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by Stanislas Dehaene (editor)
MIT Press, 2001
Review by David A. Patten, Ph.D. on Sep 6th 2002

The Cognitive Neuroscience of Consciousness

This book achieves its aim of demonstrating how recent advances in cognitive neuroscience have contributed to our understanding of conscious experience.  The book is a reprint of a special issue of Cognition: International Journal of Cognitive Science.  Consequently, its audience is not the layperson, but philosophers, psychologists, or anyone else who has given serious scholarly thought to the nature of consciousness.  The volume brings together eight articles from leading proponents of the cognitive neuroscience approach to understanding consciousness and the mind in general.  The articles can be divided into three basic types.  Some of the authors utilize a cognitive neuroscientific approach to explaining empirical data, others address methodological concerns, and still others wrestle with philosophical questions about what it is that is being explained.  There appears to be a wide range of agreement amongst the authors concerning the basic tenets of the program: subjectively experienced mental phenomena can be studied objectively, most mental processing takes place unconsciously, most mental processes are modular, mental states are token identical to brain states, and mental states are type identical to functional states.  There also seems to be general convergence upon what is called a “global neuronal workspace model” of consciousness.  For the most part, the collection comes across as a team effort with each member performing his or her own well defined function.  There are a small number of intramural disagreements, some significant (is phenomenal experience real or illusory?), but even here there is agreement on how to approach the problems.

            In the introductory article, Dehaene and Naccache introduce us to the global neuronal workspace hypothesis. The thesis brings together the idea that the mind is modular with the idea that all mental states are brain states.  The proposal is that we can isolate and identify a broad range of mental acts, then locate the regions of the brain that are active when we perform them.  There are distinct, though not necessarily anatomically isolated, neural systems that are dedicated to processing different types of information.  Modules perform their function automatically, and the information in one module is not ordinarily available to other modules.  The great number of autonomous, domain specific, and informationally encapsulated modules makes it possible to explain a great deal of the complexity of human behavior.  We do not need to be conscious of much of what we do in order to do it.  Nevertheless, we sometimes do need to know what our minds are doing and it certainly appears that we often are aware of what we are thinking.  So the question is: what is going on in the brain that accounts for my consciousness of a particular mental state of which I am conscious? According to the global neuronal workspace model, the subjective experience of being in a particular conscious state is explained in terms of the interconnection among certain high-order mental modules, specifically the perceptual, motor, evaluational, attentional, and long term memory systems.  That is, the contents of a given mental module are conscious when they are accessed by these five systems.  This is what “global availability” is meant to refer to.  The global workspace, is not a space at all, despite its name.  The authors maintain that this account explains why some sorts of mental processes are impervious to consciousness – those processes are not connected to the workspace.  The authors also make the bold claim that the so-called “hard problems” – free will, qualia, sense of self, evolution of consciousness –  will disappear after a satisfactory framework for understanding consciousness has been constructed (p. 29).       

The second article, by Driver and Vuilleumier, is a good representative of the empirical work being done by cognitive neuroscientists.  It relies heavily on empirical studies done on monkeys and brain damaged humans.  The general pattern of these studies is to specify the cognitive functions an organism can and cannot perform as the result of a lesion in a particular part of the brain.  Of specific interest are those lesions that allow the organism to continue to represent and manipulate some aspect of his environment, but without the conscious awareness of such cognitive activity that, in humans at least, is characteristic of such cognitive activity.  What these studies are designed to show is that due to the modularity of the mind, the organism is sometimes capable of performing certain complex cognitive tasks in the absence of conscious awareness.  In these rare cases the cerebral substrates that enable the mind to perform these tasks are unaffected by the lesion, but the module’s connection to higher order modules (such as long-term memory, intentional action) are damaged, thus accounting for the organism’s lack of consciousness of what he is doing.

            In this article we are presented with the phenomena of neglect and extinction.  People with a certain sort of brain damage act as if half of their physical environment were not there.  For example, they will read only one side of the newspaper, or, if asked to sketch an object that is in front of them, they will draw only one half of it.  (Shockingly, these individuals are typically unaware of their deficit.)  There is nothing wrong with these individuals’ sensory faculties.  They are neither blind, nor incapable of processing visual information.  There remains, in fact, much residual information processing.  Hence the neglect patient perceives the “neglected” information, but is not aware that she does so; her perception is unconscious.  What is illuminating is just how much a person is capable of doing with information she doesn’t know she has.

            In the third article Kanwisher takes up the problem of finding the necessary conditions for a mental state’s being conscious. She argues against the activation strength hypothesis, i.e. that a mental state is conscious if the neural process underlying it is powerful enough.  Her focus is to show that a mental state’s connectivity to workspace neurons is an additionally necessary condition for conscious awareness of that state.  “(I)t seems reasonable to hypothesize that awareness of a particular element of perceptual information must entail not just a strong enough neural representation of that information, but also access to that information by most of the rest of the mind/brain” (105).   Kanwisher steers a careful course in the article, avoiding the scylla of having to posit a homunculus witness to the neural event, and the Charybdis of implying that isolated brain processes magically become conscious in virtue of their mere occurrence.

