Relationships between global motion and global form processing, practice, cognitive and visual processing in adults with dyslexia or visual discomfort

Visual processing and decision-making in autism and dyslexia: Insights from cross-syndrome approaches

Atypical visual processing has been reported in developmental conditions like autism and dyslexia, and some accounts propose a causal role for visual processing in the development of these conditions. However, few studies make direct comparisons between conditions, or use sufficiently sensitive methods, meaning that it is hard to say whether atypical visual processing tells us anything specific about these conditions, or whether it reflects a more general marker of atypical development. Here I review findings from two computational modelling approaches (equivalent noise and diffusion modelling) and related electroencephalography (EEG) indices which we have applied to data from autistic, dyslexic and typically developing children to reveal how the component processes involved in visual processing and decision-making are altered in autism and dyslexia. The results identify both areas of convergence and divergence in autistic and dyslexic children's visual processing and decision-making, with implications for influential theoretical accounts such as weak central coherence, increased internal noise, and dorsal-stream vulnerability. In both sets of studies, we also see considerable variability across children in all three groups. To better understand this variability, and further understand the convergence and divergence identified between conditions, future studies would benefit from studying how the component processes reviewed here relate to transdiagnostic dimensions, which will also give insights into individual differences in visual processing and decision-making more generally.

Integration of visual motion and orientation signals in dyslexic children: an equivalent noise approach

Dyslexic individuals have been reported to have reduced global motion sensitivity, which could be attributed to various causes including atypical magnocellular or dorsal stream function, impaired spatial integration, increased internal noise and/or reduced external noise exclusion. Here, we applied an equivalent noise experimental paradigm alongside a traditional motion-coherence task to determine what limits global motion processing in dyslexia. We also presented static analogues of the motion tasks (orientation tasks) to investigate whether perceptual differences in dyslexia were restricted to motion processing. We compared the performance of 48 dyslexic and 48 typically developing children aged 8 to 14 years in these tasks and used equivalent noise modelling to estimate levels of internal noise (the precision associated with estimating each element's direction/orientation) and sampling (the effective number of samples integrated to judge the overall direction/orientation). While group differences were subtle, dyslexic children had significantly higher internal noise estimates for motion discrimination, and higher orientation-coherence thresholds, than typical children. Thus, while perceptual differences in dyslexia do not appear to be restricted to motion tasks, motion and orientation processing seem to be affected differently. The pattern of results also differs from that previously reported in autistic children, suggesting perceptual processing differences are condition-specific.

Reduced 2D form coherence and 3D structure from motion sensitivity in developmental dyscalculia

Developmental dyscalculia (DD) is a specific learning disability affecting the development of numerical and arithmetical skills. The origin of DD is typically attributed to the suboptimal functioning of key regions within the dorsal visual stream (parietal cortex) which support numerical cognition. While DD individuals are often impaired in visual numerosity perception, the extent to which they also show a wider range of visual dysfunctions is poorly documented. In the current study we measured sensitivity to global motion (translational and flow), 2D static form (Glass patterns) and 3D structure from motion in adults with DD and control subjects. While sensitivity to global motion was comparable across groups, thresholds for static form and structure from motion were higher in the DD compared to the control group, irrespective of associated reading impairments. Glass pattern sensitivity predicted numerical abilities, and this relation could not be explained by recently reported differences in visual crowding. Since global form sensitivity has often been considered an index of ventral stream function, our findings could indicate a cortical dysfunction extending beyond the dorsal visual stream. Alternatively, they would fit with a role of parietal cortex in form perception under challenging conditions requiring multiple element integration.

