1. a The Robotics Institute , Carnegie Mellon University , Pittsburgh, PA, 15213, U.S.A.
2. b Department of Electrical and Systems Engineering , Oakland University , Rochester, Michigan, 48309, U.S.A.
3. c Department of Electrical Engineering , University of Pittsburgh , Pittsburgh, PA, 15260, U.S.A.
4. d Department of Neurological Surgery, Electrical Engineering and Mechanical Engineering , University of Pittsburgh , Pittsburgh, PA, 15260, U.S.A.