Jacken?doff, Wallace Chafe, Thomas Natsoulas, Peter S. White, Matthew Erdelyi, Arthur Reber, Jerome L. Singer, Theodore Melnechuk, Stephen Grossberg, Mardi J. Horowitz, David Spiegel, James Greeno, Jonathan Cohen, and Diane Kramer. I am especially grateful to Donald Norman, David Galin, and Mardi J. Horowitz for their open-minded and encouraging attitude, which was at times sorely needed.
I am grateful for support received as a Cognitive Science Fellow at the University of California, San Diego, funded by the Alfred P. Sloan Foundation, in 1979-80; and for a Visiting Scientist appointment in 1985-6 at the Program for Conscious and Unconscious Mental Processes, Langley Porter Neuropsychiatric Institute, University of California, San Francisco, supported by the John D. and Catherine T. MacArthur Foundation, and directed by Mardi J. Horowitz. The MacArthur Foundation is to be commended‹h______‹ for its thoughtful and historically significant decision to support research on conscious and unconscious functions. Finally, the Wright Institute and its President, Peter Dybwad, were extremely helpful in the final stages of this work.
The editorial board of Cambridge University Press showed rare intellectual courage in accepting this book for its distinguished list at a time when the theory was largely unknown. I think that is admirable, and I trust that the result justifies their confidence.
Bernard J. Baars January, 1987 The Wright Institute Berkeley, California
Chapter One
What is to be explained? Some preliminaries.
The study ... of the îdistributionï of consciousness shows it to be exactly such as we might expect in an organ added for the sake of steering a nervous system grown too complex to regulate itself.
--- William James (1890)
1.0 Introduction.
1.1 Some history and a look ahead.
1.11 The rejection of conscious experience: Behaviorism and the positivist philosophy of science. 1.12 Empirical evidence about conscious experience: clear cases and fuzzy cases. 1.13 Modern theoretical languages are neutral with respect to consciousness.
1.2 What is to be explained? A first definition of the topic.
1.21 Objective criteria for conscious experience. 1.22 Contrastive analysis to focus on conscious experience îas suchï. 1.23 Using multiple contrasts to constrain theory. 1.24 Examples of the method: perception and imagery. 1.25 Are abstract concepts conscious? 1.26 Some possible difficulties with this approach. 1.27 ... but is it îreallyï consciousness?
1.3 Some attempts to understand conscious experience. 1.31 Four common hypotheses. 1.32 Current models. 1.34 Limited capacity: Selective attention, dual tasks, and short term memory. 1.35 The Mind's Eye. 1.36 Cognitive architectures: distributed systems with limited capacity channels. 1.37 The Global Workspace (GW) approach attempts to combine all viable metaphors into a single theory.
1.4 Unconscious specialized processors: A gathering consensus. 1.41 There are many unconscious representations. 1.42 There are many unconscious specialized processors. 1.43 Neurophysiological evidence. 1.44 Psychological evidence. 1.45 General properties of specialized processors.
1.5 Some common themes in this book. 1.51 The role of unconscious specialists. 1.52 Conscious experience reflects the operation of an underlying limited-capacity system. 1.53 Every conscious event is shaped by enduring unconscious systems which we will call "contexts". 1.54 Conscious îpercepts and imagesï are different from conscious îconceptsï. 1.55 Are there fleeting "conscious" events that are difficult to report, but that have observable effects?
1.6 The course of theory development in this book.
1.0 Introduction.
Chances are that not many hours ago, you, the reader, woke up from what we trust was a good night's sleep. Almost certainly you experienced the act of waking up as a discreet beginning of something new, something richly detailed, recallable and reportable, something that was not happening even a few minutes before. In the same way we remember going to sleep as an îendï to our ability to experience and describe the world. The world this morning seemed different from last night --- the sun was out, the weather had changed, one's body felt more rested. Hours must have passed, things must have happened without our knowledge. "We were not conscious," we say, as if that explains it.
At this moment you can probably bring to mind an image of this morning's breakfast. It is a conscious image --- we can experience again, though fleetingly, the color of the orange juice, the smell of hot coffee, the taste and texture of corn flakes. Where were those images just before we made them conscious? "They were unconscious", we say, or "in memory", as if that explains it.
At this instant you, the reader, are surely conscious of some aspects of the act of reading --- the color and texture of this page, and perhaps the inner sound of îthese wordsï. Further, you can become conscious of certain beliefs --- a belief in the existence of mathematics, for example --- although beliefs do not consist of sensory qualities in the same way that orange juice has taste, or the way a mental image of corn flakes recreates the experience of a certain crunchy texture. In contrast to your conscious experiences, you are probably înotï conscious of the feeling of your chair in this instant; nor of a certain background taste in your mouth; of that monotonous background noise; of the sound of music or talking in the background; of the complex syntactic processes needed to understand this phrase; of your intentions regarding a friend; of the multiple meanings of ambiguous words, as in îthis caseï; of your eye movements; of the complex vestibular processes that are keeping you oriented to gravity; of your ability to drive a car. Even though you are not currently conscious of them, there is a great deal of evidence to support the idea that all of these unconscious events are being represented and actively processed in your nervous system.
The fact that we can predict all these things with considerable confidence indicates that conscious experience is something knowable, at least in its boundaries. But what does it mean that at this moment îthisï event is likely to be conscious, and îthatï one unconscious? What role does the distinction between conscious and unconscious events play in the running of the nervous system? That is the central question explored in this‹j______‹ book. Asking the question this way allows us to use the very large empirical literature on these matters, to constrain theory with numerous reliable facts. A small set of ideas can explain many of these facts. These ideas are consistent both with modern cognitive theory, and also with many traditional notions about consciousness. We briefly review some of these traditional ideas now.
1.1 Some history and a look ahead.
Consciousness seems so obvious in its daily manifestations, yet so puzzling on closer examination. In several millenia of recorded human thought it has been viewed variously, --- as a fact that poses fundamental questions about the nature of reality; --- as the natural focus for scientific psychology; --- as a topic which psychology must îavoidï at all cost; --- as a non-existent or "epiphenomenal" by-product of brain functioning; --- and finally, as an important unsolved problem for psychology and neuroscience.
Consciousness has had its ups and downs with a vengeance, especially in the last hundred years. Even today, more sense and more nonsense is spoken of consciousness, probably, than of any other aspect of human functioning. The great problem we face here is how to tip the balance in favor of sense, and against nonsense.
In thinking about conscious experience we are entering a stream of ideas that goes back to the earliest known writings. Any complete account of human thought about human experience must include the great technical literatures of Vedanta Hinduism, Buddhism, and Taoism; but it must also include European philosophy from Plato to Jean-Paul Sartre, as well as the various strands of mystical thought in the West. Indeed, the history of ideas in all developed cultures is closely intertwined with ideas of perception, knowledge, memory, imagination, and the like, all involving conscious experience in different ways. We cannot trace this fascinating story here in detail. Our main purpose is not to interpret the great historical literature, but to develop a îtheoryï that will simplify our understanding of conscious experience, just as any good theory simplifies its subject matter. But we will very briefly set the historical context.
When scientific psychology began in the 19th century it was intensely preoccupied with consciousness. By contrast, the 20th century so far has been remarkable for its rejection of the whole topic as "unscientific". Some psychologists in this century have even argued that conscious experience does not exist, a view that‹j______‹ has never been seriously held before, in the long history of human thought. Nevertheless, many of these same radical skeptics have uncovered evidence that is directly relevant to the understanding of conscious experience. Though their findings are often described in ways that avoid the word "consciousness," their evidence stands, no matter what we call it. We shall find this evidence very useful.
