Healthy volunteers and patients with aphasia due to stroke may be eligible for this study. All candidates must be 18 years of age and older. Patients' aphasia must have occurred as the result of a stroke that occurred more than 12 months before entering the study. In addition, their stroke must not have affected the brainstem or cerebellum. Candidates will be screened with a medical history, brief physical examination, and questionnaire about handedness. Participants will undergo the following tests and procedures: