Multiple Drafts: Exploring Consciousness and Computation

1. Cognitive Computing: 2012 Consciousness and Computation: human and machine intelligence 4. MULTIPLE DRAFTS (DENNETT) Mark Bishop

2. The Cartesian theatre • ‘The observer’ in the mind takes information from all sources to form her ‘point of view’; she watches the play of life in her personal Cartesian theatre. • The ‘Cartesian theatre’ is the notional site in the brain where all such sources of information ‘come together’. • For Descartes, it is the pineal gland; linking res cogitans & res extensa. • The notional site where discriminations across all modalities are put into registration ready for subjective judgement. • But is this really so? • “There is no cell or group of cells in the brain of such anatomical or functional pre-eminence as to appear to be the keystone or centre of gravity of the whole system”, • (William James (1890); emphasized in Dennett’s, ‘Consciousness Explained’). (c) Bishop: Consciousness and Computation

3. On multiple drafts • Dennett’s ‘multiple drafts’ theory of consciousness is a physicalist/cognitivist theory of conscious, which rejects the Cartesian Theatre and in its place views the mind in terms of transient sites of ‘information processing’. • The theory is described in depth in Dennett’s 1991 book, ‘Consciousness Explained’. • The book purports to offer a high-level explanation of consciousness which is consistent with support for the possibility of strong AI. (c) Bishop: Consciousness and Computation

4. The ‘multiple drafts’ motif • For any given agent-environment interaction there are a variety of ‘sensory inputs’ and a variety of ‘interpretations’ of these inputs. • The sensory inputs arrive in the brain and are interpreted at different times; so a given interaction/event can give rise to a succession of discriminations, constituting the equivalent to the multiple-drafts (revisions) of a narrative or story. • As soon as each discrimination is accomplished by neurons in the brain, it becomes immediately available for eliciting a report and/or subsequent behaviour; it does not have to wait to be further processed and passed-on for subsequent presentation in the ‘Cartesian theatre’. (c) Bishop: Consciousness and Computation

5. The observer, in time • Dennett’s ‘multiple drafts’ model emphasizes conscious experience as taking time to occur • “Percepts do not instantaneously arise in the mind in their full richness”. • Furthermore the ‘multiple drafts’ model 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 in the brain, rather than some singular view containing our experience. • I.e. There is “no central experiencer [who] confers a durable stamp of approval on any particular draft”. (c) Bishop: Consciousness and Computation

6. Access consciousness • Multiple drafts purports to explain consciousness in terms of what Ned Block has termed ‘access consciousness’ alone, denying the independent existence of ‘phenomenal consciousness’. • Dennett is [in] famously disparaging about ‘qualia freaks’. • Dennett argues that "Everything real has properties, and since I don't deny the reality of conscious experience, I grant that conscious experience has properties”. • For Dennett, once we've explained a perception fully in terms of how it affects us, there is nothing left to explain; specifically, there is no such thing as a perceptive-experience which may be considered in and of itself (a quale). • Having related all consciousness to properties, he concludes that the properties cannot be meaningfully distinguished from our judgments about them. (c) Bishop: Consciousness and Computation

7. Temporal anomalies of consciousness • In a seminal paper from 1992 – ‘Time and the Observer’- Dennett discusses several temporal anomalies of consciousness, which become non-problems under the ‘multiple drafts’ hypothesis: • Colour phi, (Goodman/Kolers); • Cutaneous rabbit, (Geldard & Sherrick); • Referral backwards in time, (Libet); • Subject delay of conscious intention, (Libet); • The ‘pyschic’ slide projector, (Walters) (c) Bishop: Consciousness and Computation

