It has been known for several years that overlays and tinted spectacles can help children with dyslexia. But their use remains controversial, partly because no one knows exactly how they work.
Research by the University of Essex, to be published later this year, shows that colour helps many people with nerve-related eye problems such as migraine to read more easily.
But a second study involving all 380 children at The Avenue middle school in Norwich may provide other important clues. The pupils have undergone reading-rate tests, to see if they improve when tinted overlays are used, and how long that improvement lasts once use is stopped.
The project is led by Professor Arnold Wilkins, head of the visual perception unit at the University of Essex, who hopes to replicate earlier findings that such overlays have a "carry- over" effect.
Last year, his team discovered that about 40 children who had been using overlays for four months could read 10 per cent faster with or without colour.
"Overlays may act like a temporary prop," he says. "When you're learning to read, text is a jumble of meaningless shapes, but then reading becomes more of a linguistic task. Using coloured overlays may get children over that hump from letter-by-letter reading to word recognition."
In September, researchers tested the Norwich children's rate of reading random-order, closely-spaced words. The following month most of the 8 to 11-year-olds began using overlays, and at the end of February, their reading speed will be re-assessed. They will also be tested to check whether they read phonically or by word-shape recognition.
"My idea is gradually to get whole counties screening children for colour problems," Professor Wilkins says. "I hope every school will have at least one testing kit and a teacher trained to use it, with perhaps whole classes screened early in their school career."
Essex University is to host a one-day conference on colour in January 2000. Details: 01206 872 381. For information on overlays: National Colour Helpline on 01206 872 130