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PubMed1995

Family patterns of developmental dyslexia, part II: behavioral phenotypes.

The motor control of bimanual coordination and motor speech was compared between first degree relatives from families with at least 2 dyslexic family members, and families where probands were the only affected family members. Half of affected relatives had motor coordination deficits; and they came from families in which probands also showed impaired motor coordination. By contrast, affected relatives without motor deficits came from dyslexia families where probands did not have motor deficits. Motor coordination deficits were more common and more severe among affected offspring in families where both parents were affected than among affected offspring in families where only one parent was affected. However, motor coordination deficits were also more common and more severe in affected parents when both parents were affected than among affected parents in families where only one parent was affected. We conclude that impaired temporal resolution in motor action identifies a behavioral phenotype in some subtypes of developmental dyslexia. The observed pattern of transmission for motor deficits and reading impairment in about half of dyslexia families was most congruent with a genetic model of dyslexia in which 2 codominant major genes cosegregate in dyslexia pedigrees where the proband is also motorically impaired.

Adolescent↗

PubMedDate not supplied

The prevalence of dyslexia among art students.

It is widely held opinion that dyslexia is associated with remarkably artistic creativity. Speculations on different brain structures and brain functions have been proposed as an explanation. Very few objective studies have been reported that confirm the conjectures on the relationship between dyslexia and artistic creativity. Two studies are reported on the prevalence of dyslexia among university students-one group of art students and one group of students from non-art disciplines. The admission to the art schools were extremely demanding, possibly implying that the students were genuinely talented, and that their choice of training did not reflect a compensation for failure in conventional academic fields. Art academy students reported significantly more signs of dyslexia than non-art university students. Objective testing showed that art students had significantly poorer phonological skills than non-art students. Thus, according to self-reports combined with objective testing, the incidence of dyslexia was far higher among art students.

Adult↗

PubMedDate not supplied

Dyslexia: nature and nurture.

This paper explores the balance of genetic and environmental influences on dyslexia in generally supportive educational environments. Evidence from family studies suggests and research with identical and fraternal twins confirms the presence of strong genetic influences on dyslexia, though the way dyslexia is defined influences the degree of genetic influence. The behavioural genetic evidence is supported with molecular genetic evidence from DNA analyses suggesting regions on several different chromosomes where genes related to dyslexia are likely to be found. The behavioural and molecular genetic analyses are also applied to different component word reading skills (orthographic coding and phonological decoding) as well as to related language skills (phoneme awareness) to better understand the genetic and cognitive pathways to dyslexia.

Dyslexia↗

PubMed2004

Deficits in dyslexia: barking up the wrong tree?

Reviews of the dyslexia literature often seem to suggest that children with dyslexia perform at a lower level on almost any task. Richards et al. (Dyslexia 2002; 8: 1-8) note the importance of being able to demonstrate dissociations between tasks. However, increasingly elegant experiments, in which dissociations are found, almost inevitably find that the performance of children with dyslexia is lower as tasks become more difficult! By looking for deficits in dyslexia, could we be barking up the wrong tree? A methodological approach for circumventing this potential problem is discussed.

Attention↗

PubMed2004

The cognitive deficits responsible for developmental dyslexia: review of evidence for a selective visual attentional disorder.

There is strong converging evidence suggesting that developmental dyslexia stems from a phonological processing deficit. However, this hypothesis has been challenged by the widely admitted heterogeneity of the dyslexic population, and by several reports of dyslexic individuals with no apparent phonological deficit. In this paper, we discuss the hypothesis that a phonological deficit may not be the only core deficit in developmental dyslexia and critically examine several alternative proposals. To establish that a given cognitive deficit is causally related to dyslexia, at least two conditions need to be fulfilled. First, the hypothesized deficit needs to be associated with developmental dyslexia independently of additional phonological deficits. Second, the hypothesized deficit must predict reading ability, on both empirical and theoretical grounds. While most current hypotheses fail to fulfil these criteria, we argue that the visual attentional deficit hypothesis does. Recent studies providing evidence for the independence of phonological and visual attentional deficits in developmental dyslexia are reviewed together with empirical data showing that phonological and visual attentional processing skills contribute independently to reading performance. A theoretical model of reading is outlined in support of a causal link between a visual attentional disorder and a failure in reading acquisition.

