Sound, not sight, major cause of dyslexia

by Sarah Sipek
Mar 6, 2013

For 10-year-old Christopher Anderson, school was a cloud of distractions that he couldn’t seem to break through. He had trouble reading and paying attention to his teacher was nearly impossible with all the competing noises.

All that changed when the child was given a personal radio receiver that allowed him to tune out the static and tune in to his studies.

Researchers at Northwestern University’s Auditory Neuroscience Laboratory investigated the underlying biological causes of dyslexia and found that a child’s reading ability is directly related to how efficiently the brain encodes sound. The study’s results, published in the current issue of the Journal of Neuroscience, suggest that personal listening devices can improve reading ability by limiting the sounds that the brain encodes.

Dyslexia is a learning disability that impairs a person’s ability to either read or comprehend the written word. According to Nina Kraus, the study’s co-author and a professor of neurobiology and physiology at Northwestern University’s School of Communication, reading ability is often associated with auditory skills, including auditory memory and attention as well as rhyming ability.

The National Center for Learning Disabilities estimates that 15-20 percent of school-aged children suffer from some language-based learning disability. The most common is dyslexia.

Jane Hornickel, a co-author of the study and post-doctoral fellow at Northwestern, said the findings coincide with the current understanding of how children learn to read.

“The first steps are learning the meaningful sounds of speech,” she said. “Children are taught what each letter sounds like, so when they are given a word like, ‘cat,’ they can match up each letter with its sound, and sound out the word.”

Much like muscle memory, repetition teaches the brain to automatically associate a sound with a letter. The technique is known as mapping and depends on the brain’s ability to consistently respond in the same way when presented with a sound, she said. Northwestern University researchers have found that personal FM radios help children with dyslexia to better encode sounds, which improves their reading ability.

The study tested 100 participants primarily from the Hyde Park Day School, which specializes in teaching children with learning disabilities. Hornickel and her colleagues used an electrocardiogram to measure the brain’s responses to 6,000 speech sounds.

“A clear hierarchy emerged,” she said. “The best readers showed the same level of brain response each time a sound was presented to them, average readers were in the middle and the poorest readers had little consistency in brain response.”

The results were not surprising to Katherine Fouks, a certified special education teacher and principal of Acacia Academy in La Grange Highlands, a private school that offers programs for students with a range of learning disabilities including dyslexia.

“Approximately 80 percent of children with dyslexia have auditory issues,” she said. “It has nothing to do with their intelligence. It’s just that they’re deficient in that sensory area.”

Acacia Academy uses a multisensory approach to dyslexia therapy that includes both seeing and hearing a word as well as techniques such as tapping out consonants to emphasize word sounds.

In Hornickel’s study, children were fitted with assisted listening devices in order to correct the encoding problem.

“Essentially it’s an FM radio attached to a child’s ear,” Hornickel said. “The teacher wears a microphone and her voice is transmitted directly into the students ear. All the other background noise and distractions are blocked out.”

Students who wore the device for an entire school year improved their encoding consistency and became more efficient readers, she said.

Particularly encouraging was the improved ability in encoding consonants.

“Vowel sounds are easy,” Hornickel said. “They are loud and robust so the brain locks onto them. Consonants are shorter and more difficult to recognize.”

Despite the positive results, Fouks warned against assuming that this is the only effective treatment for dyslexia.

“Dyslexia must still be treated on an individual basis,” Fouks said. “It’s about finding the child’s weakness and working with them on phonics or spelling or auditory processing. Treatments like that work 100 percent of the time.”