La conscience et ses illusions

En somme, répondre avec Dennett à l’antique impératif socratique du “Connais-toi toi-même” exige d’accepter l’idée, jugée déprimante par beaucoup d’esprits encore pieux, que nous ne sommes rien d’autre que nos cerveaux… plus les illusions que se font nos cerveaux quant à ce qu’ils sont.

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Conversations on consciousness
Published by Oxford University Press, Oxford, 2005, hardback ISBN 0 19 280622-X and 2006, paperback ISBN 0 19 280623 8

Susan Blackmore interviews Dan Dennett …

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“Daniel Dennett, c’est le Diable…” Cette exclamation de Burton Voorhees, respectable professeur de mathématiques à l’université d’Athabasca, est sans doute un peu exagérée. Mais à considérer la radicalité dont fait preuve celui qu’elle vise, il n’est pas exclu qu’elle présente un fond de vérité… La parution de De beaux rêves, dans lequel Dennett répond à certaines objections et entreprend de dissiper les songes philosophiques qu’il estime être à leur racine, offre une occasion de revenir sur la pensée d’un auteur crucial.

Les positions philosophiques de cet auteur aussi stimulant que controversé sont influencées à la fois par le naturalisme de W.V.O. Quine, qui avance que ce qui touche à “l’esprit” peut être compris et expliqué comme n’importe quel autre phénomène naturel – “nous sommes tous faits, écrit-il avec son sens habituel de la provocation, de robots dépourvus d’esprit et de rien de plus” -, et par la philosophie du langage ordinaire (L. Wittgenstein, J. Austin, G. Ryle…) qui le conduit à prendre néanmoins en compte la manière particulière dont nous formulons et interprétons ce qui se passe en nous.

Certes, ce que nous appelons la conscience paraît l’ineffable même, “célébrée à la manière d’un mystère situé au-delà de la science, impénétrable du dehors”, une expérience si intérieure et privée que seule la personne concernée y aurait accès, de sorte que toute entreprise pour l’expliquer (philosophiquement ou scientifiquement) relèverait du voeu pieux. Qui d’autre que moi pourrait avoir accès à la dimension qualitative de ce qui se passe en moi, comprendre la sensation précise que me procure telle nuance de bleu, ou encore savoir ce que j‘éprouve en mangeant de la pâte d’amande ou en faisant l’amour – en somme : connaître l’effet que cela fait d‘être moi ? Cette idée se rattache, le plus souvent, à l’hypothèse dite dualiste, selon laquelle les faits de conscience (perceptions, croyances, désirs…) relèveraient d’un ordre spécifique et séparé, auquel ne s’appliqueraient pas les lois ordinaires régissant les phénomènes du monde physique, et constitueraient de ce fait, selon la formule de Spinoza, “un empire dans un empire”.

Telle est précisément la thèse que Dennett avait entrepris de réfuter dans un précédent livre, La Conscience expliquée. Il y revient aujourd’hui, en prenant en compte les progrès de la recherche en neurosciences. Sa stratégie consiste à relever les principaux arguments mobilisés en faveur du caractère ineffable ou séparé de la conscience, afin d’en faire apparaître l’inconsistance. Ainsi, pour reprendre une célèbre expérience de pensée discutée par Dennett, imaginons Marie, isolée depuis toujours du monde, qu’elle n’aurait connu que par l’intermédiaire d’un écran noir et blanc, mais disposant d’une connaissance encyclopédique des données scientifiques disponibles sur la perception des couleurs : il n’y a, affirme Dennett au rebours de l’opinion dominante, aucune raison de supposer qu’elle éprouvera le moindre émerveillement ou la plus petite surprise le jour où elle sera confrontée pour la première fois à un monde coloré “en vrai”. Selon lui, la richesse soi-disant indicible dont se compose notre rapport conscient au monde ne contient rien de plus que ce qui est susceptible d‘être décrit et expliqué par un discours scientifique neutre, procédant à “une extrapolation objective raisonnée à partir de structures discernables dans le comportement des sujets”.

