Dyslexia
Encyclopedia
Dyslexia is a very broad term defining a learning disability
that impairs a person's fluency or comprehension accuracy in being able to read, and which can manifest itself as a difficulty with phonological awareness
, phonological decoding
, orthographic coding
, auditory short-term memory
, or rapid naming
.
Dyslexia is separate and 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
. It is believed that dyslexia can affect between 5 to 10 percent of a given population although there have been no studies to indicate an accurate percentage.
There are three proposed cognitive subtypes of dyslexia: auditory, visual and attentional. 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.
Accomplished adult dyslexics may be able to read with good comprehension, but they tend to read more slowly than non-dyslexics and may perform more poorly at nonsense word reading (a measure of phonological awareness) and spelling. Dyslexia is not an intellectual disability, since dyslexia and IQ
are not interrelated, as a result of cognition developing independently.
There are many definitions of dyslexia but no official consensus has been reached.
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".
MedlinePlus
and the National Institutes of Health
define dyslexia as "a reading disability resulting from the inability to process graphic symbols".
The National Institute of Neurological Disorders and Stroke
gives the following definition for dyslexia:
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.
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. However, the distinction between surface and phonological dyslexia has not replaced the old empirical terminology of dysphonetic versus dyseidetic types of dyslexia. The surface/phonological distinction is only descriptive, and devoid of any aetiological assumption as to the underlying brain mechanisms (Galaburda and Cestnick 2003). Studies have, however, alluded to potential differential underlying brain mechanisms in these populations given performance differences (Cestnick et al.). 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.
One common misconception about dyslexia is that dyslexic readers write words backwards or move letters around when reading. In fact, this only occurs in a very small population of dyslexic readers. Dyslexic people are better identified by writing that does not seem to match their level of intelligence from prior observations. Additionally, dyslexic people often substitute similar-looking, but unrelated, words in place of the ones intended (what/want, say/saw, help/held, run/fun, fell/fall, to/too, who/how etc.).
– 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 alphabetic orthographies that employ only 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. Logographic writing systems, notably Japanese
and Chinese character
s, have graphemes that aren't linked directly to their pronunciation, which pose a different type of dyslexic difficulty.
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.
.
The following conditions may be contributory or overlapping factors, as they can lead to difficulty in reading:
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, and may be observed as stuttering
, cluttering
or hesitant speech.
Early intervention is very helpful.
Especially for undergraduates, some consideration of what 'reading' is and what it is for can be useful. There are techniques (reading the first sentence [and/or last] of each paragraph in a chapter, for example) which can give an overview of content. This can be sufficient for some purposes. Since stress and anxiety are contributors to a dyslexic's weaknesses in absorbing information, removing these can assist in improving understanding. When a dyslexic knows that not every reading experience must be onerous, it greatly helps their mental approach to the task.
The best approaches acknowledge that the objective in helping to improve a dyslexic's 'reading' is not to 'read-like-a-non-dyslexic-does', but to find a way of extracting information from text that works efficiently for someone who processes such information differently from the majority.
For dyslexia intervention with alphabet writing systems the fundamental aim is to increase a child's awareness of correspondences between graphemes and phoneme
s, 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.
The best form of approach is determined by the underlying neurological cause(s) of the dyslexic symptoms.
Context sensitive spell checkers combined with text-to-speech systems offer forms of assistive technology
to dyslexia users, supporting reading and writing.
There is some evidence that the use of specially tailored fonts may provide some measure of assistance for those suffering from dyslexia; however scientific confirmation of this currently appears to be limited to a single master's thesis.
, and especially to languages of European
origin. However, substantial research is also available regarding dyslexia for speakers of Arabic, Chinese, and Hebrew.
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
.
That dyslexia is neurobiological in origin is supported by what Lyon et al. proclaimed as "overwhelming and converging data from functional brain imaging investigations" (2003, p. 3). The results of these studies suggest that there are observable differences in how the dyslexic brain functions when compared to the brain of a typical reader. Using fMRI, Shaywitz found that good readers show a consistent pattern of strong activation in the back of the brain with weaker activation in the front of the brain during reading tasks. In contrast, the brain activation pattern in dyslexics is the opposite during reading tasks—the frontal part of the brain becomes overactive with weaker activation in the back. Shaywitz points out "It is as if these struggling readers are using the systems in the front of the brain to try to compensate for the disruption in the back of the brain."
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, with some implication that the observed neural manifestation of developmental dyslexia is task-specific (i.e., functional rather than structural).
A University of Hong Kong study argues that dyslexia affects different structural parts of children's brains depending on the language which the children read. The study focused on comparing children that were raised reading English and children raised reading Chinese. This is supported in a review by T. Hadzibeganovic et al. (2010).
A University of Maastricht (Netherlands) study revealed that adult dyslexic readers underactivate superior temporal cortex for the integration of letters and speech sounds.
.
Several candidate genes have been identified, including at the two regions first related to dyslexia: DCDC2
and KIAA0319
on chromosome 6, and DYX1C1
on chromosome 15.
A 2007 review reported that no specific cognitive processes are known to be influenced by the proposed susceptibility genes.
A unifying theoretical framework of three working memory
components provides a systems perspective for discussing past and new findings in a 12-year research program that point to heterogeneity in the genetic and brain basis and behavioral expression of dyslexia.
