Concepts and Categories

1. Concepts and Categories

2. 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

3. 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

4. What is Categorization Based on? • Similarity? • Similarity as shared features • But which features?

5. 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) • What’s the difference? Internal structure • Hybrid models: defining & characteristic features

6. 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 =============================================================== mean 28278051.3746 1 28278051.3746 297.222 0.000 *** R/ 2283391.4564 24 95141.3107 A 34087.6919 1 34087.6919 3.430 0.076 AR/ 238495.4094 24 9937.3087

7. 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)

8. Types of Concepts • Natural kind concepts • Artifacts • Conventionally defined • Other types?

9. 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

10. 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.

11. 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)

12. 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?