This research is concerned with the development and testing of psychological theories of similarity structure and similarity judgments. Similarity is a concept fundamental to virtually all aspects of cognition, theoretical and applied. For example, theories of memory rely on the observation that people often are reminded of similar events, and theories of learning predict transfer on the basis of similarity between learning and test conditions. In everyday life, the errors people make are often based on the use of inappropriate similarity matches, and a good deal of learning and transfer of training appears to be governed by what people find similar. Thus, an adequate theory of similarity is essential for theoretical advances in understanding cognition and in their application. This research stems from the fundamental insight that similarity of two things depends not only on the similarity of features or parts, but also on how those parts are put together, the relations among the parts. Previous research has demonstrated the advantages of formal mathematical models in understanding the role of attributes in similarity. The current research will apply and extend these previous formalisms to incorporate the contribution of relations to similarity, in addition to the role of attributes. Separating structure from processing principles is crucial for understanding a variety of experimental results, such as (1) that the similarity of object A to object B may be different from the similarity of B to A, (2) that the similarity of A to B may depend on what other objects are present, and (3) that adding the same property to objects A and B may change which one of the them is judged to be more similar to object C. Preliminary research indicates that these observations depend importantly on whether similarity is based on attributes, relations, or mixtures of attributes and relations. Most of the studies involve presenting people with material (e.g., geometric forms, descriptions of objects) and asking them to make similarity judgments. In other studies, reaction times and errors in various tasks will provide an indirect measure of similarity. Computer simulations of similarity and analogy will model the experimental results. The research will also begin the study of the role of structural similarity in learning and concept formation.
