Bilingual infants control their languages as they listen

Krista Byers-Heinlein, Elizabeth Morin-Lessard, Casey Lew-Williams

Research output: Contribution to journalArticlepeer-review

79 Scopus citations


Infants growing up in bilingual homes learn two languages simultaneously without apparent confusion or delay. However, the mechanisms that support this remarkable achievement remain unclear. Here, we demonstrate that infants use language-control mechanisms to preferentially activate the currently heard language during listening. In a naturalistic eye-tracking procedure, bilingual infants were more accurate at recognizing objects labeled in same-language sentences (“Find the dog!”) than in switched-language sentences (“Find the chien!”). Measurements of infants’ pupil size over time indicated that this resulted from increased cognitive load during language switches. However, language switches did not always engender processing difficulties: the switch cost was reduced or eliminated when the switch was from the nondominant to the dominant language, and when it crossed a sentence boundary. Adults showed the same patterns of performance as infants, even though target words were simple and highly familiar. Our results provide striking evidence from infancy to adulthood that bilinguals monitor their languages for efficient comprehension. Everyday practice controlling two languages during listening is likely to explain previously observed bilingual cognitive advantages across the lifespan.

Original languageEnglish (US)
Pages (from-to)9032-9037
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number34
StatePublished - Aug 22 2017

All Science Journal Classification (ASJC) codes

  • General


  • Bilingualism
  • Code switching
  • Infancy
  • Language control
  • Language processing


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