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Recategorisation
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Gerald
Edelman's theories are rooted in neurology. In fact, he
insists that this is the only foundation for a successful theory of
consciousness: the answers are not to be found in quantum physics,
philosophical speculation,
or computer programming.
The structure of the
brain is accordingly a key factor. The neurons in the brain wire
themselves up in complex and idiosyncratic patterns patterns during
growth and then experience: no two people are wired the same way.
The neurons do come to compose a number of structures, however. They
form groups which tend to fire together, and for Edelman these
groups are the basic operating unit of the brain. The other
main structures are maps. An
uncontroversial example here might be the way some sheets of neurons
reproduce the pattern of activity on the retina at the back of the
eye (with some stretching and squashing), but Edelman sees similar
strucures as applying much more widely, and mapping not just sensory
inputs, but each other and other kinds of neuronal activity. The
whole system is bound together by re-entrant connections, sets
of paths which provide parallel connections from group A to
Group B and Group B back to Group A.
The principle which
makes this structure work is Neuronal Group Selection, or Neural
Darwinism. Some patterns are reinforced by experience,
while many others are eliminated in a selective process which
resembles evolution. Edelman draws an analogy with the immune
system, which produces a huge variety of random antibodies: those
which link successfully to a foreign substance reproduce rapidly.
This explains how the body can quickly produce antibodies for
substances it has never encountered before (and indeed for
substances which never existed in the previous history of the
planet): and in an analogous way the Theory of Neuronal Group
Selection (TNGS) explains how the brain can recognise objects in the
world without having a huge inherited catalogue of patterns, and
without an
homunculus to do
the recognising for it.
The re-entrant connections between neuronal groups in different parts
of the brain co-ordinate impressions from the different senses to
provide a coherent, consistent, continuous experience; but re-entry
is also the basic mechanism of recategorisation, the fundamental
process by which the brain carves up the world into different things
and recognises those it has encountered before. The word
recategorisation is potentially confusing here for two reasons: first, it
is not to be taken as implying the existence of a prior set of
categories: in fact, every act of recognition modifies the category;
nor is it meant to suggest any parallel with Kant's categories,
which limit how we
can understand the world. Very much the reverse, in fact.
Edelman attaches
great importance to
higher-order processes - concepts are maps of maps, and arise from the
brain's recategorising its own activity. Concepts by themselves only
constitute primary (first-order) consciousness: human consciousness
also features secondary consciousness (concepts
about concepts), language, and a concept of the self, all built
on the foundation of first-order concepts.
The final key
idea in the theory, another one with a slightly misleading
name isvalue, a word used here to
describe inbuilt tendencies towards particular behaviour. These
forms of behaviour may be driven by what we value in a fairly
straightforward sense - seeking food, for example, but they also
include such inherent actions as the hand's natural tendency to
grasp. Edelman seems to think that, like a computer, if left to
itself the brain might sit and do nothing. It's the value systems
which supply the basic drives. This sort of set-up has been modelled
in a series of robots rather cheekily named Darwin I to
IV.
Edelman is
emphatically opposed to the idea that
the brain is a computer
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however. |
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Being
anti-computationalist but using robots to support your theory seems
a little strange. It needn't
be strictly contradictory,
of course, but it does expose the curious fact that while
Edelman insists the brain is not a computer, all the processes he describes
seem perfectly capable of computerisation. He gives two
reasons for not considering the brain a computer: one, that individual brains
are wired up in very different ways; and two, that reality is
not an orderly program feeding into the brain. Neither of these
is convincing. Computers can differ enormously in physical detail
while remaining essentially the same - how much similarity is
there between a PC and a model Turing machine, for example -
and wiring differences between brains might perhaps count as differences
in pre-loaded software rather than anything more fundamental. Certainly
reality does not structure itself like a program, but
why should it? The analogy is with data, not with the program: you
have to think of the brain as a computer which has its software loaded
already and is dealing with the data coming down a wire from
cameras (eyes), microphones (ears), and so on. I see no problem
with
that. |
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The argument is a bit more
specific than you make out. Edelman points out that the
selective processes he has in mind have an unusual feature he
calls 'degeneracy' (I'm not quite sure why). Degeneracy means
that the same output can be reached in a whole range of
different ways. This is a feature of the immune system as well
as mental processes, but it doesn't look much like an
algorithm. Of course there are other arguments against
considering
the brain a computer, but I think Edelman's main point is that to deal with
reality, you have to be able to arrange the streams of
mixed-up and ever-changing data from the senses into
coherent objects. Your computer with a camera attached finds
this impossible except in cases where the 'reality' has been
made artificially simple - a 'toy world' - and the
computer has been set up in advance with lots of information
about how to recognise the objects in the 'toy world'. I know
you're going to tell me that great strides have been made, and
that you only need another couple of decades and it'll
all be sorted.
