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

Published on Oct 1, 2021in Brain Sciences3.394
· DOI :10.3390/BRAINSCI11101313
Reinhard Werth9
Estimated H-index: 9
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.
#1Reinhard Werth (LMU: Ludwig Maximilian University of Munich)H-Index: 9
Background: Flawless reading presupposes the ability to simultaneously recognize a sequence of letters, to fixate words at a given location for a given time, to exert eye movements of a given amplitude, and to retrieve phonems rapidly from memory. Poor reading performance may be due to an impairment of at least one of these abilities. Objectives: It was investigated whether reading performance of dyslexic children can be improved by changing the reading strategy without any previous training. Me...
Reading is a rapid, distributed process that engages multiple components of the ventral visual stream. To understand the neural constituents and their interactions that allow us to identify written words, we performed direct intra-cranial recordings in a large cohort of humans. This allowed us to isolate the spatiotemporal dynamics of visual word recognition across the entire left ventral occipitotemporal cortex. We found that mid-fusiform cortex is the first brain region sensitive to lexicality...
#9Enrico Schulz (LMU: Ludwig Maximilian University of Munich)H-Index: 2
The visual word form area (VWFA) in the left ventral occipito-temporal (vOT) cortex is key to fluent reading in children and adults. Diminished VWFA activation during print processing tasks is a common finding in subjects with severe reading problems. Here, we report fMRI data from a multicentre study with 140 children in primary school (7.9–12.2 years; 55 children with dyslexia, 73 typical readers, 12 intermediate readers). All performed a semantic task on visually presented words and a matched...
#1Sang-Han Choi (KU: Korea University)H-Index: 2
#2Gangwon Jeong (SNU: Seoul National University)H-Index: 2
Last. Zang-Hee Cho (SNU: Seoul National University)H-Index: 56
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Abstract The extrastriate cortex in the human visual cortex is divided into two distinct clusters: the “what-information” processing area and the “where-information” processing area. It is widely accepted that the “what-information” cluster is processed through the ventral stream to the temporal cortex, and the “where-information” cluster through the dorsal stream to the parietal cortex. In human neuroanatomy, fiber bundles for the ventral stream (such as the inferior longitudinal fasciculus) ar...
#1Rania A. Masri (USYD: University of Sydney)H-Index: 5
#2Ulrike Grünert (USYD: University of Sydney)H-Index: 51
Last. Paul R. Martin (USYD: University of Sydney)H-Index: 53
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Two main subcortical pathways serving conscious visual perception are the midget-parvocellular (P), and the parasol-magnocellular (M) pathways. It is generally accepted that the P pathway serves red-green color vision, but the relative contribution of P and M pathways to spatial vision is a long-standing and unresolved issue. Here, we mapped the spatial sampling properties of P and M pathways across the human retina. Data were obtained from immunolabeled vertical sections of six postmortem male ...
#1Tatsuya Jitsuishi (Chiba University)H-Index: 2
#2Atsushi Yamaguchi (Chiba University)H-Index: 20
The intraparietal sulcus (IPS) in the posterior parietal cortex (PPC) is well-known as an interface for sensorimotor integration in visually guided actions. However, our understanding of the human neural network between the IPS and the cortical visual areas has been devoid of anatomical specificity. We here identified a distinctive association fiber tract "IPS-FG" to connect the IPS areas and the fusiform gyrus (FG), a high-level visual region, by white matter dissection and tractography. The ma...
#1Florentina Soto (WashU: Washington University in St. Louis)H-Index: 25
#2Jen-Chun Hsiang (WashU: Washington University in St. Louis)H-Index: 3
Last. Daniel KerschensteinerH-Index: 27
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Summary In humans, midget and parasol ganglion cells account for most of the input from the eyes to the brain. Yet, how they encode visual information is unknown. Here, we perform large-scale multi-electrode array recordings from retinas of treatment-naive patients who underwent enucleation surgery for choroidal malignant melanomas. We identify robust differences in the function of midget and parasol ganglion cells, consistent asymmetries between their ON and OFF types (that signal light increme...
#1Sven P. Heinrich (University of Freiburg)H-Index: 17
#2Torben Blechenberg (University of Freiburg)H-Index: 1
Last. Michael Bach (University of Freiburg)H-Index: 60
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PURPOSE The effect of duration of optotype presentation on visual acuity measures has been extensively studied under photopic conditions. However, systematic data on duration dependence of acuity values under mesopic and scotopic conditions is scarce, despite being highly relevant for many visual tasks including night driving, and for clinical diagnostic applications. The present study aims to address this void. METHODS We measured Landolt C acuity under photopic (90 cd/m2), mesopic (0.7 cd/m2),...
#1Arnaud Beauny (ULB: Université libre de Bruxelles)H-Index: 3
#2Adélaïde de Heering (ULB: Université libre de Bruxelles)H-Index: 14
Last. Axel Cleeremans (ULB: Université libre de Bruxelles)H-Index: 63
view all 6 authors...
Can people categorize complex visual scenes unconsciously? The possibility of unconscious perception remains controversial. Here, we addressed this question using psychophysical methods applied to unmasked visual stimuli presented for extremely short durations (in the μsec range) by means of a custom-built modern tachistoscope. Our experiment was composed of two phases. In the first phase, natural or urban scenes were either absent or present (for varying durations) on the tachistoscope screen, ...
Many studies report a deficit in working memory in children with Developmental Dyslexia (DD) and Developmental Coordination Disorder (DCD) compared to children with Typical Development (TD). In thi...
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