1. BERKELEY, G. An essay towards a new theory of vision. (First published in 1709.) In C. M. Turbayne (Ed.),Works on vision: George Berkeley. Indianapolis and New York: Bobbs-Merrill, 1963.
2. KATZ, D.The world of colour. London: K. Paul, Trench, Trubner & Co., 1935.
3. MICHOTTE, A.Causalité, permanence et realité phénoménales. Louvain, Belgium: Publications Universitaires, 1962.
4. PEIPER, A.Cerebral function in infancy and childhood. Translation of the 3rd rev. German ed. by Benedict Nagler and Hilde Nagler. New York: Consultants Bureau, 1963.
5. PIAGET, J., & INHELDER, B.La psychologie de l’enfant. Paris: Presses Universitaires de France, 1966. (Also translated from the French by Helen Weaver, New York, Basic Books, 1969.)