Re: Searle: Is the Brain a Digital Computer?

From: HARNAD Stevan (
Date: Mon Mar 19 2001 - 20:20:48 GMT

On Tue, 6 Mar 2001, Hunt Catherine wrote:

> Hunt:
> although the mind can be seen as a set
> of reactions to procedures or applications, the mind is also specific to
> the person that it belongs...
> different minds produce different results.

(1) Entering icy water, shivering, chattering teeth, turning blue,
gasping "it's freezing cold!", along with all the internal "reactions"
inside your nervous system can all be "seen" as feeling cold, but that
doesn't make it the same as actually feeling cold. It's easy, for
example, to design a robot that "reacts" just like that to stepping
into cold water, externally and even internally, if you like, but
feels nothing.

(2) Differences between minds are irrelevant: They all feel.

> Hunt:
> I wonder if scientific theory will ever be able to understand the human
> brain. Unless there is a complete comprehension of the mind, I doubt that
> we will ever get near to simulating the human mind with a computer
> program.

Tow different issues:

(i) Will we ever be able to understand the human brain? (Who knows?
But why not? We've understood everything else so far.)

(ii) Will we be able to simulate the mind computationally? Not sure
what you mean: Simulate T2/T3/T4/T5? The Church/Turing Thesis says
there's no reason we shouldn't be able to. Actually generate a
thinking/feeling mind by simulating T2/T3 etc.? Why should that
happen; simulating a plane won't generate flying. But if we actually
design a T3 robot, will it have a mind? Who knows? And who is to be
any the wiser, if it is totally indistinguishable from a real person
with a mind?

> Hunt:
> identical mathematical operations can be performed by the digital computer
> and the mind - 1+1=2 for instance. A digital computer can run a program
> that reacts to bright light by protecting itself in some way in the same
> way that a human might either shut or squint the eyes to block out the
> light. But this is not simulating the complete human mind, just a mere
> subset of functions.

That is Granny Argument #10:

> Hunt:
> human minds work in different ways. Some minds might be similar,
> but I would imagine that is highly unlikely that two minds are identical
> in every way. The mind is unique to an individual, so how can there be a
> simulation of the human mind? Which human mind? Mine, Searle's,
> Salcedo's...?

Now explain to me how that exact same argument would not also apply to
the impossibility of simulating the liver or the kidney, or an
airplane, or anything at all? All individuals differ. But the point
is that in each case you are modeling a genetic KIND (and your
particular candidate, whether it's an artificial liver or an
artificial mind-- whether T2, T3, T4 or T5) will be both an individual
(THAT liver, and that mind) and an example of a kind.

Nor is this related to the question of computational simulation, which
you would separate from the question of T-testing. A T3 robot is
synthetic, man-made, etc., but it is not a computer simulation. Only
T2 (the pen-pal simulation) is equivocal between computer-simulation
and the "real thing".

> Also, Salcedo comments that the mind works in different ways and identical
> internal processes might produce different outcomes. On the other hand,
> differing internal processes might produce the same outcomes with a number
> of people. How would it be possible to model this with a computer
> simuation? I argue that it would be impossible.
> Hunt:
> What is a 'Cartesian soul'?

The mind: In "Cogito Ergo Sum" ("I Think, Therefore I Exist")
Descartes made famous (though he did not invent) the difference between
body and mind.

To quickly recap. Descartes used the method of "doubt": I will doubt
everything that is not 100% certain. The fact that I doubt it does not
mean it's not true, just that I can't be sure. So let's whether there
is anything about which I CAN be sure, in the way I can be sure of the
truths of mathematics. (I know they must be true, on pain of
contradiction.) Is there anything else, anything at all, that I can be
equally sure about?

Well, there's the world around me. The laws of science. But how can I
be sure they're right? Maybe our theories are wrong, or tomorrow
things will change. Not sure. And how can I even be sure there IS a
world? Couldn't I just be dreaming or hallucinating it all? And
doesn't that include my body? How can I be sure I have a body
(patients with their legs cut off are "sure" they still have a
[phantom] limb)? So is everything other than what can be proved
mathematically open to doubt?

No, there is one other thing: When I sit here, doubting everything,
there's one thing I can't doubt, and that is that I am doubting! I may
be wrong about what is true or false, but I can't be wrong
about what I'm BELIEVING is true or false, just as I can't be wrong
about having a toothache (though I could be wrong about having a
tooth). I cannot doubt that there are experiences (FEELINGS) going on.
And since I'm the one feeling these feelings (not someone else -- I
cant be sure there's anyone else, and even if there as, I can't be
sure that someone else feels anything: reactions are not the same as

So "Cogito Ergo Sum" "I think therefore I am" Which should really be
"Feelings are Being Felt" (so let's just call "me" the one who is
feeling the feelings).

But the trouble with this second piece of certainty is that the only
thing it is certain about is the mind (feeling, thinking), not the
body or any other thing in the world.

Now Descartes was also a religious believer (either that, or he did it
out of political necessity). So he called this "thing" that must
exist, with 100% certainty this "res cogitans" ("thinking thing") the
soul, the same soul the Christians believe in, as distinct from the
body (immaterial, immortal...)

> Hunt:
> How does Searle come to the conclusion that there are 0's and 1's flowing
> through the brain.

He could pick lots of things, but how about the on/off firing of

> Hunt:
> cognition is not understood well enough to explain reactions to
> external stimuli...

Yet. But I wouldn't want to base my conclusion about whether or not
cognition is just computation on what happens to have been explained
by cognitive science so far...

> Hunt:
> Searle and Salcedo both assert that it is false to say that the brain is
> an information processing device. To a certain extent, I disagree with
> this assertion. The brain does process information. We react to external
> stimuli and we do this by assessing the information given in terms of the
> state of the environment and react accordingly. If this is not information
> processing, then what is? However, I do think that it is wrong to see the
> brain as 'just an information processing device'. I think that is what
> Searle and Salcedo are doing.

I agree with you. It is the "just" that is at issue. (But it is
redundant now to talk about "information processing." It just repeats
what we were saying about computation.)

> Another point I will make is the reference made by Salcedo to the brain
> being completely interconnected to all other human senses at the same
> time. During lectures we have explored the idea of the brain being
> stripped of all external organs, such as the skin and the eyes etc. and
> the possibility that it will still function as a brain, and I just
> wondered where that idea fitted in with Salcedo's commnents. As I
> understand, he is making the assumption that in order to function as a
> brain, it has to be connected to two arms, two legs, eyes that work,
> tastebuds that work.. What happens in the case of a blind person, or
> someone who has lost their sense of taste or smell. Is Salcedo suggesting
> that their brains cannot function because they are not connected to all
> their human senses?

A certain amount of body and brain can go, but the mind still stays.
But take away enough brain, and the mind goes too.

Stevan Harnad

This archive was generated by hypermail 2.1.4 : Tue Sep 24 2002 - 18:37:24 BST