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Daniel Dennett's Multiple Drafts Model of Consciousness is a physicalist theory of consciousness based upon cognitivism, which views the mind in terms of information processing. The theory is described in depth in his book, Consciousness Explained, written in 1991. As the title states, the book proposes a high-level explanation for consciousness, which is consistent with support for the possibility of strong AI.

The Multiple Drafts theory is operationalist. As Dennett says: "There is no reality of conscious experience independent of the effects of various vehicles of content on subsequent action (and hence, of course, on memory)."

Dennett's thesis is that our modern understanding of consciousness is marred by remnants of René Descartes's now-obsolete ideas. To show this, he starts with a description of the phi illusion. In this experiment, two different coloured lights, with an angular separation of a few degrees at the eye, are flashed in succession. If the interval between the flashes is less than a second or so, the first light that is flashed appears to move across to the position of the second light. Furthermore, the light seems to change colour as it moves across the visual field. A green light will appear to turn red as it seems to move across to the position of a red light. Dennett asks how we could see the light change colour before the second light is observed.

Dennett argues that conventional explanations of the colour change boil down to either Orwellian or Stalinesque hypotheses, which are the result of Descartes' continued influence. In an Orwellian hypothesis, the subject comes to one conclusion, then goes back and changes that memory in light of subsequent events. This is akin to George Orwell's Nineteen Eighty-Four, where records of the past are routinely altered. In a Stalinesque hypothesis, the two events would be reconciled prior to entering the subject's consciousness, with the final result presented as fully resolved. This is akin to Joseph Stalin's show trials, where the verdict has been decided in advance and the trial is just a rote presentation.

e can suppose, both theorists have exactly the same theory of what happens in your brain; they agree about just where and when in the brain the mistaken content enters the causal pathways; they just disagree about whether that location is to be deemed pre-experiential or post-experiential. hey even agree about how it ought to "feel" to subjects: Subjects should be unable to tell the difference between misbegotten experiences and immediately misremembered experiences.

As in the above quote, Dennett argues that there is no principled basis for picking one theory over the other, because they share a common error by supposing that there is a special time and place where unconscious processing become consciously experienced, entering what Dennett calls the 'Cartesian theater'. Both theories require us to cleanly divide a sequence of perceptions and reactions into before and after the instant that they reach the seat of consciousness, but he denies that there is any such moment, as it would lead to infinite regress. Instead, he asserts that there is no privileged place in the brain where consciousness happens. Dennett states that, "here does not exist a process such as 'recruitment of consciousness'(into what?), nor any place where the 'vehicle's arrival' is recognized (by whom?)." (Dennett & Kinsbourne 1995)

"Cartesian materialism is the view that there is a crucial finish line or boundary somewhere in the brain, marking a place where the order of arrival equals the order of "presentation" in experience because what happens there is what you are conscious of. Many theorists would insist that they have explicitly rejected such an obviously bad idea. But the persuasive imagery of the Cartesian Theater keeps coming back to haunt us — laypeople and scientists alike — even after its ghostly dualism has been denounced and exorcized.

With no theater, there is no screen, hence no reason to re-present data after it has already been analyzed. Dennett says that, "the Multiple Drafts model goes on to claim that the brain does not bother 'constructing' any representations that go to the trouble of 'filling in' the blanks. That would be a waste of time and (shall we say?) paint. The judgement is already in so we can get on with other tasks!" In other words the Multiple Drafts model holds that stimuli are analysed after the event and that no modelling of the stimuli, such as filling in colours and shapes, occurs.

According to the model, there are a variety of sensory inputs from a given event and also a variety of interpretations of these inputs. The sensory inputs arrive in the brain and are interpreted at different times, so a given event can give rise to a succession of discriminations, constituting the equivalent of multiple drafts of a story. As soon as each discrimination is accomplished, it becomes available for eliciting a behaviour; it does not have to wait to be presented at the theatre.

