Baby talk. It is how many adults speak to babies: slowly, using shorter sentences, talking at a higher pitch, and putting more emphasis on certain vowels. Examples include, “Where are your shoooes?” And, “Oh, this tastes gooood.”

New research from Princeton University in New Jersey found something else special about how adults -- in this case mothers -- speak to their very young children.

“We found for the first time that mothers shift their vocal timbre,” said Elise Piazza, a postdoctoral researcher at Princeton University’s Neuroscience Institute.

Timbre is what makes a sound appear different than words or music with the same pitch and loudness.

Piazza added: “Timbre is best defined as the unique quality of a sound. Barry White’s silky voice sounds different from Tom Waits’ gravelly one -- even if they’re singing the same note.”

Using special equipment, Piazza and other Princeton researchers found that mothers shared similar changes in timbre when speaking to babies.

Piazza offers this example from the research. First, a mother talking to her baby.
“A bunny and a mouse.”

And here is the same mother talking to an adult.
“He had four teeth coming in at once.”

Piazza explains how people change their timbre.
“Timbre is influenced by your entire vocal tract--from your vocal cords all the way up to your lips,” she told VOA.

“When you move your tongue and lips to make different vowels (‘ba’, ‘bi’, ‘bo’), you’re actually changing timbre,” she said.

The researchers tried to capture the sounds mothers used with their babies at home.

“We chose to record mothers playing with and reading to their own babies just like they would at home,” Piazza said. She wanted the discussions to be as natural as possible.

The research offers new ways to show differences between how adults speak to babies, compared to fellow adults.

The research was not limited just to English speakers. Researchers listened to discussions in nine other languages: Mandarin, Polish, Russian, Spanish, Cantonese, German, Hebrew, French and Hungarian.

Piazza said the research can be used to learn more about how people discuss different situations.

For example, she said, it could include how people change their timbre when speaking to friends or managers at work; how candidates speak to voters; and how people speak to their boyfriends, girlfriends and spouses.

The Princeton research follows earlier research on baby talk.

In 2014, researchers from the University of Washington and University of Connecticut looked at thousands of verbal discussions between parents and babies. They compared regular speaking voices and baby talk.

Patricia Kuhl is co-director of the University of Washington’s Institute for Learning & Brain Sciences and a co-author of the baby talk report.

She said researchers found that use of baby talk led to better early language development.

The more parents emphasized certain vowels (such as in the phrase “how are youuuu?”) and raised the pitch of their voices, the more the one-year-olds babbled, Kuhl said.

Babbling, which is making sounds that do not make sense, is considered an early step to word production.