1. Boring, E. G. A new ambiguous figure.Amer. J. Psychol., 1930, 42, 444–445.
2. Botwinick, J. Husband and father-in-law: A reversible figure.Amer. J. Psychol., 1961, 74, 312–313.
3. Dali, S. The secret life of Salvador Dali. New York: Burton C. Hoffman, Dial Press, 1942.
4. Fisher, G. H. Materials for experimental studies of ambiguous and embedded figures. Res. Buil. No. 4, Department of Psychology, University of Newcastle upon Tyne, 1966.
5. Hill. W. E. My wife and my mother-in-law.Puck, 1915, 6th Nov.