Expressive timing in infant-directed singing between 3 and 6 months

This longitudinal study compared the temporal characteristics of maternal singing at 3 and then at 6 months. Infant-directed (ID) singing is claimed to have different functions in preverbal communication. However few studies have focused on the specific characteristics of ID singing that change across the first months of life. We aimed to explore these changes between 3 and 6 months because musical routines become prominent in the repertoire of games parents and infants spontaneously play during a period referred to as 'the period of games'. We focused specifically on expressive timing because it reflects how mothers dynamically adapt their singing to their infant's states of attention and involvement. We aimed to determine whether the expressive timing cues of maternal singing would be different at 3 and then at 6 months. To this end, the interactions of 18 mother-infant dyads were recorded while mothers were singing a popular French playsong for their infant at 3 and then at 6 months. Acoustic analyses revealed that mothers showed final-lengthening and tempo slowing for both age groups, but marked the ends of the hierarchical structural units of the song more saliently with their 6-month-olds. Unexpectedly, infant sex was also found to affect maternal singing: more exaggerated phrase-lengthening patterns were observed in singing to girls.