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July 2013

Visual System Differences in Dyslexia Do Not Cause Reading Problems

By Carolyn D. Cowen

The jury is in on yet another long-standing debate about dyslexia. The verdict is important and nuanced.

The phonological basis for dyslexia’s hallmark difficulties in learning to read has been established for decades as the predominant explanation of dyslexia. Nevertheless, another explanation—a weakness in processing visual stimuli—has persisted and remains a subject of debate. Now, a new study provides strong evidence about the role of the brain’s visual system in dyslexia.

This study, published on line June 6 in the journal, Neuron, found that while a specific difference can be seen in the brain’s visual system in subjects with dyslexia, this difference is not the culprit behind the reading difficulties. More likely, this difference is the consequence of less reading experience. And, to paraphrase Shakespeare, saying that children with dyslexia have less reading experience than their peers is like saying that night follows day. 

This breakthrough study found that, yes, people with dyslexia do have subtle visual system differences—as many of those with dyslexia and their teachers have long reported—but, no, these visual differences do not cause the condition and its associated reading difficulties. In fact, the findings suggest, it may be the other way around; reading difficulties discourage reading, which in turn, probably means that children with dyslexia do not experience the same “reading-induced change in the visual system” that is seen in typical readers.

You may be wondering what this means for intervention. Hold that thought while we dig deeper into the research.

Controlling for Reading Experience: Visual System Differences Not Seen

Researchers used functional brain imaging to show less activity in the “magnocellular” visual system in children with dyslexia compared to non-dyslexic children matched on age. However, this difference no longer was seen when children with dyslexia were compared to younger, non-dyslexics matched on reading ability, suggesting that the observed difference might be tied to reading level. Georgetown University, where the study was conducted, provided a press release that sheds additional light on the findings:

“Our results do not discount the presence of this specific type of visual deficit,” says senior author Guinevere Eden, Ph.D., director for the Center for the Study of Learning at Georgetown University Medical Center (GUMC) and past-president of The International Dyslexia Association. “In fact, our results confirm that differences do exist in the visual system of children with dyslexia, but these differences are the end-product of less reading, when compared with typical readers, and are not the cause of their struggles with reading.”

In recent correspondence with The Examiner, Eden said:

I have had a longstanding interest in the visual system through my graduate work with John Stein at Oxford. When I came to the US and did my postdoctoral fellowship at NIH, we conducted the first fMRI study of dyslexia ever (published in Nature in 1996) and showed differences in the visual system. These appeared consistent with the behavioral and anatomical findings that had been reported on the magnocellular visual system (in addition to the phonological based problems). We did not know, however, if these differences were the cause of the reading problems, and it is this question that is addressed by this new study.

Visual System Activity: Enhanced by Reading Intervention

As part of the study, children with dyslexia received intensive reading intervention focused largely on phonological and orthographic skills (provided by Lindamood-Bell Learning Processes). The children made significant gains in reading, as expected. But another result was surprising. The brain’s visual system activity also increased, which suggests that reading helps mobilize this system.

Scientists have been chipping away at many of dyslexia’s baffling, sometimes controversial mysteries, revealing a much clearer view of the condition and sharpening the focus of intervention. This study helps render historical debate moot regarding the existence of visual weaknesses in dyslexia. They exist; but they do not cause dyslexia. This study also has important implications for intervention. If reading experience bolsters visual system function, this suggests that training the visual system will not cure dyslexia.

In the Georgetown University press release, Olumide Olulade, PhD, the study’s lead author, put it this way:

While our study showed that there is a strong correlation between people’s reading ability and brain activity in the visual system, it does not mean that training the visual system will result in better reading. We think it is the other way around. Reading is a culturally imposed skill, and neuroscience research has shown that its acquisition results in a range of anatomical and functional changes in the brain.

What is the take-away for parents and teachers of children with dyslexia? Clearly, the focus should remain on scientifically based and clinically proven reading instruction.

An excellent video abstract accompanies the Georgetown University paper—“Abnormal Visual Motion Processing is Not a Cause of Dyslexia,” in Neuron—and can be viewed by clicking here. (The full article requires a subscription to the journal, but the video abstract does not.)

Previous Dyslexia Studies: Do They Generalize to Females?

Neuroscientists at Georgetown University have been busy. In May, they published another breakthrough study (featured in The Examiner’s May issue). This one, titled “Sex-Specific Gray Matter Volume Differences in Females with Developmental Dyslexia,” was published on line in the journal  Brain Structure and Function. (There is a fee to access the full article, but its abstract and first two pages can be viewed free of charge.)

This study, which investigated dyslexia in males and females, was the first to directly compare the brain anatomy of female children and adults with and without dyslexia. Researchers found significant differences in brain anatomy when comparing men and women with dyslexia to control groups without the condition, suggesting that dyslexia may have a different brain-based manifestation tied to gender. This finding challenges assumptions that results in studies of men can generalize to both sexes (less than 20% in all previous studies have been female).

Click here and here for even more information about both studies and their implications.

The Challenge: Make a Difference in Lives

One by one, science is resolving mysteries, settling disputes, and challenging assumptions surrounding dyslexia, while delving ever deeper into its complexities. The last two decades have produced a remarkable body of work, including the breakthrough findings from Georgetown University mentioned in this article. Examiner readers and those who follow dyslexia-related issues via social media have unprecedented, almost real-time access to this exciting research as it unfolds.

The challenge, of course, is to translate this body of work into effective practices and policies that actually make a difference in the lives of people with dyslexia. In this regard, the work of The International Dyslexia Association (IDA) is more important than ever. IDA is dedicated to both the study and treatment of dyslexia and related difficulties learning to read and write.

These exciting research breakthroughs should galvanize us to achieve equally exciting breakthroughs in removing the educational barriers that undercut success not only for people with dyslexia, but also for many others at risk for reading difficulties. How can you help? One way is to promote IDA’s Knowledge and Practice Standards for Teachers of Reading. Please share it among your colleagues and friends and via social media. Partner with IDA in promoting high standards for comprehensive and rigorous training of teachers.


We thank Guinevere Eden, Ph.D., for her assistance with this article.

Carolyn D. Cowen, Ed.M, is the Social Media Editor/Strategist for The International Dyslexia Association Examiner. She also is a Founding Board Member of Literate Nation 


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