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PubMed1990

Developmental dyslexia in women: neuropathological findings in three patients.

Brains from male cases with dyslexia show symmetry of the planum temporale and predominantly left-sided cerebrocortical microdysgenesis. We now report on three women with dyslexia. In all brains, the planum temporale was again symmetrical. Also, in two of the brains, multiple foci of cerebrocortical glial scarring were present. In both women, many of the scars were myelinated, suggesting origination during late intrauterine or early postnatal life. In one, scars were mainly left perisylvian and involved portions of the vascular border zone of the temporal cortex. In the other, scars were more numerous and occurred in the border zone of the anterior, middle, and posterior cerebral arteries symmetrically. All three cases showed to a variable extent brain warts, molecular layer ectopias, and focal architectonic dysplasia identical to those seen in the male cases. Two women had primary brain neoplasms, an oligodendroglioma and a low-grade astrocytoma, respectively, and two women showed small angiomas. Reexamination of previously reported male cases disclosed one with myelinated glial scars. Two control brains with asymmetrical plana temporale showed myelinated glial scars as well. The significance of the anatomical findings is discussed, and possible etiological factors are considered with known effects of autoimmune diseases on the nervous system.

Adult↗
PubMedDate not supplied

Surface and phonological subtypes of adult developmental dyslexia.

In order to assess the efficacy of phonological versus surface dyslexia subtyping within an adult dyslexic population, 45 adult dyslexics were assessed on the Castles and Coltheart (1993) irregular word and non-word reading tasks. Based on the performance of a matched group of 28 non-dyslexics, between 62 and 75% of the dyslexics were divided into phonological and surface subtypes. Phonological dyslexics were those individuals who presented evidence of relatively poor or inefficient non-word reading, whereas the surface dyslexics were those who indicated relative difficulties with irregular word reading. The proportions of dyslexics within each subtype varied according to the use of accuracy-based or latency-based procedures, but were consistent with previous findings with children. Subsequent comparisons between the groups on measures of phonological processing, lexical access and word knowledge/recognition indicated few differences between the two subtypes and, in particular, no differences on measures of phonological ability. The lack of observed differences on such measures casts doubt on the efficacy of this procedure for explaining individual differences amongst adult dyslexics and as a practical procedure for diagnosis and intervention.

Adult↗
PubMed2006

Stability of IQ measures in teenagers and young adults with developmental dyslexia.

A follow-up study was performed to investigate the stability of IQ measures in a group of dyslexic teenagers and young adults. Earlier research had shown contradictory results. The 65 subjects, 12 years old on the average at first test, were retested after a mean interval of six and a half years. There was a significant relative decrease in verbal IQ (VIQ), which was interpreted as either an effect of low reliability of tests used, or an effect of the dyslexic individuals' less experience with reading and writing, and as a consequence, a lag in verbal ability, the second interpretation being in line with earlier findings in groups of children with learning disabilities. Performance IQ improved significantly and the tentative interpretation was that of a compensatory process, in the sense that the dyslexic children might develop a more visual, intuitive and creative way to process information and solve problems. The conclusion was that caution should be taken, before making important decisions on the basis of a single intelligence test, and that dyslexic children might be at risk to lag behind their peers in terms of VIQ, especially if they are not provided with suitable special education.

Adolescent↗
PubMed2006

Longitudinal case-studies of developmental dyslexia in Norwegian.

This study examined retrospectively the preschool cognitive and linguistic profiles and emergent literacy skills in four Norwegian dyslexic children. The aim was to identify prognostic indicators that were associated with the reading impairments observed in an earlier study of these children. In comparison to a control group of at-risk children who were normal readers at age 10, three of the four dyslexic children exhibited either stagnation or a decline in speech accuracy in the presence of a vocabulary growth spurt at age 2-3 years. Skills in phonological awareness seemed to vary inconsistently with both early speech development and emergent literacy across the four cases. Delayed development in emergent literacy turned out to be the most potent prognostic indicator of later reading disorders. The study was guided by lexical restructuring theories of dyslexia.

Awareness↗
PubMed2000

Sulcal/gyral pattern morphology of the perisylvian language region in developmental dyslexia.

Two systems for classification of morphology of the perisylvian cortical area have been suggested, that of Steinmetz et al. (1990) and that of Witelson and Kigar (1992). This study examines whether the variations in placement of these convolutions in the language cortex are related to diagnosis of dyslexia in a clinic-referred sample of 55 children ages 8 to 12 years. Additionally, the systems are compared to determine their relationship to neurolinguistic performance. In this study, the Steinmetz et al. (1990) system captured morphological distinctions which were relevant to performance on neurolinguistic measures, while Witelson and Kigar's (1992) system did not. Under neither system was morphology associated with diagnosis of dyslexia.

Attention Deficit Disorder with Hyperactivity↗
PubMed1996

The nonword reading deficit in developmental dyslexia: evidence from children learning to read German.

