Categorization

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Categorization

• Psy 494
• Dr. Talia Ben-Zeev

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Categorization

• Concepts vs. Categories
• Concept a mental representation of a category
  or a class of entities

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Importance of Concepts

• 1. Reasoning and inference making
• 2. Making future predictions
• 3. Instantiating goals in planning

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Fundamental Questions

• 1. What makes a category cohere?
• 2. What is the effect of context on
  categorization?
• 3. Do different concepts require different
  explanations?

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Types of Concepts

Artifacts
Natural Kinds
Ad-hoc
Abstract
Social
basic, superordinate, and subordinate
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Views of concept acquisition
Classical
Similarity-based views

probabilistic
exemplar
Theory-based views
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The Classical View
A
concept is defined by a set of

features that are individually

necessary and jointly sufficient
(Bruner
, Goodnow
,
Austin, 1956

Katz, 1972 Katz Fodor
, 1963)
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Implications of theclassical view
1. membership boundaries are clear cut
2. membership has no gradedness
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Criticisms of theclassical view
1. category membership is often

fuzzy
2. it has hardships classifying

natural kinds
3. cannot explain typicality effects
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The probabilistic view
Rosch Mervis (1975)
Concepts are organized by a family

resemblance (W
ittgenstein, 1953)
membership is defined by an object
s similarity

to a prototype
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The probabilistic view Similarity to a Prototype
Similarity to a prototype is a function of the

number
weight
psychological salience
of features that the object and prototype share
Tversky (1977) The weights of an object
s

attributes can be combined as follows
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Advantages of the probabilistic view
1. explains typicality effects
2. applies to a larger set of concepts
3. helps explain the fuzzy boundary

issue
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Criticisms of the probabilistic view

1. Does not take context into account
2. Difficulties explaining complex categories

(e.g., pet fish)
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The exemplar view
Concepts are formed based on separate

descriptions of individual exemplars which are

stored in memory
T
ypicality effects occur when a person draws

on all past examples weighted by similarity to

a new object
A
more typical exemplar (chair/furniture) has more

overlapping features with stored exemplars as

compared with a non-typical exemplar (vase)
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Contributions of the exemplar view
1. Explains context effects
2. Explains complex categories

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Criticisms of theexemplar view

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Similarity-based models A few thorny problems
Similarity-based models are
(a) hard to distinguish from each other
Similarity is often too underconstrained
(Goldstone, 1994)
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Explanation- or Theory-Based View
Instances of a concept are related by an

explanatory structure
The physician example (Murphy 1993)
This structure stems from the kind of theories

people hold
Psychological essentialism (Medin Ortony
, 1989)
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Explanation- or Theory-Based View
A
few open questions
1. What are the constraints on theories that

people hold?
2. What is the difference between theories

and background knowledge?
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Future Directions
How can we integrate similarity and
theory-based approaches?