8. Time and the observer • Consider lightning. • Typically we see a flash before we hear the sound, as light travels faster through air than sound. • However auditory processing performed faster than visual. • The above result in a theoretical human ‘horizon of simultaneity’ of about 10m from sense organs. • Where stimuli are perceived as arriving at the same time. • Such that stimuli are centrally available to the brain at the same time. • Spatial smearing: what what counts as the finish line? • As we know neuron signal processing is relatively slow. • But if there is no one point in the brain where all signals come together it may be that in point A of the brain signals about sound arrives first and in point B signals about light; so what do we perceive as happening first ?? • Temporal smearing: when everyday assumptions have to be replaced • The human capacity to make conscious discriminations of temporal order drops to chance when the difference in onset is on the order of 50msec. (c) Bishop: Consciousness and Computation

9. Apparent motion – the phi phenomenon • Two dots, less than 4 degrees apart, blink in rapid succession. • An illusion of movement is perceived • One dot moves in a smooth path between the two dot positions. • The basis of cinema and television. (c) Bishop: Consciousness and Computation

10. On colour phi • But what happens if the dots are of different colour, say red & green? • Do we see two flashing dots? • Or one dot changing colour • Abrupt change at some point on trajectory • Smooth change across trajectory. • Usual perception is of one dot abruptly changing colour half way along the path. • But how can we perceive a colour change to red, before the red dot appears? (c) Bishop: Consciousness and Computation

11. Temporal revision (a) Orwellian • Orwellian, post-experiential change to memory: • Memory is tampered with/overwritten by some other factor disturbing the temporal order of events • Perhaps memory of another woman with glasses contaminates the memory • But there was a brief moment when memory was correct (c) Bishop: Consciousness and Computation

12. Temporal revision (b) Stalinesque • Here, a ‘false court’ is set up in mind where previous facts tint the final judgements: • A ‘fact’ can be altered by the prior knowledge such as memory of woman with glasses; • Here a hallucination of a woman-with-glasses occurs as the woman-without-glasses walks by; there is no moment when the memory is correct. • In the field of colour phi there is intense debate between the Stalinesque and Orwellian revisions of the Cartesian theatre; with nothing to choose between them, both accounts can be made to fit all the data. (c) Bishop: Consciousness and Computation

13. Cutaneous rabbit • The subjects arm is rested on a cushion on a table. • A mechanical tapping device is located at three positions about 1 foot apart. • At one site there are 5 taps; followed by 2 at the next site up the arm followed by 3 in the highest position. • Taps are perceived as a small creature hopping up intermediate points on the arm. • But how after the first taps does the brain ‘know’ there will be others? • NB. If the experimenter presents only the first set of taps there is no illusion. (c) Bishop: Consciousness and Computation

14. Libet (1) - Referral backwards in time • Direct stimulation on the somatosensory cortex results in a tingle at the corresponding site on the body. • There is a delay of 500mS after stimulation to reach generate ‘neuronal adequacy’ • The stage at which cortical processes culminate to yield the ‘conscious experience’ of a tingle. • Stimulation of the hand region in right somatosensory cortex results in perception of a tingle on the left hand. • Similarly a real – electrical - stimulation of the left hand also results in the perception a tingle. (c) Bishop: Consciousness and Computation

15. Stimulation of hand and cortex • So when Libet stimulated the left cortex shortly before the left hand, one would predict the subject perceives right hand stimulation before the left. • In fact Libet observed the opposite – real left hand stimuli felt first! • Even when Libet stimulated both cortex and hand simultaneously, the subject perceived the real hand stimulation first! • Even though the signal has much longer to travel (nerve impulse has to propagate up the arm etc). • It appears as if when the real hand was stimulated the event was somehow automatically ‘referred backwards in time’; spooky … (c) Bishop: Consciousness and Computation

16. Libet (2) – The subjective delay of conscious intent • Libet asked subject to spontaneously decide to flex the wrist of one hand. • At the same time there is a clock ticking • E.g. A dot traversing a circle on an oscilloscope. • Subjects asked to note position of the dot at the precise time they formed the intention to flex their wrist. • Subject EEG shows a ‘readiness potential’ about 350-400mS before the conscious decision to act! • Hence Libet suggests that the, “cerebral initiation of a spontaneous process begins unconsciously”. • Is conscious epiphenomenal? (c) Bishop: Consciousness and Computation

17. The psychic slide projector • In 1963 Grey Walter (the Cybernetician of robot-turtle fame) inserted electrodes into the motor cortex of a group of subjects to see if particular bursts of neuronal activity were the precursors to intentional action. • Each patients looked at slides from a carousel projector and could advance the slides at will by depressing a button. • But the button was a dummy; the slides were advanced when particular signal was detected by the implanted electrodes. • The patients were very startled by this and reported that the slide projector was anticipating their actions! • The subjects reported a ‘strange sensation’ :- they never quite had time to ‘veto’ the conscious button push, as they noticed the slide already changing! (c) Bishop: Consciousness and Computation

18. Adding a delay between button press and slide advance • If the strange sensation is detected immediately – the effect may be considered Stalinesque. • Alternatively, if the effect requires a retrospective revision/reinterpretation of events to try and make sense it may be considered Orwellian. • But if, say, we add a longer delay [e.g. 300mS as predicted by Libet’s experiments] then the strange ‘pre-cognitive effects’ disappear .. • .. all the patients now report that the strange sensation (of not being able to veto the change) has gone. (c) Bishop: Consciousness and Computation

19. Problems with time? • Of course one can easily make these problems disappear by taking a hardcore behaviourist stance • I.e. Simply refuse to take introspective reports seriously. • Otherwise, unless we abandon a foundational principle – that cause precedes effect – it seems that we have a problem.. • However Dennett argues that this is a problem rooted in the Cartesian theatre. (c) Bishop: Consciousness and Computation

20. Seat of consciousness • In the MULTIPLE DRAFTS hypothesis, Dennett suggests that there is no one place in the brain where “it [sense data] all comes together” to form a unique multi-modal representation of the world that determines say, temporal properties of events. • Conversely information is distributed across the brain: • some is verbalised; • some ‘memorised’ in semantic readiness/emotional states etc; • some ‘dies out’ without a trace. • The brain must ‘bind’ these separate contents of mind, but the binding mechanisms are themselves spatially distributed, hence the point of view of the observer is fundamentally ‘spatially smeared’. • Resulting in a temporal smear of several hundred milliseconds and during this period our common sense assumptions on timing ‘need to be replaced’. • In many cases when stimulus onset is around 50mS, discrimination of temporal order of two stimuli is no better than chance. (c) Bishop: Consciousness and Computation

21. Multiple Drafts: cf. Consciousness Explained, (pp. 113-115) • Although the brain is a massive parallel processing system, feature detections only occur once in the brain; such that once information has been processed it is not sent elsewhere. • That is, once a localized, specialized "observation" has been made, the information content thus fixed does not have to be sent somewhere else to be re-discriminated by some "master" discriminator • However all perceptual operations are multi-track processes of ‘editorial revision’ - interpretation and elaboration of sensory inputs - over hundreds of milliseconds. • Like a narrative stream undergoing continual editing, information entering the nervous system is under continuous ‘editorial revision’from now and forever onwards; there is no final narrative. • How local discriminations contribute to the conscious narrative is subject to continual amendment by other [competing] processes in the brain forming the changing ‘stream of consciousness’. (c) Bishop: Consciousness and Computation

22. Editorial revision in Multiple Drafts • These editorial processes occur over large fractions of a second, during which time various additions, incorporations, emendations, and over-writings of content can occur, in various orders. • We don’t directly experience what happens on our retinas, in our ears, on the surface of our skin. • What we actually experience is a product of many processes of interpretation — editorial processes, in effect. • They take in relatively raw and one-sided representations, and yield collated, revised, enhanced representations, and they take place in the streams of activity occurring in various parts of the brain. (c) Bishop: Consciousness and Computation

