The Link Between Dyslexia And The Way The Brain Encodes Sounds
In the popular mind, the reading disability dyslexia is often imagined to be some kind of visual problem: not being able to see the difference between the letters “b” and “d,” for example.In fact, research shows that dyslexia is related to the way the brain processes sound. Here’s an interesting new study on this
relationship, reported by Northwestern University:“‘We have discovered a systematic relationship between reading ability and the consistency with which the brain encodes sounds,’ says Nina Kraus, a professor of neurobiology, physiology and communication at Northwestern.
Kraus her coauthor, Jane Hornickel, recorded the automatic brain wave responses of 100 school-aged children to speech sounds. The researchers found that the very best readers encoded the sound most consistently, while the poorest readers encoded it with the greatest inconsistency. Presumably, the brain’s response to sound stabilizes when children learn to successfully connect sounds with their meanings.
In prior work in Northwestern’s Auditory Neuroscience Laboratory, Kraus and her colleagues found that the inconsistency with which the poorest readers encode sound could be ameliorated through training. In an earlier study, children with reading impairments were fitted for a year with assistive listening devices that transmitted their teacher’s voice directly into their ears. After a year, the children showed improvement not only in reading but also in the consistency with which their brains encoded speech sounds, particularly consonants.
Use of the devices focused youngsters’ brains on the meaningful sounds coming from their teacher, diminishing other, extraneous distractions, said Kraus. After a year of use, the students had honed their auditory systems and no longer required the assistive devices to keep their reading and encoding advantage.
People rarely have difficulty encoding vowel sounds, which are relatively simple and long, according to Kraus. It is consonant sounds—sounds which are shorter and more acoustically complex—that are most likely to be incorrectly categorized by the brain. ‘Understanding the biological mechanisms of reading puts us in a better position to both understand how normal reading works and to ameliorate it where it goes awry,’ says Kraus.
‘Our results suggest that good readers profit from a stable neural representation of sound, and that children with inconsistent neural responses are likely at a disadvantage when learning to read,’ Kraus adds. ‘The good news is that response consistency can be improved with auditory training.’
Kraus and Hornickel’s paper, ‘Unstable Representation of Sound: A Biological Marker of Dyslexia,’ appears in the Feb. 20 issue of The Journal of Neuroscience.” (Read more here.)