Attentional limits in visual search with and without dorsal parietal dysfunction: space-based window or object-based span?

Attentional resource and distribution are specifically impaired in simultanagnosia, and also in the visuo-attentional form of developmental dyslexia. Both clinical conditions are conceived as a limitation of simultaneous visual processing after superior parietal lobule (SPL) dysfunction (review in Valdois et al., 2019). However, a reduced space-based attentional window (i.e. a limited visual eccentricity at which the target object can be identified, Khan et al. 2016) has been demonstrated in simultanagnosia versus a reduced object-based span (i.e. a limited number of objects processed at each fixation, Bosse et al., 2007) in developmental dyslexia. In healthy individuals, the cost in reaction times per item in serial search tasks suggests that a group of objects is processed simultaneously at a time, but this group is also undefined and depends on the visual complexity of the task. Healthy individuals and a patient with simultanagnosia performed serial search tasks involving either symbols (made of separable features) or objects made of non-separable features, and with distractors that were either all identical or all dissimilar. We used a moving window paradigm to determine whether the task was performed with a "working space" versus a "working span" limitation in control group and in patient with bilateral SPL damage. We found that healthy individuals performed search in a color task comprising non-separable feature objects and dissimilar distractors with a limited space-based attentional window; this attentional window, as well as the mean saccade amplitude used to displace it across the visual display, were independent of set size, thus inconsistent with an object-based attentional span. In the symbol task comprising a feature-absent search in which all feature-present distractors were dissimilar, we observed that mean saccade amplitude decreased with set size and that search performance could not be mimicked by a moving window of a single diameter; instead participants seemed to process a fixed number of symbols at a time (object-based span). Following bilateral SPL lesions, patient IG demonstrated a similar space-based search process in the color search task with a normal attentional window. In contrast, her cost-per-item in the symbol task increased dramatically, demonstrating a clear deficit of simultaneous object perception. These results confirmed the specific contribution of the SPL to the visual processing of multiple objects made of separable features (like letters), and more dramatically when they are all different, which explains the specific difficulty for a reading beginner in case of SPL dysfunction.

Orthographic depth and developmental dyslexia: a meta-analytic study

Cross-cultural studies have suggested that reading deficits in developmental dyslexia (DD) can be moderated by orthographic depth. To further explore this issue and assess the moderating role of orthographic depth in the developmental cognitive trajectories of dyslexic and typical readers, we systematically reviewed 113 studies on DD that were published from 2013 to 2018 and selected 79 in which participants received an official DD diagnosis. Each study was classified according to orthographic depth (deep vs. shallow) and participant age (children vs. adults). We assessed the difference between DD and control groups' performance in reading tasks and in a wide range of cognitive domains associated with reading (phonological awareness (PA), rapid automatized naming (RAN), short-term working memory (WM), and nonverbal reasoning), including age and orthographies as moderators. We found an age-by-orthography interaction effect in word reading accuracy and a significant effect of age in pseudoword reading accuracy, but we found no effect of age and orthographic depth on the fluency parameters. These results suggest that reading speed is a reliable index for discriminating between DD and control groups across European orthographies from childhood to adulthood. A similar pattern of results emerged for PA, RAN, and short-term/WM. Our findings are discussed in relation to their impact on clinical practice while considering the orthographic depth and developmental level.

Increased reliance on top-down information to compensate for reduced bottom-up use of acoustic cues in dyslexia

Speech recognition is a complex human behavior in the course of which listeners must integrate the detailed phonetic information present in the acoustic signal with their general linguistic knowledge. It is commonly assumed that this process occurs effortlessly for most people, but it is still unclear whether this also holds true in the case of developmental dyslexia (DD), a condition characterized by perceptual deficits. In the present study, we used a dual-task setting to test the assumption that speech recognition is effortful for people with DD. In particular, we tested the Ganong effect (i.e., lexical bias on phoneme identification) while participants performed a secondary task of either low or high cognitive demand. We presumed that reduced efficiency in perceptual processing in DD would manifest in greater modulation in the performance of primary task by cognitive load. Results revealed that this was indeed the case. We found a larger Ganong effect in the DD group under high than under low cognitive load, and this modulation was larger than it was for typically developed (TD) readers. Furthermore, phoneme categorization was less precise in the DD group than in the TD group. These findings suggest that individuals with DD show increased reliance on top-down lexically mediated perception processes, possibly as a compensatory mechanism for reduced efficiency in bottom-up use of acoustic cues. This indicates an imbalance between bottom-up and top-down processes in speech recognition of individuals with DD.

