Research

18 pages, 2921 KiB

Open AccessArticle

Later but Not Weaker: Neural Categorization of Native Vowels of Children at Familial Risk of Dyslexia

by Ao Chen

Brain Sci. 2022, 12(3), 412; https://doi.org/10.3390/brainsci12030412 - 21 Mar 2022

Viewed by 2053

Although allophonic speech processing has been hypothesized to be a contributing factor in developmental dyslexia, experimental evidence is limited and inconsistent. The current study compared the categorization of native similar sounding vowels of typically developing (TD) children and children at familial risk (FR) [...] Read more.

Although allophonic speech processing has been hypothesized to be a contributing factor in developmental dyslexia, experimental evidence is limited and inconsistent. The current study compared the categorization of native similar sounding vowels of typically developing (TD) children and children at familial risk (FR) of dyslexia. EEG response was collected in a non-attentive passive oddball paradigm from 35 TD and 35 FR Dutch 20-month-old infants who were matched on vocabulary. The children were presented with two nonwords “giep” [ɣip] and “gip” [ɣIp] that contrasted solely with respect to the vowel. In the multiple-speaker condition, both nonwords were produced by twelve different speakers while in the single-speaker condition, single tokens of each word were used as stimuli. For both conditions and for both groups, infant positive mismatch response (p-MMR) was elicited, and the p-MMR amplitude was comparable between the two groups, although the FR children had a later p-MMR peak than the TD children in the multiple-speaker condition. These findings indicate that FR children are able to categorize speech sounds, but that they may do so in a more effortful way than TDs. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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20 pages, 1752 KiB

Open AccessArticle

Evidence of Altered Functional Connectivity at Rest in the Writing Network of Children with Dyslexia

by Claire Gosse, Laurence Dricot and Marie Van Reybroeck

Brain Sci. 2022, 12(2), 243; https://doi.org/10.3390/brainsci12020243 - 10 Feb 2022

Cited by 2 | Viewed by 3114

Abstract

Aim. Handwriting abilities in children with dyslexia (DYS) are not well documented in the current literature, and the presence of graphomotor impairment in addition to spelling impairment in dyslexia is controversial. Using resting-state functional connectivity (RSFC), the present study aims to answer the [...] Read more.

Aim. Handwriting abilities in children with dyslexia (DYS) are not well documented in the current literature, and the presence of graphomotor impairment in addition to spelling impairment in dyslexia is controversial. Using resting-state functional connectivity (RSFC), the present study aims to answer the following question: are there markers of graphomotor impairment at rest in DYS children? Method. The participants were children with DYS and typically developing (TD) children (n = 32) from French-speaking primary schools (M_age = 9.3 years). The behavioural evaluation consisted of spelling and handwriting measures. Participants underwent a resting-state fMRI scan. Results. Analyses of RSFC focused on a brain region responsible for graphomotor processes—the graphemic/motor frontal area (GMFA). The RSFC between the GMFA and all other voxels of the brain was measured. Whole-brain ANOVAs were run to compare RSFC in DYS and TD children. The results demonstrated reduced RSFC in DYS compared to TD between the GMFA and brain areas involved in both spelling processes and motor-related processes. Conclusions. For the first time, this study highlighted a disruption of the writing network in DYS. By identifying functional markers of both spelling and handwriting deficits at rest in young DYS participants, this study supports the presence of graphomotor impairment in dyslexia. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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19 pages, 1005 KiB

Open AccessArticle

Direct and Indirect Effects of Blood Levels of Omega-3 and Omega-6 Fatty Acids on Reading and Writing (Dis)Abilities

by Francesca Borasio, Marie-Louise Syren, Stefano Turolo, Carlo Agostoni, Massimo Molteni, Alessandro Antonietti and Maria Luisa Lorusso

Brain Sci. 2022, 12(2), 169; https://doi.org/10.3390/brainsci12020169 - 27 Jan 2022

Cited by 3 | Viewed by 2691

Abstract

The purpose of the present study was to investigate whether there are associations between polyunsaturated fatty acid (PUFA) blood levels, reading/writing performance and performance in neuropsychological tasks. Moderate to strong correlations were found between PUFA levels (specific omega-6/omega-3 ratios) and reading/writing abilities, and [...] Read more.

