Mothers shift the tone of their voice when talking to babies.
We’re all familiar with “baby talk,” the high pitched, “cooing” short words and phrases we use when speaking to infants.
However, scientists have begun to realize that “baby talk” is much more complicated than just short words and phonetic modifications.
A recent study shows that when mothers talk to their babies, the timbre of their voice shifts in a very distinct way — so much so that a machine learning algorithm could almost immediately identify between “baby talk” and normal adult speech.
According to to the Merriam-Webster dictionary, timbre is “the quality given to a sound by its overtones, such as the resonance by which the ear recognizes and identifies a voiced speech sound.”
In other words, timbre is basically the unique, identifiable quality of each sound; it’s what helps you distinguish one voice from another voice or one instrument from another instrument, even when both are using the same pitch and rhythm.
While baby talk may seem to be a cute but trivial practice, it is found to play an important role in different facets of our development, according to Princeton University. These include language learning, emotional learning, language structure and syllabic deconstruction.
In order to quantify specific aspects of baby talk, principal researcher Elise Piazza of Princeton University decided to look at the vocal patterns parents automatically fall into when speaking to their young children.
To do so Piazza recorded twelve English speaking mothers, once when they were talking to their seven to 12 month old child and once when speaking to another adult.
The researchers first quantified each mother’s vocal timbre using a measurement called the mel-frequency cepstrum.
This allowed researchers to see a clear difference between the timbre of the mother’s voice when talking to another adult and when talking to their child.
Furthermore the difference in timbre was consistent across the 12 different mothers; a computer algorithm could clearly differentiate between any mother’s “normal” speech and their “baby” speech.
According to Jenny Saffran, a professor of psychology at the University of Wisconsin-Madison, this study is significant because it focuses on changes in timbre within the relationship between mothers and babies.
“This is the first study to ask whether [mothers] also change the timbre of their voice, manipulating the kinds of features that differentiate musical instruments from one another,” Saffran said in a press release.
This new study shows that it is a unique feature of the way we speak to babies.
Next the researchers wanted to see if this timbre shift was consistent across different languages. They recruited 12 more mothers, all of whom were non-English speakers, and repeated their experiment.
According to Piazza, the quantified timbre shift was consistent; the difference in timbre for a mother speaking English wasn’t significantly different from a mother speaking Mandarin, Polish or Russian.
“These 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,” Piazza said in a press release.
The next step of this research is to study exactly how timbre shifts affect a baby’s learning. It is currently believed that this difference in timbre may be what helps babies distinguish their mother’s voice from other noises and sounds they hear.