Usually when we wish to study something --- a rock, a chemical reaction, or the actions of a friend --- we begin with simple observation. But conscious experience is difficult to observe in a straightforward way. We cannot observe someone else's experience directly, nor can we study our own experience in the way we might study a rock or a plant. One great problem seems to be this: Conscious experience is hard to study because we cannot easily stand îoutsideï of it, to observe the effects of its presence and absence. But generally in science, we gain knowledge about any event by comparing its presence and absence; that is after all what the experimental method is about. If we try to vary the degree of our own consciousness --- between waking, drowsiness, and sleep, for example --- we immediately lose our ability to observe. How do you observe the coming and going of your own consciousness? It seems futile, like a dog chasing its own tail. There is a vicious circle in attempting to observe conscious experience, one that hobbles the whole history of scientific attempts to understand consciousness.
The difficulty in studying îunconsciousï processes is even more obvious --- by definition, we cannot directly observe them at all. Unconscious processes can only be inferred, based on our own experience and on observation of others. Throughout recorded history, individual thinkers have held that much more goes on unconsciously than common sense would have us believe, but this realization did not catch on very widely until the middle of the 19th century, and then only in the face of much resistance (Ellenberger, 1970). Acknowledging the power of unconscious processes means giving up some of our sense of control over ourselves, a difficult thing to do for many people.
In sum, throughout recorded history it has been remarkably difficult for philosophers and scientists to study and talk sensibly about îeitherï conscious îorï unconscious events. Even as scientific psychology was being founded in the 19th century, psychologists became caught up in these difficulties. Such early luminaries as Wilhelm Wundt and William James îdefinedï psychology as the quest for the understanding of conscious experience. William James, the preeminent American psychologist of the 19th century, is still an extraordinary source of insight into conscious functioning, and we will quote him throughout this book. But James must be treated with great caution, because of his strong philosophical preconceptions. He insisted, for example, that all psychological facts must ultimately be îreducedï to conscious experiences. For James, conscious experience, one of the most puzzling phenomena in psychology, was to be the‹j______‹ foundation for a scientific psychology. But building on a foundation that is itself puzzling and badly understood is a recipe for futility --- it undermines the scientific enterprise From the start (Baars, 1986a). James raised a further problem by getting hopelessly entangled in the great foundation problem of psychology, the mind/body problem, which Schopenhauer called "die Weltknoten" --- the "world-knot" (ref. p. in James). At various points in his classic îPrinciples of Psychologyï (1890) James tried to reduce all phenomena to conscious experiences (mentalism), while at others he tried to relate them to brain processes (physicalism); this dual reduction led him to mind/body dualism, much against his will. Conflicting commitments created endless paradoxes for James. In some of his last writings (1904), he even suggests that "consciousness" should be dispensed with altogether, though momentary conscious îexperiencesï must be retained! And he insistently denied the psychological reality of îunïconscious processes. These different claims are so incompatible with each other as to rule out a clear and simple foundation for psychological science. Thus many psychologists found James to be a great source of confusion, for all his undoubted greatness. And James himself felt confused. By 1893(?) he was writing in despair, "The real in psychics seems to "correspond" to the unreal in physics, and îvice versaï; and we are sorely perplexed" (p. 460).
Toward the end of the 19th century other scientific thinkers --- notably Pierre Janet and Sigmund Freud --- began to infer unconscious processes quite freely, based on observable events such as post-hypnotic suggestion, conversion hysteria, multiple personality, slips of the tongue, motivated forgetting, and the like. Freud's insights have achieved extraordinary cultural influence (Ellenberger, 1970; Erdelyi, 1985). Indeed the art, literature, and philosophy of our time is utterly incomprehensible without his ideas and those of his opponents like Jung and Adler. But Freud had curiously little impact on scientific psychology, in part because his demonstrations of unconscious influences could not be brought easily into the laboratory --- his evidence was too complex, too rich, too idiosyncratic and evanescent for the infant science of psychology to digest.
1.11 The rejection of conscious experience: Behaviorism and the positivist philosophy of science.
The controversy and confusion surrounding consciousness helped lead to the behavioristic revolution, starting about 1913. Behaviorism utterly denied that conscious experience was a legitimate scientific subject, but it promised at least a‹j______‹ consistent physicalistic basis on which psychology could build. For some radical behaviorists the existence of consciousness was a paradox, an epiphenomenon, or even a threat to a scientific psychology: "Consciousness", wrote John Watson in 1925, "is nothing but the soul of theology" (p. 3; viz., Baars, 1986a). Watson's behaviorism quickly achieved remarkable popularity. In various forms this philosophy of science held a dominant position in American universities until very recently.
But physicalistic psychology was not limited to America. Similar philosophies became dominant in other countries, under different labels. In Russia, Pavlov and Bekhterev espoused a physicalistic psychophysiology, and in England and parts of the European continent, the positivist philosophy of science had much the same impact. Thus at the beginning of the 20th century many psychologists rejected consciousness as a viable topic for psychology. Naturally they rejected îunïconscious processes as well --- if one cannot speak of conscious phenomena, one cannot recognize unconscious ones either.
The conventional view is that 19th century psychology was rejected by behaviorists and others because it was unreliable and subjectivist, because it was mired in fruitless controversy, and because it was unscientific. However, modern historical research has cast doubt on this view in all respects (Blumenthal, 1979, 1984; Danziger, 1979; Baars, 1986a). It now appears that psychologists like Wilhelm Wundt used objective measures most of the time, and employed introspection only rarely. Even a cursory reading of James' great text (1890) indicates how many "modern" empirical phenomena he knew. Numerous important and reliable effects were discovered in the 19th century, and many of these have been rediscovered since the passing of behaviorism: basic phenomena like selective attention, the capacity limits of short term memory, mental imagery, context effects in comprehension, and the like. Major controversies occurred, as they do today, but primarily about two topics which we must also address in this book: (1) the evidence for imageless thought, indicating that much "intelligent" processing goes on unconsciously (e.g. Woodworth, 1915), and (2) the question whether there is such a thing as a conscious command in the control of action (James, 1890/1980, p. ; Baars, 1986b; viz., Ch. 7). But these were important, substantive controversies, not mere metaphysical argumentation. They were perhaps unsolvable at the time because of conceptual difficulties faced by the late 19th century, some of which have been resolved today. These include the difficulties encountered by William James with unconscious processes and mentalistic reductionism.
As for introspection itself --- reports of conscious experience, sometimes by trained observers --- it is used almost universally in contemporary psychology, in studies of perception, imagery, attention, memory, explicit problem-solving, and the like (e.g. Stevens, 1966; Kosslyn, 1980; Ericsson & Simon, 1984). No doubt methodological improvements have been made, but the‹j______‹ basic technique of asking subjects, "What did you just perceive, think, or remember?" is extremely widespread. We do not call it "introspection," and we often avoid thinking that subjects in experiments answer our questions by consulting their own experience. But surely our subjects themselves think of their task in that way, as we can learn simply by asking them. They may be closer to the truth in that respect than many experimenters who are asking the questions.
In rejecting consciousness as well as the whole psychology of common sense, behaviorists were supported by many philosophers of science. Indeed, philosophers often tried to dictate what was to be genuine psychology and what was not. Ludwig Wittgenstein, in his various phases of development, inveighed against "mentalistic language" --- the language of psychological common sense --- as "a general disease of thinking" (Malcolm, 1967). In his later work he argued against the possibility of a "private language" --- i.e., that people can really know themselves in any way. His fellow philosopher Gilbert Ryle presented very influential arguments against inferred mental entities, which he ridiculed as "ghosts in the machine" and "homunculi." Ryle believed that all mentalistic inferences involved a mixing of incompatible categories, and that their use led to an infinite regress (1949).
