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PubMed1999

A functional lesion in developmental dyslexia: left angular gyral blood flow predicts severity.

Functional imaging studies have shown reduced regional cerebral blood flow (rCBF) in temporal and inferior parietal regions in dyslexia. To relate such abnormalities to the severity of dyslexia, correlations between reading skill and rCBF during a series of reading tasks and visual fixation were mapped for 17 right-handed dyslexic men, ages 18-40, and 14 matched controls. These correlations uniquely identified the left angular gyrus as the most probable site of a functional lesion in dyslexia: Here, higher rCBF was associated with better reading skill in controls (p <.01), but with worse reading skill in dyslexia (p <.01). This suggests that greater reliance on this region normally facilitates reading, but impairs reading in dyslexia. Thus, developmental dyslexia may share a common localization with alexia.

Adolescent↗
PubMed2001

Dyslexia and visual-spatial talents: compensation vs deficit model.

There are both theoretical and empirical reasons to support the hypothesis that dyslexia is associated with enhancement of right-hemisphere, visual-spatial skills. However, the neurological evidence is neutral with respect to whether dyslexic visual-spatial abilities should be superior (a compensation model) or inferior (a deficit model). In three studies we tested the hypothesis that dyslexia is associated with superior visual-spatial skills. Individuals with dyslexia not only failed to show superiority on a range of visual-spatial tasks, even when tasks were presented without time constraints, but also demonstrated a deficit on many tasks. Whereas we found attentional problems associated with dyslexia, these did not explain our findings. Results are discussed in terms of the apparent conflict between the failure to find any visual-spatial talent associated with dyslexia and the fact that dyslexia is overrepresented in certain visual-spatial professions.

Adult↗
PubMed1990

Neurophysiological heterogeneity and the definition of dyslexia: preliminary evidence for plasticity.

Developments in the field of quantified electroencephalography have enhanced visualization of brain function in the learning disabilities. Optimal utilization of these techniques requires that populations under study be unambiguously defined. Evidence from the literature demonstrates that brain electrical activity of children with reading disability is more extensive and differs from that seen in children with "dyslexia-pure". Preliminary data are presented demonstrating that electrophysiological change seen in children with dyslexia-plus (dyslexia and attentional deficit disorder) could not be predicted by knowledge of electrophysiologic change in children with dyslexia-pure alone and attentional deficit disorder alone. Data from our laboratory are summarized to show that within dyslexia-pure the anomic, dysphonemic and global Denckla subtypes differ electrophysiologically from one another. Of particular interest is the demonstration that regions of electrophysiological difference among these subtypes may reflect compensatory mechanisms rather than pathological change. Finally, a case study is presented demonstrating advantageous effects of remediation upon brain electrical function. As both spontaneous and environmentally induced change in brain function can be documented, developmental dyslexia in its broadest terms appears to represent a more dynamic or plastic process than previously appreciated.

Anomia↗
PubMed2005

Adults with dyslexia demonstrate space-based and object-based covert attention deficits: shifting attention to the periphery and shifting attention between objects in the left visual field.

Performance on a covert visual attention task is compared between a group of adults with developmental dyslexia (specifically phonological difficulties) and a group of age and IQ matched controls. The group with dyslexia were generally slower to detect validly-cued targets. Costs of shifting attention toward the periphery when the target was invalidly cued were significantly higher for the group with dyslexia, while costs associated with shifts toward the fovea tended to be lower. Higher costs were also shown by the group with dyslexia for up-down shifts of attention in the periphery. A visual field processing difference was found, in that the group with dyslexia showed higher costs associated with shifting attention between objects in they LVF. These findings indicate that these adults with dyslexia have difficulty in both the space-based and the object-based components of covert visual attention, and more specifically to stimuli located in the periphery.

Adult↗
PubMed2005

Process dissociation of sight vocabulary and phonetic decoding in reading: a new perspective on surface and phonological dyslexias.

Recent research on developmental dyslexia has suggested a phonological core deficit hypothesis (e.g., Manis, Seidenberg, Doi, McBride-Chang, & Peterson, 1996; Stanovich, Siegel, & Gottardo, 1997) whereby pure cases of developmental phonological dyslexia (dysfunctional phonetic decoding processing but normal sight vocabulary processing) can exist, but pure cases of developmental surface dyslexia (dysfunctional sight vocabulary processing but normal phonetic decoding processing) should not. By applying Jacoby's (1991) and Lindsay and Jacoby's (1994) process dissociation procedure to the reading of regular and exception words, we present a method that serves to estimate readers' reliance on sight vocabulary and phonetic decoding during real word recognition. These reliance estimates are then used in Castles and Coltheart's (1993) regression-based approach to identify normal readers and developmental dyslexics. This new method: (1) allows one to explore normal reading acquisition and both the delay and deviance accounts of developmental dyslexia, (2) provides an alternative to matching dyslexics to both chronological-age and reading-age control groups, and (3) uses only real words. We present evidence that pure cases of developmental surface dyslexia can be obtained with both Castles and Coltheart's measure as well as our own, and that developmental surface dyslexia is not simply a delayed reading deficit. The theoretical importance and utility of estimates of reliance on sight vocabulary and phonetic decoding is discussed.

Child↗
PubMed2005

Reduced auditory M100 asymmetry in schizophrenia and dyslexia: applying a developmental instability approach to assess atypical brain asymmetry.

Although atypical structural and functional superior temporal gyrus (STG) asymmetries are frequently observed in patients with schizophrenia and individuals with dyslexia, their significance is unclear. One possibility is that atypical asymmetries reflect a general risk factor that can be seen across multiple neurodevelopmental conditions--a risk factor whose origins are best understood in the context of Developmental Instability (DI) theory. DI measures (minor physical anomalies (MPAs) and fluctuating asymmetries (FAs)) reflect perturbation of the genetic plan. The present study sought to assess whether the presence of peripheral indices of DI predicts anomalous functional auditory cortex asymmetry in schizophrenia patients and dyslexia subjects. The location of the auditory M100 response was used as a measure of functional STG asymmetry, as it has been reported that in controls (but not in subjects with schizophrenia or dyslexia) the M100 source location in the right hemisphere is shifted anterior to that seen for the left hemisphere. Whole-brain auditory evoked magnetic field data were successfully recorded from 14 male schizophrenia patients, 21 male subjects with dyslexia, and 16 normal male control subjects. MPA and FA measures were also obtained. Replicating previous studies, both schizophrenia and dyslexia groups showed less M100 asymmetry than did controls. Schizophrenia and dyslexia subjects also had higher MPA scores than normal controls. Although neither total MPA nor FA measures predicted M100 asymmetry, analyses on individual MPA items revealed a relationship between high palate and M100 asymmetry. Findings suggest that M100 positional asymmetry is not a diagnostically specific feature in several neurodevelopmental conditions. Continued research examining DI and brain asymmetry relationships is warranted.

Adult↗
PubMed2004

Developmental neglect dyslexia in a Hebrew-reading child.

This paper describes for the first time a detailed study of a child with neglect dyslexia. NT is 10-year-old child, with left word-based neglect dyslexia, without clinical signs of visuo-spatial neglect. Since he is a native speaker of Hebrew, which is read from right to left, his neglect dyslexia manifests in omissions and substitutions of final letters. He is severely impaired in single words, with 96% of his errors being omissions and substitutions of final letters. When presented with more than one word, in word pairs, sentences or text, he neglects the left part of each word, but never omit whole words on the left side of the page. His reading improves considerably when the same word is presented vertically or when manipulations are done to shift his attention to the left--with coloured final letters, flashing light, or tapping his finger to the left of each word. NT's neglect dyslexia is very selective, with good reading of numbers and symbols, and even good performance on letter sequences when no reading is required. A dissociation is also detected between his impaired reading due to neglect dyslexia and his normal performance on conventional clinical tests of general visual neglect visual of line, object and letter cancellation, line bisection, object drawing and copying. His neglect dyslexia seems to be developmental as no abrupt onset is reported.

