1. Introduction to Categorization Theory (Goldstein Ch 9: Knowledge)
Psychology 355: Cognitive Psychology Instructor: John Miyamoto 05/15/2018: Lecture 08-2
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2. Outline Categorization – what is it?
Discussed Last Week
Categorization – what is it?
How are objects placed into categories?
The definitional theory of categorization
Problems with the definitional theory of categorization
Prototype theory of categorization
Exemplar theory of categorization
Today
Psych 355, Miyamoto, Spr '18 ##

3. Definitional Approach to Categorization Has Problems as a Basis for a Psychological Model
How do we discover the definitions? For many categories, it is doubtful that necessary and sufficient features exist.
Example: If we call someone "friendly," what are necessary and sufficient features for calling someone friendly?
The definitional approach cannot explain typicality effects in categorization.
E.g., it does not explain typicality effects in categorization response time. See the Rosch color priming study to be described later.
E.g., it does not explain typicality effects in semantic memory experiments (Goldstein calls this the "sentence verification technique").
Psych 355, Miyamoto, Spr '18
Prototype Theory of Categorization

4. Prototype Theory of Categorization
Cognitive psychologists were dissatisfied with the definitional approach to representing cognitive categories.
Eleanor Rosch: Categories are organized around a category prototype.
Category prototype represents typical features of category members.
Family resemblances.
Next: Digression regarding family resemblances
Psych 355, Miyamoto, Spr '18
Family Resemblance Idea - Background

5. Family Resemblance Idea - Background
Composite
A "family resemblance" photograph – popular in late 19th & early 20th century.
Take multiple exposure photo of all family members.
Only the common features are retained.
The photo looks like everyone in the family, but is not any one person.
Images downloaded from:
Psych 355, Miyamoto, Spr '18
Continuation of Present Slide with Composite Image

6. Family Resemblance Idea - Background
Composite
A "family resemblance" photograph – popular in late 19th & early 20th century.
Take multiple exposure photo of all family members.
Only the common features are retained.
The photo looks like everyone in the family, but is not any one person.
Ludwig Wittgenstein –
early 20th century philosopher.
Proposed that the structure of a concept is like a family resemblance photo.
Images downloaded from:
Paul Wittgenstein Concert pianist Lost right arm in WW I
Psych 355, Miyamoto, Spr '18
Family Resemblance in Concept Theory

7. Family Resemblance & Concepts
Famous example: Wittgenstein says that there are no necessary and sufficient conditions for something to be a "game", but there is a family resemblance among games.
Playing checkers or bridge; playing football; skipping rope; children play acting as if, e.g., having a tea party; trash talking
Similarly, there are no necessary & sufficient conditions for something to be a chair, but there is a family resemblance among chairs.
Psych 355, Miyamoto, Spr '18
Return to Slide Showing the Prototype Theory of Categorization

8. Prototype Theory of Categorization
Eleanor Rosch proposed:
cognitive representations of categories are like family resemblances.
categories have prototypes – category structure is created by the relationship between category members and the category prototype.
Prototypes (mental representation of a concept) are like family resemblance photographs – they retain the typical characteristics of many particular examples.
Psych 355, Miyamoto, Spr '18
Examples of Birds & the Prototypical Bird Image

9. A Prototypical "Bird" Image (for an Urban American)
The prototypical "bird" image is simililar to the average of many bird images.
Not Prototypical "Bird" Image
Psych 355, Miyamoto, Spr '18
Basic Claim of Prototype Theory

10. Basic Claim of Prototype Theory
Categorization decisions are based on the similarity of a specific instance to the prototype of a category.
Is it a bird?
compare
compare
Psych 355, Miyamoto, Spr '18
Two Basic Questions (Not Answered in Psych 355)

11. Two Basic Questions (not answered in Psych 355)
"Similarity to the Prototype" – What does this mean? What does it mean to "mentally compute" the similarity between two things?
How do we (psychologists) figure out the properties of a category prototype?
There is no single best method. Here are two ways.
Typicality Ratings: Subjects rate how typical various objects are of a category, e.g., rate the degree to which robins (or penguins) are typical birds. Prototypical objects are high in rated typicality.
Property listing: Ask subjects to list the properties of category members, e.g., list the properties of "robin", "penguin", "eagle", "ostrich" "hawk", "sparrow", etc. Assumption: The commonly listed properties are the properties of the prototype.
Psych 355, Miyamoto, Spr '18
Summarize Evidence for Prototype Theory

12. Evidence for a Prototype Theory of Categorization
Semantic memory experiment: (Goldstein calls this the sentence verification technique)
Dependent variable = response time for deciding whether a sentence is true or false.
Subjects are faster to verify that prototypical objects are in a category than non-prototypical objects.
“A sparrow is a bird" – FAST; "A penguin is a bird" – SLOW
Prototypical objects have high family resemblance (share many properties) with other category members.
List features of sparrows – share many features with other birds List features of penguins – share fewer features with other birds
Prototypical objects are named first if subjects are asked to list examples of a category.
List types of birds: Robin, sparrow, hawk, eagle, ....., penguin, ostrich, ...
Category names prime prototypical objects more than non-prototypical objects. (See next slides.)
Psych 355, Miyamoto, Spr '18
Digression – What Is Priming?

