Visual search performance in dyslexia

Reading problems and their connection with visual search and attention

Attention has been hypothesized to act as a sequential gating mechanism for the orderly processing of letters and words. These same visuoattentional processes are often assumed to partake in some but not all types of visual search. In the current study, 24 dyslexic and 36 typical readers completed an attentionally demanding visual conjunction search. Visual feature search served as an internal control. It has been suggested that reading problems should go hand in hand with specific problems in visual conjunction search-particularly elevated conjunction search slopes (time per search item)-often interpreted as a problem with visual attention. Results showed that reading problems were associated with slower visual search, especially conjunction search. However, reading deficits were not associated with increased conjunction search slopes but instead with increased search intercepts, traditionally not interpreted as reflecting attention. We discuss these results in the context of hypothesized visuoattentional problems in dyslexia. Remaining open to multiple interpretations of the data, the current study demonstrates that difficulties in visual search are associated with reading problems, in accordance with growing literature on visual cognition problems in developmental dyslexia.

Prismatic adaptation coupled with cognitive training as novel treatment for developmental dyslexia: a randomized controlled trial

Despite intense and costly treatments, developmental dyslexia (DD) often persists into adulthood. Several brain skills unrelated to speech sound processing (i.e., phonology), including the spatial distribution of visual attention, are abnormal in DD and may represent possible treatment targets. This study explores the efficacy in DD of rightward prismatic adaptation (rPA), a visuomotor adaptation technique that enables visuo-attentive recalibration through shifts in the visual field induced by prismatic goggles. A digital intervention of rPA plus cognitive training was delivered weekly over 10 weeks to adolescents with DD (aged 13-17) assigned either to treatment (N = 35) or waitlist (N = 35) group. Efficacy was evaluated by repeated measures MANOVA assessing changes in working memory index (WMI), processing speed index (PSI), text reading speed, and words/pseudowords reading accuracy. rPA treatment was significantly more effective than waitlist (p ≤ 0.001; ηp2 = 0.815). WMI, PSI, and reading speed increased in the intervention group only (p ≤ 0.001, ηp2 = 0.67; p ≤ 0.001, ηp2 = 0.58; p ≤ 0.001, ηp2 = 0.29, respectively). Although modest change was detected for words and pseudowords accuracy in the waitlist group only (words: p ≤ 0.001, d = 0.17, pseudowords: p = 0.028; d = 0.27), between-group differences were non-significant. rPA-coupled cognitive training enhances cognitive and reading abilities in adolescents with DD. This innovative approach could have implications for early remedial treatment.

Toward the characterization of a visual form of developmental dyslexia: Reduced visuo-attentional capacity for processing multiple stimuli made of separable features

Some dyslexics cannot process multiple letters simultaneously. It has been argued that this reduced visuo-attentional (VA) letter span could result from poor reading ability and experience. Here, moving away from reading context, we showed that dyslexic group exhibited slower visual search than normal readers group for "symbols", defined as graphic stimuli made up of separable visual features, but not for filled objects. Slowness in symbol visual search was explained by reduced VA field and atypical ocular behaviour when processing those letter-like stimuli and was associated with reduced VA letter span and impaired elementary visuo-spatial perception. Such a basic visual search deficit can hardly be attributed to poor reading ability and experience. Moreover, because it is specific to letter-like stimuli (i.e., "symbols"), it can specifically hinder reading acquisition. Symbol visual search can easily be tested in the pre-reading phase, opening up prospects for early risk detection and prevention of VA dyslexia.

[Formula: see text] Visual selective attention and visual search performance in children with CVI, ADHD, and Dyslexia: a scoping review

Visual selective attention refers to the selection of relevant visual elements in a scene whilst ignoring irrelevant visual elements. Visual Selective Attention Dysfunctions (VSAD) are prevalent in children with Cerebral Visual Impairment (CVI), Attention Deficit Hyperactivity Disorder (ADHD), and Dyslexia. An important issue in the pediatric neuropsychological practice is how to discriminate between the task performance of these populations. We conducted a scoping review of the literature on visual search performance (VSP) in children with CVI, ADHD, and Dyslexia, aged 6-12 years. After a systematic selection process, 35 studies were included. Results suggest that all patient groups have some degree of impaired VSP compared to typically developing children. Children with CVI tend to react slower and less accurately. VSP impairments in children with ADHD are characterized by poor accuracy rather than reaction time. Children with Dyslexia tend to be slower and less accurate, depending on stimulus type. Besides VSAD, it is argued that other neurocognitive mechanisms might influence VSP, such as speed-accuracy trade-off or an executive functioning deficit in ADHD and a phonological deficit in Dyslexia. This paper further discusses the differences and similarities in visual search performance between the groups. The sparse data in children with an official diagnosis of CVI and the technical inconclusive data on children with ADHD and Dyslexia demonstrate complexity of discriminating between these populations in clinical practice based on VSP. New and more quantitative VSP parameters, such as eye tracking-based measures, may contribute to a refined classification among CVI, ADHD, and Dyslexia.

Is learning a logographic script easier than reading an alphabetic script for German children with dyslexia?

PURPOSE

Developmental dyslexia in alphabetic languages (DD) is characterized by a phonological deficit. Since logographic scripts rely predominantly on visual and morphological processing, reading performance in DD can be assumed to be less impaired when reading logographic scripts.

METHODS

40 German-speaking children (18 with DD, 22 not reading-impaired-group C; 9-11 years) received Chinese lessons. Eye movements (EM) were recorded during naming single alphabetic words, pictures (confrontational) and Chinese characters to be named in German and Chinese. The main outcome variables were: Articulation latency, numbers and durations of fixations. Quality of life (QoL) was assessed by questionnaires.

RESULTS

While reading alphabetic words, articulation latencies and numbers of fixations were significantly higher for group DD than for group C (AL-DD = 1.13, AL-C = 0.84, p< .001; FN-DD = 3.50; FN-C = 2.00, p< .001). For naming pictures and Chinese characters in German and in Chinese, no significant group differences were found for any of the EM variables. The percentage of correct answers was high for German naming (DD = 86.67%, C = 95.24%; p = .015) and lower for Chinese naming in both groups, but significantly lower in group DD, especially for Chinese naming (DD = 56.67%, C: 83.77%; p = .003). QoL differed between groups from the children's perspective only at posttest. Parents of group DD perceived their children`s QoL to be lower compared with parents of group C at pre- and posttest.

