When singing and speaking to young infants, people alter their voices in a way that is consistent across cultures, according to a study published in Nature Human Behaviourthis week. The findings suggest that the way in which humans speak and sing to infants may have a common, evolved function.
Evidence from many animal species shows that vocalizations often have a clear function, such as alarm calls alerting others to nearby predators. Previous research in humans has shown that both lullabies and the way in which parents speak to children have a soothing effect on infants. This suggests that these vocalizations may also have a common function, but cross-cultural evidence for this is limited.
Courtney Hilton and colleagues used a collection of 1,615 recordings of human speech and song from 21 societies across 6 continents, and applied computational analyses to study the acoustic features that differentiate adult- and infant-directed vocalizations. The authors found that acoustic features consistently differed between infant- and adult-directed recordings. For example, infant-directed recordings had purer timbres, songs were more subdued, and speech had a higher pitch. They played the recordings to 51,065 English-speaking people from 187 countries (although, for many of the participants, English was not their primary language), and found that listeners could guess when vocalizations were directed at infants more accurately than by chance.
The results add to our understanding of human speech and song, and suggest that we alter our vocalizations towards infants in a way that is consistent across cultures and widely recognizable, and may have a common function.
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