Dyslexia may stem from how the brain processes sight and sound together - rather than simply a problem "decoding" the written word - reported researchers from Wake Forest University Baptist Medical Center today at the annual Society for Neuroscience meeting in New Orleans.
"For the first time, there is evidence that dyslexia is a multi-sensory disorder," says Mark Wallace, associate professor of neurobiology and anatomy. "It isn't solely a problem with visual processing or with language. This is a novel way of looking at the disorder."
Wallace said the finding could lead to a simple test for early diagnosis - even before school age - and better methods for teaching people with reading disabilities.
"Until now, experts have thought that dyslexia was either a visual processing problem or a problem involving language areas of the brain," said Wallace. "But our study suggests that it's actually a problem combining visual information with auditory information."
For the study, 36 people with dyslexia and 29 people without the disorder were tested on their ability to tell which of two lights appeared first.
The participants sat in front of a video monitor and pushed a button to report their perception. In both dyslexic and non-dyslexic individuals, sounds presented through headphones were found to help performance.
When lights were accompanied by a sound, participants were better at discriminating lights presented very close together in time. For participants without dyslexia, the sound needed to occur within about 150 milliseconds of the light to get such a benefit. Longer intervals failed to help. People with dyslexia, however, showed benefits even with delays as long as 350 milliseconds.
"In essence, the brain fuses things that happen very close together in time, and for dyslexics, this fusion appears to happen over longer periods of time than in non-dyslexic persons," said Wallace. "We believe this time difference is the fundamental problem that dyslexics have when learning to read. Early reading involves matching what you see with what you hear. But in dyslexics, we believe this matching process is disrupted. The sights and sounds of words are inappropriately matched. So, while the average person very quickly matches the written word "dog" with the sound "dog," a child with dyslexia may have much more difficulty."
Lynn Flowers, a co-researcher, said the study demonstrates that lifelong dyslexic individuals integrate visual and auditory information differently than good readers. "The study did not use letters and speech sounds, suggesting that there may be a very basic sensory integration deficit in dyslexia that underlies reading difficulties," Flowers said.
Wallace said the finding suggests better ways to teach people with reading disabilities.
"We believe that the most effective approaches will use a combination of visual and auditory cues," he said. "Because the brain is very changeable in young children, we hope that by using such methods early, we could change the brain's architecture so that the children could process sight and sound normally."
He said the finding provides a basis for the effectiveness of a method called the Orton-Gillingham approach that relies on the use of sight and sound together to teach reading.
Wallace said the test could be used for early diagnosis because it doesn't involve reading, just the ability to push a button when a light comes on.
The researchers are now using functional magnetic resonance imaging, a technology for viewing the brain and seeing which areas "light up" when they are activated, to learn more about the disorder.
"We're exploring what happens in the brain when a person with dyslexia reads," said Wallace. "The future is exciting. We hope this is the first in a long series of studies to learn more about this common and often debilitating disorder."