Like a number of other theories, the Multiple Drafts model understands conscious experience as taking time to occur, such that "percepts do not instantaneously arise in the mind in their full richness" (Dennett & Kinsbourne 1995). The distinction is that Dennett's theory denies any clear and unambiguous boundary separating conscious experiences from all other processing. According to Dennett, consciousness is to be found in the actions and flows of information from place to place, rather than some singular view containing our experience. There is "no central experiencer confers a durable stamp of approval on any particular draft" (Dennett & Kinsbourne 1995)

Different parts of the neural processing assert more or less control at different times. For something to reach consciousness is akin to becoming famous, in that it must leave behind consequences by which it is remembered. To put it another way, consciousness is the property of having enough influence to affect what the mouth will say and the hands will do. Which inputs are "edited" into our drafts "is not an exogenous act of supervision, but part of the self-organizing functioning of the network, and at the same level as the circuitry that conveys information bottom-up" (Dennett & Kinsbourne 1995).

The conscious self is taken to exist as an abstraction visible at the level of the intentional stance, akin to a body of mass having a 'center of gravity'. Analogously, Dennett refers to the self as the 'center of narrative gravity', a story we tell ourselves about our experiences. Consciousness exists, but not independently of behavior and behavoral disposition, which can be studied through heterophenomenology.

The origin of this operationalist appoach can be seen in Dennett's immediately earlier work. Dennett (1988) explains consciousness in terms of access consciousness alone, he argues that "Everything real has properties, and since I don't deny the reality of conscious experience, I grant that conscious experience has properties". Having related all consciousness to properties, he concludes that they cannot be meaningfully distinguished from our judgements about them. He writes:

The infallibilist line on qualia treats them as properties of one's experience one cannot in principle misdiscover, and this is a mysterious doctrine (at least as mysterious as papal infallibility) unless we shift the emphasis a little and treat qualia as logical constructs out of subjects' qualia-judgments: a subject's experience has the quale F if and only if the subject judges his experience to have quale F. We can then treat such judgings as constitutive acts, in effect, bringing the quale into existence by the same sort of license as novelists have to determine the hair color of their characters by fiat. We do not ask how Dostoevski knows that Raskolnikov's hair is light brown.

In other words, he's saying that, once we've explained a perception fully in terms of how it affects us, there is nothing left to explain, especially not a perception considered in and of itself; a quale. Instead, the subject's honest reports of how things seem to them are inherently authoritative on how things seem to them, but not on the matter of how things actually are.

So when we look one last time at our original characterization of qualia, as ineffable, intrinsic, private, directly apprehensible properties of experience, we find that there is nothing to fill the bill. In their place are relatively or practically ineffable public properties we can refer to indirectly via reference to our private property-detectors — private only in the sense of idiosyncratic. And insofar as we wish to cling to our subjective authority about the occurrence within us of states of certain types or with certain properties, we can have some authority — not infallibility or incorrigibility, but something better than sheer guessing — but only if we restrict ourselves to relational, extrinsic properties like the power of certain internal states of ours to provoke acts of apparent re-identification. So contrary to what seems obvious at first blush, there simply are no qualia at all.

The key to the Multiple Drafts Model is that, after removing qualia, explaining consciousness boils down to explaining the behavior we recognize as conscious. Consciousness is as consciousness does.

Critical Responses to Multiple Drafts

Dennett's theory has received some criticism. At least part of this is because of the tone of his presentation. As one grudging supporter admits, "there is much in this book that is disputable. And Dennett is at times aggravatingly smug and confident about the merits of his arguments . All in all Dennett's book is annoying, frustrating, insightful, provocative and above all annoying." (Korb 1993)

Much of the criticism asserts that Dennett's theory attacks the wrong target, failing to explain what it claims to. Some even parody the title of the book as "Consciousness Explained Away", accusing him of greedy reductionism. Another line of criticism disputes the accuracy of Dennett's characterizations of existing theories:

The now standard response to Dennett’s project is that he has picked a fight with a straw man. Cartesian materialism, it is alleged, is an impossibly naive account of phenomenal consciousness held by no one currently working in cognitive science or the philosophy of mind. Consequently, whatever the effectiveness of Dennett’s demolition job, it is fundamentally misdirected (see, e.g., Block, 1993, 1995; Shoemaker, 1993; and Tye, 1993). (O'Brien and Opie 1999)

Multiple Drafts is also attacked for making a claim to novelty. It may be the case, however, that such attacks mistake which features Dennett is claiming as novel. Korb states that, "I believe that the central thesis will be relatively uncontentious for most cognitive scientists, but that its use as a cleaning solvent for messy puzzles will be viewed less happily in most quarters." (Korb 1993) In this way, Dennett uses uncontroversial ideas towards more controversial ends, leaving him open to claims of unoriginality when uncontroversial parts are focused upon.