CONCLUSIONS

Children with dyslexia performed as well as group C during naming Chinese characters in German and in Chinese regarding their EM variables, presumably because they processed Chinese characters by the visuo-spatial pathway with direct access to the semantic system. However, the significantly lower percentage of correct answers especially during Chinese naming showed that group DD had more difficulties naming Chinese characters than group C, which could be attributed to their phonological deficit, among other factors.

TRIAL REGISTRATION

German clinical trials register (DRKS00015697).

The visual basis of reading and reading difficulties

Most of our knowledge about the neural networks mediating reading has derived from studies of developmental dyslexia (DD). For much of the 20th C. this was diagnosed on the basis of finding a discrepancy between children's unexpectedly low reading and spelling scores compared with their normal or high oral and non-verbal reasoning ability. This discrepancy criterion has now been replaced by the claim that the main feature of dyslexia is a phonological deficit, and it is now argued that we should test for this to identify dyslexia. However, grasping the phonological principle is essential for all learning to read; so every poor reader will show a phonological deficit. The phonological theory does not explain why dyslexic people, in particular, fail; so this phonological criterion makes it impossible to distinguish DD from any of the many other causes of reading failure. Currently therefore, there is no agreement about precisely how we should identify it. Yet, if we understood the specific neural pathways that underlie failure to acquire phonological skills specifically in people with dyslexia, we should be able to develop reliable means of identifying it. An important, though not the only, cause in people with dyslexia is impaired development of the brain's rapid visual temporal processing systems; these are required for sequencing the order of the letters in a word accurately. Such temporal, "transient," processing is carried out primarily by a distinct set of "magnocellular" (M-) neurones in the visual system; and the development of these has been found to be impaired in many people with dyslexia. Likewise, auditory sequencing of the sounds in a word is mediated by the auditory temporal processing system whose development is impaired in many dyslexics. Together these two deficits can therefore explain their problems with acquiring the phonological principle. Assessing poor readers' visual and auditory temporal processing skills should enable dyslexia to be reliably distinguished from other causes of reading failure and this will suggest principled ways of helping these children to learn to read, such as sensory training, yellow or blue filters or omega 3 fatty acid supplements. This will enable us to diagnose DD with confidence, and thus to develop educational plans targeted to exploit each individual child's strengths and compensate for his weaknesses.

The visual-attention span deficit in developmental dyslexia: Review of evidence for a visual-attention-based deficit

The visual attention span (VAS) deficit hypothesis in developmental dyslexia posits that a subset of dyslexic individuals shows a multielement parallel processing deficit due to reduced visual attention capacity. However, the attention-based interpretation of poor performance on VAS tasks is hotly debated. The purpose of the present paper is to clarify this issue through a critical review of relevant behavioural and neurobiological findings. We first examine the plausibility of alternative verbal interpretations of VAS performance, evaluating whether performance on VAS tasks might reflect verbal short-term memory, verbal coding or visual-to-verbal mapping skills. We then focus on the visual dimensions of VAS tasks to question whether VAS primarily reflects visuo-attentional rather than more basic visual skills. Scrutiny of the available behavioural and neurobiological findings not only points to a deficit of visual attention in dyslexic individuals with impaired VAS but further suggests a selective endogenous attentional system deficit that relates to atypical functioning of the brain dorsal attentional network. The overview clarifies the debate on what is being measured through VAS tasks and provides insights on how to interpret the VAS deficit in developmental dyslexia.

Links between organized visual search and reading ability in French primary school children

Visual search skills develop substantially during the primary school years, and in parallel with children's reading achievement. Reading requires an efficient visual search and exposure to reading from the left to the right could also influence the way we explore space. No study, however, made links between visual search strategies and reading ability. In this study, 70 primary school children performed a cancellation task (Bells test) and reading tests. Our results showed that reading was closely linked to visual search accuracy but also to visual search organization, even after controlling for age for some measures. Along with the development of reading abilities, children made fewer revisitation, moved more to the nearest unmarked targets than to the farthest ones and explored more in lines. It appears, therefore, essential to take more into account the visual search organization of children with reading impairments such as dyslexia.

Disrupted Spatial Organization of Cued Exogenous Attention Persists Into Adulthood in Developmental Dyslexia

Purpose: Abnormal exogenous attention orienting and diffused spatial distribution of attention have been associated with reading impairment in children with developmental dyslexia. However, studies in adults have failed to replicate such relationships. The goal of the present study was to address this issue by assessing exogenous visual attention and its peripheral spatial distribution in adults with developmental dyslexia.

Methods: We measured response times, accuracy and eye movements of 18 dyslexics and 19 typical readers in a cued discrimination paradigm, in which stimuli were presented at different peripheral eccentricities.

Results: Results showed that adults with developmental dyslexia were slower that controls in using their mechanisms of exogenous attention orienting. Moreover, we found that while controls became slower with the increase of eccentricity, dyslexics showed an abnormal inflection at 10° as well as similar response times at the most distant eccentricities. Finally, dyslexics show attentional facilitation deficits above 12° of eccentricity, suggesting an attentional engagement deficit at far periphery.

Conclusion: Taken together, our findings indicate that, in dyslexia, the temporal deficits in orientation of attention and its abnormal peripheral spatial distribution are not restricted to childhood and persist into adulthood. Our results are, therefore, consistent with the hypothesis that the neural network underlying selective spatial attention is disrupted in dyslexia.

Short Vestibular and Cognitive Training Improves Oral Reading Fluency in Children with Dyslexia

(1) Background: This study explored the effect of short vestibular and cognitive training on the reading speed in dyslexic children. (2) Methods: The reading speed was evaluated by using a reading test (Évaluation de la Lecture en FluencE, ELFE) in a crossover design before (baseline) and after vestibular training (post VT) and no vestibular training (post no VT). Nineteen dyslexic children (9.48 ± 0.15 years) participated in the study. The vestibular and cognitive training (software developed by BeonSolution S.r.l.) consisted in four exercises presented on a Wacom tablet 10″ done for 16 min per session two times per week for four weeks; each exercise was composed of eight levels with increased difficulty. (3) Results: Following vestibular and cognitive training, dyslexic children increased their reading speed; interestingly, such an increase persisted at least one month after training. (4) Conclusions: Vestibular and cognitive training could improve the vestibular network, which is well known for being involved in several cognition functions leading to reading improvement in dyslexic children. Adaptive mechanisms could be responsible for maintaining such improvement for at least one month.

