lec07-2 - Prototype & Exemplar Theories of Categorization...

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Prototype & Exemplar Theories of Categorization and (separate topic) Basic Level of Categorization Psychology 355: Cognitive Psychology Winter Quarter 2009 2/18/2009
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P 355, Miyamoto, Winter '09 2 Outline • Prototype Theory of Categorization (finish) • Exemplar Theory of Categorization (briefly) • Is there a basic level of categorization? Next: How Do We Decide What Category an Object Belongs To?
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P 355, Miyamoto, Winter '09 3 How do we decide what to call a new object? • Suppose you encounter a novel object, e.g., you encounter a large screen on wheels that you can roll from room to room or different positions within a room. The screen is attached to a digital photo device that displays a long sequence of color photos on the screen. Question: Do you call this object "furniture"? • Prototype theory – Categorization decisions are made by comparing new items to a prototype that is stored in memory. Categorizations are based on the similarity of the new items to the prototype. o Decide whether this novel object is "furniture" by comparing the novel object to the prototype of the "furniture" category. • Exemplar theory – Categorization decisions are made by comparing new items to multiple specific old items that are stored in memory. Categorizations are based on the similarity of the new items to the old items. o Decide whether this novel object is "furniture" by comparing the novel object to many specific memories of "furniture." Next: Feature Representation of a Prototypical Bird
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P 355, Miyamoto, Winter '09 4 Properties of Bird Species and the Prototypical Bird Robin Sparrow Heron Penguin Bird Prototype Flies + + + + Sings + + −− + Lays eggs + + + + + Small + + + Has feathers + + + + + Nests + + in trees Eats + + insects Next: Comments on the Prototypical Bird
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P 355, Miyamoto, Winter '09 5 Prototype Example: The Prototypical Bird • The "bird" prototype is a mental representation of typical features of birds. • Unlike an actual bird, it can have some features left blank. o See the preceding slide. The "eats insects" property is left blank in the "bird" prototype. o E.g., Is the prototypical "UW undergrad" male or female? Blond or brown haired? Wearing a brown shirt or a blue shirt? The prototype may be blank for these specific properties. Next: Some Qualifications Regarding the Idea of a Prototype
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P 355, Miyamoto, Winter '09 6 Some Qualifications Regarding the Idea of a Prototype • Goldstein textbook: The prototype of a category is formed by averaging the category members that we have encountered in the past. o Not quite right. If you average the features of UW undergrads to find the prototype for this category, what is the average sex going to be? What is the average location at birth? Some of these features will be blank. • Technically, the "bird" prototype is not the same as a specific bird species, e.g., a sparrow, even if sparrows have many features in common with the "bird" prototype. Nevertheless, cognitive psychologists like Goldstein often write as if a prototype is equivalent to a specific typical category member.
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This note was uploaded on 10/05/2009 for the course PSYCH 355 taught by Professor Miyamoto during the Winter '08 term at University of Washington.

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lec07-2 - Prototype & Exemplar Theories of Categorization...

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