IUBio

Toward a Science of Consciousness 1998

Neil Rickert rickert at cs.niu.edu
Fri Apr 24 15:24:58 EST 1998


modlin at concentric.net writes:
>In <6hqj4a$pt5 at ux.cs.niu.edu>, rickert at cs.niu.edu (Neil Rickert) writes:

>  [responding to my attempts to distinguish "computation" from the 
>   input/output activities which supply data for computation]

>>Perhaps the reason I keep posting that I disagree, is that I
>>disagree.

>Ok Neil.  Please.  What is it that you disagree with?   
>What is your definition of computation?

A computation is a set of causal operation which take place in the
world, and which have a certain kind of mathematical description.

>Under your rules, is a Turing machine capable of computation?

No.  It is capable of formal computation, but not of computation,
where formal computation is a mathematical idealization of
computation.

It is worth pointing out here that mathematicians carefully
distinguish between pure mathematics and applied mathematics.  Most
mathematicians particularly value pure mathematics, and I count
myself amongst that 'most'.  Generally, pure mathematics comes higher
in the pecking order than applied mathematics.

The Turing machine has always been considered part of pure
mathematics.

Computation has always been considered something done in applied
mathematics.

>Under your definitions,  if I load a program and some data into a PC, 
>and start the program running, can the PC compute some function of that 
>data without using any further I/O?

That's a tricky question.  Even though there is no further I/O, there
are still causal operations going on in the machine, and presumably
these could be probed with suitable measuring instrumentation.  If
you are talking about those causal operations, then you can make a
case that computation is still taking place.

>I do understand that you consider interfaces with the outside world to 
>be much more important to cognition than any computation which may be 
>involved.

Let's talk about the computer on my desk, instead of cognition,
although the same points apply.

When a computation is being carried out on my computer, a series of
causal operations is taking place, using electrical signals and other
kinds of physical operations.  There is also a symbol manipulating
game used in our theories of computation to describe what is
happening.  Whether we should say that the symbol manipulation game
is actually going on is itself a tricky question.  I prefer to say
that the symbol manipulation game is part of a description language,
rather than part of the computation.

If somebody should come up with a completely different symbol
manipulation game to describe what is happening in my computer, that
would not change what the computer is doing.  The exact same causal
actions would be going on.  And if a computer is sufficiently
complex, it is very likely that there are alternative symbol
manipulation games that could be used to describe the processing.
When I am using the computer for ordinary things (like writing this
message), I care only about the causal operations.  The particular
choice of symbol manipulation game which somebody might choose to in
their description language is completely irrelevant to the
computation that is going on, as far as I am concerned as a user of
the computer.

It seems to me that you are emphasizing only the symbol manipulation
game, and ignoring the causal operations which I consider to be at
the heart of computation.  I prefer to think of the symbol
manipulation game as a story involving purely theoretical entities.
In that sense it is comparable to scientific use of massless charges,
frictionless motion, and other such theoretical entities.  We value
these theoretical entities because of the way we can use them in our
predictive theories.  But we don't actually believe they are more
than convenient fictions.

>           But I also thought that you agreed that somehow there was
>some computation involved in figuring out what to do with the data you
>get through sensors, and deciding what other information to go looking
>for, and all that sort of stuff.

Sure there is.  But that computation consists of causal operations,
rather than the symbol manipulating game we might use to describe
those operations.

>I've seen you tell others that it didn't matter whether the interior 
>processing was done with neural nets or an analog computer or a digital 
>computer, that all of them could do the same things.

That's not quite what I have said.  Given a particular computation
considered as a sequence of causal operations done in real time, it
does not matter what particular additional machinery was used to
implement those causal operations.  But it does very much matter
whether a particular piece of hardware is capable of carrying out the
required causal operations within the allowable time frame.




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