TIME & THE OBSERVER: THE WHERE & WHEN OF CONSCIOUSNESS
IN THE BRAIN
by Dennett & Kinsbourne
This article challenges the idea of Cartesian materialism - the idea
there is a central locus in the brain where information is
experienced. Contrasts it with the Multiple Drafts model, where all
varieties of mental activity are accomplished in the brain by
parallel, multitrack processes of interpretation and elaboration of
sensory inputs. So there is no point in asking, for example, where
the vision and sound of cow come together to form a `cow'
experience, rather information entering the nervous system is under
continuous editorial revision. We don't directly experience what
happens on our retinas, in our ears, on our skin etc. What we
experience is a product of editorial processes. Also, feature
detection only has to occur once, ie it does not have to be sent
somewhere else to be rediscriminated, as it does not need to be
represented for the benefit of what Dennett calls a `Cartesian
audience'. It would be a mistake to ask when it becomes conscious as
these discriminations yield, over time, something like a narrative
stream, but at any point in time there are multiple drafts of
narrative fragments in various stages of editing in various places
in the brain. The multiple draft model avoids the mistake of
thinking there is a final canonical narrative.
However, in the open peer commentary, several investigators do not
feel that the idea of a single stream of consciousness is mistaken.
For example, Aronson suggests that while we may have parallel
distributed and fragmented traces of various inputs, these may be
accompanied by a sort of metatrace that corresponds to our conscious
narrative. This is rendered unlikely by the neurologist,Damasio's
assertion that there is no place in the brain where all sensorimotor
signals converge in space and time. Nevertheless, this does not
forbid the likelihood of there being several `mini theatres' where
signals are integrated and become consciously accessible. Farah
points to a study, for example, that demonstrates that the parietal
lobe is needed for visual percepts to reach consciousness. The
article aims in particular to explore the way the brain represents
time. Dennett challenges our intuition that our stream of
consciousness consists of events occurring in sequence, and that at
a given instant, every element in that sequence can be classified as
having already occurred, or having not occurred there yet. He points
out that stimuli originating in the toe have further to travel than
stimuli originating in the brain and asks how the brain ensures
central simultaneity of representation for distally simultaneous
stimulu. Heargues that imposing a synchronicity on operations
imposes delays, as other processing is put on hold until the slowest
stimulus arrives: `why should vitally important signals from the
forehead dawdle in the anteroom just because there might someday be
an occasion when concurrent signals from the toes need to converge
with them somehow?'. Dennett concedes that causes precede effects,
but says that it does not matter in what order representings occur
so long as they occur in time to contribute to the control of
overall behaviour. Temporal inferences can be drawn by comparing the
content of several data arrays, but this real time does not
necessarily have to coorrespond to represented time.
Dennett discusses Libet's reports that when a patients left cortex
was stimulated (represents right Hand) and then his left hand was
stimulated, the patients reported feeling stimulation in the left
hand prior to the right hand. This generated a lot of discussion,
which Dennett feels is based on the mistaken assumption that
consciousness occurs at a fixed time, `since cognition and
control-and hence consciousness is distributed around in the brain,
no moment can count as the precise moment at which each conscious
event happens'
Dennett & Kinsbourne discuss anomalies of consciousness by
contrasting theories arising from the Cartesian theatre model with
those from their multiple draft model. The example which they make
extensive use of is as follows. A woman walks by with no glasses,
but you remember her as wearing glasses. The two explanations
arising from the Cartesian model are: 1. `Orwellian' revision - you
saw her with no glasses, but a split second later your memory is
revised or contaminated so you believe she had glasses (perhaps you
saw someone else with glasses) or 2. `Stalinesque' revision - you
actually hallucinated the glasses from the moment yu saw the woman.
These possibilities correspond with ideas of top-down and bottom up
processing respectively. The question arises whether the mistake
occurs before or after the vision of the woman reached
consciousness. Dennett & Kinsbourne point out that there is no way
you could distinguish what happened from the subjects own testimony
or knowledge. So far this is quite uncontroversial. However they go
on to claim that the question itself is flawed and could not be
answered, as the onset of consciousness does not occur at a precise
temporally located point. The multiple drafts model thus renders
such questions meaningless, and suggests that any definition of one
moment as conscious will be somewhat arbitrary. Their model
emphasizes that the creation of conscious experience is not a batch
process, but is continuous. Judgements and decisions are not
inscribed in the brain in isolation, but have consequences, for
guiding action and modulating further judgements and thus creating
larger fragments which we call conscious narrative.
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