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How do Bilingual Infants Separate their Languages?

Language discrimination and separation in bilingual infants

Interview conducted by François Grosjean.

One of the most intriguing phenomena in bilingualism is how infants who acquire two or more languages from birth manage to discriminate and separate their languages. They have to distinguish and differentiate the spoken input they perceive into distinct languages. How do they do it, we keep asking ourselves. Professor Janet Werker of the University of British Columbia is known the world over for her work on the perception of speech by bilingual infants. She has been one of the pioneers of research on language discrimination and separation, among other domains, and she has very kindly accepted to answer a few of our questions.

In your publications, you write that bilingual infants are more sensitive to the perceptual details of languages than monolingual infants. Can you explain what you mean?

Bilingual infants seem to listen more closely to the actual acoustics of speech sounds, hearing – for example – differences in the strength of the puff of air in one “P” vs. another (put your fingers in front of your mouth when you say “pat” and you’ll know what I mean). They also seem to be more sensitive to visual differences when watching talking faces, and notice, for example, the precise way the mouth or other facial muscles move when a word is being produced.

You also state that bilingual infants are better able to track multiple cues simultaneously. Can you give an example?

The languages of the world have different basic grammars which results in different word orders. In English there are prepositions (e.g. from Vancouver) whereas in Japanese there are post-positions (e.g. Tokyo kara). Also, in English determiners come before nouns (e.g. the house) whereas in Japanese, it is the opposite. Words such as prepositions (from) and determiners (the) are very common, but are lower in pitch and/or shorter in duration than words like nouns. Monolingual learning infants can use word frequency in a made-up language to figure out the grammar. Bilingual infants can use word frequency PLUS pitch and/or duration!

Languages have phonetic categories with specificities, e.g. some languages have short and long vowels, some have nasal vowels, etc. How does this internal structure help bilingual infants separate their languages?

Some studies suggest that bilingual infants are able to use the existence of different kinds of phonemes to help situate the speech they are hearing within one or another of their native languages. While more work is needed to ensure that this is the case, it seems as if bilingual Japanese-English infants can listen for Japanese grammar and words when they hear, for example, both long and short vowels in speech, but listen for English grammar and English words when they hear clear “r” and “l” sounds in the speech of someone talking to them.

Languages also have allowable sequences of phonemes (sounds) which don't occur in other languages. Can this also help bilingual infants separate their languages and can you give an example?

There is evidence from our colleagues in Spain, Nuria Sebastian-Galles and Laura Bosch, that bilingual Spanish-Catalan infants are sensitive to the allowable sequences of sounds (phonotactics) in their two languages. Catalan allows consonant clusters at the ends of words, whereas Spanish doesn’t. Infants were tested on their preference for lists of words that either did or did not contain consonant clusters. Preference was measured by examining looking time to a display while the words were heard. While the monolingual infants listened longer to words that could be in their native language, the bilingual learning infants showed more mixed preferences, driven by the language they were hearing most at home. As in the example above with phonemes, sensitivity to phonotactics could also help bilinguals separate their two languages.

Bilingual infants are attuned to the prosody (e.g. the rhythm) of their languages. How does this help?

Sensitivity to the rhythm of the two languages helps in two ways. First, it can help bilingual infants keep their two languages apart while simultaneously learning each (but without confusing it with the other). In addition, rhythm correlates with word order, so bilingual infants could use rhythm to help flag where nouns, verbs, prepositions, determiners, etc., might be in the speech they are hearing.

Infants often look intensely at those who speak to them and pick up on visual cues. Do bilingual infants use this in any way?

All of us can tell, sometimes, whether someone talking is speaking our native language or not just by watching their facial movements. As noted above, bilingual infants seem to watch talking faces more closely than do monolingual infants, and hence may use the visual cues in talking faces to provide another cue as to which language is being spoken. Studies in other laboratories show that bilingual infants look more at the mouth than do monolingual infants (who look mostly at the eyes, particularly by 10 months of age), providing even more information that they are tracking ‘phonetic’ properties in facial movements (see here for a post on this topic). In current work we are also exploring the hypothesis that bilingual infants who grow up in bi-ethnic homes might be able to use ethnicity in the face as a cue to the language that will be spoken.

In a recent paper with your Padmapriya Kandhadai and D. Kyle Danielson you state that bilingual infants may be able to use cultural information in their surroundings to track the properties of each language. What do you mean exactly?

As in the example above with faces of different races, we suggest that bilingual/bicultural infants may be able to use other aspects of their two cultures to keep their languages apart, or to prime them to expect one or the other of their two languages. There is work with bilingual Mandarin-English adults that shows that seeing an iconic image from one culture, e.g. a picture of the Great Wall, speeds up access to Chinese words and slows down, or mixes up, access to English words.

Some bilingual infants get more input in one language than in the other, hence are dominant in that language. What impact does this have in their task of differentiating languages?

This is still an open question, but the research to date would suggest that as long as some threshold level of input is used in each language, the two languages will still be kept distinct.

What current questions concerning language differentiation are of particular interest?

One exciting question that comes from the work of Krista Byers-Heinlein at Concordia University in Montreal, is how language mixing effects language differentiation. Many bilingual children grow up with a lot of intermingled language input (see here) but they still separate their languages. Whether mixing has an impact on this process is still not well understood.

For a full list of "Life as a bilingual" blog posts by content area, see here.

Photo of a young mom with baby from Shutterstock.


Werker, J. F. & Byers-Heinlein, K. (2008). Bilingualism in infancy: First steps in perception and comprehension. Trends in Cognitive Sciences, 12(4), 144-151.

Kandhadai, P., Danielson, D. K. & Werker, J. F. (2014). Culture as a binder for bilingual acquisition. Trends in Neuroscience and Education, 3, 24-27.

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