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From: stevens@prodigal.psych.rochester.edu (Greg Stevens)
Subject: Re: Thought Question
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In <3ehbfp$8oh@agate.berkeley.edu> <jerrybro@uclink2.berkeley.edu> writes:
>stevens@prodigal.psych.rochester.edu (Greg Stevens) wrote:

>> My point was merely that computation is not a task that can be carried
>> out at different speeds if its input is time dependent.  What the
>> brain does could be done at different speeds (assuming its function is
>> otherwise unchanged) if its input was at a correlated speed.

>I agree with your meaning, though I would choose different words
>for it.  Computers can fulfil a function which is not itself
>computation (obviously, since you could throw one at my head :).

That actually is unrelated to my point.  If I am inputting numbers
at a rate of 1 number per second on a keyboard and the computer is
performing realtime operations on my input, it will certainly make a 
difference if the processor speed only allows it to process 1 number
every other second or 1 number every second.  In the former case,
it will get behind, and if its output in turn effects my input later
on, there is a sensetive dependance that leads to the computer not
being ABLE to perform the same task at one speed as it would at another.

This is the case with the computation of a brain driving.  It receives
input at a certain rate and needs to process it at a certain rate.
If it gets behind, the output (your behavior as a driver) changes the
input (where you see you are on the road) and if you get behind and
can't react in time, you crash.  But it's all still computation.

> Another objection is that a computation
>gives a specific answer to each specific question.  

Not with probabilistic algorithms.

>If a computer
>gives a different answer, it has performed a different computation.

Not if it is performing a probabilistic or non-deterministic computation.

>Computers are typically used in tasks that require that they
>perform certain computations and not others.  A computer is
>reliable when it performs computations flawlessly.  Brains are
>not, as far as I know, reliable in this way.  They are not
>relied upon to perform any particular computations flawlessly,
>and on those occasions when they are, they frequently give
>wrong answers.  

You mean computations like keeping us alive? Or do you mean computations
like transforming retinal-stimulation information into an image?  How
do you know that our brain ever performs computations in a "flawed" way,
when the only thing you have to measure against is other brain
computations (perception)?

>So it seems on the face of it a real stretch to
>try identify what the brain does with what computers do.

It depends on the computer, really.  If you're only looking at computers
as they are used in business and recreation, of course.  But none of
them claimed to be AI either.  No one, as far as I know, has claimed that
computers ARE intelligent -- the question is CAN they be.

And saying that what computers DO (or are used for) is different from
what brains DO (or are used for) is quite different from arguing that
brains are not computational in nature (or can not be interpreted 
that way).

Greg Stevens

stevens@prodigal.psych.rochester.edu

