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PubMed2001

Callosal transfer in different subtypes of developmental dyslexia.

Sixteen controls (age 6-13) and 20 native Italian children with developmental dyslexia (age 7-15) received a test of callosal transfer of tactile information. Among the dyslexic children, 7 had a diagnosis of L-type, 7 of P-type and 6 of M-type dyslexia according to Bakker's classification. Both control children and children with dyslexia made a significantly larger number of errors in the crossed localization condition (implying callosal transfer of tactile information) vs. the uncrossed condition. In the same condition, children with dyslexia made a significantly larger number of errors than controls. In the crossed localization condition L-types and M-types made a significantly larger number of errors than P-types and controls, while there was no significant difference in performance between P-types and controls. These findings are discussed in terms of defective callosal transfer or deficient somatosensory representation in children with L- and M-dyslexia.

Adolescent↗
PubMed1999

Dyslexia, gender, and brain imaging.

Future brain imaging studies of dyslexia should have a sufficient number of males and females to detect possible gender differences in the neurological underpinning of this disorder. Detailed knowledge about such differences may clarify our understanding of the structural and functional impairments which lead to the phonological deficits that characterize dyslexia. Functional brain imaging studies have shown that males and females exhibit different patterns of brain activation during phonological processing. Further differences between the brains of males and females have been suggested by studies of normal brain development, morphology, and functional activation during reading. Animal studies have shown that lesions, similar to those seen in postmortem studies of dyslexia, affect rapid auditory processing in males, but not in females. The large body of research on gender differences in brain development, functional organization, and activation during reading tasks urges separation of males and females in dyslexia research in order to minimize variance and to detect subtle, but functionally-relevant, differences. Well-controlled studies, with large numbers of male and female dyslexics, may produce more sensitive and accurate identification of the neurological substrates of dyslexia.

Auditory Cortex↗
PubMed2003

Contrast sensitivity in subgroups of developmental dyslexia.

It has been proposed that developmental dyslexia is associated with a deficit in the magnocellular pathway of the visual system. Other research focuses upon the heterogeneous nature of developmental dyslexia, and evidence that subgroups of dyslexia may be identified based on selective deficits in specific component reading skills. This study tested the hypothesis that visual processing deficits may be present in different subgroups of developmental dyslexia by comparing the visual contrast sensitivity of three subgroups of dyslexic children (phonological, surface and mixed) and controls. The stimulus designed to measure magnocellular visual function was a low spatial frequency Gaussian blob, flickered sinusoidally at a temporal frequency of 8.33 Hz. The control stimulus, designed to measure parvocellular visual function, was a relatively high spatial frequency Gaussian windowed grating (8 c/deg) slowly ramped on and off. There were no significant differences between the groups of dyslexic and control children in contrast sensitivity to either stimulus. The findings do not support the existence of a magnocellular system deficit in dyslexia.

Child↗
PubMed2001

Is there a relationship between speech and nonspeech auditory processing in children with dyslexia?

A group of 8 young teenagers with dyslexia were compared to age-matched control participants on a number of speech and nonspeech auditory tasks. There were no differences between the control participants and the teenagers with dyslexia in forward and simultaneous masking, nor were there any differences in frequency selectivity as indexed by performance with a bandstop noise. Thresholds for backward masking in a broadband noise were elevated for the teenagers with dyslexia as a group. If this deficit in backward masking had an influence on speech perception, we might expect the perception of "ba" versus "da" to be affected, as the crucial second formant transition is followed by a vowel. On the other hand, as forward masking is not different in the two groups, we would expect the perception of "ab" versus "ad" to be unaffected, as the contrastive second formant transition is preceded by a vowel. Overall speech identification and discrimination performance for these two contrasts was superior for the control group but did not differ otherwise. Thus, the clear group deficit in backward masking in the group with dyslexia has no simple relationship to the perception of crucial acoustic features in speech. Furthermore, the deficit for nonspeech analogues of the speech contrasts (second formants in isolation) was much less marked than for the speech sounds, with 75% of the listeners with dyslexia performing equivalently to control listeners. The auditory deficit cannot therefore be simply characterized as a difficulty in processing rapid auditory information. Either there is a linguistic/phonological component to the speech perception deficit, or there is an important effect of acoustic complexity.

