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Archive for July, 2009

A ‘Trippy’ Network Model

by on Jul.31, 2009, under Cognitive Science

Associative network models of semantic memory such as those proposed by Collins and Loftus (1975) have successfully explained complex psychological phenomenon such as priming effects. In a nutshell, a given stimulus such as a word activates a node representing the word in long term memory. The activation spreads outward from the starting node to neighboring nodes that are related in meaning or context; ‘semantically related.’ If the neighboring nodes become activated enough, the elements represented by those nodes are at the level of awareness within the individual. For example, in the David Lynch film ‘Wild At Heart’ a character states “My dog barks. [pause]. In your mind you picture a dog even though I have not told you what my dog looks like.” The experience of visualizing a particular dog given only a ‘dog prime’ could be explained, in part, by spreading activation in a semantic network model. Of course, in normal circumstances the activation only spreads so far and then decays.

In researching this topic I ran across a rather original if not entertaining paper that found psilocybin, the psychoactive chemical in hallucinogenic mushrooms, changes the behavior of spreading activation as measured by a lexical decision task (Spitzer et. al. 1996). In sum, it appears to ‘de-focus’ the spread so that words with less direct relationships begin to benefit from priming. For example, color-red is a direct pair whereas lemon-sweet is indirect. The psilocybin group showed a greater relative increase in reaction time for indirect relationships versus no relationship with respect to the placebo group. The study speculates that subjective effects of ‘mind expansion’ may be due to increased availability of remote semantic nodes, as if spreading activation is potentiated.

Collins, A.M. & Loftus, E.F. (1975). A spreading activation theory of semantic processing. Psychological Review, 82, 407-428.

Spitzer M., Thimm M., Hermle L., Holzmann P., Kovar K., Heirnann H., Gouzoulis-Mayfrank E., Kischka U., Schneider F. (1996). Increased Activation of Indirect Semantic Associations under Psilocybin. Society of Biological Psychiatry, 39, 1055-1057.

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