ABSTRACT
This Chapter and the next, which consider the correspondences between postnatal brain growth and psychological development during the first year, are not detailed reviews of all that has been learned. The emphasis in this Chapter is on the changes that occur during the transition between 2 and 3 months; Chapter 4 focuses on the transition between 7 and 12 months. The behavioral clusters that define these two transitions are linked to maturational changes in brain organization, suggesting, but not proving, that the alterations in anatomy and physiology are important foundations for the behavioral phenomena. We assume that these maturational processes occur in healthy infants exposed to the objects, events, and people that are characteristic of most environments.
