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Speech Discrimination in Bilingual Infants

Research findings on bilingual infants are fascinating

Post written by François Grosjean.

Anything that has to do with bilingual infants captures our attention, as it should. (See here for how newborn infants are attuned to their bilingual mothers' languages). One particularly exciting domain pertains to how early and how well they discriminate the sounds of their different languages.

In an interesting study, a team of University of British Columbia researchers led by Janet Werker used a visual fixation procedure to study the development of phonetic representations in English monolingual and English-French bilingual infants. The infants were tested individually. They sat on their caretaker's lap and watched a checkerboard on a monitor. While doing so they heard an intermediate syllable "ba" [pa] which was perceived as "pa" by adult French speakers and as "ba" by adult English speakers. In what follows, we'll refer to it as intermediate "ba" [pa].

The syllable was repeated a number of times through a loudspeaker positioned above the checkerboard until there was habituation (this was seen by the fact that the infants' eyes wandered away from the board). At that point, one of two new syllables was presented. One, [ba], was perceived as a clear "ba" by both English and French adult speakers, and the other, [pha], was perceived as a clear "pa" by both groups. If infants could discriminate the new sound, then their interest would be revived and they would start looking at the checkerboard again. Researchers talk of dishabituation when this happens.

The results were fascinating. First, monolingual and bilingual infants behaved in exactly the same way when they were 6 to 8 months old. They dishabituated to the clear "ba" syllable [ba] but not to the clear "pa" [pha] syllable. However, when 10 to 12 month old infants were tested, the results from the two groups were quite different. The English monolingual infants looked significantly longer at the board when they heard the clear "pa" syllable (this syllable was now heard as different from the intermediate syllable) but not when they heard the clear "ba" syllable (both the intermediate syllable "ba" [pa] and the clear syllable [ba] were now a "ba" for them, hence no dishabituation). Thus, they still had two categories although the boundary between the two had shifted.

What about the bilingual infants? Unlike their monolingual peers, they showed dishabituation to BOTH the clear "ba" and "pa" syllables. The intermediate "ba" [pa] was perceived as different from the clear "pa" [pha]. There is an English phonetic boundary between the two, hence the disabituation. And the intermediate "ba" [pa] was also heard as different from the clear "ba" [ba] as there is a French phonetic boundary between the two. Thus the infants showed the existence of two phonetic boundaries, one for English and one for French. The authors concluded by stating that infants exposed to two languages from birth are equipped to process each language in a native manner, at least at the phonetic level.

Before discussing this further, we can ask ourselves whether any type of exposure to two languages (through human interaction, DVDs, audio input, etc.) will encourage infants to develop the phonetic categories of their languages. University of Washington researcher Patricia Kuhl and her colleagues replied negatively based on a study they undertook. They exposed 9 month-old American infants to twelve sessions with Chinese native-speakers who read and played with them in Mandarin. A second group of similar infants received the same amount of Mandarin language exposure but only through DVDs and audio input.

The results were clear. Whereas the live human exposure infants acquired the Mandarin phonetic contrast, the second group did not. This shows that phonetic learning doesn't rely only on raw auditory sensory information. According to the authors, the presence of a live person interacting with an infant generates interpersonal social cues that attract the infant's attention and motivate learning.

What are the lessons to be learned from this type of research? If infants are exposed to two languages through human interaction, they will acquire the phonetic categories of the languages by the end of their first year approximately. (If the two languages have many similar sounds, then they make take a bit more time). But we should keep in mind that phonetic categories are just some of the building blocks of language. There are many others at all linguistic levels (morphology, syntax, semantics, discourse, etc.) and these will be acquired over several years.

Does all this mean that bilingualism must at all cost start during the first year? The answer is no. In fact, children who acquire their two languages simultaneously are far rarer than bilingual children who acquire their languages successively. As I wrote in an earlier post (see here), there is no upper age limit for acquiring a new language and then continuing one's life with two or more languages. Nor is there any limit in the fluency that one can attain in the new language with the exception of pronunciation skills. Admittedly the latter are harder to acquire by the middle teens, but this is still many years after infancy.

Photo courtesy of Professor Janet Werker of the Infant Studies Centre, University of British Columbia, Vancouver, Canada.


Burns, T., Yoshida, K., Hill, K., and Werker, J. (2007). The development of phonetic representation in bilingual and monolingual infants. Applied Psycholinguistics, 28, 455-474.

Kuhl, P K., Tsao, F.-M. & Liu, H.-M. (2003). Foreign-language experience in infancy: Effects of short-term exposure and social interaction on phonetic learning. Proceedings of the National Academy of Sciences of the United States of America, 100 (15), 9096-9101.

"Life as a bilingual" posts by content area (see here).

François Grosjean's website.