Attention↗

PubMed1997

Surface dyslexia in nonfluent progressive aphasia.

This article presents the case of a 59-year-old male, JH, with a 6-year history of primary progressive aphasia (PPA), a disorder characterized by isolated language deterioration with relative preservation of other cognitive abilities. JH also shows typical features of surface dyslexia, a reading disorder exemplified by the selective preservation of phonological reading. One recent theory is that surface dyslexia in individuals with PPA results from a loss of semantic knowledge. In this paper we consider an additional possibility and present data supporting the notion that surface dyslexia may also arise from the malfunction in the links between semantic representations and phonology. JH has remarkably preserved lexical semantic knowledge when assessed on tasks that do not require verbal output. Further, item-by-item comparisons of his oral reading and comprehension ability show no significant correspondence between his reading and semantic knowledge. These findings lead us to conclude that, in JH's case, the surface dyslexia is attributable not to a semantic deficit per se but rather to the inability to access phonological information from semantics. JH's language profile is considered in relation to potential sources of surface dyslexia and other cases of progressive aphasia.

Aphasia, Broca↗

PubMed2002

Deaf poor readers' pattern reversal visual evoked potentials suggest magnocellular system deficits: implications for diagnostic neuroimaging of dyslexia in deaf individuals.

Deafness and developmental dyslexia in the same individual may jointly limit the acquisition of reading skills for different underlying reasons. A diagnostic marker for dyslexia in deaf individuals must therefore detect the presence of a neurobiologically based dyslexia but be insensitive to the ordinary developmental influences of deafness on reading skill development. We propose that the functional status of the magnocellular visual system in deaf individuals is potentially such a marker. We present visual evoked potential (VEP) evidence that adult deaf poor readers as a group display magnocellular system deficits not observed in deaf good readers. We recorded pattern-reversal VEPs to high- and low-contrast checkerboard stimuli, which primarily activate the parvocellular and magnocellular pathways, respectively. Principal components analysis of these VEPs produced a time-ordered sequence of three early components that displayed interactions between reading skill and stimulus contrast across multiple scalp recording sites. Deaf poor readers displayed an abnormal absence of contrast-sensitive VEP responses at occipital sites during early visual processing (75 ms poststimulus), whereas deaf good readers showed the expected early contrast-sensitive occipital VEP responses. Over the subsequent 225 ms, the occipital VEP behavior of deaf poor readers closely approximated that of deaf good readers. The VEPs of deaf poor readers were apparently characterized by delayed responses to low-contrast stimuli compared with deaf good readers. Our results provide the first neurobiological evidence that developmental dyslexia exists within the deaf population and is associated with the same underlying magnocellular system deficit that has been observed in hearing dyslexics. Direct neural imaging of the status of the magnocellular visual system in deaf individuals may eventually provide differential diagnosis of developmental dyslexia in the deaf population.

Adult↗

PubMed2003

Balance and gait in children with dyslexia.

Tests of postural stability have provided some evidence of a link between deficits in gross motor skills and developmental dyslexia. The ordinal-level scales used previously, however, have limited measurement sensitivity, and no studies have investigated motor performance during walking in participants with dyslexia. The purpose of this study was to investigate if continuous-scaled measures of standing balance and gait could discriminate between groups of impaired and normal readers when investigators were blind to group membership during testing. Children with dyslexia ( n=22) and controls ( n=18), aged 10-12 years, performed walking tests at four different speeds (slow-preferred-fast-very fast) on an even and an uneven surface, and tests of unperturbed and perturbed body sway during standing. Body movements were registered by a triaxial accelerometer over the lower trunk, and measures of reaction time, body sway, walking speed, step length and cadence were calculated. Results were controlled for gender differences. Tests of standing balance with eyes closed did not discriminate between groups. All unperturbed standing tests with eyes open showed significant group differences ( P<0.05) and classified correctly 70-77.5% of the subjects into their respective groups. Mean walking speed during very fast walking on both flat and uneven surface was > or =0.2 m/s ( P< or =0.01) faster for controls than for the group with dyslexia. This test classified 77.5% and 85% of the subjects correctly on flat and uneven surface, respectively. Cadence at preferred or very fast speed did not differ statistically between groups, but revealed significant group differences when all subjects were compared at a normalised walking speed ( P< or =0.04). Very fast walking speed as well as cadence at a normalised speed discriminated better between groups when subjects were walking on an uneven surface compared to a flat floor. Continuous-scaled walking tests performed in field settings may be suitable for motor skill assessment as a component of a screening tool for developmental dyslexia.

