Cause Of Dyslexia Research Articles

What causes dyslexia? Identifying the causes and effective compensatory therapy.

BackgroundChildren are diagnosed as dyslexic when their reading performance is much below that which could be expected for their educational level and cannot be explained by a sensory, neurological or psychiatric deficit or by a low IQ. Although poor reading is a major obstacle to school and career achievement, the causes of dyslexia are unclear and traditional therapies are often unsuccessful. To determine the causes of dyslexia, experiments must demonstrate under which conditions a reading disorder occurs and whether the reading performance improves if these conditions are abolished or compensated. To avoid irreproducible results, experiments must be repeated and the effect size must be calculated.ObjectivesThe aims of the study were to investigate the rate and location of misread letters within pseudowords, prove the effectiveness of compensatory reading therapy and demonstrate the reproducibility of the experimental results. The influence of reading therapy on the rate of eye movements opposite to the reading direction was investigated and causes of a poor reading performance were identified.MethodsThe rate and location of misread letters were investigated by tachystoscopic presentation of pseudowords containing between three and six letters. Presentation time, fixation time, and the time it takes to begin pronouncing the words (speech onset latency) were changed until 95% of the pseudowords were recognized correctly. On the basis of these results, the children learned a reading strategy that compensated the causes of the reading disorder. The therapy was demonstrated to be highly effective and it was shown that the results of the therapy were reproducible.ResultsIt was shown that misread letters occurred at all locations in pseudowords, regardless of the word's length. Inadequate fixation, excessively large saccadic amplitudes, reduced ability to simultaneously recognize a sequence of letters, a longer required fixation time and a longer required speech onset latency were all identified as causes of dyslexia. Each of the studies included in the meta-analysis were much more efficient than conventional therapeutic methods. The overall effect size with a value of Hedges' G = 1.72 showed that the therapy had a reproducible and stable effect.ConclusionsThe causes of dyslexia can be revealed by a dual-intervention approach consisting of a pseudoword experiment and learning a compensatory reading strategy. Reading performance improves immediately if the identified causes of dyslexia are compensated by an appropriate reading therapy.

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

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

A blind student with dyslexia - An overview of the problem

The basic purpose of this paper is to present selected theoretical and empirical facts concerning dyslexia, taking into account specific reading and spelling disorders experienced by the sighted and the blind who normally use a tactile writing system (braille) to read and write. The article’s content is focused on such key issues as: the terminology (a review of definitions), the symptomatology and etiology of dyslexia. In the light of the collected qualitative data and empirical research findings, dyslexia is likely to occur in blind braille-reading and braille-writing students. The symptoms of dyslexia may be observable in both contracted and uncontracted braille. They may be linked to the phonological processing deficits. The causes of dyslexia in the blind population can be explained in line with the genetic conception and the magnocellular theory by Stein and colleagues. However, it is necessary to design more complex studies on braille dyslexia in the future.

Investigating Auditory Spectral and Temporal Resolution Deficits in Children with Reading Difficulties.

The types of reading difficulties experienced by children are highly heterogeneous in nature, which makes diagnosis and intervention difficult. Over the past 30 years, there has been much debate over the cause of dyslexia. The two most popular theories for phonological deficits in dyslexia are the rate-processing constraint hypothesis, which relates to short timescale processing, and the temporal sampling framework hypothesis, which relates to longer timescale processing. To investigate the relationship between sublexical (i.e., nonword) reading skills and auditory spectral and temporal resolution patterns in children with reading difficulties using the Phoneme Identification Test (PIT) and the Parsing Syllable Envelopes Test (ParSE). These tests were developed to assess the rate-processing constraint and the temporal sampling framework hypotheses, respectively. We hypothesized that a proportion of children who have sublexical reading difficulties may have an underlying auditory-resolution deficit which may impact their ability to form letter-sound correspondences. We predicted that children's sublexical reading difficulties may not be explained by one theory, but instead that both theories may describe different types of reading difficulties found in different children. We also hypothesized that children with lexical (i.e., irregular word) reading difficulties but intact sublexical reading skills would not show atypical results on PIT or ParSE. Behavioral experimental clinical study with children who have reading difficulties. Sixteen children with nonword, irregular word, or mixed reading difficulties diagnosed by the Castles and Coltheart Test 2. Children completed a test battery consisting of a hearing screen and tests of reading, auditory resolution, phonological awareness, attention, spatial auditory processing, auditory memory, and intelligence. Categorization and correlational analyses were conducted. All four children with a pure sublexical reading deficit also had an auditory-resolution deficit. Four of seven children with a mixed reading deficit had an auditory-resolution deficit. Only one of five children with a lexical reading deficit had an auditory-resolution deficit. Individual children's specific deficits were related to either rate processing (n = 5) or temporal sampling (n = 4), but never both. Children's nonword reading scores were strongly correlated with their performance on the PIT in noise, but not with the PIT in quiet or the ParSE. Children's irregular word scores were not significantly correlated with their performance on the PIT in quiet or in noise, or the ParSE, as hypothesized. Strong correlations were also found between children's nonword scores and their phonological awareness scores. The results of this study suggest that neither the rate-processing hypothesis nor the temporal sampling framework is the single cause of reading difficulties in children. Instead, both of these hypotheses are likely to account for different types of reading deficits found in children. This is an important finding as the specific mechanisms driving different reading impairments must be identified to create tools to better diagnose and treat different types of reading difficulties. Further investigation of the PIT and ParSE as potential diagnostic tools for specific auditory-resolution-based reading difficulties in a larger group of children is currently underway.