Delaying feedback compensates for impaired reinforcement learning in developmental dyslexia

A theoretical framework suggests that developmental dyslexia is characterized by abnormalities in brain structures underlying the procedural learning and memory systems while the declarative learning and memory systems are presumed to remain intact or even enhanced (Procedural Deficit Hypothesis). This notion has been supported by a substantial body of research, which focused on each system independently. However, less attention has been paid to interactions between these memory systems which may provide insights as to learning situations and conditions in which learning in dyslexia can be improved. The current study was undertaken to examine these important but unresolved issues. To this end, probabilistic reinforcement learning and episodic memory tasks were examined in participants with dyslexia and neurotypicals simultaneously within a single task. Feedback timing presentation was manipulated, building on prior research indicating that delaying feedback timing shifts striatal-based probabilistic learning, to become more hippocampal-dependent. It was hypothesized that if the procedural learning and memory systems are impaired in dyslexia, performance will be impaired under conditions that encourage procedural memory engagement (immediate feedback trials) but not under conditions that promote declarative memory processing (long delayed feedback trials). It was also predicted that the ability to incidentally acquire episodic information would be preserved in dyslexia. The results supported these predictions. Participants with dyslexia were impaired in probabilistic learning of cue-outcome associations compared to neurotypicals in an immediate feedback condition, but not when feedback on choices was presented after a long delay. Furthermore, participants with dyslexia demonstrated similar performance to neurotypicals in a task requiring incidental episodic memory formation. These findings attest to a dissociation between procedural-based and declarative-based learning in developmental dyslexia within a single task, a finding that adds discriminative validity to the Procedural Deficit Hypothesis. Just as important, the present findings suggest that training conditions designed to shift the load from midbrain/striatal systems to declarative memory mechanisms have the potential to compensate for impaired learning in developmental dyslexia.

Clinical profile of reading ability and reading and writing achievement of children with borderline full-scale intellectual quotient: a prospective study

Background

Poor reading ability is one of the common causes of low academic performance. In previous studies, children with dyslexia were found to demonstrate poor academic achievement due to poor reading ability. However, the relationship between academic achievement and reading ability in children with a borderline full-scale intellectual quotient (FSIQ) is unknown. This study aimed to clarify the clinical characteristics of children with borderline FSIQ and poor reading ability, and differentiate these characteristics from those of children with higher FSIQ and poor reading ability.

Methods

A total of 126 children (aged 6–15 years) identified as having low academic performance were enrolled. The reading ability of children was assessed through their performance on the hiragana (Japanese syllabary) reading task, while their reading and writing achievement was assessed through their reading and writing score on the Kaufman Assessment Battery for Children, Second Edition. Children were categorized into two groups based on their FSIQ score (FSIQ > 85 and 85 ≥ FSIQ ≥ 70). Reading ability in children was evaluated by referring to the linear relationship between FSIQ and the standard deviation value of reading tasks in typically developing children. A one-way analysis of variance (ANOVA) was performed to examine clinical characteristics between higher and lower FSIQ groups. Associations between reading and writing achievement, reading ability, and ages of children were assessed using Pearson’s product-moment correlation coefficients for the higher and lower FSIQ groups.

Results

Poorer reading and writing achievement was associated with poorer reading ability in the higher FSIQ group. Conversely, poorer reading and writing achievement and poor reading ability were associated with older age in the lower FSIQ group.

Conclusions

Poor reading and writing achievement were associated with older age, not with poor reading ability in the lower FSIQ group. Children with lower FSIQ need appropriate educational interventions based on independent assessments to further their academic achievement and reading ability. Moreover, they need more frequent evaluations of their academic achievement than do children with higher FSIQ and poor reading ability since they are more likely to be at a lower academic achievement level at an older age.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-021-02865-z.

Visual attention span and phonological skills in Chinese developmental dyslexia

BACKGROUND

It has been debated whether visual attention span deficit was independent from phonological deficit in alphabetic developmental dyslexia. Yet, this issue has never been examined in Chinese developmental dyslexia.

AIM

The aim of the present study was to concurrently investigate visual attention span deficit and phonological deficit in Chinese developmental dyslexia, and examine the relationship between them.

METHODS

A total of 45 Chinese dyslexic and 43 control children aged between 8 and 11 years old participated in this study. A visual one-back paradigm with both verbal stimuli (character and digit strings) and nonverbal stimuli (color dots and symbols) was employed for measuring visual attention span. Phonological skills were measured by three dimensions: phonological awareness, rapid automatized naming, and verbal short-term memory.

RESULTS

Chinese dyslexic children showed deficits in verbal visual attention span and all three dimensions of phonological skills, but not in nonverbal visual attention span. Phonological skills significantly contributed to explaining variance of reading skills and classifying dyslexic and control memberships. Almost all Chinese dyslexic participants who showed a deficit in visual attention span also showed a phonological deficit.

CONCLUSION

The study suggests that visual attention span deficit is not independent from phonological deficit in Chinese developmental dyslexia.

A neural index of inefficient evidence accumulation in dyslexia underlying slow perceptual decision making

Visual processing deficits have been widely reported in developmental dyslexia however the locus of cognitive dysfunction remains unclear. Here, we examined the neural correlates of perceptual decision-making using a dot-motion task and electroencephalography (EEG) and investigated whether presenting deficits were unique to children with dyslexia or if they were also evident in other, typically developing children with equally immature reading systems. Sixty-eight children participated: 32 with dyslexia (DD; 16 females); 21 age-matched controls (AM; 11 females) and 15 reading-matched controls (RM; 9 females). All participants completed a bilaterally presented random-dot-motion task while EEG was recorded. Neural signatures of low level sensory processing (steady state visual evoked potentials; SSVEPs), pre-target attentional bias (posterior α power), attentional orienting (N2), evidence accumulation (centro-parietal positive decision signal; CPP) and execution of a motor response (β) were obtained to dissect the temporal sequence of perceptual decision-making. Reading profile provided a score of relative lexical and sublexical skills for each participant. Although all groups performed comparably in terms of task accuracy and false alarm rate, the DD group were slower and demonstrated an earlier peak latency, reduced slope and lower amplitude of the CPP compared with both AM and RM controls. Reading profile was found to moderate the relationship between word reading ability, reaction time as well as CPP indices showing that lexical dyslexics responded more slowly and had a shallower slope, reduced amplitude and earlier latency of CPP waveforms than sublexical dyslexics. These findings suggest that children with dyslexia, particularly those with relatively poorer lexical abilities, have a reduced rate and peak of evidence accumulation as denoted by CPP markers yet remain slow in their overt response. This is in keeping with hypotheses that children with dyslexia have impairment in effectively sampling and processing evidence about visual motion stimuli.

Neurophysiological tracking of speech-structure learning in typical and dyslexic readers

Statistical learning, or the ability to extract statistical regularities from the sensory environment, plays a critical role in language acquisition and reading development. Here we employed electroencephalography (EEG) with frequency-tagging measures to track the temporal evolution of speech-structure learning in individuals with reading difficulties due to developmental dyslexia and in typical readers. We measured EEG while participants listened to (a) a structured stream of repeated tri-syllabic pseudowords, (b) a random stream of the same isochronous syllables, and (c) a series of tri-syllabic real Dutch words. Participants' behavioral learning outcome (pseudoword recognition) was measured after training. We found that syllable-rate tracking was comparable between the two groups and stable across both the random and structured streams of syllables. More importantly, we observed a gradual emergence of the tracking of tri-syllabic pseudoword structures in both groups. Compared to the typical readers, however, in the dyslexic readers this implicit speech structure learning seemed to build up at a slower pace. A brain-behavioral correlation analysis showed that slower learners (i.e., participants who were slower in establishing the neural tracking of pseudowords) were less skilled in phonological awareness. Moreover, those who showed stronger neural tracking of real words tended to be less fluent in the visual-verbal conversion of linguistic symbols. Taken together, our study provides an online neurophysiological approach to track the progression of implicit learning processes and gives insights into the learning difficulties associated with dyslexia from a dynamic perspective.

