References
- Alpert , A. 1928 . The solving of problem situations by preschool children: An analysis . Teach. Coll., Columbia Univ. Pub., Contrib. Educ. , No. 323
- Lewin , K. 1936 . Principles of Topological Psychology , New York : McGraw-Hill .
- McGraw , M. B. and Price , E. D. Plate Glass Test (16 mm. film) , New York : Columbia University .