Re: Schyns Comms 04-06 burgund charles cleeremans

From: HARNAD Stevan (harnad@cogsci.soton.ac.uk)
Date: Sat Mar 07 1998 - 15:32:31 GMT


On Thu, 5 Mar 1998, Wright Jon wrote:

> The notion of a prototype is certainly more flexible than if the
> category had to be determined entirely by a set of invariant features.
> The best example of a category is used when analysis a new object and
> the features of that object might be mapped onto the features of the
> new one and a certain level of agreement in the mapping process would
> permit membership of the new object to the category.

Yes, but to recognise that a particular object, and its prototype are
both members of the same category may well require the detection of
features. (Don't confuse "invariant" in the sense of inflexible with
"invariant" in the sense of being a shared reliable way of telling the
members of the category from the nonmembers: the invariant features
could be a long list, combined with and's, or's, if's then's and
not's, and it may be very flexible, covering a lot of cases, but it will
be "invariant" in the sense of providing an all-or-none basis for
making an all-or-none categorisation decision, and making it correctly
every time.)

> > "alternative materials may elicit feature creation more readily than
> > traditional materials because they are more likely to be processed in a
> >specific subsystem. In contrast, stimuli that are readily decomposable
> > into familiar parts may be processed more effectively in an abstract
> >subsystem."
>
> Does this mean that abstract subsystems involve the categorisation of
> more unusual (=less well rehearsed) features? If a categorisation task
> requires objects to be sorted according to the presence of a vertical
> line, for example, line drawings would be better stimuli than real
> objects since real objects contain other features beyond those in
> visual recognition which would make the decomposition into abstract
> features harder.

Line-drawn faces MAY be easier to categorise (when they are) because
they preserve the right features (the invariant ones) that allow you to
sort them, leaving out a lot of the irrelevant variation. In that
sense, they are already doing some of the abstracting for you.
But often our categorisation capacity must deal with the full blooming,
buzzing confusion of the world, not a conveniently simplified cartoon
world.

> Prototypes are more fuzzy but as categories are modified by the
> inclusion or rejection of later examples it seems that the definition
> of a category really is flexible, but with a 'most typical' member to
> compare all others against. Membership might be decided by a sufficient
> amount of similarity.

Sometimes (say in a law-court), you need to identify who did it
absolutely, not just as the candidate who is closest to your "prototype"
of who did it.



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