The purpose of the present study was to investigate whether there are associations between polyunsaturated fatty acid (PUFA) blood levels, reading/writing performance and performance in neuropsychological tasks. Moderate to strong correlations were found between PUFA levels (specific omega-6/omega-3 ratios) and reading/writing abilities, and the former and neuropsychological test scores. Mediation models analyzing the direct and indirect effects of PUFA on reading and writing scores showed that the effects of fatty acids on learning measures appear to be direct rather than mediated by the investigated visual and auditory neuropsychological mechanisms. The only significant indirect effect was found for the difference in accuracy between the left and right visual fields in visual-spatial cueing tasks, acting as a mediator for the effect of PUFA ratios on writing accuracy. Regression analyses, by contrast, confirmed the roles of phonological awareness and other visual attentional factors as predictors of reading and writing skills. Such results confirm the crucial role of visual-spatial attention mechanisms in reading and writing, and suggest that visual low-level mechanisms may be more sensitive to the effects of favorable conditions related to the presence of higher omega-3 blood levels. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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10 pages, 1264 KiB

Open AccessArticle

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

by Simona Caldani, Lionel Moiroud, Carole Miquel, Vanessa Peiffer, Alessandro Florian and Maria Pia Bucci

Brain Sci. 2021, 11(11), 1440; https://doi.org/10.3390/brainsci11111440 - 29 Oct 2021

Cited by 2 | Viewed by 2786

Abstract

(1) Background: This study explored the effect of short vestibular and cognitive training on the reading speed in dyslexic children. (2) Methods: The reading speed was evaluated by using a reading test (Évaluation de la Lecture en FluencE, ELFE) in a crossover design [...] Read more.

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

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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20 pages, 3239 KiB

Open AccessArticle

Predicting Dyslexia and Reading Speed in Adolescents from Eye Movements in Reading and Non-Reading Tasks: A Machine Learning Approach

by Alae Eddine El Hmimdi, Lindsey M Ward, Themis Palpanas and Zoï Kapoula

Brain Sci. 2021, 11(10), 1337; https://doi.org/10.3390/brainsci11101337 - 11 Oct 2021

Cited by 11 | Viewed by 2804

Abstract

There is evidence that abnormalities in eye movements exist during reading in dyslexic individuals. A few recent studies applied Machine Learning (ML) classifiers to such eye movement data to predict dyslexia. A general problem with these studies is that eye movement data sets [...] Read more.

There is evidence that abnormalities in eye movements exist during reading in dyslexic individuals. A few recent studies applied Machine Learning (ML) classifiers to such eye movement data to predict dyslexia. A general problem with these studies is that eye movement data sets are limited to reading saccades and fixations that are confounded by reading difficulty, e.g., it is unclear whether abnormalities are the consequence or the cause of reading difficulty. Recently, Ward and Kapoula used LED targets (with the REMOBI & AIDEAL method) to demonstrate abnormalities of large saccades and vergence eye movements in depth demonstrating intrinsic eye movement problems independent from reading in dyslexia. In another study, binocular eye movements were studied while reading two texts: one using the “Alouette” text, which has no meaning and requires word decoding, the other using a meaningful text. It was found the Alouette text exacerbates eye movement abnormalities in dyslexics. In this paper, we more precisely quantify the quality of such eye movement descriptors for dyslexia detection. We use the descriptors produced in the four different setups as input to multiple classifiers and compare their generalization performances. Our results demonstrate that eye movement data from the Alouette test predicts dyslexia with an accuracy of 81.25%; similarly, we were able to predict dyslexia with an accuracy of 81.25% when using data from saccades to LED targets on the Remobi device and 77.3% when using vergence movements to LED targets. Noticeably, eye movement data from the meaningful text produced the lowest accuracy (70.2%). In a subsequent analysis, ML algorithms were applied to predict reading speed based on eye movement descriptors extracted from the meaningful reading, then from Remobi saccade and vergence tests. Remobi vergence eye movement descriptors can predict reading speed even better than eye movement descriptors from the meaningful reading test. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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12 pages, 1295 KiB

Open AccessArticle

Dyslexics’ Fragile Oculomotor Control Is Further Destabilized by Increased Text Difficulty

by Lindsey M. Ward and Zoi Kapoula

Brain Sci. 2021, 11(8), 990; https://doi.org/10.3390/brainsci11080990 - 27 Jul 2021

Cited by 8 | Viewed by 2147

Abstract

Dyslexic adolescents demonstrate deficits in word decoding, recognition, and oculomotor coordination as compared to healthy controls. Our lab recently showed intrinsic deficits in large saccades and vergence movements with a Remobi device independent from reading. This shed new light on the field of [...] Read more.

