1. PIAGET, J. Quantification, conservation and nativism. Science, 1968, 162, 976–979.
2. PIAGET, J., & INHELDER, B.Mental imallery in the child, London: Routledge & Kegan Paul, 1971 (Firat published in 1966).
3. PICK, H. L., JR., & PICK, A. D. Sensory and perceptual development. In P. H. Mussen (Ed.),Carmichael’s manual of child Psychology. Vol. 1. Chapter II. New Yolk: Wiley, 1970. Pp. 773–847.
4. WERTHEIMER, M. Untersuchungen zur Lehre von der Gestalt. Psychologische Forschung, 1923, 4, 301–350.