Language Learning Disabilities: How Can I Help My Students with Dyslexia?

Abstract
 
 This paper showed the language learning method in teaching disabilities students with dyslexia problem. In this article the main focus is how to teach the dyslexia students in reading skill. Furthermore, in this study also explain the causes of dyslexia which are neurological and cognitive factor. Beside of that, the characteristics of children with dyslexia divided into two stages: early childhood (preschool or kindergarten, Grade 1-3, and Grade 4-8) and middle childhood with dyslexia (High school, college, and adult). And the last teacher has important role in teaching for the students with reading disabilities and difficulties (dyslexia). Teacher can guide the student in learning, give them an interesting activities by using good strategy. 
 
 Keyword: Reading Skill, Dyslexia, and Language Learning.

Corrigendum: Training on Movement Figure-Ground Discrimination Remediates Low-Level Visual Timing Deficits in the Dorsal Stream, Improving High-Level Cognitive Functioning, Including Attention, Reading Fluency, and Working Memory.

[This corrects the article DOI: 10.3389/fnhum.2017.00236.].

Cognitive-linguistic profiles of Chinese typical-functioning adolescent dyslexics and high-functioning dyslexics

Dyslexia is a developmental disability affecting the acquisition of reading and writing skills, and its developmental nature makes longitudinal research of great importance. This study therefore investigated the cognitive-linguistic profiles of the typical-functioning dyslexics and high-functioning dyslexics with longitudinal cohorts of Chinese-speaking adolescents diagnosed with childhood dyslexia. These two dyslexic groups of fifty students (with 25 typical-functioning dyslexics) were assessed in Grade 2 (Time 1) and in Grade 8 (Time 2), whereas 25 typically developing controls were assessed at Time 2. Students were administered measures of phonological awareness, morphological skills, visual-orthographic knowledge, rapid naming, verbal working memory, and literacy skills. Results showed that, at Time 2, both dyslexic groups performed less well than the control group on most of the measures. Deficits in rapid naming were particularly salient in both dyslexic groups. Comparing the two dyslexic groups, the typical-functioning dyslexics had more multiple deficits than the high-functioning dyslexics. Findings highlight the importance of rapid naming deficits as potential universal causes of dyslexia and the utility of targeting visual-orthographic knowledge and morphological skills in supporting the development of dyslexic adolescents.

Training on Movement Figure-Ground Discrimination Remediates Low-Level Visual Timing Deficits in the Dorsal Stream, Improving High-Level Cognitive Functioning, Including Attention, Reading Fluency, and Working Memory.

