1. Center for Telematics and Information Technology (CTIT), University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
2. Philips Consumer Lifestyle Advanced Technology, High Tech Campus 37, 5656 AE, Eindhoven, The Netherlands E-mail: {marleen.schut,kees.tuinenbreijer}@philips.com
3. User Experience Group, Philips Research, High Tech Campus 34, 5656 AE, Eindhoven, The Netherlands E-mail: joyce.westerink@philips.com