2006 Fiscal Year Final Research Report Summary
A comparative study on the formation of prototype categories
| Project/Area Number |
16530465
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Experimental psychology
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| Research Institution | Chiba University |
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Principal Investigator |
JITSUMORI Masako Chiba University, Faculty of Letters, Professor, 文学部, 教授 (80127662)
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| Co-Investigator(Kenkyū-buntansha) |
SUTO Noboru Chiba University, Faculty of Letters, Professor, 文学部, 教授 (40154611)
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| Project Period (FY) |
2004 – 2006
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| Keywords | Experimental Psychology / Comparative Cognition / Comparative Psychology / Cognition / Behavior / Evolution |
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| Research Abstract |
We created artificial categories by mimicking properties of natural category, using colored rectangles as the features comprising the categories. One is family resemblance relationship ; the highly variable exemplars were structured by a similarity network with the features correlating to one another in each category. Another is polymorphous rule ; no single feature was essential for distinguishing the categories. Humans showed difficulty in learning the categories and then responded to novel stimuli in an all-or-none fashion based on the rules they acquired. Pigeons learned the categories with ease and then showed a prototype effect in accord with the degrees of family resemblance. Because the stimuli defined as the prototypes of the categories contained the features that most frequently occurred in the given category, the best discrimination at the prototypes was readily explained by feature learning and exemplar learning.
In the next experiment, we trained pigeons to discriminate morphed images of human faces. The training exemplars in each category were created by blending a single unique face M with each of the original faces (A, B, C, and D) and their 50% morphs. To examine the effects of exemplar learning, we tested the pigeons with additional intermediate morphs that ranged between M and each of the original faces on a face-morph dimension. The pigeons' generalization gradient increased as a function of morph proportion of M of the positive category and decreased as a function of morph proportion of M of the negative category, a phenomena similar to the caricature effect of category features. Both the exemplar learning and feature learning models failed to predict the finding. The classification task used in this study might have enabled the pigeons to abstract the facial features shared by the category members and to respond to novel faces based on the degrees of common component.
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