References
- Barker , R. and Wright , H. 1955 . Midwest and Its Children , Evanston , Ill. : Row Peterson .
- Osgood , C. E. , Suci , G. and Tannenbaum , P. 1957 . The Measurement of Meaning , Urbana , Ill. : Univ. Illinois Press .
- Piaget , J. and Inhelder , B. 1956 . The Child's Conception of Space , New York : Norton .