Functional Connectivity in Developmental Dyslexia during Speed Discrimination

A universal signature of developmental dyslexia is literacy acquisition impairments. Besides, dyslexia may be related to deficits in selective spatial attention, in the sensitivity to global visual motion, speed processing, oculomotor coordination, and integration of auditory and visual information. Whether motion-sensitive brain areas of children with dyslexia can recognize different speeds of expanded optic flow and segregate the slow-speed from high-speed contrast of motion was a main question of the study. A combined event-related EEG experiment with optic flow visual stimulation and functional frequency-based graph approach (small-world propensity ϕ) were applied to research the responsiveness of areas, which are sensitive to motion, and also distinguish slow/fast -motion conditions on three groups of children: controls, untrained (pre-D) and trained dyslexics (post-D) with visual intervention programs. Lower ϕ at θ, α, γ1-frequencies (low-speed contrast) for controls than other groups represent that the networks rewire, expressed at β frequencies (both speed contrasts) in the post-D, whose network was most segregated. Functional connectivity nodes have not existed in pre-D at dorsal medial temporal area MT+/V5 (middle, superior temporal gyri), left-hemispheric middle occipital gyrus/visual V2, ventral occipitotemporal (fusiform gyrus/visual V4), ventral intraparietal (supramarginal, angular gyri), derived from θ-frequency network for both conditions. After visual training, compensatory mechanisms appeared to implicate/regain these brain areas in the left hemisphere through plasticity across extended brain networks. Specifically, for high-speed contrast, the nodes were observed in pre-D (θ-frequency) and post-D (β2-frequency) relative to controls in hyperactivity of the right dorsolateral prefrontal cortex, which might account for the attentional network and oculomotor control impairments in developmental dyslexia.

The use of visual search to assess attention

BACKGROUND

Under some conditions, the time required for a visual search increases with the number of elements to be searched. It has been suggested that the overall search time reflects the duration that attention is devoted to each element multiplied by the number of elements. On this basis, it has been proposed that visual search time can be used as a measure of attention capability in dyslexic readers. However, there is evidence to suggest that the search time reflects task difficulty rather than attentional factors. Many dyslexic readers suffer from various sensory deficits. These deficits would effectively increase task difficulty for these readers. Here we use computer simulations to investigate the potential effects of sensory deficits on visual search.

METHOD

Visual search was modelled on a computer within the framework of signal detection theory as a matter of detecting a noisy signal from a series of noisy distractors. Sensory deficits were modelled as decreased discriminability.

RESULTS

Consistent with previous observations, we find that discriminability, which decreases with the number of distractors, may have a substantial effect on the search time. With regard to the effects of sensory deficits, we find that under low discriminability conditions, small sensory deficits may cause pronounced increases in search time.

CONCLUSION

The finding that small sensory deficits may cause pronounced increases in search time makes it specifically problematic to use visual search to test attention in individuals who suffer from sensory deficits. This applies particularly to dyslexic individuals, many of whom have been shown to suffer from visual deficiencies.

Visual search efficiency and functional visual cortical size in children with and without dyslexia

Dyslexia is characterised by poor reading ability. Its aetiology is probably multifactorial, with abnormal visual processing playing an important role. Among adults with normal reading ability, there is a larger representation of central visual field in the primary visual cortex (V1) in those with more efficient visuospatial attention. In this study, we tested the hypothesis that poor reading ability in school-aged children (17 children with dyslexia, 14 control children with normal reading ability) is associated with deficits in visuospatial attention using a visual search task. We corroborated the psychophysical findings with neuroimaging, by measuring the functional size of V1 in response to a central 12° visual stimulus. Consistent with other literature, visual search was impaired and less efficient in the dyslexic children, particularly with more distractor elements in the search array (p = 0.04). We also found atypical interhemispheric asymmetry in functional V1 size in the dyslexia group (p = 0.02). Reading impaired children showed poorer visual search efficiency (p = 0.01), needing more time per unit distractor (higher ms/item). Reading ability was also correlated with V1 size asymmetry (p = 0.03), such that poorer readers showed less left hemisphere bias relative to the right hemisphere. Our findings support the view that dyslexic children have abnormal visuospatial attention and interhemispheric V1 asymmetry, relative to chronological age-matched peers, and that these factors may contribute to inter-individual variation in reading performance in children.

Eye movement patterns in Iranian dyslexic children compared to non-dyslexic children

OBJECTIVE

Dyslexia is the most common learning disorder that affects 5-10% of school aged children. Eye movement abnormalities and visual processing deficits have been reported in some of dyslexic children. Objective of this study is to compare the eye-movement patterns of Iranian dyslexic children with those of non-dyslexic children as they perform the oculomotor tests and to explore the relationship between their eye-movement patterns and their reading ability.

METHODS

Binocular eye movements were recorded by oculomotor subtype of videonystagmography (VNG) testing on 30 dyslexic children and 20 non-dyslexic age-matched children (aged 8-12) in both genders. Dyslexic children were diagnosed with DSM-V scale by experts in reading disorder centers. Gain of the pursuit and optokinetic tests and the latency, accuracy and velocity of the saccade test were measured in both groups of dyslexic and non-dyslexic children. The independent samples t-test, Chi-square test and linear regression test in SPSS v. 21 were used to analyze behavioral and eye-movement parameters.

RESULTS

Compared to the non-dyslexic group, dyslexic children presented lower gain in pursuit and optokinetic tests, and increased latency with decreased accuracy in saccade test. All behavioral and eye-movement parameters without saccade velocity differed significantly among two groups.

CONCLUSION

The atypical eye movement patterns observed in dyslexic children suggests a deficiency in the visual information processing and an immaturity of brain structures responsible for oculomotor skills.