23. The core themes in Dennett’s ‘Multiple Drafts’ hypothesis • Feature detections or discriminations only have to be made once. • That is, once a particular “observation” of some feature has been made, by a specialized, localized portion of the brain, the information content thus fixed does not have to be sent somewhere else to be re-discriminated by some “master” discriminator. • In other words, discrimination does not lead to a representation of the already discriminated feature for the benefit of the audience in the Cartesian Theatre .. • For there is no Cartesian Theatre! (c) Bishop: Consciousness and Computation

24. Multiple drafts, consciousness and time • In the multiple drafts model there are multiple representational processes in the brain all competing to become the ‘official’ version • Certain drafts are persistent, forming the version that gets verbally reported, while others fade away. • On this view, there is no fact of the matter about when an experience ‘enters’ consciousness, because there is no single conscious version of events: • there is just a stimulus leading to the production of multiple drafts; • only one of which finally leads to the verbal report; • and the verbally reported draft is not to be equated with ‘the’ conscious version. (c) Bishop: Consciousness and Computation

25. Multiple drafts and the colour phi illusion • In the colour phi illusion the following process occur: • (a) Red dot discriminated then (b) a green dot is discriminated; • (c) In parallel the motion detection system is operating • The motion detection system produces a best fit plausible ‘draft to consciousness’ before either (a) or (b) can be reported. • However if we delay the onset of (b) the ‘reported’ phi phenomenology changes. • See flickering dots and not the phi phenomena. (c) Bishop: Consciousness and Computation

26. A multiple drafts explanation of the ‘psychic slide projector’ • Under a multiple drafts interpretation the question of Orwellian or Stalinesque memory revisions also fades away. • This is because the sense the subjects reported of not quite having had time to "veto" the initiated button push when they "saw the slide was already changing" is simply a natural interpretation for the brain to settle on (eventually) given the various contents made available at various times for incorporation into the conscious narrative. • With a longer time delay the brain has time to settle on a different narrative. (c) Bishop: Consciousness and Computation

27. Dennett on consciousness • “Human consciousness is a huge collection of memes (meme effects in brains) that can be best understood as the operation of a von Neumannesque virtual machine implemented in the parallel architecture of a brain that was not designed for any such activity”, (Consciousness explained, p. 210). • “If you ask yourself ‘What would I do in this situation if I were a thousand-channel-wide parallel processor?’ you draw a blank; you don’t have any personal familiarity with — any “direct access to” — processes happening in a thousand channels at once, even though that is what is going on in your brain. Your only access to what is going on in your brain comes in a sequential “format” that is strikingly reminiscent of the von Neumann architecture”, (Consciousness explained, p. 215). • A commitment to Strong AI follows from Dennett’s proposal, as being conscious is entirely reduced to a matter of implementing the right ‘von Neumannesque’ virtual machine on a suitably parallel processor. (c) Bishop: Consciousness and Computation

28. Criticisms from Revonsuo and Puccetti • Revonsuo • The theory does not allow us to understand a distinction between real and apparent (hallucinatory) streams of consciousness. • Puccetti • Multiple Drafts theory cannot properly deal with cerebral commissurotomy (split-brain) persons. • Two centers of consciousness, as reported in the standard literature for split-brain patients, would be problematic for Multiple Drafts as Multiple Drafts theory suggest splitting the corpus callosum would have no effect – narrative stream will still flow. (c) Bishop: Consciousness and Computation

29. Searle’s criticisms • Multiple drafts is not a real theory of consciousness: • it does not address what makes brain states conscious states; • At best it addresses how processes become conscious. • It is wrong to say that because science is objective it cannot recognise the reality of subjective states. • Arguments about, for example temporal paradoxes, do not show qualia do not exist. • The simple distinction between appearance and reality, to which Dennett appeals, does not hold for subjective conscious states as in these cases appearance IS the reality, (cf. Revonsuo). (c) Bishop: Consciousness and Computation