Introduction to Categorization Theory

Transcription

1 Introduction to Categorization Theory (Goldstein Ch 9: Knowledge) Psychology 355: Cognitive Psychology Instructor: John Miyamoto 05/15/2018: 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.

2 Psych 355, Miyamoto, Spr '18 2 ## Outline Categorization what is it? How are objects placed into categories? The definitional theory of categorization Discussed Last Week Problems with the definitional theory of categorization Prototype theory of categorization Exemplar theory of categorization Today

3 Definitional Approach to Categorization Has Problems as a Basis for a Psychological Model 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 cannot explain typicality effects in 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 '18 3

4 Psych 355, Miyamoto, Spr '18 4 Family Resemblance Idea - Background 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 represents typical features of category members. Family resemblances. Next: Digression regarding family resemblances

5 Family Resemblance Idea - Background Composite A "family resemblance" photograph popular in late 19 th & early 20 th 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: Continuation of Present Slide with Composite Image Psych 355, Miyamoto, Spr '18 5

6 Family Resemblance Idea - Background Composite A "family resemblance" photograph popular in late 19 th & early 20 th 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: Ludwig Wittgenstein early 20 th century philosopher. Proposed that the structure of a concept is like a family resemblance photo. Paul Wittgenstein Concert pianist Lost right arm in WW I Family Resemblance in Concept Theory Psych 355, Miyamoto, Spr '18 6

7 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 '18 7

8 Psych 355, Miyamoto, Spr '18 8 Examples of Birds & the Prototypical Bird Image Prototype Theory of Categorization Eleanor Rosch proposed: (a) cognitive representations of categories are like family resemblances. (b) 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 family resemblance photographs they retain the typical characteristics of many particular examples.

9 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 '18 9

10 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 Is it a bird? compare Two Basic Questions (Not Answered in Psych 355) Psych 355, Miyamoto, Spr '18 10

11 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? Summarize Evidence for Prototype Theory Psych 355, Miyamoto, Spr '18 11

12 Evidence for a Prototype Theory of Categorization Semantic memory experiment: (Goldstein calls this the sentence verification technique) Dependent variable = response time for deciding whether a sentence is true or false. Subjects are faster to verify that prototypical objects are in a 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 fewer 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.) Digression What Is Priming? Psych 355, Miyamoto, Spr '18 12

13 Psych 355, Miyamoto, Spr '18 13 Rosch's Color Priming Experiment Digression What is Priming? Definition: Priming is the facilitation of the response to Stimulus B by prior exposure to a similar Stimulus A. How is priming used in the study of cognitive processes? Priming can be used to measure the degree to which two stimuli, A and B, are psychologically similar. Priming can be used to measure the degree to which two cognitive tasks, X and Y, require overlapping cognitive processes. (Example is given on the following slides.)

14 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 (no priming stimulus) Prime Stimulus Response..... "yes"..... "yes"..... "no" Primed Condition in the Color Matching Task Psych 355, Miyamoto, Spr '18 14

15 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 priming stimulus is logically irrelevant) Prime Stimulus Response "green" spoken aloud "yes" "green" spoken aloud "yes" "pink" spoken aloud "no" Results for Priming with Color Matching Psych 355, Miyamoto, Spr '18 15

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 priming helps a lot more than: "green" spoken aloud primes "yes" for priming helps, but not as much Theoretical Interpretation of Results for Priming & Color Matching Psych 355, Miyamoto, Spr '18 16

17 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: or If the target pair is close in color to the prototype, e.g., is close to, then the subject is primed to see the color of the target pair, 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 less primed to see the color of the target pair, so the subject is slower to see that the colors match. Conclusion: The spoken category name, "green", causes the subject to produce a mental representation of the prototype of "green." Schematic Diagram of this Theoretical Interpretation Psych 355, Miyamoto, Spr '18 17

18 Theoretical Model for the Priming in Color Matching (cont.) Priming Stimulus Target Stimulus Hear "Green" Spoken Aloud Access the Prototype for the Green Color Prime Other Colors that are Similar to the Prototype of Green Main Point: Categorizations activate prototypes. Prototypes prime judgments for stimuli that are similar to the prototype. Summary of Prototype Theory Psych 355, Miyamoto, Spr '18 18

