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Understanding the Causes of Dyslexia for Effective Intervention

Dr. Martha Burns

Dr. Martha Burns is a noted neuroscientist, author, and leading expert on how children learn.
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For most of the 40-plus years the term "dyslexia" has been in existence -- and although the diagnosis has long been considered a "learning disability" -- it has been based on comparisons with average readers. Simply put, a child could be diagnosed with dyslexia if he or she shows an IQ in the "normal" range but falls at or below the 10th percentile on standardized reading tests. This cut-off has been arbitrary, often varying from district to district and based on Response to Intervention (RTI) criteria. As a result, a child who falls at the 12th percentile might be considered a poor reader while a child at the 10th percentile would be diagnosed with dyslexia.

For parents who have a child diagnosed with dyslexia, it is obvious early in the educational process that their bright child is not just behind in reading, but dumbfounded by the written word. A child with dyslexia seems to struggle at every turn.

Special educators, neurologists, and psychologists have understood that, too, and since the 1970s have assumed dyslexia has a neurological basis. "Dyslexia" stems from the Greek alexia, which means "loss of the word," and was the diagnostic term used when adults lost the ability to read after a brain injury. Dyslexia was a term adopted to confer a lesser, though still neurologically-based, form of reading impairment in children. However, determining the neurological basis has been elusive until recently.

The Search for a Neurological Basis

In early attempts at researching the underlying causes of dyslexia in the 1970s, there were no technological medical procedures to study brain processes that might be involved in reading normally or abnormally. Because of the inability to determine the neurological cause(s) of dyslexia, in some educational circles it became synonymous with "developmental reading disorder," and the cause was deemed unimportant. Rather, the goal was to develop and test interventions and measure their outcomes, without an effort to relate the interventions to underlying causation.

A major limitation to that approach is that it is symptom-based, yet determining the cause is essential to identifying an effective solution. When we clump children together into a single diagnostic category based on test scores, we not only fail to address what might be causing the dyslexia, but we also ignore variability in performance that limits our ability to identify individual differences.

Fortunately, advances in neuroscience, buttressed since the late 1990s by neuroimaging and brain electrophysiological technology, have led to an emerging consensus about the causes of dyslexia -- underlying capacities essential for learning to read, which emerge through brain development, are less developed in children diagnosed with dyslexia.

And the best news is that those processes are amenable to carefully designed training approaches.

The Dyslexic Brain

In the early to mid-2000s, research on the underlying basis of dyslexia pointed to a primary problem with the phonological processing of speech sounds. Early research, summarized in Stanislas Dehaene's Reading in the Brain (2009), identified problems with phonological awareness, or the ability to segment words into their component speech sounds. More recent research has delineated why that problem exists.

These findings have led to an emerging consensus, well summarized by Jane Hornickel and Nina Kraus in the Journal of Neuroscience in 2012: dyslexia is primarily an auditory disorder that arises from an inability to respond to speech sounds in a consistent manner. And Finn and colleagues at Yale published research in August 2014 (PDF, 4.7MB) indicating that this underlying problem with perception of speech sounds, in turn, affects the development of brain networks that enable a student to link a speech sound to the written letter.

Based on this research, reading interventions for dyslexia should be most effective if they combine auditory perceptual training and memory for speech sounds (phonological memory) with exercises that require relating speech sounds to the written letter (phonemic awareness and targeted decoding). And, in fact, neuroscience research bears that out. Temple et al (2003) used fMRI to show that when a program with that type of intervention was used intensively (five days a week for six weeks) with 35 students (as well as three adults) diagnosed with dyslexia, not only did decoding and reading comprehension improve significantly, but brain regions active in typical readers during phonological awareness tasks were activated.

Added to the neuroscience research on causation is additional scientific research conducted by education specialists on variability in patterns of dyslexia and the importance of individualizing interventions. Some children diagnosed with dyslexia read words as a whole and guess at internal detail, showing major problems with phonological awareness. But other children may over-decode to the point that they have trouble reading irregular sight words and read too slowly to comprehend what they have read.

Ryan S. Baker and his colleagues at Columbia University, Polytechnique Montréal, Carnegie Mellon, and other universities are researching the factors necessary for effective tutoring of students with learning issues (PDF, 682KB). Their research indicates that an effective tutor is one who considers variability and has the ability to diagnose what a student knows and does not know, and then adapt interventions to the diagnosis. For example, if a student has trouble with decoding, interventions that emphasize phonological awareness and provide additional practice with decoding are often helpful. But for children who over-decode, programs that build fluency through repetitive guided oral reading practice may be more useful. Baker and his colleagues have taken this research an extra step to determine the most effective intelligent tutoring systems -- technological interventions that can free up the teacher by providing adaptive tutoring programs individualized to each student.