Auditory Threshold↗
PubMed2001

Language development and symbolic play in children with and without familial risk for dyslexia.

The purposes of this study were to investigate (a) whether children in families with a positive history of dyslexia were more likely to show delays in language development than children without family risk and (b) whether a delayed onset of expressive language (late talking) predicted later language development. We analyzed the language development of 200 children longitudinally at 14, 24, 30, and 42 months and assessed their symbolic play at 14 months. Half of the children (N = 106) were from families with a history of dyslexia (the Dyslexia Risk [DR] group), and other children served as age-matched controls. Parental reports and structured tests were used to assess children's receptive and expressive language and symbolic play. No differences emerged between the two groups in receptive language, symbolic play, or on the Bayley MDI. The groups, however, diverged in expressive language measures. The maximum sentence length at 2 years and object naming and inflectional morphology skills at 3.5 years were higher for the control group than for the DR group. Reynell receptive score at 2.5 years provided the greatest unique contribution to the prediction of the children's receptive and expressive language. Children's risk status did not contribute to receptive language, but provided a significant contribution to their expressive language at 3.5 years, even after the variance associated with parental education and children's previous language skills was controlled. Late talkers in the DR group differed from the other members of the DR group in both receptive and expressive language at 3.5 years, although in the control group children with a late-talking history performed at age-level expectations. The findings suggest that children with a familial risk for dyslexia and with a history of late talking are at higher risk for delays in language acquisition than children without the familial risk for dyslexia.

Dyslexia↗
PubMed2001

Rapid auditory processing and phonological ability in normal readers and readers with dyslexia.

According to a prominent theory, the phonological difficulties in dyslexia are caused by an underlying general impairment in the ability to process sequences of rapidly presented, brief sounds. Two studies examined this theory by exploring the relationships between rapid auditory processing and phonological processing in a sample of 82 normally reading children (Study 1) and by comparing 17 children with dyslexia to chronological-age and reading-age control participants on these tasks (Study 2). In the normal readers, moderate correlations were found between the measure of rapid auditory processing (Auditory Repetition Task, or ART) and phonological ability. On the ART, the dyslexia group performed at a level similar to that of the reading-age control group but obtained scores that were significantly below those of the chronological-age control group. This difference was due to a subgroup of 4 children in the dyslexia group who had particular difficulty with the ART. The phonological skills of these individuals were not worse than those of the children in the dyslexia group who were unimpaired on the ART. The discussion argues that there is no evidence that phonoogical difficulties are secondary to impairments of rapid auditory processing, as measured by the ART, and highlights the need to examine the strategic and cognitive demands involved in tasks of rapid auditory processing.

Adolescent↗
PubMedDate not supplied

Phonological training in children with dyslexia using temporally modified speech: a three-step pilot investigation.

Three separate studies were successively carried out to investigate the usefulness of intensively training children with dyslexia with daily exercizes based on the temporal processing theory of dyslexia, according to which these children would be specifically unable to process brief and rapidly changing auditory stimuli. The speech modification, similar for the three studies, was close to that proposed by Merzenich et al. (1996) and Tallal et al. (1996), including both artificial slowing of natural speech stimuli and amplification of brief, unstable portions of the speech signal. In the first study, 12 children, aged 10-12 years, received either such modified speech or normal speech for 1 h a day, 5 days a week, over 5 weeks, and they were assessed on phonological tasks before, during and after training. A significant advantage for the modified speech group was found both in pre-post-training improvement and in day-to-day progression on phonological performance. In a second study, 29 children with dyslexia, aged 5-12, received a similar training, but for only 15 min a day, 7 days a week, over 6 weeks, part at the speech therapist office, part in their own homes. The finding of comparable improvement in a more 'natural' environment and in children over a wider age range indicates both the efficacy and feasibility of the method in usual clinical practice. However, this study also showed that one of four children did not improve as expected, prompting a third study where 23 other children underwent specific tasks presumably exploring various aspects of temporal processing in order to find predictors of training efficacy. A 'temporal order judgement' (TOJ) task was found best correlated with post-training improvement, suggesting that one use this task for selecting the best candidates for temporo-phonological training. Moreover, such correlation provided further argument in favour of the temporal deficit theory of dyslexia, not only by showing a link between a purely temporal task and ultimate phonological performance, but also by demonstrating that TOJ performance itself improves after phonological training. Finally, and taken together, these studies provide further justification for a rational, indication-based temporo-phonological treatment of dyslexia. Possible neural substrates of the relevant mechanisms are discussed in the light of recent experimental and brain-imaging studies.

Child↗
PubMed2003

Brain mechanisms for reading in children with and without dyslexia: a review of studies of normal development and plasticity.

In this article we review our experience with the application of magnetic source imaging (MSI), the newest of the functional imaging methods, to the study of brain mechanisms for reading among children who read normally and among those with dyslexia. After giving a general description of MSI, we present evidence for reliable and valid maps of the brain mechanism for aural language comprehension as well as for reading. Next, we present data from 39 normal readers, 40 children with dyslexia, and 30 younger children at risk for developing a reading disability. These data show different brain activation maps for individual children with dyslexia and children at risk for dyslexia than for those of normal readers. Such differences most likely reflect aberrant brain organization underlying phonological decoding, rather than variables such as degree of effort. Finally, we present preliminary data demonstrating that the aberrant activation profiles of children with dyslexia may return to normative patterns as a result of a successful reading intervention that enables children to improve phonological decoding skills.

Adolescent↗
PubMed2000

The neurological basis of developmental dyslexia: an overview and working hypothesis.

Five to ten per cent of school-age children fail to learn to read in spite of normal intelligence, adequate environment and educational opportunities. Thus defined, developmental dyslexia (hereafter referred to as dyslexia) is usually considered of constitutional origin, but its actual mechanisms are still mysterious and currently remain the subject of intense research endeavour in various neuroscientific areas and along several theoretical frameworks. This article reviews evidence accumulated to date that favours a dysfunction of neural systems known to participate in the normal acquisition and achievement of reading and other related cognitive functions. Historically, the first arguments for a neurological basis of dyslexia came from neuropathological studies of brains from dyslexic individuals. These early studies, although open to criticism, for the first time drew attention towards a possible abnormality in specific stages of prenatal maturation of the cerebral cortex and suggested a role of atypical development of brain asymmetries. This has prompted a large amount of subsequent work using in vivo imaging methods in the same vein. These latter studies, however, have yielded less clear-cut results than expected, but have globally confirmed some subtle differences in brain anatomy whose exact significance is still under investigation. Neuropsychological studies have provided considerable evidence that the main mechanism leading to these children's learning difficulties is phonological in nature, namely a basic defect in segmenting and manipulating the phoneme constituents of speech. A case has also been made for impairment in brain visual mechanisms of reading as a possible contributing factor. This approach has led to an important conceptual advance with the suggestion of a specific involvement of one subsystem of vision pathways (the so-called magnosystem hypothesis). Both phonological and visual hypotheses have received valuable contribution from modern functional imaging techniques. Results of recent PET and functional MRI studies are reported here in some detail. Finally, one attractive interpretation of available evidence points to dyslexia as a multi-system deficit possibly based on a fundamental incapacity of the brain in performing tasks requiring processing of brief stimuli in rapid temporal succession. It is proposed that this so-called 'temporal processing impairment' theory of dyslexia could also account for at least some of the perceptual, motor and cognitive symptoms very often associated with the learning disorder, a coincidence that has remained unexplained so far.

Articulation Disorders↗
PubMed2002

Pure severe dyslexia after a perinatal focal lesion: evidence of a specific module for acquisition of reading.

A child with a small, residual "localized" perinatally acquired left hemisphere temporal tip lesion is described. He presents with pure and severe dyslexia and average to high-average cognitive skills, which are usually in the low-average range in patients with developmental dyslexia. A highly circumscribed deficit of rote auditory verbal memory was the only deficit other than the dyslexia; his verbal semantic memory and visuospatial memory were intact. Two previously reported cases present a similar functional profile and lesion locus. This profile indicates that there may exist, at birth, a localized neural network dedicated to "reading acquisition" and that the layout of this network may differ from the systems identified as defective in developmental dyslexia, as well as in cases of acquired dyslexia in adults.

Atrophy↗
PubMed1992

Dyslexia; ophthalmological aspects 1991.

Dyslexia or specific reading disability is an important and frequent handicap afflicting 5-10% of the population. It is basically a disorder of acquisition of written language, probably due to a poorly developed phonological awareness, which in turn may be neurologically related. As anatomical correlates symmetry of the planum temporale and ectopies in the cerebral cortex have been suggested. Functional correlates are discovered with brain electrical mapping and stimulation of brain structures during neuro surgery. From an ophthalmological point of view there are no relations between dyslexia and ocular problems including refractive errors and accommodation, problems of binocular control and stereopsis, eye dominance instability etc. However, contrast sensitivity seems to be reduced in dyslexics for the middle range of spatial frequencies, which may be related to impaired function of the 'transient' visual system. With regard to eye movements, there is no firm experimental proof for any disturbances in dyslexia, be it with the different movement systems or in the best movement direction. 'Backward saccades' or regressions are typical not only for dyslexic reading but in all types of reading when comprehension is poor. Although there is no treatment for dyslexia itself that can be based on ophthalmological findings, the ophthalmologist must after careful examination discover and treat any ocular, orthoptic or neuroophthalmological problem that may make reading difficult for the dyslexic child. The ophthalmologist must explain to the child and the parents that dyslexia usually has no ophthalmological or visual cause but is a disability with a neurobiological background, still unknown, in which the only efficient treatment is within the area of pedagogy.

Dyslexia↗
PubMed2004

Two visual motion processing deficits in developmental dyslexia associated with different reading skills deficits.

Developmental dyslexia is associated with deficits in the processing of visual motion stimuli, and some evidence suggests that these motion processing deficits are related to various reading subskills deficits. However, little is known about the mechanisms underlying such associations. This study lays a richer groundwork for exploration of such mechanisms by more comprehensively and rigorously characterizing the relationship between motion processing deficits and reading subskills deficits. Thirty-six adult participants, 19 of whom had a history of developmental dyslexia, completed a battery of visual, cognitive, and reading tests. This battery combined motion processing and reading subskills measures used across previous studies and added carefully matched visual processing control tasks. Results suggest that there are in fact two distinct motion processing deficits in developmental dyslexia, rather than one as assumed by previous research, and that each of these deficits is associated with a different type of reading subskills deficit. A deficit in detecting coherent motion is selectively associated with low accuracy on reading subskills tests, and a deficit in discriminating velocities is selectively associated with slow performance on these same tests. In addition, evidence from visual processing control tasks as well as self-reports of ADHD symptoms suggests that these motion processing deficits are specific to the domain of visual motion, and result neither from a broader visual deficit, nor from the sort of generalized attention deficit commonly comorbid with developmental dyslexia. Finally, dissociation between these two motion processing deficits suggests that they may have distinct neural and functional underpinnings. The two distinct patterns of motion processing and reading deficits demonstrated by this study may reflect separable underlying neurocognitive mechanisms of developmental dyslexia.

Adult↗
PubMed2006

Unlocking the nature of the phonological-deep dyslexia continuum: the keys to reading aloud are in phonology and semantics.

It has been argued that normal reading and acquired dyslexias reflect the role of three underlying primary systems (phonology, semantics, and vision) rather than neural mechanisms dedicated to reading. This proposal is potentially consistent with the suggestion that phonological and deep dyslexia represent variants of a single reading disorder rather than two separate entities. The current study explored this possibility, the nature of any continuum between the disorders, and the possible underlying bases of it. A case series of patients were given an assessment battery to test for the characteristics of phonological and deep dyslexia. The status of their underlying phonological and semantic systems was also investigated. The majority of participants exhibited many of the symptoms associated with deep dyslexia whether or not they made semantic errors. Despite wide variation in word and nonword reading accuracy, there was considerable symptom overlap across the cohort and, thus, no sensible dividing line to separate the participants into distinct groups. The patient data indicated that the deep-phonological continuum might best be characterized according to the severity of the individual's reading impairment rather than in terms of a strict symptom succession. Assessments of phonological and semantic impairments suggested that the integrity of these primary systems underpinned the patients' reading performance. This proposal was supported by eliciting the symptoms of deep-phonological dyslexia in nonreading tasks.

Aged↗
PubMed2000

The overstimulated state of dyslexia: perception, knowledge, and learning.