From a modern psychological point of view, the problem is that these philosophers made strong empirical claims that are more properly left to science. Whether people can reliably report their own mental processes is an empirical question. Whether inferred mental entities like "consciousness," "thinking" and "feeling" are scientifically useful is a decision that should be left to psychological theory. In fact, there is now extensive evidence that mental images can be reported in very reliable and revealing ways (Cooper & Shepard; Kosslyn; others). Other mental events, like intentions, may be more difficult to report, as we shall see below (6.0, 7.0, 9.0). Similarly, a vast amount of research and theory over the past twenty years indicates that inferred mental entities can be scientifically very useful, as long as they are anchored in specific operational definitions and expressed in explicit theory (e.g. Neisser, 1967; Anderson, 1983; Miller & Johnson-Laird, 1976). Sometimes mentalistic inferences are indeed flawed and circular, as Ryle argued so strongly. But not always. The job is to make scientific inferences properly. If we were to avoid all inference we would lose the power of theory, an indispensible tool in the development of science.
In one way, however, philosophies of science like behaviorism may have advanced the issue --- namely by insisting that all psychological entities could be viewed "from the outside," as objects in a single physical universe of discourse. For some psychologists consciousness could now be treated as a natural phenomenon (to be sure, with a subjective aspect), but basically like any other event in the world. In this light the most significant observations about consciousness may be found in‹j______‹ remarks by two well-known psychologists of the time --- Clark Hull, a neobehaviorist, and Edwin G. Boring, an operationist and the preeminent historian of the period. In 1937 Hull wrote that:
"... to recognize the existence of a phenomenon (i.e. consciousness) is not the same as insisting upon its basic, i.e. logical, priority. Instead of furnishing a means for the solution of problems, consciousness appears to be itself a problem needing solution." (p. 855)
And Boring some years later (1953) summarized his own thinking about introspection by saying that:
"Operational logic, in my opinion ... shows that human consciousness is an inferred construct, a capacity as inferential as any of the other psychological realities, and that literally immediate observation, the introspection that cannot lie, does not exist. All observation is a process that takes time and is subject to error in the course of its occurrence."
This is how we view conscious experience in his book: as a a theoretical construct that can often be inferred from reliable evidence; and as a basic problem needing solution. Within the behavioristic framework it was difficult to build theory, because of resistance to inferred, unobservable constructs. Today, the new cognitive metatheory has overcome this reluctance. The cognitive metatheory encourages psychologists to go beyond raw observations, to infer explanatory entities if the evidence for them is compelling (Baars, 1986a). This is not such a mysterious process --- it is what human beings are always doing in trying to understand their world. No one has ever publicly observed a wish, a feeling of love or hate, or even a pain in the belly. These are all inferred constructs, which we find useful to understand other people's actions, and sometimes even our own.
It cannot be overemphasized that such inferences are not unique to psychology. All sciences make inferences that go beyond the observables. The atom was a highly inferential entity in the first century of its existence; so was the gene; so was the vastness of geological time, a necessary assumption for Darwinian theory; and other scientific constructs too numerous to list here. Cognitive psychology applies this commonsensical epistemology in a way that is more explicit and testable than it is in everyday life. In this way, scientific psychologists have once again begun to speak of meaning, thought, imagery, attention, memory, and recently, conscious and unconscious processes --- all inferred concepts that have been tested in careful experiments and stated in increasingly adequate theories.
Our view here is that îbothï conscious and unconscious processes involve inferences from publicly observable data. Thus conscious and unconscious events reside in the same domain of discourse --- the domain of inferred psychological events. From‹j______‹ this perspective William James was wrong to insist that all psychological events must be reduced to conscious experiences, and behaviorists were equally wrong to insist that we cannot talk about consciousness at all. Once we accept a framework in which we simply try to understand the factors underlying the observations in exactly the way geologists try to understand rocks --- that is to say, by making plausible and testable inferences about the underlying causes --- the way becomes much clearer.
Today we may be ready to think about conscious experience without the presuppositional obstacles that have hobbled our predecessors (e.g. Posner, 1978; Mandler, 1975ab; Shallice, 1972). If that is true, we are living at a unique moment in the history of human thought. We may have a better chance to understand human conscious experience now than ever before. Note again --- this is not because we are wiser or harder-working than our predecessors, or even because we have more evidence at our disposal. We may simply be less encumbered by restrictive assumptions that stand in the way of understanding. Many scientific advances occur simply when obstructive assumptions are cleared away (Chapter 5). Such "release from fixedness" is noteworthy in the work of Copernicus and Galileo, Darwin, Freud, and Einstein. While we do not compare our work with theirs, the fact remains that progress can often be made simply by giving up certain presupposed blind spots.
1.12 Empirical evidence about conscious experience: clear cases and fuzzy cases.
There are many clear cases of conscious experience. The reader may be conscious of this page, of images of breakfast, and the like. These clear cases are used universally in psychological research. When we ask a subject in a perception experiment to discriminate between two sounds, or to report on a perceptual illusion, we are asking about his or her conscious experience. Commonsensically this is obvious, and it is clearly what experimental subjects believe. But scientific psychologists rarely acknowledge this universal belief. For example, there is remarkably little discussion of the conscious aspect of perception in the research literature. The multi-volume îHandbook of Perceptionï has only one index reference to consciousness, and that one is purely historical (Carterette & Friedman, 19xx). Nevertheless, reports about the subjects' experiences are used with great reliability and accuracy in psychological research. In addition to so many clear cases, there are many fuzzy cases where it may be quite difficult to decide whether some psychological event is conscious or not. There may be fleeting‹j______‹ "flashes" of conscious experience that are difficult to report, as William James believed. There are peripheral "fringe" experiences that may occur while we are focused on something else. Early psychologists reported that abtract concepts have fleeting conscious images associated with them (Woodworth, 1915), and indeed the writings of highly creative people like Mozart and Einstein express this idea. Such examples are much more difficult to verify as conscious than the clear cases discussed above.
îThe zero©point problem.ï
This kind of uncertainty sometimes leads to seemingly endless controversy. For example, there is much debate about whether subliminal perceptual input is conscious or not (Marcel, 1983ab, Cheesman & Merikle, 1984; Holender, 1986). Likewise there is great argument about the evidence for "blind sight", where patients with occipital damage can name objects which they claim not to experience (Weisskrantz, 1980; Natsoulas, 1982a; Holender, 1986). It is regrettable that so much current thinking about consciousness revolves around this "zero©point problem," which may be methodologically quite beyond us today. Progress in most scientific research comes from first looking at the easy, obvious cases. Only later, using knowledge gained from the clear cases, can one resolve the truly difficult questions. Newton first used prisms to analyze light; only later was his analysis extended to difficult cases like color filters and the wave©particle issue. If Newton had begun with these difficult cases, he would never have made his discoveries about light. In science, as in law, hard cases make bad law.
In this book we will make an effort to build on clear cases of conscious and unconscious processes. We will try to circumvent the "zero point problem" as much as possible (e.g. 5.7). We use a "high criterion" for consciousness: We want people to report a conscious experience that is independently verifiable. Ordinary conscious perception obviously fits this definition, but it also includes such things as the conscious aspects of mental images, when these can be verified independently. On the unconscious side, we also set a high criterion: unconscious processes must be inferrable on the basis of strong, reliable evidence, and they must înotï be voluntarily reportable even under the optimum conditions (Ericsson & Simon, 1984). Syntactic processing provides a strong example of such a clearly unconscious event. Even professional linguists who study syntax every working day do not claim to have conscious access to their own syntactic processes.
