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PubMed2002

The cognitive profile and multiple-deficit hypothesis in Chinese developmental dyslexia.

The present study was conducted to examine the cognitive profile and multiple-deficit hypothesis in Chinese developmental dyslexia. Thirty Chinese dyslexic children in Hong Kong were compared with 30 average readers of the same chronological age (CA controls) and 30 average readers of the same reading level (RL controls) in a number of rapid naming, visual, phonological, and orthographic tasks. Chinese dyslexic children performed significantly worse than the CA controls but similarly to the RL controls on most of the cognitive tasks. The rapid naming deficit was found to be the most dominant type of cognitive deficit in Chinese dyslexic children. Over half of the dyslexic children exhibited deficits in 3 or more cognitive areas, and there was a significant association between the number of cognitive deficits and the degree of reading and spelling impairment. The present findings support the multiple-deficit hypothesis in Chinese developmental dyslexia.

Child↗
PubMed2002

Crowding effects on word identification in developmental dyslexia.

The effect of crowding on the identification of words was examined in normal readers and subjects with developmental dyslexia. In Experiment 1, a matching task was used. Words were presented either alone or embedded in other words. Vocal reaction times (RT) of dyslexics were slower and more sensitive to the presence of the surrounding stimuli than those of control subjects. Similar results were obtained in a control experiment using the same task for strings of symbols (isolated or crowded) instead of words. These data indicate that differences in crowding in control and dyslexic subjects arise at a pre-linguistic level. In Experiment 2, vocal RTs to word reading were measured. Two conditions putatively reducing the effect of crowding were tested: increasing inter-letter spacing and blurring. A moderate increase of inter-letter spacing produced faster vocal RTs in dyslexics, while no effect was present in normal controls. Moderate blurring of stimuli did not change dyslexics' RTs, while normal readers became slower. Group and individual results are discussed to evaluate the extent to which crowding contributes to the genesis of developmental dyslexia.

Adolescent↗
PubMed1990

Rate variables and automatized naming in developmental dyslexia.

The rate variable in rapid automatized naming (RAN) was investigated in 50 adolescent and 40 adult students with developmental dyslexia, in matched normal controls, and in learning-disabled students without reading difficulties. Visual stimuli depicting familiar colors and common objects were presented in isolation at three film speeds and three exposure times. Film speed and exposure time contributed as independent variables to error rate; and dyslexic subjects of both age groups made significantly more naming errors than controls. Dyslexic subjects also responded with longer naming latencies than controls when the same RAN stimuli were presented in a continuous sequential mode as a matrix of rows and columns. Naming latencies in the sequential presentation were highly correlated with naming errors in the film version. The implications of reduced naming rates for nongraphological stimuli in developmental dyslexia are discussed.

Adolescent↗
PubMed1998

Metabolic abnormalities in developmental dyslexia detected by 1H magnetic resonance spectroscopy.

BACKGROUND: Neurological and physiological deficits have been reported in the brain in developmental dyslexia. The temporoparietal cortex has been directly implicated in dyslexic dysfunction, and substantial indirect evidence suggests that the cerebellum is also implicated. We wanted to find out whether the neurological and physiological deficits manifested as biochemical changes in the brain. METHODS: We obtained localised proton magnetic resonance spectra bilaterally from the temporo-parietal cortex and cerebellum of 14 well-defined dyslexic men and 15 control men of similar age. FINDINGS: We found biochemical differences between dyslexic men and controls in the left temporo-parietal lobe (ratio of choline-containing compounds [Cho] to N-acetylaspartate [NA] p< or =0.01) and right cerebellum (Cho/NA, p< or = 0.01; creatine [Cre] to NA p< or =0.05; (not significant). We found lateral biochemical differences in dyslexic men in both these brain regions (Cho/NA in temporo-parietal lobe, left vs right, p< or =0.01; Cre/NA in cerebellum, left vs right, p< or =0.001). We found no such lateral differences in controls. There was no significant relation between the degree of contralateral chemical difference and handedness in dyslexic or control men. INTERPRETATION: We suggest that the observed differences reflect changes in cell density in the temporo-parietal lobe in developmental dyslexia and that the altered cerebral structural symmetry in dyslexia is associated with abnormal development of cells or intracellular connections or both. The cerebellum is biochemically asymmetric in dyslexic men, indicating altered development of this organ. These differences provide direct evidence of the involvement of the cerebellum in dyslexic dysfunction.

