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      Immaturity of the Oculomotor Saccade and Vergence Interaction in Dyslexic Children: Evidence from a Reading and Visual Search Study

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          Abstract

          Studies comparing binocular eye movements during reading and visual search in dyslexic children are, at our knowledge, inexistent. In the present study we examined ocular motor characteristics in dyslexic children versus two groups of non dyslexic children with chronological/reading age-matched. Binocular eye movements were recorded by an infrared system (mobileEBT®, e(ye)BRAIN) in twelve dyslexic children (mean age 11 years old) and a group of chronological age-matched (N = 9) and reading age-matched (N = 10) non dyslexic children. Two visual tasks were used: text reading and visual search. Independently of the task, the ocular motor behavior in dyslexic children is similar to those reported in reading age-matched non dyslexic children: many and longer fixations as well as poor quality of binocular coordination during and after the saccades. In contrast, chronological age-matched non dyslexic children showed a small number of fixations and short duration of fixations in reading task with respect to visual search task; furthermore their saccades were well yoked in both tasks. The atypical eye movement's patterns observed in dyslexic children suggest a deficiency in the visual attentional processing as well as an immaturity of the ocular motor saccade and vergence systems interaction.

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          Most cited references43

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          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.
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            Dyslexia: a deficit in visuo-spatial attention, not in phonological processing.

            Developmental dyslexia affects up to 10 per cent of the population and it is important to understand its causes. It is widely assumed that phonological deficits, that is, deficits in how words are sounded out, cause the reading difficulties in dyslexia. However, there is emerging evidence that phonological problems and the reading impairment both arise from poor visual (i.e., orthographic) coding. We argue that attentional mechanisms controlled by the dorsal visual stream help in serial scanning of letters and any deficits in this process will cause a cascade of effects, including impairments in visual processing of graphemes, their translation into phonemes and the development of phonemic awareness. This view of dyslexia localizes the core deficit within the visual system and paves the way for new strategies for early diagnosis and treatment. Copyright 2009 Elsevier Ltd. All rights reserved.
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              To see but not to read; the magnocellular theory of dyslexia.

              Developmental dyslexics often complain that small letters appear to blur and move around when they are trying to read. Anatomical, electrophysiological, psychophysical and brain-imaging studies have all contributed to elucidating the functional organization of these and other visual confusions. They emerge not from damage to a single visual relay but from abnormalities of the magnocellular component of the visual system, which is specialized for processing fast temporal information. The m-stream culminates in the posterior parietal cortex, which plays an important role in guiding visual attention. The evidence is consistent with an increasingly sophisticated account of dyslexia that does not single out either phonological, or visual or motor deficits. Rather, temporal processing in all three systems seems to be impaired. Dyslexics may be unable to process fast incoming sensory information adequately in any domain.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2012
                16 March 2012
                : 7
                : 3
                : e33458
                Affiliations
                [1 ]Laboratoire de Psychologie et Neuropsychologie Cognitives, FRE 3292 CNRS - Université Paris Descartes, Boulogne Billancourt Cedex, France
                [2 ]Service de Psychopathologie de l'enfant et de l'adolescent, Hôpital Robert Debré, Paris, France
                [3 ]Service d'Ophtalmologie, Hôpital Robert Debré, Paris, France
                [4 ]e(ye)BRAI, Ivry-sur-Seine, France
                California Pacific Medicial Center Research Institute, United States of America
                Author notes

                Conceived and designed the experiments: MPB MS. Performed the experiments: MBP NN MS. Analyzed the data: MPB MS. Contributed reagents/materials/analysis tools: Selected dyslexic children: CLG. Did visual examination for children: EBQ. Wrote the paper: MPB NN EBQ CLG MS.

                Article
                PONE-D-11-21943
                10.1371/journal.pone.0033458
                3306409
                22438934
                6b2508b0-6d2c-44c8-bcac-48260f4d3409
                Bucci et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                History
                : 4 November 2011
                : 13 February 2012
                Page count
                Pages: 8
                Categories
                Research Article
                Biology
                Neuroscience
                Medicine
                Mental Health
                Psychology
                Cognitive Psychology
                Ophthalmology
                Pediatrics
                Public Health

                Uncategorized
                Uncategorized

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