[1] Northwestern Univ, Dept Mech Engn, Evanston, IL 60208 USA
[2] Northwestern Univ, Dept Biomed Engn, Evanston, IL 60208 USA
[3] Northwestern Univ, Dept Psychol, Evanston, IL 60208 USA
[4] Rehabil Inst Chicago, Chicago, IL 60611 USA
[5] Coll William & Mary, Dept Psychol, Williamsburg, VA 23187 USA