The reciprocal relationship between maternal infant-directed singing and infant gaze.

Infant-directed (ID) playsongs and lullabies have distinct acoustic properties connected to their functions to elicit and diffuse infant attention, respectively. In the performative context of ID singing, it is crucial that infants and caregivers adjust to each other for the songs' function to be reached. In this study, we observed face-to-face ID singing between mothers and their 7-month-old infants and measured variability in maternal singing (i.e., spectral flux) around the onset of infant social gaze toward the mother. Results showed that maternal acoustic variability and infant attention were increased in playsongs over lullabies. Furthermore, mothers increased their acoustic variability both before and after the onset of infant social gaze, especially in playsongs. These findings suggest that mothers increase acoustic variability both to modulate and respond to infant attention, and infants respond to more variable singing by paying more attention to the singing caregiver. Thus, we propose that ID singing interactions are reciprocal, linking infant attentional displays and maternal acoustic responses.