Le point le plus sensible et sans doute le plus difficile à admettre de la théorie de Dennett est sa critique de ce qu’il nomme le “théâtre cartésien”. A savoir l’idée d’un point de vue unique et continu qui coïnciderait avec ce qu’on appelle la conscience ou l’expérience intime, et qui serait au fond ce à quoi je me réfère lorsque je fais usage des mots “je”, “moi”… Dennett s’efforce de démontrer qu’il n’existe pas de “moi total” qui serait le spectateur désincarné de notre vie mentale, car il n’y a pas dans le cerveau de point unique correspondant à un prétendu “siège” de notre pensée ou de notre personnalité, mais seulement de multiples flux d’activité localisés dans des zones très diverses du cerveau.

“CÉLÉBRITÉ CÉRÉBRALE”

Or il est parfaitement possible d’admettre que ces processus et sous-processus neuronaux spécialisés pensent par eux-mêmes sans avoir besoin d‘être coordonnés par une entité spéciale qui correspondrait à notre prétendu moi. A cette fiction cartésienne du moi, Dennett substitue son modèle (d’obédience darwinienne) de la “célébrité cérébrale” : au lieu de devoir rejoindre on ne sait trop quelle scène privilégiée pour devenir conscients, les contenus cérébraux d’abord inconscients “peuvent remporter quelque chose qui ressemble plutôt à ce qu’est la notoriété, dans une lutte avec d’autres contenus eux-mêmes en quête de notoriété (ou potentiellement en passe de l’obtenir)”. Dans le cerveau, pas de roi ou de “contrôleur officiel des programmes de la télévision d’Etat”, mais des populations de machines neuronales et de processus machiniques entretenant des relations “plus démocratiques, en fait quelque peu anarchistes”. Cela implique du même coup (à l’inverse, là encore, de ce que supposait Descartes) que nous ne disposons paradoxalement d’aucun point de vue privilégié dans la connaissance de cela même qui se déroule “en” nous : une perspective “en troisième personne” sera tout aussi légitime, et dans certains cas, plus pertinente.

En somme, répondre avec Dennett à l’antique impératif socratique du “Connais-toi toi-même” exige d’accepter l’idée, jugée déprimante par beaucoup d’esprits encore pieux, que nous ne sommes rien d’autre que nos cerveaux… plus les illusions que se font nos cerveaux quant à ce qu’ils sont.

Stéphane Legrand

Article paru dans l‘édition du journal Le Monde du 04.07.08.

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4 thoughts on “La conscience et ses illusions”

  1. Facing Up to the Problem of Consciousness
    Consciousness poses the most baffling problems in the science of the mind. There is nothing that we know more intimately than conscious experience, but there is nothing that is harder to explain. All sorts of mental phenomena have yielded to scientific investigation in recent years, but consciousness has stubbornly resisted. Many have tried to explain it, but the explanations always seem to fall short of the target. Some have been led to suppose that the problem is intractable, and that no good explanation can be given.

    The easy problems and the hard problem
    There is not just one problem of consciousness. “Consciousness” is an ambiguous term, referring to many different phenomena. Each of these phenomena needs to be explained, but some are easier to explain than others. At the start, it is useful to divide the associated problems of consciousness into “hard” and “easy” problems. The easy problems of consciousness are those that seem directly susceptible to the standard methods of cognitive science, whereby a phenomenon is explained in terms of computational or neural mechanisms. The hard problems are those that seem to resist those methods.

    The easy problems of consciousness include those of explaining the following phenomena:

    the ability to discriminate, categorize, and react to environmental stimuli;
    the integration of information by a cognitive system;
    the reportability of mental states;
    the ability of a system to access its own internal states;
    the focus of attention;
    the deliberate control of behavior;
    the difference between wakefulness and sleep.
    All of these phenomena are associated with the notion of consciousness. For example, one sometimes says that a mental state is conscious when it is verbally reportable, or when it is internally accessible. Sometimes a system is said to be conscious of some information when it has the ability to react on the basis of that information, or, more strongly, when it attends to that information, or when it can integrate that information and exploit it in the sophisticated control of behavior. We sometimes say that an action is conscious precisely when it is deliberate. Often, we say that an organism is conscious as another way of saying that it is awake.

