X-Message-Number: 14729
Date: Wed, 18 Oct 2000 20:25:31 -0400
From: Thomas Donaldson <>
Subject: more about brains and computers

A reply to the various people who don't like even the SUGGESTION that
our brains aren't computers:

First, as I said before, I was making a suggestion not proposing a
thesis. But I should still explain it a bit more, it seems. 

In terms of the issues raised, I will say first that I'd like a bit 
better definition of just what an "information processor" is, and
what is "information". There is a subtlety here: any symbolic
statement of the state of ANY machine, no matter what it does, constitutes
information. That's clear. But is the actual state of the machine 
an expression of information? I am saying that it is not. The ability
to set up symbols which EXPRESS the state of the machine is fine and
useful, but those symbols remain a symbolic expression only.

Moreover, even an ordinary computer tied in with some kind of sensory
system and some kind of action system will basically use a symbolic
system to express the state of its perception. Doing so isn't necessary
and may turn out to be inefficient. Sure, with lots more power than our
brain such a system might work just as well, but a lot of that power
is spent on doing something which brains do by not acting symbolically.

Finally, I will point out that no machine yet has the ability to 
constantly rewire itself in the way brains do. It's easy to see how to
make such a brain if we assume only a small number of nerve cells: 
just set it up with all possible connections and then turn off some
of those connections. But even the most primitive mammal has enough
brain neurons that such a proposal becomes impossible in practice,
even if it remains possible in theory. So more effort is needed. AS
I said in my original message, we may yet build such a machine; 
whether it qualifies as a Turing machine is a question which needs
answering, not one which is obvious. Is the world itself a Turing
machine? I would say it is not.

		Best wishes and long long life to all,

			Thomas Donaldson

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