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Study Reveals How Language Develops in Bilingual Children

When bilingual children learn any two languages from birth each language proceeds on its own independent course, at a rate that reflects the quality of the children鈥檚 exposure to each language.


By gisele galoustian | 4/20/2017

A new study of Spanish-English bilingual children by researchers at published in the journal聽Developmental Science聽finds that when children learn two languages from birth each language proceeds on its own independent course, at a rate that reflects the quality of the children鈥檚 exposure to each language.聽

In addition, the study finds that Spanish skills become vulnerable as children鈥檚 English skills develop, but English is not vulnerable to being taken over by Spanish. In their longitudinal data, the researchers found evidence that as the children developed stronger skills in English, their rates of Spanish growth declined. Spanish skills did not cause English growth to slow, so it鈥檚 not a matter of necessary trade-offs between two languages.

鈥淥ne well established fact about monolingual development is that the size of children鈥檚 vocabularies and the grammatical complexity of their speech are strongly related. It turns out that this is true for each language in bilingual children,鈥 said , Ph.D., lead author of the study, a psychology professor in 抖M女仆鈥檚 , and director of the . 鈥淏ut vocabulary and grammar in one language are not related to vocabulary or grammar in the other language.鈥

For the study, Hoff and her collaborators David Giguere, a graduate research assistant at 抖M女仆 and Jamie M. Quinn, a graduate research assistant at Florida State University, used longitudinal data on children who spoke English and Spanish as first languages and who were exposed to both languages from birth. They wanted to know if the relationship between grammar and vocabulary were specific to a language or more language general. They measured the vocabulary and level of grammatical development in these children in six-month intervals between the ages of 2 and a half to 4 years.

The researchers explored a number of possibilities during the study. They thought it might be something internal to the child that causes vocabulary and grammar to develop on the same timetable or that there might be dependencies in the process of language development itself. They also considered that children might need certain vocabulary to start learning grammar and that vocabulary provides the foundation for grammar or that grammar helps children learn vocabulary. One final possibility they explored is that it may be an external factor that drives both vocabulary development and grammatical development.聽聽

鈥淚f it鈥檚 something internal that paces language development then it shouldn鈥檛 matter if it鈥檚 English or Spanish, everything should be related to everything,鈥 said Hoff. 鈥淥n the other hand, if it鈥檚 dependencies within a language of vocabulary and grammar or vice versa then the relations should be language specific and one should predict the other. That is a child鈥檚 level of grammar should predict his or her future growth in vocabulary or vice versa.鈥

Turns out, the data were consistent only with the final possibility 鈥 that the rate of vocabulary and grammar development are a function of something external to the child and that exerts separate influences on growth in English and Spanish. Hoff and her collaborators suggest that the most cogent explanation would be in the properties of children鈥檚 input or their language exposure. 聽

鈥淐hildren may hear very rich language use in Spanish and less rich use in English, for example, if their parents are more proficient in Spanish than in English,鈥 said Hoff. 鈥淚f language growth were just a matter of some children being better at language learning than others, then growth in English and growth in Spanish would be more related than they are.鈥

聽Detailed results of the study are described in the article, 鈥.鈥

鈥淭here is something about differences among the children and the quality of English they hear that make some children acquire vocabulary and grammar more rapidly in English and other children develop more slowly,鈥 said Hoff. 鈥淚 think the key takeaway from our study is that it鈥檚 not the quantity of what the children are hearing; it鈥檚 the quality of their language exposure that matters. They need to experience a rich environment.鈥

This project is supported by the National Institutes of Health (NIH) through grant number R01 HD068421.

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