Pupil-Indexed Noninvasive Neuromodulation

Inclusion Criteria: ALL PROSPECTIVE SUBJECTS: 1. 18-75 years of age PROSPECTIVE SUBJECTS DIAGNOSED WITH STROKE: 2. Diagnosis of a single stroke resulting in hand impairment 3. Diagnosis of stroke at least six months prior to the time of participation Exclusion Criteria: ALL PROSPECTIVE SUBJECTS: 1. History of vestibular disorders or dizziness 2. Difficulty maintaining alertness and/or remaining still 3. Pregnant or expecting to become pregnant 4. Diagnosis of neurological and/or musculoskeletal disorder(s) (other than stroke) that affect movement 5. Ocular disease and/or impairment in more than one eye 6. History of seizure and/or epilepsy 7. Implants, devices, or foreign objects in the brain/body that are incompatible with MRI 8. Body size that is incompatible with MRI scanner dimensions 9. Anyone already enrolled and actively participating in another greater than minimal risk study. PROSPECTIVE SUBJECTS DIAGNOSED WITH STROKE: 10. Other impairments secondary to stroke (e.g., attention, cognition, etc.) that would interfere with the ability to understand study goals or follow simple instructions, as judged by the investigators.