දුර්අක්‍ෂරතාව

විකිපීඩියා, නිදහස් විශ්වකෝෂය වෙතින්
වෙත පනින්න: සංචලනය, සොයන්න
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දුර්අක්ෂරතාව
(ඩිස්ලෙක්සිඅ') (Dyslexia)
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and related disorders
Education · Neuropsychology

RELATED CONDITIONS

Acquired dyslexia  · Alexia
Auditory Processing Disorder
Dyscalculia · Dysgraphia
Dyslexia · Dyspraxia

THEORIES

Double deficit · Magnocellular
Perceptual noise exclusion
Phonological deficit

RELATED TOPICS

IDEA · Literacy
Reading acquisition · Spelling
Recording for the Blind & Dyslexic

LISTS

Assessments · Fields
People · Publications
Topics
Fiction · Treatments

ඩිස්ලෙක්සිඅ'(English- 'Dyslexia) යනුlearning disability that manifests itselfprimarily as a difficulty with written language,particularly with reading. It is separate anddistinct from reading difficulties resulting from other causes, such asa non-neurological deficiency with vision or hearing, or from poor orinadequate reading instruction.[1] Evidencesuggests that dyslexia results from differences in how brain processeswritten and spoken language. Although dyslexia is thought to be theresult of a neurological difference, it is not an intellectualdisability. Dyslexia is diagnosed in people of all levels ofintelligence.[2]


තිබූ පුද්ගලයන්[සංස්කරණය]

The following is a list of notable people who have been diagnosed with dyslexia.

ඉතිහාසය[සංස්කරණය]

Identified by Oswald Berkhan in 1881, [59] theterm 'dyslexia' was later coined in 1887 by Rudolf Berlin, anophthalmologist practicing in Stuttgart,ජර්මනිය.[60]He used the term to refer to a case of a young boy who had a severeimpairment in learning to read and write in spite of showing typicalintellectual and physical abilities in all other respects.

In1896, W. Pringle Morgan, a British physician, from Seaford, EastSussex, England published a description of a reading-specificlearning disorder in a report to the British Medical Journal titled"Congenital Word Blindness". This described the case of a14-year-old boy who had not yet learned to read, yet showed normalintelligence and was generally adept at other activities typical ofchildren of that age.[61]

Duringthe 1890s and early 1900s, James Hinshelwood, a Britishophthalmologist, published a series of articles in medical journalsdescribing similar cases of congenital word blindness, which he definedas "a congenital defect occurring in children with otherwise normal andundamaged brains characterised by a difficulty in learning to read." Inhis 1917 book Congenital Word Blindness, Hinshelwood asserted thatthe primary disability was in visual memory for words and letters, anddescribed symptoms including letter reversals, and difficulties withspelling and reading comprehension.<refname=Hinshelwood1917>Hinshelwood, J. (1917). Congenital Word-blindness. HK Lewis \&Co., ltd.. </ref>

An early researcher indyslexia was Samuel T. Orton, a neurologist who workedprimarily with stroke victims. In 1925 Orton met a boy who could notread and who exhibited symptoms similar to stroke victims who had lostthe ability to read. Orton began studying reading difficulties anddetermined that there was a syndrome unrelated to brain damage thatmade learning to read difficult. Orton called the conditionstrephosymbolia (meaning 'twisted signs') to describe his theory thatindividuals with dyslexia had difficulty associating the visual formsof words with their spoken forms.[62] Orton observed that readingdeficits in dyslexia did not seem to stem from strictly visualdeficits.[63] Hebelieved the condition was caused by the failure to establishhemispheric dominance in thebrain.[64] He also observed that thechildren he worked with were disproportionately left- or mixed-handed,although this finding has been difficult to replicate.[65] Orton's hypothesis concerninghemispheric specialization was borne out by post-mortem studies in the1980s and 1990s establishing that the left planum temporale, abrain area associated with language processing, is physically largerthan the corresponding right area in the brains of non-dyslexicsubjects, but that these brain areas are symmetrical or slightly largeron the right for dyslexic subjects.[66] FMRI imaging studies ofchildren and young adults reported in 2003 provide further support,demonstrating that increases in age and reading level are associatedwith a suppression of right hemispheric activity.[67] <refname=Turkeltaub2003>Turkeltaub, P.E.; Gareau, L.; Flowers, D.L.; Zeffiro, T.A.; Eden, G.F. (2003). "Development of neural mechanisms for reading" ([dead link]search). Nature Neuroscience 6 (7): 767–773. doi:10.1038/nn1065. http://www.owlnet.rice.edu/~dburgund/480-580_04/papers/turkeltaub_1.pdf. Retrieved 2007-06-17. </ref>

Influencedby the kinesthetic work of Helen Keller and Grace Fernald, andlooking for a way to teach reading using both left and right brainfunctions,[68] Orton later workedwith psychologist and educator Anna Gillingham to develop aneducational intervention that pioneered the use of simultaneousmultisensory instruction. The Orton-Gillingham approach to remedialreading instruction is still widely used and forms the basis of manyreading intervention programs. [69]