Dorsal and Ventral Stream Function in Children With Developmental Coordination Disorder

Dorsal stream cortical networks underpin a cluster of visuomotor, visuospatial, and visual attention functions. Sensitivity to global coherence of motion and static form is considered a signature of visual cortical processing in the dorsal stream (motion) relative to the ventral stream (form). Poorer sensitivity to global motion compared to global static form has been found across a diverse range of neurodevelopmental disorders, suggesting a “dorsal stream vulnerability.” However, previous studies of global coherence sensitivity in Developmental Coordination Disorder (DCD) have shown conflicting findings. We examined two groups totalling 102 children with DCD (age 5–12 years), using the “Ball in the Grass” psychophysical test to compare sensitivity to global motion and global static form. Motor impairment was measured using the Movement-ABC (M-ABC). Global coherence sensitivity was compared with a typically developing control group (N = 69) in the same age range. Children with DCD showed impaired sensitivity to global motion (p = 0.002), but not global form (p = 0.695), compared to controls. Within the DCD group, motor impairment showed a significant linear relationship with global form sensitivity (p < 0.001). There was also a significant quadratic relationship between motor impairment and global motion sensitivity (p = 0.046), where poorer global motion sensitivity was only apparent with greater motor impairment. We suggest that two distinct visually related components, associated with global form and global motion sensitivity, contribute to DCD differentially over the range of severity of the disorder. Possible neural circuitry underlying these relationships is discussed.

Visual Dysfunction in Chinese Children With Developmental Dyslexia: Magnocellular-Dorsal Pathway Deficit or Noise Exclusion Deficit?

Many studies have suggested that children with developmental dyslexia (DD) not only show phonological deficit but also have difficulties in visual processing, especially in non-alphabetic languages such as Chinese. However, mechanisms underlying this impairment in vision are still unclear. Visual magnocellular deficit theory suggests that the difficulties in the visual processing of dyslexia are caused by the dysfunction of the magnocellular system. However, some researchers have pointed out that previous studies supporting the magnocellular theory did not control for the role of “noise”. The visual processing difficulties of dyslexia might be related to the noise exclusion deficit. The present study aims to examine these two possible explanations via two experiments. In experiment 1, we recruited 26 Chinese children with DD and 26 chronological age–matched controls (CA) from grades 3 to 5. We compared the Gabor contrast sensitivity between the two groups in high-noise and low-noise conditions. Results showed a significant between-group difference in contrast sensitivity in only the high-noise condition. In experiment 2, we recruited another 29 DD and 29 CA and compared the coherent motion/form sensitivity in the high- and low-noise conditions. Results also showed that DD exhibited lower coherent motion and form sensitivities than CA in the high-noise condition, whereas no evidence was observed that the group difference was significant in the low-noise condition. These results suggest that Chinese children with dyslexia have noise exclusion deficit, supporting the noise exclusion hypothesis. The present study provides evidence for revealing the visual dysfunction of dyslexia from the Chinese perspective. The nature of the perceptual noise exclusion and the relationship between the two theoretical hypotheses are discussed.

Beyond the global motion deficit hypothesis of developmental dyslexia: A cross-sectional study of visual, cognitive, and socio-economic factors influencing reading ability in children

Although primarily conceptualized as a disorder of phonological awareness, developmental dyslexia is often associated with broader problems perceiving and attending to transient or rapidly-moving visual stimuli. However, the extent to which such visual deficits represent the cause or the consequence of dyslexia remains contentious, and very little research has examined the relative contributions of phonological, visual, and other variables to reading performance more broadly. We measured visual sensitivity to global motion (GM) and global form (GF), performance on various language and other cognitive tasks believed to be compromised in dyslexia (phonological awareness, processing speed, and working memory), together with a range of social and demographic variables often omitted in previous research, such as age, gender, non-verbal intelligence, and socio-economic status in an unselected sample (n = 132) of children aged 6-11.5 yrs from two different primary schools in Edinburgh, UK. We found that: (i) Mean GM sensitivity (but not GF) was significantly lower in poor readers (medium effect size); (ii) GM sensitivity accounted for only 3% of the variance in reading scores; (iii) GM sensitivity deficits were observed in only 16% of poor readers; (iv) the best predictors of reading performance were phonological awareness, non-verbal intelligence, and socio-economic status, suggesting the importance of controlling for these in future studies of vision and reading. These findings suggest that developmental dyslexia is unlikely to represent a single category of neurodevelopmental disorder underpinned by lower-level deficits in visual motion processing.