Dyslexia is far more than a learning disorder; it has significant impact on personality organization. While dyslexia usually begins to manifest most clearly in early latency when the challenge of learning to read is at its height, often the dyslexic child's ego development and functioning has already been adversely affected. The literature from neuropsychology suggests that dyslexia is a subtle language-processing disorder that affects emotional, cognitive, and social development. The neuroanatomical literature also suggests a significant correlation between the neurodevelopmental basis for dyslexia, the caregiving environment, and psychological development. These two bodies of literature and analytic observations of a dyslexic patient suggest that the dyslexic individual may have a neurological deficit that increases vulnerability to overstimulation. The author hypothesizes that emotional and cognitive states result and reappear within the analytic encounter. This complicates clinical assessment and technical decisions. The author presents an analytic case and examines (1) the impact of deficit on the development of conflict; (2) the impact of the overwhelmed ego on the mastery of developmental tasks; and (3) the impact of dyslexia on dysgnosia, transference, and analytic process and technique.

Adult↗
PubMedDate not supplied

Persistence of phonological processing deficits in college students with dyslexia who have age-appropriate reading skills.

This study investigated the phonological processing skills of university students with dyslexia. Fifty-nine students participated in this study: 28 with reading disabilities based on recent psychological assessments and a history of early and persistent reading problems; and 31 controls. The two groups did not differ on estimates of verbal and nonverbal abilities. The dyslexia group performed significantly less well on standardized measures of reading and spelling. However, the dyslexia group scores on these measures fell within the average range. The main dependent variables were subsumed under three areas of phonological processing: phonological awareness, phonological recoding in lexical access, and phonological recoding in working memory. The control group performed significantly better on all phonological processing measures, particularly those measures involving accuracy and response times. Despite age-appropriate performances on standardized reading and spelling measures, phonological processing deficits persisted in the dyslexia group. These findings support the causal role of phonological awareness in the acquisition of reading skills and indicate that differences in phonological processing skills are still evident in a sample of university students with dyslexia compared a group matched on age and education.

Adolescent↗
PubMedDate not supplied

The strategies adopted by Dutch children with dyslexia to maintain their self-esteem when teased at school.

This article reports on a study of children's narratives about the relationships between dyslexia and being teased at school and explores the dynamics between dyslexia, being bullied, self-esteem, and psychosocial problems. We reconstructed four profiles of inner logic in the children's reactions to being teased or humiliated as a consequence of their dyslexia. Most children with dyslexia protect themselves against teasing and feeling worthless by concealing both their emotions and their academic failures. Others, however, concentrate on their academic progress, and their self-esteem seems to be strengthened by fighting against dyslexia.

Affect↗
PubMed1994

Cognitive patterns of children with dyslexia: a comparison between groups with high and average nonverbal intelligence.

We tested the hypothesis that children with dyslexia identified by word decoding deficit will be poor in specific cognitive processes that require successive processing and rapid articulation, irrespective of their high or average nonverbal IQ. Children with dyslexia and normally achieving children between 9 years and 11 years of age were divided into four groups comprising average-IQ and high-IQ children with dyslexia and normal readers. All children were administered measures of planning, attention-arousal, simultaneous and successive processes, phonemic segmentation, and nonverbal IQ. Results confirmed the hypothesis: The cognitive tasks that differentiated children with dyslexia from nondyslexic children irrespective of IQ were the successive tasks, as well as two tasks of attention that required articulation and/or phonological coding. Tasks that demanded both phonological coding and articulation correctly classified children with dyslexia and nondyslexic children up to 80%. The importance of remedial training appropriate for alleviating the cognitive and word decoding deficits is discussed.

Analysis of Variance↗
PubMed1994

Neurolinguistic differentiation of children with subtypes of dyslexia.

A detailed analysis of the types of childhood dyslexia proposed by Boder (1973) and Bakker (1990) revealed characteristic patterns of organization of intellectual functions, of hemispheric specialization, and of reading errors in right-handed children with dyslexia. Children with L-type dyslexia (10 subjects) evidenced a large number of reading errors (e.g., substitutions of nouns and verbs), low scores in verbal short-term memory, and right-ear advantage (REA) in dichotic listening. Children with P-dyslexia (18 subjects) evidenced few reading errors, a short attention span, low performance in visual-motor coordination (WISC-R coding), and an absence of REA in dichotic listening. Children with M-type dyslexia (10 subjects) showed numerous reading errors (e.g., substitution of syllables and words), low performance in visual-motor coordination items (coding), and REA in dichotic listening.

Brain↗