Incontrast, Dearborn, Gates, Bennet and Blau considered a faulty guidanceof the seeing mechanism to be the cause. The data collected in 1931 byTinker and Goodenough (The J.Educ. Psych.)(26) seemed to support thisthesis. They sought to discover if a conflict between spontaneousorientation of the scanning action of the eyes from right to left andtraining aimed at the acquisition of an opposite direction would allowan interpretation of the facts observed in the dyslexic disorder andespecially of the ability to mirror-read. To this end the authorsasked four adults to read a text reflected in a mirror for ten minutesa day for five months. In all subjects, the words were not perceived intheir globality but required a meticulous analysis of the letters andsyllables. They also demonstrated total or partial inversions evensometimes affecting the order of the words in a sentence. They revealeda curious impression of not just horizontal but also verticalinversions. These are errors that exist amongst dyslexics and theysuffer from the aggravating circumstance inherent in all learning. Whatremained to be demonstrated was that there exists a preference amongstdyslexics, without sensory deficiency, or mental retardation, or anybackwardness in speech or language, towards scanning with the eyes fromright to left. Proof of this was provided in a work conducted underClement Launay in 1949 (thesis G. Mahec Paris 1951). In adultsubjects the reading of a series of 66 tiny lower-case letters,5 mm high, spaced 5 mm apart, first from left toright and then from right to left was more easily and quickly done inthe left to right direction. For former dyslexic children, asubstantial number read a series of 42 letters with equal speed in bothdirections and some (10%) read better from right to left than from leftto right. The phenomenon is clearly linked to the dynamics of sight asit disappears when the space between letters is increased, transformingthe reading into spelling. This experience also explains the ability tomirror-read. This reading test can also be used to diagnose seriouscases of dyslexia.

In the 1970s, a new hypothesis,based in part on Orton's theories, emerged that dyslexia stems from adeficit in phonological processing or difficulty inrecognizing that spoken words are formed by discrete phonemes (forexample, that the word CAT comes from the sounds [k], [æ], and [t]). Asa result, affected individuals have difficulty associating these soundswith the visual letters that make up written words. Key studies of thephonological deficit hypothesis include the finding that thestrongest predictor of reading success in school age children isphonological awareness,[70] and that phonological awareness instruction can improvedecoding skills for children with readingdifficulties.[71]

The advent ofneuroimaging techniques to study brain structure and functionenhanced the research in the 1980s and 1990s. Since then, interest inthe neurologically based causes has persisted. Current models of therelation between the brain and dyslexia generally focus on some form ofdefective or delayed brain maturation. More recently,genetic research has provided increasing evidencesupporting a genetic origin of dyslexia <refname=Collins>Collins, David and Rourke,Byron (October 2003). [taylorandfrancis.metapress.com/index/H47FWM65HHJAP0K6.pdf "Learning-disabled Brains: AReview of the Literature"] (PDF). Journal of Clinical andExperimental Neuropsychology 25 (7): 1011–1034. doi:10.1076/jcen.25.7.1011.16487. taylorandfrancis.metapress.com/index/H47FWM65HHJAP0K6.pdf. Retrieved 2007-07-11. </ref>.

Researchersare searching for a link between the neurological and genetic findings,and the reading disorder. There are many previous and current theoriesof dyslexia, but one that has much support from research is that,whatever the biological cause, dyslexia is a matter of reducedphonogical awareness, the ability to analyze and link the units ofspoken and written languages. [72].

උප වර්ග (Subtypes of developmental dyslexia)[සංස්කරණය]

Studiesby Castles and Coltheart suggest that developmental dyslexia includesat least two prevalent and distinct varieties or subtypes of dyslexia.Subtypes include surface dyslexia and phonological dyslexia.Understanding these subtypes is useful in diagnosing learning patternsand developing approaches for overcoming impairments that may be visualperception impairments or speech discrimination deficits. Thesesubtypes are based on differing patterns of underlying symptoms, assupported by a finding using large-scale data from comparative studiesof reading patterns in dyslexic and normal readers <refname=castles> Castles, A., & Coltheart, M. (1993). Varieties ofdevelopmental dyslexia. Cognition, 47(2), 149-180 </ref>. In thestudy by Castles and Coltheart, 56 dyslexic boys and 56 non-dyslexicboys as a control group were tested. During the test, the boys readaloud words and non-words that were presented to them. The researchersfound that surface dyslexics (subjects who have poor lexical skills, orcan’t make out irregular words well) had a mean difference of 14.4words between reading regular words versus irregular words, however,the mean difference in subjects with phonological dyslexia (subjectswho can’t use sub lexical skills, or can’t make out non-words) was only7.75 words which was comparable to the control group <refname=castles />. The majority of their subjects showed signs ofphonological dyslexia. Twenty-nine subjects showed that their non-wordreading skills were poorer than their irregular word reading skills.However, sixteen subjects showed the opposite where their irregularword reading skills were poorer than their non-word reading skills andwere called surface dyslexics [73].

Surface dyslexia

Surfacedyslexia is characterized by subjects who can read known words but whohave trouble reading words that are irregular [74].Surface dyslexia is the outcome of an individual who cannot functionusing the lexical procedure for reading out loud. The lexical procedureincludes sounding out a word through the use of a past word alreadyknown [73]. In Castles and Coltheart’sstudy, both control and dyslexic subjects were shown a card with a wordthat is irregular or that isn’t pronounced as it looks. Fifteen of the51 dyslexics were below the confidence limit set by the controlsubjects on ability to read irregular words. These subjects were thencalled surface dyslexics [75].

Phonological dyslexia

Phonologicaldyslexia is characterized by subjects who can read aloud both regularand irregular words but have difficulties with non-words and withconnecting sounds to symbols, or with sounding out words <refname=castles/>. Phonological processing tasks predict readingaccuracy and comprehension. This subtype is the most predominant formof dyslexia [74]. In Castles and Coltheart’s study, they had56 dyslexic boys and 56 non-dyslexic boys read words and non-wordsgiven to them. The majority of the boys, 55%, showed a phonologicaldyslexic pattern [73].In Castles and Coltheart’sstudy, dyslexic subjects and control subjects were asked to readnon-words listed on a card, 17 out of 51 cases of dyslexics were belowthe confidence limit in non-word reading, which was derived by thecontrol group of subjects their own age. These phonological dyslexicshave a lower non-word reading level than expected by reviewing theirirregular word reading level [75].Phonological dyslexia is the outcome of a subject who cannot functionusing the sub lexical (pronunciations are constructed from smallerorthographic components) procedure for reading out loud <refname=castles /> .In Castles and Coltheart’s study, dyslexic andcontrol subjects read words off a note card; the researchers found thatwhile reading irregular words, the dyslexic subjects scored comparableto the control subjects because sub lexical skills were not involved inthis test [73].

