posted 3/07/06
Reading assignment:  Chapter 10

Why is it important to group items into categories?

• Organize the world
• Apply knowledge to ____________________
• Recognize repeated encounters with one object as the same thing
• Distinguish between categories

• ___________ = mental representation
• ___________ = set of examples picked out by the concept.

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1. Classical View

• Category membership is defined by a list of ____________and ______________ features
• E.g. triangles are plane figures with 3 corners and 3 sides
• Concepts have clear-cut boundaries
• All members are equally ___________________
• When concepts are organized heirarchically, the concept includes the defining features of its _______________
• Since chickens are birds, chickens have the necessary and sufficient features of birds

• Failure to specify _______________ (What's the definition of a game? )
• Unclear cases or fuzzy categories (Is a rug furniture? )
• Use of ______________ features (Birds fly )
• Nested concepts (Chicken is a good animal but a bad bird example )
• ____________ effects  (Is the Pope a bachelor?)

• Concepts are summary representations of characteristic features
• Features need only be _______________, not necessary, to be included
• _______________ is a category member (real or hypothetical) that shares the largest number of features with all category members
• Category membership is defined by _________________ - similarity to the prototype
• No defining features
• Category boundaries are fuzzy or unclear
• Category members can range in their typicality

• Prototypicality ratings
• ______________ times
• More prototypical instances categorized ___________
• Prototypical members listed first
• Prototypical members learned first
• Prototypical members are used as a reference point (en ellipse is almost a circle)
• Family resemblance is maxmized at the ___________ level

• Categories don't have a definition, just ______________________
• Items more similar to the prototype will be judged more typical
• Items that are equally similar to prototypes from two different categories will be ________________
• Since there are no necessary and sufficient features, the prototype can contain unnecessary features.

• Is prototype the average or the ________?
• Experts tend to categorize using the ideal
• ____-derived categories based on an ideal
• E.g., things to wear in the snow
• People know more than the central tendency
• Also know ________ among features
• E.g., small birds more likely to sing
• Context effects
• E.g., harmonica is a typical musical instrument at campfire but not at a concert hall
• Prototypes should obey _____________
• Each item is more similar to its own prototype than other prototypes
• But, categorization decisions don't always follow typicality
• E.g., A bat is more similar to the bird prototype than to the mammal prototype, but we know its a mammal.
• People are perfectly happy to apply typicality ratings to well-defined categories
• E.g., 3 is a better odd number than ___, even though both are definitely odd
• Typicality ratings might be flawed task

• Categories are not stored as defining features or as prototypes.
• Instead, they are stored as the ____________ themselves
• For example, the bird category is stored as representations of particular birds
• New instances are categorized by ____________________________

• Categories don't have definitions; they have lists of exemplars
• Items more similar to many of the exemplars are judged more __________ than other items
• Items equally similar to the exemplars from two different categories will be unclear cases
• Exemplars are stored by all of their features, even _____________ ones

• ________ categories: e.g., things to save during a fire
• Easy to generate exemplars
• Hard to generate a prototype
• ____________ of features (as well as central tendency) is stored (Rips, 1989)
• Subjects asked about average size of quarters and pizzas.
• Then shown a 5" circle size exactly in between the two
• Subjects judged it to be a pizza because pizza size ________, but quarter size doesn't

• Doesn't explain how concept was ___________ in the first place.
• Explains _______________ of new instances, but not prediction, reasoning, etc. so well.

Are there any classical categories?

• Some categories have definitions
• Triangle
• Odd number
• Even so, some instances are judged more prototypical than others
• Core features (definition) vs. Identifying features
• Identifying features used for fast indentification
• Sometimes conflict with core features, which explains unclear cases

Psychological _____________________

• Objects have an essence (underlying nature) that makes them what they are
• These underlying core features differ for different types of categories:
• Nominal kind (clear definitions)
• Natural kind (naturally occurring)
• ___________ (constructed to serve a function)

• Rips (1989)
• Animal that looks like a bird suffers an accident that causes it to look like an insect. It can mate with a bird, though, and produce bird offspring
• Subjects judged it as more similar to ________t, but classified it as really a _________
• Carey (1982)
• If found out that the a raccoon had skunk insides, subjects judge it to be a skunk (biological definition)
• A birdfeeder that was made out of a coffeepot is still really a birdfeeder (___________ definition)