1. PSY 323 – Cognition
Chapter 9:
Knowledge

2. Categorization Categorization Concept
Process by which things are placed into groups
Concept
Mental groupings of similar objects, events, ideas, and people
Knowing about something is in a category gives us a great deal of information about it.

3. How Are Objects Placed Into Categories?
Classic View
Definitional approach to categorization
Probabilistic Theories
The Prototype Approach
The Exemplar Approach

4. Click on picture for definition from dictionary.com 
Classic View
Definitional approach to categorization
We create categories based on a system of rules or definitions
Rules must identify necessary and sufficient features (often referred to as concepts)
Example: The category of Bachelor
Click on picture for definition from dictionary.com 

5. Limitations to Classic View
Do we really use rules to create categories?
Our semantic memory probably doesn’t rely on such things
Many everyday categories are rule-breakers

6. Limitations to Classic View
Graded Membership
Members of a category vary in how truly they fit the category

7. Birds: which one looks more like “bird”?

8. This probably would have received a high score…

9. Maybe it just needs to share a family resemblance?
Wittgenstein (1953)

10. Classic View Limitations
Wittgenstein (1953)
Family resemblance refers to the idea that things in a particular category resemble one another in a number of ways
Thus, instead of setting definite criteria that every member of a category must meet, the family resemblance approach allows for some variation within a category

11. Probabilistic Theories
The Prototype Approach
The central core instance of a category
The average of all your experiences
Idealized representation (doesn’t correspond exactly to any member)

12. The Prototype Approach
Morph all of these images together to give you the prototype of a dog

13. The Prototype Approach
Lee, Byatt, & Rhodes (2000)
Participants more accurately recognized a caricature of Arnold Schwarzenegger than a real picture of Arnold

14. The Prototype Approach
Typicality Effects/Frequency Would you categorize this as a vehicle?

15. For one month, airplanes scored extremely high in this category…
Novac (2003)

16. Testing the Prototype Notion
Malt & Smith (1984)
TR = Typicality Rating (based on 0-7 scale)
FRUIT
BIRD
STIMULUS TR
Apple
6.2
Robin
6.9
Peach
5.8
Seagull
6.3
Pear
5.2
Owl
5.0
Watermelon
4.1
Chicken
3.9
Coconut
3.1
Penguin
2.6
Olive
2.2
Bat
1.5 .

17. Evidence Supporting Prototype Approach
Family Resemblance
Distribution of attributes
Ratings task
Typicality
Sentence Verification Task: Yes/No questions
Picture Identification Task: Yes/No questions
Naming
Production tasks

18. Family Resemblance Test
Rosch & Mervis (1975)
Distribution of attributes (features)
The most typical item in a category has the most features in common with other members of the category will be given highest rating
These items are ideal examples and may be referred to as “prototype”
See next slide 

19. Demo: Family Resemblance Test
Chair
Sofa
Bed
Mirror
Telephone TV
Take 30s to write down the characteristics for each of the items 
Rosch & Mervis (1975)

20. Family Resemblance Test
Procedure
Ratings task
Participants judged objects on a scale of 1 (good example of a category) to 7 (poor example)
Results
Rosch & Mervis (1975)

21. Sentence Verification Task
Typicality Effect
Statements about prototypical objects are verified quickly.
Is an apple a fruit?  Yes / No
Is pomegranate a fruit?  Yes / No
Smith et al. (1974)

22. Naming: Production Tasks
Prototypical Objects Are Named First
When participants are asked to list as many objects in a category as possible, they tend to list the most prototypical members of the category first
Mervis et al. (1976)

23. Limitations to Prototype Theory
Circularity Problem
How do we know what experiences should be averaged to form a category without knowing what the category is ahead of time?
Early studies used the same data to explain why something was a prototype and why something was not a prototype

24. Probabilistic Theories
Exemplar Theory
Mentally taking in each experience or encounter one has had with members of that category; thinking about examples
Exemplars are actual members of a category that someone has encountered in the past

25. An exemplar for “role model”

26. “I am not a role model” 1993 Nike commercial caused much controversy
After all these years, still not a role model

27. Advantages of the Exemplar Approach
Takes into account atypical cases
Doesn’t simply discard them

28. WHICH APPROACH WORKS BETTER: PROTOTYPES OR EXEMPLARS?
Based on the results of a number of research studies, some researchers have concluded that people may use both approaches
It has been proposed that as we initially learn about a category, we may average exemplars into a prototype; then, later in learning, some of the exemplar information becomes stronger
Other research indicates that the exemplar approach may work best for small categories, such as “U.S. presidents” or “Mountains taller than 15,000 feet,” and the prototype approach may work best for larger categories, such as “birds” or “automobiles”

29. Hierarchical Organization of Categories
Superordinate
Largest number of features
Used most often
Furniture, Animal
Basic Level
Chair, Bird
Subordinate
Bean Bag, Robin
Rosch & Mervis (1975)

30. Basic-Level is Special
People almost exclusively use basic-level names in free-naming tasks
Children learn basic-level concepts sooner than other levels
Basic-level is much more common in adult discourse than names for superordinate categories
Different cultures tend to use the same basic-level categories, at least for living things

31. Semantic Network Model
Nodes represent concepts in memory
Relations represented links among sets of nodes
Spreading activation
Robin
Property
Wings

32. Collins & Quillian’s Model (1969)
Spreading activation
Activation is the arousal level of a node
Spreads down links
Used to extract information from network
Structure is hierarchical
Time to retrieve information based on number of links
See next slide 

33. Collins & Quillian’s Model (1969)
Has skin
Animal
Breathes
Eats
Has fur
Has fins
Fish
Dog
barks
swim
4 legs
Has gills
Is pink
Has spots
Dalmatian
Salmon
Is edible
Skinny tail
Black &
white
Lays eggs upstream

34. Credits
Some of the slides in this presentation prepared with the assistance of the following web sites: