To a 4-to-6-month-old baby, a talking face that can be seen but not heard still speaks volumes. Infants in that age range can distinguish between two languages solely by looking at a speaker’s face, without hearing a sound, a new study suggests.
This ability declines between 6 months and 8 months of age, at least for infants exposed to only one language at home, reports a team led by psychologist Whitney M. Weikum of the University of British Columbia in Vancouver. Previous studies had found that performance drops on similar perceptual tasks toward the end of a baby’s first year. Infants around that age, for example, lose the ability to match monkeys’ facial movements to the corresponding sounds (SN: 4/22/06, p. 246).
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However, 8-month-olds can visually discriminate between two spoken languages if they live in bilingual families that use those same tongues, Weikum’s group finds.
“Visual information about speech may play a more critical role [in language learning] than previously anticipated,” Weikum says. It’s not yet clear what facial cues babies use to monitor a speaker’s language, she says.
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She and her colleagues describe their findings in the May 25 Science.
The researchers first studied 36 infants, equally split among 4-, 6-, and 8-month-olds, from English-speaking homes. Each baby sat on his or her mother’s lap and viewed a series of silent video clips in which a woman who was bilingual in English and French read sentences from a storybook in one of the languages.
After a while, infants consistently looked away from the clips, indicating boredom. The woman then read sentences from the other language. Only 4- and 6-month-olds returned to gazing at the clips, a sign of renewed attention or interest.
Another 36 infants of the same ages from English-speaking homes viewed the woman silently reading one set of sentences in English or French. When the babies showed signs of boredom, the woman began reciting different sentences in the same language. At all ages, babies showed no interest in new, same-language sentences.
Among 24 infants raised in families speaking both English and French, 8-month-olds, as well as 4- and 6-month-olds, looked substantially longer at clips after the woman switched from one language to the other.
The new findings support the idea that babies possess a set of perceptual filters that enable them to deal with broad classes of information, remarks psychologist David J. Lewkowicz of Florida Atlantic University in Boca Raton. Experiences during the initial months of life refine these perceptual sensitivities.
The next step is to see whether infants can match the face and voice of a person uttering a foreign language, and whether this matching ability also declines near the end of the first year, Lewkowicz says.