The researchers studied 329 children, aged 2 months to 48 months, and found that for each additional hour of television exposure, there was a decrease of 770 words (7 percent) heard from an adult by the children. The study also found that the more hours spent watching television, the fewer vocalizations infants made when adults talked to them.

"Some of these reductions are likely due to children being left alone in front of the television screen, but others likely reflect situations in which adults, though present, are distracted by the screen and not interacting with their infant in a discernable manner," wrote Dr. Dimitri A. Christakis, of Seattle Children's Hospital, and colleagues.

"At first blush, these findings may seem entirely intuitive. However, these findings must be interpreted in light of the fact that purveyors of infant DVDs claim that their products are designed to give parents and children a chance to interact with one another, an assertion that lacks empirical evidence," they noted.

The researchers added that their results may help explain previous findings of a link between television viewing and delayed language development.

"Given the critical role that adult caregivers play in children's linguistic development, whether they talk to their child while the screen is on may be critical and explain the effects that are attributed to content or even amount of television watched," the team wrote. "That is, whether parents talk less (or not at all) during some types of programs or at some times of the day may be as important in this age group as what is being watched."

The study appears in the June issue of the Archives of Pediatrics & Adolescent Medicine.

More information

The U.S. National Institute on Deafness and Other Communication Disorders outlines speech and language milestones.