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PubMedDate not supplied

Definition and treatment of dyslexia: a report by the Committee on Dyslexia of the Health Council of The Netherlands.

A committee of the Health Council of the Netherlands prepared a report on the definition and treatment of dyslexia at the request of the Minister of Health, Welfare, and Sport (see Note). The Health Council, as charged by the Health Act, is to inform the government on the state of science with respect to public health issues. The Council is entirely funded by the government but otherwise completely independent (an independence guaranteed by law). The committee was formed to answer questions regarding the provisions and funds needed for the treatment of persons with dyslexia, neuropsychological treatment modalities, in particular, and the role of speech and language therapists. Definitive decision making about reimbursement by the Dutch National Health Service for treatment by speech and language therapists in cases of dyslexia was on hold, pending the committee's report. Specific attention was requested for the following aspects: the definition of dyslexia (the characteristic symptoms of this category of developmental language disabilities); the consequences of the proposed definition for indication and treatment; the appropriate methods of treatment; the involvement of several possible professionals (e.g., neuropsychologist, remedial teacher, speech and language therapist), as well as the role of the neurologist during and in relation to the treatment process; and those situations in which treatment should be the responsibility of the health care system. This article summarizes the committee's considerations and conclusions on these different aspects.

Adolescent↗
PubMed1991

Interventions based on the multiple connections model of reading for developmental dyslexia and acquired deep dyslexia.

This paper deals with intervention strategies for developmental and acquired dyslexia. In Study 1 two alternative strategies for developmental surface dyslexia (dysfunctional connection between the whole word orthographic code and the phonetic or name code) were compared. In both the initial study and replication study, a modification of the selective reminding technique was superior to a traditional multisensory technique in beginning readers, presumably because it facilitated word finding or prelexical access to a phonetic code. In Study 2 an adolescent with acquired deep dyslexia (dysfunctional connection between letter and phonemic codes) who had had his angular gyrus (site of grapheme-phoneme correspondence) surgically removed, recovered reading function after a four-month phonemic analysis training program. Further research is needed to evaluate the efficacy of theory-based intervention strategies in children with developmental reading disorders unrelated to focal lesions and in adults with acquired reading disorders related to focal lesions.

Journal Article↗
PubMed1986

[Dyslexia and late dyslexia and analphabetism from the otologic-audiologic-phoniatric viewpoint].

The special dyslexia in childhood may be interpreted as a functional disorder. Foundation of each treatment is the difference to pseudodyslexia. The exclusion of a conduction hearing loss or sensorineural hard of hearing including the recognition of a verbal communication disturbance should be made regularly. The late dyslexia amongst youth and the illiteracy of adults increases more and more. There should be the integration of otologic-audiologic-phoniatric assessment and a multifaceted diagnosis and treatment concept.

Agraphia↗
PubMed2003

Dyslexia and psychosocial factors. A follow-up study of young Norwegian adults with a history of dyslexia in childhood.

The present study is a follow-up of two different groups of young adults with a history of dyslexia problems in childhood. Group A was drawn from a larger longitudinal study where students were diagnosed with dyslexia at age 10. Group B was recruited at a child psychiatric clinic and also had dyslexic problems. Measures of educational level, life satisfaction and psychosocial factors were applied. The assessment was carried out by means of tests, questionnaires and personal interviews. The results showed lower levels of educational attainment in group B as well as lower satisfaction with health, friends and education compared to group A and a normative group. Both dyslexic groups showed more psychiatric problems than those in the normative sample.

Adolescent↗
PubMed2002

Prevalence and clinical characteristics of dyslexia in primary school students.

BACKGROUND: Dyslexia is the most common subtype of learning disabilities with a prevalence ranging from 5-10 per cent. The central difficulty in dyslexia is the phonological awareness deficit. The authors have developed a screening test to assess the reading ability of Thai primary school students. OBJECTIVE: 1. To study the prevalence of dyslexia in first to sixth grade students at Wat Samiannaree School. 2. To study the clinical characteristics such as sex, neurological signs, verbal intelligence and comorbid attention deficit hyperactive disorder (ADHD) of the dyslexia group. METHOD: A total of 486 first to sixth grade students were administered "Raven's progressive matrices test" for estimation of intellectual functioning. Those who scored below the fifth percentile were labeled as mental retardation and excluded from the study. The students' reading ability was evaluated by 3 steps; first by classroom teachers using some items of the screening test, second by the researchers examining some more items individually, and third by the special educator assessing more details in reading and phonology. The students who had a reading ability two-grade levels below their actual grades and impairment in phonology were diagnosed with dyslexia. RESULTS: The prevalence of dyslexia and probable dyslexia were found to be 6.3 per cent and 12.6 per cent, respectively. The male to female ratio of dyslexia was 3.4:1. The dyslexia group had significantly lower Thai language scores than those of the normal group (p < 0.05). All of the dyslexia group had a normal grossly neurological examination but 90 per cent showed positive soft neurological signs. Mean verbal intellectual quotient score in the dyslexia group assessed by using Wechsler Intelligence Scales for Children--Revised was 76 +/- 7. The comorbid ADHD was 8.7 per cent in the dyslexia group. CONCLUSION: Dyslexia was a common problem among primary school students in this study. Further studies in a larger population and different socioeconomic statuses are required to determine the prevalence of dyslexia in the general population. The authors suggest evaluating the reading ability carefully by using a test that can detect phonological awareness deficit in all children who have learning problems.

