1. Laboratory of Sensorimotor Research, National Eye Institute, Bethesda, MD 20892, USA; Department of Neurology, Georgetown University School of Medicine, Washington, DC 20007, USA; Mahoney Center for Mind and Brain, Keck Center for Cognition and Plasticity, Center for Neurobiology and Behavior, Departments of Neurology and Psychiatry, Columbia University College of Physicians and Surgeons, and the New York State Psychiatric Institute, New York, NY 10032, USA.