The Potential to Retrain the Brain

Our understanding of dyslexia has come very far in the past 40 years, with neurophysiological models developed in just the past five years explaining the underlying capacities required for reading and the best methods for individualized adaptive interventions. Fortunately, treatment options have kept pace with the research, and children with dyslexia today have the potential to train their brains to overcome the learning difficulties that earlier generations were destined to carry with them for a lifetime.

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John Zoccola's picture

Thank you for this article, Dr. Burns. Education Week is hosting a webinar called "Every Child Reading," featuring acclaimed researched and educator. Margie Gillis, on October 28 at 2pm EST.

One of the key subjects covered to be covered will be how teachers can ensure that all children, including millions impacted by dyslexia--the most common type of reading disability--learn to read and write proficiently.

I think you will find it helpful and insightful. Here is a link which will take you to the description and registration page:

Thanks again for the great information.

Rowe Kaple's picture

The term Dyslexia. has always been confusing to everyone. It originally was conceptualized because of those who exhibited directional confusion. This became combined with reversals and inversion and backwardness.

It is my conviction from the studies I have conducted examining movement behavior, was because we did not understand that for many, the human mind was capable of using movement directionality from two sides. This being it's top side and it's opposite movement side.

Because of this ability to sense in two different directions, when learning to write many who had this ability unknowingly used the bottom sense to learn writing letters. Unfortunately because the condition was unrecognized, those many bright minds, were detoured from connection of the sense of feeling the shapes of written words with how they were heard and seen. This invisible condition slowed down their progress, especially when learning phonics.

Consequently because it was not recognized for what it was, phonics became the target for remediation. Consequently, Dyslexia and what it originally implied was lost.

And, yes, motor behavior is a difficult to fMRI, another problem with correctly identifying RPS (reversed positioning sensation).

Rowe Kaple's picture

The original research for the information above:
Physical and Behavioral Markers Help Identify Written Language Disability (WLD) Related to Attention Deficit Hyperactivity Disorder (ADHD)
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Dr. Ariful Haque's picture
Dr. Ariful Haque
Editor in Chief at International Journal of Microbiology and Mycology

Very interesting article and we should do more research dyslexia to overcome this challenge. And also we need to understand the patient of dyslexia.

JL's picture

This is a great synopsis of some of the current research and new ideas about dyslexia. What is frustrating for me is that early intervention rarely takes place in public schools using a wait and see approach that makes kids feel like they are dumb when they are not (often quite intelligent, but frustrated by school and literacy). Part of the problem is that dyslexia is not in the DSM-5, so school based evaluations and outside psychological assessments only come up with a "specific learning disability" while being anything but specific for teachers.

Lastly, I wonder about the phonological and auditory aspect leaving out what I see in what I have always assumed were typically dyslexic children, including my own. The difficulty with spelling often results in quite phonological spelling patterns, but trouble with vowels patterns that are often silent when auditory. My daughter uses the sight word in context to ignore much of the middle of the word, often getting it right. And I don't often see children who need reading support who also have speech or articulation issues. This makes me curious to know if there is some kind of visual component that has not been discovered through the current research. There does seem to be an anecdotal connection to the reversals, and being left handed or ambidextrous with children who have trouble with conventional spelling. Has anyone seen any research on this aspect of dyslexia (or if it is something different)?

Jodi's picture

This is an interesting article. It was interesting to read on the current research and ideas about dyslexia. I teach first grade and I am concerned that one my students may have dyslexia. This article gave wonderful insight into this topic.

MomFS's picture

My son was deemed dyslexic by his school. He is in third grade, age 9.
He scored a Full Scale IQ 123(94%ile) on the Wechsler Intelligence Scale for Children
with Verbal Comprehension 118 (88%ile), Visual Spatial 122 (93%ile), Fluid Reasoning 137 (99%ile), Working Memory 107 (68%ile) and Processing Speed 89 (23%ile).

It seems clear from the tests that his Working Memory and Processing Speed need work.
So how do I help him get better at reading and overcome the stress that comes with reading? What resources are available to me as a parent to help train my child?

Rowe Kaple's picture

Read:Effects of Physical Rotational Movement Difference and Handwriting Position on Academic Achievement and Learning Disabilities was published in Vol. 6 No.3, 2015. The DOI is 10.4236/psych.2015.63024
It gives you information regarding how fixing his handwriting can have major impact on reading.


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