Child↗

PubMed2005

Acquired dyslexia in a Turkish-English speaker.

The Turkish script is characterised by completely transparent bidirectional mappings between orthography and phonology. To date, there has been no reported evidence of acquired dyslexia in Turkish speakers leading to the naïve view that reading and writing problems in Turkish are probably rare. We examined the extent to which phonological impairment and orthographic transparency influence reading disorders in a native Turkish speaker. BRB is a bilingual Turkish-English speaker with deep dysphasia accompanied by acquired dyslexia in both languages. The main findings are an effect of imageability on reading in Turkish coincident with surface dyslexia in English and preserved nonword reading. BRB's acquired dyslexia suggests that damage to phonological representations might have a consequence for learning to read in Turkish. We argue that BRB's acquired dyslexia has a common locus in chronic underactivation of phonological representations in Turkish and English. Despite a common locus, reading problems manifest themselves differently according to properties of the script and the type of task.

Aged↗

PubMed1994

Dyslexia, handedness and syndromes of psychosis-proneness.

In an earlier study, adult dyslexia was found to be strongly associated with positive schizotypal traits, and particularly with unusual perceptual experiences. However, recent evidence suggests that the structure of psychosis-proneness in normals may involve three or four distinct yet related dimensions. Therefore a further study was conducted, using a wider range of measures, to explore associations between dyslexia and these different syndromes of psychosis-proneness. Relationships with handedness were also investigated. If three syndromes of psychosis-proneness were delineated, broadly corresponding to "Active", "Withdrawn" and "Schneiderian/Unreality" syndromes of schizophrenia, dyslexics showed elevations on both positive syndromes (Active and Unreality), but not on the negative, Withdrawn syndrome. With a four-factor model only one dimension, perceptual/cognitive anomalies, distinguished dyslexics from controls. These findings confirm an association between dyslexia and positive, but not negative, schizotypal traits. Mixed-handedness was strongly associated with dyslexia, and in controls with those measures of psychosis-proneness involving unusual perceptual experiences. This suggests that reduced lateralization may be a feature common to both dyslexia and the Unreality syndrome of schizotypy, which may help to account for the strong relationship between them.

Adolescent↗

PubMed1995

Possible relevance of phospholipid abnormalities and genetic interactions in psychiatric disorders: the relationship between dyslexia and schizophrenia.

The fatty acids of cell membrane phospholipids are essential for normal membrane structures, for the functioning of membrane-bound and membrane-associated proteins and for normal cell-signalling responses. In dyslexia, there is evidence for reduced incorporation of docosahexaenoic acid and arachidonic acid into cell membranes, while in schizophrenia, there is evidence for an increased rate of docosahexaenoic acid and arachidonic acid loss from membranes because of enhanced phospholipase A2 activity. The presence of both defects will cause a much greater degree of abnormality than either one alone. It is hypothesized that unequivocal clinical schizophrenia may occur when both genes are present in the same individual. The dyslexia gene along will produce dyslexia while the schizophrenia gene alone may produce bipolar or schizoaffective disorders. These proposals could explain: 1. The reduced asymmetry of the brain, especially of the planum temporale in both schizophrenia and dyslexia; 2. The schizotypal personality characteristics of dyslexics; 3. The increased risks of dyslexia in families with a schizophrenic proband; 4. The increased risks of bipolar and schizoaffective disorders in families with a schizophrenic proband; 5. The earlier onset and possibly increased severity of both disorders in males since females have a lower requirement for arachidonic acid and docosahexaenoic acid; 6. The absence of selective pressure against schizophrenia since reproduction would be impaired only when the schizophrenic gene coexisted with a dyslexic gene. The schizophrenic gene alone might even lead to improved reproductive performance.

