Cognitive Processes PSY 334

1. Cognitive ProcessesPSY 334 Chapter 5 – Meaning-Based Knowledge Representation

2. Conceptual Knowledge • Concept -- an abstraction formed from multiple experiences. • Propositions – eliminate perceptual details but keep relationships among elements. • Categories – eliminate perceptual details but keep general properties of a class of experiences. • Used to make predictions. • Two kinds: semantic networks, schemas

3. Semantic Networks • Quillian – information about categories stored in a network hierarchy. • Nodes are categories. • Isa links related categories to each other. • Nodes have properties associated with them. • Properties of higher level nodes are also true of lower level nodes linked to them. • Categories are used to make inferences.

4. Psychological Reality of Networks • Collins & Quillian – asked subjects to judge the truth value of sentences: • Canaries can sing – 1310 ms • Canaries have feathers – 1380 ms • Canaries have skin – 1470 ms • Frequently used facts also verified faster, so stored with node: • Apples are eaten • Apples have dark seeds

5. Schemas • Schema – stores specific knowledge about a category, not just properties: • Uses a slot structure mixing propositional and perceptual information. • Slots specify default values for what is generally or typically true. • Isa statement makes a schema part of a generalization hierarchy. • Part hierarchy.

6. Psychological Reality of Schemas • Brewer & Treyens – subjects left in a room for 35 sec, then asked to list what they saw there: • Good recall for items in schema • False recall for items typically in schema but missing from this room. • 29/30 recalled chair, desk; 8 recalled skull • 9 recalled books when there were none

7. Degrees of Category Membership • Members of categories can vary depending on whether their features satisfy schema constraints: • Gradation from least typical to most typical. • Rosch – rated typicality of birds from 1-7: • Robin = 1.1 • Chicken = 3.8. • Faster judgments of pictures of typical items, higher sentence-frame ratings.

8. Disagreements at Category Boundaries • McCloskey & Glucksberg – subjects disagree about whether atypical items belong in a category: • 30/30 apple is a fruit, chicken is not a fruit • 16/30 pumpkin is a fruit • Subjects change their minds when tested later. • Labov – boundaries for cups and bowls change with context.

9. Event Concepts (Scripts) • Schank & Abelson – stereotypic sequences of actions called scripts. • Bower, Black & Turner – script for going to a restaurant. • Scripts affect memory for stories: • Story elements included in script well remembered, atypical elements not recalled, false recognition of script items. • Items out of order put back in typical order.

10. Two Theories • What happens mentally when we categorize? • Two theories are being debated. • Abstraction theory -- we abstract and store the general properties of instances. • Prototype theory. • Instance theory -- we store the multiple instances themselves and then compare average distances among them.

11. Neural Nets for Learning Schemas • Gluck & Bower – designed a neural net that abstracts central tendencies without storing instances. • Patients with four symptoms classified into two hypothetical diseases. • One disease 3 times more frequent than the other. • Error correction changes the strength of associations in the network (delta rule). • Model predicted subject decisions well.

12. Evidence From Neuroscience • People with temporal lobe deficits selectively impaired in recognizing natural categories but not artifacts (tools) • People with frontoparietal lesions unaffected for biological categories but cannot recognize artifacts (tools). • Artifacts may be organized by what we do with them whereas biological categories are identified by shape.