Cognitive
Psychology
Semantic Networks
Lesson VI: Organization of Memory
module 29
University of Idaho
Cognitive
Psychology
© Steffen Werner - 2004
Organization.29. 1
Representation of concepts in
semantic network models
Abstract models of knowledge representation
– Motivated by computer science, artificial intelligence,
and psycholinguistics
– Concepts are represented as nodes in a network
– Relations are represented by links between nodes
– This node “represents” the proposition that birds have
feathers (bird, feathers, and “have” are concepts)
University of Idaho
Cognitive
Psychology
© Steffen Werner - 2004
Organization.29. 2
Hierarchical semantic networks
Hierarchical network models
– Relations are specified at highest possible levels
– Relations are “inherited” at lower levels
– Exceptions are specifically marked
Advantage: Cognitive economy
– Things only need to be specified once and not repeated
– Efficient type of representation
Predictions of hierarchical models
– The time to verify the relation between different
concepts is a direct function of the number of links
between the two concepts
– Hierarchy determines the number of links
University of Idaho
© Steffen Werner - 2004
Organization.29. 3
1
Cognitive
Psychology
Hierarchical model
Collins & Quillian (1969)
Strict hierarchy of concepts
– Inheritance leads to cognitive economy
– Rigid organization of knowledge
University of Idaho
Cognitive
Psychology
© Steffen Werner - 2004
Organization.29. 4
Sentence verification times
Collins & Quillian (1969)
– Verification times depend on the distance (number of
nodes) between concept and property / superset
University of Idaho
Cognitive
Psychology
© Steffen Werner - 2004
Organization.29. 5
Semantic network models
Fate of strictly hierarchical models
– Even though they have great “economy”, they often
make wrong predictions
– It takes longer to verify “a lion is a mammal” than to
verify “a lion is an animal”
– Frequency of use needs to be represented
Non-hierarchical models, tangled hierarchies
– Relations can be defined at any level
– Increased flexibility where a particular piece of
knowledge is represented
Links between nodes can be weighted
– Concepts that are strongly associated might have
stronger connections
University of Idaho
© Steffen Werner - 2004
Organization.29. 6
2
Cognitive
Psychology
Spreading activation theory
Spreading activation - processing assumptions
– Many semantic network models assume a spread of
activation as means of information processing
– Activation nicely explains priming effects
University of Idaho
© Steffen Werner - 2004
Organization.29. 7
3