Arachidonic Acid↗

PubMed2005

Dorsal stream deficits suggest hidden dyslexia among deaf poor readers: correlated evidence from reduced perceptual speed and elevated coherent motion detection thresholds.

Prelingual deafness and developmental dyslexia have confounding developmental effects on reading acquisition. Therefore, standard reading assessment methods for diagnosing dyslexia in hearing people are ineffective for use with deaf people. Recently, Samar, Parasnis, and Berent (2002) reported visual evoked potential evidence that deaf poor readers, compared to deaf good readers, have dorsal stream visual system deficits like those previously found for hearing dyslexics. Here, we report new psychometric and psychophysical evidence that deficits in dorsal stream function, likely involving extrastriate area MT, are associated with relatively poor reading comprehension in deaf adults. Poorer reading comprehension within a group of 23 prelingually deaf adults was associated with lower scores on the Symbol Digit Modality Test, a perceptual speed test commonly used to help identify dyslexia in hearing people. Furthermore, coherent dot motion detection thresholds, which reflect the functional status of area MT, correlated negatively with reading scores in each visual quadrant. Elevated motion thresholds for deaf poor readers were not due to general cognitive differences in IQ but were specifically correlated with poor perceptual speed. With IQ controlled, a highly reliable right visual field advantage for coherent motion detection was found. Additional analyses suggested that the functional status of dorsal stream motion detection mechanisms in deaf people is related to reading comprehension, but the direction and strength of lateralization of those mechanisms is independent of reading comprehension. Our results generally imply that dyslexia is a hidden contributor to relatively poor reading skill within the deaf population and that assessment of dorsal stream function may provide a diagnostic biological marker for dyslexia in deaf people.

Adolescent↗

PubMed2005

Implicit and explicit processing in deep dyslexia: Semantic blocking as a test for failure of inhibition in the phonological output lexicon.

The failure of inhibition hypothesis posits a theoretical distinction between implicit and explicit access in deep dyslexia. Specifically, the effects of failure of inhibition are assumed only in conditions that have an explicit selection requirement in the context of production (i.e., aloud reading). In contrast, the failure of inhibition hypothesis proposes that implicit processing and explicit access to semantic information without production demands are intact in deep dyslexia. Evidence for intact implicit and explicit access requires that performance in deep dyslexia parallels that observed in neurologically intact participants on tasks based on implicit and explicit processes. In other words, deep dyslexics should produce normal effects in conditions with implicit task demands (i.e., lexical decision) and on tasks based on explicit access without production (i.e., forced choice semantic decisions) because failure of inhibition does not impact the availability of lexical information, only explicit retrieval in the context of production. This research examined the distinction between implicit and explicit processes in deep dyslexia using semantic blocking in lexical decision and forced choice semantic decisions as a test for the failure of inhibition hypothesis. The results of the semantic blocking paradigm support the distinction between implicit and explicit processing and provide evidence for failure of inhibition as an explanation for semantic errors in deep dyslexia.

Analysis of Variance↗

PubMed2006

An attempt to simulate letter-by-letter dyslexia in normal readers.

We attempted to simulate the main features of letter-by-letter (LBL) dyslexia in normal readers through stimulus degradation (i.e. contrast reduction and removal of high spatial frequencies). The results showed the word length and the letter confusability effects characteristic of LBL dyslexia. However, the interaction of letter confusability and N size (i.e. a facilitatory effect only for low confusability targets) previously observed in LBL dyslexics [Arguin, M., Fiset, S., & Bub, D. (2002). Sequential and parallel letter processing in letter-by-letter reading. Cognitive Neuropsychology, 19, 535-555; Arguin, M., & Bub, D. (2006). Parallel processing blocked by letter similarity in letter dyslexia: a replication. Cognitive Neuropsychology, 22, 589-602; Fiset, D., Arguin, M. & McCabe, E. (2005a). The breakdown of parallel letter processing in letter-by-letter dyslexia. Cognitive Neuropsychology, 22, 1-22] was not found. Our results suggest that the type of visual degradation employed here may only partially correspond to the visual deficit present in LBL dyslexia and that this degradation may have prevented the normal readers from accessing visual information available to LBL dyslexics when they use the compensatory strategy of serial letter processing.