In the fourth article, Merikle, Smilek, and Eastwood take up the important  methodological problem of measuring perception without awareness, i.e. unconscious perception.  Unfortunately, much of the article is concerned with demonstrating that perception without awareness is possible – a claim that is hardly controversial and that is addressed by every other article anyhow.  The crucial methodological issue in question is whether awareness ought to be measured objectively or subjectively.  An objective measure of awareness would count any ability to make a discrimination as evidence for awareness of what is being discriminated.  Subjective measures of awareness, by contrast, take seriously subjects’ claims not to be aware of the items which, it turns out, they can distinguish at rates better than chance.  What is at stake is the definition of ‘consciousness’ (or ‘awareness’).  Can ‘consciousness’ be defined in a way that ignores the subject’s first-person perspective?  If we use objective measures of consciousness, it can.  While the authors do make a solid argument in favor of prioritizing subjective measures, they often seem to be pulling their punches against the use of objective measures.  Hence, the authors do not seem to adequately emphasize that the philosophy underlying the reliance on objective measures (behaviorism) is antithetical to the project of cognitive neuroscience as conceived of by most of the other authors of this book.  For example, Dennett makes clear that he thinks “every study reported in every article in this volume has been conducted according to the tenets of heterophenomenology” (p. 231).  Heterophenomenology is a method for understanding the subjective, first-person, aspects of consciousness.  Heterophenomenology, Dennett maintains, takes subjectivity seriously “by taking the reports of subjects seriously as reports of their subjective experience” (p. 230).  Dehaene and Naccache also emphasize quite clearly that the aim of cognitive neuroscience is to account for the subjective experience of consciousness.  They write: “In various daily life and psychophysical testing situations, (people) use phrases such as ‘I was not conscious of X’, ‘I suddenly realized that Y’, or ‘ I knew that Z, therefore I decided to do X’.  In other words, they use a vocabulary of psychological attitudes such as believing, pretending, knowing, etc., that all involve to various extents the concept of ‘being conscious’. . .   The task of cognitive neuroscience is to identify which mental representations and, ultimately, which brain states are associated with such reports.” (p. 3).  It seems as if this chapter’s task was to dispatch the behaviorist’s notion of ‘consciousness,’ but the authors seem to stop short, contenting themselves with dismissing it as too ‘conservative’ (p. 125).

            While it includes some intriguing proposals, the fifth article, by Parvizi and Damasio, is almost exclusively of interest to other neuroscientists doing technical research on the human brain.  A typical sentence looks like: “Both the superficial dorsal horn and the caudal spinal trigeminal subnucleus receive primary afferents through unmyelinated C-fibers and lightly myelinated Ad fibers which convey signals related to pain and temperature.” Unless the reader is capable of making sense of sentences like that, he would be well advised to look elsewhere to find out what Parvisi and Damasio are trying to do.    

The sixth article, by Jack and Shallice, is the most ambitious in the volume.  The authors set out to determine the function of consciousness.  They believe that just as Watson and Crick had to know the function of the gene before they could discover the double helix structure of DNA, so too, must we know the function of consciousness before we can find its physical structure in the brain.  The authors begin with folk psychological criteria for determining the function of consciousness: we are sometimes ‘conscious of’ something and we sometimes ‘consciously’ perform some action (p. 165). They propose that the challenge ahead is to enumerate the sorts of processes that require consciousness, calling such processes ‘type-C.’   “Type-C processes are defined as processes that can only operate effectively on information when normal subjects report awareness of that information” (p. 170).  This definition seems arbitrary and counter-intuitive since most people think that non-linguistic animals are conscious.  What the authors are really looking for, however, are processes that require self-reflexive awareness, or introspection. And the issue seems to be that when we introspect, we report having experiences that have non-physical properties; and since there are no  non-physical properties, we cannot be having the experiences we report having.  The solution, they propose, is that the reporting just is the awareness; we do not enter into a conscious state, witness it, then report it.  Rather the ability to make the report, somehow, is the experiencing.  The authors call this the endowing view because the type-C process is supposed to endow awareness, not just enable an allegedly already conscious state to become reportable (172).  The authors then go on to identify numerous processes that they think are strong candidates to be type-C processes.  This article has the advantage of being the most overt in its statement of the goal of cognitive neuroscience: “The closest that science can come to accounting for subjectivity is through elucidating the mechanisms that allow us to understand ourselves from our own point of view” (p. 190).  So, the goal is not to explain the subjective properties of consciousness, but to explain the mechanisms of human understanding that lead us to believe that consciousness has irreducibly subjective properties. 

            The last two articles, one by Block, the other by Dennett, take on the form of a debate over whether and how the cognitive neuroscientific framework must leave some aspect of conscious experience unexplained.  Block takes the position that there are three distinct types of consciousness and that the authors of this volume are concerned, or should be concerned, exclusively with reflexive consciousness.  Cognitive neuroscience does not address phenomenality, he argues.  Global access to an otherwise isolated mental state may explain the person’s consciousness of that particular mental state, but even without such reflexive consciousness, Block suggests,  mental states have phenomenal properties: there is something it is like to be in them.  In fact, it is the phenomenal properties that reflexive consciousness is consciousness of. “Reflexivity involves phenomenality plus more – reflection on the phenomenality” (p. 213).  Dennett counters that there is no such “will-of-the-wisp” property of consciousness.    A conscious state is conscious in virtue of the effects it has, if phenomenal properties have no effect, they are a philosopher’s illusion.  It does seem that Dennett gets the best of the argument since Block must resort to appealing to unconscious phenomenal properties, i.e. states that it is like something to be in, even though we have no awareness of being in them.

            On the whole this is an exceptional book and well worth reading if you are interested in learning what cognitive neuroscience can contribute to our understanding of mind.  It is a breath of fresh air compared to the numerous hackneyed debates over whether such a contribution is, in principle, possible.

 

© 2002 David A. Patten

 

David A. Patten, Ph.D., Department of Philosophy, SUNY Stony Brook, NY.