Adult↗
PubMed1997

Connectionism, phonology, reading, and regularity in developmental dyslexia.

Tests of the "phonological deficit" account of developmental dyslexia have produced apparently inconsistent results. We show how a connectionist approach to dyslexic reading development can resolve the paradox. A "dyslexic" model of reading was created by reducing the quality of the phonological representations available to the model during learning. The model behaved similarly to dyslexic children in that it had a selectively reduced ability to process nonwords, but showed normal effects of words' spelling-to-sound regularity. An experimental test of the model's predictions confirmed that dyslexic children perform similarly, in that they are impaired on irregular words to the same extent as nondyslexic children. It is concluded that developmentally dyslexic reading can indeed be understood in terms of impaired phonological representations and that the adoption of a modeling approach resolves an apparent paradox in the experimental literature.

Child↗
PubMed1997

A magnetic resonance imaging study of planum temporale asymmetry in men with developmental dyslexia.

BACKGROUND: Imaging studies have suggested anomalous anatomical asymmetries in language-related regions of the temporal and parietal lobes in individuals with developmental dyslexia. Autopsy studies have reported unusual symmetry of the planum temporale (PT) in patients with dyslexia. Methodological limitations characterize much of this literature, however. OBJECTIVE: To examine the size and asymmetry of the PT and its extension into the parietal lobe (planum parietale [PP]) in men with well-characterized, persistent dyslexia by using magnetic resonance imaging and 3-dimensional surface rendering techniques. METHODS: The brains of 16 right-handed dyslexic men aged 18 to 40 years and 14 matched control subjects were studied with magnetic resonance imaging. Most of these subjects were previously studied with positron emission tomography, which demonstrated functional abnormalities in temporal and parietal brain regions in the dyslexic group. The area of the PT was determined with the aid of 3-dimensional surface-rendering techniques. The size of the PP was estimated by measuring the length of the posterior ascending ramus on 3 parasagittal slices. RESULTS: Approximately 70% to 80% of both groups showed equivalent leftward (left > right) asymmetries of the PT; approximately 50% to 60% showed equivalent rightward (right > left) asymmetries of the PP. These asymmetries showed equivalent moderate inverse correlations with each other in both groups. CONCLUSIONS: These results challenge the notion that anomalous asymmetry of the PT is strongly associated with developmental dyslexia. Given the heterogeneity of the dyslexic population, some subgroup of dyslexic individuals (i.e., those with developmental language disorders) may show unusual symmetry or reversed asymmetry in this region. However, anomalous asymmetry of the planum did not contribute to functional abnormalities demonstrated in these patients by positron emission tomography.

Adolescent↗
PubMed2003

Do the reading disabilities of children with cleft fit into current models of developmental dyslexia?

OBJECTIVE: The purpose of this study was to determine whether the reading problems of children with cleft fit models of developmental dyslexia. DESIGN: The study compared children with nonsyndromic cleft lip and palate who had reading disability (n = 46) with those who did not have reading disability (n = 46). The children were matched for age, sex, and grade. The two groups were compared (t tests) on measures of verbal expression, phonemic awareness, and rapid naming. Also, regression analyses compared the relative relationships of these variables to reading disability. PARTICIPANTS: Children were selected from 154 patients originally screened. RESULTS: Children with reading disability scored significantly lower on rapid naming and verbal expression, with no differences found on phonemic awareness. Rapid naming was shown to have the most significant association with reading disability. CONCLUSION: Children with nonsyndromic cleft lip and palate show symptoms similar to a naming-memory deficit model of developmental dyslexia. Reading treatment should avoid sight word approaches and focus on oral phonics treatment.

Anomia↗
PubMed2002

Amplitude envelope onsets and developmental dyslexia: A new hypothesis.

A core difficulty in developmental dyslexia is the accurate specification and neural representation of speech. We argue that a likely perceptual cause of this difficulty is a deficit in the perceptual experience of rhythmic timing. Speech rhythm is one of the earliest cues used by infants to discriminate syllables and is determined principally by the acoustic structure of amplitude modulation at relatively low rates in the signal. We show significant differences between dyslexic and normally reading children, and between young early readers and normal developers, in amplitude envelope onset detection. We further show that individual differences in sensitivity to the shape of amplitude modulation account for 25% of the variance in reading and spelling acquisition even after controlling for individual differences in age, nonverbal IQ, and vocabulary. A possible causal explanation dependent on perceptual-center detection and the onset-rime representation of syllables is discussed.

