Significations et usages de Dyslexia

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Dyslexia is a very broad term defining a learning disability that impairs a person's fluency or comprehension accuracy in being able to read,^[1] and which can manifest itself as a difficulty with phonological awareness, phonological decoding, orthographic coding, auditory short-term memory, or rapid naming.^[2][3] Dyslexia is distinct from reading difficulties resulting from other causes, such as a non-neurological deficiency with vision or hearing, or from poor or inadequate reading instruction.^[4][5] It is believed that dyslexia can affect between 5 and 10 percent of a given population although there have been no studies to indicate an accurate percentage.^[6][7][8]

There are three proposed cognitive subtypes of dyslexia: auditory, visual and attentional.^{[7][9][10][11][12][13]} Reading disabilities, or dyslexia, is the most common learning disability, although in research literature it is considered to be a receptive language-based learning disability.^[14] Researchers at MIT found that people with dyslexia exhibited impaired voice-recognition abilities.^[15]

Adult dyslexics can read with good comprehension, but they tend to read more slowly than non-dyslexics and perform more poorly at spelling and nonsense word reading, a measure of phonological awareness.^[16] Dyslexia and IQ are not interrelated as a result of cognition developing independently.^[17]

  Classification

The World Federation of Neurology defines dyslexia as "a disorder manifested by difficulty in learning to read despite conventional instruction, adequate intelligence and sociocultural opportunity".^[18]

The National Institute of Neurological Disorders and Stroke gives the following definition for dyslexia:

"Dyslexia is a brain-based type of learning disability that specifically impairs a person's ability to read. These individuals typically read at levels significantly lower than expected despite having normal intelligence. Although the disorder varies from person to person, common characteristics among people with dyslexia are difficulty with spelling, phonological processing (the manipulation of sounds), and/or rapid visual-verbal responding. In adults, dyslexia usually occurs after a brain injury or in the context of dementia. It can also be inherited in some families and so on, and recent studies have identified a number of genes that may predispose an individual to developing dyslexia."^[1]

Other published definitions are purely descriptive or embody causal theories. Varying definitions are used for dyslexia from researchers and organizations around the world; it appears that this disorder encompasses a number of reading skills, deficits and difficulties with a number of causes rather than a single condition.^[19][20]

Castles and Coltheart describe phonological and surface types of developmental dyslexia by analogy to classical subtypes of alexia (acquired dyslexia) which are classified according to the rate of errors in reading non-words.^[21][22] However, the distinction between surface and phonological dyslexia has not replaced the old empirical terminology of dysphonetic versus dyseidetic types of dyslexia.^[20][22][23] The surface/phonological distinction is only descriptive, and devoid of any etiological assumption as to the underlying brain mechanisms.^[24] Studies have, however, alluded to potential differential underlying brain mechanisms in these populations given performance differences.^[25][26][27] The dysphonetic/dyseidetic distinction refers to two different mechanisms; one that relates to a speech discrimination deficit, and another that relates to a visual perception impairment.

  Signs and symptoms

Some early symptoms that correlate with a later diagnosis of dyslexia include delays in speech,^[28] letter reversal or mirror writing,^[29][30] and being easily distracted by background noise.^[31] At later ages symptoms can include a difficulty identifying or generating rhyming words, or counting syllables in words (phonological awareness),^[32] a difficulty segmenting words into individual sounds, or blending sounds to make words,^[33] a difficulty with word retrieval or naming problems,^[34][35][36] commonly very poor spelling^[37] which has been called dysorthographia (orthographic coding), and tendencies to omit or add letters or words when writing and reading are considered classic signs.^[38] A common misconception about dyslexia is that dyslexic readers write words backwards or move letters around when reading – this only occurs in a very small population of dyslexic readers.^[39] Dyslexic people are better identified by writing that does not seem to match their level of intelligence from prior observations.

  Cause

Researchers have been trying to identify the biological basis of dyslexia since it was first identified by Oswald Berkhan in 1881^[40] and the term dyslexia coined in 1887 by Rudolf Berlin.^[41][42] The theories of the etiology of dyslexia have and are evolving with each new generation of dyslexia researchers, and the more recent theories of dyslexia tend to enhance one or more of the older theories as understanding of the nature of dyslexia evolves.

  Effect of language orthography

The complexity of a language's orthography or spelling system – formally, its orthographic depth – has a direct impact on how difficult it is to learn to read that language. English has a comparatively deep orthography within the Latin alphabet writing system, with a complex orthographic structure that employs spelling patterns at several levels: principally, letter-sound correspondences, syllables, and morphemes. Other languages, such as Spanish, have mostly alphabetic orthographies that employ letter-sound correspondences, so-called shallow orthographies. It is relatively easy to learn to read languages like Spanish; it is much more difficult to learn to read languages with more complex orthographies such as English.^[43] Logographic writing systems, notably Japanese and Chinese characters, have graphemes that are not linked directly to their pronunciation, which pose a different type of dyslexic difficulty.^{[13][44][45][46]}

