No wonder Americans call television the "boob tube". Infants vocalise less and hear fewer words from nearby adults when the TV is on, a new study of recorder-toting infants suggests.
"There's no question that human voice and human words are what babies need," says Dimitri Christakis, a paediatrician at the University of Washington in Seattle, who led the study. "The data are not yet conclusive about the fact that television is harmful, but they continue to mount."
Christakis' team equipped 329 infants, aged between 2 and 48 months, with lightweight recorders that captured every noise they heard in a 24-hour period. A computer program – shown in a previous study to be 82 per cent accurate – then determined whether each sound came from the infant, an adult or the television.
The analysis showed that for every hour of television an infant is exposed to – they don't understand television programmes, Christakis says – he or she hears 770 fewer words from adults, on average, a 7 per cent reduction. Infants watching TV also utter fewer "googoos" and "gagas" and interact less with adults than children whose parents use the off switch more enthusiastically.
Developing brain
That finding is backed up by observations made by Daniel Anderson, a psychologist at the University of Massachusetts in Amherst, and colleague Heather Kirkorian. They found that infants exposed to television hear 20 per cent fewer words from their parents during every hour of programming that they watch.
"Parents are less engaged with the children if the television is on," says Anderson, whose findings will be published in a study currently in press at the journal Child Development.
Given that a staggering 30 per cent of US households keep a television on at all times, this can have a substantial effect on an infant's development, according to Christakis.
"The newborn brain is very much a work in progress. All that cognitive stimulation is critical to the underlying architecture that's developing," he says. "Every word that babies hear, and every time they hear it, is extremely important."
'Minimise exposure'
The audio analysis software wasn't sophisticated enough to determine whether the infants were being exposed to shows aimed at infants or adults. But Christakis says that even programming aimed at children doesn't always live up to its billing. "Many of these DVDs that target infants claim that they promote parent-child interaction – which they don't," he says.
Christakis was part of a 2007 study which found that infants who watched some such programmes actually scored lower on tests of language development than children who weren't exposed to them. "The take-home message for parents is to minimise television exposure during the first two years," Christakis says, a stance endorsed by the American Academy of Pediatrics.
"Children over two learn a lot of vocabulary from television, that's very clear," says Anderson. "The real question comes with baby videos and that remains really controversial."