Double deficit dyslexia

Researchershave identified a deficit related to “naming speed”, which relates tothe ability of students to rapidly verbalize the names of symbols suchas letters and numbers when tested [76]. In their study, Wolf and Bowers tested out naming speedby having their subjects name a symbol as quickly as possible whenshown on a flash card. Difficulties in naming speed exist inconjunction with a phonological deficit, is characterized as doubledeficit dyslexia Many parents who have dyslexic children will/<refname = "Wolf-p91"/>.

Variations and related conditions[සංස්කරණය]

Dyslexiais a learning disability. It has many underlying causes that arebelieved to be a brain-based condition that influences the ability toread written language. It is identified in individuals who fail tolearn to read in the absence of a verbal or nonverbal intellectualimpairment, sensory deficit (e.g., a visual deficit or hearing loss),pervasive developmental deficit or a frank neurological impairment.

Thefollowing conditions may also be contributory or overlapping factors,or underlying cause of the dyslexic symptoms as they can lead todifficulty reading:

  • Auditory processing disorder is acondition that affects the ability to encode auditory information. Itcan lead to problems with auditory working memory and auditorysequencing. Many dyslexics have auditory processing problems includinghistory of auditory reversals. Auditory processing disorder isrecognized as one of the major causes of dyslexia.
  • Cluttering is a speech fluency disorder involving both therate and rhythm of speech, and resulting in impaired speechintelligibility. Speech is erratic and dysrhythmic, consisting of rapidand jerky spurts that usually involve faulty phrasing. The personalityof the clutterer bears striking resemblance to the personalities ofthose with learningdisabilities.[77]
  • Dyspraxia is a neurological condition characterized by amarked difficulty in carrying out routine tasks involving balance,fine-motor control, and kinesthetic coordination. Problems with shortterm memory and organization are typical of dyspraxics. This is mostcommon in dyslexics who also have attention deficit disorder.
  • Verbal dyspraxia is a neurological condition characterized bymarked difficulty in the use of speech sounds, which is the result ofan immaturity in the speech production area of the brain.
  • Dysgraphia is a disorder which expresses itself primarilyduring writing or typing, although in some cases it may also affecteye-hand coordination in such direction or sequence oriented processesas tying knots or carrying out a repetitive task. Dysgraphia isdistinct from Dyspraxia in that the person may have the word to bewritten or the proper order of steps in mind clearly, but carries thesequence out in the wrong order.
  • Dyscalculia is aneurological condition characterized by a problem with learningfundamentals and one or more of the basic numerical skills. Oftenpeople with this condition can understand very complex mathematicalconcepts and principles but have difficulty processing formulas andeven basic addition and subtraction.
  • Scotopic sensitivitysyndrome, also known as Irlen Syndrome, is a term used todescribe sensitivity to certain wavelengths of light which interferewith proper visual processing. See also Orthoscopics andasfedia.

Cross-Cultural Incidence Rate Comparison[සංස්කරණය]

Catherine McBride-Chang is a researcher in this area.

Scientific research[සංස්කරණය]

න්‍යායන් (Theories of developmental dyslexia)[සංස්කරණය]

Thefollowing theories should not be viewed as competing, but viewed astheories trying to explain the underlying causes of a similar set ofsymptoms from a variety of research perspectives and background.

පරිනාමීය උපකල්පනය (Evolutionary hypothesis)[සංස්කරණය]

Thistheory posits that reading is an unnatural act, and carried out byhumans for an exceedingly brief period in our evolutionary history(Dalby, 1986). It has been less than a hundred years that most westernsocieties promoted reading by the mass population and therefore theforces that shape our behavior have been weak. Many areas of the worldstill do not have access to reading for the majority of the population.There is no evidence that "pathology" underlies dyslexia but muchevidence for cerebral variation or differences. It is these essentialdifferences that are taxed with the artificial task of reading.[78] The native reading hypothesis of dyslexiais another evolutionary theory which argues that because spokenlanguage is naturally learned in the first few years of development,similarly, written language is best learned at the same early age. Itsuggests that many forms of dyslexia are therefore, to some extent, aresult of introducing reading too late in neurodevelopment. This meansthat the typically late reading of dyslexics might sometimes be thecause of dyslexia, rather than the other way around, and many casesof dyslexia might be prevented by the earlier introduction of readinginstruction.[79]

Phonological hypothesis[සංස්කරණය]

Thephonological hypothesis postulates thatdyslexics have a specific impairment in the representation, storageand/or retrieval of speech sounds. It explains dyslexics' readingimpairment on the basis that learning to read an alphabetic systemrequires learning the grapheme/phoneme correspondence, i.e. thecorrespondence between letters and constituent sounds of speech. Ifthese sounds are poorly represented, stored or retrieved, the learningof grapheme/phoneme correspondences, the foundation of reading byphonic methods for alphabetic systems, will be affectedaccordingly.[80]

Rapid auditory processing theory[සංස්කරණය]

Therapid auditory processing theory is an alternative to the phonologicaldeficit theory, which specifies that the primary deficit lies in theperception of short or rapidly varying sounds. Support for this theoryarises from evidence that dyslexics show poor performance on a numberof auditory tasks, including frequency discrimination and temporalorder judgment. Backward masking tasks, in particular, demonstrate a100-fold (40 dB) difference in sensitivity between normals anddyslexics. [81] Abnormal neurophysiologicalresponses to various auditory stimuli have also been demonstrated. Thefailure to correctly represent short sounds and fast transitions wouldcause further difficulties in particular when such acoustic events arethe cues to phonemic contrasts, as in /ba/ versus /da/. There is alsoevidence that dyslexics may have poorer categorical perception ofcertain contrasts.[80]