Attention↗
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↗
PubMed2004

Support for EKN1 as the susceptibility locus for dyslexia on 15q21.

Dyslexia has been linked to a number of chromosomal regions including 15q. Recently a gene, EKN1, with unknown function in the linked region, was identified via a translocation breakpoint. This gene was further supported as a susceptibility locus by association studies in a Finnish sample. We investigated the possibility of this locus as a susceptibility gene contributing to dyslexia, analyzed as a categorical trait, and analyzed key reading phenotypes as quantitative traits using six polymorphisms including the two previously reported to be associated with dyslexia. In our sample of 148 families identified through a proband with reading difficulties, we found significant evidence for an association to dyslexia analyzed as a categorical trait and found evidence of association to the reading and related processes of phonological awareness, word identification, decoding, rapid automatized naming, language ability, and verbal short-term memory. However, association was observed with different alleles and haplotypes than those reported to be associated in a Finnish sample. These findings provide support for EKN1 as a risk locus for dyslexia and as contributing to reading component processes and reading-related abilities. Based on these findings, further studies of this gene in independent samples are now required to determine the relationship of this gene to dyslexia.

Child↗
PubMed2001

Perceptual discrimination of speech sounds in developmental dyslexia.

Experiments previously reported in the literature suggest that people with dyslexia have a deficit in categorical perception. However, it is still unclear whether the deficit is specific to the perception of speech sounds or whether it more generally affects auditory function. In order to investigate the relationship between categorical perception and dyslexia, as well as the nature of this categorization deficit, speech specific or not, the discrimination responses of children who have dyslexia and those of average readers to sinewave analogues of speech sounds were compared. These analogues were presented in two different conditions, either as nonspeech whistles or as speech sounds. Results showed that children with dyslexia are less categorical than average readers in the speech condition, mainly because they are better at discriminating acoustic differences between stimuli belonging to the same category. In the nonspeech condition, discrimination was also better for children with dyslexia, but differences in categorical perception were less clear-cut. Further, the location of the categorical boundary on the stimulus continuum differed between speech and nonspeech conditions. As a whole, this study shows that categorical deficit in children with dyslexia results primarily from an increased perceptibility of within-category differences and that it has a speech-specific component. These findings may have profound implications for learning and re-education.

Adolescent↗
PubMed2000

Acquired dyslexia.

Disorders of reading are frequently encountered in patients with acquired cerebral lesions. Investigations in the past few decades have improved our understanding of these disorders. In this article we review the peripheral dyslexias, including neglect dyslexia, attentional dyslexia, and pure alexia (or alexia without agraphia), as well as the "central" dyslexias, including deep, surface, and phonological dyslexia. Current accounts of acquired dyslexia are also discussed. Finally, we briefly describe the reading tasks that serve to differentiate the different reading disorders.

Agraphia↗
PubMed2003

Neural deficits in children with dyslexia ameliorated by behavioral remediation: evidence from functional MRI.

Developmental dyslexia, characterized by unexplained difficulty in reading, is associated with behavioral deficits in phonological processing. Functional neuroimaging studies have shown a deficit in the neural mechanisms underlying phonological processing in children and adults with dyslexia. The present study examined whether behavioral remediation ameliorates these dysfunctional neural mechanisms in children with dyslexia. Functional MRI was performed on 20 children with dyslexia (8-12 years old) during phonological processing before and after a remediation program focused on auditory processing and oral language training. Behaviorally, training improved oral language and reading performance. Physiologically, children with dyslexia showed increased activity in multiple brain areas. Increases occurred in left temporo-parietal cortex and left inferior frontal gyrus, bringing brain activation in these regions closer to that seen in normal-reading children. Increased activity was observed also in right-hemisphere frontal and temporal regions and in the anterior cingulate gyrus. Children with dyslexia showed a correlation between the magnitude of increased activation in left temporo-parietal cortex and improvement in oral language ability. These results suggest that a partial remediation of language-processing deficits, resulting in improved reading, ameliorates disrupted function in brain regions associated with phonological processing and produces additional compensatory activation in other brain regions.

