Dyslexia is a syndrome in which a person's reading and/or writing ability is significantly lower than that which would be predicted by his or her general level of intelligence. People are diagnosed as dyslexic when their reading problems cannot be explained by a lack of intellectual ability, inadequate instruction, or sensory problems such as poor eyesight. Because reading is a complex mental process, dyslexia has many potential causes. From a neurophysiological perspective, dyslexia can be diagnosed by close inspection of the morphology of the brain, usually upon autopsy. Dyslexia is also associated with phonological difficulties, such as enunciation.
Variations and related disorders
Dyslexia is not a disease or a mental problem; it is an orientation problem which can be compensated for (to some degree, though never completely eradicated) with the proper tools. The dyslexic is a three dimensional thinker. This gets in the way of being able to read because written characters are two dimensional. The dyslexic tries to give a third dimension which causes the problem. Dyslexics are usually above normal intelligence because they have to be able to cope in a world where the other 80-85% of the population is oriented naturally. While there are theories that an MRI done at school age can show differences in the dyslexic brain patterns, these people can learn to cope in the world and be very successful. Several famous people, such as Leonardo Da Vinci, Winston Churchill, Robin Williams, Cher, Tom Cruise, Quentin Tarantino, and Ansel Adams have had this condition. Scotopic sensitivity syndrome is a form of dyslexia which makes it very difficult for a person to read black text on white paper, particularly when the paper is slightly shiny.
In addition to the typical forms of dyslexia, there are numerous related disorders:
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Dyspraxia- a neurological disorder characterised by a marked difficulty in carrying out routine tasks involving balance, fine-motor control, and kinesthetic coordination.
- Verbal Dyspraxia - a neurological disorder characterised by marked difficulty in the use of speech sounds, which is the result of an immaturity in the speech production area of the brain.
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Dysgraphia- a neurological disorder characterised by distorted and incorrect writing.
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Dyscalculia- a neurological disorder characterised by a problem with learning fundamentals and one or more of the basic numerical skills. Often people with this disorder can understand very complex mathematical concepts and principles but have difficulty processing formulas and even basic addition and subtraction.
Facts and statistics
5-15% of the population can be diagnosed as suffering from various degrees of dyslexia.
Dyslexia and other similar disabilities are much more commonly reported in males than in females. Most researchers agree that there is a fairly even gender balance amongst dyslexics, but that the acted-out frustration of dyslexic boys tends to draw more attention from teachers. Since referrals for special education service are linked to such attention, classes and programs designed to help such children often have more boys than girls in them.
Studying dyslexia is very valuable for understanding intelligence and creativity. Dyslexia illustrates the power of inborn wiring of the brain in developing mental skills . At the same time it can show how inborn limitations can be overcome by using the compensatory power of the brain.
Dyslexia's main manifestation is a difficulty in developing reading skills in elementary school children. Those difficulties result from reduced ability to link up visual symbols with sounds. In the past, dyslexia was mistakenly thought to have a motivational background. Contrary to that erroneous belief, modern research has shown that dyslexia is a condition largely inborn. In other words, dyslexia is a condition that children are born with and not the result of poor parenting or the environment. Some have disagreed with these findings, however, and believe that while dyslexia may sometimes be inborn it is often attributable to lack of phonics training when learning to read and the preponderance of the whole language system.
Researchers studying the brains of dyslexics have found that in reading tasks dyslexics show reduced activity in the left inferior parietal cortex. Otherwise, dyslexics are known to often show higher than average intelligence. There are marked anatomical differences between dyslexic brains and normal brains.
Famous dyslexics
A number of eminent scholars throughout history have suffered from varying degree of dyslexia. Among those speculated to have been afflicted with dyslexia are: Albert Einstein, Thomas Edison, Alexander Graham Bell, Michael Faraday, Walt Disney and many others.
Partly in an effort to remove the stigma attached to the disorder, many people have confirmed that they have dyslexia to varying degrees:
The list above indicates that those who show reading difficulties in childhood can also cope well with their deficiency later in lives and become avid readers, skilled writers, and entrepreneurs. Some of the people listed in this grouping have erroneously been classified as being dyslexic, however. Albert Einstein, for example, did not posess characteristics of dyslexia, according to many biographers.
Physiology and treatment
Even a few weeks of intense phonological training (often involving breaking down and rearranging sounds to produce different words) can help noticeably improve reading skills. Unlike in normal adults, phonological training shows an increase in the activity in the right temporoparietal cortex .
This part of the brain works in spatial tasks and may be the main compensatory structure in phonological training. This is the sister region of the left temporoparietal cortex responsible for visual motion processing which is underactive in many dyslexics. The earlier the phonological regimen is taken on, the better the overall result. Advanced brain scans could identify children at risk of dyslexia before they can even read, although it is thought that simple tests of balance could do the same. It has also been shown that early diagnosis and treatment can almost completely redidiate the symptoms of dyslexia.
One hypothesis for some of the symptoms of dyslexia is a lack of overall short-term memory. Typically a dyslexic will not remember your name, and will suffer an undue amount of difficulty in transcribing (for example) a phone number. These problems could be attributed to difficulty in laying down short-term memories.
It is not that uncommon for dyslexics who have trained themselves to cope with their affliction, to develop uncannily efficient visual memories which aid in reading and comprehending large quantities of information much faster than is typical. Adversely, some dyslexics may show a natural dislike of reading and, in consequence, compensate by developing unique verbal communication skills , inter-personal expertise, and leadership skills. Different people adopt different strategies for living with the same affliction.