Between these clear cases of conscious and unconscious events there is a vast range of intermediate cases (Figure 1.11). In this book we start with clear cases of conscious and unconscious events, seek a plausible theory to explain them, and then use this theoretical scaffolding to decide some of the fuzzier cases. But we will start simply.
We began this chapter with some claims about the reader's own experience. The reader is momentarily conscious of most words in the act of reading, but at the same time competing streams of potentially conscious information are likely to be unconscious (or barely conscious); syntactic processes are unconscious; most conceptual presuppositions are unconscious (Chapter 4); habituated stimuli are unconscious; imageable memories, as of this book's cover, can be momentarily conscious, but are currently unconscious; and so on. These inferences are supported by a great deal of solid, reliable evidence. Such clear cases suggest that we can indeed speak truthfully about some conscious and unconscious events.
1.13 Modern theoretical languages are neutral with respect to conscious experience.
Current theories speak of information processing, representation, adaptation, transformation, storage, retrieval, activation, and the like, without assuming that these are necessarily conscious events. This may seem obvious today, but it is actually a painfully achieved historic insight into the right way to do psychological theory (Baars, 1986a). William James, as noted above, felt strongly that all psychological events must be reducible to conscious experiences, while the behaviorists denied the relevance of either consciousness or unconsciousness. Either position makes it impossible to compare similar conscious and unconscious events, and to ask the question, "Precisely what is the difference between them?" Because it is neutral with respect to conscious experience, the language of information processing gives us the freedom to talk about inferred mental processes as either conscious or unconscious. This is a giant step toward clarity on the issues.
1.2 What is to be explained? A first definition of the topic.
What is a theory of consciousness a theory of? In the first instance, as far as we are concerned, it is a theory of the nature of experience. The reader's private experience of îthisï word, his or her mental image of yesterday's breakfast, or the‹j______‹ feeling of a toothache --- these are all contents of consciousness. These experiences are all îperceptualï and îimaginalï. (In this book we will use the word "imaginal" to mean internally generated quasi-perceptual experiences, including visual and auditory images, inner speech, bodily feelings, and the like.)
For present purposes we will also speak of îabstract but immediately expressible conceptsï as conscious --- including our currently expressible beliefs, intentions, meanings, knowledge, and expectations. Notice that these abstract concepts are experienced differently from perceptual and imaginal events (Natsoulas, 1978a; Baars, 1986b, and throughout this book). Abstract concepts do not have the same rich, clear, consistent qualities that we find in the visual experience of this book: no color, texture, warmth, size, location, clear beginning and ending, etc. Perceptual and imaginal experiences are characterized by such qualities. Conceptual events are not. In contrast to qualitative conscious îexperiencesï we will sometimes refer to abstract conceptual events in terms of conscious îaccessï.
This issue is closely related to the question of îfocalï vs. îperipheralï consciousness. The reader right now is conscious of îthese wordsï. But much ancillary information is immediately available, as if it exists vaguely in some periphery of awareness. Some of it is in short-term memory and can be immediately brought to mind (1.x). Some of it is in the sensory periphery, like a kind of background noise. And some of it may consist of ideas that are always readily available, such as one's ability to stand up and walk to the next room. Again, it is probably better to think about peripheral events in terms of immediate conscious îaccessï, rather than prototypical conscious îexperienceï.
Common sense calls both qualitative experiences and non- qualitative concepts conscious. Similarly, common sense may call both focal and peripheral events conscious. For the time being we will follow this usage îifï the events in question meet our operational criteria, discussed below. A complete theory must explain both the similarities îandï differences between these reports. Later in this book we will also explore the notion of îconscious controlï, as a plausible way of thinking about volition (7.0).
In reality, of course, every task people engage in involves all three elements: conscious experience, access, and control. Ultimately we cannot understand the role of consciousness if we do not explore all three. However, one can make the case that conscious qualitative experience is fundamental to the understanding of the other aspects and uses of consciousness. Thus in this book we first address the puzzle of conscious experience (Chapters 2 and 3), then explore conscious access (Chapters 4 and 5), proceed to conscious control (Chapters 6 and 7), and finally consider the integrated functioning of all three‹j______‹ elements (Chapters 8, 9 and 10).
The first order of business, then, is to find a usable objective criterion for the existence of a conscious event. When would any reasonable person agree that someone just had some experience? What is reliable objective evidence that a person just saw a banana, felt a sharp toothache, remembered the beauty of a flower, or experienced a new insight into the nature of conscious experience?
1.21 Objective criteria: Gaining access to the phenomena.
In the course of this book we will often appeal to the reader's personal experience, but only for the sake of illustration. From a scientific point of view, all evidence can be stated in entirely objective terms. We can define a useful (though not perfect) objective criterion for conscious events. There may be arguments against this first operational definition, but it marks out a clear domain which almost everyone would consider conscious. Within this domain we can proceed with theory construction, and then consider more difficult cases.
For now, we will consider people to be conscious of an event if (1) they can say immediately afterwards that they were conscious of it îandï (2) we can independently verify the accuracy of their report. If people tell us that they experience a banana when we present them with a banana but not with an apple, we are satisfied to suppose that they are indeed conscious of the banana. îAccurate, immediate consciousness reportï is in fact the most commonly used criterion today. It is exactly what we obtain already in so many psychological experiments.
It is important not to confuse a useful operational definition with the reality of conscious experience. Surely many claimed experiences are not conveniently verifiable ©©© dreams, idiosyncratic images, subtle feelings, etc. But this is not necessary for our purpose, since we can rely upon the many thousands of experiences of all kinds that can indeed be verified. In the usual scientific fashion, we are deliberately setting a high criterion for our observations. We prefer to risk the error of doubting the existence of a conscious experience when it is actually there, rather than the opposite error of assuming its existence when it is not there.
For example, in the well-known experiment by Sperling (1960), subjects are shown a 3x3 grid of letters or numbers for a fraction of a second. Observers typically claim that they can see all the letters, but they can only recall three or four of them. Thus they pass the "consciousness report" criterion suggested‹j______‹ above, but they fail by the accuracy criterion. However, it is troubling that subjects --- and experimenters serving as subjects --- continue to insist that they are momentarily conscious of îallï the elements in the array. Sperling brilliantly found a way for observers to reveal their knowledge objectively, by asking them îafterï the exposure to report îanyï randomly cued letter. Under these circumstances people can accurately report any arbitrary letter, suggesting that they do indeed have fleeting access to all of them. Since the response cue is only given after the physical information has disappeared, it is clear that the correct information must have come from memory, and not from the physical display. Now we can be quite confident that subjects in the Sperling experiment do have momentary conscious access to all the elements in the visual display. Both the accuracy and the "consciousness report" criterion are satisfied.
The Sperling experiment serves as a reminder that conscious events may decay in a few hundred milliseconds, so that immediate report is often essential (Ericsson & Simon, 1984). Sometimes even very recent events can be hard to recall --- very fleeting ones for example, or novel stimuli that cannot be "chunked" into a single experience, or stimuli that are followed by distraction or surprise. Indeed, the very act of retrieving and reporting recent material may interfere with accurate recall. But in general, recent events make for the best consciousness reports.
