Have you ever noticed a baby watching your mouth while you speak? They all do it - but only at very specific ages.
A new study just published in the Proceedings of the National Academy of Sciences reports that babies pay selective attention to either the eyes or mouth of the speaker, depending on the infant's age and developmental stage. Watching a speaker's mouth probably helps babies learn to shape the words they hear. Watching the speaker's eyes helps them master social cues.
The ingenious experiment to assess changes in babies' attention to facial features was conducted by scientists at Florida Atlantic University. The researchers tested 179 infants at ages 4, 6, 8, or 12 months. All the babies were from English-speaking uni-lingual families. Each infant was shown a 50-second movie of a woman talking in either English or Spanish. The baby's eye gaze was recorded with standard eye-tracking methods. See a photo of the testing set-up here.
Babies learn to lip-read when they start to babble
Infants at 4 months looked significantly longer at the speaker's eyes than the mouth. At 6 months, they looked equally at the eyes and the mouth. At 8 months, the infants looked mainly at the mouth of the speaker. "Babies start to lip-read when they learn to babble," said primary researcher David Lewkowitz.
At 12 months, the infants begin to shift their gaze back from the mouth to the eyes of the speaker. With a growing language mastery, the babies can at that time afford to look back at the speaker's eyes to improve their understanding of the words' emotional and social meaning.
Babies surprised by an unfamiliar language
Lewkowitz and graduate student Amy Hansen-Tift also tested infants by showing them a speaker of an unfamiliar language (Spanish). The results were the same, except that the 12-month shift from mouth to eyes did not occur. The 12-month-olds continued to watch the mouth of the Spanish speaker, presumably because mastery of the language sounds had not occurred. The scientists also reported that infants watching Spanish speakers showed increasing pupil dilation between 8 and 12 months, an indication of surprise at finding an unfamiliar language.
A future tool for autism screening?
It's known that 2-year-olds with autism tend to avoid eye contact and instead watch speakers' mouths. Lewkowitz said that it's possible his study could be helpful in screening children on the road to autism. But autism researchers say there is no research showing that children who continue to look at the mouths of native-language speakers past the age of 1 year are more likely to develop autism or other communication problems than are children who switch to looking at eyes.
How is this useful for parents?
Pediatrician and author Dr. Martin T. Stein says he tells parents to "narrate their lives" to their children at each moment, to improve their language and speech development. Given this new information about how children learn language, he says he'll now tell parents to narrate their lives while looking at their children's faces.
David Lewkowitz' publications and research pages.
Keywords: infants baby language baby talk learning to talk language acquisition babies lip-read David Lewkowitz Amy Hansen-Tift Florida Atlantic University