1. Machine Learning Group, Technische Universität Berlin, 10587 Berlin, Germany
2. Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany
3. Physics and Materials Science Research Unit, University of Luxembourg, L-1511 Luxembourg, Luxembourg
4. Max-Planck-Institut für Informatik, Saarbrücken, Germany
5. Department of Brain and Cognitive Engineering, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-713, South Korea