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Chapter 9

PSY270 Chapter 9.docx

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University of Toronto St. George
Kristie Dukewich

Chapter 9: Knowledge Concept: a mental representation that is used for a variety of cognitive functions, including memory, reasoning, and using and understanding language Categorization: the process by which things are placed into groups called categories (“pointers to knowledge”) Categories are tools that are essential for our understanding of the world. One of the most important functions of categories is to help us to understand individual cases we have never seen before. Once you know that something is in a category, you know a lot of general things about it and can focus your energy on specifying what‟s special about this particular object. How Are Objects Placed into Categories? Why Definitions Don’t Work for Categories Definitional approach to categorization: deciding whether something is a member of a category by determining whether a particular object meets the definition of the category The problem with this approach is that not all the members of everyday categories have the same features. Family resemblance: proposed to deal with the problem that definitions often do not include all members of a category; refers to the idea that things in a particular category resemble one another in a number of ways; allows for some variation within a category The idea of family resemblance has led psychologists to propose that categorization is based on determining how similar an object is to some standard representation of a category. The Prototype Approach: Finding the Average Case Prototype approach to categorization: membership in a category is determined by comparing the object to a prototype that represents the category Prototype: a “typical” member of the category The “typical” prototype is based on an average of members of a category that are commonly experienced. Prototypicality: High prototypicality: a category member closely resembles the category prototype (a “typical” member of a category) Low prototypicality: a category member does not closely resemble a typical member of the category  Prototypical Objects Have High Family Resemblance o When an item‟s characteristics have a large amount of overlap with the characteristics of many other items in a category, this means that the family resemblance of these items is high (and vice versa). o Items high on prototypicality have a high family resemblance; items low on prototypicality have a low family resemblance  Statements About Prototypical Objects Are Verified Rapidly o Sentence verification technique: used to determine how rapidly people could answer questions about an object‟s category 1. Ptcs presented with statements 2. Ptcs asked to answer “yes” if it‟s true and “no” if it‟s false 3. Ptcs responded faster for objects that are high in prototypicality (ex: „apple‟ for the category „fruit‟) than they did for objects that are low in prototypicality (ex: „pomegranate‟) (typicality effect)  Prototypical Objects Are Named First o When ptcs are asked to list as many objects in a category as possible, they tend to list the most prototypical members of the category first.  Prototypical Objects are Affected More By Priming o Priming occurs when presentation of one stimulus facilitates the response to another stimulus that usually follows closely in time. o Prototypical members of a category are affected by a priming stimulus more than are nonprototypical members. The Exemplar Approach: Thinking About Examples Exemplar approach to categorization: also involves determining whether an object is similar to a standard object; however, whereas the standard for the prototype approach is a single “average” member of the category, the standard for the exemplar approach involves many examples, each one called an exemplar Exemplars: actual members of the category that a person has encountered in the past The exemplar approach explains the typicality effect by proposing that objects that are like more like the exemplars are classified faster. Which Approach Works Better: Prototypes or Exemplars? One advantage of the exemplar approach is that by using real examples, it can more easily take into account atypical cases such as flightless birds. The exemplar approach can also deal more easily with variable categories like games. 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. Thus, early in learning we would be poor at taking into account “exceptions”, such as ostriches or penguins, but later, exemplars for these cases would be added to the category. Other research indicates that the exemplar approach may work best for small categories, and the prototype approach may work best for larger categories. Is There a Psychologically “Privileged” Level of Categories? Hierarchical organization: larger, more general categories are divided into smaller, more specific categories, creating a number of levels of categories Although it is possible to demonstrate that there is a basic level of categories with special psychological properties, the basic level may not be the same for everyone. Rosch’s Approach: What’s Special About Basic Level Categories? There are different levels of categories, ranging from general (like “furniture”) to specific (like “kitchen table”), and when people use categories they tend to focus on one of these levels. Three levels of categories: 1. Superordinate level (global) – “furniture” 2. Basic level – “table” 3. Subordinate level (specific) – “kitchen table” Starting at the basic level and moving up to the global level causes the loss of a lot of information; however, going from the basic level to specific level provides a gain of only a little information. How Knowledge Can Affect Categorization In order to fully understand how people categorize objects, it is necessary to consider not only the properties of the objects, but the learning and experience of the people perceiving these objects. The level that is “special” – meaning that people tend to focus on it – is not the same for everyone. Generally, people with more expertise and familiarity with a particular category tend to focus on more specific info that Rosch associated with the specific level. Representing Relationships Between Categories: Semantic Networks Semantic network approach: proposes that concepts are arranged in networks Introduction to Semantic Networks: Collins and Quillian’s Hierarchical Model The network consists of nodes that are connected by links (related to each other in the mind). Each node represents a category or concept, and concepts are placed in the networks so that related concepts are connected. In addition, properties associated with each concept are indicated at the nodes. It is a hierarchical model because it consists of levels arranged so that more specific concepts are the bottom, and more general concepts are at higher levels. Cognitive economy: storing shared properties just once at a higher level node Although cognitive economy makes the network more efficient, it does not account for individual differences between members of a category (the “exceptions”). To fix this problem, these “exceptions” are stored next to the member at a more specific level. The time it takes for a person to retrieve information about a concept should be determined by the distance that must be traveled through the network. Ex: “A canary is an animal” takes longer to respond to than “a canary is a bird” Spreading activation: activity that spreads out along any link that is connected to an activated node Ex: activating the canary-to-bird pathway activates additional concepts that are
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