Dyslexia A Junk Diagnosis: No

Some people think that dyslexia is a "junk diagnosis" or "a myth".   I don't, in a scientific sense, although it can be used as an excuse ("Oh, she can't learn to read--she's dyslexic.")

Again thanks to Kevin McGrew, a recent publication:

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

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.

Full article: Download shaywitz2006.pdf

The scientific consensus in the US is that the disruption in the neural systems resulting in phonological problems.  Elsewhere, there's more of a focus on a more geneeral suite of problems, both sensory and motor.

There's a good, not-too-technical survey article:

Curr Opin Neurobiol. 2003 Apr;13(2):212-8.

Developmental dyslexia: specific phonological deficit or general sensorimotor dysfunction?

* Ramus F.

Laboratoire de Sciences Cognitives et Psycholinguistique (EHESS/ENS/CNRS), 54 boulevard Raspail, 75006, Paris, France. ramus@iscp.ehess.fr

Dyslexia research now faces an intriguing paradox. It is becoming increasingly clear that a significant proportion of dyslexics present sensory and/or motor deficits; however, as this 'sensorimotor syndrome' is studied in greater detail, it is also becoming increasingly clear that sensory and motor deficits will ultimately play only a limited role in a causal explanation of specific reading disability.

You can read the whole thing online (as an html file) here

http://tinyurl.com/3y982p

Another case-study article here:

Dev Sci. 2006 May;9(3):237-55; discussion 265-9

The role of sensorimotor impairments in dyslexia: a multiple case study of dyslexic children.

* White S, Milne E,Rosen S, Hansen P, Swettenham J, Frith U,Ramus F.

Institute of Cognitive Neuroscience, University College London, UK. s.white@ucl.ac.uk

Abstract: This study attempts to investigate the role of sensorimotor impairments in the reading disability that characterizes dyslexia. Twenty-three children with dyslexia were compared to 22 control children, matched for age and non-verbal intelligence, on tasks assessing literacy as well as phonological, visual, auditory and motor abilities. The dyslexic group as a whole were significantly impaired on phonological, but not sensorimotor, tasks. Analysis of individual data suggests that the most common impairments were on phonological and visual stress tasks and the vast majority of dyslexics had one of these two impairments. Furthermore, phonological skill was able to account for variation in literacy skill, to the exclusion of all sensorimotor factors, while neither auditory nor motor skill predicted any variance in phonological skill. Visual stress seems to account for a small proportion of dyslexics, independently of the commonly reported phonological deficit. However, there is little evidence for a causal role of auditory, motor or other visual impairments.
PMID: 16669791 [PubMed - indexed for MEDLINE]

The bottom line:

Dyslexia is associated with :

phonological deficits (most common deficit)
auditory deficits (other than phonological--less common)
visual-processing deficits--less common
motor-control difficulties--less common

Some dyslexic kids have just one--most commonly phonological deficits. A subset of dyslexic kids have more than one (or all four)--but the last three have not been shown to have a strong effect on reading acquisition.

Comments

[Liza]

Hi Liz, thanks for the helpful comment you left in my post today.

This article (and your post) is another great find. I added a link to here on that "Overcoming Dyslexia" post I did.

[John Hayes]

I was going to respond to yesterday's post but here will do.

There are gold standards for testing if a program actually is effective in dyslexia. 1)Improved phonemic awareness 2) improved decoding 3)improved comprehension 4) improved reading speed.

That gold standard is true for the majority of dyslexics. For visual dyslexics , the minority who always seem to be left out, #1 is replaced with seeing the written word in a clear, focused and stable manner. Also a small point, I use accuracy instead of decoding because misreading words that cause a lack of fluency seems to be the larger problem for visual dyslexics. # 3 and 4 are also indeed necessary for a successful intervention.( program does not seem like the best word when dealing with visual dyslexia as the results are usually instantaneous )

From a featured article yesterday

Curr Opin Neurobiol. 2003 Apr;13(2):212-8.

Developmental dyslexia: specific phonological deficit or general sensorimotor dysfunction?

To summarize, A minority of dyslexics seem to have visual problems. At least visual stress seems dissociated from the phonological deficit ,and is therefor a possible independent cause of reading disability. However the underlying biological cause of these visual disorders and their precise impact on reading still need to be elucidated. The hypothesis of magnocellular origin does not seem to be well supported.

The effect the See Right Dyslexia Glasses is based on the removal of autofluorescence that occurs in the eyes of everyone. While it would be nice to know whether visual dyslexics have more autofluorescent proteins or are just more sensitive to autofluorescence doesn't matter when the wavelengths of light that cause the autofluorescence are filtered out. There are no references that relate autofluorescence and dyslexia. Here is a link to an instrument developed by NASA for measuring autofluorescence in the cornea of astronauts to monitor changes that may occur on any Mars flight. http://zeta.lerc.nasa.gov/grcbio/VisionResearch/technologies/autofluorescence.html I hypothesize that dyslexics that describe seeing a page as if behind a waterfall probably have high levels of autofluorescent proteins in the cornea causing a generalized scatter of visual noise.

The location of autofluorescence in other parts of the eye either alone or in combination are the cause of other visual problems. There is one visual problem that is not associated with reading that is statistically higher in dyslexics than the general population and that is poor depth perception. The See Right Dyslexia Glasses restore normal depth perception 100% of the time for those dyslexics with poor depth perception. I hypothesize the cause of the poor depth perception is having a large difference in the amount of autofluorescence in either eye. That this varies between eyes is well documented. Removing the visual noise caused by autofluorescence allows each eye to see normally and normal depth perception is restored.

From yesterday's post

Dev Sci. 2006 May;9(3):237-55; discussion 265-9

The role of sensorimotor impairments in dyslexia: a multiple case study of dyslexic children.

* White S, Milne E,Rosen S, Hansen P, Swettenham J, Frith U,Ramus F.

Institute of Cognitive Neuroscience, University College London, UK.

Analysis of individual data suggests that the most common impairments were on phonological and visual stress tasks and the vast majority of dyslexics had one of these two impairments................ Visual stress seems to account for a small proportion of dyslexics, independently of the commonly reported phonological deficit.

Visual dyslexia , sometimes called visual stress, is as real as dyslexia. That the magnocellular origin of the problem has been wrongly used for years to try to explain it does not mean it doesn't exist. It means the magnocellular origin theory was wrong.

Loved your references.

Your conclusion that

Dyslexia is associated with :

phonological deficits (most common deficit)
auditory deficits (other than phonological--less common)
visual-processing deficits--less common
motor-control difficulties--less common

Some dyslexic kids have just one--most commonly phonological deficits. A subset of dyslexic kids have more than one (or all four)--but the last three have not been shown to have a strong effect on reading acquisition.

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Seems only to be supported by your references for auditory and motor-control factors but not

the minority who have visual-processing deficits.