Collin and Quillian (1969) were among the first to develop a systematic model of semantic memory suggesting that it is organized in a hierarchical network. The major concepts are represented as nodes (e.g., fish) and each node is associated with features related to the concept (e.g., has fins). According to this model, sentences that should be similar in hierarchical distance (e.g., a crow is a bird & a penguin is a bird) should be similarly semantically related. However, it takes us longer to realize that a penguin is a bird compared to a crow suggesting that this is not the case.
Collin and Loftus (1975) put forth the spreading activation theory which helps to rectify the above problem - it considers typicality effects (discussed in earlier post). Their theory suggests that instead of hierarchies, semantic memory is organized by semantic distance (or relatedness). According to this theory, when a person encounters some sort of sensory input about a concept, the appropriate node is activated in semantic memory. The activation then spreads to nearby nodes that are most strongly associated or related semantically. In this way, activation would spread quicker from “bird” to “crow” than from “bird” to “penguin”.
Collins, A. M., & Quillian, M. R. (1969). Retrieval time from semantic memory. Journal of verbal learning and verbal behavior, 8(2), 240-247.
Collins, A. M., & Loftus, E. F. (1975). A spreading-activation theory of semantic processing. Psychological review, 82(6), 407.