Dynamics of Non-Verbal Vocalizations and Hormones during Father-Infant Interaction

Although researchers have established the roles of oxytocin (OT) in promoting affiliative bonds and cortisol (CT) in adapting to stress, the investigation of their interplay with non-verbal behaviors has only recently begun. In this study, we employed social signal-processing techniques to investigate relationships between non-verbal features: infant and father vocalizations, infant-directed speech, speech turn-taking (STT) and hormonal dynamics (OT and CT). Thirty-five fathers were asked to interact with their infants following the fathers self-administration of OT or placebo. We consider the three episodes of the Still Face (SF) paradigm: (1) a baseline normal interaction episode, (2) the SF episode, in which the father becomes unresponsive and maintains a neutral facial expression, and (3) a reunion in which parents and their infants re-engage in interaction. This paradigm elicited stress in the infant. Statistical relationships are assessed by correlation analysis and linear mixed models (LMMs). The results indicate that (i) infant vocalization and STT are key social cues regulating interactions during the stress-inducing and reunion episodes, with infant vocalization leading the interaction dynamics; (ii) father empty pause was the main adaptive behavior of fathers after SF; (iii) OT did not modulate infant STT or father STT/fatherese; (iv) CT appeared to modulate the interaction.