A popular hypothesis for the reading difficulties experienced by dyslexics is difficulty in bringing both eyes into focus on the same point. Such problems explain why dyslexics often confuse the sequence of written letters or numbers, as the end of the word is literally being seen first by one eye, then the beginning of the word is seen by the other eye. Studies in which young children are taught reading skills while wearing an eyepatch have shown very promising results. This is based upon the theory that, because children benefit more from learning to read than being confocal, the former should take precedence over the latter.
In 1979, anatomical differences in the brain of a young dyslexic were documented. Albert Galaburda of Harvard Medical School noticed that language centers in dyslexic brains showed microscopic flaws known as ectopias and microgyria. Both affect the normal six-layer structure of the cortex. An ectopia is a collection of neurons that have pushed up from lower cortical layers into the outermost one. A microgyrus is an area of cortex that includes only four layers instead of six.
These flaws affect connectivity and functionality of the cortex in critical areas related to sound and visual processing. These and similar structural abnormalities may be the basis of the inevitable and hard to overcome difficulty in reading.
Several genetic regions on chromosomes 1 and 6 have been found that might be linked to dyslexia. In all likelihood, dyslexia is a conglomeration of disorders that all affect similar and associated areas of the cortex. With time, science is likely to identify and classify all individual suborders with benefits to our understanding of how low-level genetic flaws can affect the wiring of the brain and enhance or reduce a particular component of human mental capacity.
Some studies have concluded that speakers of languages whose orthography has a strong correspondence between letter and sound (e.g. Korean and Italian) have a much lower incidence of dyslexia than speakers of languages where the letter is less closely linked to the sound (e.g. English and French). (Source: http://www-tech.mit.edu/V121/N12/shorts2_12.12w.html )
Whether today's models of dyslexia are correct or not, the main lesson of dyslexia is that minor genetic changes affecting the layering of the cortex in a minor area of the brain may impose inborn limitations on the overall intellectual function. At the same time, dyslexia shows that the brain exhibits a strong ability to compensate for its inborn or acquired limitations, and intense training can often result in miraculous turnabouts.
Lack of public support
In the United States and in the United Kingdom, some people say that there is a lack of adequate support and a general disinterest in the learning disabilities of children in public schools. This has recently lead to legal action by private parties against public schools in the United States and in the United Kingdom.
In English law, the failure of schools to diagnose and provide remedial help for dyslexia became grounds for personal injury litigation in 1999 following a House of Lords decision in the case of Pamela Phelps . Students aside, there is virtually no support for dyslexics in the UK once they leave school.
The British Disability Discrimination Act also covers dyslexia.
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"In some cases, people have 'coping strategies' which cease to work in certain circumstances (for example, where someone who stutters or has dyslexia is placed under stress). If it is possible that a person's ability to manage the effects of the impairment will break down so that these effects will sometimes occur, this possibility must be taken into account when assessing the effects of the impairment."
- [Paragraph A8, Guidance to the Definitions of Disability]
Readings
- de Lacoste-Utamsing, C., and Holloway, R., Sexual Dimorphism in the Human Corpus Callosum, Science, Vol 216, 1982.
- Dennis, M., Impaired Sensory and Motor Differentiation with CC Agenesis: A Lack of Callosal Inhibition during Ontogeny? Neuropsychologia, vol 14 p. 455-469, 1976.
- Duffy, F., Denkla, M., Bartels, P., and Sandini, G., Dyslexia: Regional Differences in Brain Electrical Activity by Topographic Mapping, Annals of Neurology, vol 7 #5, 1980
- Ettlinger, G., Blakemore, C. B., Milner, A. D., and Milner J., Agenesis of the Corpus Callosum: A behavioral Investigation, Brain, vol 75, 1972.
- Ferriss, G. S., and Dorsen, M., Agenesis of the Corpus Callosum: Neuropsychological Studies, Cortex, vol2, #2, 1975.
- Gazzaniga, M. S., Cognitive and Neurologic Aspects of Hemispheric Disconnection in the Human Brain, Discussions in Neurosciences, vol 4, #4, FESN, 1978.
- Gazzaniga, M., Consistency and Diversity in Brain Organization, Annals of the New York Academy of Sciences, vol 299, Ps 415-424, 1977.
- Gladstone, M., and Best, C. T., Developmental Dyslexia: The Potential Role of Interhemispheric Collaboration in Reading Acquisition, Hemispheric Function and Collaboration in the Child, Ed., Catherine Best, Academic Press 1983.
- Gross, K., Rothenberg, S., Schottenfield, S., and Drake, C., Duration Thresholds for Letter Identification in Left and Right Visual Fields for Normal and Reading-Disabled Children, Neuropsvchologia, vol 6, 1978.
- Gross-Glenn, K., and Rothenberg, S., Evidence for Deficit in Interhemispheric Transfer of Information in Dyslexic Boys, International Journal of Neuroscience, vol 24, 1984.
- Haggerty, R., and Stamm, J. S., Dichotic Auditory Fusion Levels in Children with Learning-Disabilities, Neuropsychologia, vol 16, 3, 1978.
- Harris, A. J., Lateral Dominance and Reading Disability, Journal of Learning Disabilities, vol 12, #5 1979.
- Horowitz, B., Rumsey, J.M. and Donohue, B.C., Functional Connectivity of the Angular Gyrus in Normal Reading and Dyslexia, Proceedings of the National Academy of Sciences, vol 95, July 21, 1998
- Hynd, G.W. et al., Dyslexia and Corpus Callosum Morphology, Archives of Neurology, vol 52, Jan., 1995
See also
External links
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Last updated: 10-11-2005 08:53:51