There are many ways to verify the accuracy of report. In perception, psychophysics, and memory experiments, we can check the stimulus directly. Studies of mental imagery typically look for internal consistency. For example, the well-known experiments by Shepard and Cooper (1973) show that in rotating mental images, the time of rotation is a highly predictable linear function of the degree of rotation. This very precise result helps validate the subjects' claim that they are indeed representing the rotating image mentally. Studies of explicit problem solving typically look for accuracy of results, subgoals, timing, and characteristic errors (Ericsson & Simon, 1984). And so on. Notice by the way that accuracy does not guarantee consciousness by itself. Aspects of mental rotation may not be conscious, for instance. Likewise, reports of a conscious experience do not guarantee that it has actually occurred. There is much evidence that people sometimes manufacture memories, images, perceptual experiences, and intentions that are demonstrably false (e.g., Nisbett & Wilson, 1977). This is why we set the criterion of îbothï the report of a conscious experience îandï accuracy.
Notice that saying "I just experienced a banana" is a metacognitive act --- it is a report îaboutï a previous mental event. Consciousness no doubt exists even without this kind of‹j______‹ metacognition --- it surely continues if we do not report it afterwards, even to ourselves. In states of deep absorption in a novel or a film, or in hypnosis, people may not be able to reflect on their experiences without disrupting the absorbed state (7.x), but they are quite conscious all the same. This suggests that there may be more direct ways of assessing conscious experience than the operational definition we advance here. In fact, as we discover more evidence that correlates with this definition, better operational criteria will no doubt emerge. If we find that people who are conscious by the "accurate report" criterion also have excellent recognition memory for the experience, we may "bootstrap" upward, and "accurate recognition memory" may then supersede accurate report. Or someone might discover a neural event that correlates infallibly with conscious experience, defined by accurate consciousness report; the neural event may also work when people cannot report their experience. Over time, as confidence grows in this measure, it may begin to supersede the current definition. But for now, "accurate, immediate consciousness report" is still the most obviously valid criterion.
Our first operational definition extends beyond perceptual events to purely mental images, bodily feelings, inner speech, and the like, when people can give accurate reports of having been conscious of such events. These kinds of conscious events are often called "qualitative conscious contents," because they have qualities like color, weight, taste, location in space and time, etc. In addition to qualitative conscious events, people talk about other mental contents as "conscious" if they are immediately available and expressable. Thus people can give accurate reports about their current beliefs, ideas, intentions, and expectations: But these things do not have qualities like taste or texture or color. Ideas like democracy or mathematics, a belief in another person's good intentions, and the like --- these events are non-qualitative or abstract. Nevertheless, they can in principle satisfy our operational definition, and certainly in the common meaning of "consciousness" we speak often of our conscious beliefs, ideas, and intentions. The relationship between qualitative and non-qualitative conscious contents will be a running theme in this book. Chapter 7 suggests a resolution of this problem.
Note that accurate, immediate consciousness report takes for granted a whole cognitive apparatus that any complete theory must explain. For example, it presupposes the ability to act voluntarily; this is closely related to conscious experience (see Chapter 7). Further, any theory must eventually give a principled account of the operational definitions that led to it in the first place. In the beginning we can choose measures simply because they seem plausible and useful. But eventually, in the spiraling interplay of measure and theory, we must also explain them. ‹j______‹å
1.22 Contrastive analysis to focus on conscious experiences îas such.ï
We will focus on the notion of consciousness îas suchï by contrasting pairs of similar events, where one is conscious but the other is not. The reader's conscious image of this morning's breakfast can be contrasted with the same information when it was still in memory, and unconscious. What is the difference between conscious and unconscious representations of the same thing? Similarly, what is the difference between the reader's experience of his or her chair immediately after sitting down, and the current habituated representation of the feeling of the chair? What is the difference between the meaning conveyed by this sentence, and the same meaning in memory, and therefore not currently available? Or between currently accessible ideas and the presupposed knowledge that is necessary to understand those ideas, but which is not currently available? All these cases involve contrasts between closely comparable conscious and unconscious events.
These contrasts are like experiments, in the sense that we vary one thing --- conscious experience of or access to the event --- and try to hold everything else constant. And indeed many experiments of this type have been published. In studies on selective attention, on subliminal perception, and on automaticity, similar conscious and unconscious events are routinely compared (e.g. MacKay, 1973, Libet, 1978; Marcel, 1983a; Sokolov, 1963; Shiffrin & Schneider, 1977). If contrastive analysis is just like doing an experiment, what is the difference between it and any perceptual experiment? It lies only in what is being compared. In perceptual experiments we might compare a 20 decibel sound to a 30 decibel sound, both of them conscious events. But in contrastive analysis, we compare two mental representations, one of a 30 decibel sound before habituation (which is conscious) to the mental representation of the same sound after habituation, when it is unconscious (1.xx, Sokolov, 1963). Contrastive analysis allows us to observe the difference between the presence and absence of conscious experiences "from the outside." We can do this through reliable inferences from observed behavior to some inferred mental event, which may be inferrable even when the subject's experience of it is lost.
1.23 Using multiple contrasts to constrain theory.
This book is concerned with "cumulative constraints" on conscious experience (Posner, 1982). As we noted in the Preface, we can look to multiple domains of evidence, so that strengths in one domain may compensate for weaknesses in another. A great deal of empirical work is required before the hypotheses advanced in this book can be considered solid. But the power of theory is precisely to make inferences about the unknown, based on what is known. As Broadbent (1958) has noted,
"The proper road for progress ... is to set up theories whch are not at first detailed, although they are capable of disproof. As research advances the theory will become continually more detailed, until one reaches the stage at which further advance is made by giving exact values ... previously left unspecified in equations whose general form was known." (Quoted by Posner, 1982, p. 168)
Our approach in this book is integrative and global rather than local. We will also find a strong convergence between the "system architecture" suggested in this book and other current cognitive theories, even though the evidence we consider is quite different (e.g. Anderson, Newell, Norman & Shallice, Reason.). This is encouraging.
1.24 Some examples of the method: perception and imagery.
îPerception as conscious stimulus representation.ï
Perception is surely the most richly detailed domain of conscious experience. In perceptual research we are always asking people what they experience, or how one experience compares to another. And we always check the accuracy of those reports. Thus research in perception and psychophysics almost always fits the criterion of "accurate report of consciousness." Someone might argue that perceptual illusions are by definition inaccurate, so that the study of illusions seems to be an exception to the rule (viz. Gregory, 1966). But in fact, even perceptual illusions fit our operational definition of conscious experience: that definition is concerned after all with îaccurate report with respect to the subject's experienceï, not with whether the experience itself matches the external world. We cannot check the accuracy of reported illusions by reference to the external world, but other validity checks are routinely used in the laboratory. Perceptual illusions are highly predictable and stable across subjects. If someone were to claim an utterly‹j______‹ bizarre illusory experience that was not shared by any other observer, that fact would be instantly recognized. For such an idiosyncratic illusory experience we would indeed be in trouble with our operational definition. Fortunately, there are so many examples of highly reliable perceptual reports that we can simply ignore the fuzzy borderline issues, and focus on the clear cases.
Now we can apply a contrastive analysis to perceptual events. We can treat perception as input representation (e.g. Rock, 1982; Lindsay & Norman, 1977; Marr, 1982), and contrast perceptual representations to stimulus representations that are not conscious. Table 1.24a shows these contrasts. There is evidence suggesting that "unattended" streams of information are processed and represented even though they are not conscious (e.g. MacKay, 1973; but see Holender, 1986). Further, habituated perceptual events --- those to which we have become accustomed --- apparently continue to be represented in the nervous system (Sokolov, 1963; see section 1.xx). There is evidence that perceptual events are processed for some time before they become conscious, so that there are apparently unconscious input representations (Libet, 1978; Neisser, 1967). Then there are numerous ambiguities in perception, which involve two ways of structuring the same stimulus. Of these two interpretations, only one is conscious at a time, though there is evidence that the other is also represented (e.g. Swinney, 1979; Tanenhaus, Carlson & Seidenberg, 1985). There is evidence, though somewhat controversial, that visual information that is centrally masked so that it cannot be experienced directly, continues to be represented and processed (Marcel, 1983a; Holender, 1986; Cheesman & Merikle, 1984). And finally, there are many contextual representations and processes that shape a perceptual interpretation, but which are not themselves conscious (see 4.0).
