1Max Planck Institute For Biological Cybernetics, Tübingen, Germany, 2IMPRS for Cognitive and Systems Neuroscience, Eberhard Karls University of Tübingen, Tübingen, Germany, 3Institute for Biomedical Engineering, UZH and ETH Zürich, Zürich, Switzerland, 4Physikalisch-Technische Bundesanstalt, Berlin, Germany