    There is no real issue about whether these phenomena can be explained scientifically. All of them are straightforwardly vulnerable to explanation in terms of computational or neural mechanisms. To explain access and reportability, for example, we need only specify the mechanism by which information about internal states is retrieved and made available for verbal report. To explain the integration of information, we need only exhibit mechanisms by which information is brought together and exploited by later processes. For an account of sleep and wakefulness, an appropriate neurophysiological account of the processes responsible for organisms’ contrasting behavior in those states will suffice. In each case, an appropriate cognitive or neurophysiological model can clearly do the explanatory work.

    If these phenomena were all there was to consciousness, then consciousness would not be much of a problem. Although we do not yet have anything close to a complete explanation of these phenomena, we have a clear idea of how we might go about explaining them. This is why I call these problems the easy problems. Of course, “easy” is a relative term. Getting the details right will probably take a century or two of difficult empirical work. Still, there is every reason to believe that the methods of cognitive science and neuroscience will succeed.

    The really hard problem of consciousness is the problem of experience. When we think and perceive, there is a whir of information-processing, but there is also a subjective aspect. As Nagel (1974) has put it, there is something it is like to be a conscious organism. This subjective aspect is experience. When we see, for example, we experience visual sensations: the felt quality of redness, the experience of dark and light, the quality of depth in a visual field. Other experiences go along with perception in different modalities: the sound of a clarinet, the smell of mothballs. Then there are bodily sensations, from pains to orgasms; mental images that are conjured up internally; the felt quality of emotion, and the experience of a stream of conscious thought. What unites all of these states is that there is something it is like to be in them. All of them are states of experience.

    It is undeniable that some organisms are subjects of experience. But the question of how it is that these systems are subjects of experience is perplexing. Why is it that when our cognitive systems engage in visual and auditory information-processing, we have visual or auditory experience: the quality of deep blue, the sensation of middle C? How can we explain why there is something it is like to entertain a mental image, or to experience an emotion? It is widely agreed that experience arises from a physical basis, but we have no good explanation of why and how it so arises. Why should physical processing give rise to a rich inner life at all? It seems objectively unreasonable that it should, and yet it does.

    If any problem qualifies as the problem of consciousness, it is this one. In this central sense of “consciousness”, an organism is conscious if there is something it is like to be that organism, and a mental state is conscious if there is something it is like to be in that state. Sometimes terms such as “phenomenal consciousness” and “qualia” are also used here, but I find it more natural to speak of “conscious experience” or simply “experience”. Another useful way to avoid confusion (used by e.g. Newell 1990, Chalmers 1996) is to reserve the term “consciousness” for the phenomena of experience, using the less loaded term “awareness” for the more straightforward phenomena described earlier. If such a convention were widely adopted, communication would be much easier; as things stand, those who talk about “consciousness” are frequently talking past each other.

    The ambiguity of the term “consciousness” is often exploited by both philosophers and scientists writing on the subject. It is common to see a paper on consciousness begin with an invocation of the mystery of consciousness, noting the strange intangibility and ineffability of subjectivity, and worrying that so far we have no theory of the phenomenon. Here, the topic is clearly the hard problem – the problem of experience. In the second half of the paper, the tone becomes more optimistic, and the author’s own theory of consciousness is outlined. Upon examination, this theory turns out to be a theory of one of the more straightforward phenomena – of reportability, of introspective access, or whatever. At the close, the author declares that consciousness has turned out to be tractable after all, but the reader is left feeling like the victim of a bait-and-switch. The hard problem remains untouched.