The purpose of this study was to determine whether neurotraining to discriminate a moving test pattern relative to a stationary background, figure-ground discrimination, improves vision and cognitive functioning in dyslexics, as well as typically-developing normal students. We predict that improving the speed and sensitivity of figure-ground movement discrimination (PATH to Reading neurotraining) acts to remediate visual timing deficits in the dorsal stream, thereby improving processing speed, reading fluency, and the executive control functions of attention and working memory in both dyslexic and normal students who had PATH neurotraining more than in those students who had no neurotraining. This prediction was evaluated by measuring whether dyslexic and normal students improved on standardized tests of cognitive skills following neurotraining exercises, more than following computer-based guided reading (Raz-Kids (RK)). The neurotraining used in this study was visually-based training designed to improve magnocellular function at both low and high levels in the dorsal stream: the input to the executive control networks coding working memory and attention. This approach represents a paradigm shift from the phonologically-based treatment for dyslexia, which concentrates on high-level speech and reading areas. This randomized controlled-validation study was conducted by training the entire second and third grade classrooms (42 students) for 30 min twice a week before guided reading. Standardized tests were administered at the beginning and end of 12-weeks of intervention training to evaluate improvements in academic skills. Only movement-discrimination training remediated both low-level visual timing deficits and high-level cognitive functioning, including selective and sustained attention, reading fluency and working memory for both dyslexic and normal students. Remediating visual timing deficits in the dorsal stream revealed the causal role of visual movement discrimination training in improving high-level cognitive functions such as attention, reading acquisition and working memory. This study supports the hypothesis that faulty timing in synchronizing the activity of magnocellular with parvocellular visual pathways in the dorsal stream is a fundamental cause of dyslexia and being at-risk for reading problems in normal students, and argues against the assumption that reading deficiencies in dyslexia are caused by phonological or language deficits, requiring a paradigm shift from phonologically-based treatment of dyslexia to a visually-based treatment. This study shows that visual movement-discrimination can be used not only to diagnose dyslexia early, but also for its successful treatment, so that reading problems do not prevent children from readily learning.

A specific implicit sequence learning deficit as an underlying cause of dyslexia? Investigating the role of attention in implicit learning tasks.

Recently, a general implicit sequence learning deficit was proposed as an underlying cause of dyslexia. This new hypothesis was investigated in the present study by including a number of methodological improvements, for example, the inclusion of appropriate control conditions. The second goal of the study was to explore the role of attentional functioning in implicit and explicit learning tasks. In a 2 × 2 within-subjects design 4 tasks were administered in 30 dyslexic and 38 control children: an implicit and explicit serial reaction time (RT) task and an implicit and explicit contextual cueing task. Attentional functioning was also administered. The entire learning curves of all tasks were analyzed using latent growth curve modeling in order to compare performances between groups and to examine the role of attentional functioning on the learning curves. The amount of implicit learning was similar for both groups. However, the dyslexic group showed slower RTs throughout the entire task. This group difference reduced and became nonsignificant after controlling for attentional functioning. Both implicit learning tasks, but none of the explicit learning tasks, were significantly affected by attentional functioning. Dyslexic children do not suffer from a specific implicit sequence learning deficit. The slower RTs of the dyslexic children throughout the entire implicit sequence learning process are caused by their comorbid attention problems and overall slowness. A key finding of the present study is that, in contrast to what was assumed for a long time, implicit learning relies on attentional resources, perhaps even more than explicit learning does. (PsycINFO Database Record

Screening for Dyslexia Using Eye Tracking during Reading.

Dyslexia is a neurodevelopmental reading disability estimated to affect 5–10% of the population. While there is yet no full understanding of the cause of dyslexia, or agreement on its precise definition, it is certain that many individuals suffer persistent problems in learning to read for no apparent reason. Although it is generally agreed that early intervention is the best form of support for children with dyslexia, there is still a lack of efficient and objective means to help identify those at risk during the early years of school. Here we show that it is possible to identify 9–10 year old individuals at risk of persistent reading difficulties by using eye tracking during reading to probe the processes that underlie reading ability. In contrast to current screening methods, which rely on oral or written tests, eye tracking does not depend on the subject to produce some overt verbal response and thus provides a natural means to objectively assess the reading process as it unfolds in real-time. Our study is based on a sample of 97 high-risk subjects with early identified word decoding difficulties and a control group of 88 low-risk subjects. These subjects were selected from a larger population of 2165 school children attending second grade. Using predictive modeling and statistical resampling techniques, we develop classification models from eye tracking records less than one minute in duration and show that the models are able to differentiate high-risk subjects from low-risk subjects with high accuracy. Although dyslexia is fundamentally a language-based learning disability, our results suggest that eye movements in reading can be highly predictive of individual reading ability and that eye tracking can be an efficient means to identify children at risk of long-term reading difficulties.

Dyslexia: is it genetic and what does this mean for social inclusion?