While acknowledging that reading disability is a valid scientific curiosity, and that "seeking greater understanding of the relationship between visual symbols and spoken language is crucial" and that while there was "potential of genetics and neuroscience for guiding assessment and educational practice at some stage in the future", they conclude that "there is a mistaken belief that current knowledge in these fields is sufficient to justify a category of dyslexia as a subset of those who encounter reading difficulties".
Organizations
Learning disability
Learning disability is a classification including several disorders in which a person has difficulty learning in a typical manner, usually caused by an unknown factor or factors...
that impairs a person's fluency or comprehension accuracy in being able to read, and which can manifest itself as a difficulty with phonological awareness
Phonological awareness
Phonological awareness refers to an individual's awareness of the phonological structure, or sound structure, of spoken words. Phonological awareness is an important and reliable predictor of later reading ability and has, therefore, been the focus of much research.- Overview :Phonological...
, phonological decoding
Phonology
Phonology is, broadly speaking, the subdiscipline of linguistics concerned with the sounds of language. That is, it is the systematic use of sound to encode meaning in any spoken human language, or the field of linguistics studying this use...
, orthographic coding
Orthography
The orthography of a language specifies a standardized way of using a specific writing system to write the language. Where more than one writing system is used for a language, for example Kurdish, Uyghur, Serbian or Inuktitut, there can be more than one orthography...
, auditory short-term memory
Working memory
Working memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...
, or rapid naming
Rapid automatized naming
Rapid automatized naming is a task that measures how quickly individuals can name aloud objects, pictures, colors, orsymbols...
.
Dyslexia is separate and 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
Reading education
Reading education is the process by which individuals are taught to derive meaning from text.Government-funded scientific research on reading and reading instruction began in the U.S. in the 1960s. In the 1970s and 1980s, researchers began publishing findings based on converging evidence from...
. It is believed that dyslexia can affect between 5 to 10 percent of a given population although there have been no studies to indicate an accurate percentage.
There are three proposed cognitive subtypes of dyslexia: auditory, visual and attentional. 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.
Accomplished adult dyslexics may be able to read with good comprehension, but they tend to read more slowly than non-dyslexics and may perform more poorly at nonsense word reading (a measure of phonological awareness) and spelling. Dyslexia is not an intellectual disability, since dyslexia and IQ
Intelligence quotient
An intelligence quotient, or IQ, is a score derived from one of several different standardized tests designed to assess intelligence. When modern IQ tests are constructed, the mean score within an age group is set to 100 and the standard deviation to 15...
are not interrelated, as a result of cognition developing independently.
Classification
Spoken language is a universal form of human communication. The visual notation of written language is not found in all cultures and is relatively new with regards to human evolution.There are many definitions of dyslexia but no official consensus has been reached.
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".
MedlinePlus
MedlinePlus
MedlinePlus is a free Web site that provides consumer health information for patients, families, and Health care providers. The site brings together information from the United States National Library of Medicine, the National Institutes of Health , other U.S. government agencies, and...
and the National Institutes of Health
National Institutes of Health
The National Institutes of Health are an agency of the United States Department of Health and Human Services and are the primary agency of the United States government responsible for biomedical and health-related research. Its science and engineering counterpart is the National Science Foundation...
define dyslexia as "a reading disability resulting from the inability to process graphic symbols".
The National Institute of Neurological Disorders and Stroke
National Institute of Neurological Disorders and Stroke
The National Institute of Neurological Disorders and Stroke is a part of the U.S. National Institutes of Health . It conducts and funds research on brain and nervous system disorders and has a budget of just over US$1.5 billion...
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".
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.
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. However, the distinction between surface and phonological dyslexia has not replaced the old empirical terminology of dysphonetic versus dyseidetic types of dyslexia. The surface/phonological distinction is only descriptive, and devoid of any aetiological assumption as to the underlying brain mechanisms (Galaburda and Cestnick 2003). Studies have, however, alluded to potential differential underlying brain mechanisms in these populations given performance differences (Cestnick et al.). 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
The symptoms of dyslexia vary according to the severity of the disorder as well as the age of the individual.Preschool-aged children
It is difficult to obtain a certain diagnosis of dyslexia before a child begins school, but many dyslexic individuals have a history of difficulties that began well before kindergarten. Children who exhibit these symptoms early in life have a higher likelihood of being diagnosed as dyslexic than other children. These symptoms include:- delays in speech
- slow learning of new words
- difficulty in rhyming words, as in nursery rhymes
- low letter knowledge
- letter reversal or mirror writing (for example, "Я" instead of "R")
Early primary school children
- Difficulty learning the alphabet or letter order
- Difficulty with associating sounds with the letters that represent them (sound-symbol correspondence)
- Difficulty identifying or generating rhyming words, or counting syllables in words (phonological awarenessPhonological awarenessPhonological awareness refers to an individual's awareness of the phonological structure, or sound structure, of spoken words. Phonological awareness is an important and reliable predictor of later reading ability and has, therefore, been the focus of much research.- Overview :Phonological...
) - Difficulty segmenting words into individual sounds, or blending sounds to make words (phonemic awarenessPhonemic awarenessPhonemic awareness is a subset of phonological awareness in which listeners are able to hear, identify and manipulate phonemes, the smallest units of sound that can differentiate meaning...