19 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 '18 19

20 Exemplar Theories of Categorization Basic Idea Exemplar theory is a competitor to prototype theory. 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 '18 20

21 How Exemplars Lead to Categorization Retrieve 4 Dog Exemplars Retrieve 3 Non-Dog Exemplars Same Idea Written Out Verbally Psych 355, Miyamoto, Spr '18 21

22 Exemplar Theory of Categorization - Example Suppose we are trying to decide whether object A is a member of category X. E.g., X is a shaggy, four-legged creature. Is X a dog? Exemplar theory says we do the following: 1. Retrieve memories of specific dogs (exemplars) that we have encountered. 2. Retrieve memories of relevant non-dogs, e.g., memory of a cat; memory of a stuffed animal; memory of a raccoon; etc. 3. Mentally compute the total similarity of the current instance to memories of positive and negative exemplars (exemplars of dogs and non-dogs). 4. Decide that X is a dog if X is more similar to the memories of dogs than to memories of relevant non-dogs. Summary of Exemplar Theory Psych 355, Miyamoto, Spr '18 22

23 Prototype Theory and Exemplar Theory Both Predict the Main Findings in Categorization Studies Semantic memory experiment (sentence verification) Which statements are easier or harder to verify? (Faster or slower RT) Prototypical objects have high family resemblance with other category members. I.e., prototypical objects share many features 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 All of the above can be predicted by prototype theory and exemplar theory. Psych 355, Miyamoto, Spr '18 23 Comparison of Prototype Theory to Exemplar Theory - END

24 Psych 355, Miyamoto, Spr '18 END - OR Time Permitting, Present Example of Race Priming 24 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 and contrast categories. 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.

25 Time Permitting: Case of Amadou Diallo Psych 355, Miyamoto, Spr '18 25 Case of Amadou Diallo

26 Case of Amadou Diallo Psych 355, Miyamoto, Spr '18 Payne s Study of Race Priming of Weapons Identification 26 Source: 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.

27 Race Priming of Weapons Categorization Payne, B. K. (2001). Prejudice and perception: The role of automatic and controlled processes in misperceiving a weapon. Journal of Personality and Social Psychology, 81, Payne (2001): Weapon versus non-weapon identification. Dependent variable = response time. Subjects: 24 women, 7 men (all white) Question: Is there an automatic association between black faces and weapons? 2 x 2 Design: {Priming Stimulus} x {Test Stimulus} Psych 355, Miyamoto, Spr '18 27

28 Race Priming of Weapons Categorization Payne, B. K. (2001). Prejudice and perception: The role of automatic and controlled processes in misperceiving a weapon. Journal of Personality and Social Psychology, 81, Priming Stimulus X Test Stimuli X TASK: Decide whether the test stimulus is a weapon or a tool. DEPENDENT VARIABLE: Response Time Arrangement of Results in a 2 x 2 Table Psych 355, Miyamoto, Spr '18 28

29 Race Priming of Weapons Categorization Payne, B. K. (2001). Prejudice and perception: The role of automatic and controlled processes in misperceiving a weapon. Journal of Personality and Social Psychology, 81, Prime is White Prime is Black Test Stimulus is a Weapon Test Stimulus is a Tool RT? RT? RT? RT? TASK: Decide whether the test stimulus is a weapon or a tool. DEPENDENT VARIABLE: Response Time Results for Race Priming Psych 355, Miyamoto, Spr '18 29

30 Race Priming of Weapons Categorization Payne, B. K. (2001). Prejudice and perception: The role of automatic and controlled processes in misperceiving a weapon. Journal of Personality and Social Psychology, 81, Prime is White Prime is Black Test Stimulus is a Weapon Test Stimulus is a Tool > < Weapon identification is faster when the prime is black. Non-weapon identification is faster when the prime is white. Results for Race Priming Psych 355, Miyamoto, Spr '18 30

31 Theoretical Model for the Race Priming Experiment Priming Stimulus (Face) Target Stimulus (Object in Hand) Perceiving the Race of an Individual Access the Prototype for the Race & Gender of Individual Prime Other Judgments About the Individual Main Point: Categorizations can affect important decisions. Psych 355, Miyamoto, Spr '18 31 END