1. Helmholtz Research Institute, Utrecht University, Utrecht, The Netherlands
2. Vision Center Laboratory, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037–1099, USA
3. Helmholtz Research Institute, Utrecht University, Utrecht, The Netherlands, Department of Psychonomics, Utrecht University, Heidelberglaan 2, NL-3584 CS Utrecht, The Netherlands