Visual Search in Chinese Children With Attention Deficit/Hyperactivity Disorder and Comorbid Developmental Dyslexia: Evidence for Pathogenesis From Eye Movements

In this study, a visual search task was conducted on children with comorbid attention deficit/hyperactivity disorder (ADHD) and developmental dyslexia (DD), children with pure ADHD, and typically developing children to explore the pathogenesis of comorbidity between ADHD and DD. Participants searched for the target character from five characters in each trial during the task. The distractors included orthographically similar characters, homophones, unrelated characters, and characters of a different color (i.e., red). Results showed that the clinical groups produced longer first fixation duration than the control group in all types of distractors. Children with ADHD comorbid DD were also more susceptible to characters with the distracting red color in gaze duration and total viewing time than were children with pure ADHD and healthy controls. The implication of comorbidity (ADHD + DD) on the pathogenesis was discussed. These results may be helpful for the diagnosis and treatment of ADHD with comorbid DD.

Global and Local Visual Processing in Rate/Accuracy Subtypes of Dyslexia

Words are processed in both a global and local manner. Studies on global versus local processing styles in individuals with and without dyslexia are inconclusive. In the present study, we investigated whether distinct patterns of global/local visual processing were associated with more precisely defined dyslexia profiles. Previous studies on dyslexia provide evidence of accuracy- and rate-based subtypes, with impairment in one dimension alongside normal performance in the other. In the current study, three groups of adult readers: rate disability, accuracy disability, typical development, were presented with nonlinguistic global /local congruency task. The results revealed that the rate disability group had deficiencies performing the global task while the accuracy disability group had deficiencies in the local task. These results are discussed in the context of global/local word processing and in relation to dyslexia. Specifically, they suggest that different patterns of global/local processing are observed between different types of dyslexics, and imply that practitioners should modify their treatment based on the specific deficiency.

It is the egg, not the chicken; dorsal visual deficits present in dyslexia are not present in illiterate adults

Some individuals with dyslexia demonstrate deficits in reading, visual attention, and visual processing which can be attributed to a functional failure of the magnocells in the visual system or in the dorsal visual pathway. The study examines the role of magno/dorsal function in dyslexic adults compared with normal, illiterate, and semi-literate readers. Coherent motion and coherent form were used in Experiment 1, and the frequency doubling illusion and static-gratings were used in Experiment 2. If a magno/dorsal deficit is demonstrated for dyslexic readers but not illiterate, semi-literate, and normal reading adults, then the deficit cannot be attributed to reading experience. Illiterate adults performed the same as normal and semi-literate readers in coherent motion and frequency doubling tasks, and all three groups performed better than the dyslexic readers. There was no difference between any of the groups in the coherent form or static grating tasks. Together, these studies show that illiterate and semi-literate adults do not demonstrate a magno/dorsal deficit that is a characteristic of some sufferers of dyslexia. Therefore, magno/dorsal deficits in dyslexia are unlikely to be a consequence of failing to learn to read but rather provides evidence to suggest a causal role for reduced visual magno/dorsal processing.

Tablet computer games to measure dorsal stream performance in good and poor readers

Evidence suggests a link between deficits in visuo-spatial attention, and subsequent reading ability. However, all the research in the area thus far has been conducted using traditional, lab-based psychophysics, with very tightly controlled visual parameters. In order to take this research further, such as using visuo-spatial tasks for remediation purposes, it must be established that such tasks can be taken out of the laboratory, 'gamified', and still predict reading ability. This study aimed to determine if subtle visual deficits in poor readers could be detected outside a traditional laboratory, in relatively uncontrolled settings using portable game-like technology. Classic visual search and change detection programs, thought to rely on the visual dorsal stream, were modified to a game-like format. They were administered on a portable computer tablet within the participants' school setting. Whilst IQ predicted reading rate, visuo-spatial tasks such as visual search speed, and change detection, each accounted for unique variance in reading rate over and above IQ, age and phonological ability. These results are consistent with the visuo-spatial attention deficit hypothesis, and provide support for the development of portable computerised games that may assess and potentially target this deficit in poor readers.

Meta-analytic findings reveal lower means but higher variances in visuospatial ability in dyslexia

Conflicting empirical and theoretical accounts suggest that dyslexia is associated with either average, enhanced, or impoverished high-level visuospatial processing relative to controls. Such heterogeneous results could be due to the presence of wider variability in dyslexic samples, which is unlikely to be identified at the single study level, due to lack of power. To address this, this study reports a meta-analysis of means and variances in high-level visuospatial ability in 909 non-dyslexic and 956 dyslexic individuals. The findings suggest that dyslexia is associated not only with a lower mean performance on visuospatial tasks but also with greater variability in performance. Through novel meta-analytic techniques, we demonstrate a negative effect size for mean differences (-.457), but a positive effect size for SD differences (+.118; SD ratio = 1.107). In doing so, this is the first study to demonstrate impoverished visuospatial processing of the majority of individuals with dyslexia in addition to greater variance in performance in this group. The findings advocate for further consideration of both the presence of, and reasons for, increased variance in perception, attention, and memory across neurodevelopmental disorders.

Representational Bias in the Radial Axis in Children With Dyslexia: A Landmarks Alignment Study

To better identify the distinctive characteristics of space representation in the radial dimension, we have proposed a new paradigm: the landmarks alignment task where two parallel aluminum bars were radially presented. Children had to move a landmark along one bar and place it at the same location as the reference landmark placed by the examiner on the parallel bar. The major interest of this task was its capacity to assess space representation in the radial dimension when considering a spatial landmark that oriented the subject's attention toward the orthogonal dimension. The most important result showed that in the radial dimension children with dyslexia exhibited a forward bias on the left bar, meaning a mental underrepresentation of the leftward peripersonal space and/or a mental overrepresentation of the rightward peripersonal space. Furthermore, reading discrepancies were correlated with radial forward bias on the left bar. The experiment was also conducted in the lateral axis, showing a pseudoneglect behavior in children without dyslexia. Our landmarks alignment task had the advantage of being able to assess space representation in a complex environment. The forward radial representational bias in children with dyslexia could have implications for spatial orientation in peripersonal workspace in school situations.

Sluggish dorsally-driven inhibition of return during orthographic processing in adults with dyslexia

Dyslexia (D) is a neurodevelopmental reading disorder characterized by phonological and orthographic deficits. Before phonological decoding, reading requires a specialized orthographic system for parallel letter processing that assigns letter identities to different spatial locations. The magnocellular-dorsal (MD) stream rapidly process the spatial location of visual stimuli controlling visuo-spatial attention. To investigate the visuo-spatial attention efficiency during orthographic processing, inhibition of return (IOR) was measured in adults with and without D in a lexical decision task. IOR is the delay in responding to stimuli displayed in a cued location after a long cue-target interval. Only adults with D did not showed IOR effect during letter-string recognition, despite the typical left-hemisphere specialization for word identification. A specific deficit in coherent-dot-motion perception confirmed an MD-stream disorder in adults with D. Our results suggest that adults with D might develop an efficient visual word form area, but a dorsal-attentional dysfunction impairs their reading fluency.

