Spreading-Activation Theory

1. Spreading-Activation Theory • Quillian (1962, 1967) proposed a spreading-activation theory of human semantic processing • memory search as activation spreading from two or more concept nodesin a semantic network until an intersection was found • Priming in semantic memory – spreading activation from the node of the primed concept • QUILLIAN’S THEORY OF SEMANTIC MEMORY • conceptscorrespond to particular senses of words or phrases • aconcept as a node in a network, with properties of the concept represented as labeled relational links to other concept nodes

2. Spreading-Activation Theory • Links are pointers, usually go in both directions between two concepts • Links can have different criterialities, which are numbers indicating how essential each link is to the meaning of the concept • The full meaning of any concept is the whole network as entered from the concept node • The search in memory between concepts involves tracing out in parallel along the links from the node of each concept specified by the input words • at each node reached, an activation tag is left that specifies the starting node and the immediate predecessor

3. Spreading-Activation Theory • Common Misinterpretations of Quillian’ Theory • The idea of cognitive economy (Anderson & Bower, 1973; Conrad, 1972) • Strong theory of cognitive economy (Conrad, 1972) • All properties are stored only once in memory and must be retrieved through a series of inferences for all words except those that they most directly define • Requires erasing info whenever it applies at a more general level • Weal theory of cognitive economy • People surely store certain properties at more than one level in the hierarchy

4. Spreading-Activation Theory • Quillian’s theory that all links are equal • Links were assumed t have differential accessibilities (criteriality) • Rips et al. (1973) – intermediate nodes are necessary for a network model to explain the reaction time differences in categorizing different birds • Smith et al. (1974) – feature model can account for data that network models cannot (a concept consists of a set of values on a large number of semantic dimensions) • Categorization judgment (Juola and Atkinson, 1971) • a categorization judgment proceeds from the instance to the category but Quillian’s theory (1966, 1969) assumes the search proceeds from both the instance and category in parallel

5. Spreading-Activation Theory • Anderson and Bower (1973) reject a Quillian-like model of a parallel search, while acknowledging that their data are compatible with a parallel model whose search rate is slower in proportion to the number of paths that must be searched • THE EXTENDED THEORY • Local Processing Assumptions • When a concept is processed, activation spreads out along the paths of the network in a decreasing gradient. • The longer a concept is continuously processed, the longer activation is released from the node of the concept at a fixed rate • Activation decreases over time and/or intervening activity

6. Spreading-Activation Theory • With the assumption that activation is a variable quantity, the notion of intersection requires a threshold for firing • Global Assumptions about Memory Structure and Processing • The conceptual (semantic) network is organized along the lines of semantic similarity (Fig 1) • The means of concepts are stored in a lexical network (or dictionary) that is organized along lines of phonemic (and to some degree orthographic) similarity • Loftus’s data lead to the further assumption that a person can control whether he primes the lexical network, the semantic network, or both

7. Spreading-Activation Theory

8. Spreading-Activation Theory Assumptions about Semantic Matching Process In order to decide whether or not a concept matches another concept, enough evidence must be collected to exceed either a positive or a negative criterion If the memory search finds that there is a superordinate (or a negative superordinate) connection from X to Y, that fact alone can push the decision over the positive (or negative) criterion

9. Spreading-Activation Theory If the memory search finds properties on which X and Y match (i.e., common properties), this is positive evidence proportional to the criteriality of the property for Y The Wittgenstein strategy is a variant of the property comparison strategy The mutually exclusive subordinates strategy was necessary for programming a computer to answer questions Counterexamples also can be used as negative evidence

10. Spreading-Activation Theory • RECENT EXPERIMENTS • Production Experiments of Loftus • Freedom and Loftus (1971) • produce an instance of a category that began with a given letter or was characterized by a given adjective (name a fruit that begins with the letter A or a fruit that is red) • faster when the category was given first than when either the letter or the adjective was given first?

11. Spreading-Activation Theory • Loftus (1973b) used four kinds of category-instance pairs • Pairs where both the category and instance evoked the other with high frequency (e.g., tree – oak) • Pairs where the category evoked the instance with high frequency, but the instance evoked the category with low frequency (seafood – shrimp) • Pairs where the category evoked the instance with low frequency, but the instance evoked the category with high frequency (insect – butterfly) • Pairs where both the category and instance evoked the other with low frequency (cloth – orlon) • Category first  a and b equal, faster than c and d • Instance first  a and c equal, faster than b and d

12. Spreading-Activation Theory • Grober and Loftus (1974) • noun-adjective (fruit – red), noun-letter (fruit – A) • a noun-adjective trial occurs in the semantic network and requires the further step of retrieving the corresponding name in the lexical network • On the other hand, a noun-letter trials occur at the name in the lexical network. Therefore, the name does not need to be retrieved • Loftus and Cole (1974) – dictionary-network model • noun-adjective-letter or noun-letter-adjective • faster when the adjective is presented before the letter

13. Spreading-Activation Theory • Juola and Atkinson’s Study with Multiple Categories • category-search model (Landauer and Meyer, 1972) – subjects searches through instances of the categories in memory seeking a match for the stimulus word • as the number of categories or words in the memory set increases, RT for the category-matching task should increase at a greater slope than RT for the word-matching task

14. Spreading-Activation Theory • Effects of Typicality and Semantic Relatedness in Categorization Tasks • semantic similarity speeds up positive decisions and slows down negative decisions • the way evidence is aggregated • distinguishing properties slows down the positive decision – matching properties slows down a negative decision • related to those cases where a superordinate connection is found • accessibility will be highly correlated with typicality ratings • Holyoak and Glass (1975) – two different cases where semantic relatedness or typicalitydoes not produce the usual effect on RT for negative judgments – mutually exclusive subordinates and counterexample

15. Spreading-Activation Theory • Relation of the Theory to the Model of Smith, Shoben, Rips • the meaning of a concept by semantic features of two kinds: defining features (a member of concept) and characteristics features (not necessarily for concept membership) • in a categorization task, the two concepts are first compared in Stage 1 with respect to all their features, both characteristic and defining • second comparison in Stage 2 based on just the defining features • there is no feature that is absolutely necessary for any category • the model of Smith et al. has several inherent difficulties without the use of superordinate links • when people have superordinate info stored, they do not use it • people seldom know the defining properties of concepts