Any theory of the conscious component of perception must somehow explain all of these contrasts. The problem is therefore very strongly bounded. One cannot simply make up a theory to explain one of the contrasts and expect it to explain the others.
-----------------------------------------------------------------------------------------
Table 1.24a ------------------------------------------------------------------------------------------
Contrastive Evidence in Perception.
îConscious Eventsï îComparable Unconscious Eventsï
1. Perceived stimuli 1. Processing of stimuli lacking in intensity or duration, centrally masked stimuli. 2. Pre-perceptual processing. 3. Habituated or automatic stimulus processing. 4. Unaccessed meanings of ambiguous stimuli. 5. Contextual constraints on the interpretation of percepts. 6. Unattended streams of perceptual input.
-----------------------------------------------------------------------------------------
Several psychologists have suggested that perception has a special relationship to consciousness (Wundt, 1912; Freud, 198x; Skinner, 1974; Merleau-Ponty, 1964). This is a theme we will encounter throughout this book. A rough comparison of major input, output, and intermediate systems suggests that consciousness is closely allied with the îinputï side of the nervous system. While perceptual processes are obviously not conscious in detail, the outcome of perception is a very rich domain of information to which we seem to have exquisitely detailed conscious access. By comparison, imagery seems less richly conscious, as are inner speech, bodily feelings, and the like. Action control seems even less conscious --- indeed, many observers have argued that the most obviously conscious components of action consist of feedback from actions performed, and anticipatory images of actions planned. But of course, action feedback is itself perceptual, and imagery is quasi-perceptual (see 1.25 and Chapter 7). The conscious components of action and imagery resemble conscious perception.
Likewise, thought and memory seem to involve fewer conscious details than perception. Even in short term memory we are only conscious of the item that is currently being rehearsed, not of the others; and the conscious rehearsed item in short term memory often has a quasi-perceptual quality. We are clearly not‹j______‹ conscious of information in long term memory or in the semantic, abstract component of memory. In thinking and problem-solving we encounter phenomena like incubation to remind us that the details of problem solving are often carried out unconsciously (Chapter 6). Again, the most obviously conscious components in thinking and memory involve imagery or inner speech --- and these resemble perceptual events. The thoughts that come to mind after incubation often have a perceptual or imaginal quality (John- Steiner, 1986). In sum, when we compare input events (perception and imagery) with output (action) and mediating events (thought and memory), it is the input that seems most clearly conscious in its details. This kind of comparison is very rough indeed, but it does suggest that perception has a special relationship to consciousness (viz., 1.54).
îImagery: Conscious experience of internal events.ï
We can be conscious of images in all sensory modalities, especially vision; of inner speech; and of feelings associated with emotion, anticipatory pleasure, and anticipatory pain. These experiences differ from perception in that they are internally generated. There are now a number of techniques for assessing imagined events that can meet our operational definition of conscious experience, though the imagery literature has been more concerned with accuracy of the imagery reports than with asking whether or not the image was conscious. For example, a famous series of experiments by Shepard and Cooper () shows that people can rotate mental images, and that the time needed for rotation is a linear function of the number of degrees of rotation. This very precise result has been taken as evidence for the accuracy and reliability of mental images. But it is not obvious that subjects in this task are continuously conscious of the image. It is possible that in mentally rotating a chair, we are conscious of the chair at 0, 90, and 180 degrees, and less conscious at other points along the circle (Table 1.2x).
-------------------------------------------------------------------------------------- Table 1.24b -------------------------------------------------------------------------------------- Contrastive Evidence in Imagery. (*)
îConscious Eventsï îComparable Unconscious Eventsï
1. Images retrieved and 1. Unretrieved images in generated in all memory. modalities. 2. New visual images. 2. Automatized visual images. 3. Automatic images that encounter some unexpected difficulty. 4. Inner speech: Currently 4. Currently unrehearsed words rehearsed words in in Short-Term Memory. Short-Term Memory. 5. Automatized inner speech? ----------------------------------------------------------------------------------------- (*) "Images" are broadly defined here to include all quasi- perceptual events occurring in the absence of external stimulation, including inner speech and emotional feelings. --------------------------------------------------------------------------------------
îAssessing the consciousness of mental images.ï
Fortunately researchers in imagery have begun to address the issue of consciousness more directly. Pani (1982) solicited consciousness reports in a verifiable mental imagery task. His results are very systematic, and consistent with historical views of imagery. Pani's subjects were asked to memorize several visual shapes (Figure 1.xx), which were arbitrary, so that previous learning would not be a factor. As shown in Figure 1.3, the test
shapes were designed along a similarity dimension, so that any two adjacent shapes would be relatively similar, while more distant shapes were correspondingly different. Now Pani asked his subjects to perform a discrimination task: They were to keep one shape in mind, and select which of two stimulus figures came closest to the one they had in mind. By making the two visual figures more or less similar to each other, he was also able to vary the difficulty of the task. The more similar the two stimuli were, the more difficult the discrimination.
Imagery reports were collected as a function of practice and‹j______‹ difficulty, and the results were quite clear-cut: The îmoreï practice, the îlessï subjects were conscious of the mental figure. Indeed, consciousness of the imaged figure drops very predictably with practice, even over 18 trials, with a correlation of ©90%. When the discrimination is made more difficult, the mental image tended to come back to consciousness.
Pani's is in many ways a prototype experiment, one we will return to several times. It shows several important things. First, it suggests that even though the mental representation of the figure becomes less consciously available with practice, it continues to be used in the task. Discrimination accuracy did not drop off with practice, even though conscious access did. This result invites a contrastive analysis: after all, some sort of mental representation of the target image continues to exist, whether conscious or not; what is the difference between the conscious image and the unconscious representation? Note also the rapid recovery of the conscious image when difficulty increased. In Chapter 5 we will argue that both fading and recovery of the conscious image can be explained in terms of novelty, informativeness, and predictability. The more predictable the mental representation, the less likely it is to fade; the more novel, informative, and difficult it is, the more likely it is to be conscious.
îThe importance of inner speech.ï
Inner speech is one of the most important modes of experience. Most of us go around the world talking to ourselves, though we may be reluctant to do so out loud. We may be so accustomed to the inner voice that we are no longer aware of its existence "metacognitively", leading to the paradoxic of people asking themselves, "îWhatï inner voice?" But experiments on inner speech show its existence quite objectively and reliably (e.g., Klapp, Greim, & Marshburn, 1981). For several decades Singer and his colleagues have studied inner speech simply by asking people to talk out loud, which they are surprisingly willing to do (e.g. Pope and Singer, 1978). There is good evidence from this work that the inner voice maintains a running commentary about our experiences, feelings, and relationships with others; it comments on past events and helps to make plans for the future (Klinger, 1971). Clinical researchers have trained children to talk to themselves in order to control impulsive behavior (Meichenbaum & Goodman, 1971), and there are many hundreds of experiments in the cognitive literature on verbal Short Term Memory, which is roughly the domain in which we rehearse telephone numbers, consider different ideas, and talk to ourselves generally (e.g. Baddeley, 1976). Thus we actually know a great deal about inner speech, even though much of the evidence may be listed under other headings.
