1. Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Room E310, Evanston, IL 60208; Center for Bionic Medicine, Rehabilitation Institute of Chicago, 345 East Superior Street, Room 1309, Chicago, IL 60611 e-mail:
2. Center for Bionic Medicine, Rehabilitation Institute of Chicago, 345 East Superior Street, Room 1309, Chicago, IL 60611; Department of Physical Medicine and Rehabilitation, Northwestern University, 710 North Lake Shore Drive, Chicago, IL 60611 e-mail:
3. Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Room E310, Evanston, IL 60208; Sensory Motor Performance Program, Rehabilitation Institute of Chicago, 345 East Superior Street, Room 1396, Chicago, IL 60611 e-mail:
4. Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Room B224, Evanston, IL 60208 e-mail:
5. Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Room E310, Evanston, IL 60208; Center for Bionic Medicine, Rehabilitation Institute of Chicago, 345 East Superior Street, Room 1309, Chicago, IL 60611; and Department of Physical Medicine and Rehabilitation, Northwestern University, 710 North Lake Shore Drive, Chicago, IL 60611 e-mail: