Babies as young as four months old can tell whether a speaker has switched languages from visual cues alone, but only those who grow up in a bilingual home seem to hang on to the ability, researchers have found.

In Friday's issue of the journal Science, Whitney Weikum, a doctoral student in neuroscience at the University of British Columbia, and her colleagues report the results of their tests on 96 infants who were shown video clips of bilingual speakers.

Caregivers wore darkened glasses to prevent influencing babies in the study, who watched silent video clips of bilingual speakers.
(Janet Werker/University of British Columbia)

The study is the first to show young babies are prepared to tell languages apart using only visual information, Weikum said.

The researchers tested infants at four, six and eight months of age from English-only homes and six and eight-month-olds from bilingual English and French homes.

Each group was shown silent video clips of bilingual speakers, who recited sentences first in one language and then switched to the other.

"We expected that if the baby noticed the change in the language, they would start watching the screen again," Weikum told CBC News.

The babies did just that. At four and six months, babies paid closer attention and watched the video for longer when the speakers switched languages, which suggests the infants were able to discern the change from visual information alone.

While six-month-olds from monolingual and bilingual environments could tell languages apart visually, by eight months of age, only babies from bilingual homes who were familiar with both languages continued to be able to do so, the researchers found.

Early second language immersion

The results suggest that by eight months, only babies learning more than one language maintain their ability to use visual language information. If not, their sensitivity for other languages declines, Weikum said.

"It's as if they're prepared to learn any or more than one of the world's languages," said study co-author Janet Werker, a psychology professor at UBC. "They stop using that information that they don't need, and they continue to sharpen and use the information that they do."

The study goes against the adage that babies are empty vessels waiting to be filled, Werker said. Instead, they start with many tools, maybe more than they need, she said.

The researchers said they don't have an answer for parents who want to know if they should try to immerse their children in a second language by four months, and if there will be detriments if they don't. They hope to address those questions as their work continues.

It is also not clear why infants can tell languages apart without hearing them, said study co-author Athena Vouloumanos, a psychology professor at McGill University in Montreal.

"One possibility is the rhythms of the language," Vouloumanos said. "English and French are actually in different rhythmical classes — English is a stress-based language, while French is syllable-based."

With files from the Canadian Press