This paper presents a spreading-activation theory of human semantic processing, which can be applied to a wide range of recent experimental results. The theory is based on Quillian's theory of semantic memory search and semantic preparation, or priming. In conjunction with this, several of the miscondeptions concerning Qullian's theory are discussed. A number of additional assumptions are proposed for his theory in order to apply it to recent experiments. The present paper shows how the extended theory can account for results of several production experiments by Loftus, Juola and Atkinson's multiple-category experiment, Conrad's sentence-verification experiments, and several categorization experiments on the effect of semantic relatedness and typicality by Holyoak and Glass, Rips, Shoben, and Smith, and Rosch. The paper also provides a critique of the Smith, Shoben, and Rips model for categorization judgments. Some years ago, Quillian 1 (1962, 1967) proposed a spreading-activation theory of human semantic processing that he tried to implement in computer simulations of memory search (Quillian, 1966) and comprehension (Quillian, 1969). The theory viewed memory search as activation spreading from two or more concept nodes in a semantic network until an intersection was found. The effects of preparation (or priming) in semantic memory were also explained in terms of spreading activation from the node of the primed concept. Rather than a theory to explain data, it was a theory designed to show how to build human semantic structure and processing into a computer. This research was supported by the National Institute of Education, U.S. Department of Health, Education, and Welfare, Project 1-0420, under Contract OEC-1-71-0100(508) with Bolt Beranek and Newman Inc. Revision of the paper was supported by a grant from the John Simon Guggenheim Memorial Foundation to the first author. We would like to thank Stephen Woods, Colin MacLeod, Mark L. Miller, and the reviewers for their comments on previous drafts of this paper. Requests for reprints should be sent to Allan M. Collins at Bolt Beranek and Newman Inc., SO Moulton Street, Cambridge, Massachusetts 02138. 1 Quillian's theory of priming appeared in the unpublished version of the 1967 paper (i.e., CIP Paper No. 70, Carnegie Institute of Technology, Since the theory was proposed, there have been a number of experiments investigating retrieval and priming in semantic memory. In the present paper, we attempt to show how an elaboration of Quillian's basic theory can account for many of the results. In the first section, we briefly review the original theory while trying to correct a number of the common misunderstandings concerning it. In the second section, we extend the theory in several respects, and in the third section show how the extended theory deals with some recent experimental findings. In the fourth section we compare the theory to the model of Smith, Shoben, and Rips (1974) . The fact that Quillian's theory was developed as a program for a digital computer imposed certain constraints on the theory, which Quillian felt were psychologically unrealistic. We will recount the theory as he proposed it, and then elaborate the theory in psychological terms. The theory made a number of assumptions about structure and processing in human semantic memory. A brief discussion of these assumptions follows. People's concepts contain indefinitely large amounts of information. Quillian used the example of a machine. If one asks people to tell everything they know about machines,
Spreading activation was first introduced by Collins et al. as a theory of human semantic processing REF .
A spreading-activation theory of semantic processing.
Psychological Review
Computer Science