A three-time point longitudinal investigation of the arcuate fasciculus throughout reading acquisition in children developing dyslexia

Although the neural basis of dyslexia has intensively been investigated, results are still unclear about the existence of a white matter deficit in the arcuate fasciculus (AF) throughout development. To unravel this ambiguity, we examined the difference in fractional anisotropy (FA) of the AF between children developing dyslexia and children developing typical reading skills in a longitudinal sample with three MRI time points throughout reading development: the pre-reading stage (5-6 years old), the early reading stage (7-8 years old) and the advanced reading stage (9-10 years old). Applying along-the-tract analyses of white matter organization, our results confirmed that a white matter deficit existed in the left AF prior to the onset of formal reading instruction in children who developed dyslexia later on. This deficit was consistently present throughout the course of reading development. Additionally, we evaluated the use of applying a continuous approach on the participants' reading skills rather than the arbitrary categorization in individuals with or without dyslexia. Our results confirmed the predictive relation between FA and word reading measurements later in development. This study supports the use of longitudinal approaches to investigate the neural basis of the developmental process of learning to read and the application of triangulation, i.e. using multiple research approaches to help gain more insight and aiding the interpretation of obtained results.

Characteristics of the joint position sense in children with developmental dyslexia

[Purpose] Developmental dyslexia is a disorder in which reading and writing of characters is difficult. The present study investigated age-dependent joint position sense of the forearm and wrist and whether children with developmental dyslexia have less joint position sense than typically developing children. [Participants and Methods] The participants were comprised of 84 typically developing elementary school students, 12 university students, and 2 children with developmental dyslexia. Joint position sense was evaluated using the reproduction method based on four tasks. The participants were divided into three age groups. The children with developmental dyslexia were compared with the typically developing children in the same age group. [Results] Significant negative correlations were found between the reproduction error of the typically developing children and that of the university students in most tasks. The children with developmental dyslexia showed increased reproduction error relative to the reproduction error of the typically developing children in the same age group in 4 of the 8 tasks. [Conclusion] The accuracy of the joint position sense improved with development. However, the joint position sense of the children with developmental dyslexia was lower than that of the typically developing children in the same age group. The difficulty in writing experienced by children with developmental dyslexia may be related to joint position sensing impairment due to impaired joint position sense.

Failure of resting-state frontal-occipital connectivity in linking visual perception with reading fluency in Chinese children with developmental dyslexia

It is widely accepted that impairment in visual perception impedes children's reading development, and further studies have demonstrated significant enhancement in reading fluency after visual perceptual training. However, the mechanism of the neural linkage between visual perception and reading is unclear. The purpose of this study was to examine the intrinsic functional relationship between visual perception (indexed by the texture discrimination task,TDT) and reading ability (character reading and reading fluency) in Chinese children with developmental dyslexia (DD) and those with typical development (TD). The resting-state functional connectivity (RSFC) between the primary visual cortex (V1, BA17) and the entire brain was analyzed. In addition, how RSFC maps are associated with TDT performance and reading ability in the DD and TD groups was examined. The results demonstrated that the strength of the RSFC between V1 and the left middle frontal gyrus (LMFG, BA9/BA46) was significantly correlated with both the threshold (SOA) of the TDT and reading fluency in TD children but not in DD children. Moreover, LMFG-V1 resting-state connectivity played a mediating role in the association of visual texture discrimination and reading fluency, but not in character reading, in TD children. In contrast, this mediation was absent in DD children, albeit their strengths of RSFC between V1 and the left middle frontal gyrus (LMFG) were comparable to those for the TD group. These findings indicate that typically developing children use the linkage of the RSFC between the V1 and LMFG for visual perception skills, which in turn promote fluent reading; in contrast, children with dyslexia, who had higher TDT thresholds than TD children, could not take advantage of their frontal-occipital connectivity to improve reading fluency abilities. These findings suggest that visual perception plays an important role in reading skills and that children with developmental dyslexia lack the ability to use their frontal-occipital connectivity to link visual perception with reading fluency.

