Watching TV is likely to set back the development of language skills among children, says a new study.
Young children and their adult care givers were found to utter fewer vocalisations, used fewer words and engaged in fewer conversations when watching TV.
The population-based study, completed in the home environment, was led by Dimitri A Christakis, paediatrics professor at the University of Washington (U-W) School of Medicine.
"We've known that television exposure during infancy is associated with language delays and attentional problems, but so far it has remained unclear why," said Christakis.
"This study is the first to demonstrate that when the television is on, there is reduced speech in the home. Infants vocalize less and their care givers also speak to them more infrequently."
The study looked at infants aged two months to four years old; a total of 329 children were studied. The children wore a small, business card-sized, two ounce digital recorder on random days monthly for up to two years.
A specially designed vest with a chest pocket held the recorders at a specific distance from the mouth, and captured everything the child said and also heard during continuous 12 to 16 hour periods.
The study found that each additional hour of TV was also associated with a decrease of 770 words the child heard from an adult during the recording session.
This represented a seven percent decrease in words heard, on average. There were significant reductions in both adult female and male word counts. From 500 to 1,000 fewer adult words were spoken per hour of TV, said an U-W release.
"Adults typically utter approximately 941 words per hour. Our study found that adult words are almost completely eliminated when television is audible to the child," added Christakis.
These findings were published in the June issue of Archives of Paediatrics & Adolescent Medicine.