Over one third of American pre-schoolers live in homes where the television is on most of the time, even if no one's watching, and a new study says the effect of background TV on interactions between parents and young children is definitely negative.

The researchers studied about 50 1-, 2-, and 3-year-olds, each of whom was with one parent, at a university child study center.   Half of the one-hour session, parents and children were in a playroom without TV; in the other half-hour, parents chose an adult-directed program to watch , like Jeopardy. The researchers observed how often parents and children talked with each other, how actively involved the parents were in their children's play, and whether parents and children responded to each other's questions and suggestions.

When the TV was on, the researchers found, both the quantity and the quality of interactions between parents and children dropped. Specifically, parents spent about 20 percent less time talking to their children and the quality of the interactions declined, with parents less active, attentive, and responsive to their youngsters.

"Although previous research found that background television disrupts young children's solitary play, this is the first study to demonstrate its impact on the quantity and quality of parent-child interactions," according to the researchers. "Given that high-quality parent-child interaction plays an important role in children's development, the study challenges the common assumption that background TV doesn't affect very young children if they don't look at the screen," the researchers added. "We need to pay greater attention to children's early, chronic exposure to TV."

The study in the journal Child Development was done by researchers at the University of Massachusetts.