Prototype and Exemplar Theories of Concepts

Psy315h - Class 21

(This page last updated 1 November, 2005.)

We will explore four ways of representing concepts. This page will describe two methods, and the remaining two are described on the pages before and after this one.

2. Prototypes

• Single exemplar selected as prototype
  • May be real exemplar, or combination of features from different exemplars
• Membership in category determined by similarity to prototype
• Higher similarity = better member of category
• A category defined by a prototype will have graded membership and a fuzzy boundary.
  • Some items will be very similar to the prototype, and will clearly be a member.
  • Other items will be less similar to the prototype, but may still be similar enough to be classified as a member.
• Allows for categories with family resemblance structure.

Experiments that Support the Idea that Concepts are Represented by Prototypes

1. Production
2. Typicality Ratings
3. Picture Identification
4. Sentence Verification
5. Induction of Unfamiliar Properties
6. Making Up Sentences

   See the description of these experiments in the textbook.

Converging Evidence

• Results from all of these different types of experiments support the same sort of category structure.
• The category members that get the highest typicality ratings and that are named first also produce the fastest sentence verification , etc.

   

3. Exemplars

• Rather than relying on a single prototype, we can also represent a category by storing many or all known exemplars of the category.
• When a new item is encountered, it is compared against all the members.
• Of course, this increases the memory requirement.
• Exemplar theories of concepts can also explain graded membership.
  • The more exemplars that a stimulus matches, the better it fits into a category.
• The experimental results that support prototypes can generally be explained by exemplar theories.

One Advantage of Exemplar Models over Prototype Models

• Exemplar models can preserve information about the correlation of different features within a category.
• Medin et. al. (1982) showed that subjects do use information about correlated features.
  • Their subjects first studied a set of examples to learn a category. Then they had to decide whether new instances belonged in the category or not.
  • After learning the category of patients with burlosis, subjects receive pairs of new patients and must decide which is more likely to have burlosis.
  • Both patients have the same number of symptoms, but in the first patient, the last two symptoms are correlated, while in the second patient they are not. None of the earlier patients had a pattern like the second patient.
  • Subjects were more likely to pick the first patient.
  • See description of Medin et. al. in textbook for more details.
• Some evidence suggests that prototypes are more likely to be used than exemplars after long experience with a concept.

   

next class: Concepts as Implicit Theories
  
Psych 315H: Cognitive Psychology Kyle Cave Psychology Dept. U. Mass.