Brain↗
PubMed2003

Visual-sequential and visuo-spatial skills in dyslexia: variations according to language comprehension and mathematics skills.

This study focused on visual-sequential and visuo-spatial functions in a group of 39 heavily dyslexic children, compared to a Control group. Mean age was 12.72 (SD 1.71). The dyslexia group was divided into three subgroups by language comprehension and mathematics skills. Only on a visual-sequential task was no difference seen between the groups. The main differences occurred between the two dyslexic subgroups with no language comprehension impairment, but with varying mathematics skills. Whereas the subgroup with good mathematics skills scored within the upper ranges, the mathematics-impaired subgroup showed significantly lower scores. The third dyslexic subgroup, with both language comprehension and mathematics impairments, performed within the norm. The study indicates a dissociation between language comprehension and visuo-spatial skills in dyslexia, which has implications for how variations in dyslexia should be understood. The results also show that the visuo-spatial impairments seen in one of the dyslexia subgroups lead to two ways of understanding mathematics impairment when it co-occurs with dyslexia: (1) as a visuo-spatial problem; (2) as a linguistic problem. These distinctions should imply different intervention strategies in dyslexia.

Adolescent↗
PubMed2003

Comorbid auditory processing disorder in developmental dyslexia.

OBJECTIVE: The primary objective of this study was to investigate the extent of comorbid auditory processing disorder (APD) in a group of adults with developmental dyslexia. An additional objective was to compare performance on auditory tasks to results from standardized tests of reading in an attempt to generate a clinically useful profile of developmental dyslexics with comorbid APD. DESIGN: A group of eleven persons with developmental dyslexia and 14 age- and intelligence-matched controls participated in the study. Behavioral audiograms, 226-Hz tympanograms, and word recognition scores were obtained binaurally from all subjects. Both groups were administered the frequency-pattern test (FPT) and duration-pattern test (DPT) monaurally (30 items per ear) in both the left and right ear. Gap detection results were obtained in both groups (binaural presentation) using narrowband noise centered at 1 kHz in an adaptive two-alternative forced-choice (2-AFC) paradigm. The FPT, DPT, and gap detection results were analyzed for interaural (where applicable), intergroup, and intragroup differences. Correlations between performance on the auditory tasks and the standardized tests of reading were examined. Additive logistic regression models were fit to the data to determine which auditory tests proved to be the best predictors of group membership. RESULTS: The persons with developmental dyslexia as a group performed significantly poorer than controls on both the FPT and DPT. Furthermore, the group differences were significant in both monaural conditions. On the FPT and DPT, five of the eleven participants with dyslexia performed below the widely used clinical criterion for APD of 70% correct in either ear. All five of these participants performed below criterion on the FPT, whereas four of the five additionally performed below 70% on the DPT. The data also were analyzed by fitting a series of stepwise logistic regression models, which indicated that gap detection did not significantly predict group membership, whereas the FPT and DPT were significant predictors. The addition of the FPT score after the DPT did not result in a significant change in the residual deviance. CONCLUSIONS: Approximately half of the participants with developmental dyslexia showed clinically significant diminished performance on the FPT and DPT indicative of APD. These results indicate that the percentage of persons with developmental dyslexia and comorbid APD may be substantial enough to warrant serious clinical considerations.

Acoustic Impedance Tests↗
PubMed2002

Auditory processing in children with dyslexia.

BACKGROUND: It has been claimed that children with dyslexia show a general impairment in the processing of rapid auditory stimuli. However, most previous studies in this field have focused on children with language impairment or children who do not meet accepted criteria for dyslexia. METHODS: In the present study, the processing of rapid non-verbal auditory stimuli (complex tones) was examined in a population-based sample of 24 children with dyslexia, 10 to 12 years of age, and a matched control group. RESULTS: The dyslexia group showed reduced tone processing relative to the control group, with significant main effects of tone duration, inter-stimulus interval and task complexity. The deficit was not specific for temporal order errors, and could not be explained by differences in short-term memory or verbal IQ. However, correlations between tone processing and reading ability were generally low or absent. CONCLUSION: Although a general processing deficit for rapid auditory stimuli in dyslexia was confirmed, its relevance for reading problems and hence for treatment programmes for dyslexia is questioned.

