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Results for “Developmental dyslexia”

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PubMed2005

Children with developmental dyslexia show a left visual "minineglect".

We investigated the performance of children with developmental dyslexia on a visual line bisection task. Dyslexic children did not show the overestimation of the left visual field (pseudoneglect) characteristic of normal adult vision. These results suggest that children with developmental dyslexia present selective deficits in visual attention, probably involving neural structures located in the right posterior parietal cortex.

Adult↗

PubMed1996

Developmental dyslexia: passive visual stimulation provides no evidence for a magnocellular processing defect.

Livingstone et al. [Livingstone, M. S., Rosen, G. D., Drislane, F. W. and Galaburda, A. M. Physiological and anatomical evidence for a magnocellular defect in developmental dyslexia. Proceedings of the National Academy of Science U.S.A. 88, 7943-7947, 1991] presented evidence for a defect of the magnocellular visual processing stream in developmental dyslexia. We attempted to replicate this effect using transient and steady-state VEPs to checkerboard reversal stimuli in a group of adult developmental dyslexics. Several different reversal rates and contract levels were utilized. No differences were found between the dyslexic and control groups for the low-contrast, rapidly reversing patterns, nor for any combination of stimulus rate or contrast that was tested. Thus, these findings do not support a magnocellular processing deficit in developmental dyslexia.

Adult↗

PubMed2004

[Educational implications of the cognitive impairment in developmental dyslexia].

AIMS: In this study we review the main theories put forward to account for developmental dyslexia, as well as the intervention procedures deriving from these theories that enjoy the most empirical support. DEVELOPMENT: Developmental dyslexia is a complex disorder that reflects cognitive impairment related to neurobiological anomalies, although researchers still do not agree on fundamental aspects regarding its aetiology. There are at present a number of different theories that can be grouped in two antagonistic lines of work. On the one hand, one of them considers that the exclusive and direct cause of dyslexia is a specific cognitive disorder. On the other hand, however, there are several theories that consider the impairments experienced by dyslexic patients to be part of a wide range of tasks and processes that are secondary to an underlying primary deficit. As a consequence of the progress made in the characterisation of dyslexia, an unprecedented effort has been made in recent decades in the development of intervention programmes and in the analysis of their effectiveness. CONCLUSIONS: Research into the explanation for dyslexia finds itself faced with the challenge of determining whether the different cognitive problems identified in dyslexic patients represent different cognitive routes towards the same dyslexic phenotype, whether they correspond to different types of dyslexia or whether they refer to the sum of the problems resulting from different comorbid conditions. Until this issue is resolved, as educators, we must carry out more comprehensive evaluations in order to determine the profile of the difficulties that are experienced in each particular case and to be able to tailor the interventions employed in this enigmatic problem.

Cognition Disorders↗

PubMed2006

Static postural control in children with developmental dyslexia.

The present investigation tries to better understand potential association and causal relationship between phonological and postural impairment due to developmental dyslexia. The study included 50 boys with developmental dyslexia and selected on the basis of their overall reading difficulties, and 42 control boys. Body sway during a quite standing posture eye open and eye closed on a force platform were tested in the two groups of subjects that were between 10 and 13 years of age. Analysis of classical parameters quantifying the centre of pressure (CP) displacements along antero-posterior and lateral axes showed a significant difference between the two groups. Dyslexic children showed on average greater instability, with greater length, variability and mean power frequency of CP displacements with or without vision. Our results demonstrate that postural parameters may discriminate between children with dyslexia and age-equivalent controls.

Adolescent↗

PubMed2004

Large-scale neural correlates of developmental dyslexia.

Recent work in the field of developmental dyslexia has emphasized the large-scale neural aspects of the disorder as measured by means of contemporary imaging techniques, electrophysiology, and post-mortem analyses. This article presents findings from these research domains and comprehensively reviews their relevance with respect to the behavioral and cognitive profiles of dyslexia. Large-scale alterations were observed in the perisylvian region across paradigms. Convergent evidence has also been reported in terms of hemispheric balance. Specifically, deviances in cerebral asymmetry associated with atypical organization of the left hemisphere were found in both children and adults with dyslexia. Emerging research encompassing high-temporal resolution methods such as magnetoencephalography (MEG) suggests right-hemisphere involvement and points to the complexity of the developmental disorder. A combined approach of structural imaging and MEG, and most importantly theory driven behavioral tasks may shed light on dynamics and trajectories of the neurobiology of dyslexia.

Adult↗

PubMed1993

Varieties of developmental dyslexia.

This paper reviews and evaluates the evidence for the existence of distinct varieties of developmental dyslexia, analogous to those found in the acquired dyslexic population. Models of the normal adult reading process and of the development of reading in children are used to provide a framework for considering the issues. Data from a large-sample study of the reading patterns of developmental dyslexics are then reported. The lexical and sublexical reading skills of 56 developmental dyslexics were assessed through close comparison with the skills of 56 normally developing readers. The results indicate that there are at least two varieties of developmental dyslexia, the first of which is characterised by a specific difficulty using the lexical procedure, and the second by a difficulty using the sublexical procedure. These subtypes are apparently not rare, but are relatively prevalent in the developmental dyslexic population. The results of a second experiment, which suggest that neither of these reading patterns can be accounted for in terms of a general language disorder, are then reported.

Age Factors↗

PubMed2006

From genes to behavior in developmental dyslexia.

All four genes thus far linked to developmental dyslexia participate in brain development, and abnormalities in brain development are increasingly reported in dyslexia. Comparable abnormalities induced in young rodent brains cause auditory and cognitive deficits, underscoring the potential relevance of these brain changes to dyslexia. Our perspective on dyslexia is that some of the brain changes cause phonological processing abnormalities as well as auditory processing abnormalities; the latter, we speculate, resolve in a proportion of individuals during development, but contribute early on to the phonological disorder in dyslexia. Thus, we propose a tentative pathway between a genetic effect, developmental brain changes, and perceptual and cognitive deficits associated with dyslexia.

Animals↗

PubMed2006

Do children with developmental dyslexia show a selective visual attention deficit?

The authors investigated the performance of children with developmental dyslexia on a number of visual tasks requiring selective visual attention. Dyslexic children did not show the overestimation of the left visual field (pseudo-neglect) characteristic of normal adult vision. The performance of dyslexic children in texture segmentation and feature search tasks was identical to that of control children matched for age, gender and intelligence. However, when tested on conjunction tasks for orientation and form, dyslexic children showed shorter reaction times and a dramatically increased number of errors. Differences between the two groups decreased with increasing age. These results suggest that children with developmental dyslexia present selective deficits in visual attention.

Adolescent↗

PubMed2005

Accuracy and speed of orthographic processing in persons with developmental dyslexia.

A group of 39 persons (20 male and 19 female, 11.0 to 32.5 yr.) with developmental dyslexia and 42 controls (21 male and 21 female, 11.2 to 32.3 years) were compared on computerized tests of sight word reading, nonword decoding, and spelling recognition. The subjects with developmental dyslexia performed significantly slower and less accurately than controls on all tasks. Further, the effect size of the group differences was larger for the older group. Within-group analyses showed a significant difference by age group on accuracy. Only the control group showed a significant age difference between groups on response time. Mean accuracy and response times for the reading-disabled subjects resembled shifted versions of the control group means. These results agree with previous reports that phonological deficits persist for reading-disabled adults and suggest a test of whether the discrepancy between reading-disabled and typically achieving readers may actually increase across age groups.

Adolescent↗

PubMed2006

Further evidence that the KIAA0319 gene confers susceptibility to developmental dyslexia.

The DYX2 locus on chromosome 6p22.2 is the most replicated region of linkage to developmental dyslexia (DD). Two candidate genes within this region have recently been implicated in the disorder: KIAA0319 and DCDC2. Variants within DCDC2 have shown association with DD in a US and a German sample. However, when we genotyped these specific variants in two large, independent UK samples, we obtained only weak, inconsistent evidence for their involvement in DD. Having previously found evidence that variation in the KIAA0319 gene confers susceptibility to DD, we sought to refine this genetic association by genotyping 36 additional SNPs in the gene. Nine SNPs, predominantly clustered around the first exon, showed the most significant association with DD in one or both UK samples, including rs3212236 in the 5' flanking region (P = 0.00003) and rs761100 in intron 1 (P = 0.0004). We have thus refined the region of association with developmental dyslexia to putative regulatory sequences around the first exon of the KIAA0319 gene, supporting the presence of functional mutations that could affect gene expression. Our data also suggests a possible interaction between KIAA0319 and DCDC2, which requires further testing.

5' Untranslated Regions↗

PubMedDate not supplied

[The neurobiology of developmental dyslexia: a survey].

One of the most common disorders affecting the ability to read is developmental dyslexia, which, unlike the alexia related to a loss of the capacity to read associated with brain damage, refers to a specific disorder in the acquisition of reading skills and becomes apparent in reiterated persistent difficulties in learning to read. A number of studies have attempted to detect structural and functional abnormalities that might be the origin of problems in learning to read. The use of functional neuroimaging techniques such as positron emission tomography (PET), spectroscopic magnetic resonance imaging (SMRI) and functional magnetic resonance imaging (fMRI) enables us to measure changes in the metabolic activity associated with alterations in the neuronal networks involved in the reading process. In this review, different studies are analysed in an attempt to identify alterations in the cortico subcortical regions which could be the origin of the developmental dyslexia. Results show that in dyslexics there is a temporoparietooccipital disconnection, and a disconnection with the left frontal cortex as regards the demands for fast auditory processing, as well as abnormalities in the connections between the temporoparietal cortex and the cerebellum with other regions of the brain. Such findings suggest that the altered areas of the brain do not only show a characteristic pattern of hypoactivation, but also that these alterations could be the cause of this malady. We highlight the importance of these findings in the diagnosis and rehabilitation of this population.

Dyslexia↗

PubMed1999

Tactile perception in developmental dyslexia: a psychophysical study using gratings.

Multiple sensory abnormalities have been reported in individuals with developmental dyslexia, especially in the visual and auditory systems. We used gratings of alternating ridges and grooves to investigate tactile perception in this disorder using two tasks: spatial acuity-dependent discrimination of grating orientation and discrimination of gratings varying in ridge width. Compared to age-matched normal subjects, dyslexics were significantly impaired on grating orientation discrimination, with mean thresholds that were nearly twice normal. Unlike normal subjects, their performance on this task was slightly but significantly worse on the dominant hand than on the non-dominant hand. Dyslexics also showed a substantial but non-significant trend for impairment on grating ridge width discrimination. A group of subjects with attention deficit disorder did not differ significantly from normal on any of these measures. These findings expand the range of perceptual deficits reported in developmental dyslexia. Possible explanations for the results, including difficulties with temporal processing, abnormal lateral masking or parietal lobe dysfunction are discussed.

Adolescent↗

PubMed2004

Morphological awareness in developmental dyslexia.

This study examines morphological awareness in developmental dyslexia. While the poor phonological awareness of dyslexic children has been related to their difficulty in handling the alphabetical principle, less is known about their morphological awareness, which also plays an important part in reading development. The aim of this study was to analyze in more detail the implications of the phonological impairments of dyslexics in dealing with larger units of language such as morphemes. First, the performance of dyslexic children in a series of morphological tasks was compared with the performance of children matched on reading-level and chronological age. In all the tasks, the dyslexic group performed below the chronological age control group, suggesting that morphological awareness cannot be developed entirely independently of reading experience and/or phonological skills. Comparisons with the reading-age control group indicated that, while the dyslexic children were poorer in the morphemic segmentation tasks, they performed normally for their reading level in the sentence completion tasks. Furthermore, they produced more derived words in the production task. This suggests that phonological impairments prevent the explicit segmentation of affixes while allowing the development of productive morphological knowledge. A second study compared dyslexic subgroups defined by their degree of phonological impairment. Our results suggest that dyslexics develop a certain type of morphological knowledge which they use as a compensatory reading strategy.

Attention↗

PubMed1977

Developmental dyslexia: two right hemispheres and none left.

Developmental dyslexia may be associated with (i) bi-hemisphere representation of spatial functions, in contrast to the right-hemisphere specialization observed in normal children, and (ii) typical left-hemisphere representation of linguistic functions, as is observed in normal children. The bilateral neural involvement in spatial processing may interfere with the left hemisphere's processing of its own specialized functions and result in deficient linguistic, sequential cognitive processing and in overuse of the spatial, holistic cognitive mode. This pattern of cognitive deficits and biases may lead dyslexics to read predominantly with a spatial-holistic cognitive strategy and neglect the phonetic-sequential strategy. Such an approach in learning to read phonetically coded languages, such as English, many be inefficient and limited.

Adolescent↗

PubMed2002

[The importance of interdisciplinary staff in the diagnosis of developmental dyslexia: case report].

We describe the work of the interdisciplinary staff of FCM/UNICAMP for the diagnosis of developmental dyslexia, evaluating a 9 years old boy from the second year of a first grade public school. The procedure consisted of four stages: 1) Interview with the mother (anamnesis); 2) neuropsychological evaluation; 3) specific evaluation for reading and writing skills; 4) complementary exams. The results revealed that the child presented normal intelligence, normal auditory and visual function but difficulties in reading specific test, in auditory short-term memory (specially in auditory sequences), and in phonological conscience, as well as slowness, lack of concentration, slight neurological signs and hypoperfusion of the mesial portion of the temporal lobe. These data suggest that the child has developmental dyslexia of mixed type, requiring psychopedagogic follow-up.

Auditory Threshold↗

PubMed2000

The angular gyrus in developmental dyslexia: task-specific differences in functional connectivity within posterior cortex.

Converging evidence from neuroimaging studies of developmental dyslexia reveals dysfunction at posterior brain regions centered in and around the angular gyrus in the left hemisphere. We examined functional connectivity (covariance) between the angular gyrus and related occipital and temporal lobe sites, across a series of print tasks that systematically varied demands on phonological assembly. Results indicate that for dyslexic readers a disruption in functional connectivity in the language-dominant left hemisphere is confined to those tasks that make explicit demands on assembly. In contrast, on print tasks that do not require phonological assembly, functional connectivity is strong for both dyslexic and nonimpaired readers. The findings support the view that neurobiological anomalies in developmental dyslexia are largely confined to the phonological-processing domain. In addition, the findings suggest that right-hemisphere posterior regions serve a compensatory role in mediating phonological performance in dyslexic readers.

Adolescent↗

PubMed2004

Developmental dyslexia and specific language impairment: same or different?

Developmental dyslexia and specific language impairment (SLI) were for many years treated as distinct disorders but are now often regarded as different manifestations of the same underlying problem, differing only in severity or developmental stage. The merging of these categories has been motivated by the reconceptualization of dyslexia as a language disorder in which phonological processing is deficient. The authors argue that this focus underestimates the independent influence of semantic and syntactic deficits, which are widespread in SLI and which affect reading comprehension and impair attainment of fluent reading in adolescence. The authors suggest that 2 dimensions of impairment are needed to conceptualize the relationship between these disorders and to capture phenotypic features that are important for identifying neurobiologically and etiologically coherent subgroups.

Child↗

PubMed2004

Neural changes following remediation in adult developmental dyslexia.

Brain imaging studies have explored the neural mechanisms of recovery in adults following acquired disorders and, more recently, childhood developmental disorders. However, the neural systems underlying adult rehabilitation of neurobiologically based learning disabilities remain unexplored, despite their high incidence. Here we characterize the differences in brain activity during a phonological manipulation task before and after a behavioral intervention in adults with developmental dyslexia. Phonologically targeted training resulted in performance improvements in tutored compared to nontutored dyslexics, and these gains were associated with signal increases in bilateral parietal and right perisylvian cortices. Our findings demonstrate that behavioral changes in tutored dyslexic adults are associated with (1) increased activity in those left-hemisphere regions engaged by normal readers and (2) compensatory activity in the right perisylvian cortex. Hence, behavioral plasticity in adult developmental dyslexia involves two distinct neural mechanisms, each of which has previously been observed either for remediation of developmental or acquired reading disorders.

Adult↗