Semantic Memory Memory for meaning Permanent memory store of general world knowledge Mental thesaurus, dictionary, or encyclopedia Language, concepts, decisions, etc. Whereas episodic memory differs widely from individual to individual, semantic memory is similar across individuals

Two Models of Semantic Memory Collins and Quillian Network Model Smith Feature Comparison Model Each makes two assumptions of semantic memory: 1) Structure 2) Process of retrieval

Collins and Quillian Network Model Two fundamental assumptions of semantic memory: Structure: Nodes in a network Process of retrieval: Spreading activation

Collins and Quillian Network Model Structure: Nodes in a network Each concept in semantic memory is represented by a node, a point or location in semantic space

Collins and Quillian Network Model Structure: Nodes in a network Each concept in semantic memory is represented by a node, a point or location in semantic space.

Collins and Quillian Network Model Structure: Nodes in a network Nodes are linked together by pathways, directional associations between concepts. Every concept is related to every other concept.

Collins and Quillian Network Model Structure: Nodes in a network Each pathway has a label defining the relationship between the concepts: Isa statements and property statements form propositions

Collins and Quillian Network Model Process of Retrieval: Spreading Activation An individual concept becomes activated

Collins and Quillian Network Model Process of Retrieval: Spreading Activation This activation spreads to adjacent nodes, activating them as well

Collins and Quillian Network Model Process of Retrieval: Spreading Activation Activation continues to spread through the network, but the level of activation decreases with each “step”

Collins and Quillian Network Model Process of Retrieval: Spreading Activation Consider the activation caused by “Can a robin can breathe?”

Collins and Quillian Network Model Process of Retrieval: Spreading Activation The nodes ROBIN and BREATHE spread activation through the network.

Collins and Quillian Network Model Process of Retrieval: Spreading Activation The intersection of two spreads of activation is found indicating critical concepts; a decision stage operates to determine validity of intersection

Smith’s Feature Comparison Model Two fundamental assumptions of semantic memory: Structure: Feature lists Process of retrieval: Feature comparison

Smith’s Feature Comparison Model Structure: Feature Lists Semantic memory is a collection of Feature Lists Each concept represented as a list of semantic features: simple, one-element characteristics of the concept Features are ordered in a list in terms of definingness: The most defining features for a concept are at the top of the list

Smith’s Feature Comparison Model Structure: Feature Lists Defining features: Features absolutely essential to the concept (e.g. Birds are living objects) Characteristic features: Features common to, but not essential to, a concept’s meaning (e.g. Birds fly)

Smith’s Feature Comparison Model Process of Retrieval: Feature Comparison General example: True or false: “An A is a B”? Stage 1: Global Feature Comparison Access required concepts and randomly select features about each concept Features compared and similarity score determined High: “Yes”, Low: “No”, or Intermediate: Go to Stage 2

Smith’s Feature Comparison Model Process of Retrieval: Feature Comparison General example: True or false: “An A is a B”? Stage 2: Comparison of Defining Features Access defining features of each concept Determine if defining features match Features match: “Yes” Features mismatch: “No”

Smith’s Feature Comparison Model Process of Retrieval: Feature Comparison

Clashing Evidence for the Models General Task: Sentence Verification Key issues: Cognitive Economy Property Statements Typicality Effects

Clashing Evidence for the Models Cognitive Economy (Bad for: C & Q; Good for: S) Wings Wings Bird Bird Feathers Feathers Robin Robin Red Breast Wings Blue Eggs Feathers

Clashing Evidence for the Models Property Statements (Bad for: S; Good for: C & Q) E.g.: A canary is a small bird with yellow wings According to Smith: Look up feature lists for five concepts CANARY, BIRD, SMALL, YELLOW, and WINGS This requires a list of “Things that are small”; “Things that are yellow”; “Things with wings” Collins & Quillian incorporate property statements into their network so it doesn’t face this problem

Clashing Evidence for the Models Typicality Effects (Bad for: C & Q; Good for: S) Not all members of a category are equal Typical members of a category can be judged faster This is captured with Smith’s similarity score but not explained by Collins & Quillian: Robin Sparrow Bird Chicken Penguin

A Hybrid Model No strict cognitive economy Property statements available Typical members of a category stored more closely Properties more important to concept stored more closely

A Final Wrinkle Recent ERP research is now suggesting that RT effects (e.g. typicality effects) in semantic memory may be associated with decision processes rather than retrieval processes What’s the problem? Such effects have lead to model revisions that add semantic distance between nodes (e.g. the hybrid model just described.) Such revisions may not be appropriate. Current models of semantic memory have yet to adequately address this finding