දෘෂ්‍ය න්‍යාය (Visual theory)[සංස්කරණය]

Thevisual theory (Lovegrove et al., 1980; Livingstone et al., 1991; Steinand Walsh, 1997) reflects another long standing tradition in the studyof dyslexia, that of considering it as a visual impairment giving riseto difficulties with the processing of letters and words on a page oftext. This may take the form of unstable binocular fixations, poorvergence, or increased visual crowding. The visual theory does notexclude a phonological deficit, but emphasizes a visual contribution toreading problems, at least in some dyslexic individuals. At thebiological level, the proposed etiology of the visual dysfunctionis based on the division of the visual system into two distinctpathways that have different roles and properties: the magnocellular and parvocellular pathways. The theorypostulates that the magnocellular pathway is selectively disrupted incertain dyslexic individuals, leading to deficiencies in visualprocessing, and, via the posterior parietal cortex, to abnormalbinocular control and visuospatial attention. Evidence formagnocellular dysfunction comes from anatomical studies showingabnormalities of the magnocellular layers of the lateral geniculatenucleus (Livingstone et al., 1991), psychophysical studies showingdecreased sensitivity in the magnocellular range, i.e. low spatialfrequencies and high temporal frequencies in dyslexics, and brainimaging studies.[80]

අනුමස්තිෂ්ක න්‍යාය (Cerebellar theory)[සංස්කරණය]

Yetanother view is represented by the automaticity/cerebellar theory ofdyslexia. Here the biological claim is that the dyslexic's cerebellumis mildly dysfunctional and that a number of cognitive difficultiesensue. First, the cerebellum plays a role in motor control andtherefore in speech articulation. It is postulated that retarded ordysfunctional articulation would lead to deficient phonologicalrepresentations. Secondly, the cerebellum plays a role in theautomatization of overlearned tasks, such as driving, typing andreading. A weak capacity to automatize would affect, among otherthings, the learning of grapheme-to-phoneme correspondences. Supportfor the cerebellar theory comes from evidence of poor performance ofdyslexics in a large number of motor tasks, in dual tasks demonstratingimpaired automatization of balance, and in time estimation, a non-motorcerebellar task. Brain imaging studies have also shown anatomical,metabolic and activation differences in the cerebellum ofdyslexics.[80]

Magnocellular theory[සංස්කරණය]

Thereis a unifying theory that attempts to integrate all the findingsmentioned above. A generalization of the visual theory, themagnocellular theory postulates that the magnocellular dysfunction isnot restricted to the visual pathways but is generalized to allmodalities (visual and auditory as well as tactile). Furthermore, asthe cerebellum receives massive input from various magnocellularsystems in the brain, it is also predicted to be affected by thegeneral magnocellular defect (Stein et al., 2001). Through a singlebiological cause, this theory therefore manages to account for allknown manifestations of dyslexia: visual, auditory, tactile, motor and,consequently, phonological. Beyond the evidence pertaining to each ofthe theories described previously, evidence specifically relevant tothe magnocellular theory includes magnocellular abnormalities in themedial as well as the lateral geniculate nucleus of dyslexics' brains,poor performance of dyslexics in the tactile domain, and theco-occurrence of visual and auditory problems in certaindyslexics.[80]

Perceptual visual-noise exclusion hypothesis[සංස්කරණය]

Theconcept of a perceptual noiseexclusion (Visual-Noise) deficit is an emerging hypothesis, supportedby research showing that dyslexic subjects experience difficulty inperforming visual tasks such as motion detection in the presence ofperceptual distractions, but do not show the same impairment when thedistracting factors are removed in an experimentalsetting.[82] The researchers have analogized their findingsconcerning visual discrimination tasks to findings in other researchrelated to auditory discrimination tasks. They assert that dyslexicsymptoms arise because of an impaired ability to filter out both visualand auditory distractions, and to categorize information so as todistinguish the important sensory data from the irrelevant.<refname=Sperling2005>Sperling, Anne J.; Lu, Z.L.; Manis, F.R.; Seidenberg, M.S. (2005). "Deficits in perceptual noise exclusion in developmental dyslexia". Nature Neuroscience 8: 862–863. doi:10.1038/nn1474. ISSN 1097-6256. http://www.nature.com/neuro/journal/v8/n7/abs/nn1474.html. Retrieved 2007-06-12. </ref>

Research using functional brain scan technology[සංස්කරණය]

AUniversity of Hong Kong study argues that dyslexia affects differentstructural parts of children's brains depending on the language whichthe children read.[83]The study focused on comparing children that were raised readingEnglish and children raised reading Chinese. Using MRI technologyresearchers found that the children reading English used a differentpart of the brain than those reading Chinese. Researchers weresurprised by this discovery and hope that the findings will help leadthem to any neurobiological cause for dyslexia.[83]

Research also indicates[සංස්කරණය]

ජානමය සාධක (Genetic factors)[සංස්කරණය]

Afamilial component to reading disorders was identified in the 1950s,and twin studies beginning in the early 1980s onward suggest thatreading ability and disability is a heritable trait. Molecular studieshave since linked several forms of dyslexia to geneticmarkers.[84] [85] [86].

Geneticresearch in families and twins with dyslexia have identified over ninechromosome regions as being associated with susceptibility to dyslexia.As is common in complex genetics, several of studies have not yet beenreplicated. [87]

However, several candidate genes have been identified, including at the two regions first related to dyslexia: DCDC2 [88] and KIAA0319 on chromosome 6, and DYX1C1 on chromosome 15.

