Monday, September 24, 2007

Different Types of Dyslexia

More progress in identification of different types of dyslexia:

From the Hansen group at Oxford (college dyslexics) Excerpt: "The results revealed a striking heterogeneity of profiles. Nine dyslexics exhibited only a phonological deficit; one a phonological and a visual magnocellular deficit; a further three a phonological and a cerebellar deficit; two either a cerebellar or a visual magnocellular deficit."

These findings once again highlight the importance of comprehensive assessments in the diagnosis of dyslexia, and reinforces the "more than reading" aspect of the condition.



What this field really needs are more case histories of dyslexic individuals throughout the life cycle. Scientific research is too narrow in their selection of experimental endpoints; what we do not know is how dyslexia unfolds from early childhood into successful adulthood. Knowing more what the different developmental variations are will help us target educational or other remediations as well as know when to avoid pointless frustrations and learn how to wait and /or apply accommodations.

From an imaging group (below), more support for heterogeneity in dyslexia presentation; this recent volumetric study from Stanford suggests there are many sites of potential differences among dyslexic vs. non-dyslexic groups. It's not just a reading / phonology disorder. Areas that "light up" suggest anatomical differences that affect visual processing, memory, and motor planning.




Cognitive Profiles of Adult Dyslexics pdf
Brain Differences Between Dyslexics and Non-Dyslexics

10 comments:

  1. Agnes6:25 AM

    I am fascinated by this subject; I have a daughter who I suspect is dyslexic in some way, perhaps mildly, but has been identified as gifted. She's in fifth grade at a public elementary school and because she maintains decent grades and is in the weekly pullout class she would not be a candidate for any extra help. I have tried to talk to the GT teacher but she is unhelpful (not that she means to be; she just doesn't seem to know much). I noticed that my daughter had rather a large dicrepancy in her scores on a cognitive skills test and when I approached people at the school they looked at me as if I was some sort of curiosity --which on some level I can understand as there are lots of kids who actually have serious problems coping with the work at their grade level and passing proficiency tests, etc. I'm not currently in a position to get her tested professionally. I need to do some reading and this web site seems to be a good place to start. Thanks!

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  2. Anonymous7:14 AM

    I really appreciate you posting this report as it confirms what I already knew about my dyslexic son. Several dyslexic teachers stated that dyslexia was only a phonological problem. However I was certain that he was also dealing with visual, auditory, and memory processing issues. After first working to improve his slow processing I was then able to move to improving his phonological issues with success.

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  3. Anonymous9:37 AM

    I am so happy to find this blog. I have a four year old son in kindergarten. He is having difficulty with eye contact, attention span and eye hand coordination. He appears "out of it" although he is very bright. He knows his alphabet and all the sounds the letters make but he balks when he has to do any close up work. At the age of twenty three months he had surgery to correct strabismus in both eyes. The difference in him was so dramatic he was like another child - as if he was seeing for the first time. I thought that was it for that problem. I do not know if he is dyslexic or it goes back to his strabismus problem. He was tested by the school district and the visual motor integration ,in the many tests he was given, was from 53 to 56 ( very low scores). The teacher basically does not want him in her class because of his needs. We have made an appointment with a behavioral optometrist and hopefully will get some answers.

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  4. First, let me check my understanding on the concept of "visual magnocellular deficit".

    My understanding is formed in part from this

    http://hubel.sfasu.edu/courseinfo/SL99/MAGNOC.HTM


    It was proposed that when you read, light strikes the photoreceptors in the retina, from which information is processed in the midbrain by the magno and parvo cells. After the information passes through these two types of cells, it moves to the visual cortex for further processing. This major pathway is slowed down by an abnormality in the dyslexic mind, causing the two kinds of visual information to be presented in the improper sequence. (Newman, 1998)

    In other words, the deficit is in the visual processing pathway, and so is not something that can be remediated by (for example) special lenses or colored overlays.

    However, it is in some sense a question of the timing in processing in the brain.

    Secondly, I'd also like to comment on the Hansen group's reported finding: (a) (N=9) is danged small and (b) all the subjects studied were previously identified as dyslexic.

    As to (a): I'd be a lot more impressed by these findings if N=90 or even better yet, N=900.

