Introduction to Categorization Theory (Goldstein Ch 9: Knowledge) Psychology 355: Cognitive Psychology Instructor: John Miyamoto 05/17/2016: Lecture 08-2 Note: This Powerpoint presentation may contain macros that I wrote to help me create the slides. The macros aren’t needed to view the slides. You can disable or delete the macros without any change to the presentation.

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 '16

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 '16

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 '16

Knowing the Category Provides a Lot of Information Definition of Categorization Psych 355, Miyamoto, Spr '16

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 '16

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 '16

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 '16

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 1 - 3. Problems with the Definitional Approach Psych 355, Miyamoto, Spr '16

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 '16

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 '16

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 '16

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: http://slantoflight.org/?p=553 Continuation of Present Slide with Composite Image Psych 355, Miyamoto, Spr '16

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: http://slantoflight.org/?p=553 Paul Wittgenstein Concert pianist Lost right arm in WW I Family Resemblance in Concept Theory Psych 355, Miyamoto, Spr '16

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. Return to Slide Showing the Prototype Theory of Categorization Psych 355, Miyamoto, Spr '16

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 '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 '16

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 '16

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 '16

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 '16

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 '16

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 prime is logically irrelevant) Prime Stimulus Response "green" spoken aloud "yes" "pink" spoken aloud "no" Results for Priming with Color Matching Psych 355, Miyamoto, Spr '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: "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 '16

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 '16

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 '16

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 '16

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 '16

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 '16

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 '16

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 versus total similarity. 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). Case of Amadou Diallo Psych 355, Miyamoto, Spr '16

Case of Amadou Diallo Source: http://en.wikipedia.org/wiki/Amadou_Diallo_shooting. 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. Payne’s Study of Race Priming of Weapons Identification Psych 355, Miyamoto, Spr '16

Race Priming of Weapons Categorization Priming Stimulus Test Stimuli * Payne (2001): Weapon versus non-weapon identification. Dependent variable = response time. Subjects: 24 women, 7 men (all white) What do you predict if their are automatic associations of black faces with weapons? Results for Race Priming Psych 355, Miyamoto, Spr '16

Race Priming of Weapons Categorization Priming Stimulus Test Stimuli Payne Exp. 1. Prime is white. Prime is black. Test stimulus is a weapon. 441 > 423 Test stimulus is a tool. 446 < 454 Weapon identification is faster when the prime is black. Non-weapon identification is faster when the prime is white. Diagram that Summarizes the Theoretical Interpretation of This Finding Psych 355, Miyamoto, Spr '16

Theoretical Model for the Race Priming Experiment 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. END Psych 355, Miyamoto, Spr '16