Key points are not available for this paper at this time.
*United Medical and Dental Schools of Guy 's and St. Thomas ' Hospitals, St. Thomas' Hospital, London SEI 7EH, U.K. **Department of Psychology, University College London, Gower Street, London WC1E 6BT U.K. Submitted August 1, 1985; accepted August 23, 1985.
Richardson et al. (1986) studied this question.