Are two languages at a time too much for the mind? Caregivers and teachers should know that infants growing up bilingual have the learning capacity to make sense of the complexities of two languages just by listening. In a study, an international team of researchers, including those from Princeton University, report that bilingual infants as young as 20 months of age efficiently and accurately process two languages.
Infants can differentiate between languages
The study, published in Proceedings of the National Academy of Sciences, found that infants can differentiate between words in different languages. “By 20 months, bilingual babies already know something about the differences between words in their two languages,” said Casey Lew-Williams, an assistant professor of psychology and co-director of the Princeton Baby Lab, where researchers study how babies and young children learn to see, talk and understand the world. He is also the co-author of the paper.
“They do not think that ‘dog’ and ‘chien’ [French] are just two versions of the same thing,” Lew-Williams said. “They implicitly know that these words belong to different languages.”
How the study was done
To determine infants’ ability to monitor and control language, the researchers showed 24 French-English bilingual infants and 24 adults in Montreal pairs of photographs of familiar objects. Participants heard simple sentences in either a single language (“Look! Find the dog!”) or a mix of two languages (“Look! Find the chien!”). In another experiment, they heard a language switch that crossed sentences (“That one looks fun! Le chien!”). These types of language switches, called code switches, are regularly heard by children in bilingual communities.
The researchers then used eye-tracking measures, such as how long an infant’s or an adult’s eyes remained fixed on a photograph after hearing a sentence, and pupil dilation. Pupil diameter is an involuntary response to how hard the brain is “working” and is used as an indirect measure of cognitive effort.
The researchers tested bilingual adults as a control group. They used the same photographs and eye-tracking procedure tested on bilingual infants to examine whether these language-control mechanisms were the same across a bilingual speaker’s life.
Results of the study
The researchers found that bilingual infants and adults incurred a processing “cost” when hearing switched-language sentences, and their pupils dilated at the moment of the language switch. However, this switch cost was reduced or eliminated when the switch was from the non-dominant to the dominant language, and when the language switch crossed sentences.
“We identified convergent behavioral and physiological markers of there being a ‘cost’ associated with language switching,” Lew-Williams said. Rather than indicating barriers to comprehension, the study “shows an efficient processing strategy where there is an activation and prioritization of the currently heard language,” Lew-Williams said.
One of the most obvious implications of these results is that we needn’t be concerned that children growing up bilingual will confuse their two languages. Indeed, rather than being confused as to which language to expect, the results indicate that even toddlers naturally activate the vocabulary of the language that is being used in any particular setting.
The bilingual advantage
Lew-Williams suggests that this study confirms that bilingual infants monitor and control their languages while listening to the simplest of sentences and provides a likely explanation of why bilinguals show cognitive advantages across the lifespan. Children and adults with dual-language proficiency have been observed to perform better in “tasks that require switching or the inhibiting of a previously learned response,” Lew-Williams said.
“Researchers used to think this ‘bilingual advantage’ was from bilinguals’ practice dealing with their two languages while speaking,” Lew-Williams said. “We believe that everyday listening experience in infancy — this back-and-forth processing of two languages — is likely to give rise to the cognitive advantages that have been documented in both bilingual children and adults.”
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