Visual motion sensitivity and reading

Interaction of phonological awareness and 'magnocellular' processing during normal and dyslexic reading: behavioural and fMRI investigations

We investigated whether phonological deficits are a consequence of magnocellular processing deficits in dyslexic and control children. In Experiment 1, children were tested for reading ability, phonological awareness, visuo-magnocellular motion perception, and attention shifting (sometimes considered as magnocellular function). A two-step cluster analysis of the behavioural scores revealed four clusters of children. Phonological awareness was correlated with attention (cluster musical sharp1) or motion detection (cluster musical sharp2), whereas attention and motion detection were correlated in cluster musical sharp3. In cluster musical sharp4, all variables were uncorrelated. In Experiment 2, the same variables plus auditory discrimination were tested with fMRI in a sub-sample of Experiment 1. Although dyslexics had reduced activation in visual or auditory cortex during motion detection or auditory discrimination, respectively, they had increased right frontal activation in areas 44 and 45 in all 'magnocellular' (including auditory) tasks. In contrasts, during phonological decisions, there was higher activation for good readers than dyslexics in left areas 44 and 45. Together, the two experiments give insight into the interplay of phonological and magnocellular processing during reading. Distinct left versus right frontal effects reveal partly different underlying neural mechanisms. These data contradict the view that phonological processing deficits in dyslexia necessarily result from impaired magnocellular functioning.

Binocular function in school children with reading difficulties

INTRODUCTION

Prior findings suggest that poor readers tend to have poor binocular vision skills, but data on the binocular abilities of children with poor reading skills are lacking. Our aim was to characterize distance and near horizontal heterophoria, distance and near horizontal fusional vergence ranges, accommodative convergence/accommodation (AC/A) ratio, near point of convergence, and stereopsis in poor-reading school-age children without dyslexia selected from a non-clinical population.

METHODS

We conducted a cross-sectional study on 87 poor readers and 32 control children (all 8-13 years of age) in grades three to six recruited from eleven elementary schools in Madrid, Spain. With best spectacle correction in each subject, distance and near horizontal heterophoria measurements were obtained using the von Graefe technique, distance and near horizontal fusional vergence ranges were obtained using Risley rotary prisms, the AC/A ratio was measured using the gradient method, near point of convergence (NPC) was evaluated by the standard push-up technique using a transilluminator, and stereoacuity was tested with the Randot stereotest.

RESULTS

Mean distance base-in break and base-in recovery values were nearly 2 Delta lower (p < 0.01) in the poor readers than those recorded in the control group. However, mean distance base-out vergences (blur, break and recovery), mean distance and near horizontal heterophoria, mean near horizontal fusional vergence ranges, mean AC/A ratio, mean near point of convergence (NPC), and mean stereoacuity did not differ significantly between the poor readers and controls.

CONCLUSIONS

This study provides information on the binocular ability of children with poor reading skills but without dyslexia. Our findings suggest reduced distance base-in break and base-in recovery, such that distance fusional vergence ranges should always be assessed in children who complain of reading difficulties.

Auditory and visual stream segregation in children and adults: an assessment of the amodality assumption of the 'sluggish attentional shifting' theory of dyslexia

Among the hypotheses relating dyslexia to a temporal processing disorder, Hari and Renvall (Hari, R., Renvall, H., 2001. Impaired processing of rapid stimulus sequences in dyslexia. Trends. Cognit. Sci. 5, 525-532.) argued that dyslexic individuals would show difficulties at an attentional level, through sluggish attentional shifting (SAS) in all sensory modalities. However, the amodality assumption of the SAS theory was never straightforwardly assessed in the same group of dyslexic participants using similar paradigms in both the visual and auditory modalities. Here, the attentional sequential performance of control and dyslexic participants was evaluated using rapid serial presentation paradigms measuring individual stream segregation thresholds in the two modalities. The first experiment conducted on French dyslexic children with a phonological disorder revealed an SAS only in the auditory modality only which was strongly related to reading performance. The second experiment carried out on British dyslexic young adults with a phonological disorder using the same auditory segregation task but a different visual paradigm revealed an SAS in both the visual and the auditory modalities. In addition, a relationship was found in this group between SAS, poor reading and poor phonological skills. Two further control experiments showed that differences in task design or participants' language between Experiments 1 and 2 could not account for the differences in terms of visual segregation patterns. Overall, our results support the view that the auditory SAS plays a role in developmental dyslexia via its impact on phonological abilities. In addition, a visual temporal disorder in dyslexia might emerge at a later developmental stage, when the visual system normally becomes more expert at rapid temporal processing.

Project DyAdd: Fatty acids and cognition in adults with dyslexia, ADHD, or both

Both attention deficit hyperactivity disorder (ADHD) and dyslexia are suggested to co-occur with altered fatty acid (FA) metabolism, but it is unknown how FAs are associated with the cognitive domains that characterize these disorders. In the project DyAdd, we investigated the associations between FAs in serum phospholipids and phonological processing, reading, spelling, arithmetic, executive functions, and attention. Healthy controls (n=36), adults with ADHD (n=26), dyslexia (n=36), or both (n=9) were included in the study. FAs included saturated, monounsaturated, total polyunsaturated, n-3, and n-6 FAs, together with n-6/n-3, AA/EPA, and LA/ALA ratios. When all the study subjects were included in the analyses, especially polyunsaturated FAs (PUFAs) were positively associated with cognition, but reading was least associated with FAs. These associations were modulated by gender, intelligence, n-3 PUFA intake, and group. Accordingly, within the ADHD group, only few associations emerged with PUFAs, n-6 PUFAs, and cognitive domains, whereas in the dyslexia group the more prevalent associations appeared with PUFAs and n-3 PUFAs.

Paying attention to reading: the neurobiology of reading and dyslexia

Extraordinary progress in functional brain imaging, primarily advances in functional magnetic resonance imaging, now allows scientists to understand the neural systems serving reading and how these systems differ in dyslexic readers. Scientists now speak of the neural signature of dyslexia, a singular achievement that for the first time has made what was previously a hidden disability, now visible. Paralleling this achievement in understanding the neurobiology of dyslexia, progress in the identification and treatment of dyslexia now offers the hope of identifying children at risk for dyslexia at a very young age and providing evidence-based, effective interventions. Despite these advances, for many dyslexic readers, becoming a skilled, automatic reader remains elusive, in great part because though children with dyslexia can be taught to decode words, teaching children to read fluently and automatically represents the next frontier in research on dyslexia. We suggest that to break through this "fluency" barrier, investigators will need to reexamine the more than 20-year-old central dogma in reading research: the generation of the phonological code from print is modular, that is, automatic and not attention demanding, and not requiring any other cognitive process. Recent findings now present a competing view: other cognitive processes are involved in reading, particularly attentional mechanisms, and that disruption of these attentional mechanisms play a causal role in reading difficulties. Recognition of the role of attentional mechanisms in reading now offer potentially new strategies for interventions in dyslexia. In particular, the use of pharmacotherapeutic agents affecting attentional mechanisms not only may provide a window into the neurochemical mechanisms underlying dyslexia but also may offer a potential adjunct treatment for teaching dyslexic readers to read fluently and automatically. Preliminary studies suggest that agents traditionally used to treat disorders of attention, particularly attention-deficit/hyperactivity disorder, may prove to be an effective adjunct to improving reading in dyslexic students.

Perisaccadic mislocalization in dyslexia

Evidence from experiments designed to elicit the phenomenon of perisaccadic mislocalization of briefly presented probe stimuli suggests that mechanisms implicated in the planning of a saccade are also implicated in the means by which spatial constancy is maintained across saccades. We postulated that impairments of visual attention observed in dyslexic readers may arise from impairment of mechanisms that also subserve the maintenance of spatial constancy, leading to visual confusion during reading. To test this hypothesis, we compared the performance of adults with dyslexia with that of non-impaired control participants on a task designed to elicit perisaccadic mislocalization. Typically in such tasks, when probes are presented close to saccade onset, mislocalization of all probes, including those presented beyond the saccade target, are mislocalized in the direction of the saccade target, a phenomenon known as perisaccadic spatial compression. In addition, a second tendency, in which all probes are mislocalized in the direction of the saccade itself is referred to as shift. Dyslexic participants showed attenuated perisaccadic compression effects relative to those found in control participants, while the degree to which the reported positions of the probes were shifted in the direction of the saccade did not differ significantly between groups. We propose that compression errors are likely to arise from predictive mechanisms that normally maintain spatial constancy across saccades. Our finding was therefore interpreted as support for the hypothesis that predictive spatial constancy mechanisms may be disrupted in dyslexia.

[The reader brain: natural and cultural story]

The report of cases of pure alexia suggests that some regions of the neural system are dedicated to reading-specific visual processing abilities. Pure alexia results from the disruption or the disconnection of the visual word form area, a region reproducibly located within the left occipito-temporal sulcus and encoding the abstract identity of strings of visual letters. The functional specialization of this area suggests that it is initially plastic and becomes attuned to the orthographic regularities that constrain letter combination during the acquisition of literacy. The visual word form area further belongs to the network of areas that are consistently implicated in studies of people with developmental dyslexia. Developmental dyslexia is typically interpreted as resulting from a core phonological disorder and most neuroimaging studies showed reduced activity in the left perisylvian regions which have a role in phonological processes. Although low level visual and/or visual attentional disorders have been consistently reported suggesting a visual basis of developmental dyslexia, these disorders typically co-occurred with phonological problems so that the phonological deficit was viewed as the most plausible cause of the poor reading outcome of dyslexic children. In the last years however, dissociations have been reported in developmental dyslexia between phonological processing deficits and a particular kind of visual disorder, a visual attention span deficit characterised by a reduction in the number of distinct orthographic units which can be processed simultaneously in a single fixation. Large sample studies revealed that a non trivial number of dyslexic children exhibit a visual attention span disorder and that this disorder typically dissociates from phonological impairments in the dyslexic population. Neuroimaging studies suggest involvement of the parietal lobes - in particular the superior parietal lobules - in visual attention span and these brain regions are less active in people with developmental dyslexia. A visual attention span disorder thus appears as a second core disorder related to a parietal dysfunction in developmental dyslexia. Further studies are required to determine whether the phonological disorder or the visual attention span disorder independently contribute to the development of the visual word form area during literacy acquisition. These neurobiological dysfunctions are further modulated by environmental factors such as language characteristics, remedial interventions or socio-economic status. Future studies would help better understanding the interactions between neurobiological and environmental factors and the potential influence of the later on the development of the visual word form area.

Dyslexia: a review of two theories

Optometrists will frequently see patients, who may have a diagnosis or a suspected diagnosis of dyslexia (specific reading disorder) and will need to manage and counsel such patients. There are many propounded theories on the cause(s) of dyslexia. Although most professionals in this area consider that dyslexia is chiefly a linguistic disorder, the possibility of a visual component is contentious. This article is a selective review of two commonly discussed theories that suggest a visual component in dyslexia; the magnocellular deficit theory and Meares-Irlen syndrome.

A few remarks on relating reaction time to magnocellular activity

Studies have found dyslexic readers to have longer reaction times than nondyslexic readers. These results have been discussed relative to the hypothesis that dyslexia is caused by a magnocellular deficit. We here point out that attempts to link reaction times in dyslexic readers to magnocellular sensitivity face at least two serious problems: (a) The reaction time differences between dyslexics and controls appear too large to be attributable to deficits in the magnocellular system; (b) there is evidence to suggest that in the case of stimuli with contrast above about 10% behavioral reaction times may reflect parvocellular rather than magnocellular activity.

Treatment effects of Fast ForWord demonstrated by magnetoencephalography (MEG) in a child with developmental dyslexia

Treatment effects of Fast ForWord, hypothesized to ameliorate temporal processing deficits, were demonstrated by magnetoencephalography in a child with dyslexia using four paradigms: Word/Non-word Reading (NW), Grapheme-to-Phoneme Matching (GP), Verbal, and Spatial Working Memory (VWM, SWM). Shifts in brain activation from right inferior frontal and temporal to left frontal, bilateral supramarginal, and transverse temporal regions occurred during GP. During NW, shifts progressed from (1) right or bilateral anterior and superior to (2) left, inferior frontal, to (3) left, superior posterior temporoparietal, to (4) left, inferior, posterior temporooccipital regions. Reading and written language improvements were noted in passage comprehension and spelling.

Visual memory transformations in dyslexia

Representational Momentum refers to observers' distortion of recognition memory for pictures that imply motion because of an automatic mental process which extrapolates along the implied trajectory of the picture. Neuroimaging evidence suggests that activity in the magnocellular visual pathway is necessary for representational momentum to occur. It has been proposed that individuals with dyslexia have a magnocellular deficit, so it was hypothesised that these individuals would show reduced or absent representational momentum. In this study, 30 adults with dyslexia and 30 age-matched controls were compared on two tasks, one linear and one rotation, which had previously elicited the representational momentum effect. Analysis indicated significant differences in the performance of the two groups, with the dyslexia group having a reduced susceptibility to representational momentum in both linear and rotational directions. The findings highlight that deficits in temporal spatial processing may contribute to the perceptual profile of dyslexia.

