Re: Computation

From: Harnad, Stevan (
Date: Sun Feb 04 1996 - 16:31:36 GMT

> From: "Lucas, Melody" <>
> Date: Sun, 4 Feb 1996 16:09:47 GMT
> Computation is symbol manipulation on the basis of their shapes which
> is systematically interpretable. Computational systems are symbol
> systems. The success of AI in mimicking human cognition has encouraged
> some psychologists to think that due to a computer's and a human's
> functional indistinguishability, they are one and the same. The Church
> - Turing thesis supported this, by using the analogy of the Turing
> machine (T1); a machine which manipulates an infinitely long tape which
> holds binary codes. The machine plays, fast - forwards and pauses the
> tape on the basis of rules which dictate every action dependent on its
> internal states. Turing thought that he could prove computation was
> cognition if he could make someone believe that a computer (T2) was a
> person. He achieved the deception by having subjects write to a
> 'penpal' which was actually a computer. But, in contrast with popular
> belief, he failed to prove C=C.

You prejudge it all if you call it "mimicking" and "deception."
Computationalism is not meant to be a trick. It is the hypothesis that
cognition is LITERALLY computation. The Turing Test is meant to require
that the computer be able to do everything the human can do, so well
that humans cannot tell the computer and the human apart.

Also, a reminder that the word "proof" belongs only in mathematics
(though it is used in law courts too...). In science we only have
evidence supporting or refuting a hypothesis or prediction. C=C is a
hypothesis, and you need to give the positive evidence in its favour.

> A characteristic shared by computation and cognition is implementation
> - independence (Pylyshyn disagrees with this).

What is implementation-independence, and how/why does Pylyshyn disagree?
Doesn't he agree that the brain is irrelevant, and only the software

IWhy/how is implementation-independence positive evidence for C=C?

> We are investigating the
> formal properties, not the physical ones. A different piece of hardware
> with a different piece of software may be performing the same
> computation. Likewise, the cognition performed by a human - being is
> irrelevant to the biological composition of the brain (although
> obviously correlated).

How/why is this relevant to C=C? asks kid-bro...

> Additional evidence to suggest C=C is that
> computers can effectively simulate events, for example, a computer can
> simulate an aeroplane in flight. However, the plane is not really
> flying, so simulation may be computation, but the plane is not a real
> plane and is not really flying.

Not clear what is positive evidence here (positive means favourable),
and why. Sort out the positive evidence from the negative.

> Searle presented the Chinese Room argument to illustrate what a
> computer actually does and to disclaim T1 and T2.

What are T1 and T2?

> He suggested that a
> person could use a set of symbols without actually understanding the
> meaning of it (by using rules such as if X, then Y; If P then not Q
> etc.) The man in the Chinese Room could only use the Chinese language
> as if he were using a chinese - chinese dictionary. One symbol would
> just lead to an explanation of more squiggles and squoggles. This leads
> to the symbol grounding problem; people understand because they ground
> the symbols in sensory experience.

Kid brother totally confused here: What is positive evidence for what
here? What was Searle trying to show, and why? And what does the symbol
grounding problem have to do with positive evidence for

> Even a robot which had light
> transducers and pressure sensors (T3) does not cognize, because
> transduction is not computation.

Not clear what your point is. The hypothesis of computationalism is that
cognition is computation, and you are supposed to be making the best
case that can be made FOR the correctness of that hypothesis. You can
balance it with the negative evidence too, but only after you have made
the best positive case. What does transduction (which is, you are
right, not computation) have to do with the case for computation?

> If such a robot could ground symbols,
> it would not have intrinsic intentionality (Searle) i.e. it would not
> be capable of autonomous thought, an external interpreter would always
> be necessary.

What does symbol grounding mean, and what does it have to do with the
evidence for computationalism? And what do Searle's arguments against
robots (which are not just computers, hence not examples of pure
computationalism) have to do with the case for or even against
computation? What is "intrinsic intentionality"? Kid-bro is badly
confused at this point!

> To accept cognition and computation as one and the same would be
> homuncular (if this holds, humans would manipulate symbols and need a
> 'little man' to read and understand it).

According to Pylyshyn, the opposite is true: ONLY computation is
nonhomuncular. Make the positive case first, then move on to criticism.
Searle's argument that computation is meaningless except to an external
interpreter should only be raised once you have shown all the good
reasons one would have taken the C=C hypothesis seriously in the first

> This is not true as we do
> understand the meaning behind symbols and accepting a homunculus would
> be 'passing the buck'. The confusion arises because computers can
> appear to be understanding symbols. Computation can describe part of
> the function of cognition, but it does not hold the complete story.

It is mental imagery that stands accused of requiring a homunculus.
Computation is instead accused of requiring an external interpreter.
Yes, there are similarities there, but they need to be sorted out, and
above all, the positive evidence and arguments that FAVOUR C = C must be
clearly distinguished from the negative evidence and arguments.

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