KEY POINTS:
Doctors are being urged to help parents reduce the amount of time their children spend watching television.
Dr Shari Barkin, an American paediatrician visiting New Zealand for the Brainwave Trust, says preschool children who watch TV for more than one hour a day, and older children who watch
for more than two hours, are more likely to develop aggression, learning difficulties and attention-deficit disorders.
She has just led a five-year experiment across the United States, Canada and Puerto Rico in which paediatricians cut children's TV viewing by an average of 45 minutes a day.
They used a technique called "motivational interviewing" where they asked parents whether they were concerned about their children's TV viewing, talked about what the parents could do about it, and then gave them free minute-timers to help them enforce viewing time limits.
The idea that watching TV makes children more aggressive is still controversial. Waikato University media studies professor Geoff Lealand, who has just co-authored a study of media use by 860 children aged 8 to 13, said he was sceptical about the claim.
"There is a naivety to it in that parents will be distracted from their serious family problems and blame TV.
"The two primary sources of violence in society are two things we are unwilling to do anything about - private car ownership, which causes more violence than anything else, and alcohol."
His local study found an even split between families who laid down rules about their children's TV watching and those who did not, and found that 47 per cent of children had personal access to a TV set - often in their own bedrooms.
In Dr Barkin's US study, only 36 per cent of children had TV sets in their bedrooms and only 7 per cent of parents said they did not impose any limits on their children's viewing.
A quarter of the parents (23 per cent) restricted what children could watch, and when, on TV, 11 per cent only discussed things their children saw on TV, and 59 per cent used a mixture of restrictions, discussion and simply watching TV with their kids.
Dr Barkin said children's brains developed by "serve and return", as in a tennis match, where their experiences built up brain connections, and that inbuilt "wiring" then encouraged them to respond to new experiences in the same ways.
She said the blue range of the light from TV and computer screens affected a child's hormones.
"If you look at what's going on in your brain [when watching TV], your brain waves move into stage one hypnosis," she said. She cited other studies showing that TV exposure was associated with aggression, desensitisation, poor moral reasoning, obesity and a lower attention span.
However, other studies found TV associated with more positive social interactions, higher intelligence and better school performance.
"The difference exists in the content of the programming and the time spent engaged in media use."
SCREEN TEST
* The American Academy of Paediatricians recommends zero TV for infants under 2 and no more than one to two hours a day of educational, quality programmes for older children.
* In fact, US children aged 2 to 18 use TV and other electronic media for an average of more than four hours a day.
* Ratings show that NZ children aged 5 to 14 watch TV for two to two and a half hours a day.
* No data is available for NZ preschoolers.