Visual form perception is fundamental for both reading comprehension and arithmetic computation

Visual perception has been found to be a critical factor for reading comprehension and arithmetic computation in separate lines of research with different measures of visual form perception. The current study of 1099 Chinese elementary school students investigated whether the same visual form perception (assessed by a geometric figure matching task) underlies both reading comprehension and arithmetic computation. The results showed that visual form perception had close relations with both reading comprehension and arithmetic computation, even after controlling for age, gender, and cognitive factors such as processing speed, attention, working memory, visuo-spatial processing, and general intelligence. Results also showed that numerosity comparison's relations with reading comprehension and arithmetic computation were fully accounted for by visual form perception. These results suggest that reading comprehension and arithmetic computation might share a similar visual form processing mechanism.

Magnocellular Based Visual Motion Training Improves Reading in Persian

The visual magnocellular system is thought to play a crucial role in learning to read. Here therefore, we examined whether magnocellular based training could improve reading in children with visual reading problems. The participants were 24 male primary school students aged between 9–11 (Mean = 9.76, SD = 0.59) with specific reading difficulty. Experimental and control groups were matched for age, sex, educational level, IQ, reading abilities (measured by APRA), magnocellular performance as assessed by a random dot kinematogram (RDK) paradigm and recordings of their saccadic eye movements. The experimental group received twelve magnocellular based visual motion training sessions, twice a week over 6 weeks. During the same period, the control group played a video game with the help of a practitioner. All measures were made just prior to the training and were repeated at the 6^th, 12^th training session and one month later. The experimental group showed significant improvements in magnocellular function, visual errors and reading accuracy during the course of intervention. Follow-up assessment confirmed that these effects persisted one month later. Impaired magnocellular functioning appeared to be an important cause of poor reading in Persian. Hence magnocellular based training could help many children with specific reading difficulties. Also testing magnocellular function could be used as screening tool for detecting dyslexia before a child begins to fail at school.

Dyslexia and dyscalculia are characterized by common visual perception deficits

A number of studies have investigated the cognitive deficits underlying dyslexia and dyscalculia. Yet, it remains unclear as to whether dyslexia and dyscalculia are associated with the common visual perception deficits. The current investigation analyzed cognitive performance in children with dyslexia, dyscalculia, comorbidity, and typically developing subjects. The results showed that children with dyslexia, dyscalculia and comorbidity exhibited common deficits in numerosity processing and visual perception. Furthermore, visual perception deficits accounted for deficits in numerosity processing in all three groups. The results suggest that visual perception deficits are a common cognitive deficit underlying both developmental dyslexia and dyscalculia.

Practice makes the deficiency of global motion detection in people with pattern-related visual stress more apparent

Aims

Pattern-related visual stress (PRVS) refers to the perceptual difficulties experienced by some individuals when exposed to high contrast striped patterns. People with PRVS were reported to have reduced sensitivity to global motion at baseline testing and the difference disappears at a second estimate. The present study was to investigate the effect of practice on global motion threshold in adults with and without PRVS.

Methods

A total of 101 subjects were recruited and the Wilkins & Evans Pattern Glare Test was used to determine if a subject had PRVS. The threshold to detect global motion was measured with a random dot kinematogram. Each subject was measured 5 times at the first visit and again a month later. Receiver operating characteristic (ROC) curve analysis was applied to show the agreement between the two tests.

Results

Twenty-nine subjects were classified as having PRVS and 72 were classified as normal. At baseline, the threshold to detect global motion was significantly higher in subjects with PRVS (0.832 ± 0.098 vs. 0.618 ± 0.228, p < 0.001). After 5 sessions, the difference between the normal and subjects with PRVS increased (0.767 ± 0.170 vs. 0.291 ± 0.149, p < 0.001). In ROC analysis, the area under the curve (AUC) improved from 0.792 at baseline to 0.964 at the fifth session. After a one-month break, the difference between normal and subjects with PRVS was still significant (0.843 ± 0.169 vs. 0.407 ± 0.216, p < 0.001) and the AUC was 0.875.

Conclusion

The ability to detect global motion is impaired in persons with PRVS and the difference increased after additional sessions of practice.

