Dyslexia Revisited

RamaLast month I referenced a new bill that was signed into law in New Jersey recognizing dyslexia as a distinct entity worthy of special educational consideration.  This bill is making its way around the country, so look for it in your state soon if it hasn’t already been adopted.  Make sure your networks know about the Joint Organizational Policy Statement of the AOA and AAO on Vision, Learning and Dyslexia, as well as the new position statement from the AAO on Optometric Care for the Struggling Student.  Last week I shared the discovery of a hidden jewel, the Encyclopedia of the Human Brain.  Volume 2 contains a marvelous and succinct overview of Dyslexia by H. Branch Coslett, M.D., a neurologist who is a Professor at the University of Pennsylvania’s Center for Cognitive Neuroscience.

Dyslexia Graphic


The graphic above is from Dr. Coslett’s overview and is largely self-explanatory.  It’s a reminder that one cannot discuss dyslexia without a full, and I stress full appreciation of the role of visual processing.  Dr. Coslett introduces his material by noting that the ability to read is a relatively recent development that is dependent on both the capacity to process complex visual stimuli and the ability to link the visual stimulus to phonologic, syntactic, and other language capacities.  What he writes next should be common knowledge:

“Reading requires that the visual system efficiently process a complicated stimulus that, at least for alphabet-based languages, is composed of smaller meaningful units—letters. In part because the number of letters is small in relation to the number of words, there is often a considerable visual similarity between words (e.g., “structure” vs “stricture”). Additionally, the position of letters within the letter string is also critical to word identification (consider “mast” vs “mats”). In light of these factors, it is perhaps not surprising that reading places a substantial burden on the visual system and that disorders of visual processing or visual attention may substantially disrupt reading.”

Regarding the anatomic basis of dyslexia, Coslett concludes:

“A variety of experimental techniques, including position emission tomography, functional magnetic resonance imaging (fMRI), and evoked potentials, have been employed to investigate the anatomic basis of reading in normal subjects. Although differences in experimental technique and design inevitably lead to variability in reported sites of activation, there appears to be at least relative agreement regarding the anatomic basis of several components of the reading system.

As previously noted, most accounts of reading postulate that after initial visual processing, familiar words are recognized by comparison to a catalog of stored representations that is often termed the visual word form system. A variety of recent investigations involving visual lexical decision with fMRI, viewing of letter, and direct recording of cortical electrical activity suggests that the visual word form system is supported by inferior occipital or inferior temporooccipital cortex.”

The role of vision in dyslexia is apparent to anyone willing to connect the dots.




5 thoughts on “Dyslexia Revisited

  1. Watching the Olympics, they were commentating about the skating career of Charlie White and Meryl Davis of Ice Dancing. They stated that she felt more comfortable pairs skating than alone because “her dyslexia made her have poor depth perception.” I just couldn’t help but share this as all I can do is laugh because I’m sure her poor depth and dyslexia are not directly related but both of binocular vision origin. Media perpetuating misinformation.

  2. Thanks for the “HUGE” reference book volume, I’m afraid if I bought it I’d have to retire and likely never finish it! Kidding aside, there is one very big piece that Coslett misses in his diagram. You go to the a book with anticipation and previous book knowledge and thus try to “approximate” what you see. I believe there is much subconscious processing going on before you recognize word images…. For example, if I was to read, “John went to the store in the __________” I would recognize automobile far faster than airplane because of what I know about the world. So previous book experience and language experience all play a critical part of how you read. A good reader uses as little visual information as possible to match expectations of print. So it isn’t necessarily that we look and figure something out from scratch(unless its perhaps a brand new word ;-)!, but we have already possibles we are subconsciously processing and looking for. Maybe we should put more time and energy into the prevention of reading problems vs. simply trying to rehabilitate them.

  3. By necessity, Coslett’s diagram is a simplification. But I would also comment that your example doesn’t seem to disambiguate the phrase much if at all. “John went to the store in the _______ ” — you’re presuming that that top-down dil-in probabilities relate to transportation but it could just as easily be location. For example, John went to the store in the mall. Context has a great deal to do with anticipation and prediction in encountering stimuli in a wide variety of domains. However I do fully agree that prevention is preferable to patchwork in dealing with reading problems.

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