Child↗
PubMed1992

Evidence that dyslexia may represent the lower tail of a normal distribution of reading ability.

BACKGROUND: Dyslexia is now widely believed to be a biologically based disorder that is distinct from other, less specific reading problems. According to this view, reading ability is considered to follow a bimodal distribution, with dyslexia as the lower mode. We hypothesized that, instead, reading ability follows a normal distribution, with dyslexia at the lower end of the continuum. METHODS AND RESULTS: We used data from the Connecticut Longitudinal Study, a sample survey of 414 Connecticut children who entered kindergarten in 1983 and were followed as a longitudinal cohort. Dyslexia was defined in terms of a discrepancy score, which represents the difference between actual reading achievement and achievement predicted on the basis of measures of intelligence. Data were available from intelligence tests administered in grades 1, 3, and 5 and achievement tests administered yearly in grades 1 through 6. For each child there were 108 possible discrepancy scores ([3 x 3 years] x [2 x 6 years]) based on combinations of the ability scores (full-scale, verbal, and performance IQ) in each of three years and two achievement scores (reading and mathematics) in each of six years. We demonstrated that each of the discrepancy scores followed a univariate normal distribution and that the interrelation of two different discrepancy scores followed a bivariate normal distribution. At most, only 9 of 108 discrepancy scores (8.3 percent) and 171 of 3402 pairs of discrepancy scores (5.0 percent) were significantly different (at the 5 percent level) from the expected scores--well within the expected values for data with univariate and bivariate normal distributions, respectively. We also examined the stability of dyslexia over time. The normal-distribution model predicted (and the data indicated) that only 7 of the 25 children (28 percent) classified as having dyslexia in grade 1 would also be classified as having dyslexia in grade 3. CONCLUSIONS: Reading difficulties, including dyslexia, occur as part of a continuum that also includes normal reading ability. Dyslexia is not an all-or-none phenomenon, but like hypertension, occurs in degrees. The variability inherent in the diagnosis of dyslexia can be both quantified and predicted with use of the normal-distribution model.

Child↗
PubMed2000

Use of temporal envelope cues by children with developmental dyslexia.

This study evaluates the ability to process auditory temporal-envelope cues in a group of 6 children with dyslexia (mean age: 10;10 years;months). To address this issue, we measured (a) temporal modulation transfer functions (TMTFs), that is, the detection thresholds of sinusoidal amplitude modulation (SAM) applied to a white noise carrier, as a function of modulation frequency, fm (fm was 4, 16, 64, 256, and 1,024 Hz) and (b) identification performance for vowel-consonant-vowel (VCV) stimuli over 5 sessions. VCV stimuli were either unprocessed or digitally processed to remove the original spectral information, resulting in a time-varying speech envelope amplitude modulating a noise carrier. The same tests were conducted in 6 normal control children (mean age: 11;6 years;months) and 6 normal control adults (mean age: 24;8 years;months). SAM thresholds were similar in normal children and adults. For both normal groups, TMTFs were low pass in shape and showed low between-listener variability. TMTFs measured in children with dyslexia showed higher between-listener variability: TMTFs were band pass in 2 children, flat in 1 child, and low pass in the 3 others. Overall, SAM thresholds were higher in children with dyslexia than in normal children at fm = 4 and 1,024 Hz. Unprocessed-speech identification performance was nearly perfect in normal children and adults, and impaired in children with dyslexia. "Speech-envelope noise" identification performance was poorer in normal children and children with dyslexia than in normal adults. Performance improved across sessions in normal children and adults, but remained constant in children with dyslexia. Compared to normal children, children with dyslexia showed poorer reception of voicing, manner, and place of articulation for unprocessed speech and poorer reception of voicing for "speech-envelope noise." Taken together, these results support the hypothesis that some children with dyslexia may show abnormal auditory temporal-envelope processing. Such a deficit, in turn, may explain the difficulties of children with dyslexia with speech perception.

Adolescent↗
PubMed2001

Developmental dyslexia: an update on genes, brains, and environments.

The science of reading and developmental dyslexia has experienced spectacular advances during the last few years. Five aspects of this research are discussed in the article. (1) The holistic phenomenon of reading is complex. Many lower-level psychological processes (e.g., phonemic awareness, phonological decoding, ability to process stimuli rapidly and automatize this process, memory, ability to recognize words) contribute to a single act of reading. Conceptualizing the complex process of reading through its partly overlapping but partly independent components--which contribute to, but do not fully explain, the holistic process of reading--provides an excellent model for understanding complex hierarchies of higher mental functions. Those who master reading skills successfully and those who have difficulties doing so differ in a wide range of reading-related processes. The central deficit experienced by poor readers appears to be related to phonological processing (a complex hierarchy of functions related to processing phonemes), whereas characteristics of automatization processes seem to moderate the reading outcome for people whose phonological skills are weak. (2) There are new data addressing models of dyslexia in languages other than English. The most fascinating finding is that the model implicating phonological deficit as central to dyslexia, and the lack of ability to automatize as leading to troubled reading, appears to be universal, regardless of the specific language. However, there is an interaction effect between the characteristics of a particular language and the developmental model of dyslexia. In phonologically more difficult languages (e.g., English), the most pronounced weakness appears to occur in phonological processing, whereas in phonologically easier languages (e.g., German), the crucial role in the manifestation of dyslexia is played by the lack of the skills needed to achieve automatization. (3) There is abundant evidence that reading (i.e., any single act of reading as well as reading as a holistic process) is "cooked" by the brain. Although no unified brain map of reading has been developed, some specific areas of the brain have been implicated in different reading-related cognitive processes by different laboratories and on different samples. (4) Indisputable evidence has been accumulated suggesting the involvement of the genome in developmental dyslexia. As of now, specific regions of the genome have been identified as being intimately involved with a number of different reading-related processes. Today the field of developmental dyslexia is the only area of genetic studies of human abilities and disabilities in which linkages to the genome have been robustly replicated in independent laboratories. (5) Finally, evidence suggests that developmental dyslexia might be only one of the manifestations of a deep, underlying, anatomical syndrome. The comorbidity of developmental dyslexia with both internalizing and externalizing behavioral disturbances, as well as with other learning disabilities, underscores the need for wide-ranging cognitive and behavioral approaches in the remediation programs offered to dyslexic children.

Adolescent↗
PubMed2003

[Developmental dyslexia].

Developmental dyslexia makes up an important proportion of the known learning disorders. Until the late 1970s most research on dyslexia was carried out by educators and educational psychologists, but soon after the publication of some dyslexic cases with focal disorders of neuronal migration to the cerebral cortex, interest in the neurobiological and neurocognitive underpinnings of dyslexia grew, especially in Europe and North America. There are at least two types of developmental dyslexia--phonological and surface. Surface dyslexia refers to a disorder in which the difficulty lies in reading irregular words, whereas phonological dyslexia is characterized by difficulty with pseudowords. Phonological dyslexia is the more common of the two types. Surface dyslexia does not present a major problem in a language such as Spanish, where the number of irregular words is indeed very small. Still, in languages such as English, where irregular words are common, the phonological type of developmental dyslexia is much more common. Phonologic dyslexics have problems with phonological awareness, that is, the conscious knowledge and manipulation of speech sounds, which is the most proximate explanation for their difficulty in reading pseudowords. Many, but not all, phonologic dyslexics also have problems processing rapidly changing sounds, even if not linguistic, and some slow sounds, too. The same group tends to have visual problems, especially involving the so-called magnocellular pathway of the visual system, which, among others, has the role of analyzing movement. Accompanying these perceptual and cognitive deficits, phonologic dyslexics also show abnormal brain activation to phonological tasks, as shown in functional magnetic resonance studies (figure). In addition, dyslexic brains show focal malformations, ectopias and microgyria, of the cerebral cortex, involving mainly the left perisylvian region and the word form area in the temporo-occipital junction. There are also changes in the composition of neurons in the lateral and medial geniculate nuclei of the thalamus. Experimental studies indicate that the thalamic changes are a consequence of the focal malformations, and that they are responsible for the sound processing deficits. None of these discoveries have changed the therapeutic modalities in this condition, but it is hoped that this will be the next area of progress.

Brain↗
PubMed2000

Two translocations of chromosome 15q associated with dyslexia.

Developmental dyslexia is characterised by difficulties in learning to read. As reading is a complex cognitive process, multiple genes are expected to contribute to the pathogenesis of dyslexia. The genetics of dyslexia has been a target of molecular studies during recent years, but so far no genes have been identified. However, a locus for dyslexia on chromosome 15q21 (DYX1) has been established in previous linkage studies. We have identified two families with balanced translocations involving the 15q21-q22 region. In one family, the translocation segregates with specific dyslexia in three family members. In the other family, the translocation is associated with dyslexia in one family member. We have performed fluorescence in situ hybridisation (FISH) studies to refine the position of the putative dyslexia locus further. Our results indicate that both translocation breakpoints on 15q map within an interval of approximately 6-8 Mb between markers D15S143 and D15S1029, further supporting the presence of a locus for specific dyslexia on 15q21.

Adolescent↗
PubMed2002

[Problems associated with dyslexia].

OBJECTIVE: In this article we review the disorders of development which affect learning and may be associated with dyslexia. DEVELOPMENT: Although the cognitive basis of dyslexia is a phonological deficit, it is not uncommonly associated with other disorders whose deficit is not necessarily related to the dyslexia from a physiopathological point of view. The problems which usually accompany dyslexia are: attention deficit with hyperactivity, dysgraphia, dyscalculia and disorders of the development of coordination. The starting point for understanding this comorbidity is finding broad, dysfunctional areas of the brains of dyslexic patients beyond those theoretically involved in dyslexia. Each of these disorders may or may not occur together with dyslexia. There are even some subtypes which are defined by being associated with dyslexia, leading to the conclusion that in some cases there are underlying common mechanisms. It is necessary to avoid confusion arising over dyslexia due to comorbidity with other conditions.

Agraphia↗
PubMed1996

The visual deficit theory of developmental dyslexia.

Dyslexia is an impairment in reading that can result from an abnormal developmental process in the case of developmental dyslexia or cerebral insult in the case of acquired dyslexia. It has long been known that the clinical manifestations of developmental dyslexia are varied. In addition to their reading difficulties, individuals with developmental dyslexia exhibit impairments in their ability to process the phonological features of written or spoken language. Recently, it has been demonstrated with a variety of experimental approaches that these individuals are also impaired on a number of visual tasks involving visuomotor, visuospatial, and visual motion processing. The results of these studies, as well as the anatomical and physiological anomalies seen in the brains of individuals with dyslexia, suggest that the pathophysiology of developmental dyslexia is more complex than originally thought, extending beyond the classically defined language areas of the brain. Functional neuroimaging is a useful tool to more precisely delineate the pathophysiology of this reading disorder.

Awareness↗
PubMed1999

A candidate phenotype for familial dyslexia.

The probative analysis of genotype-phenotype relations in familial dyslexia requires operationally defined psychobiological outcome variables that are not confounded by cultural differences of orthography or other factors that may influence the clinical ascertainment and diagnosis of dyslexia. Timing precision, as expressed in coordinated motor action, was used as an objective behavioral measure that can be mapped on current knowledge of central nervous system functions as well as on the most salient non-reading deficits in developmental dyslexia. Dyslexia families with four distinct pedigrees and a normally reading reference group were the study subjects. The results indicated that impaired timing precision in bimanual coordination and in motor speech were transmitted vertically in affected members of about half of dyslexia families. Motor coordination deficits were associated with a disposition to make dysphonemic spelling errors. It is proposed that impaired timing precision identifies a behavioral phenotype in some familial dyslexia subtypes. The detailed analysis of coarticulation in speech production may be one pathway by which impaired timing precision in motor action impinges on reading and writing deficits in developmental dyslexia.

Adolescent↗
PubMed2003

Dyslexia linked to talent: global visual-spatial ability.

Dyslexia has long been defined by deficit. Nevertheless, the view that visual-spatial talents accompany dyslexia has grown, due to reports of individuals with dyslexia who possess visual-spatial strengths, findings of elevated incidence of dyslexia in certain visual-spatial professions, and the hypothesis that left-hemisphere deficits accompany right-hemisphere strengths. Studies have reported superior, inferior, and average levels of visual-spatial abilities associated with dyslexia. In two investigations, we found an association between dyslexia and speed of recognition of impossible figures, a global visual-spatial task. This finding suggests that dyslexia is associated with a particular type of visual-spatial talent-enhanced ability to process visual-spatial information globally (holistically) rather than locally (part by part).

Aptitude↗