Baby talk is good for youngsters, so parents speak it all over the world

All around the world, parents talk differently to babies than they do to adults. With their young kids, parents switch into a mode of communication known to linguists as “motherese” or infant-directed speech, and known more commonly as baby talk, a form of speech featuring long pauses and a roller coaster of pitch changes.

While parents may feel a bit silly using baby talk, they shouldn’t: Babies not only prefer listening to these exaggerated contours, but they also learn new words more easily from them.

Although scientists know a lot about the changes in rhythm and pitch in infantdirected speech, we know much less about the role of timbre, or tone color, which includes the breathiness, roughness or nasality in a voice.

The timbre of an instrument (whether buzzy, warm or twangy) clearly affects how we experience music, but its role in language is less obvious. When my colleagues and I looked into the tone color of baby talk, we made some surprising discoveries. Mothers change their overall timbre when speaking to babies, almost as if they’re morphing their voice into a different instrument to address these unique little listeners.

Timbre is a complex acoustic feature that helps us distinguish the unique flavors of sounds around us. Contorting the shape of your vocal tract (which goes from your vocal cords all the way up to your lips) results in different resonances, allowing celebrity impersonators and voice-over artists to change their overall timbre.

Because timbre refers to a more complex collection of features than pitch, rhythm or volume, it is a less well-understood property of sounds. But we do know that timbre provides an important pointer to different sound sources, thus helping us identify people, animals and objects based on their characteristic auditory “fingerprints.”

In a new study published in Current Biology, we report for the first time that mothers shift their overall vocal timbre when speaking to their infants.

In the Princeton Baby Lab, where researchers study how children learn, we recorded English-speaking mothers while they played with and read to their 7- to-12-month-old infants, and while they spoke to an adult experimenter.

We then came up with a mathematical formula for the timbre fingerprint of each mother’s voice and found that adult-directed and infantdirected speech had consistently different fingerprints.

Most surprising, in a second sample of non-English-speaking mothers, we found that this timbre shift was also highly consistent across nine diverse languages (Spanish, French, Russian, Polish, Hungarian, German, Hebrew, Mandarin and Cantonese). This suggests that these timbre shifts may represent a universal form of communication with infants.