Babies that are exposed to more than one language are soaking it up without confusion, according to researchers.
A recent study by a team of international researchers, including Princeton University, found that bilingual infants as young as 20 months are able to accurately and easily process the complexities of two different languages – just by listening.
"By 20 months, bilingual babies already know something about the differences between words in their two languages," said Casey Lew-Williams, co-author of the study and assistant professor of psychology and co-director of the Princeton Baby Lab.
"They do not think that 'dog' and 'chien' (French) are just two versions of the same thing.
"They implicitly know that these words belong to different languages."
They showed 24 French-English bilingual infants and 24 parents in Montreal pairs of photographs of familiar objects and used eye-tracking measures to test the amount of concentration used to decipher sentences. Pupil dilation indicates how hard someone's brain is "working".
Participants heard simple sentences in either a single language or in a mix of two languages. For example: "Look! Find the chien!"
And in another experiment, they heard a language switch that crossed sentences. Such as: "That one looks fun! Le chien!" Language switches, also called code switches, are often heard by children in bilingual households.
The researchers first studied the adults as a control group, using eye-tracking measures, to test if the responses were the same over time.
They found that the infants and adults experienced a similar processing "cost" when hearing switched-language sentences, and at the moment of the language switch their pupils dilated. They also discovered that the switch cost was reduced or in some cases eliminated when the switch was from the non-dominant to the dominant language.
"We identified convergent behavioural and physiological markers of there being a 'cost' associated with language switching," said Mr Lew-Williams.
"(The study) shows an efficient processing strategy where there is an activiation and prioritization of the currently heard language.
"Bilinguals across the lifespan have important similarities in how they process language."
He also said the study confirmed that bilingual infants monitor and control their languages while listening to the simplest of sentences.
"Researchers used to think this 'bilingual advantage' was from bilinguals' practice dealing with their two languages while speaking," he 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."
Janet Walker, a professor of psychology at the University of British Columbia, who was not involved in the research, said the findings would have an impact on teaching practices in bilingual settings.
"These findings advance our understanding of bilingual language use in exciting ways – both in toddlers in the initial stages of acquisition and in the proficient bilingual adult," she 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."