Perceptual and Cognitive Processes in Identification and Categorization

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9514427 ASHBY This research will investigate the perceptual and cognitive processes used in the identification and categorization of complex perceptual stimuli. The research program will develop and test a new theory that assumes category learning is a competition between two separate categorization systems. One system uses rules that can be described verbally and has access to consciousness (i.e., the verbal system), whereas the other can learn rules that are impossible to describe verbally (i.e., the implicit system). The theory will be described at three different levels. A neuropsychological version will provide a detailed description of the major brain areas and neural pathways used by the separate systems and that mediate the competition between the systems. In addition, two separate mathematical descriptions of the theory will be developed. One will provide a global level description of the dynamical behavior that the theory predicts should occur when people learn new categories. The other will provide a more detailed description that can be used to predict trial-by-trial category learning behavior. Many experiments will be conducted to test novel predictions of the theory. In addition to making predictions about category learning in normal human adults, the theory also makes specific predictions for children, the elderly, patients suffering from major depression and from diseases of the basal ganglia (e.g., Parkinson's and Huntington's disease), and for nonhuman animals. This research will improve our understanding of one of the most basic and important of cognitive processes, namely categorization. It also has the potential to increase our understanding of the cognitive effects of several major diseases and disorders, and of how cognition is affected by normal aging processes. This project will combine extensive experimentation with theoretical investigations that rely heavily on mathematical modeling techniques and recent discoveries in th e neurosciences. ***