Studies Of Developmental Dyslexia Research Articles

The visual basis of reading and reading difficulties.

Most of our knowledge about the neural networks mediating reading has derived from studies of developmental dyslexia (DD). For much of the 20th C. this was diagnosed on the basis of finding a discrepancy between children's unexpectedly low reading and spelling scores compared with their normal or high oral and non-verbal reasoning ability. This discrepancy criterion has now been replaced by the claim that the main feature of dyslexia is a phonological deficit, and it is now argued that we should test for this to identify dyslexia. However, grasping the phonological principle is essential for all learning to read; so every poor reader will show a phonological deficit. The phonological theory does not explain why dyslexic people, in particular, fail; so this phonological criterion makes it impossible to distinguish DD from any of the many other causes of reading failure. Currently therefore, there is no agreement about precisely how we should identify it. Yet, if we understood the specific neural pathways that underlie failure to acquire phonological skills specifically in people with dyslexia, we should be able to develop reliable means of identifying it. An important, though not the only, cause in people with dyslexia is impaired development of the brain's rapid visual temporal processing systems; these are required for sequencing the order of the letters in a word accurately. Such temporal, "transient," processing is carried out primarily by a distinct set of "magnocellular" (M-) neurones in the visual system; and the development of these has been found to be impaired in many people with dyslexia. Likewise, auditory sequencing of the sounds in a word is mediated by the auditory temporal processing system whose development is impaired in many dyslexics. Together these two deficits can therefore explain their problems with acquiring the phonological principle. Assessing poor readers' visual and auditory temporal processing skills should enable dyslexia to be reliably distinguished from other causes of reading failure and this will suggest principled ways of helping these children to learn to read, such as sensory training, yellow or blue filters or omega 3 fatty acid supplements. This will enable us to diagnose DD with confidence, and thus to develop educational plans targeted to exploit each individual child's strengths and compensate for his weaknesses.

MRI Measurement of Upper Cervical Spinal Cord Cross-Sectional Area in Children.

Neurological and neurodegenerative diseases can affect the spinal cord (SC) of pediatric patients. Magnetic resonance imaging (MRI) allows for in vivo quantification of SC atrophy via cross-sectional area (CSA). The study of CSA values in the general population is important to disentangle disease-related changes from intersubject variability. This study aimed at providing normative values for cervical CSA in children, extending our previous work performed with adults. Seventy-eight children (age 7-17 years) were selected from a Developmental Dyslexia study. All subjects underwent a 3T brain MRI session and any incidental findings were reported on the scans. A sagittal 1 mm3 3-dimensional T1 -weighted brain acquisition extended to the upper cervical cord was used to measure CSA at C2-C3, as well as spinal canal area and skull volume (V-scale). These three metrics were linearly fitted as a function of age to extract trends and percentage annual changes. Sex differences of CSA were assessed using least squares regression analyses, adjusting for age. We tested normalization strategies proven to be effective in reducing the intersubject variability of adults' CSA. CSA changed as a function of age at a faster rate when compared with skull volume (CSA: 1.82% increase, V-scale: .60% reduction). Sex had a statistically significant effect on CSA. Normalization methods based on canal area and skull volume reduced the CSA intersubject variability up to 16.84%. We present CSA normative values in a large cohort of children, reporting on sources of intersubject variability and how to reduce them applying normalization methods previously developed.

Neurobiological Sex Differences in Developmental Dyslexia.

Understanding sex differences at the neurobiological level has become increasingly crucial in both basic and applied research. In the study of developmental dyslexia, early neuroimaging investigations were dominated by male-only or male-dominated samples, due at least in part to males being diagnosed more frequently. While recent studies more consistently balance the inclusion of both sexes, there has been little movement toward directly characterizing potential sex differences of the disorder. However, a string of recent work suggests that the brain basis of dyslexia may indeed be different in males and females. This potential sex difference has implications for existing models of dyslexia, and would inform approaches to the remediation of reading difficulties. This article reviews recent evidence for sex differences in dyslexia, discusses the impact these studies have on the understanding of the brain basis of dyslexia, and provides a framework for how these differential neuroanatomical profiles may develop.

Planum temporale asymmetry in developmental dyslexia: Revisiting an old question.

Among the various asymmetrical structures of the human brain, the planum temporale, an anatomical region associated with a variety of auditory and language-related processes, has received particular attention. While its surface area has been shown to be greater in the left hemisphere compared to the right in about two-thirds of the general population, altered patterns of asymmetry were revealed by post mortem analyses in individuals with developmental dyslexia. These findings have been inconsistently replicated in magnetic resonance imaging studies of this disorder. In this report, we attempt to resolve past inconsistencies by analyzing the T1-weighted MR images of 81 children (mean age: 11 years, sd: 17 months), including 46 control (25 boys) and 35 dyslexic children (20 boys). We manually outlined Heschl's gyri, the planum temporale and the posterior rami of the Sylvian fissure on participants' brain images, using the same anatomical criteria as in post mortem studies. Results revealed an altered pattern of asymmetry of the planum temporale surface area in dyslexic boys only, with a greater proportion of rightward asymmetrical cases among dyslexic boys compared to control boys. Additionally, analyses of cortical thickness showed no asymmetry differences between groups for any of the regions of interest. Finally, a greater number of Heschl's gyrus full duplications emerged for the right hemisphere of dyslexic boys compared to controls. The present findings confirm and extend early post mortem observations. They also stress the importance of taking gender into account in studies of developmental dyslexia.

Remediation of developmental dyslexia: Tackling a basic memory deficit

Remediation studies of developmental dyslexia are extremely rare. We present a single case study of an 8-year-old German developmental dyslexic boy K.H. who is hypothesized to suffer from a severe memory problem, impeding the development of normal reading functions. The memory problem especially affects the storage and access to letter–sound associations. As a consequence, the boy was initially unable to accurately and quickly name most of the 26 letters of the alphabet. A multiple-baseline across-material design with a high-frequency errorless learning procedure was set up to improve letter–name associations. The intervention improved K.H.'s letter reading and even his word reading. We discuss the role of memory deficits in reading acquisition in the context of three different theoretical models. We show how such theoretical considerations can successfully guide remediation programmes.

Genes, brain, and cognition: A roadmap for the cognitive scientist

This paper reviews current progress in genetics in relation to the understanding of human cognition. It is argued that genetics occupies a prominent place in the future of cognitive science, and that cognitive scientists should play an active role in the process. Recent research in genetics and developmental neuroscience is reviewed and argued to provide a new perspective on the timeless questions of innateness and modularity. The special case of the genetic bases of language is further discussed, with the study of developmental dyslexia as an exemplary entry point. This Special Issue puts together articles providing different empirical examples and theoretical perspectives on how the integration between the different levels of description (gene, brain, and cognition) is to be achieved.

A Conservative Meta-Analysis of Linkage and Linkage-Association Studies of Developmental Dyslexia

Linkage studies of complex phenotypes such as reading ability/disability (developmental dyslexia or reading disorder) and related componential processes, where the effects attributable to individual genes appear to be modest, are critically dependent on the nature and composition of the samples and the phenotypes analyzed. Thus, it might be helpful to consider the results from individual studies collectively so that summative profiles of findings can be considered. To gain an impression of how useful such an approach might be, a conservative meta-analysis based on Fisher's pooled p values approach was performed on regional linkage/association studies of developmental dyslexia and related phenotypes published through early September 2004. The obtained results rank order the findings and stress the need to contextualize the results with more regional linkage/association studies as well as with statistical simulation studies.

Developmental dyslexia: a multilevel syndrome

The study of developmental dyslexia at several levels, from the physiological to the cognitive, has acquired a new energy in the past few years. A debate exists as to whether the condition represents primarily a disorder of perception or a deficit in cognition and metacognitive processes. Neuroanatomical research can shed some light on this debate. Investigation first in human autopsy brains followed by modelling of the findings in experimental animals indicates that anomalies exist at multiple levels and pathways. Thus areas of the brain concerned with perceptual processing, as well as those involved in cognitive and metacognitive tasks, are anatomically affected in dyslexia. Similarly, at least the visual and auditory pathways are affected by the anatomical changes. Moreover, there appears to be, at least in part, a causal relationship between the involvement at different levels and pathways, such that during development—a time of great plasticity—changes at one level or pathway propagate to affect other levels and pathways. It may be inferred from this research that dyslexia represents a complex interaction of both low-level and high-level processing deficits affecting language and perhaps visual performance. Although treatment aimed at correcting deficits at one level or pathway may be helpful, it is suggested that the best forms of treatment will need to deal with the multiple nature of the disorder. Copyright © 1999 John Wiley & Sons, Ltd.

Continuities between speech and spelling in a case of developmental dyslexia

This paper explores the relationship between speech and spelling in a single-case study of developmental dyslexia. JM, a developmental dyslexic with a well-documented history of speech, reading and spelling difficulties, was examined when he was 13–14 years old. He still had subtle articulation difficulties causing some disfluency and his use of phonetic voicing was atypical. We argue that these difficulties were recapitulated in his spelling where he was more sensitive to the prosodic aspects of words than normal spellers, exhibiting a strong tendency to spell accurately words which are stressed on the first, rather than the second syllable. He also had more difficulty with phonetic voicing and spelling errors reflected this uncertainty. Thus, when word-specific (orthographic) spelling information is unavailable, JM, like all spellers, must make use of phonological spelling strategies. In his case, these are compromised because of underlying phonological speech problems. It is argued that, while young children make use of a phonological ‘frame’ on which to organize orthographic information, dyslexics, like JM, who have inadequate phonological representations, are unable to do so. This has a detrimental effect on their acquisition of spelling.

Reading Development, Dyslexia and Phonological Skills

It is argued here that the most general information processing deficit in developmental dyslexia lies in phonological processing and that studies of individual differences in reading development where intelligence is controlled generate patterns of associations which are essentially similar to those which arise from studies of developmental dyslexia. Developmental dyslexics are shown to resemble acquired surface dyslexics but they are even more similar to younger children of equivalent reading ability. Also, it is argued that a complete understanding of the development of reading can come only from longitudinal investigations of development itself. Such studies demonstrate typical sequences of interactive growth of related skills. They show how reading changes in nature as it is learned and that a crucial early stage in its development is the adoption of an alphabetic reading strategy. The precursors of the phonological knowledge that forms the foundations of grapheme-phoneme reading are traced back throu...

A study of developmental dyslexia

(1) Twelve cases of reading disability in school children are presented. An assessment of perceptual capacities and skills is reported and the findings are interpreted with reference to the developmental history and familial factors. (2) Reading disability did not occur in isolation in the group. Directional difficulties and difficulties in drawing and copying were characteristic of the group as a whole, but in no case was there an impairment of non-verbal form perception. (3) Confusion among letters was found in 50 per cent of the cases. Letters were confused on the basis of visual resemblance and not acoustic resemblance. This finding, together with the nature of the associated disabilities led to the interpretation that dyslexia in these cases is a disorder of visual perception, often occuring independent of any defect in oral-auditory language development. (4) Evidence of minimal brain damage was found in 58 per cent of the cases. (5) The association of dyslexia with sinistrality and behaviour disorder is discussed.