Comorbidity and cognitive overlap between developmental dyslexia and congenital amusia in children

Developmental dyslexia and congenital amusia are two specific neurodevelopmental disorders that affect reading and music perception, respectively. Similarities at perceptual, cognitive, and anatomical levels raise the possibility that a common factor is at play in their emergence, albeit in different domains. However, little consideration has been given to what extent they can co-occur. A first adult study suggested a 30% amusia rate in dyslexia and a 25% dyslexia rate in amusia (Couvignou et al., Cognitive Neuropsychology 2019). We present newly acquired data from 38 dyslexic and 38 typically developing children. These were assessed with literacy and phonological tests, as well as with three musical tests: the Montreal Battery of Evaluation of Musical Abilities, a pitch and time change detection task, and a singing task. Overall, about 34% of the dyslexic children were musically impaired, a proportion that is significantly higher than both the estimated 1.5-4% prevalence of congenital amusia in the general population and the rate of 5% observed within the control group. They were mostly affected in the pitch dimension, both in terms of perception and production. Correlations and prediction links were found between pitch processing skills and language measures after partialing out confounding factors. These findings are discussed with regard to cognitive and neural explanatory hypotheses of a comorbidity between dyslexia and amusia.

Phonological memory updating and developmental dyslexia: The role of long-term knowledge

The relationship between phonological knowledge and reading is consistent both in typically developing children and in children with dyslexia. However, children with dyslexia usually show lower phonological skills. In a group of children with dyslexia 8- to 12-year-old we investigated how different long-term memory phonological associations are updated in memory, that is how are kept in mind and replaced when no longer relevant. Response times (RTs) and accuracy rates were collected. Typically, long-term memory associations are dismantled and updated with greater difficulty (longer RTs). We did not replicate these findings in children with dyslexia thus demonstrating the effects of phonological disruption during updating, a mechanism that is preserved overall. In summary, our work advances literature about how phonological knowledge impacts verbal working memory updating.

Effect of comorbid developmental dyslexia on oculomotor behavior in children with developmental coordination disorder: A study with the Developmental Eye Movement test

Studies have suggested a dysfunction in oculomotor skills in children with developmental coordination disorder (DCD). It has been proposed that the Developmental Eye Movement (DEM) test is useful in testing the dyslexics' (DD) oculomotor behavior during reading, in a simple and indirect manner. The present study aimed at exploring the oculomotor behavior in children with DCD as assessed with the DEM test. We thus compared children with DCD to children with DD and to children with both DCD and DD in order to investigate the specificity of the oculomotor difficulties, as measured by the DEM test. Results showed that 1) children with DCD presented mild atypical performance at the DEM test (error z-score only), 2) children with DD presented particularly poor performance at the DEM test, and 3) the co-morbid condition (DCD + DD) did not add to the severity of atypical performance at the DEM test. In sum, children with DCD were the less affected according to the DEM test, and children with DD (isolated or comorbid) presented the most atypical performance. Results at the DEM test did not allow to highlight clear oculomotor atypicalities in DCD. We thus concluded that more research using eye-tracking techniques is needed to explore the nature of oculomotor atypicalities in DCD children, to distinguish DD and DCD oculomotor behavior, and to understand the profile of children with dual diagnosis.

Investigating the compatibility, interchangeability, and clinical usability of BOT2-BF and BOT2-SF in primary school-aged children with and without developmental dyslexia

The aim of our study was to determine the sensitivity and specificity levels of BOT2-BF and BOT2-SF tests applied to children with developmental dyslexia and to examine their clinical usability. This study was designed as a case-controlled study. 82 (study group 41, control group 41) 7-12 year children were included. The study occurred three stages. In the first place, the similarities and differences of BOT2-BF and BOT2-SF tests observed in clinical practices were examined by taking the feedback of experts and test correlations. In the second step, BOT2-BF and BOT2-SF tests were examined with reference to the Core Outcome Set (COS) evaluation criteria. In the last step, in order to examine the sensitivity and specificity levels of the tests, assessments were performed in two groups with 1-week intervals. According to the COS results, the BOT2-BF test was examined better than the BOT2-SF test under cross-cultural validity title. The sensitivity and specificity of BOT2-SF were 0.92 and 0.51, and for BOT2-BF were 0.92 and 0.41, respectively. This study will help clinicians working on children with developmental dyslexia to decide the type of test they will use to evaluate and easy access to materials motor proficiency.

