This research will study how people learn to classify objects and how categories are represented in memory. The research will be guided by the continued development and testing of a mathematical model, the exemplar model, formalizing the view that classification decisions are based on similarity comparisons between presented objects and stored exemplars. The research will involve the study of performance relations between categorization and other choice tasks people are often asked to perform, including identification and recognition. In the categorization task, people classify items into groups; in the identification task, each item is assigned a unique response; in the recognition task, people simply judge whether items are old or new. The exemplar model and another class of model, rule- based classification models, make different predictions about the relationships among results of experiments involving the three choice tasks. Therefore, the experiments should help to distinguish between these two kinds of theories. Theoretical research accompanying the experimentation will be aimed at elucidating the nature of stimulus bias and asymmetric similarity relations. The process of categorization is among the most fundamental of mental activities. It allows people to bring order and organization to their environment, and it is a building block of more complex cognitive activities such as reasoning, thinking, and problem solving. A clear understanding of the nature of categorization processes will be instrumental in advancing our understanding of human thought.