Development of the Japanese version of the Visual Discomfort Scale

BACKGROUND

Visual stimuli, such as stripes and texts, can induce "visual discomfort" including perceptual and somatic symptoms. Individuals reporting high levels of visual discomfort might experience migraine headache and may have reduced reading efficiency due to visual perceptual difficulties. This study aimed to develop and validate the Japanese version of the Visual Discomfort Scale, which measures proneness to visual discomfort.

METHODS AND RESULTS

In Survey 1, 428 adults completed the Japanese version and a questionnaire assessing migraine morbidity. Rasch analysis revealed that the Japanese version is a unidimensional scale with a high amount of unexplained variance due to random noise rather than another dimension, and has high person and item reliabilities. Participants with migraine exhibited high scores in the Japanese version, indicating the construct validity of the scale. Survey 2 with 118 adults revealed a strong test-retest correlation for the Japanese version, indicating the stability of the scale.

CONCLUSION

The Japanese version of the Visual Discomfort Scale is a sufficiently reliable and valid scale for assessing visual discomfort, although its unidimensionality leaves room for further improvements.

New insights into the role of motion and form vision in neurodevelopmental disorders

A selective deficit in processing the global (overall) motion, but not form, of spatially extensive objects in the visual scene is frequently associated with several neurodevelopmental disorders, including preterm birth. Existing theories that proposed to explain the origin of this visual impairment are, however, challenged by recent research. In this review, we explore alternative hypotheses for why deficits in the processing of global motion, relative to global form, might arise. We describe recent evidence that has utilised novel tasks of global motion and global form to elucidate the underlying nature of the visual deficit reported in different neurodevelopmental disorders. We also examine the role of IQ and how the sex of an individual can influence performance on these tasks, as these are factors that are associated with performance on global motion tasks, but have not been systematically controlled for in previous studies exploring visual processing in clinical populations. Finally, we suggest that a new theoretical framework is needed for visual processing in neurodevelopmental disorders and present recommendations for future research.

Evaluation of visual stress symptoms in age-matched dyslexic, Meares-Irlen syndrome and normal adults

AIM

To examine the prevalence of dyslexia and Meares-Irlen syndrome (MIS) among female students and determine their level of visual stress in comparison with normal subjects.

METHODS

A random sample of 450 female medical students of King Saud University Riyadh (age range, 18-30y) responded to a wide range of questions designed to accomplish the aims of this study. The detailed questionnaire consisted of 54 questions with 12 questions enquiring on ocular history and demography of participants while 42 questions were on visual symptoms. Items were categorized into critical and non-critical questions (CQ and NCQ) and were rated on four point Likert scale. Based on the responses obtained, the subjects were grouped into normal (control), dyslexic with or without MIS (Group 1) and subjects with MIS only (Group 2). Responses were analysed as averages and mean scores were calculated and compared between groups using one way analysis of variance to evaluate total visual stress score (TVSS=NCQ+CQ), critical and non-critical visual stress scores. The relationship between categorical variables such as age, handedness and condition were assessed with Chi-square test.

RESULTS

The completion rate was 97.6% and majority of the respondents (92%) were normal readers, 2% dyslexic and 6% had MIS. They were age-matched. More than half of the participants had visited an eye care practitioner in the last 2y. About 13% were recommended eye exercises and one participant experienced pattern glare. Hand preference was not associated with any condition but Group 1 subjects (3/9, 33%) were significantly more likely to be diagnosed of lazy eye than Group 2 (2/27, 7%) and control (27/414, 7%) subjects. The mean±SD of TVSS responses were 63±14 and it was 44±9 for CQ and 19±5 for NCQ. Responses from all three variables were normally distributed but the CQ responses were on the average more positive (82%) in Group 2 and less positive (46%) in Group 1 than control. With NCQ, the responses were equally less positive in Group 1 and 2 than control. Group 2 subjects showed significantly higher TVSS (P=0.002), NCQ (P=0.006) and CQ (P=0.008) visual stress scores than control but no difference between Group 1 and control subjects, was observed for all scores (P>0.05, for all comparisons).

