Biobehavioral Correlates of Infants' Social Bidding During the Still-Face Paradigm

Positive social bidding refers to moments when infants look at an unresponsive caregiver and try to re-engage the social partner via smiling and/or vocalizing. Prior to six months of age, there is considerable variability in the extent to which infants engage in positive social bidding. In this study we explore whether infants' and mothers' cardiac vagal tone is associated with these individual differences. Mothers and their 4- to 6-month-old infants (n = 132) participated in the Face-to-Face Still-Face Paradigm (FFSF); social behaviors and respiratory sinus arrhythmia (RSA) were recorded on a moment-to-moment basis. More frequent vocal bidding during the Still-Face episode was related to infants' and mothers' physiological synchrony, as well as lower levels of infants' negative affect and higher levels of infants' RSA during face-to-face Social Play. Also, infants demonstrating more vocal bidding exhibited greater increases in RSA at the beginning and end of the Reunion phase following the Still-Face stressor. Critically, the relation between infants' physiological regulation and vocal bidding differed as a function of the FFSF episode in which RSA was measured. The implications of adopting a biobehavioral perspective on the development of positive social bidding are discussed.