Articulation Disorders↗
PubMed1988

The failure of antimotion sickness medication to improve reading in developmental dyslexia: results of a randomized trial.

Although there have been no randomized clinical trials of the efficacy of antimotion sickness medication treatment of developmental dyslexia, some children are treated in this way. We have performed two evaluations of such treatments. In Experiment 1, 12 children participated in a double-blind within-subject crossover design to test the acute (2-day) administration of four preparations: 10 mg methylphenidate, 12.5 mg meclizine, both methylphenidate and meclizine, or placebo. Improvements obtained with each drug were scattered across measures of reading fluency, balance and coordination, and eye movements, suggesting that a chronic trial would be justified. In Experiment 2, six children from Experiment 1 received 12.5 mg meclizine b.i.d. for 3 months and placebo for 3 months in a double-blind within-subject crossover design. Meclizine had no effect on reading, but it significantly improved ocular motor stability during steady fixation. This study thus failed to support the hypothesis that meclizine is of benefit in developmental dyslexia.

Child↗
PubMed2006

Developmental dyslexia: the visual attention span deficit hypothesis.

The visual attention (VA) span is defined as the amount of distinct visual elements which can be processed in parallel in a multi-element array. Both recent empirical data and theoretical accounts suggest that a VA span deficit might contribute to developmental dyslexia, independently of a phonological disorder. In this study, this hypothesis was assessed in two large samples of French and British dyslexic children whose performance was compared to that of chronological-age matched control children. Results of the French study show that the VA span capacities account for a substantial amount of unique variance in reading, as do phonological skills. The British study replicates this finding and further reveals that the contribution of the VA span to reading performance remains even after controlling IQ, verbal fluency, vocabulary and single letter identification skills, in addition to phoneme awareness. In both studies, most dyslexic children exhibit a selective phonological or VA span disorder. Overall, these findings support a multi-factorial view of developmental dyslexia. In many cases, developmental reading disorders do not seem to be due to phonological disorders. We propose that a VA span deficit is a likely alternative underlying cognitive deficit in dyslexia.

Adolescent↗
PubMed2004

More than words: a common neural basis for reading and naming deficits in developmental dyslexia?

Dyslexic individuals show subtle impairments in naming pictures of objects in addition to their difficulties with reading. The present study investigated whether word reading and picture naming deficits in developmental dyslexia can be reduced to a common neurological impairment. Eight dyslexic subjects, impaired on measures of reading, spelling and naming speed, were matched for age and general ability with 10 control subjects. Participants were scanned using PET during two experimental conditions: reading words and naming pictures in the form of corresponding line drawings. In addition, two high-level baseline conditions were used to control for visual and articulatory processes. Relative to the control group, the dyslexic participants showed reduced activation in a left occipitotemporal area during both word reading and picture naming. This was the case even in the context of intact behavioural performance during scanning. Abnormal activation in this region, as reported previously for reading, is therefore not specific to orthographic decoding but may reflect a more general impairment in integrating phonology and visual information. Our investigation points to a common neurological basis for deficits in word reading and picture naming in developmental dyslexia.

Adolescent↗
PubMed2006

Brain responses to subject-verb agreement violations in spoken language in developmental dyslexia: an ERP study.

This study investigates the presence and latency of the P600 component in response to subject-verb agreement violations in spoken language in people with and without developmental dyslexia. The two groups performed at-ceiling level on judging the sentences on their grammaticality, but the ERP data revealed subtle differences between them. The P600 tended to peak later in the left posterior region in the dyslexic group compared with the control group. In addition, the group of dyslexic subjects did not show a P600 in response to sentences with a plural NP subject. These results suggest that brain activation involved in syntactic repair is more affected by linguistic complexity in developmental dyslexia compared with non-dyslexic individuals.

Adolescent↗
PubMed1996

Prediction of group membership in developmental dyslexia, attention deficit hyperactivity disorder, and normal controls using brain morphometric analysis of magnetic resonance imaging.