Effects of transcranial stimulation in developmental neurocognitive disorders: A critical appraisal

Non-invasive brain stimulation (NIBS) has been highlighted as a powerful tool to promote neuroplasticity, and an attractive approach to support cognitive remediation. Here we provide a systematic review of 26 papers using NIBS to ameliorate cognitive dysfunctions in three prevalent neurodevelopmental disorders: Attention-Deficit/Hyperactivity Disorder (ADHD), Developmental Dyslexia and Developmental Dyscalculia. An overview of the state of research shows a predominance of studies using repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) techniques, and an unequal distribution among clinical conditions. Regarding the utility of NIBS, the results are promising but also ambiguous. Twenty-three papers reported beneficial effects, but many of these effects were found only once or were only partially replicated and some studies even reported detrimental effects. Furthermore, most studies differed in at least one core aspect, the NIBS applied, the questionnaires and cognitive tests conducted, or the age group investigated, and sample sizes were mostly small. Hence, further studies are needed to rigorously examine the potential of NIBS in the remediation of cognitive functions. Finally, we discuss potential caveats and future directions. We reason that if adequately addressing these challenges NIBS can be feasible, with potential benefits in treating neurodevelopmental disorders.

Adaptive Plasticity Under Adverse Listening Conditions is Disrupted in Developmental Dyslexia

OBJECTIVE

Acoustic distortions to the speech signal impair spoken language recognition, but healthy listeners exhibit adaptive plasticity consistent with rapid adjustments in how the distorted speech input maps to speech representations, perhaps through engagement of supervised error-driven learning. This puts adaptive plasticity in speech perception in an interesting position with regard to developmental dyslexia inasmuch as dyslexia impacts speech processing and may involve dysfunction in neurobiological systems hypothesized to be involved in adaptive plasticity.

METHOD

Here, we examined typical young adult listeners (N = 17), and those with dyslexia (N = 16), as they reported the identity of native-language monosyllabic spoken words to which signal processing had been applied to create a systematic acoustic distortion. During training, all participants experienced incremental signal distortion increases to mildly distorted speech along with orthographic and auditory feedback indicating word identity following response across a brief, 250-trial training block. During pretest and posttest phases, no feedback was provided to participants.

RESULTS

Word recognition across severely distorted speech was poor at pretest and equivalent across groups. Training led to improved word recognition for the most severely distorted speech at posttest, with evidence that adaptive plasticity generalized to support recognition of new tokens not previously experienced under distortion. However, training-related recognition gains for listeners with dyslexia were significantly less robust than for control listeners.

CONCLUSIONS

Less efficient adaptive plasticity to speech distortions may impact the ability of individuals with dyslexia to deal with variability arising from sources like acoustic noise and foreign-accented speech.

Activation time-course of phonological code in silent word recognition in adult readers with and without dyslexia

In skilled adult readers, reading words is generally assumed to rapidly and automatically activate the phonological code. In adults with dyslexia, despite the main consensus on their phonological processing deficits, little is known about the activation time course of this code. The present study investigated this issue in both populations. Participants' accuracy and eye movements were recorded while they performed a visual lexical decision task in which phonological consistency of written words was manipulated. Readers with dyslexia were affected by phonological consistency during second fixation duration of visual word recognition suggesting a late activation of the phonological code. Regarding skilled readers, no influence of phonological consistency was found when the participants were considered a homogeneous population. However, a different pattern emerged when they were divided into two subgroups according to their phonological and semantic abilities: Those who showed better decoding than semantic skills were affected by phonological consistency at the earliest stage of visual word recognition while those who showed better semantic than decoding skills were not affected by this factor at any processing stage. Overall, the findings suggest that the presence of phonological deficits in readers with dyslexia is associated with a delayed activation of phonological representations during reading. In skilled readers, the contribution of phonology varies with their reading profile, i.e., being phonologically or semantically oriented.

