Aug 29 2011

The Bilingual Brain

A new study sheds further light on how we learn language, showing the power of early exposure to language. Language is something that humans are very good at, which is a way of saying that we have cortex dedicated to and specialized for language.

The dominant hemisphere (dominant by definition, the left hemisphere in most people) contains several structures specialized for language. Wernicke’s area is the brain’s dictionary – it translates words into concepts and concepts into words. When you are trying to think of a specific word for something – that process is taking place in Wernicke’s area. There is also specialized cortex that processes auditory information, translating sounds into words, and feeding that information to Wernicke’s area. In the frontal lobe there is Broca’s area that converts words into speech – essentially this is specialized motor cortex that allows for the exquisite control of the muscles of speech necessary to produce the subtle sounds of speech. Wernicke’s area and Broca’s area are connected by a cable called the arcuate fasciculus.

It has also been known for a long time that the language cortex develops when we are very young, beginning in infancy and then pretty much locking in place by the time we are four years old. This is the “window” of development for language. For children who are raised without exposure to language by age four, they will never acquire normal fluency. If you normally developed a primary language, and then learn a second language after age four, the second language will use more brain resources – it won’t have the same language cortex encoding that the primary language does.

This window of development also applies to phonemes – the individual sounds that make up words. We learn a finite number of phonemes by age four, and then we are pretty much stuck with that set of language sounds. Children as young as 8-10 months old start to learn how to distinguish sounds that are part of speech from other sounds, and the speech sounds (phonemes) become encoded in the language cortex. After about four years old no new phonemes can be learned, and every speech sound we hear from that point forward will be slotted into an existing phoneme.

This is where the new study comes in. The researchers found that babies 8-10 months old were already developing the ability to distinguish sounds important to language – like the difference between an “r” and an “l” in English. However, they also found that babies not exposed to a language that makes this distinction, for example like a child raised in a Japanese household, will start to lose the ability to make this distinction at the same age. So by 10 month old children are already losing their ability to learn new languages, or at least the sounds that make up languages.

In addition they found that children raised in a bilingual household had a greater facility for learning language and the window of learning new sounds was extended. The researchers hypothesize that in a bilingual environment children learn that there is more than one word for everything, and they also greatly stimulate their language cortex by the task of switching between the two languages.

This study extends what was already known about the advantages of learning multiple languages by age four. This study, in fact, indicates that if you want to maximize your child’s language ability, they should be exposed to a second language from infancy.

The study looked at children raised in a bilingual household. It is unclear if the advantage extend to simply playing a second language for the children to hear, but that is not being used interactively with another person. Perhaps a video would be better than pure audio, but still that should be studied specifically before any claims are made for such products. Children may need direct human interaction to make the connection with language.

This study does add to existing evidence, and suggests that perhaps parents should be encouraged to expose children to more than one language. Language instruction might also be added to preschool and daycare programs. By the time children reach Kindergarten, it’s already too late.

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