Test #2: Chapter 7, 8, 9 (includes lecture & textbook)

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6 Apr 2011
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PSYB57 Test #2 Notes
Chapter 7 Concepts and Organization
Definitions
Concept-A mental representation of some object, event, or pattern that has stored
in it much of the knowledge typically thought relevant to that object, event
or pattern
-Helps us establish order in our knowledge base
-Allows us to categorize
Categorizatio
n-process by which things are placed into groups called categories
-allows us to make predictions & act accordingly
Category-a class or a group of similar things (objects or entities)
-shares 1 of 2 things: an essential core
-or some similarity in perceptual, bio, or fxnal properties
Functions of categorization
-Understand individual cases you have not seen before & make inferences about them
-Reduces complexity of environment
-Requires less learning/memorization
-Guide to appropriate action
-Distinctions b/w categories causes your rxns to instances depending on classification
5 distinct approaches to study of categorization and concepts:
Similarity-based Explanation-based
Classical, prototype, exemplarSchemata, knowledge-based
The classical view of categorization
-Dominant view in psych up until 70s, dates back to Aristotle
-Category membership determined by a set of defining (necessary and sufficient) properties
-Assumes concepts are not representations of specific examples but a list of characteristics
-All concepts share these fundamental characteristics, or features
-Membership in a category is clear-cut: either in or outall or none
-Aka features represented are individually necessary & collectively sufficient
-Necessary = each example must have the feature
-Sufficient = anything w/ each feature in the set is auto an instance of the concept
-Implies that all members within a category are created equal
Problems with classical view:
No defining features
for many natural-kind
categories
-e.g., Wittgensteins game
-For if you look at them you will not see anything in common at all, but
similarities, relationships, and a whole series of them at that
(Wittgenstein, 1953)
Typicality-Category is graded membership, boundaries are fuzzy
-Eleanor Rosch and colleagues: weakened attraction of the classical view
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-People judge members of a category as differing in goodness
-Robin & sparrow = good instances of a bird, chickens not as good example
-e.g., as of August 24th 2006, Pluto has now been demoted to a dwarf
planet rather than a real planet
The prototype view of categorization
-Prototype = an idealized representation of a class of objects
-Include features that are characteristic (i.e., typical) rather than necessary or sufficient
-Formed by averaging the category members we have encountered in the past
-The more characteristic features/ aspects an instant has, the more likely it is to be regarded as a
member of the category (more typical it is)
-Members within a category differ in terms of prototypicality: high vs. low
Determinants of typicality
-Family resemblance (Rosch & Mervis,1975)
-Family resemblance structure of concepts = structure in which each member has a # of features,
sharing diff features w/ diff members
-Prototypes serve as reference point
-Typical examples are classified faster than non-typical
-Typical examples share many features with other category members and few with other
categories
-*Overlapping features predicts typicality*
3 levels of categorization:
Superordinat
e-contains members that are dissimilar in several respects, broader than
basic level
-eg: musical instrument
Basic -psychologically fundamental level
-the best compromise b/w grouping similar things and differing in imp ways
-eg: piano & guitar
Subordinate-less distinct than the others
-eg: grand piano, electric guitar
Problems with the prototype view:
-fails to capture ppls knowledge about limits of conceptual boundaries
-cant tell us why certain things are certain things
-eg: why is a Pomeranian a dog? Why is a great dane a dog? It doesnt specify clear constraints
-typicality of an instance depends to some extent on context
Other views
Exemplar
-Concepts are composed of previous, individual instances (i.e., exemplars)
-Categorization occurs by comparing current instance w/ previous instances stored in memory
-Similar to prototype: necessary & defining features are not stated
-Physical similarity to previous exemplars stored in memory (i.e. Negative Matches) influenced the
categorization despite participants having a simple & sufficient categorization rule to follow
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ProsCons
-Discards less information than prototypes
-Explains why definitions dont work
-There are no definitions, just instances
-Typicality: objects that are like more of the
exemplars stored in memory are classified
faster
-Does not specify which exemplars
will be used for categorization
-Too unconstrained
-Requires that we store lots of
exemplars
Schemata
-Organized framework for representing knowledge
-Can embed themselves in one another hierarchically (eg: subschemata/ superschemata)
-Shares features with prototype (abstracted across instances) and exemplar (actual instances)
-Pros: involve both abstractions across instances (prototype view) and information about actual
instances (exemplar view)
-Cons: Does not specify boundaries among individual schemata; difficult to test empirically
Knowledge-based
-Ppl use knowledge of how to concept is organized to justify the classification, to explain why certain
instances go tgt in the same category
-Helps explain how an apparently disparate collection of objects can form a coherent category
-Barsalou (1983): What is the category?
oChildren, Pets, Photo albums, Family heirlooms, Cash (eg: things to save in a fire)
oCategory becomes coherent only when you know the purpose of the category
-Murphy & Medin (1985): Concepts as theories, instances as data
oCategorization involves
oKnowledge of how concepts are organized
oThe purpose of the category
oPeoples theories about the world
Learning new concepts
-must have some basis for generalization
-requires that we figure out attributes/ features
Explicit
Bruner et al., 1956:
Stimul
i-3 shapes (circle, square, cross)
-3 colours (black, white and striped)
-3 borders (one, two, three)
Metho
d-Participants were given an instance of a concept (black circles) without the
concept itself
-Then had to pick further cards which they thought might be instances of the
concept
-They got feedback
-Their strategies were observed
Strategies:
-most successful = conservative, then simultaneous
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