1. Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology (ETH Zurich), CLA F 34.1, Tannenstrasse 3, Zurich 8092, Switzerland e-mail:
2. Department of Mechanical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 e-mail:
3. Department of Psychology, University of Pittsburgh, 4200 Fifth Avenue, Pittsburgh, PA 15260 e-mail:
4. Department of Biological Sciences, University of Massachusetts Lowell, One University Avenue, Lowell, MA 01854 e-mail: