Types of Dyslexia

Phonological dyslexia

Phonological dyslexia is characterized by subjects who can read aloud both regular and irregular words but have difficulties with non words and with connecting sounds to symbols, or with sounding out words. In their study, Wolf and Bowers tested out naming speed by having their subjects name a symbol as quickly as possible when shown on a flash card. Difficulties in naming speed exist in conjunction with a phonological deficit, is characterized as double deficit dyslexia.

Variations and related conditions

Dyslexia is a learning disability. It has many underlying causes that are believed to be a brain-based condition that influences the ability to read written language. It is identified in individuals who fail to learn to read in the absence of a verbal or nonverbal intellectual impairment, sensory deficit (e.g., a visual deficit or hearing loss), pervasive developmental deficit or a frank neurological impairment.The following conditions may also be contributory or overlapping factors, or underlying cause of the dyslexic symptoms as they can lead to difficulty reading:

Auditory processing disorder is a condition that affects the ability to encode auditory information. It can lead to problems with auditory working memory and auditory sequencing. Many dyslexics have auditory processing problems including history of auditory reversals. Auditory processing disorder is recognized as one of the major causes of dyslexia.

Cluttering is a speech fluency disorder involving both the rate and rhythm of speech, and resulting in impaired speech intelligibility. Speech is erratic and dysrhythmic, consisting of rapid and jerky spurts that usually involve faulty phrasing. The personality of the clutterer bears striking resemblance to the personalities of those with learning disabilities.

Dyspraxia is a neurological condition characterized by a marked difficulty in carrying out routine tasks involving balance, fine-motor control, and kinesthetic coordination. Problems with short term memory and organization are typical of dyspraxics. This is most common in dyslexics who also have attention deficit disorder.

Verbal dyspraxia is a neurological condition characterized by marked difficulty in the use of speech sounds, which is the result of an immaturity in the speech production area of the brain.

Dysgraphia is a disorder which expresses itself primarily during writing or typing, although in some cases it may also affect eye-hand coordination in such direction or sequence oriented processes as tying knots or carrying out a repetitive task. Dysgraphia is distinct from Dyspraxia in that the person may have the word to be written or the proper order of steps in mind clearly, but carries the sequence out in the wrong order.

Dyscalculia is a neurological condition characterized by a problem with learning fundamentals and one or more of the basic numerical skills. Often people with this condition can understand very complex mathematical concepts and principles but have difficulty processing formulas and even basic addition and subtraction.

Scotopic sensitivity syndrome, also known as Irlen Syndrome, is a term used to describe sensitivity to certain wavelengths of light which interfere with proper visual processing.

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Dyslexia: History

Identified for the first time by Berkhan in 1881, the term 'dyslexia' was coined in 1887 by Rudolf Berlin, an ophthalmologist practicing in Stuttgart, Germany. He used the term to refer to a case of a young boy who had a severe impairment in learning to read and write in spite of showing typical intellectual and physical abilities in all other respects. In 1896, W. Pringle Morgan, a British physician, from Seaford, East Sussex, England published a description of a reading-specific learning disorder in a report to the British Medical Journal titled "Congenital Word Blindness". This described the case of a 14-year-old boy who had not yet learned to read, yet showed normal intelligence and was generally adept at other activities typical of children of that age.During the 1890s and early 1900s, James Hinshelwood, a British ophthalmologist, published a series of articles in medical journals describing similar cases of congenital word blindness, which he defined as "a congenital defect occurring in children with otherwise normal and undamaged brains characterised by a difficulty in learning to read." 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. A key early researcher in dyslexia was Samuel T. Orton, a neurologist who worked primarily with stroke victims. In 1925 Orton met a boy who could not read and who exhibited symptoms similar to stroke victims who had lost the ability to read. Orton began studying reading difficulties and determined that there was a syndrome unrelated to brain damage that made learning to read difficult. Orton called the condition strephosymbolia (meaning 'twisted signs') to describe his theory that individuals with dyslexia had 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 dominance in the brain. He also observed that the children he worked with were disproportionately left- or mixed-handed, although this finding has been difficult to replicate. Orton's hypothesis concerning hemispheric specialization was borne out by postmortem studies in the 1980s and 1990s establishing that the left planum temporale, a brain area associated with language processing, is physically larger than the corresponding right area in the brains of non-dyslexic subjects, but that these brain areas are symmetrical or slightly larger on the right for dyslexic subjects. FMRI imaging studies of children and young adults reported in 2003 provide further support, demonstrating that increases in age and reading level are associated with a suppression of right hemispheric activity. Influenced by the kinesthetic work of Helen Keller and Grace Fernald, and looking for a way to teach reading using both left and right brain functions, Orton later worked with psychologist and educator Anna Gillingham to develop an educational intervention that pioneered the use of simultaneous multisensory instruction. The Orton-Gillingham approach to remedial reading instruction is still widely used and forms the basis of many reading intervention programs. In contrast, Dearborn, Gates, Bennet and Blau considered a faulty guidance of the seeing mechanism to be the cause. The data collected in 1931 by Tinker and Goodenough (The J.Educ. Psych.) seemed to support this thesis. They wanted to know 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. To this end the authors asked four adults to read a text reflected in a mirror for ten minutes a day for a period of five months. It was confirmed that in all the subjects, the words were not perceived in their globality but required a meticulous analysis of the letters and syllables. Moreover they also demonstrated either total or partial inversions even sometimes affecting the order of the words in a sentence. What is more, they revealed a curious impression of not just horizontal but also vertical inversions. These are errors that exist amongst dyslexics and they suffer from the aggravating circumstance inherent in all learning. What remained to be demonstrated was that there exists a preference amongst dyslexics, without sensory deficiency, or mental retardation, or any backwardness in speech or language, towards scanning with the eyes from right to left. Proof of this was provided in a work conducted under Prof. Clement Launay in 1949 (thesis G. Mahec Paris 1951). In adult subjects the reading of a series of 66 tiny lowercase letters, 5mm high, spaced 5mm apart, first from left to right and then from right to left was more easily and quickly done in the left to right direction. For former dyslexic children, a substantial number read a series of 42 letters with equal speed in both directions and some (10%) read better from right to left than from left to right. 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. This reading test can also be used to diagnose serious cases of dyslexia.In the 1970s, a new hypothesis, based in part on Orton's theories, emerged that dyslexia stems from a deficit in phonological processing or difficulty in recognizing that spoken words are formed by discrete phonemes (for example, that the word CAT comes from the sounds [k], [æ], and [t]). As a result, affected individuals have difficulty associating these sounds with the visual letters that make up written words. Key studies of the phonological deficit hypothesis include the finding that the strongest predictor of reading success in school age children is phonological awareness, and that phonological awareness instruction can improve decoding skills for children with reading difficulties.The advent of neuroimaging techniques to study brain structure and function enhanced the research in the 1980s and 1990s. Since then, interest in the neurologically based causes has persisted. Current models of the relation between the brain and dyslexia generally focus on some form of defective or delayed brain maturation. More recently, genetic research has provided increasing evidence supporting a genetic origin of dyslexia. Researchers are currently searching for a link between the neurological and genetic findings, and the reading disorder. There are many previous and current theories of dyslexia, but the one that has the most support from research is that, whatever the biological cause, dyslexia is a matter of reduced phonogical awareness, the ability to analyze and link the units of spoken and written languages.

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Dyslexia: Overview

Dyslexia is most commonly characterized by difficulties with learning how to decode at the word level, to spell, and to read accurately and fluently. Dyslexic individuals often have difficulty "breaking the code" of sound-letter association (the alphabetic principle), and they may also reverse or transpose letters when writing or confuse letters such as b, d, p, q, especially in childhood. However, dyslexia is not a visual problem that involves reading letters or words backwards or upside down, nor are such reversals a defining characteristic of dyslexia .Many individuals with dyslexic symptoms involving reading, writing, and spelling also exhibit symptoms in other domains such as poor short-term memory skills, poor personal organizational skills and problems processing spoken language. These symptoms may coexist with or overlap with characteristics among others of attention-deficit hyperactivity disorder, auditory processing disorder, developmental dyspraxia, dyscalculia, and/or dysgraphia. However, dyslexia and attention deficit/hyperactivity disorder are not correlated developmental problems.Evidence that dyslexia is of neurological origin is substantial. Acquired dyslexias occur due to brain damage in the left hemisphere's key language areas, which may be a clue when it comes to developmental types. Research also suggests an association with biochemical and genetic markers. However, experts disagree over the precise definition and criteria for diagnosis, and some advocate that the term dyslexia be dropped altogether and replaced with the term reading disorder or reading disability (RD). Because reading skills occur on a continuum with no clear distinction between typical readers and dyslexic readers, some experts assert that the term dyslexia should be reserved for the two to five percent with the most severe reading deficits. Dyslexia is a lifelong condition for which there is no cure, but appropriate remedial instruction and compensatory strategies can help dyslexic individuals mitigate or overcome their difficulties with written language. A large body of evidence shows which types of instruction dyslexics need to be successful. Many dyslexics overcome early problems with literacy and go on to earn advanced degrees and pursue successful careers; a high level of motivation coupled with strong encouragement and mentorship have been identified as factors leading to their success.

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Subtypes of developmental dyslexia

Castles and Coltheart prove through their study that developmental dyslexia includes at 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 patterns and developing approaches for overcoming impairments that may be visual perception impairments or speech discrimination deficits. These subtypes are based on differing patterns of underlying symptoms, as supported by a finding using large-scale data from comparative studies of reading patterns in dyslexic and normal readers. In the study by Castles and Coltheart, 56 dyslexic boys and 56 non-dyslexic boys as a control group were tested. During the test, the boys read aloud words and non words that were presented to them. The researchers found that surface dyslexics (subjects who have poor lexical skills, or can’t make out irregular words well) had a mean difference of 14.4 words between reading regular words versus irregular words, however, the mean difference in subjects with phonological dyslexia (subjects who can’t use sub lexical skills, or can’t make out non words) was only 7.75 words which was comparable to the control group. Surface dyslexia is the outcome of an individual who cannot function using the lexical procedure for reading out loud. The lexical procedure includes sounding out a word though the use of a past word already known.

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What Is Dyslexia

Dyslexia is a learning disability that manifests primarily as a difficulty with written language, particularly with reading and spelling. It 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.Evidence suggests that dyslexia results from differences in how the brain processes written and/or verbal language. Although dyslexia is the result of a neurological difference, it is not an intellectual disability. Dyslexia occurs at all levels of intelligence; sub-average, average, above average, and highly gifted.According to the findings of a University of Hong Kong study, dyslexia affects different structural parts of children's brains depending on the language they read. The study focused on comparing children that were raised reading English and children raised reading Chinese. Using MRI technology researchers found that the children reading English used a different part of the brain then those reading Chinese. Researchers were surprised by this discovery and hope that the findings will help lead them to any neurobiological cause for dyslexia.The word dyslexia comes from the Greek words - dys- ("impaired") and lexis ("word"). People with dyslexia are called dyslexic or dyslectic

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Study: Dyslexia differs by language

By RANDOLPH E. SCHMID, AP Science Writer Tue Apr 8, 4:58 PM ET

WASHINGTON - Dyslexia affects different parts of children's brains depending on whether they are raised reading English or Chinese. That finding, reported in Monday's online edition of Proceedings of the National Academy of Sciences, means that therapists may need to seek different methods of assisting dyslexic children from different cultures."This finding was very surprising to us. We had not ever thought that dyslexics' brains are different for children who read in English and Chinese," said lead author Li-Hai Tan, a professor of linguistics and brain and cognitive sciences at the University of Hong Kong. "Our finding yields neurobiological clues to the cause of dyslexia."Millions of children worldwide are affected by dyslexia, a language-based learning disability that can include problems in reading, spelling, writing and pronouncing words. The International Dyslexia Association says there is no consensus on the exact number because not all children are screened, but estimates range from 8 percent to 15 percent of students.Reading an alphabetic language like English requires different skills than reading Chinese, which relies less on sound representation, instead using symbols to represent words.Past studies have suggested that the brain may use different networks of neurons in different languages, but none has suggested a difference in the structural parts of the brain involved, Tan explained.Tan's research group studied the brains of students raised reading Chinese, using functional magnetic resonance imaging. They then compared those findings with similar studies of the brains of students raised reading English.Guinevere F. Eden, director of the Center for the Study of Learning at Georgetown University in Washington, said the process of becoming a skilled reader changes the brain."Becoming a reader is a fairly dramatic process for the brain," explained Eden, who was not part of Tan's research team on this paper.For children, learning to read is culturally important but is not really natural, Eden said, so when the brain orients toward a different writing system it copes with it differently.For example, English-speaking children learn the sounds of letters and how to combine them into words, while Chinese youngsters memorize hundreds of symbols which represent words."The implication here is that when we see a reading disability, we see it in different parts of the brain depending on the writing system that the child is born into," Eden said.That means, "we cannot just assume that any dyslexic child is going to be helped by the same kind of intervention," she said in a telephone interview.Tan said the new findings suggest that treating Chinese speakers with dyslexia may use working memory tasks and tests relating to sensor-motor skills, while current treatments of English dyslexia focus on letter-sound conversions and sound awareness.He said the underlying cause of brain structure abnormalities in dyslexia is currently unknown."Previous genetic studies suggest that malformations of brain development are associated with mutations of several genes and that developmental dyslexia has a genetic basis," he said in an interview via e-mail."We speculate that different genes may be involved in dyslexia in Chinese and English readers. In this respect, our brain-mapping findings can assist in the search for candidate genes that cause dyslexia," Tan said.In their paper, the researchers noted that imaging studies of the brains of dyslexic children using alphabetic languages like English have identified unusual function and structure in the left temporo-parietal areas, thought to be involved in letter-to-sound conversions in reading; left middle-superior temporal cortex, thought to be involved in speech sound analysis, and the left inferior temporo-occipital gyrus, which may function as a quick word-form recognition system.When they performed similar imaging studies on dyslexic Chinese youngsters, on the other hand, they found disruption in a different area, the left middle frontal gyrus region.The study was funded by the Ministry of Science and Technology of China, the Hong Kong Research Grants Council and the University of Hong Kong.In a separate paper, published two years ago, University of Michigan researchers reported that Asians and North Americans see the world differently.Shown a photograph, North American students of European background paid more attention to the object in the foreground of a scene, while students from China spent more time studying the background and taking in the whole scene.

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