Infants’ overlapping vocalizations during maternal humming: Contributions to the synchronization of preterm dyads

Despite the neurological vulnerability of premature newborns, there is evidence that they are able to process temporal aspects of the maternal voice, as a previous study observed more overlapping vocalizations during maternal humming versus speech. However, there is a lack of knowledge about the markers of the infants’ overlapping vocalizations. Our aim was to identify the location of overlapping vocalizations during the humming and the impacts of maternal antenatal and postnatal engagement of infant-directed singing on: (1) the features of humming and (2) the infants’ overlapping vocalizations during humming. Preterm dyads (N = 36) were observed in silent, speech, and humming conditions. Microanalysis was performed using the Elan Program to identify the location of the overlapping vocalizations during the humming phrase. Infants’ overlapping vocalizations were found predominantly at the ends of each humming phrase; almost half of the overlaps occurred on the final note. More overlapping vocalizations in the final notes were observed in female infants. Antenatal and postnatal experiences of ID singing are influenced by the mothers’ nationality and contribute to maternal humming style. Preterm newborns synchronize with maternal humming, anticipating the end of musical phrases. The ability to synchronize seems to be phylogenetically associated with gender differences.