) - Difficulty with word retrieval or naming problems
- Difficulty learning to decode written words
- Difficulty distinguishing between similar sounds in words; mixing up sounds in polysyllabic words (auditory discrimination) (for example, "aminal" for animal, "bisghetti" for spaghetti)
Older primary school children
- Slow or inaccurate reading (although these individuals can read to an extent)
- Very poor spelling which has been called dysorthographia (orthographic codingOrthographyThe orthography of a language specifies a standardized way of using a specific writing system to write the language. Where more than one writing system is used for a language, for example Kurdish, Uyghur, Serbian or Inuktitut, there can be more than one orthography...
) - Difficulty reading out loud, reading words in the wrong order, skipping words and sometimes saying a word similar to another word (auditory processing disorderAuditory processing disorderAuditory Processing Disorder , also known as Central Auditory Processing Disorder is an umbrella term for a variety of disorders that affect the way the brain processes auditory information. It is not a peripheral hearing disorder as individuals with APD usually have normal peripheral hearing...
) - Difficulty associating individual words with their correct meanings
- Difficulty with time keeping and concept of time when doing a certain task
- Difficulty with organization skills (working memoryWorking memoryWorking memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...
) - Children with dyslexia may fail to see (and occasionally to hear) similarities and differences in letters and words, may not recognize the spacing that organizes letters into separate words, and may be unable to sound out the pronunciation of an unfamiliar word (auditory processing disorder)
- Tendencies to omit or add letters or words when writing and reading
Secondary school children and adults
Some people with dyslexia are able to disguise their weaknesses, even from themselves. Many students reach higher education before they encounter the threshold at which they are no longer able to compensate for their learning weaknesses.One common misconception about dyslexia is that dyslexic readers write words backwards or move letters around when reading. In fact, this only occurs in a very small population of dyslexic readers. Dyslexic people are better identified by writing that does not seem to match their level of intelligence from prior observations. Additionally, dyslexic people often substitute similar-looking, but unrelated, words in place of the ones intended (what/want, say/saw, help/held, run/fun, fell/fall, to/too, who/how etc.).
Comorbidities
Several learning disabilities often occur with dyslexia, but it is unclear whether these learning disabilities share underlying neurological causes with dyslexia. These disabilities include, but are not limited to:- DysgraphiaDysgraphiaDysgraphia is a deficiency in the ability to write primarily in terms of handwriting, but also in terms of coherence. It occurs regardless of the ability to read and is not due to intellectual impairment...
— a disorder which expresses itself primarily through writing or typing, although in some cases it may also affect eye–hand coordinationEye–hand coordinationEye–hand coordination is the coordinated control of eye movement with hand movement, and the processing of visual input to guide reaching and grasping along with the use of proprioception of the hands to guide the eyes. In simple terms, eye-hand coordination involves the coordinated vision and...
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 dyspraxiaDyspraxiaDevelopmental dyspraxia is a motor learning difficulty that can affect planning of movements and co-ordination as a result of brain messages not being accurately transmitted to the body...
in that dyspraxia is simply related motor sequence impairment. - DyscalculiaDyscalculiaDyscalculia is a specific learning disability involving innate difficulty in learning or comprehending simple arithmetic. It is akin to dyslexia and includes difficulty in understanding numbers, learning how to manipulate numbers, learning maths facts, and a number of other related symptoms...
— a neurological condition characterized by a problem with basic sense of number and quantity and difficult retrieving rote math facts. Often people with this condition can understand very complex mathematical concepts and principles but have difficulty retrieving basic math facts involving addition and subtraction. - Attention Deficit Disorder — a high degree of co-morbidity has been reported between ADD / ADHD and dyslexia, although the contributions of dyslexia-related challenges such as auditory verbal working memory to attention issues has not been well established
- ClutteringClutteringCluttering is a speech disorder and a communication disorder characterized by speech that is difficult for listeners to understand due to rapid speaking rate, erratic rhythm, poor syntax or grammar, and words or groups of words unrelated to the sentence...
— a speech fluency disorder involving both the rate and rhythm of speech, resulting in impaired speech intelligibility. Speech is erratic and nonrhythmic, consisting of rapid and jerky spurts that usually involve faulty phrasing. The personality of people with cluttering bears striking resemblance to the personalities of those with learning disabilities.
Cause
Since the symptoms of dyslexia were first identified by Oswald Berkhan in 1881, and the term 'dyslexia' coined in 1887 by Rudolf Berlin, generations of researchers have been investigating what dyslexia is and trying to identify the biological causes. 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. Theories should not be viewed as competing, but as attempting to explain the underlying causes of a similar set of symptoms from a variety of research perspectives and background.Effect of language orthography
The complexity of a language's orthography or spelling system – formally, its orthographic depthOrthographic depth
The orthographic depth of an alphabetic orthography indicates the degree to which it deviates from simple one-to-one letter-phoneme correspondence....
– 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
Latin alphabet
The Latin alphabet, also called the Roman alphabet, is the most recognized alphabet used in the world today. It evolved from a western variety of the Greek alphabet called the Cumaean alphabet, which was adopted and modified by the Etruscans who ruled early Rome...
writing system
Writing system
A writing system is a symbolic system used to represent elements or statements expressible in language.-General properties:Writing systems are distinguished from other possible symbolic communication systems in that the reader must usually understand something of the associated spoken language to...