Acoustic Stimulation↗
PubMed2006

Clinical experiences of students with dyslexia.

AIM: This paper reports a study exploring the clinical experiences of student nurses with dyslexia and its potential influence on their practice. BACKGROUND: Widened access to university education has meant an increase in the number of students with dyslexia. A limited number of studies have explored the academic experiences of dyslexic student nurses. However, nursing students in the United Kingdom spend 50% of their programme in practice settings, and there are no studies detailing their clinical experiences. METHOD: This qualitative exploratory study involved tape-recorded interviews with a convenience sample of 18 nursing students with a formal dyslexia diagnosis. Data were collected in 2003-2004 and were analysed using thematic analysis. FINDINGS: Participants described a number of personalized approaches to managing their difficulties in practice. Whilst many of these may be useful to non-dyslexic students, descriptions of, for example, avoiding answering the telephone, were inappropriate. Some participants contended with discrimination and ridicule, often choosing not to disclose their disability. Less acute clinical environments appeared to provide more satisfying working experience, and this factor may be influential in shaping future career options. Participants valued more time and an undisturbed place to complete clinical documentation. Heightened self-awareness promoted patient safety as the major concern for study participants. Positive aspects of dyslexia were never raised or acknowledged by participants. CONCLUSION: The clinical setting provides a challenging environment for nursing students with dyslexia, who find personalized ways to manage their disability. A dyslexia diagnosis continues to carry a stigma that may result in non-disclosure, with implications for the level of support available. Greater awareness of the practice-specific needs of such students is required to ensure appropriate support and public safety.

Adaptation, Psychological↗
PubMed2007

A survey-based exploration of the impact of dyslexia on career progression of UK registered nurses.

AIM: To explore the effects of dyslexia on the practice and career progression of UK registered nurses (RN). BACKGROUND: Literature suggests dyslexia can have a negative impact in the workplace and may pose particular difficulties for nurses, where accuracy in information processing activities is essential for practice. METHODS: A questionnaire was used to survey RNs with dyslexia (n = 116) and results analysed using content analysis. FINDINGS: Dyslexia provided a challenge to the everyday work of RNs, which was often met successfully using a range of individualized strategies. Career progression was achievable but compared with peers, was perceived to take longer. Disclosure of dyslexia to work-colleagues was selective and dependent on the perceived benefits. Informal support mechanisms were commonly utilized with formal management support less well defined. CONCLUSION: Dyslexia appears to have a negative impact on working practices and career progression, but remains a poorly understood and often hidden disability.

Adaptation, Psychological↗
PubMed2006

Interrelationship and familiality of dyslexia related quantitative measures.

Dyslexia is a complex gene-environment disorder with poorly understood etiology that affects about 5% of school-age children. Dyslexia occurs in all languages and is associated with a high level of social and psychological morbidity for the individual and their family; approximately 40-50% have persistent disability into adulthood. The core symptoms are word reading and spelling deficits, but several other cognitive components influence the core phenotype. A broad spectrum of dyslexia related phenotypes, including phonological decoding, phoneme awareness, orthographic processing, short-term memory, rapid naming and basic mathematical abilities, were investigated in large sample of 287 German dyslexia families. We explored the interrelationship between the component phenotypes using correlation and principal component analyses (PCA). In addition, we estimated familiality for phenotypes as well as for the factors suggested by PCA. The correlation between the component phenotypes varied between -0.1 and 0.7. The PCA resulted in three factors: a general dyslexia factor, a speed of processing factor and a mathematical abilities factor. The familiality estimates of single components and factors ranged between 0.25 and 0.63. Instead of analyzing single dyslexia-related components, multivariate analyses including factor analytic approaches may help in the identification of susceptibility genes.

Adolescent↗