In Brain Sense, I describe how the capacity for language develops in the infant brain before birth.
Brain activity in the left-hemisphere language centers can be detected in infants as young as five days. Behavioral experiments have demonstrated that days- or weeks-old infants can distinguish the "melody" of their native language from the pitches and rhythms of other languages. They can assess the number of syllables in a word and perceive a change in speech sounds (such as ba versus ga), even when they hear different speakers.
Very young babies can also pick up a change of words in a sentence. Two-month-olds can tell the difference between "the rat chased white mice" and "the cat chased white mice" even after a two-minute delay. This ability vanishes when the same sounds are played backward.
"From the first weeks of life," says French researcher Ghislaine Dehaene-Lambertz, "the human brain is particularly adapted for processing speech." Her MRI studies of infant brains have convinced her that language processing in newborns relies largely on the same brain circuits that adults use.
She has also found that a baby's native language enjoys a significant advantage in key language-processing centers of the brain. Babies show the same patterns of brain activity as adults when it comes to distinguishing the native language from a foreign one.
Now new research shows that infants born to bilingual mothers possess, at birth, the ability to discriminate two languages. "Hearing two languages regularly during pregnancy puts infants on the road to bilingualism by birth," reports the Association for Psychological Science, announcing a study published online January 29.
According to researchers Krista Byers-Heinlein and Janet F. Werker from the University of British Columbia and their colleague in France, Tracey Burns, infants born to bilingual mothers--women who spoke two languages regularly during pregnancy--exhibit different language preferences than infants born to mothers who spoke a single language during the prenatal months.
The study compared babies born to English monolinguals and babies born to Tagalog-English bilinguals. The researchers measured how fast the babies sucked when they heard either of those languages. (Sucking rate is well established as a measure of an infant's interest in a stimulus.)
In one experiment, the babies heard ten minutes of speech, with every minute alternating between English and Tagalog. The babies born to English monolingual mothers sucked faster when they heard English. They more or less ignored the Tagalog. But the babies born to bilingual mothers sucked equally fast for both English and Tagalog.
In additional experiments, the bilingual infants showed an ability to discriminate English and Tagalog--to keep one separate from the other--a necessity for mastering two languages. "These results suggest that prenatal bilingual exposure may affect infants' language preferences, preparing bilingual infants to listen to and learn both of their native languages," says the Association's press release.
"Monolingual newborns' preference for their single native language directs listening attention to that language," say the researchers. "Bilingual newborns' interest in both languages helps ensure attention to, and hence further learning about, each of their languages."
For more information:
Brynie, Faith. Brain Sense, Chapter 22, "Listening and Language."
Byers-Heinlein et al., "The Roots of Bilingualism in Newborns," Psychological Science (online).
Brynie, Faith. "Newborn Brain May Be Wired for Speech."