Picture: Stanislas Dehaene. Edge has an interesting talk by Stanislas Dehaene.  He and his team, using a range of tools, have identified ‘signatures’ of awareness; marked changes in activity in certain brain regions which accompany awareness of a particular stimulus. They made a clever use of the phenomenon of ‘masking’, in which the perception of a word can be obliterated if it follows too rapidly after the presentation of an earlier one. By adjusting the relevant delay, the team could compare the effect of a stimulus which never reached consciousness with one that did. Using this and similar techniques they identified a number of clear indications of conscious awareness: increased activity in the early stages of processing and activity in new regions, including the prefrontal cortex and inferior parietal. It appears that this is accompanied by a ‘P3 wave’ which is quite easy to detect even with nothing more sophisticated than electrodes on the scalp. Interestingly it seems that the difference between a stimulus which does not make it into consciousness and one which does emerges quite late, after as much as a quarter of a second of processing.

No-one, I suspect, is going to be amazed by the news that conscious awareness is accompanied by distinctive patterns of brain activity; but identifying the actual ‘signatures’ has direct clinical relevance in cases of coma and apparent persistent vegetative state. In principle Dehaene’s research should allow conscious reactions continuing in a paralysed patient to be identified; this possibility is being actively pursued.

More speculative and perhaps of deeper theoretical interest, Dehaene puts forward a theory of consciousness as a global neuronal workspace, another variation on the global workspace theory of Bernard Baars (an idea which keeps being picked up by others, which must suggest that it has something going for it). Dehaene offers the view that a particular function of the workspace is to allow inputs to hang around for an extended period instead of dissipating. Among other benefits, this allows the construction of chains of processing operations, something Dehaene likens to a Turing machine, though it sounds a little messier than that to me. Further ingenious experiments have lent support to this idea; the researchers were able to contrast subjects’ chaining ability when information was supplied subliminally or consciously (this may sound odd, but subjects can perform at better-than-chance levels even with subliminal stimuli).

Dehaene says that he is dealing only with one variety of consciousness – in the main it’s awareness, which in some respects is the basement level compared to the more high-flown self-reflective versions. But in passing the talk does clarify a question which has sometimes troubled me in the past about global workspace theories – why should they involve consciousness at all? It seems easy to understand that the brain might benefit from a kind of clearing house where information from different sources is shared – but couldn’t that happen, as it were, in the dark? What does the magic ingredient of consciousness add to the process?

Well, being in the global workspace means being accessible to several different systems (no intention here to commit to any particular view about modularity); and one of those systems is the vocal reporting system. So as a natural consequence of being in the workspace, inputs become things we can vocally report, things we can talk about. Things we can talk about are surely objects of consciousness in some quite high-level sense.

Dehaene does not go down this path, but I wondered how far we could take it; is there a plausible explanation of phenomenal consciousness in terms of a global workspace? If we followed the same pattern of argument we used above, we would be looking to say that conscious experiences acquired qualia because being in the workspace made them available to the qualic system, whatever that might be. I think some people, those who tend to want to reduce qualia to flags or badges that give inputs a special weight, might find this kind of perspective congenial, but it doesn’t appeal all that much to me. I would prefer an argument that related the appearance of qualia to a sensory input’s being available to a global collection of sensory and other systems; something to do with resonances across modalities; but I happily confess I have no clear idea of how or exactly why that would work either.


  1. 1. Vicente says:

    The experiments described in the talk are extremely interesting an have proven to be a fantastic brain research tool.

    In the same line, does anybody have a reference to any work where “thresholds” between reflect acts and conscious acts have been studied. Like if you move an object towards someone eye you will cause the reflect to close the eye depending on the speed of the approach. If it slow enough the individual can consciously control the situation, beyond a certain speed the reflect happens. I think it could be useful to watch brain activity patterns around this speed threshold, that causes brain switch between a conscious to an unsconscious state.

    Regarding the talk, maybe somebody could clarify me, if when the author makes statements like:

    – “It creates a digital representation out of what is initially just a probability distribution.”
    – serial vs. parallel processing
    – …it discretize…
    – simulation

    Is it just a way of talking? or is is it really considering that those processes happen, because in principle the computer science concepts used in the essay cannot be applied to brain processing directly.

    I also feel that consciousness, awarness, perception, understanding, processing concepts are a bit messed up through the talk, they are all related but are not the same, and need a more neat introduction in each point.

  2. 2. Peter says:

    Yes, the talk does slide across a number of different kinds of consciousness. In fairness, I didn’t spot any particular errors as a result; in particular Dehaene avoids the common error of claiming to have explained qualia and then offering a theory which only deals with simpler kinds of awareness.

