Memory Storage

1. Memory Storage How do we store information for the long-term in memory?

2. Two issues • Knowledge format - How, precisely, is the information being stored? • Knowledge organization - How is the information arranged in memory?

3. Knowledge format • What format is information stored in? • The issues are similar to the mental imagery debate. • Propositional Hypothesis

4. Dual-Code theory • Paivio (1971) combines elements of propositional hypothesis and Baddeley’s working memory • Verbal codes - abstract, amodal codes; possibly propositions • Imagistic codes - analog codes based on sensory modalities

5. Knowledge Organization • How is knowledge organized in memory? • The debate parallels the imagery debate - is it organized categorically, or based on sensory modality.

6. Conceptual organization • Intuitively, we believe we organize information by concepts. • Concepts are discrete ideas, like “apple” or “red”. • We then organized related concepts into collections called categories.

7. Conceptual storage • How do we store and identify concepts? • Feature theory - Categories are represented as lists of features, such as the concept STOP SIGN being represented as “red; octogon; at street corner” etc.

8. Prototype theory • A concept is represented as the “average” of all its members. • We recognize an object as being one of a given concept by comparing it to all of our stored prototypes and picking the one that’s closest • Experiments show that, when presented with arbitrary categories, people rate the prototype as more typical than individual examples. • How do we recognize very bizarre members of a category? (e.g., goofy Scandanavian chair; platypus)

9. Exemplar theory • A concept is represented by the stored exemplars of all past instances of the concept that we’ve encountered. • Easily accounts for how bizarre examples get recognized. • Computationally realistic?

10. Two syntheses • Prototype with exceptions - normal categorization works according to prototype theory, but we also store exceptions that deviate too much from the prototype. • Core-prototype - We represent the core of a concept as its required features, and maintain multiple prototypes of examples that contain typical combinations of other features. Think of them as necessary and sufficient features.

11. Conceptual organization • Hierarchy - the most popular notion is that of a conceptual hierarchy, where subordinate concepts inherit properties from their superordinate categories. • Network - Concepts are arranged in a loosely organized network, where connections between concepts are based on the relatedness of those concepts.

12. Hierarchical models • Semantic Network (Collins & Quillian, 1969)

13. Network models • Spreading Activation - Information is not organized strictly in a hierarchy. It’s more of a hodgepodge.

14. Unitary Content Hypothesis • Information in semantic memory is stored in an abstract, amodal representation with a structure based on concepts. • The theory claims that this is not just true in the mind, but in the brain as well.