To further develop interventions, the investigators need a better understanding of which task requirements (i.e. size or weight of object, location in workspace, etc.) drive a person after stroke to use 2 hands (as opposed to 1), and how the severity of their injury impacts this relationship and compare this to reaching in age-matched healthy controls subjects. A better understanding of this relationship will promote more informed development of rehabilitative interventions. This study proposes to explore in people after stroke and healthy controls: i.) how specific functional tasks requirements relate to 1 vs. 2 handed use, and ii.) how stroke severity impacts this arm use. We are proposing to study 15 individuals more than 6 months after stroke in the CSU Motor Behavior Lab for a two x 3 hour session of task-related reaching in sitting and 33 age matched (double sample size) healthy controls. The investigators will systematically vary task requirements (i.e. object size or weight, location in workspace, etc.), and record use of 1 versus 2 hands using videotaping as well as recording of quality of arm movement (kinematics) and muscle activity (EMG) in both arms.

Inclusion Criteria:

subjects post-stroke

• passive flexibility (i.e. passive range of motion) in both arms such that the elbows can be straightened within 15 degrees of normal and shoulders be flexed (lifted up) at least 90 degrees and the hand needs to be able to open at least 75% of the way
• Actively (of each subject's own accord/ability) they must be able to, without assist in sitting and standing: straighten each elbow within 15 degrees of full range of motion, lift each arm up at at least 60 degrees from at the side, open each hand from a gross grasp volitionally.
• able to lift a glass jar using 1 or 2 hands in sitting and standing 10" above the table top.
• able to come to CSU for two x 3 hour visits with or without assistance of their caregiver/significant other
• No arm/hand injury within the last 3 months. * Individuals with common visual deficits post-stroke (1 side partial visual field cut aka homonymous hemianopsia) will be included.

Healthy controls:

-age matched (double sample size); no known injury to arms within last 3 months, able to carry out experimental task, no neurologic diagnoses/perceptual or sensory deficits affecting arm movement

Exclusion Criteria:

• Individuals who have any additional/other neurologic condition (i.e. Parkinsons Disease, multiple sclerosis, spinal cord injury)
• severe perceptual neglect (tested using clock drawing test ).
• Any individual who cannot answer phone screen questions competently and/or follow simple 2 step commands during the in-person screen

adults > 18 years old chronic post-stroke with upper extremity paresis yet able to complete a reach-to-grasp task independently with their paretic arm healthy controls > 18 years old (as per above)