Developmental dyslexia: The visual attention span deficit hypothesis

The visual attention (VA) span is defined as the amount of distinct visual elements which can be processed in parallel in a multi-element array. Both recent empirical data and theoretical accounts suggest that a VA span deficit might contribute to developmental dyslexia, independently of a phonological disorder. In this study, this hypothesis was assessed in two large samples of French and British dyslexic children whose performance was compared to that of chronological-age matched control children. Results of the French study show that the VA span capacities account for a substantial amount of unique variance in reading, as do phonological skills. The British study replicates this finding and further reveals that the contribution of the VA span to reading performance remains even after controlling IQ, verbal fluency, vocabulary and single letter identification skills, in addition to phoneme awareness. In both studies, most dyslexic children exhibit a selective phonological or VA span disorder. Overall, these findings support a multi-factorial view of developmental dyslexia. In many cases, developmental reading disorders do not seem to be due to phonological disorders. We propose that a VA span deficit is a likely alternative underlying cognitive deficit in dyslexia.

Contrast responsivity in MT+ correlates with phonological awareness and reading measures in children

There are several independent sets of findings concerning the neural basis of reading. One set demonstrates a powerful relationship between phonological processing and reading skills. Another set reveals a relationship between visual responses in the motion pathways and reading skills. It is widely assumed that these two findings are unrelated. We tested the hypothesis that phonological awareness is related to motion responsivity in children's MT+. We measured BOLD signals to drifting gratings as a function of contrast. Subjects were 35 children ages 7-12 years with a wide range of reading skills. Contrast responsivity in MT+, but not V1, was correlated with phonological awareness and to a lesser extent with two other measures of reading. No correlation was found between MT+ signals and rapid naming, age or general IQ measures. These results establish an important link between visual and phonological processing in children and suggest that MT+ responsivity is a marker for healthy reading development.

The contribution of phonological awareness and visual attention in early reading and spelling

We examined the development of phonological processing, naming speed, and visual attention in kindergarten and addressed the question of their contribution to reading and spelling in grade 1. Seventy five French-speaking children were administered seven tasks at the two phases of the study, and reading and spelling were assessed in grade 1. The major findings revealed that syllable awareness and visual attention were the most important predictors of early reading and spelling, and confirm the influence of naming speed and phoneme awareness on specific skills. These observations strongly suggest that written language acquisition relies on linguistic, perceptual and cognitive cross-modal skills and highlight the need for diversifying written language measures and analyzing their specific predictors.

Attention, dyslexia, and the line-motion illusion

Dyslexic readers have been found to have a reduced line-motion illusion. This has been interpreted as evidence for an attention deficit of magnocellular origin. We show that this interpretation has severe problems: 1) to link reduced line-motion illusion to attention overlooks other factors, 2) to link the line-motion illusion specifically to the magnocellular system is problematic because the illusion can be obtained with isoluminant stimuli, 3) reduced illusory motion in dyslexic individuals may reflect sensory deficits, and 4) to link dyslexia specifically to the magnocellular system is in general problematic.

Auditory processing, speech perception and phonological ability in pre-school children at high-risk for dyslexia: A longitudinal study of the auditory temporal processing theory

This study investigates whether the core bottleneck of literacy-impairment should be situated at the phonological level or at a more basic sensory level, as postulated by supporters of the auditory temporal processing theory. Phonological ability, speech perception and low-level auditory processing were assessed in a group of 5-year-old pre-school children at high-family risk for dyslexia, compared to a group of well-matched low-risk control children. Based on family risk status and first grade literacy achievement children were categorized in groups and pre-school data were retrospectively reanalyzed. On average, children showing both increased family risk and literacy-impairment at the end of first grade, presented significant pre-school deficits in phonological awareness, rapid automatized naming, speech-in-noise perception and frequency modulation detection. The concurrent presence of these deficits before receiving any formal reading instruction, might suggest a causal relation with problematic literacy development. However, a closer inspection of the individual data indicates that the core of the literacy problem is situated at the level of higher-order phonological processing. Although auditory and speech perception problems are relatively over-represented in literacy-impaired subjects and might possibly aggravate the phonological and literacy problem, it is unlikely that they would be at the basis of these problems. At a neurobiological level, results are interpreted as evidence for dysfunctional processing along the auditory-to-articulation stream that is implied in phonological processing, in combination with a relatively intact or inconsistently impaired functioning of the auditory-to-meaning stream that subserves auditory processing and speech perception.