Dyslexic adolescents demonstrate deficits in word decoding, recognition, and oculomotor coordination as compared to healthy controls. Our lab recently showed intrinsic deficits in large saccades and vergence movements with a Remobi device independent from reading. This shed new light on the field of dyslexia, as it has been debated in the literature whether the deficits in eye movements are a cause or consequence of reading difficulty. The present study investigates how these oculomotor problems are compensated for or aggravated by text difficulty. A total of 46 dyslexic and 41 non-dyslexic adolescents’ eye movements were analyzed while reading L’Alouette, a dyslexia screening test, and 35 Kilos D’Espoir, a children’s book with a reading age of 10 years. While reading the more difficult text, dyslexics made more mistakes, read slower, and made more regressive saccades; moreover, they made smaller amplitude saccades with abnormal velocity profiles (e.g., higher peak velocity but lower average velocity) and significantly higher saccade disconjugacy. While reading the simpler text, these differences persisted; however, the difference in saccade disconjugacy, although present, was no longer significant, nor was there a significant difference in the percentage of regressive saccades. We propose that intrinsic eye movement abnormalities in dyslexics such as saccade disconjugacy, abnormal velocity profiles, and cognitively associated regressive saccades can be particularly exacerbated if the reading text relies heavily on word decoding to extract meaning; increased number of regressive saccades are a manifestation of reading difficulty and not a problem of eye movement per se. These interpretations are in line with the motor theory of visual attention and our previous research describing the relationship between binocular motor control, attention, and cognition that exists outside of the field of dyslexia. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

15 pages, 1169 KiB

Open AccessArticle

To Name or Not to Name: Eye Movements and Semantic Processing in RAN and Reading

by Luan Tuyen Chau, Mila Dimitrova Vulchanova and Joel B. Talcott

Brain Sci. 2021, 11(7), 866; https://doi.org/10.3390/brainsci11070866 - 29 Jun 2021

Cited by 1 | Viewed by 3797

Abstract

This study examined the well-established relationship between rapid naming and reading. Rapid automatized naming (RAN) has long been demonstrated as a strong predictor of reading abilities. Despite extensive research spanning over 4 decades, the underlying mechanisms of these causes remain a subject of [...] Read more.

This study examined the well-established relationship between rapid naming and reading. Rapid automatized naming (RAN) has long been demonstrated as a strong predictor of reading abilities. Despite extensive research spanning over 4 decades, the underlying mechanisms of these causes remain a subject of inquiry. The current study investigated the role of eye movements and semantic processing in defining the RAN-reading relationship. The participants in this study were 42 English-speaking undergraduate students at a British university. The materials included a word reading task, two conventional RAN tasks (object and digit), and two RAN-like categorization tasks (object and digit). The results obtained suggested the interdependence between rapid naming and semantic processing. Hierarchical multiple regression analyses revealed that oculomotor control remains an integral part of variability in RAN and reading performance. Taken together, our results suggest that RAN and reading measures are correlated because both require rapid and accurate retrieval of phonological representations, semantic properties of visual stimuli, and stable co-ordination of eye movements. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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20 pages, 3875 KiB

Open AccessArticle

Selecting the Most Relevant Brain Regions to Classify Children with Developmental Dyslexia and Typical Readers by Using Complex Magnocellular Stimuli and Multiple Kernel Learning

by Sara Mascheretti, Denis Peruzzo, Chiara Andreola, Martina Villa, Tommaso Ciceri, Vittoria Trezzi, Cecilia Marino and Filippo Arrigoni

Brain Sci. 2021, 11(6), 722; https://doi.org/10.3390/brainsci11060722 - 28 May 2021

Cited by 5 | Viewed by 2440

Abstract

Increasing evidence supports the presence of deficits in the visual magnocellular (M) system in developmental dyslexia (DD). The M system is related to the fronto-parietal attentional network. Previous neuroimaging studies have revealed reduced/absent activation within the visual M pathway in DD, but they [...] Read more.