This study explored the utility of using selected brain morphometric indices for predicting group membership for children with developmental dyslexia (n = 10), attention deficit hyperactivity disorder: combined type (n = 10), and a control group (n = 10). Subjects ranged in age from 6.1 to 16 years (M = 10.5 years, SD = 2.8). None of the subjects were diagnosed with mental retardation, nor did any of the subjects have a history of seizure disorder, head trauma, or other neurodevelopmental disorders. WISC-R Full Scale IQ ranged from 87 to 149 (M = 114.4, SD = 13.3) with no significant differences noted between the clinical groups. Six brain regions, as defined by MRI scans, were selected a priori for inclusion in a discriminant function analysis. Reliability of the morphometric measures ranged from 0.94 to 0.97. One significant discriminant function was generated which accounted for about 61.4% of the variance between groups. The predictive discriminant analysis using the six morphometric MRI measurements classified subjects with an overall 60% accuracy with the best accuracy found for the developmental dyslexia and control groups. A predictive discriminant analysis incorporating these six morphometric measures as well as chronological age and FSIQ increased the overall classification accuracy to 87% with the misclassfied subjects assigned to one of the clinical groups. The findings support the presumed neurological basis for many neurodevelopmental disorders. They also underline the importance of including brain morphometric measures in predictive models.

Journal Article↗
PubMed1998

[An example of how to measure the relation between developmental dyslexia and illiteracy].

The ability to read and the phonological fitness of 89 youth (average age of 21.3 years) having difficulty with social and professional integration were examined. We observed that 64% of them (n = 57) had difficulty in reading. The results of the phonological and reading tests showed that developmental dyslexia constitutes, for 56% of the subjects (n = 32), or for 36% of the population of youth with difficulties, the explanatory framework for the delay of acquisition of these capacities. Reading difficulties for these youth were significantly linked to an alteration of the phonological treatment that effects: short-term verbal memory, auditory discrimination and meta-phonological fitness. The data tends to validate the hypothesis of the existence of a functional link between developmental dyslexia and illiteracy.

Adolescent↗
PubMed1982

Symmetry and asymmetry in the human posterior thalamus. II. Thalamic lesions in a case of developmental dyslexia.

The cytoarchitecture of the brain of a patient with developmental dyslexia was analyzed. The cortical abnormalities, consisting of micropolygyria encompassing most of posterior temporoparietal area and ectopic cell collections elsewhere have been described previously. In this study, the posterior thalamus was likewise analyzed, and a bilateral disruption of cytoarchitecture was noted in the medial geniculate nucleus and the lateralis posterior nucleus, a nuclear group of probable relevance to language found to be asymmetric.

Cerebral Cortex↗
PubMed1993

Neuroanatomic basis of developmental dyslexia.

This article reviews the known neuroanatomic and neuropathologic bases of developmental dyslexia in the context of some of the functional deficits exhibited by affected individuals. Observations from autopsy brains and experimental animal models disclose problems with cerebral asymmetry, focal developmental disorders affecting the cerebral cortex, and abnormalities in the magnocellular pathway of the visual system.

Animals↗
PubMed1997

Orthographic analogies and developmental dyslexia.

Goswami (1986, 1988) has demonstrated that children can use orthographic analogies (particularly at the onset-rime level) between the spelling patterns in words to help to decode new words (e.g. using 'beak' to read 'peak'). This strategy has been shown in children as young as six years old. Since it is known that children with developmental dyslexia find it particularly difficult to read words that they have not been specifically taught (Lovett, Warren-Chaplin, Ransby & Borden, 1990), the present study investigated whether dyslexic children might be unable to use analogies. Employing a design similar to that used by Goswami (1988), it was hypothesized that dyslexics would find it difficult to transfer spontaneously knowledge of a 'clue' word to decode new words that could be read by analogy with the clue word. The results of Expt 1 indicated that the dyslexic readers read significantly fewer of the analogous words than a reading age-matched comparison group of younger children. Furthermore, none of the nine dyslexic children read as many of the analogous words as the lowest scoring control child. In a second experiment, a design similar to that of Muter, Snowling & Taylor (1994) was used with a new and larger sample of dyslexic children. In this experiment, all the children were brought to criterion in reading the clue words before the analogous words were presented. Once again, the dyslexic children read significantly fewer words that were analogous with the clue words than did a reading age-matched comparison group. The number of analogous words that the dyslexic children read was significantly correlated with their performance on a test that is sensitive to the ability to detect rhyme. It is argued that a failure to make analogies may be one of the main causes of the reading impairment experienced by children with developmental dyslexia.

Child↗