  3. 3. Vincent Melody says:

    I have read so much on the topic of consciousness and I still do not
    understand what it is. The purported telltales of consciousness are statements like ” I did this” or I am aware that I am aware that I did this” or “there is awareness aware of itself” but I don’t see how you separate or derive necessarily an entity “consciousness” from it. Anymore than there must be some entity you derive from “this was done” or “there is awareness” or There is awareness of having done this”.
    After all, bottom line, one either claims an intuition that there is such an entity (“I see internally such an entity and label it consciousness”) or you don’t have such an ituition or claim and say “oh, consciousness is a superfluous creation; it is merely a notion used to play the role of the origin of “I”, by those who imagine a need for such a thing— but it is not a real thing, and I invoke Ockham.”—- or some such.
    Ultimately, the issue is a revisitation of the nominalist vs realist
    issue; it’s a real thing or it’s just a name or notion. There doesn’t seem to be any necessity either way.
    But in some real sense words are the world–so how decide if there is or isn’t such a thing? Again, no necessity. Can just as easily say that “I” is just something that arises—but there is no entity it arises to. Or, can say there is a thing that sees (in some sense) the “I” that arises, and that is consciousness.
    From the point of view of the nominalist you are fooled into thinking that an aware and separate entity must be posited because statements like “I am aware that I am aware of x” or “this act I know was was done by me” seem to show a something talking about itself. But the arising of statements of this sort don’t require an independent entity—-anymore than “there is awareness of x” requires one. The “I” in statements don’t make the existence of an entity consciousness necessary, no matter how many times there is a seeming self reference.
    The body can easily be a suitable reference–as in “the body has connection to the notion that something has been done (or seen or known or observed)in connecton with the body”. “I” is just a convenient way of talking. And so on.

    From the realist point of view there is a real existing thing that is refered to in “I am aware that I am aware of x”–and that is the origin of the statement. Indeed the statement is supposed to make no
    sense without such an entity and so there must be one.

    there is another problem with Consciousness: the division that supposedly holds between consciousness and the content or what consciousness is conscious of. Consciousness is conscious of some object—and that object is separate completely (as with the Cartesian mind body split—)from consciousness. But if there is the notion or a sense of consciousness then that notion or sense, (according to the scheme wherein consciousness is separate from its object)—must be, not consciousness but the content of consciousness; the object seen by consciousness and not consciousness itself. If so, then any description or sense or feeling or intuition of consciousness of consciousness or even the positing of such a thing as consciousness—is content or object and cannot be consciousness itself. Once such a split is posited then paradoxically it can’t be know whether there is such a thing or not.
    What is the reply to this? It can only be that consciousness is a word that stands for a thing that is intuited –and that intuition
    is of a real thing. Just as one sees a thing and words come to describe it–so too with the thing that is labeled consciousness.
    And the rebuttal? That the above reply is words–and words are
    not consciousness–as per the scheme previously proffered– and so
    you cannot be speaking about consciousness or even know if consciousness exists. The paradox stands.
    So, to sum up, either consciousness is not separate from the word “consciousness” and not separate from a description of consciousness —and therefore not some entity independent of what can be said and is therefore just a notion, and not a entity in fact, or if it is separate, independent, it cannot be known nor even known to exist or not exist, and so is paradoxical. So give up the notion.
    Another problem with consciousness is that if we presume
    there to be a consciousness and an object consciousness is conscious of then it seems we need an additional consciousness to see that there is a consciousness and its object. In other words, If it is said “I am conscious that there is consciousness and its object”, that indicates two consciousnesses: 1.consciousness and its object, and 2. the consciousness that sees that there is this object, namely, 1.consciousness and its object. But then we need another consciousness
    to see, to be conscious of 1 and 2–which together make another object—and onward adinfinitum, more objects, more consciousnesses.
    Once there is a complete separation posited between a consciousness and an object of consciousness—
    The remedy, it may be offered, is to clarify what characterizes consciousness and what characterizes object. But the rebuttal is that as long as consciousness is split from its object–any description or
    characterization will itself be an object–and so again, paradox.
    MY own view on this is that these are points of view–that it is points of view that make up the world–and so there is no reason to
    decide whether nominalist or realist should dominate. Just enumerate the for and against and marvel at the mind!

  4. 5. Arnold Trehub says:

    This was my comment on Edge in response to Dehaene’s talk:

    Stan Dehaene has done excellent work in exploring the neuronal correlates of the brain’s global workspace. But we have to recognize that what he and his colleagues are measuring are the brain changes in response to a novel perception of a previously masked object by a person who is already conscious. I agree with Steve Pinker that a global workspace is a key function of consciousness, but it is not an explanation of consciousness. In order to understand consciousness we have to explain how the brain is able to represent a volumetric world filled with objects and events from our own privileged egocentric perspective — the problem of subjectivity. This challenge is compounded by the fact that we have no sensory apparatus for detecting the 3D space in which we live. Recent work combining empirical measures of phenomenal experience, brain imaging, and detailed neuronal modeling, are making encouraging progress in our effort to understand consciousness and subjectivity.

  5. 6. Vicente says:


    This challenge is compounded by the fact that we have no sensory apparatus for detecting the 3D space in which we live

    I don’t understand very well what you mean. How would you define or design such apparatus. We have binocular vision, we have touch, we have stereo-hearing. With all that data we construct a 3D world… I don’t think such apparatus can exist (natural or artificial).

  6. 7. Arnold Trehub says:

    Vicente: “We have binocular vision, we have touch, we have stereo-hearing. With all that data we construct a 3D world…”

    I see it differently. The sensory mechanisms that you mention cannot construct a coherent global 3D world. In my view, they provide the *content* for our brain’s egocentric *representation* of the real 3D world which is innate (retinoid space). Objects and events are projected in proper spatio-temporal register and in appropriate locations within this brain space. For example, see Fig. 5 here:


    and “Analysis and Representation of Object Relations”, here:


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