CONCLUSION

The prevalence of dyslexia and MIS among Saudi female students was 2% and 6%, respectively. Critical questions performed best for assessing visual stress symptoms in dyslexic and MIS subjects. Generally, students with MIS were more sensitive to visual stress than normal students but dyslexics were more likely to present with a lazy eye than MIS and normal readers.

The effect of magnocellular-based visual-motor intervention on Chinese children with developmental dyslexia

Magnocellular (M) deficit theory points out that the core deficit of developmental dyslexia (DD) is the impairment in M pathway, which has been evidenced in many previous studies. Based on the M deficit, some researchers found that visual intervention focusing on M deficit improved dyslexics’ M function as well as reading abilities. However, the number and reliability of these training studies were limited. Therefore, the present study conducted an M-based visual-motor intervention on Chinese children with DD to investigate the relationship between M deficit and Chinese DD. Intervention programs included coherent motion detection, visual search, visual tracking, and juggling, which were related to M function. The results showed that M function and phonological awareness of training dyslexic group were improved to a normal level as age-matched normal children after intervention, while non-training dyslexics did not. It supported M deficit theory, and suggested M deficit might be the core deficit of Chinese DD.

Visual Development and Neuropsychological Profile in Preterm Children from 6 Months to School Age

The aim of this semilongitudinal study was to investigate the development of central visual pathways in children born preterm but without major neurologic impairments and to establish their cognitive and behavioral profile at school age. Ten children born preterm were assessed at 6 months and at school age, using visual evoked potentials at both time points and cognitive and behavioral tests at school age. We also tested 10 age-matched children born full-term. At 6 months' corrected age, we found no significant differences between preterm and full-term groups for either amplitude or latency of N1 and P1 components. At school age, the preterm group manifested significantly higher N1 amplitudes and tended to show higher P1 amplitudes than the full-term group. We found no significant differences in cognitive and behavioral measures at school age. These results suggest that preterm birth affects visual pathways development, yet the children born preterm did not manifest cognitive problems.

Efficacy of a perceptual and visual-motor skill intervention program for students with dyslexia

PURPOSE

To verify the efficacy of a perceptual and visual-motor skill intervention program for students with dyslexia.

METHODS

The participants were 20 students from third to fifth grade of a public elementary school in Marília, São Paulo, aged from 8 years to 11 years and 11 months, distributed into the following groups: Group I (GI; 10 students with developmental dyslexia) and Group II (GII; 10 students with good academic performance). A perceptual and visual-motor intervention program was applied, which comprised exercises for visual-motor coordination, visual discrimination, visual memory, visual-spatial relationship, shape constancy, sequential memory, visual figure-ground coordination, and visual closure. In pre- and post-testing situations, both groups were submitted to the Test of Visual-Perceptual Skills (TVPS-3), and the quality of handwriting was analyzed using the Dysgraphia Scale.

RESULTS

The analyzed statistical results showed that both groups of students had dysgraphia in pretesting situation. In visual perceptual skills, GI presented a lower performance compared to GII, as well as in the quality of writing. After undergoing the intervention program, GI increased the average of correct answers in TVPS-3 and improved the quality of handwriting.

CONCLUSION

The developed intervention program proved appropriate for being applied to students with dyslexia, and showed positive effects because it provided improved visual perception skills and quality of writing for students with developmental dyslexia.

The need to differentiate the magnocellular system from the dorsal stream in connection with dyslexia

A number of authors have postulated a "magnocellular-dorsal stream" deficit in dyslexia. Combining the magnocellular system and the dorsal stream into a single entity in this context faces the problem that contrast sensitivity data do not point to a magnocellular deficiency linked to dyslexia, while, on the other hand, motion perception data are largely consistent with a dorsal stream dysfunction. Thus, there are data both for and against a "magnocellular-dorsal stream" deficit in connection with dyslexia. It is here pointed out that this inconsistency is abolished once it is recognized that the magnocellular system and the dorsal stream are separate entities.