, with a complex orthographic structure that employs spelling patterns at several levels: principally, letter-sound correspondences, syllables, and morphemes. Other languages, such as Spanish
Spanish language
Spanish , also known as Castilian , is a Romance language in the Ibero-Romance group that evolved from several languages and dialects in central-northern Iberia around the 9th century and gradually spread with the expansion of the Kingdom of Castile into central and southern Iberia during the...
, have alphabetic orthographies that employ only letter-sound correspondences, so-called shallow orthographies
Phonemic orthography
A phonemic orthography is a writing system where the written graphemes correspond to phonemes, the spoken sounds of the language. In terms of orthographic depth, these are termed shallow orthographies, contrasting with deep 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. Logographic writing systems, notably Japanese
Japanese writing system
The modern Japanese writing system uses three main scripts:*Kanji, adopted Chinese characters*Kana, a pair of syllabaries , consisting of:...
and Chinese character
Chinese character
Chinese characters are logograms used in the writing of Chinese and Japanese , less frequently Korean , formerly Vietnamese , or other languages...
s, have graphemes that aren't linked directly to their pronunciation, which pose a different type of dyslexic difficulty.
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.
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%. Some populations (for example, Japanese and Chinese) may have relatively small number of dyslexic schoolchildren, and some populations (for example, European, and particularly sub-Saharan African populations) might have higher dyslexia prevalence. According to some researchers, despite the significant differences between the writing systems, Italian, German and English populations suffer similarly from Dyslexia.Exacerbating conditions
Dyslexia is attributed to neurological factors that influence the individual's ability to read, write, and spell written languageWritten language
A written language is the representation of a language by means of a writing system. Written language is an invention in that it must be taught to children, who will instinctively learn or create spoken or gestural languages....
.
The following conditions may be contributory or overlapping factors, as they can lead to difficulty in reading:
- AphasiaAphasiaAphasia is an impairment of language ability. This class of language disorder ranges from having difficulty remembering words to being completely unable to speak, read, or write....
- neurologically based speech disorders, which can cause alexia (acquired dyslexia). - Attention deficit hyperactivity disorder - A disorder that occurs in between 12% and 24% of those with dyslexia.
- Auditory processing disorderAuditory processing disorderAuditory Processing Disorder , also known as Central Auditory Processing Disorder is an umbrella term for a variety of disorders that affect the way the brain processes auditory information. It is not a peripheral hearing disorder as individuals with APD usually have normal peripheral hearing...
- A condition that affects the ability to process auditory information. Auditory processing disorder is a listening disability. It can lead to problems with auditory memory and auditory sequencingSequencingIn genetics and biochemistry, sequencing means to determine the primary structure of an unbranched biopolymer...
. Many people with dyslexia have auditory processing problems including history of auditory reversals, and may develop their own logographic cuesLogographic cuesLogographic cues are visual images embedded with specific, widely understood meaning; they are pictures that represent certain words or concepts...
to compensate for this type of deficit. Auditory processing disorder is recognized as one of the major causes of dyslexia. Some children can acquire auditory processing disorder as a result of experiencing otitis mediaOtitis mediaOtitis media is inflammation of the middle ear, or a middle ear infection.It occurs in the area between the tympanic membrane and the inner ear, including a duct known as the eustachian tube. It is one of the two categories of ear inflammation that can underlie what is commonly called an earache,...
with effusion (glue ear, sticky ear, grommets) and other severe ear conditions. - Developmental dyspraxia - 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 memoryWorking memoryWorking memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...
and organization are typical of dyspraxics. - Scotopic sensitivity syndromeScotopic sensitivity syndromeScotopic sensitivity syndrome, also known as Irlen Syndrome and Visual Stress Syndrome, approximating in some ways to Meares Irlen syndrome, and 'Visual Stress', refers to visual perceptual disorder affecting primarily reading and writing based activities...
, also known as Irlen Syndrome - A term used to describe sensitivity to certain wavelengths of light which interfere with visual processingVisual processingVisual processing is the sequence of steps that information takes as it flows from visual sensors to cognitive processing. The sensors may be zoological eyes or they may be cameras or sensor arrays that sense various portions of the electromagnetic spectrum....
. - Specific language impairmentSpecific language impairmentSpecific language impairment is diagnosed when a child's language does not develop normally and the difficulties cannot be accounted for by generally slow development , physical abnormality of the speech apparatus, autistic disorder, acquired brain damage or hearing loss.-Overview:Specific...
(SLI) - A developmental language disorder that can affect both expressive and receptive language. SLI is defined as a "pure" language impairment, meaning that is not related to or caused by other developmental disorders, hearing loss or acquired brain injury. A study by the Universities of MaastrichtMaastrichtMaastricht is situated on both sides of the Meuse river in the south-eastern part of the Netherlands, on the Belgian border and near the German border...
and UtrechtUtrecht UniversityUtrecht University is a university in Utrecht, Netherlands. It is one of the oldest universities in the Netherlands and one of the largest in Europe. Established March 26, 1636, it had an enrollment of 29,082 students in 2008, and employed 8,614 faculty and staff, 570 of which are full professors....
examined speech perceptionSpeech perceptionSpeech perception is the process by which the sounds of language are heard, interpreted and understood. The study of speech perception is closely linked to the fields of phonetics and phonology in linguistics and cognitive psychology and perception in psychology...