Misunderstandings about developmental dyslexia: a historical overview

Developmental dyslexia is a reading disorder unrelated to intellectual disability, inadequate teaching systems or poor motivation for schooling. The first attempts to understand such difficulty of learning to read, connected the problem to a primary 'visual defect'. Since then, several models have been developed. In the last decades, autopsy and histopathological studies on the brain of developmental dyslexics provided neuroanatomical evidence of structural and morphological differences between the normal and dyslexic brains. Furthermore, neuroimaging studies allowed to understand the neural systems of reading and dyslexia. According to more recent studies, developmental dyslexia appears as a language-related neurodevelopmental disorder with a deficit in phonological decoding and visuospatial organization of the language code. Therefore, dyslexia is viewed as a multicomponential and complex disorder. Consequently, rehabilitation should be aimed at both the recovery of linguistic decoding processes and the improvement of visuo-spatial and attentional processes. This brief overview should be a valuable tool for a deeper understanding of dyslexic disorder. Literature searches in Medline, PsycINFO, EMBASE, Scopus, PubMed, Web of Science identified one hundred articles focusing attention on how this disorder has been considered over the years.

Differential activation of the visual word form area during auditory phoneme perception in youth with dyslexia

Developmental dyslexia is a learning disorder characterized by difficulties reading words accurately and/or fluently. Several behavioral studies have suggested the presence of anomalies at an early stage of phoneme processing, when the complex spectrotemporal patterns in the speech signal are analyzed and assigned to phonemic categories. In this study, fMRI was used to compare brain responses associated with categorical discrimination of speech syllables (P) and acoustically matched nonphonemic stimuli (N) in children and adolescents with dyslexia and in typically developing (TD) controls, aged 8-17 years. The TD group showed significantly greater activation during the P condition relative to N in an area of the left ventral occipitotemporal cortex that corresponds well with the region referred to as the "visual word form area" (VWFA). Regression analyses using reading performance as a continuous variable across the full group of participants yielded similar results. Overall, the findings are consistent with those of previous neuroimaging studies using print stimuli in individuals with dyslexia that found reduced activation in left occipitotemporal regions; however, the current study shows that these activation differences seen during reading are apparent during auditory phoneme discrimination in youth with dyslexia, suggesting that the primary deficit in at least a subset of children may lie early in the speech processing stream and that categorical perception may be an important target of early intervention in children at risk for dyslexia.

Unisensory and multisensory temporal processing in autism and dyslexia: A systematic review and meta-analysis

This study presents a comprehensive systematic review and meta-analysis of temporal processing in autism spectrum disorder (ASD) and developmental dyslexia (DD), two neurodevelopmental disorders in which temporal processing deficits have been highly researched. The results provide strong evidence for impairments in temporal processing in both ASD (g = 0.48) and DD (g = 0.82), as measured by judgments of temporal order and simultaneity. In individual analyses, multisensory temporal processing was impaired for both ASD and DD, and unisensory auditory, visual and tactile processing were all impaired in DD. In ASD, speech stimuli showed moderate impairment effect sizes, whereas nonspeech stimuli showed small effects. Greater reading and spelling skills in DD were associated with greater temporal precision. Temporal deficits did not show changes with age in either disorder. In addition to more clearly defining temporal impairments in ASD and DD, the results highlight common and distinct patterns of temporal processing between these disorders. Deficits are discussed in relation to existing theoretical models, and recommendations are made for future research.

Rare variants in dynein heavy chain genes in two individuals with situs inversus and developmental dyslexia: a case report

Background

Developmental dyslexia (DD) is a neurodevelopmental learning disorder with high heritability. A number of candidate susceptibility genes have been identified, some of which are linked to the function of the cilium, an organelle regulating left-right asymmetry development in the embryo. Furthermore, it has been suggested that disrupted left-right asymmetry of the brain may play a role in neurodevelopmental disorders such as DD. However, it is unknown whether there is a common genetic cause to DD and laterality defects or ciliopathies.

Case presentation

Here, we studied two individuals with co-occurring situs inversus (SI) and DD using whole genome sequencing to identify genetic variants of importance for DD and SI. Individual 1 had primary ciliary dyskinesia (PCD), a rare, autosomal recessive disorder with oto-sino-pulmonary phenotype and SI. We identified two rare nonsynonymous variants in the dynein axonemal heavy chain 5 gene (DNAH5): a previously reported variant c.7502G > C; p.(R2501P), and a novel variant c.12043 T > G; p.(Y4015D). Both variants are predicted to be damaging. Ultrastructural analysis of the cilia revealed a lack of outer dynein arms and normal inner dynein arms. MRI of the brain revealed no significant abnormalities. Individual 2 had non-syndromic SI and DD. In individual 2, one rare variant (c.9110A > G;p.(H3037R)) in the dynein axonemal heavy chain 11 gene (DNAH11), coding for another component of the outer dynein arm, was identified.

