PSY270H1 Chapter Notes - Chapter 9: Neuropsychology, Prototype Theory, Fault Tolerance
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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
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.
High prototypicality: a category member closely resembles the category prototype (a “typical” member of
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
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
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