Toddlers may be too young to understand Oprah's weight loss secrets or guess the consonants on Wheel of Fortune. But that doesn't mean adult television shows have no impact on them.

According to a new study, background TV that's prevalent in many homes may be detrimental to children's development - even when they aren't paying attention. The constant stream of sounds and images disrupt children's imaginary games with trucks or dolls, and hinder their ability to focus.

"If you talk to parents about what they're concerned about, it's almost always the scary stuff and the violence," Daniel Anderson, a study co-author and professor at the University of Massachusetts, said yesterday.

"They don't tend to think of games shows or sports or Oprah as having any kind of negative effect."

However, the study of 50 children ages 3, 2, and 12 months found that background TV "can be a very affective distraction," from the kind of play that's critical to helping children learn and develop, Anderson said in an interview from Amherst, Mass.

Children at those ages have a limited ability to sustain their attention and are just beginning complex and symbolic play. So giving them uninterrupted periods to practise and learn is critical, he said. Pretend play allows them to develop important tools by refining motor skills, exploring objects, role-playing and problem-solving.

The study, which appears in the July/August issue of the journal Child Development, was conducted in a lab set up as a playroom with toys and a television. Each child engaged in solitary play for half an hour with a television off and 30 minutes while an episode of Jeopardy!, including commercials, played in the background.

Researchers observed that when the TV was on, the children looked at the screen for only a few seconds at a time and less than once per minute. But it was enough to make a difference.

"Specifically, compared to no television, there was less play overall, shorter play episodes, and shorter bouts of focused attention in the presence of background television," the researchers concluded.

The kids who were exposed to the most background television in their daily lives showed no better ability to block it out, Anderson added.

There has been much debate on how TV affects very young children, but most has focused on educational TV programming or kiddie DVDs like The Wiggles. The American Academy of Pediatrics recommends no television for children under 2, and most psychologists caution that screens are no substitute for human interaction.

However, there has been little research on the impact of background television, even though a 2006 survey found that three-quarters of American families have their televisions on "almost half the time" regardless of whether anyone is watching.

Marie Evans Schmidt, lead author of the study and a research associate at the Center on Media and Child Health at Children's Hospital in Boston described it as "a potentially chronic environmental risk," and said parents should limit their young children's exposure.