Semantic Memory Part 1

Semantic Memory ______________________________________ 1) Provide a working definition of semantic memory. 2) Discuss four main approaches to understanding the structure of semantic memory:  spreading activation  feature models  prototype theory  PDP / connectionist approach 3) Highlight the strengths and weaknesses of each. 4) Discuss Bahrick's work on memory for semantic information across the lifespan. Semantic Memory ________________________________________ Semantic memory - our knowledge about the world Is the earth flat? How many pencils are in a gross? What color is the sky (in your world)? A sentence consists of a subject and a …? What is bigger, a horse or a goat? Who was the last horse to win the Triple Crown? What is a horse? What film won the Academy Award for best picture last year? Who was the first psychologist to systematically study memory by training himself to learn lists of nonsense syllables? How do you get to Judie’s? Experimental Distinctions ________________________________________ Episodic Memory a) teach you b) test you Semantic Memory just test memory What do we measure? Why? a) accuracy b) RT usually just RT Key Questions Capacity, forgetting, efficacy Experimental Procedures Otherwise, results would be uninterpretable Storage Organization Neuropsychological Dissociations - relatively rare  Semantic dementia  Amnesia? Collins & Quillian Model ___________________________________________ History: Developed from an attempt to write a program that would allow a computer to understand language. Nodes - locations that store items of data Pathways - connections between various nodes Activation - the process of accessing information from semantic memory and bringing it into consciousness (above threshold). Key concepts:  Threshold  ‘Wastebasket’ term  Spread of activation A sample Semantic Network (space) ___________________________________________ How does activation work? ___________________________________________ 1) Activation spreads from one node to another. 2) Activation takes time. 3) Activation is limited; it decays… a) over time. b) over distance. c) proportional to the # of connected paths. 4) Activation spreads automatically. 5) All pathways are not created equal; some are stronger than others. 6) Pathways are not necessarily symmetrical If I say doughnut… …sweet should also become activated. …sweet should become active before smelly. …and wait, sweet will no longer be activated. …sweet is more likely to become activated than smelly. …sweet will become activated in proportion to all other things associated with doughnut. …sweet may become activated even if you are unaware of it. If I say wife, sweet will be activated more quickly and more strongly than tennis. Wife may activate tennis more than vice versa. Hierarchical Structure of Semantic Memory ______________________________________________ Evidence in favor of Hierarchical Structure ___________________________________________ Learning via Spreading Activation ___________________________________________ 1) Activation spreads from locations for two concepts. 2) Eventually, activation meets. 3) If two concepts are frequently activated together, a new pathway is formed. 4) With practice, pathways become strengthened, thereby easing responses. ___________________________________________ Problems: 1) Semantic memory is not strictly hierarchical Response: memory is logically imperfect. EX: Is a pumpkin a fruit? 2) Does not predict typicality effects: EX: A robin is a bird. Vs. An ostrich is a bird. 3) New nodes 4) Circularity More evidence against Spreading Activation: Ratcliff & McKoon (1981) ______________________________________________ Subjects read paragraphs like this: The scientist nudged the sheriff. The sheriff stared at the spacecraft. The spacecraft transported the alien. The alien drew a weapon. The weapon vaporized the mountain. Priming: Near pairs: Far pairs: spacecraft==>sheriff spacecraft==>mountain Predictions:  More priming for near pairs.  Priming should develop more slowly for far pairs.  Priming should peak later for far pairs. Ratcliff & McKoon (1981): Results ______________________________________________ SOA 50 100 200 300 Near -3 26 52 80 Far 8 29 30 41 Feature Models ________________________________________ Concepts consist of a list of features. Automobile: DEFINING features must be present. CHARACTERISTIC features are usually present. Two Search Procedures: Easy Decisions - If the feature overlap is nearly complete, or nearly absent, decisions are made quickly. Difficult Decisions – defining features are examined one by one until a failure is observed (no) or the list is exhausted. Dimensional Feature Theory _________________________________________ Category membership/organization based on where the item falls along the defining dimensions for that particular category. Similarity scaling for a set of mammals 3 dimensions:  Size  Ferocity  Humanness Elephant Crocodile Mouse Ape Size High Moderate Low High Ferocity Low High Pretty High Moderate Similarity scaling experiments Humanness Pretty Low Very Low Low High