Physiology[සංස්කරණය]

Modernneuroimaging techniques such as functional Magnetic ResonanceImaging (fMRI) and Positron EmissionTomography (PET) have produced clear evidence of structuraldifferences in the brains of children with reading difficulties. It hasbeen found that people with dyslexia have a deficit in parts of theleft hemisphere of the brain involved in reading, which includes theinferior frontal gyrus, inferior parietal lobule, and middleand ventral temporal cortex.[89] [90]

Scientificstudies of brains donated to medical research have revealed that thereare anatomical differences in two parts of the dyslexic brain: thecerebral cortex and the thalamus. In 1979 Albert Galaburda ofHarvard Medical School noticed anatomical differences in thelanguage center in a dyslexic brain, showing microscopicdifferences known as ectopias and microgyria. Both affect thetypical six-layer structure of the cortex. Anectopia is a collection of neurons that have pushed up from thelower layers of the cortex into the outermost one. A microgyrus is anarea of cortex that includes only four layers instead of six. Thesedifferences affect connectivity and functionality of the cortex incritical areas related to auditoryprocessing and visual processing, which seems consistent with thehypothesis that dyslexia stems from a phonological awareness deficit.

Studiesof both autopsied brains and living brains using neuroimagingtechniques have shown that the brains of dyslexic children aresymmetrical, unlike the asymmetrical brains of non-dyslexic readers whohad larger left hemispheres.[91]

Scientists do not claim thatall people with dyslexia have these structural brain differences.However, the studies are evidence that some children's reading problemsare brain based. The challenge for researchers is to determine howthese structural differences affect reading acquisition.[92]

Effect of language orthography[සංස්කරණය]

Somestudies have concluded that speakers of languages whose orthographyhas a highly consistent correspondence between letter and sound (e.g.,Italian) suffer less from the effects of dyslexiathan speakers of languages where the letter-sound correspondence isless consistent (e.g. English and French).[93]

Inone of these studies, reported in Seymour et al.,[94] the word-reading accuracy offirst-grade children of different European languages was measured.English children had an accuracy of just 40%, whereas among children ofmost other European languages accuracy was about 95%, with French andDanish children somewhere in the middle at about 75%; Danish and French are known to have anirregular pronunciation.

However, this does not meanthat dyslexia is caused by orthography: instead, Ziegler etal.[95] claim that thedyslexia suffered by German or Italian dyslexics is of the same kind asthe one suffered by the English ones, supporting the theory that theorigin of dyslexia is biological. In a study by Paulescu et al.(Science, 2001) English, French, and Italian dyslexics were found tohave the same brain function signature when studied with functionalmagnetic resonance imaging (fMRI), a signature that differed fromnon-dyslexic readers. However, dyslexia has more pronounced effects onorthographically difficult languages, e.g., dyslexics have moredifficulty in English than Italian. Modern theories of some forms ofdyslexia uses orthography to test a hypothesis of psychologicalcausation

Characteristics[සංස්කරණය]

Formal diagnosisof dyslexia is made by a qualified professional, such as a neurologistor an educational psychologist. Evaluation generally includes testingof reading ability together with measures of underlying skills such astests of rapid naming, to evaluate short term memory and sequencingskills, and nonword reading to evaluate phonological coding skills.Evaluation will usually also include an IQ test to establish a profileof learning strengths and weaknesses. However, the use of a"discrepancy" between full scale IQ and reading level as a factor indiagnosis has been discredited by recent research.<refname=Fletcher1992>Fletcher, Jack M; Francis DJ, Rourke BP, Shaywitz SE, Shaywitz BA. (November 1992). "The validity of discrepancy-based definitions of reading disabilities.". J Learn Disabil 25(9):555-61, 573. 25 (9): 555–61, 573. ISSN ISSN-0022-2194. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1431539&dopt=Citation. Retrieved 2007-06-15. </ref> It often includesinterdisciplinary testing to exclude other possible causes for readingdifficulties, such as a more generalized cognitive impairment orphysical causes such as problems with vision or hearing.

Recentadvances in neuroimaging and genetics provide evidence thatcould potentially help identify children with dyslexia before theylearn to read in the future. However, such tests have not yet beendeveloped and more research is needed before such testing could beconsidered reliable.

Speech, hearing and listening[සංස්කරණය]

Speechdelays may be an early warning sign of dyslexia. Many dyslexics mayhave problems processing and decoding auditory input prior toreproducing their own version of speech. Early stuttering orcluttering can also be warning signs of dyslexia.

Manydyslexics also can have problems with speaking clearly. They can mix upsounds in multi-syllabic words (ex: aminal for animal, bisghetti forspaghetti, hekalopter for helicopter, hangaberg for hamburger, ageenfor magazine, etc.) They also can have problems speaking in fullsentences. They can have trouble correctly articulating Rs and Ls aswell as Ms and Ns. They often have "immature" speech. They may still besaying "wed and gween" instead of "red and green" in second or thirdgrade. Many dyslexics might have speech therapy in special education.They may have fast speech, cluttered speech, or hesitant speech.[96] [97]

Reading requiresthe sounding out of words. Therefore, it makes sense that children withspeech problems can end up having reading problems later. Many have problems with speech due to problems withauditory processing disorder issues.

Manydyslexics have problems with phonemic awareness. Phonemes are thesmallest units in spoken language. The Auditory related underlyingcauses of dyslexia may be partially remediated by auditory therapy orspeech therapy, which help with phonemic awareness. This may help tomake sense of phonics which may help with phonological awareness, whichis needed to sound out words.

Many acquire auditory processing disorder as an underlying cause of dyslexia from glue ear, otitis media.