Increasing evidence supports the presence of deficits in the visual magnocellular (M) system in developmental dyslexia (DD). The M system is related to the fronto-parietal attentional network. Previous neuroimaging studies have revealed reduced/absent activation within the visual M pathway in DD, but they have failed to characterize the extensive brain network activated by M stimuli. We performed a multivariate pattern analysis on a Region of Interest (ROI) level to differentiate between children with DD and age-matched typical readers (TRs) by combining full-field sinusoidal gratings, controlled for spatial and temporal frequencies and luminance contrast, and a coherent motion (CM) sensitivity task at 6%-CML6, 15%-CML15 and 40%-CML40. ROIs spanning the entire visual dorsal stream and ventral attention network (VAN) had higher discriminative weights and showed higher act1ivation in TRs than in children with DD. Of the two tasks, CM had the greatest weight when classifying TRs and children with DD in most of the ROIs spanning these streams. For the CML6, activation within the right superior parietal cortex positively correlated with reading skills. Our approach highlighted the dorsal stream and the VAN as highly discriminative areas between children with DD and TRs and allowed for a better characterization of the “dorsal stream vulnerability” underlying DD. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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Review

Jump to: Research, Other

22 pages, 400 KiB

Open AccessReview

Automaticity and Executive Abilities in Developmental Dyslexia: A Theoretical Review

by James H. Smith-Spark and Rebecca Gordon

Brain Sci. 2022, 12(4), 446; https://doi.org/10.3390/brainsci12040446 - 27 Mar 2022

Cited by 12 | Viewed by 3642

Abstract

Cognitive difficulties are well documented in developmental dyslexia but they present a challenge to dyslexia theory. In this paper, the Model of the Control of Action is proposed as a theoretical explanation of how and why deficits in both automaticity and executive abilities [...] Read more.

Cognitive difficulties are well documented in developmental dyslexia but they present a challenge to dyslexia theory. In this paper, the Model of the Control of Action is proposed as a theoretical explanation of how and why deficits in both automaticity and executive abilities are apparent in the cognitive profiles of dyslexia and how these deficits might relate to literacy difficulties. This theoretical perspective is used to consider evidence from different cognitive domains. The neuroanatomical underpinnings of automaticity and executive abilities are then discussed in relation to the understanding of dyslexia. Links between reading, writing, and executive function are considered. The reviewed evidence suggests that dyslexia theory should consider an interaction between procedural learned behaviour (automaticity) and higher-order (executive) abilities. The capacity to handle environmental interference, develop and engage adaptive strategies accordingly, and plan actions all require interactions between the cerebellum and the prefrontal cortex (PFC). Difficulties in these areas might explain both impairments in the cumulative development of literacy skills in childhood and general task management in everyday life in adulthood. It is suggested that improved measures are required to assess this cerebellar–PFC interaction and to allow early identification of future literacy difficulties, allowing implementation of timely interventions and reasonable adjustments. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

17 pages, 709 KiB

Open AccessReview

Emergent Neuroimaging Findings for Written Expression in Children: A Scoping Review

by Lara-Jeane C. Costa, Sarah V. Spencer and Stephen R. Hooper

Brain Sci. 2022, 12(3), 406; https://doi.org/10.3390/brainsci12030406 - 18 Mar 2022

Cited by 2 | Viewed by 2936

Abstract

Background: There is currently a dearth of research on the neural framework of writing tasks in children, as measured by neuroimaging techniques. Objective: This paper provides an overview of the current literature examining the neurological underpinnings of written expression in children. Design: Using [...] Read more.

Background: There is currently a dearth of research on the neural framework of writing tasks in children, as measured by neuroimaging techniques. Objective: This paper provides an overview of the current literature examining the neurological underpinnings of written expression in children. Design: Using a scoping review approach, with thorough searches of key databases, this paper presents the available literature comprising 13 different studies using both structural and functional neuroimaging techniques with the 0–18 English speaking population. Results: Studies largely presented small sample sizes, with most studies utilizing elementary or middle school-aged children. Emergent findings revealed a complex network of neural contributions to the writing process in children. There were associations between the left fusiform gyrus and orthographic coding (i.e., handwriting), and spelling and written composition measures were significantly correlated with activity in the left posterior cingulate, left precuneus, and right precuneus regions. Additionally, results revealed that good versus poor writers manifested differential brain activation patterns during many tasks associated with written expression, with good writers performing more efficiently than poor writers with respect to brain regions activated during a writing task across handwriting, spelling, and idea generation. Conclusions: The findings from this scoping review lay the foundation for future studies examining the interface between writing skills in children and underlying neural pathways that support the various components of the writing process. It will be important for future research to examine the neurological bases of the various components of written expression in children and adolescents. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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17 pages, 328 KiB