This study examined whether dyslexic children learning to read German show the same nonword reading deficit, which is characteristic of dyslexic children learning to read English (Rack, Olson, & Snowling, 1992), a deficit which is taken as evidence for a phonological impairment underlying dyslexia. Because the German writing system, in contrast to English, exhibits comparatively simple and straightforward grapheme-phoneme correspondences, the generality of the nonword reading deficit across different alphabetic systems seemed questionable. Actually, it was found that 10-year-old dyslexic children learning to read German exhibited rather high reading accuracy for nonwords when compared to that typically found among dyslexic children learning to read English. Nevertheless, the children learning German did exhibit a nonword reading deficit. Specifically, their speed for nonwords was impaired in relation to younger control (nondyslexic) children matched on reading speed for frequent words. This nonword reading deficit was observed for nonwords with little similarity to existing German words as well as for nonwords which were analogous to short, frequent content words. It is hypothesized that dyslexic children learning German do not differ from dyslexic children learning English in their underlying phonological impairment, but that they do differ with respect to the expression of this impairment.

Austria↗
PubMed1997

Phonological awareness deficits in developmental dyslexia and the phonological representations hypothesis.

The claim that the well-documented difficulties shown by dyslexic children in phonological awareness tasks may arise from deficits in the accuracy and the segmental organization of the phonological representations of words in their mental lexicons is receiving increasing interest from researchers. In this experiment, two versions of the phonological representations hypothesis were investigated by using a picture naming task and a battery of phonological measures at three linguistic levels (syllable, onset-rime, phoneme). The picture naming task was used to identify words for which dyslexic and control children had accurate vs inaccurate phonological representations, and performance in the phonological awareness tasks was then compared for the words which had precise vs imprecise representations. Findings indicated that frequency effects in the phonological awareness tasks at all levels disappeared for dyslexic and control children once representational quality was taken into account, and that the availability of sublexical units for analysis appeared to differ according to (1) the accuracy and retrieval of the phonological representation and (2) the linguistic level tapped by the phonological awareness task.

Awareness↗
PubMed1997

Are speech perception deficits associated with developmental dyslexia?

Phonological awareness and phoneme identification tasks were administered to dyslexic children and both chronological age (CA) and reading-level (RL) comparison groups. Dyslexic children showed less sharply defined categorical perception of a bath-path continuum varying voice onset time when compared to the CA but not the RL group. The dyslexic children were divided into two subgroups based on phoneme awareness. Dyslexics with low phonemic awareness made poorer /b/-/p/ distinctions than both CA and RL groups, but dyslexics with normal phonemic awareness did not. Examination of individual profiles revealed that the majority of subjects in each group exhibited normal categorical perception. However, 7 of 25 dyslexics had abnormal identification functions, compared to 1 subject in the CA group and 3 in the RL group. The results suggest that some dyslexic children have a perceptual deficit that may interfere with processing of phonological information. Speech perception difficulties may also be partially related to reading experience.

Child↗
PubMed2000

The spatial distribution of visual attention in developmental dyslexia.

The present study investigated the spatial distribution of visual attention in dyslexic and normally reading children. The performances of the two groups were investigated using two different paradigms. In experiment 1 we analyzed the distribution of processing resources both inside and outside the focus of visual attention by simply recording reaction times to the detection of a white dot target projected at different eccentricities from the fovea. The distribution of attentional resources differed significantly between the two groups of children. The eccentricity of the stimulus was significant only for normally reading children - who showed a normal gradient - as it influenced their detection speed, whereas it had no effect on dyslexic children, who exhibited a diffused distribution of visual processing resources inside the visual field. In experiment 2 we studied the distributed (unfocused) mode of attention in a visual search task by measuring reaction times to a target stimulus inside a large configuration with a variable number of distractors. Results show that as compared to normal children dyslexics are better able to distribute their attentional resources diffusely. Our conclusion is that reading disability may be characterized by a diffused distribution of visual processing resources. These data might be interpreted in the framework of studies on magnocellular deficits in dyslexia, whereby the anomalous distribution of visual attention might explain how transient pathway functioning influences the reading process.

Adolescent↗
PubMed2006

Developmental dyslexia: an update.

Dyslexia is the most common and carefully studied of the learning disabilities in school-age children. It is characterized by a marked impairment in the development of reading skills, and affects a large number of people (5-10%). Reading difficulties may also arise from poor vision, emotional problems, decreased hearing ability, and behavioral disorders, such as attention-deficit hyperactivity (ADHD). Although many areas of the brain are involved in reading, analysis of postmortem brain specimens by a variety of imaging techniques most consistently suggests that deficiency within a specific component of the language system - the phonologic module - in the temporo-parietal-occipital brain region underlies dyslexia. It is a highly familial and heritable disorder with susceptibility loci on chromosomes 1, 2, 3, 6, 11, 13, 15 and 18. Recently, four candidate genes (KIAA 0319, DYX1C1, DCDC2 and ROBO1) are shown to be associated with dyslexia. Although some of these results are controversial because of the genetic heterogeneity of the disorder, the available evidence suggests that dyslexia could be due to the abnormal migration and maturation of neurons during early development. Interestingly, in spite of genetic heterogeneity, the pathology appears to involve common phonological coding deficits. The condition can be managed by a highly structured educational training exercise.

Child↗