The visual magnocellular-dorsal dysfunction in Chinese children with developmental dyslexia impedes Chinese character recognition

The visual magnocellular-dorsal (M-D) deficit theory of developmental dyslexia (DD) is still highly debated. Many researchers have made great efforts to investigate the relationship between M-D dysfunction and reading disability. Given that visual analysis plays an important role in Chinese reading, the present study tried to examine how the M-D dysfunction affected Chinese character recognition in Chinese children with DD. Sixteen DD children with M-D deficit, fifteen DD children with normal M-D function and twenty-seven age-matched typically developing children participated in this study. A global/local decision task was adopted, in which we manipulated the spatial frequency of target characters to separate an M-D condition from an unfiltered condition. Results of reaction times and error rates showed that in the M-D condition both M-D normal dyslexics and controls exhibited a significant global precedence effect, with faster responses and lower error rates in global decision than in local decision. In contrast, this global advantage was absent for the M-D impaired dyslexics. Accordingly, we propose that the M-D impairment present in some but not all dyslexics might influence global recognition of Chinese characters in this subgroup of children with DD, which might be implicated in their difficulties in learning to read.

The visual magnocellular deficit in Chinese-speaking children with developmental dyslexia

Many alphabetic studies have evidenced that individuals with developmental dyslexia (DD) have deficits in visual magnocellular (M) pathway. However, there are few studies to investigate the M function of Chinese DD. Chinese is a logographic language, and Chinese characters are complicated in structure. Visual skills and orthographic processing abilities are particularly important for efficient reading in Chinese as compared to alphabetic languages. Therefore, it is necessary to investigate the visual M function of Chinese DD and whether the M function was associated with orthographic skills. In the present study, 26 dyslexic children (mean age: 10.03 years) and 27 age-matched normal children (mean age: 10.37 years) took part in a coherent motion (CM) detection task and an orthographic awareness test. The results showed that dyslexic children had a significantly higher threshold than age-matched children in CM detection task. Meanwhile, children with DD responded more slowly in orthographic awareness test, although the group difference was marginally significant. The results suggested that Chinese dyslexics had deficits both in visual M pathway processing and orthographic processing. In order to investigate the relationship between M function and orthographic skills, we made a correlation analysis between CM threshold and orthographic awareness by merging performance of dyslexic children and age-matched children. The results revealed that CM thresholds were positively correlated with reaction times in orthographic awareness test, suggesting that better M function was related to better orthographic processing skills.

Why do adults with dyslexia have poor global motion sensitivity?

Two experiments aimed to determine why adults with dyslexia have higher global motion thresholds than typically reading controls. In Experiment 1, the dot density and number of animation frames presented in the dot stimulus were manipulated because of findings that use of a high dot density can normalize coherence thresholds in individuals with dyslexia. Dot densities were 14.15 and 3.54 dots/deg². These were presented for five (84 ms) or eight (134 ms) frames. The dyslexia group had higher coherence thresholds in all conditions than controls. However, in the high dot density, long duration condition, both reader groups had the lowest thresholds indicating normal temporal recruitment. These results indicated that the dyslexia group could sample the additional signals dots over space and then integrate these with the same efficiency as controls. In Experiment 2, we determined whether briefly presenting a fully coherent prime moving in either the same or opposite direction of motion to a partially coherent test stimulus would systematically increase and decrease global motion thresholds in the reader groups. When the direction of motion in the prime and test was the same, global motion thresholds increased for both reader groups. The increase in coherence thresholds was significantly greater for the dyslexia group. When the motion of the prime and test were presented in opposite directions, coherence thresholds were reduced in both groups. No group threshold differences were found. We concluded that the global motion processing deficit found in adults with dyslexia can be explained by undersampling of the target motion signals. This might occur because of difficulties directing attention to the relevant motion signals in the random dot pattern, and not a specific difficulty integrating global motion signals. These effects are most likely to occur in the group with dyslexia when more complex computational processes are required to process global motion.

The effect of spectral filters on reading speed and accuracy following stroke

Purpose

The aim of the study was to determine the effect of optimal spectral filters on reading performance following stroke.

