While speaking to their babies, mothers tend to shift the timbre of their voice in a rather specific way, which could play an important role in baby's language learning as well as engaging their emotion, researchers say.
The special communicative mode, which mothers use when talking to their young infants, are known as "motherese" or "baby talk" -- somewhat musical form of speech which includes exaggerated pitch contours and short repetitive phrases.
The findings showed that the tone of this baby talk is timbre -- unique quality of a sound -- usually used to distinguish people, animals, and instruments and is the same across different languages.
"We found for the first time that mothers shift their vocal timbre when speaking to infants, and they do so in a highly consistent way across many diverse languages," said Elise Piazza, a postdoctoral research associate at the Princeton University in New Jersey, US.
According to the researchers, the unique timbre tone could help babies learn to differentiate and direct their attention to their mother's voice from the time they are born.
It also plays an important role in language learning, engaging infants' emotions and highlighting the structure in language, to help babies decode the puzzle of syllables and sentences.
For the study, appearing in the journal Current Biology, the team analysed speech of English-speaking women whose voices were recorded while they played with or read to their seven to 12-month-old infants and while they spoke to an adult experimenter.
Using an approach called machine learning, the researchers found that a computer could learn to differentiate baby talk from normal speech based on just one second of speech data.
The researchers then also analysed another group of mothers who spoke nine different languages, including Spanish, Russian, Polish, Hungarian, German, French, Hebrew, Mandarin and Cantonese.
The results showed that the timbre shift observed in English-speaking mothers was highly consistent across those languages from around the world.