Semantic Memory: Collins & Quillian

1. Semantic Memory: Collins & Quillian Kandise G. Viar Senior Seminar February 26, 2008

2. Semantic Memory • Semantic Memory is knowledge of facts and general knowledge of the sort learned in school. • Component of long-term memory.

3. Semantic Networks • A semantic network is a network model in which each node has a specific meaning. • Semantic networks therefore employ the local representation of concepts. • Adopted by cognitive psychologists as a way to explain the organizational and retrieval of information in long-term memory.

4. Characteristics of Semantic Networks • A node’s activity can spread outward along links to activate other nodes. These nodes activate others and so on… • This is called spreading activation. • Spreading activation may lose strength as it travels outward from its point of origin. • Energy decreases with increasing distance because in theory, energy encounters resistance as it passes through succeeding links and nodes. • Distance between two nodes is determined by their relatedness. • Ex: Concepts such as “shoe” and “high-heels” are semantically related and therefore close in proximity to each other. Whereas, “shoe” and “flower” are not closely related and therefore further away from each other in the semantic network.

5. Characteristics Continued… • Priming • The process of a stimulus is facilitated by the network’s prior exposure to a related stimulus. • Ex: If we are asked to think about the word “doctor” then we automatically think about things that associated with the word “doctor” like “hospital” or “drugs” or “nurse”.

6. A Hierarchical Semantic Network: Collins & Quillian (1969) • Suggested that semantic networks have a hierarchical organization, with different levels representing concepts ranging from the most abstract (broad) to down to the most concrete (specific).

7. Collins and Quillian’s Method • Used a sentence verification task. • Participants were asked to respond to individual sentences that appeared on a computer screen. • For example, “A canary is a bird” and “A canary is an animal.” • If the participant judged that the sentence was true then he or she was instructed to hit one button. • If he or she judged the sentence false then another button was to be pressed. • Participant response times were recorded.

8. Collins & Quillian’s Theory • Theorized that a correct response to one of these sentences required the overlap of spreading activation. • If the nodes have a close semantic relation, they should be in close proximity within the network. • To know whether a canary is a bird would require the activation of both a “canary” node and a “bird” node. Recognition of both concepts would activate these nodes. Activation would then radiate outward through the network from each node until each individual unit’s activation would mutually affect one another. When the activation of these two nodes overlaps then the participant can confirm that these two things are related. They can confirm the sentence. • Responses will be fast because spreading activation will have less distance to cover. • If the nodes are less related, the distance between them will be greater and response times will be longer.

9. Results • Based on the reaction times obtained from the study Collins and Quillian (1969) came up with a hypothetical memory structure for the knowledge of animals.

10. Hierarchical Model

11. Hierarchical Model Explained: Superordinate, Ordinate, and Subordinate. • The idea of an animal is abstract (broad) and therefore encompasses all kinds of animals. “Animal” is a superordinate category. • At the next level there are classes of animals: birds, cats, dogs, fish. These are placed in the ordinate category. • The subordinate category is the most concrete (specific) and corresponds to the exact species of an animal. Properties of the species are also at this level. • Ex: A node corresponding to “canary” would also have links to the superordinate level connecting it to “is yellow” and “can sing.”

12. Evaluation of the Hierarchical Model • The model is intuitively pleasing but it fails in practice because some concepts are more common than others. • Ex: A robin is a more common bird in comparison to a flamingo. People reacted faster to a sentence like, “A robin is a bird” vs. “A flamingo is a bird. • We have prototypes or idealized versions about what a “bird” is.

13. Evaluation Continued… • Participants are faster to make a correct response to, “A dog is an animal” than to “A dog is a mammal.” • This happens even though “animal” is farther away from “dog” in this hierarchical scheme.

14. Evaluation Continued… • Collins & Quillian attempted to preserve the principle of cognitive economy. This principle states that nodes should not have to be coded for more times than necessary. They only placed property nodes at their appropriate levels in the hierarchy. • Ex: “Can fly” is positioned as a property of birds only, even though it could be linked to the canary node and to the node representing every other kind of bird as well. • The relation is implied. • Research has found no difference in response time for the sentences, “A bird can fly” and “A canary can fly.”

15. References Friedenburg, J. & Silverman G. (2006) Cognitive science: An introduction to the study of the mind. Thousand Oaks, California: Sage Publications. (P. 131, 224-230) http://psych.rice.edu/mmtbn/language/wordComp/memory.gif (image)