Open AccessEditor’s ChoiceReview

Evidence from ERP and Eye Movements as Markers of Language Dysfunction in Dyslexia

by Aikaterini Premeti, Maria Pia Bucci and Frédéric Isel

Brain Sci. 2022, 12(1), 73; https://doi.org/10.3390/brainsci12010073 - 01 Jan 2022

Cited by 15 | Viewed by 3784

Abstract

Developmental dyslexia is a complex reading disorder involving genetic and environmental factors. After more than a century of research, its etiology remains debated. Two hypotheses are often put forward by scholars to account for the causes of dyslexia. The most common one, the [...] Read more.

Developmental dyslexia is a complex reading disorder involving genetic and environmental factors. After more than a century of research, its etiology remains debated. Two hypotheses are often put forward by scholars to account for the causes of dyslexia. The most common one, the linguistic hypothesis, postulates that dyslexia is due to poor phonological awareness. The alternative hypothesis considers that dyslexia is caused by visual-attentional deficits and abnormal eye movement patterns. This article reviews a series of selected event-related brain potential (ERP) and eye movement studies on the reading ability of dyslexic individuals to provide an informed state of knowledge on the etiology of dyslexia. Our purpose is to show that the two abovementioned hypotheses are not necessarily mutually exclusive, and that dyslexia should rather be considered as a multifactorial deficit. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

14 pages, 533 KiB

Open AccessEditor’s ChoiceReview

Insights into Dyslexia Genetics Research from the Last Two Decades

by Florina Erbeli, Marianne Rice and Silvia Paracchini

Brain Sci. 2022, 12(1), 27; https://doi.org/10.3390/brainsci12010027 - 26 Dec 2021

Cited by 36 | Viewed by 9971

Abstract

Dyslexia, a specific reading disability, is a common (up to 10% of children) and highly heritable (~70%) neurodevelopmental disorder. Behavioral and molecular genetic approaches are aimed towards dissecting its significant genetic component. In the proposed review, we will summarize advances in twin and [...] Read more.

Dyslexia, a specific reading disability, is a common (up to 10% of children) and highly heritable (~70%) neurodevelopmental disorder. Behavioral and molecular genetic approaches are aimed towards dissecting its significant genetic component. In the proposed review, we will summarize advances in twin and molecular genetic research from the past 20 years. First, we will briefly outline the clinical and educational presentation and epidemiology of dyslexia. Next, we will summarize results from twin studies, followed by molecular genetic research (e.g., genome-wide association studies (GWASs)). In particular, we will highlight converging key insights from genetic research. (1) Dyslexia is a highly polygenic neurodevelopmental disorder with a complex genetic architecture. (2) Dyslexia categories share a large proportion of genetics with continuously distributed measures of reading skills, with shared genetic risks also seen across development. (3) Dyslexia genetic risks are shared with those implicated in many other neurodevelopmental disorders (e.g., developmental language disorder and dyscalculia). Finally, we will discuss the implications and future directions. As the diversity of genetic studies continues to increase through international collaborate efforts, we will highlight the challenges in advances of genetics discoveries in this field. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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13 pages, 316 KiB

Open AccessReview

Common Misconceptions about the Phonological Deficit Theory of Dyslexia

by David L. Share

Brain Sci. 2021, 11(11), 1510; https://doi.org/10.3390/brainsci11111510 - 14 Nov 2021

Cited by 18 | Viewed by 11604

Abstract

In this discussion paper, I review a number of common misconceptions about the phonological deficit theory (PDH) of dyslexia. These include the common but mistaken idea that the PDH is simply about phonemic awareness (PA), and, consequently, is a circular “pseudo”-explanation or epiphenomenon [...] Read more.

