The goal of this research is to develop and test theories of human similarity processing. Similarity provides the basis for much of concept learning, transfer of knowledge from one situation to another, and generalization. Conversely, similarity can also be a source of human error, for instance when confusions between similar-looking materials or devices occur. This research will develop a new approach to encompass a range of human similarity processes, from causal and functional similarities to perceptual similarities. This approach departs from prior approaches in emphasizing the psychological processes that underlie similarity. The first set of studies will investigate interconnectivity, i.e., whether interactions between features can make some aspects of objects more salient in similarity judgments or even change the psychological interpretation of their properties. The second issue is the effect of alignment in judgments of the similarity of two figures. These studies will investigate how the seeming similarity between two figures changes as a function of how easy it is to place components of object representation in correspondence. A third set of studies will investigate the effect of similarity in constructive induction. These studies are based on the hypothesis that when people judge similarity, they sometimes align non- identical features in a way which captures only their abstract commonalities. For example, two engines, one missing a fan belt and the other with a broken generator, may be judged similar because they have dysfunctional parts. These research results will inform us about the range and flexibility of similarity processing. The next set of studies will address the dynamic process of similarity computation. In these studies, people will be asked to perform rapid similarity matches or will view similarity pairs for varying periods; this will allow comparison of fast and slow similarity judgments. If fast judgments have dynamics different from slow, interfaces and devices to which humans must respond quickly will have to be designed accordingly. The final set of studies will investigate the role of similarity in other cognitive processes. Some experiments will examine the role of similarity in category-based induction. For example, when people are told a new fact about some entity, (e.g., a tiger) they typically assume that the fact applies to other similar entities, (e.g., a lion). This research will investigate whether the similarity is symmetrical or directional and what aspects of the similarity affect further inferences that can be made. Other experiments will investigate whether the process of retrieval from memory can change the subsequent representation of the items. If items stored in memory are changed by the process that retrieves them, it suggests how gradual learning can occur and how certain similarity-based distortions can come about.
