As an important part of the plan to record and systematically deal with all observable behavioral events that constitute an infant's waking life, all social encounters between the baby and other persons that occurred during weekly observations of two infants in their everyday milieu were recorded. (Author/CB)

Previous studies have shown that American mothers, in contrast to Japanese, do more lively chatting to their babies, and that as a result, the American babies have a generally higher level of vocalization and, particularly, they respond with greater amounts of happy vocalization and gross motor activity than do Japanese babies. Thus, it appears…