‹j___ Short Term Memory is the domain of rehearsable, usually verbal memory. It has been known since Wundt that people can keep in immediate memory only 7 or so unrelated words, numbers, and even short phrases. If rehearsal is blocked, this number drops to three or four (Peterson & Peterson, 1959). It is quite clear that we are not conscious of everything in conventional Short Term Memory. In rehearsing a telephone number we are qualitatively conscious only of the currently rehearsed item, not of all seven numbers, although all seven are readily available. STM raises not just the issue of conscious experience, but also of voluntary control. We can ask people to rehearse numbers voluntarily, or we can interfere with rehearsal by asking them to do some competing, voluntary task, like counting backward by threes from 100 (Peterson & Peterson, 1959). A complete account of short-term memory must also include this voluntary control component (see Chapter 8).
There is considerable speculation that inner speech may become automatic with practice. Some clinical researchers suggest that people who are depressed may have rehearsed depressive ideation to the point of automaticity, so that they have lost the ability to control the self-denigrating thoughts (e.g., Beck, 1976). While this idea is plausible, I know of no studies that support it directly. This is a significant gap in the scientifc literature. An experiment analogous to Pani's work on visual imagery may be able to provide the missing evidence.
1.25 Are abstract concepts conscious?
Philosophers have noted for many centuries that we are conscious of the perceptual world in ways that differ from our awareness of concepts. Perception has qualities like color, taste, and texture. Concepts like "democracy" or "mathematics" do not. And yet, ordinary language is full of expressions like "I am conscious of his dilemma," "I consciously decided to commit murder" and the like. Abstract beliefs, knowledge, intentions, decisions, and the like, are said to be conscious at times. And certainly our operational definition would allow this: If someone claims to be conscious of a belief in mathematics, and we can verify the accuracy of this claim somehow, it would indeed fit the definition of an "accurate report of being conscious of something." But can we really say that people are conscious of a belief that has no experienced qualities like size, shape, color, or location in time and space?
We will suppose that it is meaningful to be conscious of some abstract concept, although the nature of the relationship between qualitative and non-qualitative experiences will be a theme throughout the book (1.xx). We can point to a number of‹j______‹ contrastive facts about our consciousness of abstract concepts. For example, the reader is probably not conscious right now of the existence of democracy, but if we were to ask whether democracy exists, this abstract fact will probably become consciously available. That is, we can contrast occasions when a concept is in memory but not "conscious" to the times when it is available "consciously." Further, there are reasons to believe that conscious access to concepts becomes less conscious with practice and predictability, just as images become less conscious with practice (5.xx). Thus consciousness of abstract concepts seems to behave much like the conscious experience of percepts and images. We will speak of conscious îexperienceï of percepts and images, and îconscious accessï to abstract concepts, intentions, beliefs, and the like. Chapter 7 will suggest a solution to the problem of the relationship between qualitative experiences and non-qualitative conscious access.
In sum, we can find several contrasts between matched conscious and unconscious events in the realms of perception, imagery and even abstract concepts. These are only two examples of the contrastive analysis method (see Baars, 1986b, for more examples). In the remainder of the book, we perform several others, as follows:
--- In Chapter 2 we contrast the îcapabilitiesï of comparable conscious and unconscious processes; --- in Chapter 3 neural mechanisms involved in îsleep andï î ïîcoma ïare contrasted with those involved in wakefulness and arousal; --- in Chapter 4 we contrast îunconscious contextual factors ï with the conscious experiences they influence. Contextual constraint seems to explain the difference between attended and unattended streams of information as well; --- in Chapter 5, we contrast îhabituated or automaticï events with similar events that are clearly conscious; --- in Chapter 6, we contrast îconscious access to problems and their solutions ïwith "incubation" and many other unconscious problem-solving phenomena; --- in Chapter 7, we extend contrastive analysis to the issue of voluntary control, by comparing îvoluntary ïactions to very similar ones that are îinvoluntary; ï --- in Chapter 8, we compare the îconscious control of attention ïto automatic, unconscious control of attention; --- and finally, in Chapter 9 we contrast îself©ïîattributedï experiences to comparable îself©ïîalienï experiences. Thus we gain a great deal of mileage from contrastive‹j______‹ analysis in this book.
1.26 Some possible difficulties with this approach.
The logic of contrastive analysis is much like the experimental method, and some of the same arguments can be raised against it. In an experiment, if A seems to be a necessary condition for B, we can always question whether A does not disguise some other factor C. This question can be raised about all of the contrasts: What if the contrasts are not minimal: what if something else is involved? What if automatic skills are unconscious because they are coded in a different, procedural format, which cannot be read consciously (Anderson, 1983)? What if subliminal stimulation is unconscious not because the stimulus has low energy, but because the duration of the resulting neural activity is too short? These are all possibilities. In the best of all possible worlds we would run experiments to test all the alternative hypotheses. For the time being, we will rely mainly on the extensive evidence that is already known, and try to account for it with the smallest set of principles that work. But any explanation is open to revision.
1.27 ... but is it really îconsciousnessï?
A skeptical reader may well agree with much of what we have said so far, but still wonder whether we are truly describing conscious experience, or whether, instead, we can only deal with incidental phenomena associated with it. Of course, in a scientific framework one cannot expect to produce some ultimate, incorrigible understanding of "the thing itself." Rather, one can aim for an incremental advance in knowledge. No matter how much we learn about conscious experience, there may always be some irreducible core of "residual subjectivity" (Natsoulas, 1978b). In this connection it is worth reminding ourselves that physicists are still working toward a deeper understanding of gravity, a centerpiece of physical science for almost four hundred years. Yet early developments in the theory of gravity were fundamental, and provided the first necessary steps on the road to current theory. We can work toward a reasonable theory,‹j______‹ but not an ultimate one.
These considerations temper the quest for better understanding. And yet, scientific theories in general claim to îapproachï the "thing itself," at least more so than competing theories. Physics does claim to understand and explain the planetary system, and biology really does seem to be gaining a genuine understanding of the mechanism of inheritance. These topics, too, were considered shocking and controversial in their time. Generally in science, if it looks like a rabbit, acts like a rabbit, and tastes like a rabbit, we are invited to presume that it is indeed îïîïa rabbit. Similarly, if something fits all the empirical constraints one can find on conscious experience, it is likely to be as close to it as we can get at this time. Of course, any claim that the current theory deals with conscious experience îas suchï depends on the reliability, validity, and completeness of the evidence.
It is customary in cognitive psychology to avoid this debate through the use of scientific euphemism like "attention," "perception," "exposure to the stimulus," "verbal report," "strategic control" and the like. These terms have their uses, but they also tend to disguise the real questions. "Strategic control" is a good way to refer to the loss of voluntary control over automatic skills (Shiffrin & Scheider, 1977; Schneider & Shiffrin, 1977). But using this term skirts the question of the connection between conscious experience and voluntary, "conscious" control. Once we label things in terms of conscious experience, this question can no longer be evaded (see Chapter 7). In this book we will find it helpful to call things by their usual names, because that tends to bring up the major issues more directly. None of the current crop of euphemisms for conscious experience conveys precisely what we mean by "conscious experience," either in life, or in this book.
1.3 Some attempts to understand conscious experience.
There is now once more a rising tide of scientific interest in conscious experience. G.A. Miller (1986) has called consciousness one of the three major "constitutive" problems of psychology --- the problems that define psychology as a discipline. It therefore makes sense to take another look at existing efforts to understand the topic. We will briefly review some common explanatory metaphors, explore some current models, and finally sketch the themes that will be developed further in this book. Again, the reader should not become discouraged by the apparent complexity and divergence of the evidence --- the rest of this book aims to capture it all in terms of a few basic ideas.