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I wasn't, though
it's true . I was just going to point out again that, however
difficult it may be to digest reality, Edelman gives us no
definite reasons to think computers couldn't do it; his robots
even demonstrates some aspects of the methods he thinks most
likely. But never mind.You expect me to attack Edelman just
because he and Searle have spoken favourably of each other:
but actually I've got nothing much against him except that I
think he's misunderstood the nature of computationalism.
Just because we haven't got USB ports in the back of our heads
it doesn't mean brain activity isn't
computable.
As for that
bit about 'degeneracy', I don't see it at all. Imagine we had
a job we wanted done by computer - we call in a hundred
consultants to tender for the project. They'll find a hundred
different ways to do it. Even if we set aside most of the
possible variation - whether to use
PCs, Macs, Unix boxes or what, Java, C++,
visual Basic or whatever. Even if we assume the required
outputs are narrowly defined and all the
tenderers have to code in bog-standard C, there'll be
thousands of variations. So I reckon computers can be
degenerate too... | |
I don't expect you to
attack Edelman at all. As a matter of fact, I'm not an unqualified
admirer myself. Take his views on qualia. The temptation for a
scientist is always to miss the point about qualia and end up
explaining the mechanics of perception instead (a different issue)
Edelman, in spite of his scientist bias, is not philosophically
naive and a lot of the time he seems to understand the point
perfectly. But in 'A Universe of Consciousness' he swerves at the
last minute and ends up talking about how the neurons could map out
a colour space - which might be interesting, but it ain't qualia.
Perhaps his co-author is to blame.
However, I'm with
him on the computer issue. Edelman's views about selection
illustrate exactly why computers can't do what the brain does. I
think his ideas on this are really important and have possibly been
undersold a bit. The thing about programming a computer to deal with
real situations is that you have to anticipate every possible kind
of problem it might come up against - but there are an infiinite
number of different kinds of problem. Now this is exactly the
kind of issue the immune system faced: it had to be ready to
deal with any molecule whatever, no matter how novel. The solution is
analogous: the immune system fills your body with a really vast
number of variant antibodies; your brain is full of an astronomical number
of different neuronal patterns. When the problem comes along,
even a completely novel one, you're going to have the correct response
waiting somewhere: and the one that matches gets reinforced and
reused. Edelman called this a Darwinian process: it isn't really
(hence Crick's joke about it really being 'neural Edelmanism'): the
remarkable thing is, it might be better
than Darwinian in this context! |
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Anything's
better than Darwin to you, up to and including spontaneous
generation and Divine Creation. |
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Nonsense! But, honestly. It's
not particularly original to suggest that the mind might use
selective or Darwinian mechanisms, (or be infected with
memes evolved in the
memosphere) but normal Darwinian selection is just obviously
not the answer. When we confront a sabre-toothed tiger or think what
to say to a question in an interview, we don't start by copying
some earlier response, try it out repeatedly and gradually refine it
by random mutation. We don't even do that in our heads, normally.
99% of the time, the response is instant, and appropriate, with
nothing random about it at all. It's a bit easier to understand
how this could be so on the Edelman theory, because some reasonably
appropriate responses could already be sloshing around in the brain
and the best one could be reinforced very
quickly. |
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I think you're going
further on that than Edelman himself would be inclined to do. In
fact, I'll give you a prediction. Eventually, Edelman himself will
come round to the view that there is nothing unique about all these
processes, and that while the brain may not be literally a computer,
its processes are computable. |
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I think not. You ought to
remember what the man said himself about changes of heart - the unit
of selection in successful theory creation is usually a dead
scientist... |
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Read: |
"Bright Air, Brilliant
Fire"
The most
accessible account of the TNGS. Although Edelman's theory is
very much a matter of neurons, the details are balanced with
some philosophical and other general background and lightened
with the occasional joke. |
"Neural Darwinism", "Topobiology", and "The Remembered
Present"
This trio together make up
the authoritative account of Edelmanism. If you want the full
version, this is it. |
"A Universe of
Consciousness" Written with Giulio Tononi. Same
theory, narrower focus, different emphasis. Those who think
qualia are the real issue, or have a particular interest in
the binding problem might prefer this
version. |
"The Mystery of Consciousness" This
collection of pieces by Searle about noteworthy conscious
entities includes a friendly summary of Edelman, whose
emphasis on biology is congenial to
Searle. |
"Wider than the Sky: The Phenomenal
Gift of Consciousness" Edelman's latest book focuses
on phenomenal experience, but it summarises a lot of his thinking in a
relatively small space - perhaps a good place to start on Edelman or get a better idea
of what he's on
about. |
Some
Links: |
Short biography
: from a conference site.
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Page
at Princeton
- complete with mugshot of the youthful Edelman
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Review of 'A Universe of
Consciousness'
- from the Guardian. Rather unenthusiastic, but some
sound points. |
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