Acknowledgements

We are indebted to Professor John Gunn and Dr. Paul Bowden of the Department of Forensic Psychiatry, Institute of Psychiatry, Maudsley Hospital, for invaluable advice on some of the clinical aspects of the study and for referral of the patients studied. We are also grateful to Professor Isaac Marks and Professor Stuart Checkley for allowing us to test some of their patients. We should like to thank Mrs. Lily Hughes for her careful typing of the manuscript. Finally we should like to thank all who participated as subjects in these experiments.

This research was supported by the Medical Research Council of the UK and by a scholarship to Dr. da Silveira from the Conselho Nacional de Desenvolvimento Cientifico e Tecnológico-CNPq Brazil.