and speech productionSpeech productionSpeech production is the process by which spoken words are selected to be produced, have their phonetics formulated and then finally are articulated by the motor system in the vocal apparatus...
in 3-year-old Dutch children at familial risk of developing dyslexia. Their performance in speech sound categorization and their production of words was compared to that of age-matched children with SLI and typically developing controls. The results of the at-risk and SLI-group were highly similar. Analysis of the individual data revealed that both groups contained subgroups with good and poorly performing children. Their impaired expressive phonology seemed to be related to a deficit in speech perceptionSpeech perceptionSpeech perception is the process by which the sounds of language are heard, interpreted and understood. The study of speech perception is closely linked to the fields of phonetics and phonology in linguistics and cognitive psychology and perception in psychology...
. The findings indicate that both dyslexia and SLI can be explained by a multi-risk model which includes cognitive processes as well as geneticGeneticsGenetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
factors.
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, and may be observed as stuttering
Stuttering
Stuttering , also known as stammering , is a speech disorder in which the flow of speech is disrupted by involuntary repetitions and prolongations of sounds, syllables, words or phrases, and involuntary silent pauses or blocks in which the stutterer is unable to produce sounds...
, cluttering
Cluttering
Cluttering is a speech disorder and a communication disorder characterized by speech that is difficult for listeners to understand due to rapid speaking rate, erratic rhythm, poor syntax or grammar, and words or groups of words unrelated to the sentence...
or hesitant speech.
Management
There is no cure for dyslexia, but dyslexic individuals can learn to read and write with appropriate educational support.Early intervention is very helpful.
Especially for undergraduates, some consideration of what 'reading' is and what it is for can be useful. There are techniques (reading the first sentence [and/or last] of each paragraph in a chapter, for example) which can give an overview of content. This can be sufficient for some purposes. Since stress and anxiety are contributors to a dyslexic's weaknesses in absorbing information, removing these can assist in improving understanding. When a dyslexic knows that not every reading experience must be onerous, it greatly helps their mental approach to the task.
The best approaches acknowledge that the objective in helping to improve a dyslexic's 'reading' is not to 'read-like-a-non-dyslexic-does', but to find a way of extracting information from text that works efficiently for someone who processes such information differently from the majority.
For dyslexia intervention with alphabet writing systems the fundamental aim is to increase a child's awareness of correspondences between graphemes and phoneme
Phoneme
In a language or dialect, a phoneme is the smallest segmental unit of sound employed to form meaningful contrasts between utterances....
s, and to relate these to reading and spelling. It has been found that training focused towards visual language and orthographic
Orthography
The orthography of a language specifies a standardized way of using a specific writing system to write the language. Where more than one writing system is used for a language, for example Kurdish, Uyghur, Serbian or Inuktitut, there can be more than one orthography...
issues yields longer-lasting gains than mere oral phonological training.
The best form of approach is determined by the underlying neurological cause(s) of the dyslexic symptoms.
Context sensitive spell checkers combined with text-to-speech systems offer forms of assistive technology
Assistive technology
Assistive technology or adaptive technology is an umbrella term that includes assistive, adaptive, and rehabilitative devices for people with disabilities and also includes the process used in selecting, locating, and using them...
to dyslexia users, supporting reading and writing.
There is some evidence that the use of specially tailored fonts may provide some measure of assistance for those suffering from dyslexia; however scientific confirmation of this currently appears to be limited to a single master's thesis.
History
- Identified by Oswald BerkhanOswald BerkhanOswald Berkhan was a German physician.Born in Blankenburg am Harz, He was one of the initiators of the "Idioten-Anstalt Neuerkerode" , which was thought to be a sanctuary for disabled and ill people...
in 1881, the term 'dyslexia' was later coined in 1887 by Rudolf Berlin, an ophthalmologist practising in StuttgartStuttgartStuttgart is the capital of the state of Baden-Württemberg in southern Germany. The sixth-largest city in Germany, Stuttgart has a population of 600,038 while the metropolitan area has a population of 5.3 million ....
, Germany, from the GreekGreek languageGreek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
prefix δυσ- (dus-), "hard, bad, difficult" + λέξις (lexis), "speech, word". - In 1896, W. Pringle Morgan published a description of a reading-specific learning disorder in the British Medical JournalBritish Medical JournalBMJ is a partially open-access peer-reviewed medical journal. Originally called the British Medical Journal, the title was officially shortened to BMJ in 1988. The journal is published by the BMJ Group, a wholly owned subsidiary of the British Medical Association...
titled "Congenital Word Blindness". - During the 1890s and early 1900s, James Hinshelwood published a series of articles in medical journals describing similar cases of congenital word blindness. In his 1917 book Congenital Word Blindness, Hinshelwood asserted that the primary disability was in visual memory for words and letters, and described symptoms including letter reversals, and difficulties with spelling and reading comprehension.
