Bilingual babies practice lip-reading long before monolingual counterparts

Babies raised in bilingual households spend significantly more time watching the mouth of the person speaking to them than their monolingual counterparts, according to a new study.

David Lewkowicz, a professor in the Department of Communication Sciences and Disorders at Northeastern University, and colleagues in Barcelona, Spain, observed bilin­gual and monolingual infants as they watched a video of a woman speaking in Spanish or Catalan. The infants were all learning one or both languages.

Lewkowicz says the idea for the study arose from previous research in which he and his colleagues had found that 4-month-old babies, despite their fascination with things that move, don’t look at a person’s mouth when they speak, but rather look only at the eyes. When babies start babbling at 8 to 10 months, they also start to shift their attention back and forth between the eyes and the mouth.

He and his colleagues wondered if bilingual babies do this any differently — and it turns out they do: bilin­gual babies focus their atten­tion on the mouth at an ear­lier age and for a longer period of time than mono­lin­gual infants. “Babies learning two different languages take advantage even more of the information that is located in the lips,” Lewkowicz says.

They found similar differences between 1-year-olds. The mono­lin­gual babies looked equally at the eyes and mouth in response to native speech, but more at the mouth in response to non-native speech, while 12-month-old bilin­gual babies looked longer at the mouth regard­less of lan­guage. In either case — native or non-native speech — bilingual babies looked longer at the speaker’s mouth than the monolingual babies.

This evidence indicates that when babies begin to focus on the mouth they “are now tuning in to the audio-visual speech signal, per se, and that they're processing this information as speech and language,” Lewkowicz explains.

The find­ings have “impor­tant impli­ca­tions for under­standing how infants acquire speech and lan­guage and shed light on how bilin­gual infants — despite their neural and behav­ioral immaturity — manage to learn two dif­ferent lan­guages as easily as mono­lin­gual infants learn one language,” according to a Northeastern University press release.

Might this insight into infant lip-reading also help adults who are trying to acquire a second language? The answer is a bit complex, says Lewkowicz, but overall probably yes.

Due to a process known as perceptual narrowing, adults — and even young children — lose perceptual sensitivity to the sounds of other languages and to the way those sounds look on the lips when someone is speaking, Lewkowicz explains. This is why it’s harder for adults to learn other languages than children.

But lip-reading while trying to learn a second language should boost comprehension, he adds. Evidence from adult studies has indicated that when adults are presented with speech in a noisy environment, or with ambiguous speech that is hard to understand, they comprehend more if they are allowed to lip-read.

The study also suggests that parents with small children need to ensure they have plenty of face-to-face time with their children and resist the temptation to speak to their children sideways while looking at their phones or computers.

“Those of us who study development know this as a fact: the best way to raise children and the best way to encourage their development is to interact with them in the most appropriate social way possible,” Lewkowicz says. “That's really how we evolved as a species, to be interacting with one another en face, if you will.”

This article is based on an interview that aired on PRI's Science Friday with Ira Flatow.