Post written by François Grosjean.

It has been known for some time that newborn infants with monolingual mothers have become sensitive in utero to some characteristics of the spoken language they are exposed to. Thus, when tested just after birth, they show a preference for their mother's voice as well as their mother's native language over another language that is rhythmically different.

But what about infants who have bilingual mothers? Do they show a preference for their mothers' TWO languages? The answer can be found in some fascinating experimental work undertaken by researchers Krista Byers-Heinlein, Tracey Burns and Janet Werker of the Infant Studies Center at the University of British Columbia.

In a first study, they took newborn infants (0 to 5 days old) and presented them with speech, alternating each minute between English and Tagalog, a language spoken as a native language or a second language by nearly all Filipinos. Half the infants had mothers with a monolingual English background and half with a bilingual, Tagalog-English, background. 

The researchers employed a testing technique that makes use of newborns' sucking reflex. The babies are given a rubber nipple to suck on and the researchers record how often they do so. The greater the amplitude of sucking, the more interested the infants are. The question asked was the following: Would both groups of infants have a high-amplitude sucking behavior when listening to English as well as to Tagalog, or would it only be those infants with bilingual mothers?

What was found was that infants with monolingual mothers marked a clear preference for English over Tagalog (their sucking rate was greater for the former). The infants with bilingual mothers, on the other hand, were interested in both languages (they did not favor one over the other). They had been in contact with their mothers' two languages prenatally and hence they responded positively to both.

The researchers then conducted two other studies to make sure that their results couldn't be explained in other ways. One such way, the "insufficient-experience" explanation, ran as follows: because the infants with bilingual mothers had received input in utero from the two languages, maybe their experience with each language had been insufficient. Hence the fact that they did not favor one language over the other.

Other newborn infants, this time with mothers who spoke both Chinese and English, were run on the same stimuli. As compared to the previous two groups, they showed an intermediary pattern. They were less interested in Tagalog than were the infants with bilingual mothers, but they were more interested in it than were the infants with English monolingual mothers. Based on the fact that Tagalog shares some characteristics with Chinese but also differs on some others, the researchers took this to mean that the newborns with mothers bilingual in Tagalog and English had indeed been sensitive in utero to characteristics of the two languages.

The other follow-up study the researchers undertook was to check that the Tagalog-English newborns had not regrouped their two languages into one broad category of familiar language sounds. Hence, they ran a discrimination study of English and Tagalog. They used a sucking habituation procedure in which the infants were habituated to a language, either English or Tagalog. Habituation was observed when, having heard a language for a period of time, they started to slow down their sucking rate (basically, the language wasn't interesting them anymore). When a preset point was reached, the other language was played to them and the researchers observed whether the infant's interest was revived, as shown by a sudden increase in sucking.

What they found was that the infants with bilingual mothers did react to the other language, in other words, that they did indeed discriminate between the two languages. They had not "lumped" the two into one broad language category.

The authors concluded that the acquired interest in the two languages these infants had been exposed to could help them pay attention to the languages and hence acquire them in their first years of life ..... IF they were raised in a bilingual environment, of course.

(For a post on how early and how well bilingual infants discriminate the sounds of their different languages in their first year of life, see here).

Photo courtesy of Heinz Albers, Wikimedia Commons.


Byers-Heinlein, K., Burns, T. C., and Werker, J. F. (2010). The roots of bilingualism in newborns. Psychological Science, 21(3), 343-348.

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