1. Institute of Informatics and Telematics (IIT); National Research Council (CNR); Via G. Moruzzi 1, 56124 Pisa Italy
2. Department of Experimental Psychology; University of Oxford; South Parks Road Oxford, OX1 3UD United Kingdom
3. Department of Information and Computer Science; Aalto University School of Science; Konemiehentie 2 - FI-02150 Espoo Finland