    David J. Chalmers

    Department of Philosophy
    University of Arizona
    Tucson, AZ 85721

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  2. Consciousness ???
    What exactly is the issue here that so divides philosophers and is the focus of such vigorous debate? In broad terms, it is the question of the place of consciousness in the world – the question of how it arises and how it is related to processes in the brain. It is hard to deny that consciousness is closely dependent on the brain. Changes in the brain can affect consciousness (think of the effects of anaesthetics and psychedelic drugs), and damage to the brain can remove it permanently (think of blindsight, for example). But how does the brain generate consciousness? How could conscious experiences arise from the activity of brain cells – individually not much different from any other cells? As Colin McGinn puts it, it seems like magic:

    “How is it possible for conscious states to depend upon brain states? How can technicolour phenomenology arise from soggy grey matter? What makes the bodily organ we call the brain so radically different from other bodily organs, say the kidneys – the body parts without a trace of consciousness? How could the aggregation of millions of individually insentient neurons generate subjective awareness? We know that brains are the de facto causal basis of consciousness, but we have, it seems, no understanding whatever of how this can be so. It strikes us as miraculous, eerie, even faintly comic. Somehow, we feel, the water of the physical brain is turned into the wine of consciousness, but we draw a total blank on the nature of this conversion. Neural transmissions just seem like the wrong kind of materials with which to bring consciousness into the world, but it appears that in some way they perform this mysterious feat. The mind-body problem is the problem of understanding how the miracle is wrought, thus removing the sense of deep mystery. We want to take the magic out of the link between consciousness and the brain.”
    (McGinn, 1989, 349)

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  3. What Happens When We Die?
    A fellow at New York City’s Weill Cornell Medical Center, Dr. Sam Parnia is one of the world’s leading experts on the scientific study of death. Last week Parnia and his colleagues at the Human Consciousness Project announced their first major undertaking: a 3-year exploration of the biology behind “out-of-body” experiences. The study, known as AWARE (AWAreness during REsuscitation), involves the collaboration of 25 major medical centers through Europe, Canada and the U.S. and will examine some 1,500 survivors of cardiac arrest. TIME spoke with Parnia about the project’s origins, its skeptics and the difference between the mind and the brain.

    What sort of methods will this project use to try and verify people’s claims of “near-death” experience?

    When your heart stops beating, there is no blood getting to your brain. And so what happens is that within about 10 sec., brain activity ceases – as you would imagine. Yet paradoxically, 10% or 20% of people who are then brought back to life from that period, which may be a few minutes or over an hour, will report having consciousness. So the key thing here is, Are these real, or is it some sort of illusion? So the only way to tell is to have pictures only visible from the ceiling and nowhere else, because they claim they can see everything from the ceiling. So if we then get a series of 200 or 300 people who all were clinically dead, and yet they’re able to come back and tell us what we were doing and were able see those pictures, that confirms consciousness really was continuing even though the brain wasn’t functioning.

    How does this project relate to society’s perception of death?

    People commonly perceive death as being a moment – you’re either dead or you’re alive. And that’s a social definition we have. But the clinical definition we use is when the heart stops beating, the lungs stop working, and as a consequence the brain itself stops working. When doctors shine a light into someone’s pupil, it’s to demonstrate that there is no reflex present. The eye reflex is mediated by the brain stem, and that’s the area that keeps us alive; if that doesn’t work, then that means that the brain itself isn’t working. At that point, I’ll call a nurse into the room so I can certify that this patient is dead. Fifty years ago, people couldn’t survive after that.

    How is technology challenging the perception that death is a moment?

    Nowadays, we have technology that’s improved so that we can bring people back to life. In fact, there are drugs being developed right now – who knows if they’ll ever make it to the market – that may actually slow down the process of brain-cell injury and death. Imagine you fast-forward to 10 years down the line; and you’ve given a patient, whose heart has just stopped, this amazing drug; and actually what it does is, it slows everything down so that the things that would’ve happened over an hour, now happen over two days. As medicine progresses, we will end up with lots and lots of ethical questions.