Oculomotor rehabilitation in children with dyslexia

Background: Dyslexia is the most common learning disorder. Visual and oculomotor deficits in dyslexic children have been reported. The purpose of this study was to measure oculomotor parameters and analyze the effect of oculomotor rehabilitation strategies on dyslexia. Methods: Binocular eye movements were recorded by oculomotor subtype of videonystagmography (VNG) testing on 30 children with dyslexia and 20 typical reader children (aged 8-12) in both genders. Dyslexic children were diagnosed with DSM-V scale by experts in reading disorder centers. We studied those children with developmental dyslexia, who had deficits in eye movements recording. Dyslexic children were divided into 2 groups of case and control. Oculomotor rehabilitation (including fixation, saccade, and tracking training) was performed in case group for 1 hour, twice weekly for 8 weeks. Before the intervention, results of oculomotor tests were compared between 3 groups (healthy, case, and control). Then, to analyze the effect of the intervention, results of oculomotor tests were compared between case and control groups in pre- and post- intervention stage. Data were analyzed by independent and paired samples t tests, ANOVA, and repeated measures tests in SPSS v. 21. Results: There were significant differences in oculomotor characteristics of dyslexic children in comparison with those reported in typical children. Oculomotor rehabilitation intervention had a positive effect on improvement of oculomotor responses and eye movements in dyslexic children. Moreover, there was no statistically significant difference between dyslexic children and non-dyslexic children in oculomotor skills after the training. Conclusion: Our results showed the positive effects of oculomotor rehabilitation on eye movements. Primary oculomotor assessment in dyslexic children and early use of oculomotor rehabilitation combined with other treatments are highly recommended.

Selective attention and the "Asynchrony Theory" in native Hebrew-speaking adult dyslexics: Behavioral and ERPs measures

The main aim of the present study was to determine whether adult dyslexic readers demonstrate the "Asynchrony Theory" (Breznitz [Reading Fluency: Synchronization of Processes, Lawrence Erlbaum and Associates, Mahwah, NJ, USA, 2006]) when selective attention is studied. Event-related potentials (ERPs) and behavioral parameters were collected from nonimpaired readers group and dyslexic readers group performing alphabetic and nonalphabetic tasks. The dyslexic readers group was found to demonstrate asynchrony between the auditory and the visual modalities when it came to processing alphabetic stimuli. These findings were found both for behavioral and ERPs parameters. Unlike the dyslexic readers, the nonimpaired readers showed synchronized speed of processing in the auditory and the visual modalities while processing alphabetic stimuli. The current study suggests that established reading is dependent on a synchronization between the auditory and the visual modalities even when it comes to selective attention.

Defective chromatic and achromatic visual pathways in developmental dyslexia: Cues for an integrated intervention programme

PURPOSE

As well as obtaining confirmation of the magnocellular system involvement in developmental dyslexia (DD); the aim was primarily to search for a possible involvement of the parvocellular system; and, furthermore, to complete the assessment of the visual chromatic axis by also analysing the koniocellular system.

METHODS

Visual evoked potentials (VEPs) in response to achromatic stimuli with low luminance contrast and low spatial frequency, and isoluminant red/green and blue/yellow stimuli with high spatial frequency were recorded in 10 dyslexic children and 10 age- and sex-matched, healthy subjects.

RESULTS

Dyslexic children showed delayed VEPs to both achromatic stimuli (magnocellular-dorsal stream) and isoluminant red/green and blue/yellow stimuli (parvocellular-ventral and koniocellular streams). To our knowledge, this is the first time that a dysfunction of colour vision has been brought to light in an objective way (i.e., by means of electrophysiological methods) in children with DD.

CONCLUSION

These results give rise to speculation concerning the need for a putative approach for promoting both learning how to read and/or improving existing reading skills of children with or at risk of DD. The working hypothesis would be to combine two integrated interventions in a single programme aimed at fostering the function of both the magnocellular and the parvocellular streams.

Visual Illusions: An Interesting Tool to Investigate Developmental Dyslexia and Autism Spectrum Disorder

A visual illusion refers to a percept that is different in some aspect from the physical stimulus. Illusions are a powerful non-invasive tool for understanding the neurobiology of vision, telling us, indirectly, how the brain processes visual stimuli. There are some neurodevelopmental disorders characterized by visual deficits. Surprisingly, just a few studies investigated illusory perception in clinical populations. Our aim is to review the literature supporting a possible role for visual illusions in helping us understand the visual deficits in developmental dyslexia and autism spectrum disorder. Future studies could develop new tools - based on visual illusions - to identify an early risk for neurodevelopmental disorders.

Event-related Potential Patterns Reflect Reversed Hemispheric Activity during Visual Attention Processing in Children with Dyslexia: A Preliminary Study

Objective

Individuals with dyslexia experience reading difficulties, whereas their other cognitive abilities seem normal. The purpose of this study was to investigate the event-related potential (ERP) patterns of children with dyslexia during a target-detection task.

Methods

Seventeen children with dyslexia and 18 children without this disorder participated in this study. We evaluated their writing and reading ability, symptoms of attention-deficit/hyperactivity disorder, and intelligence quotient. ERPs were recorded while participants performed a target-detection task, and the peak amplitude and latency of P100 and P300 were analyzed. The lateral asymmetry index (LAI) was calculated for each ERP component.

Results

The dyslexic group exhibited longer reaction times and larger P100 amplitudes than the non-dyslexic group in the right hemisphere. The P100 latency was also significantly delayed in the right hemisphere of those in the dyslexic group compared with those in the non-dyslexic group. The P300 amplitude was larger in the right hemisphere compared with left hemisphere in the dyslexic group, whereas no interhemispheric differences were observed with respect to the P300 latency. The LAI for P100 showed a significant right hemispheric dominance, whereas the LAI for P100 was significantly correlated with the accuracy of target detection in children with dyslexia.

Conclusion

Our results suggest that right hemispheric dominance acts as an ancillary system that compensates for poor reading in children with dyslexia.

