1. School of Biomedical Sciences, University of Ulster, Coleraine BT52 1SA,Northern Ireland
2. Cognitive Neuroscience, Faculty of Biology, Tübingen University, Auf der Morgenstelle 28, 72076 Tübingen, Germany
3. University of Freiburg, Chair of Pattern Recognition and Image Processing,Georges Köhler Allee 52, 79110 Freiburg, Germany