Re: Pylyshyn: Against Imagery

From: Matsers, Kate (
Date: Tue Nov 28 1995 - 05:39:21 GMT

As I have not done a summary of something noone else has read before I
have tried to explain quite a lot of it as I go along. I hope that
its not missing too much that is relevant or waffling about too much
that is irrelevant. I will add to it systematically over the next few
weeks. It should all go far more smoothly now. I have Pegasus Mail
up and running, more memory and my word processor back - please keep
your fingers crossed!

Matsers, Kate' Commentary on Computation and Cognition: Toward a
foundation for cognitive science. by Zenon W. Pylyshyn.


Pylyshyn introduces the concept of categorisation when he says that
human characteristics can not be wholly described by listing the
groups in which we (humans) can be placed, (e.g. vertebrates,
cognisers etc.). At this stage he does not actually mention that we
categorise the information we process but I can see the relevance in
the fact that we cannot be described by categories alone, surely if we
think in categories alone we will therefore never be able to fully
understand ourselves?

> ZP > What makes it possible for humans (and other members of the
> natural kind informivore) to act on the basis of representations is
> that they instantiate such representations physically as cognitive
> codes and that their behaviour is a causal consequence of operations
> carried out on these codes.

Pylyshyn then goes on to introduce the concept of computation as a
model for cognition. He explains that if a computer program can be
viewed as a model of cognition > ZP > the program must correspond to
the process people perform.

That is to say that the processes are formed in the same way. He
explains that there is strong equivalence between human cognition and
computation but that there are independent constraints upon both
computation due to its mechanical foundation and in humans due to
their biological structure. He calls this the functional architecture
and distinguishes it from rule governed or representation governed

Pylyshyn explains that the functional architecture might be fully
explained in physical or biological terms if they are known or just in
functional terms if the biological processes are not known.

He defines three levels of explanation that fall within cognitive
science: the functional architecture, the nature of the codes (their
symbol structures) and their semantic content. Clearly there are many
different perspectives and different theorists have claimed that
cognitive behaviour can be explained with only one or two of these
levels. Pylyshyn gives examples of this and then moves on to explain
why he perceives all three as important.

Pylyshyn explains that this book will not appeal to philosophers
because it will not ramble and discuss things. Equally he says that
it will not describes copious amounts of scientific studies as would
appeal to the scientific psychologist. In fact, he mentions that he
has not included much commentary on the information processing
psychology because of the many readable reviews available. Is he
saying that his book is not readable !?

Really the preface needs to be read as it is very much Pylyshyn
talking to the reader and it's hard to know which bits to select out.
It is general but gives a good insight into his way of thinking.

Chapter 1, "The explanatory vocabulary of cognition."

Cognitive Phenomena and Folk Psychology

In this section Pylyshyn introduces the concept of scientific
vocabulary the fact that two or more science (e.g. physics, biology,
psychology etc.) can explain the same phenomena but will use very
different terms and perspectives to do so.

Pylyshyn then says that folk psychology is the best method of
predicting behaviour; states that he will expand upon this later and
begins the example which he refers back to throughout the remains of
this chapter.

The example is, basically, a car swerving to avoid a pedestrian, the
car hitting a pole and the pedestrian running to the 'phone box and
dialling the numbers 9 and 1 (note that (911 is the American emergency

The point that Pylyshyn develops here is that the scientific
perspective, (and the vocabulary attributed to that science) that is
used to explain the situation affects the explanation that is
produced, and therefore which question is answered. For example, if
we concentrate upon the physical forces involved in the crash we would
not be explaining why the pedestrian ran to the 'phone box.

There is then a list of the cognitive actions the pedestrian
onlookers goes through during the accident. They provide a definition
of the pedestrian perception of the event and the why s and what of
this actions. These cognitive actions can be called intentions, and
are described using and intentional vocabulary.

Once the situation is explained using and intentional vocabulary the
situation is understandable, and we could then go on to use different
scientific vocabularies to deduce the other perspectives.

When we look for an explanation are we merely looking for an account
that makes sense, using relevant generalisations?

Cognitive systems consider what could have been as well as what was.
This is the difference between description and explanation.

Capturing Generalisations.

The point here is that cognitive terms and not merely heuristic but do
explain something that biological and behavioural approaches do not.
That is, cognitive terms enable us to capture generalisations, and
interpret things in the shape of categories we have stored as
representations within us. Behavioursim could only work here if we
had been in a very similar situation to have our behaviour reinforced.
 The generalisations are aided by expectation, and are internally
processed. Pylyshyn uses the example that if the pedestrian had been
told that the accident was a rehearsal for a T.V. show they would not
behave in a way that fitted the perceptual stimulus (and thus
generalisation of response) "accident".

> ZP > ... the relation between conditions and actions i s seen as
> meditated by beliefs as well as, perhaps, considerable reasoning or
> cognitive processing rather than merely being linked by nomological
> laws. It is this remarkable degree of stimulus independent control
> of behaviour that has been the Achilles' heel of behaviourism.

More to folllow soon........

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