Monday, January 22, 2007

Neural mechanisms of dyslexia summary

[double click on image to enlarge]

As I've written before, I always look forward to skimming the contents of Current Directions in Psychological Science for brief, contemporary “taking stock” summaries of an area of psychological research, typically by prominent researchers in the domain of inquiry.

The latest issue did not disappoint. There is a nice summary of the general consensus of the neurological research on severe reading disorders (dyslexia) by the Shawyitz team. The reference, abstract, and URL link to pdf is below. Enjoy.

  • Shaywitz, S., Mody, M. & Shaywitz, B. (2007). Neural Mechanisms in Dyslexia. Current Directions in Psychological Science, 15 (6), 278-281. (click here to view)

  • Within the last two decades, evidence from many laboratories has converged to indicate the cognitive basis for dyslexia: Dyslexia is a disorder within the language system and, more specifically, within a particular subcomponent of that system, phonological processing. Converging evidence from a number of laboratories using functional brain imaging indicates that there is a disruption of left-hemisphere posterior neural systems in child and adult dyslexic readers when they perform reading tasks. The discovery of a disruption in the neural systems serving reading has significant implications for the acceptance of dyslexia as a valid disorder—a necessary condition for its identification and treatment. Brainimaging findings provide, for the first time, convincing, irrefutable evidence that what has been considered a hidden disability is ‘‘real,’’ and these findings have practical implications for the provision of accommodations, a critical component of management for older children and young adults attending postsecondary and graduate programs. The utilization of advances in neuroscience to inform educational policy and practices provides an exciting example of translational science being used for the public good.
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hayesatlbch said...

Let's see. Researchers that have believed for years that dyslexia is phonological believe that all evidence points to a phonological cause as indicated by neurological activity. I can agree with some of the arguments but if that was entirely true for all cases there shouldn't be enough overlap that only groups of dyslexics can be identified and not individuals as dyslexic.

For the same reason I am not comfortable with the conclusion that is inferred that only high IQ people may be dyslexic. It may very well be that some disadvantaged poor children with more limited language exposure and lower IQs may very well be dyslexic also and would benefit from dyslexia intervention also. Basically without even a suggested mechanism for dyslexia only occurring in high IQ individuals I don't think it can be very productive to eliminate lower IQ individuals from consideration for dyslexia.

Researchers that have studied the visual centers of the brain have also concluded that dyslexics can be grouped by their differences there, again, without being able to identify individuals as dyslexic.

Before brain researchers will be able to identify if an individual is dyslexic by scanning I suspect that they will first need to be able to determine IQ by looking at the brain alone. Having dyslexia or a poor environment both contribute to difficulties taking IQ tests with some inaccuracies resulting from both.

Here is I believe is an intelligent insight. Perhaps the reason that looking at any one part of the brain to identify dyslexia only works on groups is that there are more factors involved. Consider this scenario .
There are 3 factors involved that each contribute to the reading dysfunction known as dyslexia. Call them language processing problems, phonological problems and visual processing problems. To focus on any one factor does not give the sensitivity needed to identify individuals as dyslexic because the other two factors are not being evaluated.

I have a different agenda and that is not to forget that a minority of dyslexics describe visual problems such as moving print and missing letters that makes reading difficult. I don't see that as a phonological problem. I sell See Right Dyslexia Glasses that are guaranteed to remove any described visual problem at . For the dyslexic with a described visual problem that makes reading difficult, removing that problem can be as helpful as years of phonological instruction.

Kevin McGrew said...

John. Thanks for your thoughtful comments. In concur re: the point about high IQ. I've never bought the idea that only average or above individuals can have brain-based severe reading problems. Also, I think this article is best viewed as a summary of the predominant opinion of brain-based dyslexia research establishment. IMHO, not all severe brain-based reading problems are due to phonological deficits. In a sense, much of the established fMRI dyslexia research can be viewed as guilty of simply looking at phonological deficits simply because that is the street light that is light....there are other domains that have not received as much "lighting"...and seem to go largely ignored in the mainstream literature. Much of the research suffers from "specification error"....namely, the failure to include other possible causal mechanisms in the research design model.