13. Digression – What is Priming?
Definition: Priming is the facilitation of the response to Stimulus B by prior exposure to a similar Stimulus A.
How is priming used in the study of cognitive processes?
Priming can be used to measure the degree to which two stimuli, A and B, are psychologically similar.
Priming can be used to measure the degree to which two cognitive tasks, X and Y, require overlapping cognitive processes.
(Example is given on the following slides.)
Psych 355, Miyamoto, Spr '18
Rosch's Color Priming Experiment

14. Rosch – Priming with Color Matching Task
Task: Say "yes" if I present two identical colors Say "no" if I present two non-identical colors.
Unprimed Condition (no priming stimulus)
Prime Stimulus Response
"yes"
"no"
Psych 355, Miyamoto, Spr '18
Primed Condition in the Color Matching Task

15. Rosch – Priming with Color Matching Task (cont.)
Task: Say "yes" if I present two identical colors Say "no" if I present two non-identical colors.
Primed Condition (the priming stimulus is logically irrelevant)
Prime Stimulus Response
"green" spoken aloud "yes"
"pink" spoken aloud "no"
Psych 355, Miyamoto, Spr '18
Results for Priming with Color Matching

16. Results: Priming with Color Matching Task
Effect of Priming is measured as the difference in RT between the unprimed and the primed stimulus
Finding: The word "green" primes the "yes" response for matching greens, but it does this more for prototypical greens than for less typical greens.
"green" spoken aloud primes "yes" for
more than:
priming helps a lot
priming helps, but not as much
Psych 355, Miyamoto, Spr '18
Theoretical Interpretation of Results for Priming & Color Matching

17. Theoretical Interpretation of Priming in Color Matching
Step 1. Subject hears the prime word "green"
Theory: Subject automatically thinks of a prototypical version of the color, e.g.,
Step 2. Subject sees the target pair:
If the target pair is close in color to the prototype, e.g., is close to , then the subject is primed to see the color of the target pair, so the subject is very fast to see that the colors match.
If it is not close in color to the prototype, e.g., is not close to , then the subject is less primed to see the color of the target pair, so the subject is slower to see that the colors match.
Conclusion: The spoken category name, "green", causes the subject to produce a mental representation of the prototype of "green." or
Psych 355, Miyamoto, Spr '18
Schematic Diagram of this Theoretical Interpretation

18. Theoretical Model for the Priming in Color Matching (cont.)
Target Stimulus
Priming Stimulus
Prime Other Colors that are Similar to the Prototype of Green
Access the Prototype for the Green Color
Hear "Green" Spoken Aloud
Main Point:
Categorizations activate prototypes.
Prototypes prime judgments for stimuli that are similar to the prototype.
Psych 355, Miyamoto, Spr '18
Summary of Prototype Theory

19. Summary of the Prototype Theory of Categorization
Basic claim: Categorization judgments are based on the similarity of an object to a prototype.
EVIDENCE
Semantic memory experiment (Goldstein calls this the sentence verification technique)
Prototypical objects have high family resemblance (share many properties) with other category members.
Prototypical objects are named first if subjects are asked to list examples of a category.
Category names prime prototypical objects more than non-prototypical objects.
Psych 355, Miyamoto, Spr '18
Exemplar Theory of Categorization

20. Exemplar Theories of Categorization – Basic Idea
Exemplar theory is a competitor to prototype theory.
Main claims of exemplar (instance) theories:
Category judgments are not based on a process of prototype abstraction and similarity of new objects to a prototype.
Category judgments are based on the similarity of new objects to a sample of previously encountered exemplars.
Psych 355, Miyamoto, Spr '18
Example of Categorization by Exemplar Model – Am I Looking at a Dog?

21. How Exemplars Lead to Categorization
Retrieve 3 Non-Dog Exemplars
Retrieve 4 Dog Exemplars
What is it?
Psych 355, Miyamoto, Spr '18
Same Idea Written Out Verbally

22. Exemplar Theory of Categorization - Example
Suppose we are trying to decide whether object A is a member of category X. E.g., X is a shaggy, four-legged creature. Is X a dog?
Exemplar theory says we do the following:
Retrieve memories of specific dogs (exemplars) that we have encountered.
Retrieve memories of relevant non-dogs, e.g., memory of a cat; memory of a stuffed animal; memory of a raccoon; etc.
Mentally compute the total similarity of the current instance to memories of positive and negative exemplars (exemplars of dogs and non-dogs).
Decide that X is a dog if X is more similar to the memories of dogs than to memories of relevant non-dogs.
Psych 355, Miyamoto, Spr '18
Summary of Exemplar Theory

23. Prototype Theory and Exemplar Theory Both Predict the Main Findings in Categorization Studies
Semantic memory experiment (sentence verification) Which statements are easier or harder to verify? (Faster or slower RT)
Prototypical objects have high family resemblance with other category members.
I.e., prototypical objects share many features with other category members.
Prototypical objects are named first if subjects are asked to list examples of a category.
Category names prime prototypical objects more than non-prototypical objects.
All of the above can be predicted by prototype theory and exemplar theory.
Psych 355, Miyamoto, Spr '18
Comparison of Prototype Theory to Exemplar Theory - END

24. Contrast Between Prototype Theory and Exemplar Theory
Both theories claim that categorization judgments are based on a judgment of similarity.
Prototype theory – categorization based on similarity of object to the prototype of a category.
Exemplar theory – categorization based on total similarity of object to exemplars of the category and contrast categories.
Prototype theory – Category structure base on prototypes
Exemplar theory assumes only that we can retrieve memories of specific instances of a category. Categorization based on similarity to these remembered instances.
Exemplar theory – no abstraction of prototypes
Maybe both theories are true but for different situations.
Some evidence suggests that exemplar theory is better for small categories (U.S. presidents) than for large categories (birds). Also exemplar theory may be better for categories with lots of variation (games).
Some evidence suggests that prototype theories are better as descriptions of early learning of categories, but later use of category begins to accumulate special case exceptions (exemplars).
Psych 355, Miyamoto, Spr '18
END - OR Time Permitting, Present Example of Race Priming

25. Time Permitting: Case of Amadou Diallo
Psych 355, Miyamoto, Spr '18
Case of Amadou Diallo

26. Case of Amadou Diallo
Source: Events took place 2/4/1999.
Amadou Diallo – 23 year old immigrant from Guinea. Diallo matched description of a dangerous serial rapist in NY city.
4 plain-clothes NY police officers shout at Diallo to stop & show hands
Diallo ignored officers; ran up steps to porch in front of apartment; lighting on porch was bad
One police officer thought Diallo had pulled out a gun, so he yelled “gun”. Officers shot at Diallo. During the shooting, one officer slipped and fell backwards, causing other officers to think he had been shot.
Later it was found that Diallo was not holding a gun. He was holding his brown wallet.
Officers fired 41 shot; Diallo was hit 19 times and died.
Psych 355, Miyamoto, Spr '18
Payne’s Study of Race Priming of Weapons Identification

27. Race Priming of Weapons Categorization
Payne, B. K. (2001). Prejudice and perception: The role of automatic and controlled processes in misperceiving a weapon. Journal of Personality and Social Psychology, 81,
Payne (2001): Weapon versus non-weapon identification. Dependent variable = response time.
Subjects: 24 women, 7 men (all white)
Question: Is there an automatic association between black faces and weapons? *
Psych 355, Miyamoto, Spr '18
2 x 2 Design: {Priming Stimulus} x {Test Stimulus}

28. Race Priming of Weapons Categorization
Payne, B. K. (2001). Prejudice and perception: The role of automatic and controlled processes in misperceiving a weapon. Journal of Personality and Social Psychology, 81,
Priming Stimulus
Test Stimuli X X *
TASK: Decide whether the test stimulus is a weapon or a tool.
DEPENDENT VARIABLE: Response Time
Psych 355, Miyamoto, Spr '18
Arrangement of Results in a 2 x 2 Table

29. Race Priming of Weapons Categorization
Payne, B. K. (2001). Prejudice and perception: The role of automatic and controlled processes in misperceiving a weapon. Journal of Personality and Social Psychology, 81,
Prime is White
Prime is Black
RT?
Test Stimulus is a Weapon *
Test Stimulus is a Tool
TASK: Decide whether the test stimulus is a weapon or a tool.
DEPENDENT VARIABLE: Response Time
Psych 355, Miyamoto, Spr '18
Results for Race Priming

30. Race Priming of Weapons Categorization
Payne, B. K. (2001). Prejudice and perception: The role of automatic and controlled processes in misperceiving a weapon. Journal of Personality and Social Psychology, 81,
Prime is White
Prime is Black
441
423
446
454
>
Test Stimulus is a Weapon *
<
Test Stimulus is a Tool
Weapon identification is faster when the prime is black.
Non-weapon identification is faster when the prime is white.
Psych 355, Miyamoto, Spr '18
Results for Race Priming

31. Theoretical Model for the Race Priming Experiment
Target Stimulus (Object in Hand)
Priming Stimulus (Face)
Access the Prototype for the Race & Gender of Individual
Prime Other Judgments About the Individual
Perceiving the Race of an Individual
Main Point: Categorizations can affect important decisions.
Psych 355, Miyamoto, Spr '18
END