Most of us could easily distinguish between spoken English and French. But could you tell the difference between an English and a French speaker just by looking at the movements of their lips? It seems like a difficult task. But surprising new evidence suggest that babies can meet this challenge at just a few months of age.
Young infants can certainly tell the difference between the sounds of different languages. Whitney Weikum and colleagues from the University of British Columbia decided to test their powers of visual discrimination.
They showed 36 English babies silent video clips of bilingual French-English speakers reading out the same sentence in one of the two languages. When they babies had become accustomed to these, Weikum showed them different clips of the same speakers reading out new sentences, some in English and some in French.
When the languages of the new sentences matched those of the old ones, the infants didn't react unusually. But when the language was switched, they spent more time looking at the monitors. This is a classic test for child psychologists and it means that the infants saw something that drew their attention. They noticed the language change.
Weikum found that the babies have this ability at 4 and 6 months of age, but lose it by their eighth month. During the same time, other studies have found that infants become worse at telling apart consonant and vowel sounds from other languages, and even musical rhythms from other cultures.
It seems that initially, infants are sensitive to the properties of a wide range of languages. But without continuing exposure, their sensitivities soon narrowed to the range that is most relevant for their mother tongue. To test this idea, Weikum repeated his experiments on bilingual infants. Sure enough, at 8 months, these babies could still visually tell the difference between English and French speakers.
We normally think of lip-reading as a trick used only by deaf people. But this study suggests that the shapes our mouths make when we talk provide all of us with very important visual clues. From a very early age, infants are programmed to sense these clues, and this so-called 'visual speech' may even help them to learn the characteristics of their native tongue.
Reference: Weikam, Vouloumanos, Navarra, Soto-Faraco, Sebastian-Galles & Werker. 2007. Visual language discrimination in infancy. Science 316: 1159.