[1] Univ London Imperial Coll Sci Technol & Med, Fac Med, Dept Psychol Med, Div Neurosci & Mental Hlth, London W6 8RF, England
[2] London Sch Hyg & Trop Med, Med Stat Unit, London WC1, England
[3] Univ Sussex, Dept Psychol, Brighton, E Sussex, England
[4] Univ London Imperial Coll Sci Technol & Med, Inst Neurol, London W6 8RF, England