[1] Univ Maryland, Dept Elect & Comp Engn, College Pk, MD 20742 USA
[2] EPFL, Idiap Res Inst, CH-1920 Martigny, Switzerland
[3] Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC V6T 1Z4, Canada
[4] MIT, MIT Media Lab, Cambridge, MA 02139 USA
[5] Cornell Univ, Sch Elect & Comp Engn, Ithaca, NY 14850 USA