Methods

Seventeen stroke subjects, aged 43–85, were considered with an age-matched Control Group (n = 17). Subjects undertook the Wilkins Rate of Reading Test on three occasions: (i) using an optimally selected spectral filter; (ii) subjects were randomly assigned to two groups: Group 1 used an optimal filter, whereas Group 2 used a grey filter, for two-weeks. The grey filter had similar photopic reflectance to the optimal filters, intended as a surrogate for a placebo; (iii) the groups were crossed over with Group 1 using a grey filter and Group 2 given an optimal filter, for two weeks, before undertaking the task once more. An increase in reading speed of >5% was considered clinically relevant.

Results

Initial use of a spectral filter in the stroke cohort, increased reading speed by ∼8%, almost halving error scores, findings not replicated in controls. Prolonged use of an optimal spectral filter increased reading speed by >9% for stroke subjects; errors more than halved. When the same subjects switched to using a grey filter, reading speed reduced by ∼4%. A second group of stroke subjects used a grey filter first; reading speed decreased by ∼3% but increased by ∼4% with an optimal filter, with error scores almost halving.

Conclusions

The present study has shown that spectral filters can immediately improve reading speed and accuracy following stroke, whereas prolonged use does not increase these benefits significantly.

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.

Dynamic visual perception and reading development in Chinese school children

The development of reading skills may depend to a certain extent on the development of basic visual perception. The magnocellular theory of developmental dyslexia assumes that deficits in the magnocellular pathway, indicated by less sensitivity in perceiving dynamic sensory stimuli, are responsible for a proportion of reading difficulties experienced by dyslexics. Using a task that measures coherent motion detection threshold, this study examined the relationship between dynamic visual perception and reading development in Chinese children. Experiment 1 compared the performance of 27 dyslexics and their age- and IQ-matched controls in the coherent motion detection task and in a static pattern perception task. Results showed that only in the former task did the dyslexics have a significantly higher threshold than the controls, suggesting that Chinese dyslexics, like some of their Western counterparts, may have deficits in magnocellular pathway. Experiment 2 examined whether dynamic visual processing affects specific cognitive processes in reading. One hundred fifth-grade children were tested on visual perception and reading-related tasks. Regression analyses found that the motion detection threshold accounted for 11% and 12%, respectively, variance in the speed of orthographic similarity judgment and in the accuracy of picture naming after IQ and vocabulary size were controlled. The static pattern detection threshold could not account for any variance. It is concluded that reading development in Chinese depends to a certain extent on the development of dynamic visual perception and its underlying neural pathway and that the impact of visual development can be specifically related to orthographic processing in reading Chinese.

Does a sensory processing deficit explain counting accuracy on rapid visual sequencing tasks in adults with and without dyslexia?

The experiments conducted aimed to investigate whether reduced accuracy when counting stimuli presented in rapid temporal sequence in adults with dyslexia could be explained by a sensory processing deficit, a general slowing in processing speed or difficulties shifting attention between stimuli. To achieve these aims, the influence of the inter-stimulus interval (ISI), stimulus duration, and sequence length were evaluated in two experiments. In the first that used skilled readers only, significantly more errors were found with presentation of long sequences when the ISI or stimulus durations were short. Experiment 2 used a wider range of ISIs and stimulus durations. Compared to skilled readers, a group with dyslexia had reduced accuracy on two-stimulus sequences when the ISI was short, but not when the ISI was long. Although reduced accuracy was found on all short and long sequences by the group with dyslexia, when performance on two-stimulus sequences was used as an index of sensory processing efficiency and controlled, group differences were found with presentation of stimuli of short duration only. We concluded that continuous, repetitive stimulation to the same visual area can produce a capacity limitation on rapid counting tasks in all readers when the ISIs or stimulus durations are short. While reduced accuracy on rapid sequential counting tasks can be explained by a sensory processing deficit when the stimulus duration is long, slower processing speed in the group with dyslexia explains the greater inaccuracy found as sequence length is increased when the stimulus duration is short.

