How the brain processes speech in a noisy environment could be a marker for dyslexia
Between 10 and 15 % of people have dyslexia. According to a recently published report, this means that dyslexia is the most common specific learning difference, affecting between 6.6 and 9.9 million people in the UK alone. Between 800 000 and 1.3 million of these are young people in education. In the UK over 80 % of dyslexic children leave school without a diagnosis, writes the Chair of the UK’s All-Party Parliamentary Group (APPG) on Dyslexia and other Specific Learning Difficulties (SpLDs). This often has a substantial impact on their academic and job prospects. The causes of the condition remain unclear, but work carried out by Mathieu Bourguignon, a researcher based at the Centre for Research in Cognition and Neurosciences, ULB, Brussels, considered the neuronal basis of dyslexia and the difficulty dyslexic readers have processing speech in noise.
Reading strategies
The phonological deficit in dyslexia, and its accentuation in the presence of noise were first identified in the early 80s. Although it is now acknowledged that dyslexia is a multifactorial disorder, the phonological deficit is still seen as the dominant factor. To appreciate the DysTrack project’s findings, it is important to understand how we read. “There are two different strategies,” explains Bourguignon, who received support under the Marie Skłodowska-Curie Actions programme. “The first is to read words letter by letter, converting each letter into its corresponding sound. The second is to read words at once, directly recognising them based on their visual image. “The first strategy is used to read unknown words, and when learning to read. The second strategy is the hallmark of fluent reading.”
An insight into how the brain processes speech
When neurons activate, small currents flow through them. These generate magnetic and electric fields that are measurable on the scalp, using appropriate sensors. The technique, called ‘magnetoencephalography’, was used by DysTrack to evaluate how the subjects’ brain activity correlated with some properties of speech signals. All in all, 99 children aged 6–12 participated in the study, 26 of whom had been diagnosed with dyslexia. All were native speakers of French. Expert neuropsychologists evaluated each participating child’s reading abilities, memory, language abilities, IQ, and other relevant skills. The children listened to around 20 minutes of a story with different types of noise played concurrently. Their brain activity was recorded using magnetoencephalography. In that setting, the researchers could correlate reading abilities with the degree of synchronisation between brain activity and speech signals, in the different noise conditions. The researchers found a modest correlation of 0.4 between measurements of the brain's ability to identify speech in cocktail-party noise and the maturity of the second reading strategy. “These results are very promising. The relationship between the ability to distinguish speech in a noisy environment and successful reading opens up new avenues of diagnosis,” says Bourguignon, “but more work would be needed to turn them into a successful application to detect dyslexia.”
From research to diagnostic tool – what comes next?
An example of potentially useful, follow-up research would be to establish if the technique can be made more accessible. “It would be fascinating to see if similar results could be obtained using more widely available electroencephalography systems.” Bourguignon, who wrote up his findings in the paper ‘Cortical tracking of speech in noise accounts for reading strategies in children’, is currently conducting a study to evaluate to which extent such markers measured in children, before they learn to read, predict their future reading abilities.
Keywords
DysTrack, dyslexia, brain activity, specific learning difference, speech, noise, brain, diagnosis, magnetoencephalography, reading
