Presentation on theme: "Time and the observer: the where and when of consciousness in the brain A. C. Dennett and M. Kinsbourne."— Presentation transcript:
Time and the observer: the where and when of consciousness in the brain A. C. Dennett and M. Kinsbourne
Is there a “central observer” in the brain? A Problem: to decide what to count as the “finishing line” in the brain.
The wrong ideas There 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.”
Dennett’s main point There is no one place in the brain through which all these causal trains must pass to deposit their contents “in consciousness.”
Dennett’s main claim The 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.
Cartesian materialism The idea of there being a centered locus in the brain Cartesian theater model of consciousness
Multiple drafts model Massively parallel operations Distributed activation patterns These patterns are drafts which are undergone constant editing
Some temporal anomalies Color phi The cutaneous “Rabbit” Referral backwards in time Subjective delay of consciousness of intention
How does the brain keep track of the temporal information? How to achieve synchrony? Two models: Delay loop mechanism Buffer memories
Representations of temporal properties The battle of New Orleans Solution to the problems of communicating information about time: by embedding representations of the relevant time information in the content of their signals
Time represented: by the postmark Time of representing: the day the letter arrives
What matters is the temporal content of events.
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.
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)
The Orwellian and Stalinesque revisions: the illusion of a distinction
Orwellian: post-experiential contaminations or revisions of memory Stalineque: pre-experiential revision
Dennett’s point The 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.
If Cartesian materialism were correct, this question would have to have an answer, even if we could not introspect it.
If Cartesian materialism is incorrect, can the distinction between pre- and post-experiential content revisions be maintained?
An examination of the color phi phenomenon shows that the distinction cannot be maintained.
Anomalies about Time Color Phi phenomenon
Dennett’s comment There is only the verbal difference between the two theories
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.”
Libet ’ s Experiment The backwards referral hypothesis
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.
(1) A continuous stimulus train at 60 pulses per second was applied to sensory cortex. (C) (2) A single pulse at threshold to the skin of the arm 200 msec later. (S) (3) C-experience was reported to occur approximately 500 msec after stimulation began. (2’) In fact it was reported to occur at approximately the time of the skin pulse, before the C-experience. (4) We might expect S- experience to occur 200 msec after C-experience.
Cortical stimulus O ms 200ms The skin stimulus This finding led Libet to propose the “subjective referral of sensory experience backwards in time” ms Conscious experience of the skin stimulus was reported. 500ms Conscious experience of the cortical stimulus was reported. 700ms Conscious experience of the skin stimulus was reported.
If half a second of neural activity is required for conscious perception, why is the skin stimulus felt first? ?
The backwards referral hypothesis Libet Sensory experience are subjectively referred back in time once neuronal adequacy has been achieved.
1.Information travels from the skin up to the relevant sensory area of cortex. 2.If,and only if, neural activity continues there for the requisite half a second, the stimulus can be consciously perceived. 3.At that point it is subjectively referred back to the actual time at which it happened. The backwards referral hypothesis Steps
Stimulate sensorimotor cortex O ms 200ms Stimulate the skin Combine the experiment (3) and (4) (3) indicate by blue; (4) indicate by red ms Conscious experience of the stimulus of skin was reported. 500ms Conscious experience of the stimulus of sensorimotor cortex was reported. Stimulate medial lemniscus Conscious experience of the stimulus of medial lemniscus was reported. 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 skin itself is stimulated.
The primary evoked potential act as a timing signal to which the sensation is referred back or “antedated”.