Nearly all parents instinctively use “baby talk,” a unique form of speech that includes exaggerated pitch contours and short, repetitive phrases.
Now, researchers have discovered another unique feature in the way parents talk to their babies: timbre, the musical quality of a voice. In the study, mothers were found to shift the timbre of their voice in a rather specific way. The findings held true regardless of a mother’s native language.
“We use timbre, the tone color or unique quality of a sound, all the time to distinguish people, animals, and instruments,” said Elise Piazza from Princeton University. “We found that mothers alter this basic quality of their voices when speaking to infants, and they do so in a highly consistent way across many diverse languages.”
Timbre is the reason it’s so easy to discern idiosyncratic voices — for example, the velvety sound of Barry White or the nasal tone of Gilbert Gottfried — even if they’re all singing the same note, Piazza said.
Piazza and her colleagues at the Princeton Baby Lab, including Drs. Marius Catalin Iordan and Casey Lew-Williams, conduct research to better understand how children learn to detect structure in the voices around them during early language acquisition.
In the new study, they decided to focus on the vocal cues that mothers adjust during baby talk without even realizing they’re doing it. The researchers recorded 12 English-speaking mothers as they played with and read to their seven to 12-month-old babies. They also recorded those mothers while they spoke to another adult.
After identifying each mother’s unique vocal fingerprint using a concise measure of timbre, the researchers found that a computer could reliably tell the difference between infant- and adult-directed speech.
In fact, using a technique known as machine learning, the team discovered that a computer could learn to differentiate baby talk from normal speech based on just one second of speech data. The researchers verified that those differences couldn’t be explained by pitch or background noise.
The next step was determining whether those differences would hold true in mothers speaking other languages. The researchers enlisted another group of 12 mothers who spoke nine different languages, including Spanish, Russian, Polish, Hungarian, German, French, Hebrew, Mandarin, and Cantonese.
Remarkably, the timbre shift observed in English-speaking mothers was highly consistent across those languages from around the world.
“The machine learning algorithm, when trained on English data alone, could immediately distinguish adult-directed from infant-directed speech in a test set of non-English recordings and vice versa when trained on non-English data, showing strong generalizability of this effect across languages,” Piazza said.
“Thus, shifts in timbre between adult-directed and infant-directed speech may represent a universal form of communication that mothers implicitly use to engage their babies and support their language learning.”
Next, the researchers plan to explore how this timbre shift helps infants learn. They hypothesize that the unique timbre fingerprint could help babies learn to identify and pay attention to their mother’s voice from the time they are born.
And although the study was conducted with mothers to keep the pitches more consistent across participants, the researchers say it’s likely the findings apply to fathers as well.
The study is published in the journal Current Biology.
Source: Cell Press