Re: Schyns Comms 04-06 burgund charles cleeremans

From: HARNAD Stevan (harnad@cogsci.soton.ac.uk)
Date: Sat Mar 07 1998 - 14:49:19 GMT


On Tue, 3 Mar 1998, Willoughby Sarah wrote:

> category members are not always obvious and clear cut. The boundaries
> of peoples categories vary according to their experiences of labelling.
> These boundaries may just be cognitive and not sensory. This would
> appear to back up the flexible feature theory. Fixed features would not
> allow for such adaption.

If our categories don't exactly agree this might seem to favour the
flexible feature theory over the fixed feature theory, but it all
depends how many fixed features there really are. If there are
relatively few, you are right. But if there are very very many fixed
features, so that there is some leeway about which of them to use to sort
out a particular category, then you and I might see it slightly
differently (without realising it -- if we knew we disagreed on certain
cases, we could fix that, once we knew which of us was right, by just
agreeing on features) because we had used different (but fixed)
features.

> The fact the identification of
> primitives has been so unsuccessful raises doubt over the theory that
> 'feature selection is the task of finding a set of feature-primitives'
> to match objects.

But flexible features have not been any easier to identify either...

> > "A distinction needs to be drawn between the definition of a category,
> > the defining features, and the features used in recognition of category
> > members, what might be called the distinctive or characteristic
> > features."
>
> It is hard to see how these features can be distinguished or how it is
> beneficial to do so. If a category is not based on the features used to
> recognise a category member, then what is it based on? This seems to be
> an unclear distinction.

You're right, but if more than one combination of features will
correctly sort things, then it is one question (1) what kinds of things
those things are (that would be a question about their "defining" or
"essential" features -- and that question would not be asked or answered
by cognitive psychologists, but by biologists, physicists, etc.) and
another question (2) how we can tell what they are. It is the second
question that the cognitive psychologists who is trying to
reverse-engineer our categorisation capacity needs to answer by
designing models that can do what we can do.

> It may be true that we form arbitrary category
> labels which do not have much to do with the way we categorise. It
> makes the concept of categories as separate storage units questionable.

Why? Biology may decree natural categories, but people (and especially
dictators) may decree arbitrary ones, but the consequences to us of
getting either kind sorted incorrectly (getting poisoned for eating
something toxic or getting shot for calling some sacred thing by the
wrong god's name) could be equally dire. So it pays to be able to get
both kinds of categories -- natural and artificial/arbitrary -- right
when necessary.

> How useful is it to categorise artificially if it is not representative
> of classes of objects in the real world? It may be useful to us to
> enable us to try and describe categories but doesn't necessarily give
> us much insight into the way that the brain processes features.

Reverse-engineering requires us to explain the things people are ABLE to
do, not just the things they have already done.



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