Max Planck Institute for Biological Cybernetics, Tübingen, Germany. jordi.grau@tuebingen.mpg.de|Max Planck Institute for Biological Cybernetics, Tübingen, Germany. jordi.grau@tuebingen.mpg.de|Max Planck Institute for Biological Cybernetics, Tübingen, Germany. jordi.grau@tuebingen.mpg.de