- 1925 Samuel T. OrtonSamuel OrtonSamuel Torrey Orton was an American physician who pioneered the study of learning disabilities. He is best known for his work examining the causes and treatment of reading disability, or dyslexia....
determined that there was a syndrome unrelated to brain damage that made learning to read difficult. Orton's theory strephosymboliaStrephosymboliaStrephosymbolia was first coined in 1925 by Samuel Orton as being an answer to the implications the term word blindness makes. Specifically this new word was created to make a distinction between itself and word-blindness, but no reasons are given for what these distinctions arise from, or what...
described individuals with dyslexia having difficulty associating the visual forms of words with their spoken forms. Orton observed that reading deficits in dyslexia did not seem to stem from strictly visual deficits. He believed the condition was caused by the failure to establish hemispheric dominanceLateralization of brain functionA longitudinal fissure separates the human brain into two distinct cerebral hemispheres, connected by the corpus callosum. The sides resemble each other and each hemisphere's structure is generally mirrored by the other side. Yet despite the strong anatomical similarities, the functions of each...
in the brain.reprinted: Orton later worked with the psychologist and educator Anna GillinghamAnna GillinghamAnna Gillingham was an educator and psychologist. Working with Dr. Samuel Orton, she trained teachers and published instructional materials regarding reading instruction, producing the Orton-Gillingham approach to reading instruction...
to develop an educational intervention that pioneered the use of simultaneous multisensory instruction. - In contrast, Dearborn, Gates, Bennet and Blau considered a faulty guidance of the seeing mechanism to be the cause. They sought to discover if a conflict between spontaneous orientation of the scanning action of the eyes from right to left and training aimed at the acquisition of an opposite direction would allow an interpretation of the facts observed in the dyslexic disorder and especially of the ability to mirror-read.
- 1949 Research conducted under G. Mahec show that the phenomenon is clearly linked to the dynamics of sight as it disappears when the space between letters is increased, transforming the reading into spelling. This experience also explains the ability to mirror-read.
- 1968 Makita suggested that dyslexia was mostly absent among Japanese children. A 2005 study shows that Makita's claim of rarity of incidence of reading disabilities in Japan to be incorrect.
- In the 1970s a new hypothesis emerged: that dyslexia stems from a deficit in phonologicalPhonologyPhonology is, broadly speaking, the subdiscipline of linguistics concerned with the sounds of language. That is, it is the systematic use of sound to encode meaning in any spoken human language, or the field of linguistics studying this use...
processing or difficulty in recognizing that spoken words are formed by discrete phonemePhonemeIn a language or dialect, a phoneme is the smallest segmental unit of sound employed to form meaningful contrasts between utterances....
s. Affected individuals have difficulty associating these sounds with the visual letters that make up written words. Key studies suggested the importance of phonological awarenessPhonological awarenessPhonological awareness refers to an individual's awareness of the phonological structure, or sound structure, of spoken words. Phonological awareness is an important and reliable predictor of later reading ability and has, therefore, been the focus of much research.- Overview :Phonological...
, - 1979 Galaburda and Kemper, and Galaburda et al. 1985, reported observations from the examination of post autopsy brains of people with dyslexia. Their studies reporting observed anatomical differences in the language centerLanguage centerThe term language center refers to the areas of the brain which serve a particular function for speech processing and production.- Current scientific consensus :...
in a dyslexic brain, taken with the similar work of Cohen et al. 1989, suggested abnormal corticalCortex (anatomy)In anatomy and zoology the cortex is the outermost layer of an organ. Organs with well-defined cortical layers include kidneys, adrenal glands, ovaries, the thymus, and portions of the brain, including the cerebral cortex, the most well-known of all cortices.The cerebellar cortex is the thin gray...
development, which was presumed to occur before or during the sixth month of foetal brain development. - 1993 Castles and Coltheart describe developmental dyslexia as two prevalent and distinct varieties using the subtypes of Alexia, Surface and Phonological Dyslexia. Manis et al. 1996, concluded that there were probably more than two subtypes of dyslexia, which would be related to multiple underlying deficits. Cestnick and Coltheart (1999) demonstrated what these underlying deficits are in part, through unveiling different profiles of phonological versus surface dyslexics. Cestnick and Jerger (2000) and Cestnick (2001) further demonstrated distinct processing differences between phonological and surface dyslexics.
- 1994 From post autopsy specimens Galaburda et al., reported : Abnormal auditory processing in people with dyslexia suggests that accompanying anatomical abnormalities might be present in the auditory system. Supported the reported behavioral findings of a left hemisphere-based phonological defect in dyslexic individuals.
- The development of neuroimagingNeuroimagingNeuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain...
technologies during the 1980s and 1990s enabled dyslexia research to make significant advances. Positron emission tomographyPositron emission tomographyPositron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
(PET) and functional magnetic resonance imagingFunctional magnetic resonance imagingFunctional magnetic resonance imaging or functional MRI is a type of specialized MRI scan used to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging...
(fMRI) studies have revealed the neural signature of adult normal reading (e.g. Fiez and Petersen, 1998; Turkeltaub et al., 2002 and phonological processing (e.g., Gelfand and Bookheimer, 2003; Poldrack et al., 1999). Employing various experimental approaches and paradigms (e.g., the detection or judgment of rhymes, nonword reading, and implicit reading), these studies have localized dysfunctional phonological processing in dyslexia to left-hemisphere perisylvian regions, especially for the alphabetic writing systemAlphabetAn alphabet is a standard set of letters—basic written symbols or graphemes—each of which represents a phoneme in a spoken language, either as it exists now or as it was in the past. There are other systems, such as logographies, in which each character represents a word, morpheme, or semantic...