1.31 Four common hypotheses.
îThe Activation Hypothesis.ï
One common suggestion is that consciousness involves îactivationï of elements in memory that reach consciousness once they cross some activation threshold. We will call this the Activation Hypothesis; it is a current favorite, because many of today's cognitive theories use the concept of activation for reasons of their own. The Activation Hypothesis was stated as early as 1824 by Johann Herbart. In a very modern vein, he wrote:
"As it is customary to speak of an entry of the ideas into consciousness, so I call îthreshold of consciousnessï that boundary which an idea appears to cross as it passes from the totally inhibited state into some ... degree of actual (conscious) ideation. ... As we may speak of the intensification and weakening of ideas, so I refer to an idea as îbelow the thresholdï if it lacks the strength to satisfy those conditions. ... it may be îmoreï or îless far below the threshold,ï according as it lacks more or less of the strength which would have to be added to it in order for it to reach the threshold. Likewise, an idea is îabove the thresholdï insofar as it has reached a certain degree of actual (conscious) ideation." (Herbart, 1824/1961, p. 40. Italics in the original.)
Studies of perception, imagery, and memory all provide some evidence for this idea. Low©intensity stimuli in a normal surround do not become conscious. When two stimuli both evoke the same association, it is more likely to become conscious than when only one stimulus evokes the association (Anderson, 19xx). And so on. Numerous phenomena involving consciousness can be explained naturally with the idea of an activation threshold. In recent years a number of models have been proposed involving‹j______‹ "spreading activation", which are in spirit not far removed from Herbart's thoughts. These models view knowledge as a network of related elements, whether they be phonemes, words, or abstract concepts. Information can spread from node to node; the degree of involvement of any element is indicated by an activation number that is assigned to each node. These models are very effective, providing a flexible and powerful theoretical language for psychology. They have been applied to modeling language, visual perception, word perception, imagery, memory retrieval, speech production, and the like (see Rumelhart, McClelland, and the PDP Group, 1986). However, in these models the strength of activation is not interpreted as the likelihood of the activated material becoming conscious.
Several theorists have made tentative suggestions that consciousness may in fact involve high©level activation. This is attractive in some ways, and indeed the model we propose in Chapter 2 may be stated in terms of activation (2.33). But we will sound the following note of caution about the use of activation alone to represent access to consciousness.
îThe trouble with unaided activationï
Activation by itself is not sufficient to produce a conscious experience. This is shown especially by phenomena like habituation and automatization of conscious experience when an event is presented over and over again. We will call these phenomena îRedundancy Effects. They ïare quite important in this book (Chapter 5). Redundancy Effects show that we generally îloseï consciousness of repeated and predictable events. This applies to perceived stimuli, but also to repeated mental images, to any practiced, predictable skill, and even to predictable components of meaning (see Chapter 5). Later in this chapter we will give arguments to the effect that Redundancy Effects involve not merely decay of activation, but an active learning process (1.41; 5.0).
In general, if we are to accept that conscious experience corresponds to activation above some threshold, as Herbart's Activation Hypothesis suggests, we must also accept the paradoxical idea that too much activation, lasting too long, can lead to a îlossï of conscious experience. Perhaps activation first rises and then declines? But then one would have to explain how a well-learned automatic skill can have low activation and still be readily available and very efficient! In learning to ride a bicycle, we lose consciousness of the details of riding even as we gain efficiency and availability of the skill. Hence activation cannot be used to explain both consciousness, and efficiency and availability. If activation is used to îexplainï consciousness, then something else is needed to account for availability and efficiency.
One is caught on the horns of a dilemma: either consciousness and activation are the same, in which case activation cannot be used to explain the efficiency and availability of automatic (unconscious) skills, or activation and consciousness are different, in which case activation cannot be the only necessary condition for conscious experience. Later in this book we interpret Redundancy Effects as evidence that conscious experience always must be îinformativeï as well as highly activated --- i.e., it involves a process that works to reduce uncertainty about the input (5.00). We are conscious of some event only as long as its uncertainty is not completely resolved. This view breaks the circularity of the unaided Activation Hypothesis, by adding another necessary condition.
We will use activation in this book as one way to model the chances of an even becoming conscious. But activation is only a necessary, not a sufficient condition of consciousness (2.33).
îThe Novelty Hypothesis.ï
The role suggested above for informative stimulation is not entirely new. It follows from another stream of thought about conscious experience. This trend, which we can call the Novelty Hypothesis, claims that consciousness is focused on mismatch, novelty, or "anti-habit". (Berlyne, 1960; Straight, 1977; Sokolov, 1963). Of course novelty is closely connected with the concept of information, and in Chapters 5 we suggest that the mathematical definition of information may be adapted to create a modern version of the Novelty Hypothesis (Shannon & Weaver, 1949).
îThe Tip-of-the-Iceberg Hypothesis.ï Another long tradition looks at consciousness as the tip of the psychological iceberg. "Tip of the Iceberg" Hypotheses emphasize that conscious experience emerges from a great mass of unconscious events (Ellenberger, 1970). In modern cognitive work conscious experience is closely associated with îlimited capacity mechanismsï (see 1.x), which represent the tip of a very large and complex iceberg of unconscious memories and mechanisms. In a different tradition, Freud's censorship metaphor attempts to explain the fact that conscious experience is only the tip of a great motivational iceberg (Erdelyi, 1985).
Curiously enough, few researchers seem to ask îwhyï our‹j______‹ conscious capacity is so limited. The limitations are quite surprising, compared to the extraordinary size, capacity, and evolutionary sophistication of the nervous system. Some psychologists suppose that there must be a physiological reason for conscious limited capacity, but of course this begs the question of its functional role. Even physiological mechanisms evolve for functional reasons. We suggest an answer to this puzzle in Chapter 2.
îThe Theatre Hypothesis.ï
A fourth popular metaphor may be called the "search light" or Theater Hypothesis. This idea is sometimes called "the screen of consciousness." An early version may be found in Plato's classic Allegory of the Cave. Plato compared ordinary perception to the plight of bound prisoners in a cave, who can see only the cave wall with the shadows projected on it of people moving about in front of a fire. The people projecting the shadows are themselves invisible; they cannot be seen directly. We humans, according to Plato, are like those prisoners --- we only see the shadows of reality. Modern versions of the Theater Hypothesis may be found in Lindsay & Norman (, p. x), Jung (), Crick (), --- and throughout this book. It has been beautifully articulated by the French historian and philosopher Hyppolite Taine (1828-1893):
"One can therefore compare the mind of a man to a theatre of indefinite depth whose apron is very narrow but whose stage becomes larger away from the apron. On this lighted apron there is room for one actor only. He enters, gestures for a moment, and leaves; another arrives, then another, and so on ... Among the scenery and on the far-off stage or even before the lights of the apron, unknown evolutions take place incessantly among this crowd of actors of every kind, to furnish the stars who pass before our eyes one by one, as in a magic lantern." (18xx/Ellenberger?, p.)
Taine managed to combine several significant features in his theater image. First, he includes the observation that we are conscious of only one "thing" at a time, as if different mental contents drive each other from consciousness. Second, he incorporates the Tip-of-the-Iceberg Hypothesis, the idea that at any moment much more is going on than we can know. And third, his metaphor includes the rather ominous feeling that unknown events going on behind the scenes are îin control ofï whatever happens on our subjective stage (cf. Chapters 4 and 5).