Development of perceptual correlates of reading performance

Performance on perceptual tasks requiring the discrimination of brief, temporally proximate or temporally varying sensory stimuli (temporal processing tasks) is impaired in some individuals with developmental language disorder and/or dyslexia. Little is known about how these temporal processes in perception develop and how they relate to language and reading performance in the normal population. The present study examined performance on 8 temporal processing tasks and 5 language/reading tasks in 120 unselected readers who varied in age over a range in which reading and phonological awareness were developing. Performance on all temporal processing tasks except coherent motion detection improved over ages 7 years to adulthood (p<0.01), especially between ages 7 and 13 years. Independent of these age effects, performance on all 8 temporal processing tasks predicted phonological awareness and reading performance (p<0.05), and three auditory temporal processing tasks predicted receptive language function (p<0.05). Furthermore, all temporal processing measures except within-channel gap detection and coherent motion detection predicted unique variance in phonological scores within subjects, whereas only within-channel gap detection performance explained unique variance in orthographic reading performance. These findings partially support the (Farmer, M.E., Klein, R.M., 1995. The evidence for a temporal processing deficit linked to dyslexia: A review. Psychon. Bull. Rev. 2, 460-493) notion of there being separable auditory and visual perceptual contributions to phonological and orthographic reading development. The data also are compatible with the view that the umbrella term "temporal processing" encompasses fundamentally different sensory or cognitive processes that may contribute differentially to language and reading performance, which may have different developmental trajectories and be differentially susceptible to pathology.

Rapid visual processing by college students in reading irregular words and phonologically regular pseudowords presented singly and in contiguity

Using normal adult readers, this study examined the relative involvement of magnocellular and parvocellular processes in reading English phonologically regular pseudowords and irregular words presented in isolation and in contiguity from left to right. The data showed that a low temporal frequency visual measure that implied more parvocellular involvement was active in processing irregular words presented singly and pseudowords presented in contiguity. However, the results failed to show the involvement of the magnocellular pathway (as implicated by low spatial and/or high temporal frequency visual measures) in reading words presented in contiguity from left to right. The discrepancy was discussed in terms of the sensitivity of the tasks used in testing the two pathways.

Temporal order judgment in dyslexia

Hari et al. (Brain 174:1373-1380, 2001) demonstrated that dyslexics showed a sluggish attention capture in both visual hemifields. Additionally, they indicated a left-right asymmetry in the perception of temporal order of two visual stimuli (they performed worse than controls only if the stimulus in the left hemifield preceded that in right hemifield). They suggested that a left-sided minineglect is associated with dyslexia. We hypothesized that if a kind of neglect syndrome is responsible for the asymmetry they found, dyslexics should not only show a left-right asymmetry in temporal order judgment of two laterally presented stimuli but also perform equally well as controls when the stimuli are vertically aligned. Our results indicated that in both tasks dyslexics performed generally worse than normal readers. The results suggest that dyslexics suffer from a more general problem of order discrimination.

Attention, reading and dyslexia

It has been proposed that magnocellular deficits cause dyslexia through reduced attention. According to one model (Vidyasagar, Clinical and Experimental Optometry 2004; 87: 4-10), attention is shifted from letter to letter during fixations and magnocellular deficits are hypothesised to cause reading problems by interfering with the ability to control the attention. The present report points out several problems in this model. 1. It requires dissociation of eye movements and attention, which may be problematic within the framework of reading. 2. There is direct evidence to indicate that reading is not carried out in a letter-to-letter manner during fixations. 3. There are aspects of the visual performance of dyslexic readers, which are difficult to attribute to inattention. 4. There are indications that attentional deficiencies of dyslexic readers are not associated with magnocellular deficits. 5. The evidence for linking magnocellular deficits to dyslexia in general is weak.

Speechreading and its association with reading among deaf, hearing and dyslexic individuals

Reading and speechreading are both visual skills based on speech and language processing. Here we explore individual differences in speechreading in profoundly prelingually deaf adults, hearing adults with a history of dyslexia, and hearing adults with no history of a literacy disorder. Speechreading skill distinguished the three groups: the deaf group were better speechreaders than hearing controls, who were better than the group with a history of dyslexia. The dyslexic group, while within range of hearing controls in terms of reading, nevertheless showed a residual deficit in speech/language processing when tested with silent speech. Within-group correlations suggested different associations between speechreading subtasks, reading and language skills. In particular, in the deaf and dyslexic groups, but not in the hearing controls, speechreading skill correlated with reading ability.

