[1] Univ Penn, Dept Bioengn, Philadelphia, PA 19104 USA
[2] Univ Penn, Dept Elect & Syst Engn, Philadelphia, PA 19104 USA
[3] Univ Calif Riverside, Dept Mech Engn, Riverside, CA 92521 USA
[4] Univ Penn, Dept Phys & Astron, Philadelphia, PA 19104 USA
[5] Univ Penn, Dept Neurol, Philadelphia, PA 19104 USA
[6] Univ Penn, Dept Psychiat, Philadelphia, PA 19104 USA
[7] Santa Fe Inst, Santa Fe, NM 87501 USA