Background: * Several studies of risk perception have demonstrated a common bias known as unrealistic optimism, in which individuals feel they are less likely than other people to experience unpleasant or harmful events in their lives, but more likely to experience pleasant or beneficial events. * Previous research has indicated that individuals with schizophrenia have less of a sense of unrealistic optimism about adverse events than individuals without schizophrenia. However, research on risk perception in schizophrenia is sparse, primarily reporting on behaviors and decisions in the laboratory that likely are influenced by risk perception. * Risk perception among substance users may be viewed in two separate categories: perception of vulnerability to adverse events and perception of vulnerability to negative outcomes associated with substance use. Research in both areas has yielded mixed results. Researchers are interested in studying the connections among schizophrenia, addiction, and risk perception in order to develop better drug use prevention and treatment programs for people with and without schizophrenia. Objectives: \- To compare unrealistic optimism bias in people with and without schizophrenia and/or drug dependence, and its association with actual risky behavior. Eligibility: * Individuals between 18 and 64 years of age who fall into one of the following study categories: * diagnoses of both drug dependence (marijuana or cocaine) and schizophrenia/schizoaffective disorder * diagnosis of drug dependence only (marijuana or cocaine) * diagnosis of schizophrenia/schizoaffective disorder only * healthy volunteers with no history of drug use or serious mental disorder Design: * The study will require a single visit to the research center for a 5- to 6-hour session. * Participants will complete questionnaires on medical and behavioral history, complete tests of thinking skills like memory and attention, complete a brief computerized decision-making task, and answer questions about risk perception. * Participants will also provide urine samples and breath carbon monoxide measurements to test for recent use of tobacco and other substances.
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