Some shared symptoms of the speech/hearing deficits and dyslexia:

  1. Confusion with before/after, right/left, and so on
  2. Difficulty learning the alphabet
  3. Difficulty with word retrieval or naming problems
  4. Difficulty identifying or generating rhyming words, or counting syllables in words (phonological awareness)
  5. Difficulty with hearing and manipulating sounds in words (phonemic awareness)
  6. Difficulty distinguishing different sounds in words (auditory discrimination)
  7. Difficulty in learning the sounds of letters
  8. Difficulty associating individual words with their correct meanings
  9. Difficulty with time keeping and concept of time
  10. Confusion with combinations of words
  11. Due to fear of speaking incorrectly, some children become withdrawn andshy or become bullies out of their inability to understand the socialcues in their environment
  12. Difficulty in organization skills

Theidentification of these factors results from the study of patternsacross many clinical observations of dyslexic children. In the UK,Thomas Richard Miles was important in such work and hisobservations led him to develop the Bangor Dyslexia Diagnostic Testඋපන්‍යාස දෝෂය: අනීතික <ref> ටැගය; අනීතික නාමයන්, නිද. පමණට වැඩි

Reading and spelling[සංස්කරණය]

  • Spelling errors — Because of difficulty learning letter-soundcorrespondences, individuals with dyslexia might tend to misspellwords, or leave vowels out of words.
  • Letter order - Dyslexicsmay also reverse the order of two letters especially when the final,incorrect, word looks similar to the intended word (e.g., spelling"dose" instead of "does").
  • Letter addition/subtraction -Dyslexics may perceive a word with letters added, subtracted, orrepeated. This can lead to confusion between two words containing mostof the same letters.
  • Highly phoneticized spelling - Dyslexicsalso commonly spell words inconsistently, but in a highly phonetic formsuch as writing "shud" for "should". Dyslexic individuals alsotypically have difficulty distinguishing among homophones such as"their" and "there".
  • Vocabulary - Having a small written vocabulary, even if they have a large spoken vocabulary.

Writing and motor skills[සංස්කරණය]

Becauseof literacy problems, an individual with dyslexia may have difficultywith handwriting. This can involve slower writing speed than average orpoor handwriting characterised by irregularly formed letters. They mayuse inappropriate words when writing.

Some studieshave also reported gross motor difficulties in dyslexia, includingmotor skills disorder. This difficulty is indicated by clumsinessand poor coordination. The relationship between motor skills andreading difficulties is poorly understood but could be linked to therole of the cerebellum and inner ear in the development of readingand motor abilities.[98]

Mathematical abilities[සංස්කරණය]

Dyslexia should not be confused with dyscalculia, a learning disability marked by severe difficulties with mathematics. Individualswith dyslexia can be gifted in mathematics while having poor readingskills. However, in spite of this they might have difficulty with wordproblems (i.e., descriptive mathematics, engineering, or physicsproblems that rely on written text rather than numbers or formulas). Individualswith dyslexia may also have difficulty remembering mathematical facts,such as multiplication tables, learning the sequence of steps whenperforming calculations, such as long division, and other mathematicswhich involve remembering the order in which numbers appear. This maybe exhibited by having a slow response in mathematical drills anddifficulty with word problems.

Creativity, arts, business[සංස්කරණය]

Dyslexicpeople often have a natural flair for one or more of the arts such asmusic, dance, drawing or acting. Dyslexic people also often possess anatural ability to see patterns in noise, producing creative abstractideas pulled out of what many would look upon as mundane sensoryenvironments[තහවුරු​ කරන්න].

A study hasfound that entrepreneurs are five times more likely to be dyslexic thanaveragecitizens[99].

The Dyslexic Renaissance[සංස්කරණය]

Recentlya movement has begun to coalesce around evidence that Dyslexia seems tobe a natural neurological variation and a useful set of traits whendealing with large and complex bodies of information. The movement torecognize Dyslexic strengths has arisen in a number of diverse fields,Neurology, Computer Graphics, Education, but was first described andpromoted in Thomas G. West's 1991 book, In the Mind's Eye. VisualThinkers, Gifted people with Dyslexia and other Learning Difficulties,Computer Images and the Ironies of Creativity.

ප්‍රතිකාර[සංස්කරණය]

Thereis no cure for dyslexia, but dyslexic individuals can learn to read andwrite with appropriate education or treatment. There is wide researchevidence indicating that specialized phonics instruction can helpremediate the reading deficits. The fundamental aim is to make childrenaware of correspondences between graphemes and phonemes, and torelate these to reading and spelling. It has been found that training,that is also focused towards visual language andorthographic issues, yields longer-lasting gains thanmere oral phonological training.[72]

Teachersare also using audiobooks as a way of teaching textbooks in an engagingway to those with dyslexia. In the UK, one of the biggest charities isListening Books, offering members a streaming service over theinternet. www.listening-books.org.uk An Australian company,ReadHowYouWant is working to make all published books available inaudiobookform[100].

Accessiblepublishing, the method by which charities and companies work toprovide books and textbooks in a variety of formats and fonts suitablefor all readers, has long been focused on developing formats to improvedyslexia by use of word patterns, phonic symbols, highlighting mirroredletters (such as b and d), and increasing the font size aswords movealong[101].

