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 ViewDefinitional approach to categorization Probabilistic TheoriesThe Prototype ApproachThe Exemplar Approach

Classic View

Definitional approach to categorization We create categories based on a system of rules or definitionsRules 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 thingsMany everyday categories are rule-breakers

Limitations to Classic ViewGraded 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 waysThus, 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 ApproachThe central core instance of a categoryThe average of all your experiencesIdealized 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/FrequencyWould 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)

.FRUIT BIRD

STIMULUS TR 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

Evidence Supporting Prototype Approach

Family ResemblanceDistribution of attributesRatings task TypicalitySentence Verification Task: Yes/No questions Picture Identification Task: Yes/No questions NamingProduction 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 ratingThese items are ideal examples and may be referred to as “prototype”

See next slide

Demo: Family Resemblance Test

ChairSofaBedMirrorTelephoneTV

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 TaskTypicality EffectStatements 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 ProblemHow 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 TheoryMentally taking in each experience or encounter one has had with members of that category; thinking about examplesExemplars 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 casesDoesn’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 approachesIt 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 memoryRelations represented links among sets

of nodesSpreading activation

Robin WingsProperty

Collins & Quillian’s Model (1969)

Spreading activationActivation is the arousal level of a nodeSpreads down linksUsed to extract information from network

Structure is hierarchicalTime 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: http://erasmus-mundus.univ-paris1.fr/fichiers_etudiants/2488_dissertation.pdf

http://www.academia.edu/6690750/Perceptual_interpretation

www.itu.dk/.../2011-Spring-HIP-Lecture09-... www.tamu.edu/faculty/takashi/.../Ch%209%20Knowledge.ppt