1. Introduction to Categorization Theory (Goldstein Ch 9: Knowledge)
Psychology 355: Cognitive Psychology Instructor: John Miyamoto 05/14/2015: Lecture 07-4
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2. Lecture probably ends here
Outline
Concepts, categorization, and knowledge
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
Lecture probably ends here
Categorization – Examples
Psych 355, Miyamoto, Spr '15

3. Categorization – Examples
Categorize objects in the physical world. E.g., tables, chairs, cars, dogs, cats, trees, water, etc.
Categorize types of people.
E.g., policemen, teachers, students, politician, etc.
E.g., friend, enemy, helpful, inconsiderate, smart, talkative, etc.
E.g., white, black, asian, ...., catholic, muslim, hindu, ....,
Abstract categories.
"___ is a crime", e.g., theft is a crime; complaining is not a crime.
"___ is a relative of mine." (Kinship is an abstraction.)
"credit" in the financial sense is an abstraction.
Inferences with Categorizations
Psych 355, Miyamoto, Spr '15

4. Inferences with Categories
Example of Reasoning with Categories
Type of Inference
I see a dog and say, "That's a mammal/dog/collie."
Categorize an object (put it into a category)
A friend tells me, "I have a collie," and I think to myself, "I hope she doesn't mind dog hair on her clothes."
Draw an inference from a categorization to other properties of the object.
A friend tells me that fluorescent light can wreck a cd that contains data. I think to myself, I wonder if the same thing is true of dvd's?
Draw an inference from a property of one category to a possible property of another category.
Categories Imply a Lot of Other Information – Cat Example
Psych 355, Miyamoto, Spr '15

5. Knowing the Category Provides a Lot of Information
Definition of Categorization
Psych 355, Miyamoto, Spr '15

6. Categorization – What is it?
Goldstein book: Categorization "is the process by which things are placed into groups called categories."
This is an incomplete definition. Below is a better definition.
The psychology of categorization has to do with:
how we assign objects or events to categories;
the structure of knowledge that we use to organize our knowledge of categories (category structure);
the inferences that we draw when we learn what categories an object or event belongs to;
how we learn new categories (Children learn new categories frequently; adults learn new categories from time to time)
These are all examples of semantic knowledge.
Distinction Btwn Concepts & Categories
Psych 355, Miyamoto, Spr '15

7. Categories and Concepts
The word "concept" emphasizes knowledge of relationships between concepts.
E.g., the concept of a cat includes knowledge of its biology, appearance, behavior, its relation to human life styles, etc.
mokita (Kivila language): “truth we all know but agree not to talk about” (Wikipedia)
Concept of "time" includes knowledge of all sorts of temporal relationships, e.g., relations of "before" and "after."
Related relations and concepts s of "duration," "instant", "concurrency", "distant past," "recent past."
The word "category" emphasizes the set of all things that are joined together under a common label.
E.g., every cat is a member of the category "cat"; every dog and every cat is a member of the category "carnivore."
Relationship between Knowledge and Categories
Psych 355, Miyamoto, Spr '15

8. Categorization and Knowledge
Goldstein calls the topic “Knowledge” – why?
This is a hypothesis – not a fact.
IMO: The structure of categories and the structure of concepts are related to the structure of knowledge, but none is identical to any of the others. ?
Definitional Approach to Category Membership
Psych 355, Miyamoto, Spr '15

9. Definitional Approach to Category Membership
Originated with Aristotle. According to the definitional approach, category membership is determined by checking a list of necessary and sufficient features.
Example: Definition of a tea cup.
Concrete object
Concave
Can hold liquids
Has a handle
Can be used to drink hot liquids
Properties 4 and 5 are debatable. Chinese tea cups. Lacquer cups. If you drop 4 and 5, then there are many objects (bowls) that satisfy
Problems with the Definitional Approach
Psych 355, Miyamoto, Spr '15

10. What Do These "Chairs" All Have in Common?
Maybe there is nothing that ALL chairs have in common, but they all share a family resemblance.
Problems with the Definitional Approach to Categorization
Psych 355, Miyamoto, Spr '15

11. Problems with the Definitional Approach
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 does not explain important aspects of human 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").
Prototype Theory of Categorization
Psych 355, Miyamoto, Spr '15

12. 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.
Family resemblances.
Next: Digression regarding family resemblances
Family Resemblance Idea - Background
Psych 355, Miyamoto, Spr '15

13. Family Resemblance Idea - Background
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
Composite
Family Resemblance in Concept Theory
Psych 355, Miyamoto, Spr '15

14. 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 is no necessary & sufficient condition for something to be a chair, but there is a family resemblance among chairs.
Return to Slide Showing the Prototype Theory of Categorization
Psych 355, Miyamoto, Spr '15

15. 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 a family resemblance photographs – they retain the typical characteristics of many particular examples.
Examples of Birds & the Prototypical Bird Image
Psych 355, Miyamoto, Spr '15

16. 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
Basic Claim of Prototype Theory
Psych 355, Miyamoto, Spr '15

17. 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
Two Basic Questions (Not Answered in Psych 355)
Psych 355, Miyamoto, Spr '15

18. 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.
Rosch’s Color Priming Experiment
Psych 355, Miyamoto, Spr '15

19. Evidence for a Prototype Theory of Categorization
Semantic memory experiment Goldstein calls this the sentence verification technique
Subjects are faster to verify that prototypical objects are in 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 few 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.)
Rosch's Color Priming Experiment
Psych 355, Miyamoto, Spr '15

20. 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
Prime Stimulus Response
"yes"
"no"
Primed Condition in the Color Matching Task
Psych 355, Miyamoto, Spr '15

21. 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
Prime Stimulus Response
"green" spoken aloud "yes"
"pink" spoken aloud "no"
Results for Priming with Color Matching
Psych 355, Miyamoto, Spr '15

22. 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:
"green" spoken aloud primes "yes" for
priming helps a lot
priming helps, but not as much
Theoretical Interpretation of Results for Priming & Color Matching
Psych 355, Miyamoto, Spr '15

23. 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 this color 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 not as primed to see this color so the subject is slower to see that the colors match.
Conclusion: The spoken category name, "green", produces a mental representation of the prototype of "green." or
Summary of Prototype Theory
Psych 355, Miyamoto, Spr '15

24. 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.
Exemplar Theory of Categorization
Psych 355, Miyamoto, Spr '15

25. Exemplar Theories of Categorization – Basic Idea
Competitor to prototype theories.
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.
Example of Categorization by Exemplar Model – Am I Looking at a Dog?
Psych 355, Miyamoto, Spr '15

26. How Exemplars Lead to Categorization
Retrieve 3 Bear Exemplars
Retrieve 4 Dog Exemplars
What is it?
Same Idea Written Out Verbally
Psych 355, Miyamoto, Spr '15

27. Exemplar Theory of Categorization - Example
Suppose we are trying to decide whether object A is a member of category X. E.g., A is a shaggy, four-legged creature. Is A 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 A is a dog if A is more similar to the memories of dogs than to memories of relevant non-dogs.
Summary of Exemplar Theory
Psych 355, Miyamoto, Spr '15

28. Summary – Exemplar Theory also Predicts the Main Categorization Findings
Exemplar theory can predict the main findings that support prototype theory.
Semantic memory experiment (sentence verification)
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.
Comparison of Prototype Theory to Exemplar Theory
Psych 355, Miyamoto, Spr '15

29. Thursday, May 14, 2015: The Lecture Ended Here
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