(Paulesu et al., 2001; for review, see Eden and Zeffiro, 1998,). However, it has been demonstrated that in nonalphabetic scripts, where reading places less demands on phonemic processing and the integration of visual-orthographicOrthographyThe orthography of a language specifies a standardized way of using a specific writing system to write the language. Where more than one writing system is used for a language, for example Kurdish, Uyghur, Serbian or Inuktitut, there can be more than one orthography...
information is crucial, dyslexia is associated with under activity of the left middle frontal gyrusMiddle frontal gyrusThe middle frontal gyrus makes up about one-third of the frontal lobe of the human brain....
(Siok et al., 2004). - 1999 Wydell and ButterworthBrian ButterworthBrian Butterworth is a professor of cognitive neuropsychology in the Institute of Cognitive Neuroscience at University College London. His research has ranged from speech errors and pauses, short-term memory deficits, dyslexia, reading both in alphabetic scripts and logograms, and mathematics and...
reported the case study of an English-Japanese bilingual with monolingual dyslexia. Suggesting that any language where orthographyOrthographyThe orthography of a language specifies a standardized way of using a specific writing system to write the language. Where more than one writing system is used for a language, for example Kurdish, Uyghur, Serbian or Inuktitut, there can be more than one orthography...
-to-phonologyPhonologyPhonology is, broadly speaking, the subdiscipline of linguistics concerned with the sounds of language. That is, it is the systematic use of sound to encode meaning in any spoken human language, or the field of linguistics studying this use...
mapping is transparent, or even opaqueWiktionaryWiktionary is a multilingual, web-based project to create a free content dictionary, available in 158 languages...
, or any language whose orthographic unit representing sound is coarse (i.e. at a whole character or word level) should not produce a high incidence of developmental phonological dyslexia, and that orthography can influence dyslexic symptoms. - 2003 Ziegler and colleagues claimed that the dyslexia suffered by German or Italian dyslexics is very similar to the one suffered by English dyslexics (readers of different—shallow versus deep orthographic systems), supporting the idea that the origin of dyslexia is mostly biological.
- 2007 Lyytinen et al. Researchers are seeking a link between the neurological and genetic findings, and the reading disorder.
- 2008 S Heim et al. in a paper titled "Cognitive subtypes of dyslexia" describe how they compared different sub-groups of dyslexics in comparison with a control group. This is one of the first studies not to just compare dyslexics with a non dyslexic control, but to go further and compared the different cognitive sub groups with a non dyslexic control group.
- 2008 Wai Ting Siok et al. in a paper titled "A structural–functional basis for dyslexia in the cortex of Chinese readers" describe how dyslexia is language dependent, and especially between alphabetic and non-alphabetic writing systems.
- 2010 KK Chung et al. investigated the "Cognitive profiles of Hong Kong Chinese adolescents with dyslexia".
Education law
There are many different national legal statutes and different national special education support structures with regard to special education provision which relate to the management of dyslexia.Film, television, and literature
There have been a number of films, television programs, and works of fiction which focus on the topic of dyslexia.Research
The majority of currently available dyslexia research relates to the alphabetic writing systemWriting system
A writing system is a symbolic system used to represent elements or statements expressible in language.-General properties:Writing systems are distinguished from other possible symbolic communication systems in that the reader must usually understand something of the associated spoken language to...
, and especially to languages of European
Languages of Europe
Most of the languages of Europe belong to Indo-European language family. These are divided into a number of branches, including Romance, Germanic, Balto-Slavic, Greek, and others. The Uralic languages also have a significant presence in Europe, including the national languages Hungarian, Finnish,...
origin. However, substantial research is also available regarding dyslexia for speakers of Arabic, Chinese, and Hebrew.
Neuroimaging
Modern neuroimagingNeuroimaging
Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain...
techniques such as functional magnetic resonance imaging
Functional magnetic resonance imaging
Functional magnetic resonance imaging or functional MRI is a type of specialized MRI scan used to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging...
(fMRI) and positron emission tomography
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
(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 frontal gyrus
The inferior frontal gyrus is a gyrus of the frontal lobe . It is labelled gyrus frontalis inferior, its Latin name...
, inferior parietal lobule, and middle and ventral temporal cortex
Brodmann area 20
-Human:Brodmann area 20, or BA20, is part of the temporal cortex in the human brain. The region encompasses most of the ventral temporal cortex, a region believed to play a part in high-level visual processing and recognition memory....
.
That dyslexia is neurobiological in origin is supported by what Lyon et al. proclaimed as "overwhelming and converging data from functional brain imaging investigations" (2003, p. 3). The results of these studies suggest that there are observable differences in how the dyslexic brain functions when compared to the brain of a typical reader. Using fMRI, Shaywitz found that good readers show a consistent pattern of strong activation in the back of the brain with weaker activation in the front of the brain during reading tasks. In contrast, the brain activation pattern in dyslexics is the opposite during reading tasks—the frontal part of the brain becomes overactive with weaker activation in the back. Shaywitz points out "It is as if these struggling readers are using the systems in the front of the brain to try to compensate for the disruption in the back of the brain."
