Presentation on theme: "A. C. Dennett and M. Kinsbourne"— Presentation transcript:
1 A. C. Dennett and M. Kinsbourne Time and the observer: the where and when of consciousness in the brainA. C. Dennett and M. Kinsbourne
2 Is there a “central observer” in the brain? A Problem: to decide what to count as the “finishing line” in the brain.
3 The wrong ideasThere is some place in the brain where “it all comes together” in a multi-modal representation or display.The representation or display is definitive of the content of conscious experience.The temporal properties of the events (representations) determine the temporal properties of the subjective “stream of consciousness.”
4 Dennett’s main pointThere is no one place in the brain through which all these causal trains must pass to deposit their contents “in consciousness.”
5 Dennett’s main claimThe brain itself is Headquarters, the place where the ultimate observer is, but it is a mistake to believe that the brain has any deeper headquarters arrival at which is the necessary or sufficient condition for conscious experience.
6 Cartesian materialism The idea of there being a centered locus in the brainCartesian theater model of consciousness
7 Multiple drafts model Massively parallel operations Distributed activation patternsThese patterns are drafts which are undergone constant editing
8 Some temporal anomalies Color phiThe cutaneous “Rabbit”Referral backwards in timeSubjective delay of consciousness of intention
9 How does the brain keep track of the temporal information? How to achieve synchrony?Two models:Delay loop mechanismBuffer memories
10 Representations of temporal properties The battle of New OrleansSolution to the problems of communicating information about time:by embedding representations of the relevant time information in the content of their signals
11 Time represented: by the postmark Time of representing: the day the letter arrives
12 What matters is the temporal content of events.
13 How are temporal properties really inferred by the brain? Content-sensitive settling (such as film studio case)It is not necessary to use time to represent time.
14 The striking fact … should be noticed, namely that perceptions of temporal order need temporally ordered perceptions.Perception of shape and color, for example, need not themselves be correspondingly shaped or colored.(Mellor 1981)
15 The Orwellian and Stalinesque revisions: the illusion of a distinction
16 Orwellian: post-experiential contaminations or revisions of memory Stalineque: pre-experiential revision
17 Dennett’s pointThe distinction between perceptual revisions and memory revisions that works crisply at other scales is not guaranteed application.We have moved into the foggy area in which the subject’s point of view is spatially and temporally smeared.The question Oewellian or Stalinque? Need have no answer.
18 If Cartesian materialism were correct, this question would have to have an answer, even if we could not introspect it.
19 If Cartesian materialism is incorrect, can the distinction between pre- and post-experiential content revisions be maintained?
20 An examination of the color phi phenomenon shows that the distinction cannot be maintained.
22 Dennett’s commentThere is only the verbal difference between the two theories
23 Libet’s two remarkable temporal factors There is a substantial delay before cerebral activities, initiated by a sensory stimulus, achieve “neural adequacy” for eliciting any resulting sensory experience (500 msec)After neural adequacy is achieved, the subjective timing of the experience is referred backwards in time, utilizing a “timing signal.”
24 The backwards referral hypothesis Libet’s ExperimentThe backwards referral hypothesis
25 Basic idea of the experiment We ask subject to report the subjective timing of an ordinary stimulus to the skin and a cortically induced sensation.
26 (1) A continuous stimulus train at 60 pulses per second was applied to sensory cortex. (C) (2’) In fact it was reported to occur at approximately the time of the skin pulse, before the C-experience.(3) C-experience was reported to occur approximately 500 msec after stimulation began.(2) A single pulse at threshold to the skin of the arm 200 msec later. (S)(4) We might expect S-experience to occur 200 msec after C-experience.
27 This finding led Libet to propose the “subjective referral of sensory experience backwards in time” 700msConscious experience of the skin stimulus was reported.200msThe skin stimulusConscious experience of the skin stimulus was reported.500msConscious experience of the cortical stimulus was reported.Cortical stimulusO msms
28 ?If half a second of neural activity is required for conscious perception, why is the skin stimulus felt first?
29 The backwards referral hypothesis Libet Sensory experience are subjectively referred back in time once neuronal adequacy has been achieved.
30 The backwards referral hypothesis Steps Information travels from the skin up to the relevant sensory area of cortex.If ,and only if, neural activity continues there for the requisite half a second, the stimulus can be consciously perceived.At that point it is subjectively referred back to the actual time at which it happened.
31 Combine the experiment (3) and (4) One of the special features of medial lemniscus when it is stimulated:Unlike the cortex, a primary evoked potential is also produced, just as it is when the skinitself is stimulated.Combine the experiment (3) and (4)(3) indicate by blue; (4) indicate by redConscious experience of the stimulus of medial lemniscus was reported.200msStimulate the skinStimulate medial lemniscusmsConscious experience of the stimulus of skin was reported.500msConscious experience of the stimulus of sensorimotor cortex was reported.Stimulate sensorimotor cortexO ms
32 The primary evoked potential act as a timing signal to which the sensation is referred back or “antedated”.