1. Wellcome Department of Cognitive Neurology, Institute of Neurology,
2. Institute of Cognitive Neuroscience and Department of Psychology, University College London, London WC1E 6BT, UK.
3. Scuola Internazionale Superiore di Studi Avanzati, Via Beirut 2–4, 34014 Trieste, Italy.
4. Royal Free and University College Medical School, Rowland Hill Street, London NW3 2PF, UK.