Adult↗

PubMed2005

Auditory perceptual grouping and attention in dyslexia.

Despite dyslexia affecting a large number of people, the mechanisms underlying the disorder remain undetermined. There are numerous theories about the origins of dyslexia. Many of these relate dyslexia to low-level, sensory temporal processing deficits. Another group of theories attributes dyslexia to language-specific impairments. Here, we show that dyslexics perform worse than controls on an auditory perceptual grouping task. The results show differences in performance between the groups that depend on sound frequency and not solely on parameters related to temporal processing. Performance on this task suggests that dyslexics' deficits may result from impaired attentional control mechanisms. Such deficits are neither modality nor language-specific and may help to reconcile differences between theories of dyslexia.

Acoustic Stimulation↗

PubMed2002

Disruption of posterior brain systems for reading in children with developmental dyslexia.

BACKGROUND: Converging evidence indicates a functional disruption in the neural systems for reading in adults with dyslexia. We examined brain activation patterns in dyslexic and nonimpaired children during pseudoword and real-word reading tasks that required phonologic analysis (i.e., tapped the problems experienced by dyslexic children in sounding out words). METHODS: We used functional magnetic resonance imaging (fMRI) to study 144 right-handed children, 70 dyslexic readers, and 74 nonimpaired readers as they read pseudowords and real words. RESULTS: Children with dyslexia demonstrated a disruption in neural systems for reading involving posterior brain regions, including parietotemporal sites and sites in the occipitotemporal area. Reading skill was positively correlated with the magnitude of activation in the left occipitotemporal region. Activation in the left and right inferior frontal gyri was greater in older compared with younger dyslexic children. CONCLUSIONS: These findings provide neurobiological evidence of an underlying disruption in the neural systems for reading in children with dyslexia and indicate that it is evident at a young age. The locus of the disruption places childhood dyslexia within the same neurobiological framework as dyslexia, and acquired alexia, occurring in adults.

Adolescent↗

PubMed2004

Cognitive profiling and preliminary subtyping in Chinese developmental dyslexia.

The present study examined the cognitive profile and subtypes of developmental dyslexia in a nonalphabetic script, Chinese. One hundred and forty-seven Chinese primary school children with developmental dyslexia were tested on a number of literacy and cognitive tasks. The results showed that rapid naming deficit and orthographic deficit were the two most dominant types of cognitive deficits in Chinese developmental dyslexia, and that rapid naming and orthographic processing had significant unique contributions to literacy performance. Seven subtypes of dyslexia--global deficit, orthographic deficit, phonological memory deficit, mild difficulty, and three other subtypes with rapid-naming-related deficits--were identified using scores of the cognitive tasks as classification measures in cluster analyses. These subtypes were validated with a behaviour checklist and three literacy measures. The authors suggested that orthographic and rapid naming deficits in Chinese dyslexic children might pose an interrelated problem in developing orthographic knowledge and representation. Therefore, orthographic-related difficulties may be the crux of the problem in Chinese developmental dyslexia.

Child↗

PubMed2006

Patterns of peripheral paralexia: pure alexia and the forgotten visual dyslexia?

The concept of visual dyslexia put forward by Marshall and Newcombe (1973) is assessed. After a long period of neglect it was resurrected in the late 1990s in a narrow form. In the current paper it is proposed that a wider form of the functional syndrome is useful to include amongst other conditions attentional dyslexia and neglect dyslexia. The variety of sub-forms would correspond to the behavioural effects of the different ways in which the orthographic processing systems can be impaired. What distinguishes the broader form from pure alexia is that the patient lacks the capacity to use a serial letter processing strategy, and so interpretation of visual dyslexia in terms of the impairment to the orthographic processing systems is not contaminated by the use of a compensatory strategy that results in processing operations which are qualitatively very different from the normal and highly opaque. The lack of a serial letter processing strategy makes visual dyslexia a much more transparent functional syndrome.

Alexia, Pure↗