Purpose This paper starts by considering what it means if dyslexia has genetic or environmental causes. The author also explains phrases used by genetic researchers and the kind of things they look for in genetic material. The purpose of this paper is to discuss two recent studies on dyslexia that shed light on either genetic or environmental causes. Design/methodology/approach One study was a thorough exploration of possible genetic differences that could be present in children experiencing reading and language difficulties. The other study examined a large sample of the Canadian public to see whether there was a link between dyslexia and having experienced physical abuse as a child or teenager. Findings The study on genetic differences found no evidence for some previously suggested genetic causes of dyslexia. Although previous studies have suggested dyslexia runs in families, the genetic contribution may have been overestimated. The study on the Canadian public found that people who reported experiencing physical abuse in their younger years were six to seven times more likely also to have a diagnosis of dyslexia. Childhood trauma is known to affect brain development. Originality/value Although this paper only discusses two papers in detail, they are two of the most recent explorations of genetic and environmental links to dyslexia. There could be a case for greater attention to possible traumatic experiences in children identified as dyslexic. Physical abuse is one possibility but should never be assumed. Families can be under strain and may need more support. However, dyslexia and the mental health difficulties that can result from childhood trauma can reduce a child’s current and future social inclusion. Early intervention may avert this outcome.

Improving Dorsal Stream Function in Dyslexics by Training Figure/Ground Motion Discrimination Improves Attention, Reading Fluency, and Working Memory.

There is an ongoing debate about whether the cause of dyslexia is based on linguistic, auditory, or visual timing deficits. To investigate this issue three interventions were compared in 58 dyslexics in second grade (7 years on average), two targeting the temporal dynamics (timing) of either the auditory or visual pathways with a third reading intervention (control group) targeting linguistic word building. Visual pathway training in dyslexics to improve direction-discrimination of moving test patterns relative to a stationary background (figure/ground discrimination) significantly improved attention, reading fluency, both speed and comprehension, phonological processing, and both auditory and visual working memory relative to controls, whereas auditory training to improve phonological processing did not improve these academic skills significantly more than found for controls. This study supports the hypothesis that faulty timing in synchronizing the activity of magnocellular with parvocellular visual pathways is a fundamental cause of dyslexia, and argues against the assumption that reading deficiencies in dyslexia are caused by phonological deficits. This study demonstrates that visual movement direction-discrimination can be used to not only detect dyslexia early, but also for its successful treatment, so that reading problems do not prevent children from readily learning.

The Emotional and Social Effects of Dyslexia

Dyslexia, is one of the disorders with a greater prevalence among the group of the learning disorders. With the passing years many studies (observations) to explain the causes of dyslexia and to show the newest interventions in this field has been made. People withdyslexia have to overcome quite a few barriersduring theirlivesin order to be able to fulfiltheir dreams and achieve their targets. The fact that some of themare not assessedat an earlyage can affect their self-esteemand theirself-concept. Once theyare assessedresearch has proved that people with dyslexia learnbetter once they aretaught in their preferred learning style(Mortimore, 2003). In dyslexia one of the most commonly missed areas is the emotional side. Teachers and parents are very good at noticing problems with reading, writing, spelling and even maths. They can miss the growing element of lack of motivation, low self-esteem and upset which develops as the child goes through school and the pressures grow greater and greater. The frustration of children with dyslexia often centers on their inability to meet expectations. Their parents and teachers see a bright, enthusiastic child who is not learning to read and write. Time and again, dyslexics and their parents hear, "He's such a bright child; if only he would try harder." Ironically, no one knows exactly how hard the dyslexic is trying. The pain of failing to meet other people's expectations is surpassed only by dyslexics' inability to achieve their goals. This is particularly true of those who develop perfectionistic expectations in order to deal with their anxiety. They grow up believing that it is "terrible" to make a mistake. However, their learning disability, almost by definition means that these children will make many "careless" or "stupid" mistakes. This is extremely frustrating to them, as it makes them feel chronically inadequate. Thisinthe long termcan cause thema lot ofproblems in their personaland social life.

