X-Message-Number: 14713
Date: Tue, 17 Oct 2000 08:00:55 -0400
From: Thomas Donaldson <>
Subject: more on brains and computers

Hi everyone!

I note the problems John K Clark has with my recent message about
how we work.

My very first impulse is to suggest that he read it again. To look at 
his last point, as to whether or not our brains can meaningfully be
considered as computers (and thus following Turing's Theorem etc etc)
I did NOT claim that they could not be, I only raised the question.

AS further discussion of this issue, I will point out first of all
that we're all aware of many machines that no one would claim were
computers. At the same time many of these machines do react to 
things happening in the world outside them: consider a Model T car,
or a lawnmower. A subsidiary but important question here is that
of whether or not symbolic thought is the only kind we do. If so,
I'd agree that there is a strong case that we can be considered
as computers. However I doubt very much that symbolism is the only
way we think. Underneath that symbolism we have other kinds of thinking
which we share with most mammals: we learn to react to events in
the world, and even think about them, without at root using 
symbolism at all. In particular, this kind of thinking takes place
on a higher level than simply using nonsymbolic objects (like
semiconductors or brain cells). Our brain cells connect to many
others, and they send and receive impulses from them. At root,
these impulses do not come from symbols but from impulses received
from the world.

Moreover, that other kind of thinking is essential to the way we
work. We learn language not by getting other language but also by
our experience of the world, which is not linguistic.

As for our parallelism, it's not important simply that most of our
brain works in parallel as the exact structure of that parallelism.
Our brain grows and destroys connections between our neurons,
constantly. This at least should raise questions as to whether
we operate like computers; I'm not saying no computer will ever
be built to do this, but if it were built that way it would behave
differently. (And perhaps we would not consider it a computer).
Closely linked with this feature is the close relation between our
drives and our thinking, which fundamentally cannot be separated.
It is not the use of symbolism, but the domination of our drives,
which characterizes our thinking ... even though we have many
drives such as curiosity which are far from primitive.

If you wish to see your brain along the model of a Turing machine,
then the first thing you should do is to work out whether or not
such a machine can model one which grows and destroys its connections 
as part of its response to the world. The second is to see whether
a Turing machine can work WITHOUT use of any symbolism. We all know
that for a real machine operating in the real world, parallelism is
necessary (otherwise if attacked it may take too long to work out
that it's being attacked and respond). In itself parallelism only
raises the problem of whether or not Turing machines dealt with
an important real-world trait; but we aren't just parallel. 
We have a structure and mode of thinking which no present computer
imitates.

			Best wishes and long long life to all,

				Thomas Donaldson

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