Conclusions

We identified the likely genetic cause of SI and PCD in one individual, and a possibly significant heterozygosity in the other, both involving dynein genes. Given the present evidence, it is unclear if the identified variants also predispose to DD and further studies into the association between laterality, ciliopathies and DD are needed.

Altered visual character and object recognition in Japanese-speaking adolescents with developmental dyslexia

Many studies have confirmed a brain dysfunction in people with developmental dyslexia (DD) in certain brain regions, including the left superior temporal gyrus and the left fusiform gyrus. However, the neurobiological substrates in Japanese-speaking people with dyslexia are not fully understood, mostly due to the uniqueness of the orthographic systems. Since a substantial part of the written Japanese includes the logographic Kanji as well as the phonographic Kana systems, the reading disability might be caused not only by a dysfunction in the phonological system, but also by a dysfunction in the visual recognition system. Previous studies reported altered hierarchical visual word form processing in the left occipitotemporal cortex; however, it remains unclear whether the altered hierarchical visual processing is language stimuli-specific. Therefore, we aimed to investigate whether (a) Japanese-speaking individuals with DD exhibit atypical hierarchical visual processing, and if so, (b) whether the altered hierarchical visual processing is language stimuli-specific or not. The present study investigated the brain activation pattern for the hierarchical component of the Kanji characters and object stimuli in typically developing (TD) adolescents and adolescents with DD using functional magnetic resonance imaging. For the Kanji characters, adolescents with DD showed a greater activation in the left occipital gyrus and right occipital fusiform gyrus, and this hyperactivity was also found for pseudo and artificial Kanji characters. These results imply reliance on an early visual system in Kanji reading in Japanese-speaking adolescents with DD. Additionally, we also investigated the brain activity for object stimuli, and adolescents with DD showed a greater activation in the bilateral occipital gyri compared with the TD adolescents. These results imply an altered hierarchical visual processing characterized by overactivation in the early visual areas, which is a not restricted to language stimulus only.

Visual and Auditory Interference Control of Attention in Developmental Dyslexia

An accumulating body of evidence highlights the contribution of general cognitive processes, such as attention, to language-related skills.

OBJECTIVE

The purpose of the present study was to explore how interference control (a subcomponent of selective attention) is affected in developmental dyslexia (DD) by means of control over simple stimulus-response mappings. Furthermore, we aimed to examine interference control in adults with DD across sensory modalities.

METHODS

The performance of 14 dyslexic adults and 14 matched controls was compared on visual/auditory Simon tasks, in which conflict was presented in terms of an incongruent mapping between the location of a visual/auditory stimulus and the appropriate motor response.

RESULTS

In the auditory task, dyslexic participants exhibited larger Simon effect costs; namely, they showed disproportionately larger reaction times (RTs)/errors costs when the auditory stimulus and response were incongruent relative to RT/errors costs of non-impaired readers. In the visual Simon task, both groups presented Simon effect costs to the same extent.

CONCLUSION

These results indicate that the ability to control auditory selective attention is carried out less effectively in those with DD compared with visually controlled processing. The implications of this impaired process for the language-related skills of individuals with DD are discussed.

A meta-analysis of reading-level match dyslexia studies in consistent alphabetic orthographies

We provide a meta-analytic review of all group-comparison studies that used reading-level match design, were conducted in highly consistent European orthographies, included children with dyslexia younger than 13 years of age as participants, and included measures of one or more of the potential causes of dyslexia. We identified 21 studies meeting these criteria that examined one or more of phonological awareness, rapid naming, verbal short-term memory, or auditory temporal processing. A random effects model analysis showed first that the groups were matched imperfectly and they differed significantly in word reading measures not used for matching. Second, there were no significant differences between the individuals with dyslexia and their reading-level-matched controls in rapid naming, phonological memory, and auditory temporal processing. Finally, the analyses for phonological awareness showed a significant effect for comparisons that involved manipulating phonemes but not for tasks that involved manipulating syllables. The results are compatible with phonological deficit theories of dyslexia, but this conclusion is qualified by observed differences in reading skills and sample selection concerns.