Coherence motion perception in developmental dyslexia: a meta-analysis of behavioral studies

The magnitude of the association between developmental dyslexia (DD) and motion sensitivity is evaluated in 35 studies, which investigated coherence motion perception in DD. A first analysis is conducted on the differences between DD groups and age-matched control (C) groups. In a second analysis, the relationship between motion coherence threshold and reading ability is considered. Globally, the mean effect size (ES) is moderate (d = 0.675, 2334 subjects) with a large value (d = 0.747) for the between-groups differences in motion perception and a smaller mean ES (d = 0.178) for the correlational studies. The influence on ES of the stimuli parameters and subjects age is analyzed. The number of dots, the age of the subjects, and the type of analysis (i.e. between-group or correlational) are significantly related to the ES. Looking at the ES values, a smaller number of dots constituting the stimuli are associated with larger ES and, interestingly, the children studies are associated with lower ES in comparison with the researches evaluating adults. The large ES value supports the importance of studying motion perception deficits in DD groups, consistently with the claim that dorsal impairment/noise-exclusion deficit could be one of the risk factor of reading difficulties.

Função motora fina de escolares com dislexia, distúrbio e dificuldades de aprendizagem

TEMA: função motora fina em escolares com dislexia, distúrbio e dificuldades de aprendizagem. OBJETIVO: este estudo teve por objetivo caracterizar o desempenho da função motora fina, sensorial e perceptiva em escolares com dislexia, distúrbio e dificuldades de aprendizagem e correlacionar estes achados à escrita destes escolares. MÉTODO: participaram deste estudo 80 escolares da 2ª à 4ª série do ensino fundamental, na faixa etária de 7 a 12 anos de idade, de ambos os gêneros, distribuídos em: GI: formado por 20 escolares com dislexia, GII: formado por 20 escolares com distúrbio de aprendizagem, GIII: formado por 20 escolares com dificuldades de aprendizagem e GIV: formado por 20 escolares sem dificuldades de aprendizagem. Os escolares foram submetidos à avaliação da função motora fina, sensorial e perceptiva e análise da escrita por meio da escala de disgrafia. RESULTADOS: os resultados evidenciaram que a maioria dos grupos apresentou desempenho inferior nas provas de FMF7 (oposição de dedos), S8 (grafoestesia) e P1 (imitar posturas). Os GI e GII foram os grupos que apresentaram desempenho inferior na maioria das provas em relação aos GIII e GIV. Quanto à grafia, observou-se que no GII todos os escolares são disgráficos. CONCLUSÃO: a presença de alterações motora fina, sensorial e perceptiva é característica de escolares com distúrbio de aprendizagem e dislexia, entretanto esta característica pode ou não ser encontrada nos escolares com dificuldades de aprendizagem, sendo, portanto, esta alteração responsável pelo comportamento disgráfico dos escolares com transtornos de aprendizagem deste estudo.

A survey of visual function in an Austrian population of school-age children with reading and writing difficulties

Background

To describe and compare visual function measures of two groups of school age children (6-14 years of age) attending a specialist eyecare practice in Austria; one group referred to the practice from educational assessment centres diagnosed with reading and writing difficulties and the other, a clinical age-matched control group.

Methods

Retrospective clinical data from one group of subjects with reading difficulties (n = 825) and a clinical control group of subjects (n = 328) were examined.

Statistical analysis was performed to determine whether any differences existed between visual function measures from each group (refractive error, visual acuity, binocular status, accommodative function and reading speed and accuracy).

Results

Statistical analysis using one way ANOVA demonstrated no differences between the two groups in terms of refractive error and the size or direction of heterophoria at distance (p > 0.05). Using predominately one way ANOVA and chi-square analyses, those subjects in the referred group were statistically more likely to have poorer distance visual acuity, an exophoric deviation at near, a lower amplitude of accommodation, reduced accommodative facility, reduced vergence facility, a reduced near point of convergence, a lower AC/A ratio and a slower reading speed than those in the clinical control group (p < 0.05).

Conclusions

This study highlights the high proportions of visual function anomalies in a group of children with reading difficulties in an Austrian population. It confirms the importance of a full assessment of binocular visual status in order to detect and remedy these deficits in order to prevent the visual problems continuing to impact upon educational development.