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Categorization

Categorization. Concepts and Categorization. Concepts allow for efficient categorization But, how are concepts represented ? What “defines” an object? Primary qualities Secondary qualities How do we decide ‘object X’ belongs with ‘category Y’?. Natural Levels of Categorization.

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Categorization

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  1. Categorization

  2. Concepts and Categorization • Concepts allow for efficient categorization • But, how are concepts represented? • What “defines” an object? • Primary qualities • Secondary qualities • How do we decide ‘object X’ belongs with ‘category Y’?

  3. Natural Levels of Categorization • Rosh et al.’s (1976) three “levels” of categorization • Superordinate level • Basic level • Subordinate level

  4. Natural Levels of Classification • Rosh et al. (1976) • Presented subjects with category labels • Subjects named as many features in common to all members of the given category label

  5. Natural Levels of Classification • Rosh et al. (1976) • Examined number of attributes at each category level • “Best” level of categorization is basic level • Why not superordinate level? • Why not subordinate level?

  6. Natural Levels of Classification • Rosh et al. (1976) basic level category “models”

  7. Tanaka and Taylor (1991) • Expertise guides classification • What is this? • And this? Vehicle (or Ship) v Starship v Ambassador Class Vehicle (or Ship) v RomulanWarbird v D’deridex Class

  8. Tanaka and Taylor (1991) • Bird experts vs. dog experts • Subjects identified pictures of specific birds and dogs (subordinate-level) or common birds and dogs (basic-level)

  9. Tanaka and Taylor (1991) • Expertise sped responses subordinate exemplars, and non-experts faster at basic level exemplars

  10. Categorization • OK, so how do we actually categorize? • Definitional approach • Compare features of item defining characteristics for categories • Problem is what defines a defining characteristic? • Nearest-neighbor rule • Select the category containing an item that is most similar to the item to be classified • Average distance rule • Select the category containing items that have the greatest average similarity to the item to be classified • Prototype rule…

  11. Category: Birds Bat (6.15) Penguin (4.53) Owl (2.96) Sparrow (1.18) 7 6 5 4 3 2 1 Low (Proto)Typicality High Typicality • Objects may be classified by comparison to prototypes • Rosch (1976) found objects differ in typicality • High prototypicality • Low prototypicality

  12. Typicality • Items are listed in order of typicality under each superodrinate category

  13. Typicality • Basic level category “models” may be prototypes

  14. Typicality • Smith, Shoben and Rips (1974) • Sentence verification task • Typicality effect

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