    But what is happening to the individual at that time? What’s really going on? Because there is a lack of blood flow, the cells go into a kind of a frenzy to keep themselves alive. And within about 5 min. or so they start to damage or change. After an hour or so the damage is so great that even if we restart the heart again and pump blood, the person can no longer be viable, because the cells have just been changed too much. And then the cells continue to change so that within a couple of days the body actually decomposes. So it’s not a moment; it’s a process that actually begins when the heart stops and culminates in the complete loss of the body, the decompositions of all the cells. However, ultimately what matters is, What’s going on to a person’s mind? What happens to the human mind and consciousness during death? Does that cease immediately as soon as the heart stops? Does it cease activity within the first 2 sec., the first 2 min.? Because we know that cells are continuously changing at that time. Does it stop after 10 min., after half an hour, after an hour? And at this point we don’t know.

    What was your first interview like with someone who had reported an out-of-body experience?

    Eye-opening and very humbling. Because what you see is that, first of all, they are completely genuine people who are not looking for any kind of fame or attention. In many cases they haven’t even told anybody else about it because they’re afraid of what people will think of them. I have about 500 or so cases of people that I’ve interviewed since I first started out more than 10 years ago. It’s the consistency of the experiences, the reality of what they were describing. I managed to speak to doctors and nurses who had been present who said these patients had told them exactly what had happened, and they couldn’t explain it. I actually documented a few of those in my book What Happens When We Die because I wanted people to get both angles – not just the patients’ side but also the doctors’ side – and see how it feels for the doctors to have a patient come back and tell them what was going on. There was a cardiologist that I spoke with who said he hasn’t told anyone else about it because he has no explanation for how this patient could have been able to describe in detail what he had said and done. He was so freaked out by it that he just decided not to think about it anymore.

    Why do you think there is such resistance to studies like yours?

    Because we’re pushing through the boundaries of science, working against assumptions and perceptions that have been fixed. A lot of people hold this idea that, well, when you die, you die; that’s it. Death is a moment – you know you’re either dead or alive. All these things are not scientifically valid, but they’re social perceptions. If you look back at the end of the 19th century, physicists at that time had been working with Newtonian laws of motion, and they really felt they had all the answers to everything that was out there in the universe. When we look at the world around us, Newtonian physics is perfectly sufficient. It explains most things that we deal with. But then it was discovered that actually when you look at motion at really small levels – beyond the level of the atoms – Newton’s laws no longer apply. A new physics was needed, hence, we eventually ended up with quantum physics. It caused a lot of controversy – even Einstein himself didn’t believe in it.

    Now, if you look at the mind, consciousness, and the brain, the assumption that the mind and brain are the same thing is fine for most circumstances, because in 99% of circumstances we can’t separate the mind and brain; they work at the exactly the same time. But then there are certain extreme examples, like when the brain shuts down, that we see that this assumption may no longer seem to hold true. So a new science is needed in the same way that we had to have a new quantum physics. The CERN particle accelerator may take us back to our roots. It may take us back to the first moments after the Big Bang, the very beginning. With our study, for the first time, we have the technology and the means to be able to investigate this. To see what happens at the end for us. Does something continue?

    By M.J. STEPHEY Tue Sep 23, 6:40 PM ET, TIME magazine

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  4. “I maintain that the human mystery is incredibly demeaned by scientific reductionism, with its claim in promissory materialism to account eventually for all of the spiritual world in terms of patterns of neuronal activity. This belief must be classed as a superstition … we have to recognize that we are spiritual beings with souls existing in a spiritual world as well as material beings with bodies and brains existing in a material world.” John Carew Eccles, Evolution of the Brain: Creation of the Self (1989) p. 241
    “I believe that there is a fundamental mystery in my existence, transcending any biological account of the development of my body (including my brain) with its genetic inheritance and its evolutionary origin. … I cannot believe that this wonderful gift of a conscious existence has no further future, no possibility of another existence under some other unimaginable conditions.”
    “Our coming-to-be is as mysterious as our ceasing-to-be at death. Can we therefore not derive hope because our ignorance about our origin matches our ignorance about our destiny? Cannot life be lived as a challenging and wonderful adventure that has meaning yet to be discovered?”
    John Carew Eccles, Facing Reality : Philosophical Adventures by a Brain Scientist (1970)

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