1 Department of Medical, Clinical, and Experimental Psychology, Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands Pain Management and Research Center, University Hospital, Maastricht, P.O. Box 5800, 6202 AZ Maastricht, The Netherlands Academic Unit of Psychiatry and Behavioural Sciences, School of Medicine, University of Leeds, Leeds LS2 9JT, UK.