Effectivetraining is given by teachers at school or kindergarten. Meta-analysisevaluating the effects of phonological awareness instruction hasshown that word reading skills of all children, those with a risk forreading problems as well as those developing typically, improved theirreading in systematic phonics instruction, a method that encourages aword to be recognised through the building of its constituent sounds.Basic phonemic awareness instruction did not, however, improve spellingin disabled readers.[102]None of the studies included measures of reading fluency.<refname=Necoechea2003>Necoechea, D. M.; Swanson, H. L. (2003). "The role of readingintervention research in the identification of children with readingdifficulties: A meta-analysis of the literature funded by theNICHD.". Advances in Learning and Behavioral Disabilities 16: 83–161. doi:10.1016/S0735-004X(03)16004-1. </ref>

The core deficit of dyslexia is in learning to read at the word level [103],and individuals with dyslexia require more practice to master skills intheir areas of deficit. In the circumstances where typically developingchildren need 30 to 60 hours training, the number of hours that hasresulted in optimistic conclusions concerning the treatability ofdyslexia is between 80 and 100 hours, or less if the intervention isstarted sufficiently early. Only approximately 20% of adults with earlyreading difficulties have acquired fluent reading skills in adulthood.[72]

FunctionalMRI (fMRI) studies have shown changes in the brains of dyslexicchildren and adults with phonics tutoring, along with improvedperformance on tests of phonemic awareness and text decoding.<refname=Shaywitz2004>Shaywitz, B.; Shaywitz, S.; Blachman, B.; Pugh, K.R.; Fulbright, R.; Skudlarski, P.; Others, (2004). "Development of left occipitotemporal systemsfor skilled reading following a phonologically based intervention inchildren" (PDF). Biological Psychiatry 55: 926–933. doi:10.1016/j.biopsych.2003.12.019. http://www.haskins.yale.edu/papers/intervention_biol_psych_200.pdf. </ref> [104] FunctionalMRI studies have also shown changes in the brain and spellingimprovement of dyslexic children taught spelling phonetically in anorthographic manner. [105]

Onefactor that characterises the field of dyslexia treatment is theincessant flow of alternative therapies for developmental andlearning disabilities. These controversial treatments includenutritional supplements, special diets, homeopathy, andosteopathy/chiropractic manipulation.[106]

Becausedyslexia has often gone undiagnosed in children, many adults sufferfrom the condition without realizing it. There is now an[107]adult dyslexia test that can help adults discover if dyslexia is thecause of some of their difficulties with reading and writing.

Facts and statistics[සංස්කරණය]

Inthe United States, researchers estimate the prevalence of dyslexia torange from three to ten percent of school-aged children though somehave put the figure as high as 17 percent.[108][109] Recent studies indicate thatdyslexia is particularly prevalent among small business owners,with roughly 20 to 35 percent of U. S. and British entrepreneurs beingaffected. Researchers theorise that many dyslexic entrepreneurs attainsuccess by delegating responsibilities and excelling at verbalcommunication.[110]

Dyslexiais diagnosed more frequently in boys. However, this may not reflect theactual occurrence of dyslexia. Evidence based on randomly selectedpopulations of children indicate that dyslexia affects boys and girlsequally; that dyslexia is diagnosed more frequently in boys appears tobe the result of sampling bias in school-identified sample populations.[111]

Dyslexia'smain manifestation is a difficulty in developing word-level readingskills in elementary school children. Those difficulties resultfrom reduced ability to associate visual symbols with verbal sounds.While motivational factors must also be reviewed in assessing poorperformance, dyslexia is considered to be developmental. Mostscientific criteria for dyslexia exclude cases that can be explained asarising from environmental factors such as lack of education or totalsensory deficits.

Dyslexia can be substantiallycompensated for with proper therapy, training, and assistivetechnology. Many coping strategies are developed subconsciously by theindividual dyslexic.

Dyslexia has many variationsdependent on the cultural choice of visual notation of speech. So thenature of the notation used in different cultures creates differenttypes of problems for their groups of dyslexics. The differencesbetween the English text and Chinese characters is a good example.

Dyslexiacan also result in minor speech difficulties (i.e. switching aroundsyllables, mispronouncing, inable to express their ideas because theycan't find the words.)

Legal and educational support issues[සංස්කරණය]

Inthe English law case of Skipper v Calderdale Metropolitan BoroughSchool (2006) EWCA Civ 238, the Court of Appeal applied Phelps v London Borough ofHillingdon (2001) 2 AC 619 as the landmark case on the failure todiagnose dyslexia, in accordance with duty of care in English law,and to hold that the appellant could pursue her claim against herschool for humiliation, lost confidence, and lost self-esteem, and forloss of earnings following its failing to diagnose and treat herdyslexia despite the fact that, as Latham LJ. The ruling states inparagraph 29:

"The extent to which her dyslexia could have beenameliorated or provided for will always remain uncertain, as will theextent to which that would have affected her performance in publicexaminations; the evidence that we have includes material to suggestthat she, not surprisingly, reacted adversely to the break-up of herparents marriage when she was 15, in other words at a critical time inher education. Whether any improvement in her examination results wouldhave led to her life taking a significantly different course will alsobe a matter for some speculation."

Some charitableorganizations like the Scottish Rite Foundation have undertaken thetask of testing for dyslexia and making training classes and materialsavailable, often without cost, for teachers andstudents.[112][113][114]

InEngland and Wales, the failure of schools to diagnose andprovide remedial can help for dyslexia following the House of Lordsdecision in the case of Pamela Phelps has created an entitlement forstudents with dyslexia in Higher education to receive supportfunded via the Disabled Students Allowance. Support can take the formof IT equipment (software and hardware) as well as personal assistance,also known as non-medical helper support. Dyslexic students will alsobe entitled to special provision in examinations such as additionaltime to allow them to read and comprehend exam questions.

The British Disability Discrimination Act 1995 also covers dyslexia.

"Insome cases, people have 'coping strategies' which cease to work incertain circumstances (for example, where someone whostutters or has dyslexia is placed under stress). If itis possible that a person's ability to manage the effects of theimpairment will break down so that these effects will sometimes occur,this possibility must be taken into account when assessing the effectsof the impairment." — Paragraph A8, Guidance to theDefinitions of Disability.