The Emotional and Social Effects of Dyslexia

Dyslexia, is one of the disorders with a greater prevalence among the group of the learning disorders. With the passing years many studies (observations) to explain the causes of dyslexia and to show the newest interventions in this field has been made. People withdyslexia have to overcome quite a few barriersduring theirlivesin order to be able to fulfiltheir dreams and achieve their targets. The fact that some of themare not assessedat an earlyage can affect their self-esteemand theirself-concept. Once theyare assessedresearch has proved that people with dyslexia learnbetter once they aretaught in their preferred learning style(Mortimore, 2003). In dyslexia one of the most commonly missed areas is the emotional side. Teachers and parents are very good at noticing problems with reading, writing, spelling and even maths. They can miss the growing element of lack of motivation, low self-esteem and upset which develops as the child goes through school and the pressures grow greater and greater. The frustration of children with dyslexia often centers on their inability to meet expectations. Their parents and teachers see a bright, enthusiastic child who is not learning to read and write. Time and again, dyslexics and their parents hear, "He's such a bright child; if only he would try harder." Ironically, no one knows exactly how hard the dyslexic is trying. The pain of failing to meet other people's expectations is surpassed only by dyslexics' inability to achieve their goals. This is particularly true of those who develop perfectionistic expectations in order to deal with their anxiety. They grow up believing that it is "terrible" to make a mistake. However, their learning disability, almost by definition means that these children will make many "careless" or "stupid" mistakes. This is extremely frustrating to them, as it makes them feel chronically inadequate. Thisinthe long termcan cause thema lot ofproblems in their personaland social life.

De la teoría fonológica a la identificación temprana de las dificultades específicas de aprendizaje de la lectura

This paper presents a review of the research issued from the frame of the Phonological Theory of developmental dyslexia. This theory has set up the means to make an early identification of specific learning difficulties in reading, and has provided theoretical support for its implementation. There are four fundamental contributions. First, the Phonological Theory argues that developmental dyslexia is a consequence of a general phonological deficit that affects different components of the phonological system being phonological awareness, lexical processing speed and verbal short-term memory the most relevant. Second, the Phonological Theory has pointed out that the primary cause of dyslexia is present from the embryonic period and that it affects oral language development before learning to read. Third, the Phonological Theory has considered oral language as the main cause of the deficit, and consequently, has highlighted the relations between Specific Language Impairment and Developmental Dyslexia. Fourth, since research has proved the significant impact of Programs for prevention and early intervention, a clear need for adding proactive strategies of early prevention and/or identification to the late reactive diagnosis strategies has arisen. Finally, it is argued that if primary causes as well as prevention and intervention resources are directly attached to language development, then, speech therapists should play a main role in the implementation of proactive strategies in the school context.

Orthographic processing deficits in developmental dyslexia: Beyond the ventral visual stream

Fast effortless reading has been associated with the Visual Word Form Area (VWFA), a region in the ventral visual stream that specializes in the recognition of letter strings. Several neuroimaging studies of dyslexia revealed an underactivation of this region. However, most of these studies used reading tasks and/or were carried out on adults. Given that fluent reading is severely impaired in dyslexics, any underactivation might simply reflect a well-established reading deficit in impaired readers and could be the consequence rather than the cause of dyslexia. Here, we designed a task that does not rely on reading per se but that tapped early visual orthographic processing that forms the basis of reading. Dyslexic children aged 8–12years and age-matched controls were asked to search for letters, digits, and symbols in 5-element strings (Experiment 1). This novel task was complemented by a classic task known to activate the VWFA, namely the passive viewing of pseudowords and falsefonts (Experiment 2). We found that in addition to significant group differences in the VWFA, dyslexic children showed a significant underactivation of the middle occipital gyrus (MOG) relative to the control group. Several areas in the MOG are known for their engagement in visuospatial processing, and it has been proposed that the MOG is necessary for ordering the symbols in unfamiliar strings. Our results suggest that the VWFA deficit might be secondary to an impairment of visuospatial processing in the MOG. We argue that efficient processing in MOG in the course of reading acquisition is critical for the development of effortless fast visual word recognition in the VWFA.

Do Children with Dyslexia Have Difficulty in Reading the Quranic Verses Too?

Dyslexia, a type of learning disability, is a neurodevelopmental disorder that affects reading, writing and spelling in children. It is one of the commonest learning disorders among school-going children. The causes of dyslexia are multifactorial and are hereditary. The objective of this study was to determine if children with dyslexia have difficulty in reading the Quranic verses too. This was a cross-sectional study conducted at a government primary school in Kuala Lumpur. All standard one pupils, a total of 200 pupils, were screened for reading, writing and numerical difficulties by the school teachers in March, 2014 using LINUS screening tool, a standardized literacy screening tool adopted by all Malaysian schools. Students who failed the first LINUS screening were given intervention by the school teachers. Six months later, the research team reassessed the pupils who failed the Linus screening. Approximately 18% (37 pupils) of the standard one pupils had dyslexia. Of these, 33 of them were Muslims and were assessed if they had difficulty reading the Quranic verses by using Iqra’, which is the basic reading material for Quranic verses. About 79% of them had difficulty reading the Quran. The majority of the children with dyslexia also had difficulty reading the Quranic verses. Thus remedial intervention for Muslim dyslexic children should also include learning to read the Quran.