Attention dysfunction subtypes of developmental dyslexia

Background

Previous studies indicate that many different aspects of attention are impaired in children diagnosed with developmental dyslexia (DD). The objective of the present study was to identify cognitive profiles of DD on the basis of attentional test performance.

Material/Methods

78 children with DD (30 girls, 48 boys, mean age of 12 years ±8 months) and 32 age- and sex-matched non-dyslexic children (14 girls, 18 boys) were examined using a battery of standardized tests of reading, phonological and attentional processes (alertness, covert shift of attention, divided attention, inhibition, flexibility, vigilance, and visual search). Cluster analysis was used to identify subtypes of DD.

Results

Dyslexic children showed deficits in alertness, covert shift of attention, divided attention, flexibility, and visual search. Three different subtypes of DD were identified, each characterized by poorer performance on the reading, phonological awareness, and visual search tasks. Additionally, children in cluster no. 1 displayed deficits in flexibility and divided attention. In contrast to non-dyslexic children, cluster no. 2 performed poorer in tasks involving alertness, covert shift of attention, divided attention, and vigilance. Cluster no. 3 showed impaired covert shift of attention.

Conclusions

These results indicate different patterns of attentional impairments in dyslexic children. Remediation programs should address the individual child’s deficit profile.

Binocular saccade coordination in reading and visual search: a developmental study in typical reader and dyslexic children

Studies dealing with developmental aspects of binocular eye movement behavior during reading are scarce. In this study we have explored binocular strategies during reading and visual search tasks in a large population of dyslexic and typical readers. Binocular eye movements were recorded using a video-oculography system in 43 dyslexic children (aged 8-13) and in a group of 42 age-matched typical readers. The main findings are: (i) ocular motor characteristics of dyslexic children are impaired in comparison to those reported in typical children in reading task; (ii) a developmental effect exists in reading in control children, in dyslexic children the effect of development was observed only on fixation durations; and (iii) ocular motor behavior in the visual search tasks is similar for dyslexic children and for typical readers, except for the disconjugacy during and after the saccade: dyslexic children are impaired in comparison to typical children. Data reported here confirms and expands previous studies on children's reading. Both reading skills and binocular saccades coordination improve with age in typical readers. The atypical eye movement's patterns observed in dyslexic children suggest a deficiency in the visual attentional processing as well as an impairment of the ocular motor saccade and vergence systems interaction.

Dyslexia: the Role of Vision and Visual Attention

Dyslexia is more than just difficulty with translating letters into sounds. Many dyslexics have problems with clearly seeing letters and their order. These difficulties may be caused by abnormal development of their visual “magnocellular” (M) nerve cells; these mediate the ability to rapidly identify letters and their order because they control visual guidance of attention and of eye fixations. Evidence for M cell impairment has been demonstrated at all levels of the visual system: in the retina, in the lateral geniculate nucleus, in the primary visual cortex and throughout the dorsal visuomotor “where” pathway forward from the visual cortex to the posterior parietal and prefrontal cortices. This abnormality destabilises visual perception; hence, its severity in individuals correlates with their reading deficit. Treatments that facilitate M function, such as viewing text through yellow or blue filters, can greatly increase reading progress in children with visual reading problems. M weakness may be caused by genetic vulnerability, which can disturb orderly migration of cortical neurones during development or possibly reduce uptake of omega-3 fatty acids, which are usually obtained from fish oils in the diet. For example, M cell membranes require replenishment of the omega-3 docosahexaenoic acid to maintain their rapid responses. Hence, supplementing some dyslexics’ diets with DHA can greatly improve their M function and their reading.

Encoding order and developmental dyslexia: a family of skills predicting different orthographic components

We investigated order encoding in developmental dyslexia using a task that presented nonalphanumeric visual characters either simultaneously or sequentially--to tap spatial and temporal order encoding, respectively--and asked participants to reproduce their order. Dyslexic participants performed poorly in the sequential condition, but normally in the simultaneous condition, except for positions most susceptible to interference. These results are novel in demonstrating a selective difficulty with temporal order encoding in a dyslexic group. We also tested the associations between our order reconstruction tasks and: (a) lexical learning and phonological tasks; and (b) different reading and spelling tasks. Correlations were extensive when the whole group of participants was considered together. When dyslexics and controls were considered separately, different patterns of association emerged between orthographic tasks on the one side and tasks tapping order encoding, phonological processing, and written learning on the other. These results indicate that different skills support different aspects of orthographic processing and are impaired to different degrees in individuals with dyslexia. Therefore, developmental dyslexia is not caused by a single impairment, but by a family of deficits loosely related to difficulties with order. Understanding the contribution of these different deficits will be crucial to deepen our understanding of this disorder.

Reading deficits in schizophrenia and individuals at high clinical risk: relationship to sensory function, course of illness, and psychosocial outcome

OBJECTIVE

The ability to read passages of information fluently and with comprehension is a basic component of socioeconomic success. Reading ability depends on the integrity of underlying visual and auditory (phonological) systems. This study investigated the integrity of reading ability in schizophrenia relative to the integrity of underlying visual and auditory function.

METHOD

The participants were 45 schizophrenia patients, 19 clinical high-risk patients, and 65 comparison subjects. Reading was assessed using tests sensitive to visual or phonological reading dysfunction. Sensory, neuropsychological, and functional outcome measures were also obtained.

RESULTS

Schizophrenia patients displayed reading deficits that were far more severe (effect size >2.0) than would be predicted based on general neurocognitive impairments (effect size 1.0-1.4). The deficits correlated highly with both visual and auditory sensory measures, including impaired mismatch negativity generation (r=0.62, N=51, p=0.0002). Patients with established schizophrenia displayed both visual and phonological impairments, whereas high-risk patients showed isolated visual impairments. More than 70% of schizophrenia patients met criteria for acquired dyslexia, with 50% reading below eighth grade level despite intact premorbid reading ability. Reading deficits also correlated significantly (rp=0.4, N=30, p=0.03) with failure to match parental socioeconomic achievement, over and above contributions of more general cognitive impairment.

CONCLUSIONS

Patients with schizophrenia display severe deficits in reading ability that represent a potentially remediable cause of impaired socioeconomic function. Such deficits are not presently captured during routine clinical assessment. Deficits most likely develop during the years immediately surrounding illness onset and may contribute to the reduced educational and occupational achievement associated with schizophrenia.

