 - Participants in three patient groups will have a current diagnosis of schizophrenia or schizoaffective disorder, drug dependence, or both. Healthy comparison participants will be free of either diagnosis. Psychiatric diagnoses will be based on DSM-IV criteria as determined by the Structured Clinical Interview for DSM-IV SCID; First et al 1997, which will be administered in either a computerized version or in the standard interview format. Participants in all four groups will be 18-64 years old, of either gender and of any raceethnicity. Specific inclusion and exclusion criteria for the participant groups are as follows: 