In ස්කොට්ලන්තය, DavidBallantine a member of the cross party group on dyslexia put forward apetition through the Scottish Parliament Petitions Website. Thepetition called:

"On the Scottish Parliament to urgethe Scottish Government to consider the need for legislation to providea standardised assessment of all schoolchildren by the age of 8 whichwill inform parents, pupils and educators as to whether the pupil is atrisk of developing a specific learning difficulty."

Thepetition was contrary to the other view that children should not beidentified with dyslexia as it was felt that a significant proportionof these children who were dyslexic and not identified did not haveappropriate learning strategies in place and that it was the right ofthe child to know if they had a learning difficulty that would inhibittheir education.

Controversy[සංස්කරණය]

Somedisagreement exists as to whether dyslexia does indeed exist as acondition, or whether it simply reflects individual differences amongdifferent readers.

"The Dyslexia Myth" is adocumentary that appeared as part of the Dispatches series produced by British broadcaster Channel4.[115]First aired in September 2005, it claims to expose myths andmisconceptions that surround dyslexia. It argues that the commonunderstanding of dyslexia is not only false but makes it more difficultto provide the reading help that hundreds of thousands of childrendesperately need. Drawing on years of intensive academic research onboth sides of the Atlantic, it challenged the existence of dyslexia asa separate condition, and highlighted the many different forms ofreading styles.

The documentary only focused on thereading difficulties that dyslexics encounter. As discussed in previousheadings, dyslexia is more than a mere reading disability, and commonlyincludes symptoms that extend beyond reading difficulties. However,these symptoms are not included in the DSM-IV list of symptoms bywhich "Reading Disorder" is diagnosed in the USA.

JulianElliot, a psychologist at Durham University in the United Kingdom,disputes the characterization of dyslexia as a medical condition, andbelieves it should be treated simply as a reading difficulty. Accordingto Elliot, "[parents] don’t want their child to be considered lazy,thick or stupid. If they get called this medically diagnosed term,dyslexic, then it is a signal to all that it’s not to do withintelligence.”[116]Elliot believes that children of all levels of intelligence maystruggle with learning to read, and that all can be helped byeducational strategies appropriate to their needs. He feels thatresources are wasted on diagnosis and testing, and favors earlyintervention programs for all struggling readers.[117]

However,John Everatt of the University of Surrey, has suggested thatdyslexic students can be distinguished from other children with lowreading achievement by testing geared to assessing their strengths aswell as weaknesses. Dyslexic children tend to score significantlybetter than other children, including non-impaired children, on testsof creativity, spatial memory, and spatial reasoning. Dyslexicchildren also perform better than other reading-impaired children ontests of vocabulary and listening comprehension. Everatt suggests thatdyslexic children may be better served by educational interventionwhich includes strategies geared to their unique strengths in additionto skill remediation, and thus recommends more comprehensive evaluationand targeted interventions. [118]

GeraldColes, an educational psychologist and formerly an associate professorof clinical psychiatry at Robert Wood Johnson Medical School andthe University of Rochester, in the United States, who has writtenextensively on literacy and learning disabilities, asserts that thereare partisan agendas behind the educational policy-makers and that thescientific research that they use to support their arguments regardingthe teaching of literacy are flawed. These include the idea that thereare neurological explanations for learning disabilities. Gerald Colesargues that school failure must be viewed and treated in the context ofboth the learning environment and the child's individual abilities,behavior, family life, and social relationships. He then presents a newmodel of learning problems, in which family and school environments arethe major determinants of academic success. In this "interactive"paradigm, the attitudes and methods of education are more importantthan inherent strengths or deficits of the individualchild.[119]

The experience of Sudbury model of democratic education schools[සංස්කරණය]

Sudburymodel of democratic education schools assert that there are many waysto study and learn. They argue that learning is a process you do, not aprocess that is done to you; That is true of everyone. It'sbasic.[120] The experience ofSudbury model democratic schools shows that there are many ways tolearnthe intervention of teaching, to say, without the interventionof a teacher being imperative. In the case of reading for instance inthe Sudbury model democratic schools some children learn from beingread to, memorizing the stories and then ultimately reading them.Others learn from cereal boxes, others from games instructions, othersfrom street signs. Some teach themselves letter sounds, otherssyllables, others whole words. Sudbury model democratic schools adducethat in their schools no one child has ever been forced, pushed, urged,cajoled, or bribed into learning how to read or write, and they havehad no dyslexia. None of their graduates are real or functionalilliterates, and no one who meets their older students could ever guessthe age at which they first learned to read orwrite.[121][122] In a similar formstudents learn all the subjects, techniques and skills in these schools.

Dyslexia in literature, film, and television[සංස්කරණය]

Dyslexiccharacters have featured in a number of works of fiction. Notable worksinclude Henry Winkler's Hank Zipzer series of children's books,and Jennifer Weiner's 2002 novel, In HerShoes (which was adapted as the 2005 film, In Her Shoes). Toki Wartooth and Skwisgaar Skwigelfboth from the TV show Metalocalypse claim to be dyslexic as they cannotread music. Shooting Fish features Dylan a dyslexic conman, whomakes his living using confidence tricks to gain money from richpeople, he attributes his lifestyle to his inability to get a job whichhe blames on his dyslexia. Additionally, there are three episodes ofThe Cosby Show which focus on dyslexia, all three having Theo asone of the major characters in the plot. Aamir Khan's famousBollywood film Taare Zameen Par tells the story of eightyear-old Ishaan (Darsheel Safary) who suffers greatly until ateacher (Aamir Khan) identifies him as dyslexic. George Lopez from thehit TV show, also named George Lopez, has dyslexia in the storyline.Dr. Christina Yang from Grey's Anatomy is also dyslexic, although onlytwo other characters know about her dyslexia.

තවද බලන්න[සංස්කරණය]

References[සංස්කරණය]

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