From a neurological perspective, different types of writing system, for example alphabetic as compared to logographic writing systems, require different neurological pathways in order to read, write and spell. Because different writing systems require different parts of the brain to process the visual notation of speech, children with reading problems in one language might not have a reading problem in a language with a different orthography. The neurological skills required to perform the tasks of reading, writing, and spelling can vary between different writing systems and as a result different neurological deficits can cause dyslexic problems in relation to different orthographies.^[44][45][46]

  Cross-cultural prevalence

Cross-cultural study of the prevalence of dyslexia is difficult as different scholars and different countries often use different criteria to distinguish the cases of dyslexia in the continuum between the able and delayed readers at schools. According to the existing literature, the prevalence of dyslexia can vary widely between cultures. For example, Christall reports differences between 1% and 33%.^[47] According to some researchers, despite the significant differences between the writing systems, Italian, German and English populations suffer similarly from dyslexia.^[48]

  Exacerbating conditions

Several learning disabilities often occur with dyslexia, but it is unclear whether these learning disabilities share underlying neurological causes with dyslexia.^[49] These disabilities include:

• Dysgraphia – a disorder which expresses itself primarily through writing or typing, although in some cases it may also affect eye–hand coordination, direction- or sequence-oriented processes such as tying knots or carrying out a repetitive task. In dyslexia, dysgraphia is often multifactorial, due to impaired letter writing automaticity, finger motor sequencing challenges, organizational and elaborative difficulties, and impaired visual word form which makes it more difficult to retrieve the visual picture of words required for spelling. Dysgraphia is distinct from dyspraxia in that dyspraxia is simply related motor sequence impairment.
• Attention Deficit Disorder^[28][50][51] – a high degree of co-morbidity has been reported between ADD/ADHD and dyslexia/reading disorders,^[52] it occurs in between 12% and 24% of those with dyslexia.^[8]
• Auditory processing disorder – A condition that affects the ability to process auditory information. Auditory processing disorder is a listening disability.^[53] It can lead to problems with auditory memory and auditory sequencing. Many people with dyslexia have auditory processing problems^[54] and may develop their own logographic cues to compensate for this type of deficit. Auditory processing disorder is recognized as one of the major causes of dyslexia.^[55][56][57]
• Developmental dyspraxia^[28] – A neurological condition characterized by a marked difficulty in carrying out routine tasks involving balance, fine-motor control, kinesthetic coordination, difficulty in the use of speech sounds, problems with short-term memory and organization are typical of dyspraxics.

Experience of speech acquisition delays and speech and language problems can be due to problems processing and decoding auditory input prior to reproducing their own version of speech,^[58][59] and may be observed as stuttering, cluttering or hesitant speech.^[20]

  Management

There is no cure for dyslexia, but dyslexic individuals can learn to read and write with educational support.^[60] There are techniques and technical aids, which manage or even conceal symptoms of the disorder.^[61] Removing stress and anxiety alone contributes to improving understanding.^[62]

For dyslexia intervention with alphabet writing systems the fundamental aim is to increase a child's awareness of correspondences between graphemes and phonemes, and to relate these to reading and spelling. It has been found that training focused towards visual language and orthographic issues yields longer-lasting gains than mere oral phonological training.^[63]

There is some evidence that the use of specially tailored fonts may provide some measure of assistance for those suffering from dyslexia.^[64][65] Intervention early on while language areas in the brain are still developing is most successful in reducing long-term impacts of dyslexia.^[66]

  History

Dyslexia was identified by Oswald Berkhan in 1881,^[67] but the term dyslexia was coined in 1887 by Rudolf Berlin, who was an ophthalmologist in Stuttgart.^[68] He used the term to refer to a case of a young boy who had a severe impairment in learning to read and write in spite of showing typical intellectual and physical abilities in all other respects.

In 1896 W. Pringle Morgan, a British physician from Seaford, East Sussex, published a description of a reading-specific learning disorder in a report to the British Medical Journal titled "Congenital Word Blindness". This described the case of a 14-year-old boy who had not yet learned to read, yet showed normal intelligence and was generally adept at other activities typical of children of that age.^[69]

  Research

The majority of currently available dyslexia research relates to the alphabetic writing system, and especially to languages of European origin. However, substantial research is also available regarding dyslexia for speakers of Arabic, Chinese, and Hebrew.^{[24][70][71][72][73]}

Genetic research into dyslexia has its roots in the examination of post-autopsy brains of people with dyslexia.^[74][75] When they observed anatomical differences in the language center in a dyslexic brain, they showed microscopic cortical malformations known as ectopias and more rarely vascular micro-malformations, and in some instances these cortical malformations appeared as a microgyrus. These studies and those of Cohen et al. 1989^[76] suggested abnormal cortical development which was presumed to occur before or during the sixth month of fetal brain development.^[22]

In the area of neurological research into dyslexia, modern neuroimaging techniques such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) have produced clear evidence of structural differences in the brains of children with reading difficulties. It has been found that people with dyslexia have a deficit in parts of the left hemisphere of the brain involved in reading, which includes the inferior frontal gyrus, inferior parietal lobule, and middle and ventral temporal cortex.^[77]

