Elise Piazza, lead author and a postdoctoral research associate with the Princeton Neuroscience Institute, said, “Motherese contains exaggerated pitch contours and repetitive rhythms that help babies segment the complex noises around them into building blocks of language.”
She added that the speaking style also helps parents capture the attention of their babies and engage them emotionally.
Piazza and her team first examined the timbre, or vocal quality, of 12 English-speaking mothers.
“We use timbre, the tone color or unique quality of a sound, all the time to distinguish people, animals, and instruments,” Piazza said in an email to Seeker. “For example, we can easily discern idiosyncratic voices, such as Barry White (famously velvety), Gilbert Gottfried (nasal), and Tom Waits (gravelly), even if they’re all singing the same note (pitch) with the same rhythm.”
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The researchers then recorded each mother as she spoke to her 7-12-month-old infant and again while she spoke to an adult in the lab. Afterwards, they quantified the profile of each woman’s vocal timbre using the mel-frequency cepstrum, which provides researchers with a representation of the speaker’s vocal fingerprint. They found that speech directed at babies and speech directed at adults had very different vocal profiles.
The differences were vast enough that a computer algorithm could classify them using only one second of recorded speech. The team suspects they would find the same distinction in the speech patterns of fathers.
Piazza and her team then examined baby talk in languages other than English. They brought in mothers who are native speakers of Cantonese, French, German, Hebrew, Hungarian, Mandarin, Polish, Russian, and Spanish. The shift in vocal timbre was “highly consistent” across all languages and may indicate that there is a universal form of infant communication.
“We think the timbre of motherese is probably similar across languages because it helps infants learn or emotionally engage in some fundamental way,” Piazza said. “However, future research will be needed to fully understand the implications of this shift for learning and social development.”
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It’s common knowledge that mothers speak to their babies differently than they do to adults, but this is the first study to show that the way they manipulate their voice is consistent across various languages.
“Our work could open up future research explorations of how speakers adjust their timbre to accommodate a wide variety of audiences,” Piazza said, adding that populations could include friends, superiors, political constituents, and romantic partners.
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