1. Social, Genetic and Developmental Psychiatry Research Center, Institute of Psychiatry, King's College London, London, England SE5 8AF, and Department of Psychology, University of Wisconsin, Madison, Wisconsin 53706;
2. Department of Psychology, 603 East Daniel Street, University of Illinois, Urbana-Champaign, Champaign, Illinois 61820;
3. Department of Psychology, Colgate University, Hamilton, New York 13346;