Presentation on theme: "Cognitive Computing: 2012 Consciousness and Computation: human and machine intelligence 4. MULTIPLE DRAFTS (DENNETT) Mark Bishop."— Presentation transcript:
Cognitive Computing: 2012 Consciousness and Computation: human and machine intelligence 4. MULTIPLE DRAFTS (DENNETT) Mark Bishop
01/04/2014(c) Bishop: Consciousness and Computation2 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 Dennetts, Consciousness Explained).
On multiple drafts Dennetts 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 Dennetts 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. 01/04/2014(c) Bishop: Consciousness and Computation3
The multiple drafts motif For any given agent-environment interaction there are a variety of sensory inputs and a variety ofinterpretations 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. 01/04/2014(c) Bishop: Consciousness and Computation4
The observer, in time Dennetts 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. 01/04/2014(c) Bishop: Consciousness and Computation5
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. 01/04/2014(c) Bishop: Consciousness and Computation6
01/04/2014(c) Bishop: Consciousness and Computation7 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)
01/04/2014(c) Bishop: Consciousness and Computation8 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.
01/04/2014(c) Bishop: Consciousness and Computation9 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.
01/04/2014(c) Bishop: Consciousness and Computation10 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?
01/04/2014(c) Bishop: Consciousness and Computation11 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
01/04/2014(c) Bishop: Consciousness and Computation12 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.
01/04/2014(c) Bishop: Consciousness and Computation13 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.
01/04/2014(c) Bishop: Consciousness and Computation14 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 generateneuronal adequacy The stage at which cortical processes culminate to yield theconscious 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.
01/04/2014(c) Bishop: Consciousness and Computation15 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 …
01/04/2014(c) Bishop: Consciousness and Computation16 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 mS before the conscious decision to act! Hence Libet suggests that the, cerebral initiation of a spontaneous process begins unconsciously. Is conscious epiphenomenal?
01/04/2014(c) Bishop: Consciousness and Computation17 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 toveto the conscious button push, as they noticed the slide already changing!
01/04/2014(c) Bishop: Consciousness and Computation18 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 Libets 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.
01/04/2014(c) Bishop: Consciousness and Computation19 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.
01/04/2014(c) Bishop: Consciousness and Computation20 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.
01/04/2014(c) Bishop: Consciousness and Computation21 Multiple Drafts: cf. Consciousness Explained, (pp ) 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.
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 dont 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. 01/04/2014(c) Bishop: Consciousness and Computation22
The core themes in DennettsMultiple 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! 01/04/2014(c) Bishop: Consciousness and Computation23
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. 01/04/2014(c) Bishop: Consciousness and Computation24
01/04/2014(c) Bishop: Consciousness and Computation25 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.
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. 01/04/2014(c) Bishop: Consciousness and Computation26
01/04/2014(c) Bishop: Consciousness and Computation27 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 dont 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 Dennetts proposal, as being conscious is entirely reduced to a matter of implementing the right von Neumannesque virtual machine on a suitably parallel processor.
01/04/2014(c) Bishop: Consciousness and Computation28 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.
01/04/2014(c) Bishop: Consciousness and Computation29 Searles 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).