    As to (b). Well. The subjects in the study were Polish adults. I do not know enought about the Polish language, the Polish educational system, or the Polish approach to dyslexia to comment. One example query: The subjects of the study are all college students are all either college students or college graduates. That is not a random sample of persons with dyslexia. As an example: what percentage of children with a dyslexia diagnosis at age eight in the US earn a college degree? The percentage is surely <100% -- therefore, sample bias (in other words, persons with dyslexia who did not enroll in college have been excluded from the sample).

    Finally I'd like to recommend to the regular [English language] readers of ENLB a new book, Proust and the Squid, by Maryanne Wolf (ISBN:0060186399)

    Professor Wolf's book is a lucid exegesis of how reading developed, and how the brain has recruited structures, previously used for evolutionarily-advantaged activities, to manage the reading task.

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  5. Thanks for your comments, everybody.

    We welcome studies like this even if the sample is small and "not representative." What is representative anyway? There are dyslexic students who fail to make it through the K-12 system, and then others who are in college, but there is a need to document the different presentations for all of these groups.

    Beware of the need for "n" in every study. The greater the "n", the fewer the tests that can be performed on them. It is a trade-off and all the different studies can provide some valuable information. The advantage of studying college or adult dyslexics is that it allows a look at the different factors at work later in the life cycle, and when basic reading skills have already been mastered.

    "Visual processing" is loosely whatever the nervous system does with the signal it receives. There is quite a lot of "processing" before the visual signals even leave the eye, although usually people are talking about visual processing in the brain.

    Don't be too quick to dismiss the effect of color for some people. Color changes change the stimuli that reach the eye, so changing the stimuli may be differently managed between different groups that vary in their efficiency of visual processing. It is a mistake to believe that color is "the only thing" or even the main factor in the visual processing challenges of dyslexics.

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  6. Anonymous10:15 PM

    Great topic! My 6 1/2 year old 2E son has an unusual form of visual dyslexia and I'm very interested in applicable research. Thank you for your important work and for sharing what is happening in the field.

    Is anyone looking at a connection between some forms of dyslexia (especially related to mirror image writing/drawing and up and down confusion--ex. p/d/q/b; n/u/z) and problems with crossing midline and/or developmental dyspraxia?

    Thank you again!

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  7. Anonymous5:27 AM

    Here is an important article I think everyone should read about dyslexia:

    http://www.guardian.co.uk/education/2005/sep/02/schools.uk6

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  8. I allowed the post from "Anonymous" above. it is about a quack who doesn't believe Dyslexia exists. It is a shame that the media likes to cover polarizing opinions, even if it may spread more misinformation. The article in the Guardian above cites an ignorant Durham University professor who doesn't believe dyslexia exists - this like many poorly informed parents who berated their dyslexic children for not reading because of "laziness". Like Yeats' father who threw a book at his head because he couldn't read well.

    The latest brain imaging studies may be helpful for educating some, but it will come as no great surprise for many dyslexics that many prejudices remain.

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  9. It's sad, and deeply invalidating to so many who struggle with the various very real problems resulting in dyslexia. The fact that there is often an emotional component (anxiety causing task avoidance, or learned helplessness / depression causing lack of effort, for example) does not mean that there is not also an underlying cognitive issue contributing to the problems. These things tend to go in self-stoking cycles. And the fact that there is not a singular cognitive profile for dyslexics, but rather that "reading failure" is a final common symptom for a variety of underlying problems, does not mean that "dyslexia" does not exist.

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  10. Anonymous7:56 AM

    I have 4 children 2 have been diagnosed as dyslexic and 1 has been diagnosed with dyslexia, dysgraphia, and ADD. I successfully homeschooled the nondyslexic child from K-12, she is now a senior in college on the honor roll. Trying to homeschool the others was a huge challenge. The two youngest are now at charter schools where they are getting excellent help with their learning differences. This has been a very long hard battle to get a proper diagnosis and appropriate educational opportunities for them. In the process of having them diagnosed we realized that my husband also has dyslexia and dysgraphia. The dyslexia is so different in everyone of them, I feel like this family would be an excellent case study for those researching this subject. In fact I have seriously considered going back to college to do this myself. I have read so much on this subject, my favorite book so far is "The Secret Life of the Dyslexic Child" by Robert Frank.

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