Inclusion Criteria- A single new focal unilateral stroke with diagnosis verified by brain imaging (MRI) or CT scan that has occurred at least 6 months prior to enrollment.
- Age 18 years of age and older.
- Upper extremity Fugl-Meyer score >=7 or <=38 (max 66). (These thresholds include neither hemiplegic nor fully recovered motor function in 14 muscles of the shoulder, elbow, and wrist.)
- Cognitive function sufficient to understand the experiments and follow instructions (Mini-Mental Status Score of 22 and higher or interview for aphasic subjects).
- Willingness to avoid any new alternative arm rehabilitative approaches for the duration of the study.
- Written informed consent to participate in the study.
Exclusion Criteria- A fixed contracture in the affected limb that prevents movement along the entire dynamic range required by either robot-assisted or intensive comparison therapy.
- Joint pain that occurs within the range of motion required by the intervention protocols (intensive comparison therapy and robot-assisted therapy).
- Enrolled in or planning to enroll in another interventional research trial that involves the upper limbs using procedures proposed to enhance or limit the function of the upper extremity (such as adjuvant rehabilitation or Botox injections) during the 36 weeks of participation.
- Prior experience with robot-assisted therapy or intensive comparison therapy for the upper limb as described in this specific study.
- A complicating medical condition that would prevent completion of the trial.
- Unable to complete the nine-month study, e.g., extended planned vacation.
- Any other known pre-existing bone diseases that might increase the risk of bone fracture or other injury from intensive comparison therapy or robot-assisted therapy.