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Exemplar Theory is a proposal concerning the way humans categorize objects and ideas in psychology. It argues that individuals make category judgments by comparing new stimuli with instances already stored in memory. The instance stored in memory is the “exemplar”. The new stimulus is assigned to a category based on the greatest number of similarities it holds with exemplars in that category. For example, the model proposes that people create the “bird” category by maintaining in their memory a collection of all the birds they have experienced: sparrows, robins, ostriches, penguins, etc. If a new stimulus is similar enough to some of these stored bird examples, the person categorizes the stimulus in the “bird” category.〔 Nosofsky, R.M., Pothos, E.M., Wills, A.J. (2011). The Generalized Context Model: An Exemplar Model of Classification. Formal Approaches to Categorization, 18-39.〕 Various versions of the exemplar theory have led to a simplification of thought concerning concept learning, because they suggest that people use already-encountered memories to determine categorization, rather than creating an additional abstract summary of representations.〔 Cave, K. (2009). Prototype and exemplar theories of concepts (). Retrieved from http://courses.umass.edu/psy315/prototype.html〕 ==Exemplar and Prototype Theory== Exemplar Theory is often contrasted with prototype theory, which proposes another method of categorization. We use both the exemplar and prototype method in making category judgments, and they often work in tandem to produce the most accurate conclusion. The two theories are similar in that they emphasize the importance of similarity in categorization: only by resembling a prototype or exemplar can a new stimulus be placed into a category. They also both rely on the same general cognitive process: we experience a new stimulus, a concept in memory is triggered, we make a judgment of resemblance, and draw a categorization conclusion. However, the specifics of the two theories are different. Prototype theory suggests that a new stimulus is compared to a single prototype in a category, while exemplar theory suggests that a new stimulus is compared to multiple known exemplars in a category. While a prototype is an abstract average of the members of a category, an exemplar is an actual member of a category, pulled from memory.〔 Mollison, M. V. Knowledge Representation. Retrieved from The categorization process for identifying which type of animal a dog is can be used to provide an example for the usage of exemplar theory. All of the traits of the dog would be taken into consideration and compared, separately, to other animals the individual has encountered before. The individual would eventually conclude that the animal is a dog as it has all of the traits previously associated with an example of a dog. The individual could come to this conclusion using the prototype theory if the dog were average looking, but what happens if the dog only has three legs and does not bark? Here prototype theory might not allow the individual to conclude that the animal is a dog because it doesn’t have prototypic traits but exemplar theory would take into account previous examples of dogs that do not bark or dogs that have injuries and are therefore missing limbs. Exemplar-based categorization approaches carefully go through all encountered examples in a given category to allow for accurate categorization. Contradictory statements have been made about the accuracy of the exemplar theory for categorization when it is compared to prototype theory. For example, one study at Arizona State University concluded that the exemplar theory is most accurate with minimal category experience and as experience is developed the prototype theory is more accurate.〔Homa, D., Sterling, S., Trepel, L. (1981) Limitation of exemplar-based generalization and the abstraction of categorical information. Journal of Experimental Psychology: Human Learning and Memory 7 (6) pp. 418-439.〕 Another study though, shows evidence that the exemplar-based approach is more accurate as you become more familiar with a category because knowledge of the members is greater than that that can be represented by a single prototype. It is clear that there are some situations where the exemplar-based approach is most accurate and others where it may not be the most accurate.〔Mack, M.L., Preston, A.R., Love, B.C. (2013) Decoding the brain’s algorithm for categorization from its neural implementation. Current Biology, 23 (20) pp. 2023-2027〕 This being said, it is evident that the brain naturally uses a combination of categorization approaches in everyday life. A study done at the University of Oregon found that prototypical averages are more likely to be forgotten than many specific examples.〔Hintzman, D.L., Ludlam, G. (1980) Differential forgetting of prototypes and old instances: Simulation by an exemplar-based classification model. Memory and Cognition in Psychonomic Society 8 (4) pp. 378-382〕 Relying only on prototypes does not allow for adequate consideration while relying only on examples can be inefficient. Exemplar theory is more flexible than prototype theory but less economical, a combination of the two balances the flexibility with the efficiency. Experience with various examples averages into an ever changing, more accurate prototype – it is not that exemplar theory and prototype theory compete against each other but that they work together, in tandem.〔Johansen, M.K., Fouquet, N., Savage, J., Shanks, D.R. (2013) Instance memorization and category influence: Challenging the evidence for multiple systems in category learning. Quarterly Journal of Experimental Psychology 66 (6) pp. 1204-1226〕〔Sternberg, R.J. (1999) The Nature of Cognition. MIT Press. Pp. 231-235〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Exemplar theory」の詳細全文を読む スポンサード リンク
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