The Role of Functional Magnetic Resonance Imaging in Understanding Reading and Dyslexia

Converging evidence from a number of lines of investigation indicates that dyslexia represents a disorder within the language system and more specifically within a particular subcomponent of that system, phonological processing. Recent advances in imaging technology, particularly the development of functional magnetic resonance imaging (fMRI), provide evidence of a neurobiological signature for dyslexia, specifically a disruption of 2 left hemisphere posterior brain systems, 1 parietal-temporal, the other occipital-temporal, with compensatory engagement of anterior systems around the inferior frontal gyrus and a posterior (right occipital-temporal) system. Furthermore, good evidence indicates a computational role for the left occipital-temporal system: the development of fluent (automatic) reading. In addition, fMRI studies of young adults with reading difficulties followed prospectively and longitudinally from age 5 through their mid 20s suggests that there may be 2 types of reading difficulties, 1 primarily reflecting a genetic basis, the other, and far more common, reflecting environmental influences. The brain systems for reading are malleable and their disruption in children with dyslexia may be remediated by provision of an evidence-based, effective reading intervention. These studies offer the promise for more precise identification and effective management of dyslexia in children, adolescents, and adults.

Is coherent motion an appropriate test for magnocellular sensitivity?

The suggestion that coherent motion may serve as a test of magnocellular sensitivity is problematic. However, the nature of the problems depends on how the "magnocellular system" is defined. If this term is limited to subcortical entities, the problems are that subcortical neurons are not directionally selective, and that their receptive fields are too small to account for the spatial summation of coherent motion. If "magnocellular system" is defined to include cortical entities, such as area MT, one is faced with the fact that this definition itself is problematic as well as the problem that area MT is known to receive parvocellular and koniocellular inputs.

Dorsal stream associations with orthographic and phonological processing

Several studies have indicated a key role for dorsal stream processing in lexical decoding. To examine this relationship further, performance on orthographic and phonological reading tests was compared with both steady-state visual evoked potentials and a putative behavioral measure of dorsal stream processing, coherent motion detection. Frequency analysis of the visual evoked potential data showed power at the second harmonic to be largely confined to dorsal stream regions, and significantly correlated with motion detection thresholds. Regression analyses showed that orthographic processing was significantly associated with the second harmonic power. Although consistent with previous reports, there remains a question as to why the orthographic visual evoked potential power relationship did not extend to include the coherent motion detection measures.

Yellow Filters Can Improve Magnocellular Function: Motion Sensitivity, Convergence, Accommodation, and Reading

The magnocellular system plays an important role in visual motion processing, controlling vergence eye movements, and in reading. Yellow filters may boost magnocellular activity by eliminating inhibitory blue input to this pathway. It was found that wearing yellow filters increased motion sensitivity, convergence, and accommodation in many children with reading difficulties, both immediately and after three months using the filters. Motion sensitivity was not increased using control neutral density filters. Moreover, reading-impaired children showed significant gains in reading ability after three months wearing the filters compared with those who had used a placebo. It was concluded that yellow filters can improve magnocellular function permanently. Hence, they should be considered as an alternative to corrective lenses, prisms, or exercises for treating poor convergence and accommodation, and also as an aid for children with reading problems.

Serum lipid fatty acids, phonological processing, and reading in children with oral clefts

Reading skill is suggested to be related to phonological processing ability and polyunsaturated fatty acids (PUFAs). Here we investigated whether fatty acids (FAs) are related to phonological processing, whether the relations between PUFAs and reading generalize to other FAs, whether these relations are mediated by phonological processing, and whether relations of FAs are specific for language-related functions. Blood samples of 49 ten-year-old children with oral clefts were collected for FA proportion analysis in serum cholesteryl esters and phospholipids. On the same day, they performed tasks of phonological processing, reading, and both verbal and nonverbal intelligence. Sequential regression analyses (adjusted for age, gender, and cleft type) showed that phonological processing was inversely related to myristic acid in phospholipids and positively related to eicosapentaenoic acid in cholesteryl esters. Reading was inversely related to palmitoleic and gammalinolenic acids in phospholipids. The relations between FAs and reading were not mediated by phonological processing and FAs related only to language-related functions.

