New research from the University of Washington’s Institute for Learning and Brain Sciences shows that bilingual babies stay open to different speech sounds for a longer period than monolingual babies and that the relative amount of each language babies are exposed to affects their vocabulary as toddlers. Not surprisingly, in a sample of English/Spanish bilingual babies, the more of one language they heard, the more of that language they spoke at 15 months.
In previous studies, the researchers have found that between eight and 10 months of age, monolingual babies become more able to distinguish the speech sounds of their native language. At the same time, their ability to distinguish foreign speech sounds declines. For instance, English-speaking babies become better able to distinguish “r” from “l” sounds at this age, while Japanese-speaking peers (who don’t hear those sounds as often) lose the ability to differentiate them.
In the current study, babies from monolingual (English or Spanish) and bilingual (English and Spanish) households wore caps fitted with electrodes to measure brain activity with an electroencephalogram, or EEG, a device that records the flow of energy in the brain. Babies heard background speech sounds in one language, then occasionally a contrasting sound in the other language.
For example, a sound that is used in both Spanish and English served as the background sound and then a Spanish “da” and an English “ta” each randomly occurred 10 percent of the time as contrasting sounds. If the brain can detect the contrasting sound, there is a signature pattern called the mismatch response that can be detected with the EEG.
Monolingual babies at 6-9 months of age showed the mismatch response for both the Spanish and English contrasting sounds, indicating that they noticed the change in both languages. But at 10-12 months of age, monolingual babies only responded to the English contrasting sound.
Bilingual babies showed a different pattern. At 6-9 months, bilinguals did not show the mismatch response, but at 10-12 months they showed the mismatch for both sounds.
This difference in development suggests that the bilingual babies “may have a different timetable for neurally committing to a language” compared with monolingual babies, said Adrian Garcia-Sierra, lead author and a postdoctoral researcher at UW’s Institute for Learning & Brain Sciences.
The researchers followed up when the babies were about 15 months old to see how many Spanish and English words the children knew. They found that early brain responses to language could predict infants’ word-learning ability. That is, the size of the bilingual children’s vocabulary was associated with the strength of their brain responses in discriminating languages at 10-12 months of age.
Early exposure to language also made a difference: Bilingual babies exposed to more English at home, including from their parents, other relatives and family friends, subsequently produced more words in English. The pattern held true for Spanish. (On a personal note, I’ve observed the same effect on my own son. At 15 months or so I think he was probably speaking more Spanish–he heard a lot of Spanish his first year of life–but now at age two he speaks more English, as his exposure to English has increased.)
The researchers say the best way for children to learn a second language is through social interactions and daily exposure to the language.
“Learning a second language is like learning a sport,” said Garcia-Sierra, who is raising his two young children as bilingual. “The more you play, the better you get.”
“When the brain is exposed to two languages rather than only one, the most adaptive response is to stay open longer before showing the perceptual narrowing that monolingual infants typically show at the end of the first year of life,” Garcia-Sierra said.