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10 Apr 2012

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Chapter 9: Concepts and Generic Knowledge
We need a way of identifying concepts that highlights what the various members of a category have in
common while also allowing exceptions to whatever rule we propose. We do this by keeping the content
of our definitions but being much more flexible in our use of the definitions
- Wittgenstiens family resemblance theory - there is probably no defining feature that every
member has. But there are features that are common which allows them to be recognizable as a
member of the family
- This can also be applied to dogs, games, furniture etc
Prototypes and Typically Effects
Prototype theory ; perhaps the best way to identify a category, to characterize a concept, is to specify
the centre of the category rather than the boundaries.
- We do this by using the ‘ideal’ dog or the ‘ideal’ family member who has all of the
family/category’s features. All judgements about dogs are made with reference to this ideal
- E.g. categorizatino would involve a comparison between a test case (the dog you are currently
looking at) and the prototype represented in your memory
- A prototype is the ideal for the category, but it is also an average of the various category
members you have encountered (e.g. the average colour of the dogs you’ve seen)
- Everyone has different prototypes
Fuzzy boundaries and graded membership
Since the category is characterized by its center (prototype) and not by its boundaries, theres no way we
can say whether something is inside of the category or outside. At best, therefore, each category will
have a fuzzy boundary with no clear specification of category membership and nonmembership
- Not all category members are equal
- Members closer to the prototype are “better” members of the category than objects father
from the prototype
- Thus, categories that depend on a prototype have graded membership with some dogs being
“doggier” than others, some books “bookier” than others and so on.
Testing the Prototype Notion
In the sentence verification task, participants are presented with a succession of sentences; their job
being to indicated whether they are true or false. RTs vary from item to time within a category. E.g. RTs
are longer for sentences like “a penguin in a bird” than “a robin is a bird”.
Why is this? Participants make these judgements by comparing the thing mentioned (e.g. penguin)to
their prototype . when there is much similarity between the two, the response time is faster.
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