Categorization Ch. 9 PDF

Categorization Ch.9 Chapter 9: Concepts and Generic Knowledge Why do we categorize? How do we categorize? What is typical? How are categories instantiated in the brain? The problem of the world: Why we categorize How can we handle the complexity of the world? Ge...

Categorization Ch.9 Chapter 9: Concepts and Generic Knowledge Why do we categorize? How do we categorize? What is typical? How are categories instantiated in the brain? The problem of the world: Why we categorize How can we handle the complexity of the world? Generalization The process of treating things as being the same Discrimination The process of treating similar things as different things Categorization The process of forming groups of objects, events, ideas that are all treated the same Mix of Generalization and Discrimination  Why do we categorize? 1. Cognitive Economy Too many objects in the world to consider each one individually 2. Inferences When we categorize, we know something about the properties of its category members This allows us to make predictions This animal has wings, I bet it can fly, and I bet it is a bird. 3. Communication In sharing concepts with others, we can communicate complex ideas via single words or phrases Chair vs. object made of typically solid matter that can support the weight of a person who places their bottom on it to rest How do we categorize? 1. Rule-Based (Classical View) Referred to as “definitions” Used when categories are well-defined 2. Prototypes Used when categories are ill-defined and well-defined 3. Exemplars Used when categories are ill-defined and well-defined  1. Rule-based Categorization This defining set of features is necessary and sufficient A stimulus X is a member of category Y if X has features F1, F2, F3,... FN. Necessary – features have to be present for inclusion E.g. Regulation of body temperature for mammals Sufficient – if these features are present, no other features are necessary for inclusion How do we categorize? Exemplars Prototypes Experienced examples Average of all exemplars The ideal (idealized) member Posner & Keele (1968, 1970) Prototypes and Exemplars Posner & Keele Phase 1: Exposure (classify items) Example members of a category (Exemplars) Prototype is never shown Phase 2 : Test: Recognition memory “old” items “new” items (including prototype) Posner & Keele Results Accuracy Overall more accurate for old items (vs. new) Even if the patterns were equally similar to prototype Over time: Accuracy of the old items decreased High false alarm rate for the Prototype Prototypes continue to be considered “old” Exemplars inform Prototypes CATEGORY A Prototype for Category B CATEGORY B WIDTH Prototype for Category A HEIGHT Exemplars and Prototypes Every concept is a mix of exemplars and prototype Early learning involves exemplars Experience involves averaging exemplars to get prototypes With more experience, we can use both Exemplars and Prototypes Every concept is a mix of exemplars and prototype Both provide information Kermit the Frog Prototypical features Is green, eats flies Exemplar (unique to Kermit) Sings, loves a pig, made of cloth  Exemplars and Prototypes Exemplars Exemplar-based reasoning: use knowledge of specific category members rather than general/prototypical information about the category. More flexible but less economical E.g. we can “tune” our concepts to match circumstances E.g. New Zealand vs. American Birds  Exemplars and Prototypes Prototypes Economical but less flexible E.g. bird  What is typical? Graded membership: Not all members of a group are equal Typicality and Graded membership Typicality Graded membership The distance from the Close to prototype = good member to the prototype member of the group Far from prototype = bad members Typicality Effects Graded membership Individuals Differences Typicality Effects Graded membership Generational Differences  Typicality Effects – Graded membership Cross cultural Differences Biscuit-cookie-cake What might cause typicality effects? Semantic Network  The Semantic Network is involved in categorization Typicality effects – Items that are more typical are responded to with higher accuracy, faster RT, considered first Accounted for by both Prototypes and Exemplars Methods: Sentence-verification task Speech production task Picture Identification Task Rating Tasks Imagery Tasks  Typicality Effects The sentence-verification task. True or false? Robins are birds