1. Frank, J. D.:Persuasion and Healing: A Comparative Study of Psychotherapy. Baltimore, Johns Hopkins Press, 1961.
2. Gantt, W. H.: Personal Communication.
3. Greenspoon, J.: The reinforcing effect of two spoken sounds on the frequency of two responses.Amer. J. Psychol.,68: 409–416, 1955.
4. Herzberg, A.:Active Psychotherapy. London, Research Books, 1945.
5. Krasner, L.: The therapist as a social reinforcement machine.In Strupp, H. H., and Luborsky, L. (eds.):Research in Psychotherapy, vol. 2. Washington, D. C., American Psychology Association, 1962.