PSYCH 240 Lecture Notes - Lecture 12: Semantic Network, Word Stem, Exemplar Theory
Lecture 11 Reading Notes
Pages 291-307
Procedural Knowledge: how to follow procedural steps for performing actions
Cognitive psychologists seek to understand the what (the form or structure) and the
how (the processes) of knowledge representation and manipulation
Converging operations: the use of multiple approaches and techniques to address a
problem; knowledge representation and processing have been investigated by
researchers from several different disciplines
The way in which knowledge is represented profoundly influences how effectively
knowledge can be manipulated for performing any number of cognitive tasks
Concept: an idea about something that provides a means of understanding the world
A concept is a fundamental unit of symbolic knowledge
Category: a hierarchy of concepts; a concept with members
A category is a group of items into which different objects or particular concepts can
be placed that belong together because they share some common features, or
because they are all similar to a certain prototype
Categories can be subdivided in various ways
Natural Categories: groupings that occur in the world, like birds or trees
Artifact categories: groupings that are designed or invented by humans to serve
particular purposes or functions, like automobiles and kitchen appliances
The speed it takes to assign objects to categories seems to be about the same for
both natural and artifact categories; many natural and artifact categories
Many natural/artifact categories are relatively stable and people agree on criteria
for the membership of those categories
Not all categories are stable; ad hoc categories: are not described in words, but are
decided in phrases; their content varies depending on the context
Concepts, in general, and categories are also used in other areas
Categories appear to have a basic level (natural level) of specificity, a level within a
hierarchy that is preferred to other levels; in this view, there is also a superordinate
and subordinate level
Basic level: neither the most abstract nor the most specific; can be manipulated by
context or expertise; basic level= most distinctive
Basic level can be shifted to subordinate level;
When people are shown pictures of objects, they identify objects at a basic level
more quickly than they identify objects at higher or lower levels
There are many theories that suggest how people decide what to put into a category
Feature-Based Concepts: A Defining View:
The classical view of concepts disassembles a concept into a set of featural
components; all those features are then necessary (and sufficient to define the
concept); together these features uniquely definite concept
Defining features: necessary attributes
Feature based view is especially common among linguists because it makes
concepts appear so orderly and systematic- but it doesn’t work as well as it seems to
Some concepts don’t readily lend themselves to feature analysis
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This approach has some flexibility so that not all defining features have to be shared
as long as members resemble each other in some way
Another problem with the view is that a violation of those defining features doesn’t
seem to change the concept we use to define them
Children learn typical instances of a category earlier than they learn atypical ones
Feature-based theory doesn’t give a complete account of concepts or categories
Some specific members seem to be better examples than others but they all have the
same defining features
We need a theory of knowledge representation that better characterizes how people
truly represent knowledge
Prototype Theory: A Characteristic View:
Prototype theory takes the approach of grouping things together by their similarity
to an averaged model of the category
Prototype: an abstract average of all the objects in the category we previously have
encountered- we have an average representation of the category
Objects that are prototypical of a category therefore have high family resemblance
Crucial for prototypes are characteristic features, which describe (characterize or
typify) the prototype but are not necessary for it
These features are common in typical examples of concepts, but not always
This theory can handle concepts that have no defining features and concepts that
have better examples of the concept ex. ostrich vs. bird
Many or most instances possess each characteristic feature
Stereotypes of different groups of people consist of a conglomerate of avg. features
Classical and Fuzzy Concepts:
Classical concepts are categories that can be readily defined through defining
features while fuzzy concepts are categories that cannot be so easily defined
Fuzzy concepts tend to evolve naturally
Classical concepts tend to be inventions that experts have devised for arbitrarily
labeling a class that has associated defining features
Classical concepts and categories may be built on defining features
Fuzzy concepts and categories are built around prototypes
We view similarity in terms of the number of features shared between an object and
prototype while some features should be weighed more heavily as being more
central to the prototype than are other features
Real-World Examples: Using Exemplars:
Some psychologists suggest that instead of a prototype, we should use multiple,
specific exemplars: typical representatives of a category
An exemplar is not necessarily averaged over all objects
Some investigators use this approach to explain how categories are both formed and
used in speeded classification situations
In particular, categories are set up by creating a rule and then by storing examples
as exemplars; objects are then compared to exemplars and decided whether or no
they belong in the category that exemplars represent
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Document Summary
Procedural knowledge: how to follow procedural steps for performing actions. Cognitive psychologists seek to understand the what (the form or structure) and the how (the processes) of knowledge representation and manipulation. Converging operations: the use of multiple approaches and techniques to address a problem; knowledge representation and processing have been investigated by researchers from several different disciplines. The way in which knowledge is represented profoundly influences how effectively knowledge can be manipulated for performing any number of cognitive tasks. Concept: an idea about something that provides a means of understanding the world. A concept is a fundamental unit of symbolic knowledge. Category: a hierarchy of concepts; a concept with members. A category is a group of items into which different objects or particular concepts can be placed that belong together because they share some common features, or because they are all similar to a certain prototype. Categories can be subdivided in various ways.