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
Lexicon
In linguistics, the lexicon of a language is its vocabulary, including its words and expressions. A lexicon is also a synonym of the word thesaurus. More formally, it is a language's inventory of lexemes. Coined in English 1603, the word "lexicon" derives from the Greek "λεξικόν" , neut...
and for auditory verbal short term memory components have been proposed, with some implication that the observed neural manifestation of developmental dyslexia is task-specific (i.e., functional rather than structural).
A University of Hong Kong study argues that dyslexia affects different structural parts of children's brains depending on the language which the children read. The study focused on comparing children that were raised reading English and children raised reading Chinese. This is supported in a review by T. Hadzibeganovic et al. (2010).
A University of Maastricht (Netherlands) study revealed that adult dyslexic readers underactivate superior temporal cortex for the integration of letters and speech sounds.
Genetic
Molecular studies have linked several forms of dyslexia to genetic markers for dyslexiaGenetic research into dyslexia
The genetic research into dyslexia has its roots in the work of Galaburda and Kemper, 1979, and Galaburda et al. 1985, from the examination of post-autopsy brains of people with dyslexia...
.
Several candidate genes have been identified, including at the two regions first related to dyslexia: DCDC2
DCDC2
DCDC2 is a gene that has been identified with the development of dyslexia . Precisely how it contributes to the disorder remains unclear. It is thought that the gene may affect the migration of nerve cells in the brain as it develops ....
and KIAA0319
KIAA0319
KIAA0319 is a protein which in humans is encoded by the KIAA0319 gene.- Clinical significance :Variants of the KIAA0319 gene have been associated with developmental dyslexia....
on chromosome 6, and DYX1C1
DYX1C1
Dyslexia susceptibility 1 candidate gene 1 protein is a protein that in humans is encoded by the DYX1C1 gene. This protein contains 420-amino acids with 3 tetratricopeptide repeat domains, thought to mediate protein–protein interactions....
on chromosome 15.
A 2007 review reported that no specific cognitive processes are known to be influenced by the proposed susceptibility genes.
A unifying theoretical framework of three working memory
Working memory
Working memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...
components provides a systems perspective for discussing past and new findings in a 12-year research program that point to heterogeneity in the genetic and brain basis and behavioral expression of dyslexia.
Controversy
In recent years there has been significant debate on the categorization of dyslexia. In particular, Elliot and Gibbs argue that "attempts to distinguish between categories of 'dyslexia' and 'poor reader' or 'reading disabled' are scientifically unsupportable, arbitrary and thus potentially discriminatory".While acknowledging that reading disability is a valid scientific curiosity, and that "seeking greater understanding of the relationship between visual symbols and spoken language is crucial" and that while there was "potential of genetics and neuroscience for guiding assessment and educational practice at some stage in the future", they conclude that "there is a mistaken belief that current knowledge in these fields is sufficient to justify a category of dyslexia as a subset of those who encounter reading difficulties".
See also
- Child developmentChild developmentChild development stages describe theoretical milestones of child development. Many stage models of development have been proposed, used as working concepts and in some cases asserted as nativist theories....
- History of the alphabetHistory of the alphabetThe origins of the alphabet are unknown, but there are several theories as to how it developed. One popular proposal — the Proto-Sinaitic theory — is that the history of the alphabet began in Ancient Egypt, more than a millennium into the history of writing...
- Learning theory (education)Learning theory (education)In psychology and education, learning is commonly defined as a process that brings together cognitive, emotional, and environmental influences and experiences for acquiring, enhancing, or making changes in one's knowledge, skills, values, and world views . Learning as a process focuses on what...
- LinguisticsLinguisticsLinguistics is the scientific study of human language. Linguistics can be broadly broken into three categories or subfields of study: language form, language meaning, and language in context....
- List of people diagnosed with dyslexia
- NeurolinguisticsNeurolinguisticsNeurolinguistics is the study of the neural mechanisms in the human brain that control the comprehension, production, and acquisition of language. As an interdisciplinary field, neurolinguistics draws methodology and theory from fields such as neuroscience, linguistics, cognitive science,...
- Philosophy of languagePhilosophy of languagePhilosophy of language is the reasoned inquiry into the nature, origins, and usage of language. As a topic, the philosophy of language for analytic philosophers is concerned with four central problems: the nature of meaning, language use, language cognition, and the relationship between language...
- Writing systemWriting systemA writing system is a symbolic system used to represent elements or statements expressible in language.-General properties:Writing systems are distinguished from other possible symbolic communication systems in that the reader must usually understand something of the associated spoken language to...
- NeurodiversityNeurodiversityNeurodiversity is a "controversial concept [that] ... regards atypical neurologicaldevelopment as a normal human difference". According to Jaarsma and Welin , the "neurodiversity movement was developed in the 1990s by online groups of autistic persons...
External links
Research papers, articles and media- Auditory and Visual Dynamic Processing: Separate Influences in Reading? by Caroline Witton, Joel B. Talcott, Peter C. Hansen, Catherine J. Stoodley & John F. Stein
- Evaluating Alternative Solutions for Dyslexia by Professor Dorothy Bishop
- Successful People with Dyslexia
Organizations
- International Dyslexia AssociationInternational Dyslexia AssociationThe International Dyslexia Association is a non-profit education and advocacy organization dedicated to issues surrounding dyslexia. It is based in Baltimore, Maryland, USA....
- Dyslexia Action (UK)
- British Dyslexia Association
- Dyslexia Research Trust