1. Concepts and Categories

2. 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 ocategorical perception = perceiving things in discrete categories rather than as points on a continuum. oCharacteristics: osharp change in probability of category labeling at the category boundary ogreater 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 typeReaction time (ms) Prototypes718.68335 Variants752.62085 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?