Magnocellular-dorsal pathway and sub-lexical route in developmental dyslexia

Although developmental dyslexia (DD) is frequently associate with a phonological deficit, the underlying neurobiological cause remains undetermined. Recently, a new model, called "temporal sampling framework" (TSF), provided an innovative prospect in the DD study. TSF suggests that deficits in syllabic perception at a specific temporal frequencies are the critical basis for the poor reading performance in DD. This approach was presented as a possible neurobiological substrate of the phonological deficit of DD but the TSF can also easily be applied to the visual modality deficits. The deficit in the magnocellular-dorsal (M-D) pathway - often found in individuals with DD - fits well with a temporal oscillatory deficit specifically related to this visual pathway. This study investigated the visual M-D and parvocellular-ventral (P-V) pathways in dyslexic and in chronological age and IQ-matched normally reading children by measuring temporal (frequency doubling illusion) and static stimuli sensitivity, respectively. A specific deficit in M-D temporal oscillation was found. Importantly, the M-D deficit was selectively shown in poor phonological decoders. M-D deficit appears to be frequent because 75% of poor pseudo-word readers were at least 1 SD below the mean of the controls. Finally, a replication study by using a new group of poor phonological decoders and reading level controls suggested a crucial role of M-D deficit in DD. These results showed that a M-D deficit might impair the sub-lexical mechanisms that are critical for reading development. The possible link between these findings and TSF is discussed.

Human speech- and reading-related genes display partially overlapping expression patterns in the marmoset brain

Language is a characteristic feature of human communication. Several familial language impairments have been identified, and candidate genes for language impairments already isolated. Studies comparing expression patterns of these genes in human brain are necessary to further understanding of these genes. However, it is difficult to examine gene expression in human brain. In this study, we used a non-human primate (common marmoset; Callithrix jacchus) as a biological model of the human brain to investigate expression patterns of human speech- and reading-related genes. Expression patterns of speech disorder- (FoxP2, FoxP1, CNTNAP2, and CMIP) and dyslexia- (ROBO1, DCDC2, and KIAA0319) related genes were analyzed. We found the genes displayed overlapping expression patterns in the ocular, auditory, and motor systems. Our results enhance understanding of the molecular mechanisms underlying language impairments.

Temporal sampling in vision and the implications for dyslexia

It has recently been suggested that dyslexia may manifest as a deficit in the neural synchrony underlying language-based codes (Goswami, 2011), such that the phonological deficits apparent in dyslexia occur as a consequence of poor synchronisation of oscillatory brain signals to the sounds of language. There is compelling evidence to support this suggestion, and it provides an intriguing new development in understanding the aetiology of dyslexia. It is undeniable that dyslexia is associated with poor phonological coding, however, reading is also a visual task, and dyslexia has also been associated with poor visual coding, particularly visuo-spatial sensitivity. It has been hypothesized for some time that specific frequency oscillations underlie visual perception. Although little research has been done looking specifically at dyslexia and cortical frequency oscillations, it is possible to draw on converging evidence from visual tasks to speculate that similar deficits could occur in temporal frequency oscillations in the visual domain in dyslexia. Thus, here the plausibility of a visual correlate of the Temporal Sampling Framework is considered, leading to specific hypotheses and predictions for future research. A common underlying neural mechanism in dyslexia, may subsume qualitatively different manifestations of reading difficulty, which is consistent with the heterogeneity of the disorder, and may open the door for a new generation of exciting research.

Space representation in children with dyslexia and children without dyslexia: contribution of line bisection and circle centering tasks

Line bisection tasks (different space locations and different line lengths) and circle centering tasks (visuo-proprioceptive and proprioceptive explorations, with left or right starting positions) were used to investigate space representation in children with dyslexia and children without dyslexia. In line bisection, children with dyslexia showed a significant rightward bias for central and right-sided locations and a leftward bias for left-sided location. Furthermore, the spatial context processing was asymmetrically more efficient in the left space. In children without dyslexia, no significant bias was observed in central lines but the spatial context processing was symmetrical in both spaces. When the line length varied, no main effect was shown. These results strengthen the 'inverse pseudoneglect' hypothesis in dyslexia. In the lateral dimension of the circle centering tasks, children showed a response bias in the direction of the starting hand location for proprioceptive condition. For radial dimension, the children showed a forward bias in visuo-proprioceptive condition and more backward error in proprioceptive condition. Children with dyslexia showed a forward bias in clockwise exploration and more accurate performance in counterclockwise exploration for left starting position which may be in accordance with leftward asymmetrical spatial context processing in line bisection. These results underline the necessity to use the line bisection task with different locations as an appropriate experimental paradigm to study lateral representational bias in dyslexia. The contribution of the present results in the understanding of space representation in children with dyslexia and children without dyslexia is discussed in terms of attentional processes and neuroanatomical substrate.

Investigating the role of visual and auditory search in reading and developmental dyslexia

It has been suggested that auditory and visual sequential processing deficits contribute to phonological disorders in developmental dyslexia. As an alternative explanation to a phonological deficit as the proximal cause for reading disorders, the visual attention span hypothesis (VA Span) suggests that difficulties in processing visual elements simultaneously lead to dyslexia, regardless of the presence of a phonological disorder. In this study, we assessed whether deficits in processing simultaneously displayed visual or auditory elements is linked to dyslexia associated with a VA Span impairment. Sixteen children with developmental dyslexia and 16 age-matched skilled readers were assessed on visual and auditory search tasks. Participants were asked to detect a target presented simultaneously with 3, 9, or 15 distracters. In the visual modality, target detection was slower in the dyslexic children than in the control group on a “serial” search condition only: the intercepts (but not the slopes) of the search functions were higher in the dyslexic group than in the control group. In the auditory modality, although no group difference was observed, search performance was influenced by the number of distracters in the control group only. Within the dyslexic group, not only poor visual search (high reaction times and intercepts) but also low auditory search performance (d′) strongly correlated with poor irregular word reading accuracy. Moreover, both visual and auditory search performance was associated with the VA Span abilities of dyslexic participants but not with their phonological skills. The present data suggests that some visual mechanisms engaged in “serial” search contribute to reading and orthographic knowledge via VA Span skills regardless of phonological skills. The present results further open the question of the role of auditory simultaneous processing in reading as well as its link with VA Span skills.

