See the many studies by child psychologist J. Piaget; J. Kagan et al., Infancy: Its Place in Human Development (1978); T. B. Brazalton, Infants and Mothers (rev. ed. 1983); J. G. Bremner, Infancy (1988).
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.