Even the notion of consciousness as drafts is not unique to Dennett. According to Hankins, Dieter Teichert suggests that Paul Ricoeur's theories agree with Dennett's on the notion that "the self is basically a narrative entity, and that any attempt to give it a free-floating independent status is misguided." Others see Derrida's (1982) representationalism as consistent with the notion of a mind that has perpetually changing content without a definitive present instant.

To those who believe that consciousness entails something more than behaving in all ways conscious, Dennett's view is seen as eliminativist, since it denies the existence of qualia and philosophical zombies. However, Dennett is not denying the existence of the mind or of consciousness, only what he considers a naive view of them. The point of contention is whether Dennett's own definitions are indeed more accurate, whether what we think of when we speak of perceptions and consciousness can be understood in terms of effect on behavior.

The role of information processing in consciousness has been criticised by John Searle who, in his Chinese room argument (Searle 1980), states that he cannot find anything that could be recognised as conscious experience in a system that relies solely on motions of things from place to place. Dennett sees this argument as misleading, arguing that consciousness is not to be found in specific part of the system, but in the actions of the whole. In essence, he denies that consciousness requires something in addition to capacity for behavior, saying that philosophers such as Searle, "just can't imagine how understanding could be a property that emerges from lots of distributed quasi-understanding in a large system" (p439).

Many philosophers have rejected Multiple Drafts for a variety of reasons. Chalmers (1996) maintains that Dennett has produced no more than a theory of how subjects report events. Block (1995) considers that Dennett's concentration on a single place through which processing flows and in which experience occurs does not represent modular theories of brain function. Bogen (1992) points out that if Cartesian materialism were true the brain is bilaterally symmetrical so there might be two Cartesian theatres so arguments against one are flawed. Velmans (1992) argues that the phi effect and the "cutaneous rabbit" illusion demonstrate that there is a delay whilst modelling occurs and that this delay was discovered by Libet. It has also been pointed out that the argument in the Multiple Drafts model does not support its conclusion (see for instance Bringsjord 1996).

Neuroscientists do not often respond to philosophical theories such as "Multiple Drafts" but the neuroscience of Dennett's claim that the gaps in experience are not "filled in" is highly debatable. In the past 15 years many of Dennett's claims that Multiple Drafts is supported by neuroscience have fallen away. Dennett (1991) maintains that the brain "does not have to fill in the blind spot" but this is inconsistent with modern neurophysiology. The visual cortex on each side contains a region that represents the blind spot of the eye on the opposite side of the head and receives data from the eye on the same side (Tong & Engel 2001), data from the other eye cannot be seen. The part of the brain representing the blind spot is literally "filled in" with ipsilateral data. Dennett claims that the brain does not need to "fill in" colour but there is a disease known as "achromatopsia", due to damage to cortical area V4, in which everything is seen in grey-scale because the ability to add colour to forms is lost. Dennett claims that the brain does not "model" motion but an area of cortex (MT/V5) has been shown to do precisely this. When area V5 is damaged patients can suffer from "akinetopsia" where the world appears to change in a succession of static frames (Rizzo et al 1995). MT/V5 is also involved in modelling the motion of groups of objects that are moving together (Muckli et al 2002 ). Even our everday experience of watching the succession of frames on television is due to cortical 'short-range apparent motion modelling' (Anderson and Anderson (1993)). EEG experiments on Event Related Potentials (cortical electrical potentials that occur after a stimulus) show that conscious experience is related to the N4 component that correlates with cortical activity about 0.5 second after an event (cf: Williams et al 2004), supporting Velman's contention that there is a delay for modelling before conscious experience. Dennett denies that there is any need for "binding" so it does not exist but Moutoussis and Zeki (1997) have shown that the outline and coloured content of moving squares can be separated in experiments, showing that the synchronisation of motion modelling and colour filling can be lost so that colour and motion can be "unbound". Even phenomena such as retinal "surround inhibition" that amplifies boundaries between colours and orientation zones in the cortical map of the retina are "modelling" in the brain.

The list above could be expanded with many more items because, as the power of neuroscientific techniques increases, it is becoming apparent that the brain is a modelling engine. The neuroscience offers strong support for the idea that modelling (Stalinesque), reporting (Orwellian), and reporting without remodelling all occur in the brain.