Lateral masking, levels of processing and stimulus category: A comparative study between normal and dyslexic readers

The lateral masking effect results in lower performance on letter recognition when items are flanked by other stimuli. Using a new paradigm based on discrimination (feature analysis) and categorization (memory access) tasks, we investigated the influence of level of processing (as addressed, respectively, by these two tasks) and stimulus type (Latin letters, Korean letters and geometrical figures) on lateral masking. In addition, performance of dyslexic and non-dyslexic adult readers was compared. The non-dyslexic participants demonstrated a classical lateral masking effect with lower performance for flanked items than isolated ones. In addition, lateral masking was stronger in the categorization than in the discrimination task and was restricted to familiar items, i.e., Latin letters and geometrical figures. Dyslexic participants showed poorer performance than non-dyslexics on processing isolated items, and the pattern of decrease in performance for lateral masking was similar to non-dyslexics. However, they also showed a stronger decrease in performance in categorization and a stronger decrease related to the lateral masking for this categorization task. Our results in normal readers suggest that lateral masking relies on the interference between the target and the flankers during feature integration that may result in marked impairment of memory access (categorization task). Poorer performance in dyslexic readers may reflect impaired parafoveal/peripheral low-level processing during feature integration that may have worsened during the flanked condition due to a target selection/spatial-attentional disorder. Moreover, dyslexic subjects presented an additional categorization deficit that may relate to a specific left-hemispheric disorder.

Implicit motor learning deficits in dyslexic adults

Children with developmental dyslexia fail to develop age-appropriate reading skills despite adequate intelligence and education. It has been suggested that dyslexics' various literacy, sensory and motor difficulties may be related to impaired cerebellar function. As the cerebellum is involved in motor learning, we measured serial reaction time performance in 40 adults (21 controls, 19 dyslexics). Dyslexic subjects performed comparably to controls during the randomly-ordered reaction time blocks, indicating that the dyslexics were as able as controls to make appropriate stimulus-response associations. However, the dyslexics failed to show the reaction time reduction that the control group showed during the repeated sequences (p = 0.018) and there was a significant group by condition effect when comparing the last two blocks of the sequence condition with the first two blocks of the final random condition (p = 0.008). Furthermore, there was a significant difference between good and poor readers on the degree of learning during the task (p = 0.015). This suggests that some dyslexics may suffer from an implicit motor learning deficit, which could generalize to non-motor learning.

Perhaps correlational but not causal: no effect of dyslexic readers' magnocellular system on their eye movements during reading

During reading, dyslexic readers exhibit more and longer fixations and a higher percentage of regressions than normal readers. It is still a matter of debate, whether these divergent eye movement patterns of dyslexic readers reflect an underlying problem in word processing or whether they are - as the proponents of the magnocellular deficit hypothesis claim - associated with deficient visual perception that is causal for dyslexia. To overcome problems in the empirical linkage of the magnocellular theory with reading, a string processing task is presented that poses similar demands on visual perception (in terms of letter identification) and oculomotor control as reading does. Two experiments revealed no differences in the eye movement patterns of dyslexic and control readers performing this task. Furthermore, no relationship between the functionality of the participants' magnocellular system assessed by the coherent motion task and string processing were found. The perceptual and oculomotor demands required during string processing were functionally equivalent to those during reading and the presented consonant strings had similar visual characteristics as reading material. Thus, a strong inference can be drawn: Dyslexic readers do not seem to have difficulties with the accurate perception of letters and the control of their eye movements during reading - their reading difficulties therefore cannot be explained in terms of oculomotor and visuo-perceptual problems.

Motor coordination difficulties in a municipality group and in a clinical sample of poor readers

The purpose of the study was to investigate incidence, severity and types of motor problems in two groups of poor readers compared to good reading controls. A group of children with severe dyslexia referred to specialist evaluation, a teacher selected municipality sample comprising the 5% poorest readers, and a control group consisting of the 5% best readers were all assessed applying a norm-based, standardized measure by Henderson and Sugden 1992; (The Movement Assessment Battery for Children. Kent: The Psychological Corporation). The three groups were compared with regard to total motor impairment scores as well as motor function within the areas of manual dexterity, ball-skills and balance. More than 50% of the children in both groups of poor readers showed definite motor coordination difficulties at or below the 5th centile, for which motor intervention is recommended. Children in both groups showed difficulties within the sub-area of manual dexterity in particular and also performed significantly worse than controls within the sub-area of balance, but not in ball-skills. The high incidence of motor coordination problems in the two groups of poor readers indicates that all children with reading difficulties should be screened for possible motor difficulties.

