An overemphasized whisper, a soothing singsong: when adults talk to small children or sing something to them, they intuitively change their voice - regardless of whether they speak Mandarin, Spanish, German or Mbendjele. This voice change appears to be common in many, if not all, cultures, writes a research team in the journal Nature Human Behaviour. This points to an evolutionary function of child-directed vocalization.
When parents talk to babies or toddlers, their voice softens, their pronunciation becomes clearer and the rate of speech slows down. Various studies have already shown which functions these acoustic characteristics fulfill: baby talk and children's songs seem to help the little ones learn language and calm them down.
Other studies have found that young children - and even dogs and horses - respond more strongly to child-directed speech than to adult-directed speech, even when the speech is in a language foreign to them.
But if baby singsong fulfills such functions, it should appear in similar patterns in different cultures around the world, the international team led by Courtney Hilton from Harvard University and Cody Moser from the University of California suspected. The researchers collected audio recordings of 410 voices from 21 urban, small town and rural communities on six continents. For example, Polish, Finnish and Swedish vocalizations were evaluated from Europe. A total of 1615 recordings were made, which were either aimed at small children or adults.
First, the computer analysis revealed clear differences between the speech and song recordings: in almost all cultures, speech addressed to children was characterized by higher pitch, a greater range, stronger intensity and higher-contrast vowels than speech addressed to adults. When singing, the distinguishing features were less pronounced, but still recognizable.
In the next step, the scientists examined the sensitivity of the listeners to the observed acoustic characteristics. To do this, they played their recordings to more than 51,000 people from 187 countries who were recruited via an English-language website. The listeners had to guess whether the recordings played were aimed at babies or adults.
They succeeded with a hit rate that made a random result unlikely - "despite the fact that the vocalizations were of largely unknown cultural, geographical and linguistic origin," says the study. "Despite the apparent differences in language, music, and infant care practices around the world, when people speak or sing to fussy babies, people across cultures change the acoustic characteristics of their vocalizations in similar and understandable ways. "
These findings supported the notion that the forms of vocalizations addressed to infants are shaped by their functions, similar to vocal signals in many non-human species.
However, this does not mean that child-oriented language and songs sound the same across all cultures. Rather, the results point to a core of universal commonalities that are also shaped by culture.
Overall, the authors admit that their study still leaves questions unanswered. The group of participants does not represent a representative section of humanity, nor does the set of acoustic recordings used. Because only people who understood the instructions on the English-language website could participate.