In this discussion paper, I review a number of common misconceptions about the phonological deficit theory (PDH) of dyslexia. These include the common but mistaken idea that the PDH is simply about phonemic awareness (PA), and, consequently, is a circular “pseudo”-explanation or epiphenomenon of reading difficulties. I argue that PA is only the “tip of the phonological iceberg” and that “deeper” spoken-language phonological impairments among dyslexics appear well before the onset of reading and even at birth. Furthermore, not even reading-specific expressions of phonological deficits—PA or pseudoword naming, can be considered circular if we clearly distinguish between reading proper—real meaning-bearing words, or real text, and the mechanisms (subskills) of reading development (such as phonological recoding). I also explain why an understanding of what constitutes an efficient writing system explains why phonology is necessarily a major source of variability in reading ability and hence a core deficit (or at least one core deficit) among struggling readers whether dyslexic or non-dyslexic. I also address the misguided notion that the PDH has now fallen out of favor because most dyslexia researchers have (largely) ceased studying phonological processing. I emphasize that acceptance of the PDH does not imply repudiation of other non-phonological hypotheses because the PDH does not claim to account for all the variance in reading ability/disability. Finally, I ask where neurobiology enters the picture and suggest that researchers need to exercise more caution in drawing their conclusions. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

19 pages, 1436 KiB

Open AccessFeature PaperReview

Words as Visual Objects: Neural and Behavioral Evidence for High-Level Visual Impairments in Dyslexia

by Heida Maria Sigurdardottir, Inga María Ólafsdóttir and Hélène Devillez

Brain Sci. 2021, 11(11), 1427; https://doi.org/10.3390/brainsci11111427 - 28 Oct 2021

Cited by 8 | Viewed by 4210

Abstract

Developmental dyslexia is defined by reading impairments that are disproportionate to intelligence, motivation, and the educational opportunities considered necessary for reading. Its cause has traditionally been considered to be a phonological deficit, where people have difficulties with differentiating the sounds of spoken language. [...] Read more.

Developmental dyslexia is defined by reading impairments that are disproportionate to intelligence, motivation, and the educational opportunities considered necessary for reading. Its cause has traditionally been considered to be a phonological deficit, where people have difficulties with differentiating the sounds of spoken language. However, reading is a multidimensional skill and relies on various cognitive abilities. These may include high-level vision—the processes that support visual recognition despite innumerable image variations, such as in viewpoint, position, or size. According to our high-level visual dysfunction hypothesis, reading problems of some people with dyslexia can be a salient manifestation of a more general deficit of high-level vision. This paper provides a perspective on how such non-phonological impairments could, in some cases, cause dyslexia. To argue in favor of this hypothesis, we will discuss work on functional neuroimaging, structural imaging, electrophysiology, and behavior that provides evidence for a link between high-level visual impairment and dyslexia. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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31 pages, 648 KiB

Open AccessReview

Is Developmental Dyslexia Due to a Visual and Not a Phonological Impairment?

by Reinhard Werth

Brain Sci. 2021, 11(10), 1313; https://doi.org/10.3390/brainsci11101313 - 02 Oct 2021

Cited by 8 | Viewed by 4670

Abstract

It is a widely held belief that developmental dyslexia (DD) is a phonological disorder in which readers have difficulty associating graphemes with their corresponding phonemes. In contrast, the magnocellular theory of dyslexia assumes that DD is a visual disorder caused by dysfunctional magnocellular [...] Read more.

It is a widely held belief that developmental dyslexia (DD) is a phonological disorder in which readers have difficulty associating graphemes with their corresponding phonemes. In contrast, the magnocellular theory of dyslexia assumes that DD is a visual disorder caused by dysfunctional magnocellular neural pathways. The review explores arguments for and against these theories. Recent results have shown that DD is caused by (1) a reduced ability to simultaneously recognize sequences of letters that make up words, (2) longer fixation times required to simultaneously recognize strings of letters, and (3) amplitudes of saccades that do not match the number of simultaneously recognized letters. It was shown that pseudowords that could not be recognized simultaneously were recognized almost without errors when the fixation time was extended. However, there is an individual maximum number of letters that each reader with DD can recognize simultaneously. Findings on the neurobiological basis of temporal summation have shown that a necessary prolongation of fixation times is due to impaired processing mechanisms of the visual system, presumably involving magnocells and parvocells. An area in the mid-fusiform gyrus also appears to play a significant role in the ability to simultaneously recognize words and pseudowords. The results also contradict the assumption that DD is due to a lack of eye movement control. The present research does not support the assumption that DD is caused by a phonological disorder but shows that DD is due to a visual processing dysfunction. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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32 pages, 3301 KiB

