Read the full article at PBS.

Mothers across languages change the timbre of their voice in similar ways when they speak to babies, Princeton University neuroscientists report today in the journal Current Biology. This finding will help researchers understand what kind of speech keeps a baby’s attention, which could improve how we teach children.

Timbre is the flavor of music and speech. It’s not a distinct pitch or loudness, but rather the unique collection of frequencies produced by a person or instrument. Timbre is what makes sound distinct: It’s why you can tell a violin from a guitar even if they are playing the same note, or Bob Dylan from Jimi Hendrix even if they are both singing “All Along the Watchtower.”

Each person’s voice box is also an instrument with a unique timbre, though it is malleable and can shift slightly. To imitate the distinct, nasally voice of Donald Duck, says lead author Dr. Elise Piazza, “I might draw back my lips and tighten the back of my throat to create a different tone color.”

It is known that mothers in many languages raise their pitch, slow down their speech and repeat phrases more often when they are trying to attract a baby’s attention. This is known as infant-directed speech, and Piazza and her colleagues wondered if it might cause shifts in timbre as well.

“We were most surprised that this timbre shift between adult-directed and infant-directed speech exhibited such a consistent pattern across such diverse languages,” Piazza said. “In addition to English, we included Spanish, Russian, Polish, Hungarian, German, French, Hebrew, Mandarin and Cantonese.”

This consistent pattern across languages was picked up by their algorithm even when the training data set only had English phrases. The reverse was true too. When they trained the algorithm with other languages, it was able to use timbre shifts to classify speech in English.

“That classifier is really effective,” Dr. Anne-Michelle Tessier said, a linguist with the University of Michigan’s Center for Human Growth and Development who was not involved with the study. But it is hard to tell if infants are as good as machines at picking up on these patterns, she said.