PSY 323 – COGNITION Chapter 9: Knowledge

 Categorization ◦ 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.

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

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)

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

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

Wittgenstein (1953)

Classic View 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

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)

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

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

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

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

Testing the Prototype Notion Malt & Smith (1984) TR = Typicality Rating (based on 0-7 scale). FRUITBIRD STIMULUSTRSTIMULUSTR Apple6.2Robin6.9 Peach5.8Seagull6.3 Pear5.2Owl5.0 Watermelon4.1Chicken3.9 Coconut3.1Penguin2.6 Olive2.2Bat1.5

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

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 

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)

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

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)

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)

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

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

An exemplar for “role model”

After all these years, still not a role model 1993 Nike commercial caused much controversy

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

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”

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

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

Semantic Network Model Nodes represent concepts in memory Relations represented links among sets of nodes Spreading activation RobinWings Property

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 

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

Credits  Some of the slides in this presentation prepared with the assistance of the following web sites:  paris1.fr/fichiers_etudiants/2488_dissertation.pdf paris1.fr/fichiers_etudiants/2488_dissertation.pdf   