Participants underwent a medical history interview and vision testing, plus a series of questionnaires (eg, handedness, alcohol and drug use) to ensure they met inclusion criteria. The groups also were similar in racial and gender distributions and in body mass index (Table 2). In order to minimize confounding effects from illicit drug use, psychoactive drug use, and psychiatric comorbidity, participants were given an extensive battery of screening tests. They performed a computer-assisted, shortened version of the Diagnostic Interview Schedule Version IV64 that provides lifetime psychiatric diagnoses according to the Diagnostic and Statistical Manual Fourth Edition criteria.65 Individuals were excluded from further participation if any source (Diagnostic Interview Schedule scores, hospital records, referrals, or personal interviews) indicated that English was not their first language, or if they had any of the following: Korsakoff’s syndrome; human immunodeficiency virus; hepatitis; cirrhosis; major head injury with loss of consciousness greater than 20 minutes; stroke; epilepsy or seizures unrelated to alcoholism; Hamilton Rating Scale for Depression66 score over 14; major depressive disorder; bipolar I or II disorder; schizoaffective disorder; schizophreniform disorder; schizophrenia; generalized anxiety disorder; or electroconvulsive therapy. All participants reported that they were not currently taking psychiatric medication and had never used illicit drugs more than once a week.