Concepts and Categories

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Concepts and Categories

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Concepts and Categories

• Concept a mental representation
• Category the set of things picked out by the
  concept
• Why do we need them?
• To make predictions
• To prevent information overload

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Effects of Categorization

• 1. categorical perception
• categorical perception perceiving things in
  discrete categories rather than as points on a
  continuum.
• Characteristics
• sharp change in probability of category labeling
  at the category boundary
• greater between-category than within-category
  discriminability
• 2. category labels' effect on perception (Tajfel
  Wilkes, 1963)
• 3. implications stereotypes

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What is Categorization Based on?

• Similarity?
• Similarity as shared features
• But which features?

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Semantic Feature Models of Concepts

• The classical view defining features
• The probabilistic view
• prototypes (Rosch, 1977) Coglab demo next
  slide
• exemplars (Medin Schaffer, 1978 Hintzman,
  1986)
• Whats the difference? Internal structure
• Hybrid models defining characteristic features

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Prototypes Coglab Results

• Pattern type Reaction time (ms)
• Prototypes 718.68335
• Variants 752.62085
• SOURCE grand mean
• A N MEAN SD SE
• 50 752.0379 228.3917 32.2995
• SOURCE A
• A N MEAN SD SE
• Variant 25 778.1483 246.9372 49.3874
• Prototy 25 725.9275 210.0015 42.0003
• FACTOR RANDOM A DATA
• LEVELS 25 2 50
• TYPE RANDOM WITHIN DATA
• SOURCE SS df MS
  F p
• 
  

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Different kinds of concepts?

• dog, tree, diamond (natural kind objects, basic
  level)
• Collie, oak, industrial diamond (natural kinds,
  subordinate level)
• animal, plant, geographical feature (natural
  kinds, super-ordinate level)
• hammer, chair, cup (artifact objects)
• felony, majority, contract (abstract,
  conventionally defined)
• candy cigarette, dog bed, phone book (non-novel
  noun-noun combinations)
• apple chair, carpet light, ear filter (novel noun
  combinations)
• Brazil, Richard Nixon, Jupiter (names)
• wife, senator, friend (social roles)
• justice, peace, existence (abstract nouns)
• bake, eat, explode (verbs)
• red, hot, large (perceptual adjectives)
• entropy, genus, photosynthesis (technical terms)

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Types of Concepts

• Natural kind concepts
• Artifacts
• Conventionally defined
• Other types?

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Similarity Re-examined

• non-reflexivity of similarity
• non-transitivity of similarity
• context-dependence of similarity (Tversky, 1977)
• similarity can not simply equal the number of
  shared features
• similarity does not always predict categorization
  
• Psychological Essentialism (for natural kinds)
• Ad-hoc categories not defined by similarity

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Theory Theories of Concepts

• Organization of concepts is knowledge-based
  rather than similarity-based (Keil, 1986, 1987
  Murphy Medin, 1985).
• People's intuitive theories are the basis for
  categorization of natural kind objects. This has
  particularly been argued for biological kinds.

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Conceptual Combination

• Modification? (brown apple)
• Separate Prototypes? (big wooden spoon)
• But sometimes the combination has a prototypical
  feature that is not typical of either noun
  individually (pet birds live in cages, but
  neither pets nor birds do)
• Extending salient characteristics?
• When nouns are alignable (zebra horse)
• But non-alignable nouns are combined using a
  different mechanism (zebra house)

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Context-Dependence of Conceptual Combination

• Sit in the apple-sauce chair.
• Is conceptual combination really about the
  structure of concepts, or is it about the
  pragmatics of language use?