See also

• Daniel Dennett
• Consciousness

References

Block, N. (1993). Book review of Dennett's Consciousness Explained. Journal of Philosophy 90, 181-193.

Block, N. (1995). On a confusion about a function of consciousness. Behavioral and Brain Sciences 18, 227-287.

Bringsjord (1996). Explaining Phi Without Dennett's Exotica: Good Ol' Computation Suffices (1996) http://citeseer.ifi.unizh.ch/bringsjord96explaining.html

Bogen, J.E. (1992). Descartes' fundamental mistake: Introspective singularity. Commentary on Daniel C. Dennett and Marcel Kinsbourne (1992) Time and the observer: The where and when of consciousness in the brain. BBS 15:183-247.

Chalmers (1996). The Conscious Mind. Oxford University Press.

Daniel C Dennett. (1988). Quining Qualia. in A. Marcel and E. Bisiach, eds, Consciousness in Modern Science, Oxford University Press 1988. Reprinted in W. Lycan, ed., Mind and Cognition: A Reader, MIT Press, 1990, A. Goldman, ed. Readings in Philosophy and Cognitive Science, MIT Press, 1993. http://ase.tufts.edu/cogstud/papers/quinqual.htm

Daniel C Dennett. (1991). Consciousness Explained. Little, Brown & Co. USA. Available as a Penguin Book.

Dennett, D. and Kinsbourne, M. (1992) Time and the Observer: the Where and When of Consciousness in the Brain. (1992) Behavioral and Brain Sciences, 15, 183-247, 1992. Reprinted in The Philosopher's Annual, Grim, Mar and Williams, eds., vol. XV-1992, 1994, pp. 23-68; Noel Sheehy and Tony Chapman, eds., Cognitive Science, Vol. I, Elgar, 1995, pp.210-274.http://ase.tufts.edu/cogstud/papers/time&obs.htm

Dennett, D. and Kinsbourne, M. (1995) Multiple Drafts (Response to Glicksohn and Salter in Behavioral and Brain Sciences, vol. 18, no. 4, 1995, pp. 810-11.) (Response to Glicksohn and Salter in Behavioral and Brain Sciences, vol. 18, no. 4, 1995, pp. 810-11.)

Derrida, J. (1982). Differance. In J. Derrida (Ed.), Margins of Philosophy, pp. 3-27. Chicago: The University of Chicago Press.

Muckli, L., Singer, W., Zanella, F.E. and Goebel, R. (2002) Integration of multiple motion vectors over space: an fMRI study of transparent motion perception. Neuroimage. 2002 Aug;16(4):843-56.

Rizzo, M., Nawrot, M. & Zihl, J. (1995). Motion and shape perception in cerebral akinetopsia.Brain, 118. 1105-1127.

O'Brien, G. and Opie, J. (1999). "A defense of Cartesian Materialism". Philosophy and Phenomenological Research 59:939-63 (1999).

Searle, J. (1980) "Minds, Brains and Programs"

Tong, F., & Engel, S. A. (2001). Interocular rivalry revealed in the human cortical blind-spot representation. Nature, 411, 195-199.

Tye, M. (1993). Reflections on Dennett and consciousness. Philosophy and Phenomenological Research 53, 893-898.

Velmans, M. (1992) Is Consciousness Integrated? Behavioral and Brain Sciences, 15 (2) 229-230 (commentary on Dennett & Kinsbourne "Time and the observer", BBS, 1992, 15(2): 183-201) Copyright Cambridge University Press

Williams LM, Liddell BJ, Rathjen J, Brown KJ, Shevrin H, Gray JA, Phillips M, Young A & Gordon E (2004). Mapping the time course of nonconscious and conscious perception of fear: An integration of central and peripheral measures. Human Brain Mapping,21, 64 - 74

External links

• The Philosophers Magazine: Philosopher of the Month, April 2003: Daniel Dennett
• 'Self and Consciousness: Multiple Perspectives' 1992, The Self as a Center of Narrative Gravity: Daniel Dennett
• 'Daniel Dennett - the intentional stance: Peter Hankins'
• 'Stage Effects in the Cartesian Theater: A review of Daniel Dennett's Consciousness Explained'
• Multiple Drafts, 1 December 2004, Peter Hankins

• Consciousness studies
• Philosophy of mind