Motion and color processing in school-age children and adults: an ERP study

Stimuli designed to selectively elicit motion or color processing were used in a developmental event-related potential study with adults and children aged 6, 7 and 8. A positivity at posterior site INZ (P-INZ) was greater to motion stimuli only in adults. The P1 and N1 were larger to color stimuli in both adults and children, but earlier to motion stimuli only in adults. Finally, the P2 was larger to color stimuli in adults but larger to motion stimuli in children, and earlier to motion stimuli only in children. The findings across components indicate development from middle childhood to adulthood in aspects of both the motion and color processing systems indexed by this paradigm, but are consistent with an hypothesis of a more protracted time course of development for the motion as compared to the color processing system.

Dyslexia (specific reading disability)

Converging evidence from a number of lines of investigation indicates that dyslexia represents a disorder within the language system and more specifically within a particular subcomponent of that system, phonological processing. Recent advances in imaging technology, particularly the development of functional magnetic resonance imaging, provide evidence of a neurobiological signature for dyslexia, specifically a disruption of two left hemisphere posterior brain systems, one parieto-temporal, the other occipito-temporal, with compensatory engagement of anterior systems around the inferior frontal gyrus and a posterior (right occipito-temporal) system. Furthermore, good evidence indicates a computational role for the left occipito-temporal system: the development of fluent (automatic) reading. The brain systems for reading are malleable and their disruption in dyslexic children may be remediated by provision of an evidence-based, effective reading intervention. In addition, functional magnetic resonance imaging studies of young adults with reading difficulties followed prospectively and longitudinally from age 5 through their mid twenties suggests that there may be two types of reading difficulties, one primarily on a genetic basis, the other, and far more common, reflecting environmental influences. These studies offer the promise for more precise identification and effective management of dyslexia in children, adolescents and adults.

A family-based association study does not support DYX1C1 on 15q21.3 as a candidate gene in developmental dyslexia

We applied a family-based association approach to investigate the role of the DYX1C1 gene on chromosome 15q as a candidate gene for developmental dyslexia (DD) to 158 families containing at least one dyslexic child. We directly sequenced exons 2 and 10 of the DYX1C1 gene and found eight single nucleotide polymorphism (SNPs), three of which (-3G>A, 1249 G>T, 1259 C>G) were suitable for the genetic analyses. We performed single- and multimarker association analyses with DD as a categorical trait by FBAT version 1.4 and TRANSMIT version 2.5.4 programs. Our sample had a power of at least 80% to detect an association between the selected phenotypes and the informative polymorphisms at a significance level of 5%. The results of the categorical analyses did not support the involvement of the DYX1C1 gene variants in this sample of dyslexics and their relatives. Quantitative and multimarker analyses, which provide greater power to detect loci with a minor effect, consistently yielded nonsignificant results. While D1X1C1 is a good candidate gene for DD, we were unable to replicate the original findings between DYX1C1 gene and DD, perhaps due to genetic heterogeneity.

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

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

Identification and characterization of a novel delta12-fatty acid desaturase gene from Rhizopus arrhizus

Based on the sequence information of Delta12-fatty acid desaturase genes (from Mucor circinelloides, Mortierella alpina, Mucor rouxii and Aspergillus nidulans), which were involved in the conversion from C18:1 to C18:2, a cDNA sequence putatively encoding a Delta12-fatty acid desaturase was isolated from Rhizopus arrhizus using the combination of reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) methods. Sequence analysis indicated that it had an open reading frame (ORF) of 1170 bp, coding for 389 amino acid residues of 45 kDa, pI of the deduced protein was 7.01. The deduced amino acid sequence of this cloned cDNA showed high identity to those filamentous fungal Delta12-desaturases mentioned above, including three conserved histidine-rich motifs and two hydrophobic domains. Functional identification was done heterologously in Saccharomyces cerevisiae strain INVScl. The result demonstrated that the deduced amino acid sequence exhibited Delta12-fatty acid desaturase activity, suggesting that this gene encoded for a membrane-bound desaturase, Delta12-fatty acid desaturase.

Visual and language processing deficits in compensated and uncompensated college students with dyslexia

In seven experiments, we investigated whether compensated and uncompensated adults with dyslexia show different patterns of deficits in magnocellular visual processing and in language processing tasks. In four visual tasks, we failed to find evidence of magnocellular deficits in either group. However, both groups of adults with dyslexia showed deficits in component language skills, and the degree of reading impairment predicted the nature and extent of these deficits. Uncompensated readers showed deficits in orthographic and especially phonological coding and awareness and were slower on rapid naming. Compensated readers showed word and nonword performance below controls but better than the uncompensated readers. The compensated group was not significantly less accurate than controls on phonological awareness, nor significantly worse overall on rapid naming.