Open AccessReview

The Neurological Basis of Developmental Dyslexia and Related Disorders: A Reappraisal of the Temporal Hypothesis, Twenty Years on

by Michel Habib

Brain Sci. 2021, 11(6), 708; https://doi.org/10.3390/brainsci11060708 - 27 May 2021

Cited by 24 | Viewed by 15978

Abstract

In a now-classic article published a couple of decades ago (Brain, 2000; 123: 2373–2399), I proposed an “extended temporal processing deficit hypothesis of dyslexia”, suggesting that a deficit in temporal processing could explain not only language-related peculiarities usually noticed in dyslexic children, but [...] Read more.

In a now-classic article published a couple of decades ago (Brain, 2000; 123: 2373–2399), I proposed an “extended temporal processing deficit hypothesis of dyslexia”, suggesting that a deficit in temporal processing could explain not only language-related peculiarities usually noticed in dyslexic children, but also a wider range of symptoms related to impaired processing of time in general. In the present review paper, I will revisit this “historical” hypothesis both in the light of a new clinical perspective, including the central yet poorly explained notion of comorbidity, and also taking a new look at the most recent experimental work, mainly focusing on brain imaging data. First, consistent with daily clinical practice, I propose to distinguish three groups of children who fail to learn to read, of fairly equal occurrence, who share the same initial presentation (difficulty in mastering the rules of grapheme–phoneme correspondence) but with differing associated signs and/or comorbid conditions (language disorders in the first group, attentional deficits in the second one, and motor coordination problems in the last one), thus suggesting, at least in part, potentially different triggering mechanisms. It is then suggested, in the light of brain imaging information available to date, that the three main clinical presentations/associations of cognitive impairments that compromise reading skills acquisition correspond to three distinct patterns of miswiring or “disconnectivity” in specific brain networks which have in common their involvement in the process of learning and their heavy reliance on temporal features of information processing. With reference to the classic temporal processing deficit of dyslexia and to recent evidence of an inability of the dyslexic brain to achieve adequate coupling of oscillatory brain activity to the temporal features of external events, a general model is proposed according to which a common mechanism of temporal uncoupling between various disconnected—and/or mis-wired—processors may account for distinct forms of specific learning disorders, with reading impairment being a more or less constant feature. Finally, the potential therapeutic implications of such a view are considered, with special emphasis on methods seeking to enhance cross-modal connectivity between separate brain systems, including those using rhythmic and musical training in dyslexic patients. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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Other

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11 pages, 589 KiB

Open AccessOpinion

Success Is Not the Entire Story for a Scientific Theory: The Case of the Phonological Deficit Theory of Dyslexia

by Pierluigi Zoccolotti

Brain Sci. 2022, 12(4), 425; https://doi.org/10.3390/brainsci12040425 - 23 Mar 2022

Cited by 5 | Viewed by 2879

Abstract

In a recent paper, Share discussed four different “Common Misconceptions about the Phonological Deficit Theory of Dyslexia” and described this theory as “a model of true scientific progress” and a clear “success story”. In this note, I argue [...] Read more.

In a recent paper, Share discussed four different “Common Misconceptions about the Phonological Deficit Theory of Dyslexia” and described this theory as “a model of true scientific progress” and a clear “success story”. In this note, I argue that at least part of the success of this theory is due to the lack of explicit predictions which make it very difficult (if possible) to test its predictions, and, possibly, falsify the theory. Some areas of pertinent research, including categorical phoneme perception, picture naming, and phonological awareness are summarized. Furthermore, two lines of research in which groups of researchers have attempted to formulate more explicit predictions are briefly outlined. It is concluded that, although much research has variously referred to the phonological deficit theory of dyslexia, the resulting large body of evidence presents a complex pattern of results which, in the absence of an explicit formulation of the theory, is extremely difficult to frame within a unitary interpretation. Overall, what seems needed is a theoretical formulation that, on the one hand, can account for the complex pattern of available evidence and, on the other hand, provide testable predictions for future research. Full article

(This article belongs to the Special Issue Neurobiological Basis of Developmental Dyslexia)

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