Incidental learning of sound categories is impaired in developmental dyslexia

Developmental dyslexia is commonly thought to arise from specific phonological impairments. However, recent evidence is consistent with the possibility that phonological impairments arise as symptoms of an underlying dysfunction of procedural learning. The nature of the link between impaired procedural learning and phonological dysfunction is unresolved. Motivated by the observation that speech processing involves the acquisition of procedural category knowledge, the present study investigates the possibility that procedural learning impairment may affect phonological processing by interfering with the typical course of phonetic category learning. The present study tests this hypothesis while controlling for linguistic experience and possible speech-specific deficits by comparing auditory category learning across artificial, nonlinguistic sounds among dyslexic adults and matched controls in a specialized first-person shooter videogame that has been shown to engage procedural learning. Nonspeech auditory category learning was assessed online via within-game measures and also with a post-training task involving overt categorization of familiar and novel sound exemplars. Each measure reveals that dyslexic participants do not acquire procedural category knowledge as effectively as age- and cognitive-ability matched controls. This difference cannot be explained by differences in perceptual acuity for the sounds. Moreover, poor nonspeech category learning is associated with slower phonological processing. Whereas phonological processing impairments have been emphasized as the cause of dyslexia, the current results suggest that impaired auditory category learning, general in nature and not specific to speech signals, could contribute to phonological deficits in dyslexia with subsequent negative effects on language acquisition and reading. Implications for the neuro-cognitive mechanisms of developmental dyslexia are discussed.

Psychophysical Evidence for Impaired Magno, Parvo, and Konio-cellular Pathways in Dyslexic Children.

Purpose:Dyslexia is one of the most common learning disabilities affecting millions of people worldwide. Although exact causes of dyslexia are not well-known, a deficit in the magnocellular pathway may play a role. We examined possible deficiency of magnocellular, as compared to parvocellular and koniocellular pathway function by measuring luminance and color perception.Methods:Visual stimuli consisted of a series of natural images, divided into layers of luminance, red-green and blue-yellow, which probed magnocellular, parvocellular, and koniocellular pathways, respectively. Thirteen children with dyslexia and 13 sex- and age- matched controls performed three psychophysical tasks. In the first task, subjects were instructed to match the contrast of luminance (magno) and red-green (parvo) images to that of the blue-yellow (konio) images. In the second task, subjects detected the isoluminant point of red-green images to probe parvocellular pathway. In the third task, temporal processing was assessed by measuring reaction time and percentage of correct responses in an identification task using four categories of images, activating all three pathways.Results:The dyslexic group had significantly elevated luminance and color contrast thresholds and higher isoluminant point ratio in comparison to the control group. Furthermore, they had significantly less correct responses than the control group for the blue-yellow images.Conclusion:We may suggest that dyslexic subjects might suffer from both magnocellular and parvocellular deficits. Moreover, our results show partial impairment of the koniocellular pathway. Thus, dyslexia might be associated with deficits in all three visual pathways.

What can spelling errors tell us about the causes and treatment of dyslexia?

Until recently the majority of research undertaken into dyslexia focused on English‐speaking dyslexics, who tend to make significantly more phonological than visual errors. This led to a major assumption about the possible cause of dyslexia being a lack of phonological awareness. According to the phonological deficit theory, the level of phonological consistency of a language determines not only the reading speed but also the amount and types of reading and spelling errors made by dyslexic people. This theory has been seriously challenged by the results of a number of studies in more phonologically consistent languages, such as Greek, Italian and Japanese, where morphology seemed to play a more crucial role than the phonological structure of a language per se. The 116 dyslexic people who took part in this experiment were matched on age, sex, IQ and psycho‐educational performance. A total of 58 US English‐speaking dyslexic people were compared to 58 Greek dyslexic people. Both groups met the diagnostic criteria. Results demonstrated that Greek dyslexics were found to make significantly fewer phonological errors (11.0%) than the US dyslexics (85.5%, p < .000), but comparatively more visual (66.8% to US 14.0%, P < .000) and grammatical errors (22.2% to US 0.1%, p < .000) than their English‐speaking counterparts. These data showed highly significant quantitative and qualitative spelling differences. Greek dyslexics could be accurately differentiated from the US English dyslexics based on the three types of spelling errors.