The purpose of this study is to better understand the neural correlates of higher-order cognition, both in the healthy brain and in schizophrenia, and to determine how these mechanisms are modulated by transcranial direct current stimulation (tDCS) at frontal and occipital scalp sites. Testing the effects of tDCS at these scalp sites on cognitive task performance will help us understand the roles of the brain regions corresponding to these sites during higher-order cognitive processing (language comprehension, cognitive control, and related attention and memory processes). Behavioral and electrophysiological (EEG) measures will be used to assess cognitive performance. The investigator's overarching hypothesis is that stimulating prefrontal circuits with tDCS can improve cognitive control performance, and ultimately performance on a range of cognitive tasks, as compared to stimulating a different cortical region (occipital cortex) or using sham stimulation. This study is solely intended as basic research in order to understand brain function in healthy individuals and individuals with schizophrenia. This study is not intended to diagnose, cure or treat schizophrenia or any other disease.

Inclusion Criteria:

• Participants must be able to sufficiently speak and understand English so as to be able to understand and complete cognitive tasks.
• All subjects must have the ability to give valid informed consent.

Inclusion Criteria for Patients with Schizophrenia Only:

• Diagnosis of schizophrenia, schizophreniform or schizoaffective disorder
• No medication changes in the prior month
• No medication changes anticipated in the upcoming month
• Stable outpatient or partial hospital status
• Normal IQ (>70; IQ will be measured by administering the Wechsler Abbreviated Scale of Intelligence (WASI) test)

Exclusion Criteria:

• Pacemakers
• Implanted electrical (brain and spinal) stimulators
• Implanted defibrillator
• Metallic implants
• Skin damage or skin conditions such as eczema at the sites where electrodes will be placed
• Hair styles hindering the placement of electrodes
• Cranial pathologies
• Head trauma
• Epilepsy
• Mental retardation
• Any known history of neurological disorders (including epilepsy, amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), stroke, cerebral palsy, any DSM-5 axis I psychiatric disorder (for healthy control subjects), autism)
• Uncorrected vision problems that would hinder cognitive testing (this also pertains to subjects with color blindness in tasks where discriminating colored objects/items is necessary for successful performance)
• Pregnancy
• Substance dependence in the past six months
• Substance abuse in the past month

Select data from this study may be submitted to the National Institute of Mental Health Data Archive (NDA). NDA is a data repository run by the National Institute of Mental Health (NIMH) that allows researchers studying mental illness to collect and share de-identified information with each other. The data repository is accessible only to qualified investigators. All subject data will be de-identified (subject names will not be used) and each subject will have a separate identifier called a Global Unique Identifier (GUID) to remove any possibility that "the identities of the subjects cannot be readily ascertained or otherwise associated with the data by the repository staff or secondary data users." (45 CFR, 46.102).