The classical view is that categorisation occurs on the basis of a set
of features that are necessary and sufficient for category membership.
This view was heavily criticised by Rosch. Rosch viewed categorisation
as a form of cognitive economy (to 'reduce the infinite differences
among stimuli to behaviourally and cognitively usable proportions')
which reflects the structure of the perceived world (i.e. fins occur
more often with scales than with feathers). Category membership was
judged by how close to a prototype an object was. This involved a
judgement on how typical a potential member was to a particular
category. She defined levels of categorisation; the vertical and the
horizontal. The vertical referred to the level of inclusiveness;
superordinate (say, machine) the basic (computer) and the subordinate
(IBM 486SX Processor). The horizontal referred to the segmentation of
categories at the same level (e.g. machine, animal, vegetable). Rosch
disagreed with the classical view on a number of points. First, she
purported that subjects often cannot tell you the list of features on
which they base their categorisations. Second, that some stimuli are
more typical than others, and are thus more quickly categorised.
It came to light that this argument not only clouds the job of the
psychologist by mixing the metaphysical with the psychological but also
confuses the whole question of what categorisation is. The qualities of
the stimulus per se are irrelevant. We, as psychologists, are
attempting to discover how a human being abstracts some information
from a stimulus and ignores the rest. Watnabe's ugly duckling theorem
describes how every 'thing' can have an infinite amount of
characteristics, i.e. everything has negative and positive attributes
(e.g. red or not red). How do we select the information which
categorises one thing from the next with any degree of accuracy amongst
this great mass of information? Funes could not abstract category -
relevant information and saw every event as being unique, leading to
extensive problems with recognition of everyday things. He lacked the
ability to disregard certain characteristics from objects / events
which is something apparently necessary for 'normal' daily
functioning.
The overriding conclusion is that the environment selects categories,
the human does not. It does so by means of their consequences, not by
their features or typicality. For instance, learning either by theft or
honest toil that toadstools are the ones that make you sick, but
mushrooms are edible. Finally, assignment of objects / events to levels
of categories is arbitrary; it varies among people and should thus be
considered as a network.
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