Brain activation studies using PET to study language have produced a breakthrough in understanding of the neural basis of language over the past decade. A neural basis for the visual lexicon and for auditory verbal short-term memory components have been proposed,^[78] with some implication that the observed neural manifestation of developmental dyslexia is task-specific (i.e., functional rather than structural).^[79]

  Gene-environment interaction

Research has examined gene–environment interactions in reading disability through twin studies, which estimate the proportion of variance associated with environment and the proportion associated with heritability. Studies examining the influence of environmental factors such as parental education,^[80] and teacher quality^[81] have determined that genetics have more influence-supportive environments than less optimal environments. Instead, it may just allow those genetic risk factors to account for more of the variance in outcome, because environmental risk factors that affect that outcome have been minimized.^[82]

As the environment plays a large role in learning and memory, it is likely that epigenetic modifications play an important role in reading ability. Animal models and measures of gene expression and methylation in the human periphery are used to study epigenetic processes, both of which have limitations in extrapolating to the human brain.^[83]

  See also

Child development History of the alphabet Learning theory (education) Linguistics List of artistic depictions of dyslexia List of people diagnosed with dyslexia Neurolinguistics

Philosophy of language Writing system Neurodiversity Dyslexie See more articles related to Dyslexia

  References

  External links

Organizations

• International Dyslexia Association
• Dyslexia Action (UK)
• British Dyslexia Association
• Dyslexia Research Trust
• Learning Ally, formerly Recording for the Blind & Dyslexic
• The Brain Foundation.Singapore

Topics related to Dyslexia       Developmental disorders: Dyslexia and related specific developmental disorders (F80–F83, 315) General conditions Speech and language impairments / communication disorders Expressive language disorder Landau–Kleffner syndrome Language disorder Lisp Mixed receptive-expressive language disorder Specific language impairment Speech disorder Scholastic skills/ learning disorder Developmental dyslexia Dysgraphia (Disorder of written expression) Dyscalculia Motor function Developmental dyspraxia Other Auditory processing disorder Scotopic sensitivity syndrome Related topics Dyslexia research Management of dyslexia/Dyslexia interventions Reading acquisition Writing system Spelling Literacy Irlen filters Learning Ally Neuropsychology Lists Languages by Writing System People with dyslexia Dyslexia in fiction M: PSO/PSI mepr dsrd (o, p, m, p, a, d, s), sysi/epon, spvo proc(eval/thrp), drug(N5A/5B/5C/6A/6B/6D)       Symptoms and signs: Speech and voice / Symptoms involving head and neck (R47–R49, 784) Acute Aphasias Expressive aphasia · Receptive aphasia · Conduction aphasia  · Anomic aphasia · Global aphasia  · Transcortical sensory aphasia · Transcortical motor aphasia  · Mixed transcortical aphasia Progressive Aphasias Progressive nonfluent aphasia  · Semantic dementia  · Logopenic progressive aphasia Other speech disturbances Speech disorder · Apraxia of speech · Auditory verbal agnosia · Dysarthria · Schizophasia · Aprosodia/Dysprosody Specific language impairment · Thought disorder · Pressure of speech · Derailment · Clanging · Circumstantiality Symbolic dysfunctions Developmental dyslexia/Alexia · Agnosia (Astereognosis, Prosopagnosia, Visual agnosia)  · Gerstmann syndrome · Developmental dyspraxia/Apraxia (Ideomotor apraxia) · Dyscalculia/Acalculia · Agraphia Voice disturbances Dysphonia/Aphonia Other Auditory processing disorder · Epistaxis · Headache · Post-nasal drip · Neck mass M: PSO/PSI mepr dsrd (o, p, m, p, a, d, s), sysi/epon, spvo proc(eval/thrp), drug(N5A/5B/5C/6A/6B/6D) M: MOU anat/devp noco/cofa(c)/cogi/tumr, sysi proc (peri), drug (A1)       Literacy Teaching literacy Reading education in the USA • Phonics • Whole language • Dick and Jane • National Council of Teachers of English • NCLB • Family literacy • Adolescent literacy Defining literacy Functional illiteracy • Critical literacy Literacy internationally International Reading Association • List of countries by literacy rate • Literacy in India • International Literacy Day • List of Chinese administrative divisions by illiteracy rate Major contributors to literacy Frank Laubach • Paulo Freire • Griffith Jones • Marie Clay Related concepts Agricultural literacy • Aliteracy • Asemic writing  • Computer literacy • Cultural literacy • Dyslexia • Diaspora literacy • Ecological literacy • Electracy • Emotional literacy • Financial literacy • Health literacy • Information literacy • Information and media literacy • Literacy test • Media literacy • Mental health literacy • Mental literacy • New literacies • Numeracy • Oracy • Orality • Oral literature • Postliterate society • Racial literacy • Scientific literacy • Statistical literacy • Technological literacy • Transliteracy • Visual literacy • Writing system       Writing systems Overview History of writing History of the alphabet Graphemes Scripts in Unicode Lists Writing systems Languages by writing system / by first written account Undeciphered writing systems Inventors of writing systems Types Featural alphabets Alphabets Abjads Alphasyllabaries / Abugidas Syllabaries Semi-syllabaries Ideogrammic Pictographic Logographic Numeral