Sensitivity to social contingency from mothers and strangers in 2-, 4-, and 6-month-old infants

Infants' sensitivity to changes in social contingency was investigated by presenting 2-, 4-, and 6-month-old infants with 3 episodes of social interaction from mothers and Strangers: 2 contingent interactions and 1 noncontingent replay. Three orders were presented: (a) contingent, noncontingent, contingent; (b) contingent, contingent, noncontingent; and (c) noncontingent, contingent, contingent. Contingency and carryover effects were shown to both mothers and strangers in the different orders of presentation. Infants were more visually attentive to contingent interactions than to the noncontingent replay when contingent interactions occurred prior to the replay, and the infants' level of attention to the noncontingent replay carried over to subsequent contingent interactions. The 4- and 6-month-old infants showed contingency and carryover effects by their visual attention and smiling. Examination of effect sizes for attention suggests 2-month-old infants may be beginning to show the effects. Reasons for age changes in sensitivity to social contingency are discussed.