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).