Categorization Concept Formation Traditional Research: Show subjects a series of arbitrary patterns and have them judge whether each is an example of the concept being tested. Limitations are that they are not related to the real world

Categorization Natural Categories Concepts and categories that occur in the real world Members do not belong to their categories in simple yes/no fashion Categories have fuzzy boundaries with ill-defined membership for many category instances No single feature is absolutely necessary as a criterion of category membership Membership in a category is a matter of degree

Back to Spreading Activation Four important principles associated with this idea: 1) Activation spreads 2) Spreading takes time 3) Activation becomes diffuse as it spreads 4) Activation decays over time If semantic relatedness is the organizing principle of semantic memory, then relatedness should play a big role in these principles The test: Priming

Priming in Semantic Memory In essence: How does the processing of a prime affect the processing of a target? Does thinking about one concept “bring to mind” other concepts? If so, they are “connected” in semantic memory

Priming in Semantic Memory How can we use this to test the association between semantic relatedness and spreading activation? - Distance of spread - Speed of spread

Priming in Semantic Memory Distance of Spread: Vary “steps” between prime and target STIMULUS 1: ROBIN Activation added to Robin

Priming in Semantic Memory Distance of Spread: Vary “steps” between prime and target STIMULUS 1: ROBIN Activation spreads through network

Priming in Semantic Memory Distance of Spread: Vary “steps” between prime and target STIMULUS 2: BIRD Does activation get this far?

Priming in Semantic Memory Distance of Spread: Vary “steps” between prime and target STIMULUS 2: FEATHERS Does activation get this far?

Priming in Semantic Memory Distance of Spread: Vary “steps” between prime and target STIMULUS 2: BREATHES Does activation get this far?

Priming in Semantic Memory Speed of Spread: Vary time between prime and target How long does it take activation to go from Robin to Bird?

Priming in Semantic Memory There are two major ways to set up these experiments:

Empirical Demonstrations of Priming Freedman and Loftus (1971) Name a member of a category defined by a prime and a target Conclusion: Category faster than letter or color Prime Target Result P Fruit No Priming Red Fruit No Priming Fruit P Priming Fruit Red Priming

Empirical Demonstrations of Priming Loftus and Loftus (1974) Same methodology as Freedman & Loftus Difference: Trials have various SOAs (within trials) and sometimes repeated the category of a previous trial (across trials) TRIAL 1 TRIAL 2 TRIAL 3 TRIAL 4 Lag 0: Fruit-P Fruit-B Animal-D Building-L Lag 2: Fruit-P Animal-D Building-L Fruit-B

Empirical Demonstrations of Priming Loftus and Loftus (1974)

Empirical Demonstrations of Priming Loftus and Loftus (1974) Within trials: Category more facilitation than letter or color Across trials: Facilitation less at longer lags SOAs: Facilitation better at longer SOAs

Empirical Demonstrations of Priming Rosch (1975) Are two things members of the same category? Prime: Category name (related) or “Blank” (neutral) Targets: Typical or atypical category members Trout Sparrow BLANK No priming Robin Sparrow BIRD Lots of priming Penguin Ostrich BIRD Less priming

Empirical Demonstrations of Priming Meyer and Schvaneveldt (1971) Lexical Decision Task

Empirical Demonstrations of Priming Neely (1977) Insert figure 7-13

Empirical Demonstrations of Priming Neely (1977) At small SOAs, there is facilitation between related words even tough it is unexpected. At larger SOAs, this facilitation disappears.

Empirical Demonstrations of Priming Marcel (1980) Immediately after prime, present a mask Prevents conscious awareness of seeing prime Even without conscious awareness, prime affects target Child Infant

Summary of Priming Related primes speed processing: Activation spreads from one concept to another Reduced relatedness or typicality of concepts decreases priming: Activation spreads to most related concepts Longer SOAs increase priming: Spreading activation takes time

Summary of Priming Longer lags decrease priming: Activation decays Priming at very short SOAs and despite conscious expectations: Priming is automatic Priming occurs without awareness: Priming is implicit

Context and Priming Work in context is interested in large-scale semantic representations that involve episodic and semantic knowledge - Comprehension of sentences and paragraphs - Comprehension of spoken conversations

Contextual Ambiguity and Priming What does the word bank mean? 1. We had trouble finding the bank. 2. We were swimming at the bank. 3. We were making a deposit at the bank. Sentence 2 primes RIVER; Sentence 3 primes MONEY Context primes a particular concept of bank