Atypical balance between occipital and fronto-parietal activation for visual shape extraction in dyslexia

Reading requires the extraction of letter shapes from a complex background of text, and an impairment in visual shape extraction would cause difficulty in reading. To investigate the neural mechanisms of visual shape extraction in dyslexia, we used functional magnetic resonance imaging (fMRI) to examine brain activation while adults with or without dyslexia responded to the change of an arrow’s direction in a complex, relative to a simple, visual background. In comparison to adults with typical reading ability, adults with dyslexia exhibited opposite patterns of atypical activation: decreased activation in occipital visual areas associated with visual perception, and increased activation in frontal and parietal regions associated with visual attention. These findings indicate that dyslexia involves atypical brain organization for fundamental processes of visual shape extraction even when reading is not involved. Overengagement in higher-order association cortices, required to compensate for underengagment in lower-order visual cortices, may result in competition for top-down attentional resources helpful for fluent reading.

Developmental dyslexia and vision

Developmental dyslexia affects almost 10% of school-aged children and represents a significant public health problem. Its etiology is unknown. The consistent presence of phonological difficulties combined with an inability to manipulate language sounds and the grapheme-phoneme conversion is widely acknowledged. Numerous scientific studies have also documented the presence of eye movement anomalies and deficits of perception of low contrast, low spatial frequency, and high frequency temporal visual information in dyslexics. Anomalies of visual attention with short visual attention spans have also been demonstrated in a large number of cases. Spatial orientation is also affected in dyslexics who manifest a preference for spatial attention to the right. This asymmetry may be so pronounced that it leads to a veritable neglect of space on the left side. The evaluation of treatments proposed to dyslexics whether speech or oriented towards the visual anomalies remains fragmentary. The advent of new explanatory theories, notably cerebellar, magnocellular, or proprioceptive, is an incentive for ophthalmologists to enter the world of multimodal cognition given the importance of the eye's visual input.

Visual search deficits are independent of magnocellular deficits in dyslexia

The aim of this study was to investigate the theory that visual magnocellular deficits seen in groups with dyslexia are linked to reading via the mechanisms of visual attention. Visual attention was measured with a serial search task and magnocellular function with a coherent motion task. A large group of children with dyslexia (n = 70) had slower serial search times than a control group of typical readers. However, the effect size was small (η(p)(2)  = 0.05) indicating considerable overlap between the groups. When the dyslexia sample was split into those with or without a magnocellular deficit, there was no difference in visual search reaction time between either group and controls. The data suggest that magnocellular sensitivity and visual spatial attention weaknesses are independent of one another. They also provide more evidence of heterogeneity in response to psychophysical tasks in groups with dyslexia. Alternative explanations for poor performance on visual attention tasks are proposed along with avenues for future research.

The influence of contrast on coherent motion processing in dyslexia

The aim of the experiments was to investigate how manipulating the contrast of the signal and noise dots in a random dot kinematogram (RDK), influenced on motion coherence thresholds in adults with dyslexia. In the first of two experiments, coherent motion thresholds were measured when the contrasts of the signal and noise dots in an RDK were manipulated. A significantly greater processing benefit was found for the group with dyslexia than a control group when the signal dots were of higher contrast than the noise dots. However, a significant processing disadvantage was found for the group with dyslexia relative to the control group when the signal dots were of lower contrast than the noise dots. These findings were interpreted as supporting evidence for the noise exclusion hypothesis of dyslexia. In Experiment 2, the effect on coherent motion thresholds of presenting a cue that alerted observers to which stimuli, high or low contrast contained the signals dots was investigated. When the cue directed attention to low contrast signal dots presented in high contrast noise, coherent motion thresholds were only enhanced for the group with dyslexia. This manipulation produced equivalent coherent motion thresholds in the reader groups. In other conditions, the group with dyslexia had significantly higher coherent motion thresholds than the control group. It was concluded that adults with dyslexia who show evidence of a coherent motion deficit (37% of the dyslexia group in each experiment), have a specific difficulty in noise exclusion. This appears to occur as consequence of a sensory processing deficit in the magnocellular or dorsal stream.

Immaturity of the oculomotor saccade and vergence interaction in dyslexic children: evidence from a reading and visual search study

Studies comparing binocular eye movements during reading and visual search in dyslexic children are, at our knowledge, inexistent. In the present study we examined ocular motor characteristics in dyslexic children versus two groups of non dyslexic children with chronological/reading age-matched. Binocular eye movements were recorded by an infrared system (mobileEBT®, e(ye)BRAIN) in twelve dyslexic children (mean age 11 years old) and a group of chronological age-matched (N = 9) and reading age-matched (N = 10) non dyslexic children. Two visual tasks were used: text reading and visual search. Independently of the task, the ocular motor behavior in dyslexic children is similar to those reported in reading age-matched non dyslexic children: many and longer fixations as well as poor quality of binocular coordination during and after the saccades. In contrast, chronological age-matched non dyslexic children showed a small number of fixations and short duration of fixations in reading task with respect to visual search task; furthermore their saccades were well yoked in both tasks. The atypical eye movement's patterns observed in dyslexic children suggest a deficiency in the visual attentional processing as well as an immaturity of the ocular motor saccade and vergence systems interaction.

Dorsal stream involvement in recognition of objects with transient onset but not with ramped onset

Background

Although the ventral visual stream is understood to be responsible for object recognition, it has been proposed that the dorsal stream may contribute to object recognition by rapidly activating parietal attention mechanisms, prior to ventral stream object processing.

Methods

To investigate the relative contribution of the dorsal visual stream to object recognition a group of tertiary students were divided into good and poor motion coherence groups and assessed on tasks classically assumed to rely on ventral stream processing. Participants were required to identify simple line drawings in two tasks, one where objects were presented abruptly for 50 ms followed by a white-noise mask, the other where contrast was linearly ramped on and off over 325 ms and replaced with a mask.

Results

Although both groups only differed in motion coherence performance (a dorsal stream measure), the good motion coherence group showed superior contrast sensitivity for object recognition on the abrupt, but not the ramped presentation tasks.

Conclusions

We propose that abrupt presentation of objects activated attention mechanisms fed by the dorsal stream, whereas the ramped presentation had reduced transience and thus did not activate dorsal attention mechanisms as well. The results suggest that rapid dorsal stream activation may be required to assist with ventral stream object processing.