KEY POINTS:
Four-month-old babies can discriminate between different languages merely by studying the facial movements of the speaker according to a pioneering study of speech development in infants.
Even with the sound turned off on a video recording, babies were able to tell whether someone had switched from speaking English to speaking French, the scientists who conducted the study found.
The researchers believe that this "visual speech" ability is a critical component of language learning and is something that is retained for longer in babies brought up in bi-lingual homes who learn two languages at once.
Babies are acutely tuned in to the human face and can even recognise basic facial features at birth.
The latest study demonstrates just how important facial movements are to language learning, the scientists report in the journal Science.
"Talking faces are among the most dynamic and salient stimuli available to infants, and the facial movements accompanying speech influence adult and infant speech perception," said Whitney Weikum, a doctoral student at the University of British Columbia in Canada and lead author of the study.
Apart from the sounds made by a talking face, babies appear to be able used the movements to determine whether someone has switched from one language to another, Ms Weikum said.
"We already know that babies can tell languages apart using auditory cues.
But this is the first study to show that young babies are prepared to tell languages apart using only visual information," she said.
The study was based on three groups of infants from monolingual, English-speaking families at different ages of life - four, six and eight months.
Two other groups of infants of the same ages, but this time from bilingual English-French families were also used.
The scientists showed each group silent video clips of three bilingual French-English speakers who recited sentences first in English or French, and then switched to the other language, Ms Weikum said.
The young age groups, at four and six months, from both monolingual and bilingual homes were able to tell the languages apart, based on the fact that they would watch the clips for significantly longer periods if the speaker switched language.
However, at eight months of age, the babies from the monolingual homes appear to lose this ability.
Yet the babies from bilingual families were still able to tell each language apart based on the visual information alone.
"This suggests that by eight months, only babies learning more than one language need to maintain this ability," Ms Weikum said.
"Babies who only hear and see one language don't need this ability, and their sensitivity to visual language information from other languages declines," she said.
The study concluded that young babies need to use "visual speech" as part of the language-learning process but they lose this as they get older because the auditory aspect becomes more important.
Bilingual babies, however, retain this ability for visual speech for longer because of the extra effort needed to discriminate between the two languages they are learning.
"Traditionally, visual speech has been regarded as a redundant signal in verbal communication.
The present research shows that visual speech information alone is sufficient for language discrimination in infancy," Ms Weikum said.
- INDEPENDENT
