The role of dyadic affect in play and infant sex in predicting infant response to the still-face situation.

This study was designed to examine mothers' and 3-month-old infants' affect in play and infant sex as predictors of infants' response to the still-face situation. Infants who evidenced negative affect in play were likely to respond with negative displays during a subsequent still-face situation. Maternal positivity in play was positively correlated with infants' social gaze in the still-face situation. In addition, maternal positivity and infant sex significantly interacted in predicting infant affective response in the still-face situation. For girls, maternal positivity was associated with decreased expressivity. For boys, maternal positivity was associated with early positive bids, which were followed by negative bids and moderately negative affect. Finally, maternal positivity and its interaction with infant sex provide unique information beyond the carry-over effect from infant affect in play to infant response to the still-face. Results are discussed in terms of patterns of individual and joint regulation.