Too much television may hamper a baby's ability to learn language and speak, according to a new study.

Dr. Dimitri A. Christakis, of the University of Washington in Seattle, and his team said their findings are worrying because exposure to television can lessen human interaction which is essential to learn language and develop broader thinking.

"The effect of having a television on is that babies do speak less and they're spoken to less," said Christakis.

The researcher studied 329 children, aged two to 24 months old who wore pager-sized devices that recorded all audible sounds at the child's chest level.

Children wore the device while they were awake for one day each month. The average number of recorded sessions per child was about eight. For the first three months, parents were told to turn off all sources of ambient noise, such as TV or radio, while for the last three months, they were told this wasn't necessary.

The researchers used a software program developed by the LENA Foundation of Boulder, Colorado, which helped fund the study, to analyze the audio recordings.

The more hours of TV recorded in a session, the fewer times a child spoke, the fewer words he or she heard from adults, and the fewer conversational turns the child took.

For every additional hour the TV was on, the number of adult words spoken fell by 771.

The researchers, who reported their findings in the journal Archives of Pediatrics & Adolescent Medicine, said adults speak about 941 words an hour.

"It's almost as if television displaces talk completely," Christakis said.

While some of the reduction in speech could have been because children were left alone in front of the TV, he added, it's also likely that adults were distracted by the TV and less likely to interact with the child.

He pointed out that 30 per cent of U.S. households admit to having the TV on all the time, even when no one is watching. The findings also call into question claims by makers of DVDs and videos for kids that these products promote parent-child interaction.

"I get asked by parents all the time how am I supposed to make dinner if I can't sit my child in front of the TV," Christakis said.

He suggested an alternative would be to sit the child on the kitchen floor with a pan and a spoon to play with.