[1] NIMH, Neuropsychol Lab, NIH, Bethesda, MD 20892 USA
[2] UCL, Sobell Dept Motor Neurosci & Movement Disorde, Inst Neurol, London, England
[3] Inst Psychiat, Cognit Schizophrenia & Imaging Lab, London, England
[4] Kings Coll London, Dept Psychiat, London WC2R 2LS, England