A Brief Review of Current Research on Reading Difficulties and Approaches to Intervention.
Taeko Bourque, Jo-Anne LeFevre, Heather Douglas https://drive.google.com/file/d/1AoKd4OJ3wzwB4vVRBCBMGTlB7IGyF4iX/view?usp=sharing
“Even with good instruction, approximately 10% of people struggle to acquire adequate literacy skills, possibly due to deficits in key cognitive processes such as phonological awareness, attention, or sensory processing. In this paper, we describe current research on how students learn to read. Decoding skill (i.e., translating letters to sounds to access word meaning) is the foundation for learning to read; decoding difficulties form a bottleneck for developing adequate reading skills. Although interventions that directly target decoding help students with reading problems to improve their skills, some students continue to have reading difficulties. Decoding training using phonics should be central to whole class instruction. However, reading difficulties have multiple causes and correlates, and so interventions that combine phonics with training of related cognitive and attentional skills may be beneficial for readers who continue to struggle despite good instruction. Online programs that provide integrated decoding and fluency training may provide effective and accessible interventions for struggling readers.”
Visual Motion and Decision-Making in Dyslexia: Reduced Accumulation of Sensory Evidence and Related Neural Dynamics.
Catherine Manning, Cameron D. Hassall, Laurence T. Hunt, Anthony M. Norcia, Eric-Jan Wagenmakers, Margaret J. Snowling, Gaia Scerif and Nathan J. Evans Journal of Neuroscience 5 January 2022, 42 (1) 121-134 https://www.jneurosci.org/content/42/1/121#sec-17
“Reduced sensitivity to visual information has been reported in dyslexia, with a lively debate about whether these differences causally contribute to reading difficulties. In this large preregistered study with a blind modeling approach, we combine state-of-the art methods in both computational modeling and EEG analysis to pinpoint the stages of processing that are atypical in children with dyslexia in two visual motion tasks that vary in their requirement for noise exclusion. We find reduced evidence accumulation in children with dyslexia across both tasks, and identify a neural marker, allowing us to link brain and behavior. We show that children with dyslexia exhibit general difficulties with extracting sensory evidence from global motion displays, not just in tasks that require noise exclusion.”
Eye movements in reading and information processing: 20 years of research
Rayner, K. (1998). Psychological Bulletin, 124(3), 372–422. https://doi.org/10.1037/0033-2909.124.3.372 https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.294.4262&rep=rep1&type=pdf
“Recent studies of eye movements in reading and other information processing tasks, such as music reading, typing, visual search, and scene perception, are reviewed. The major emphasis of the review is on reading as a specific example of cognitive processing. Basic topics discussed with respect to reading are (a) the characteristics of eye movements, (b) the perceptual span, (c) integration of information across saccades, (d) eye movement control, and (e) individual differences (including dyslexia). Similar topics are discussed with respect to the other tasks examined. The basic theme of the review is that eye movement data reflect moment-to-moment cognitive processes in the various tasks examined. Theoretical and practical considerations concerning the use of eye movement data are also discussed.“
The dependence of visual scanning performance on saccade, fixation, and perceptual metrics
Matthew H. Phillips, Jay A. Edelman, March 2001 | https://doi.org/10.1016/j.visres.2007.12.020
“The principal finding of this study was that both within and across sessions, saccade metrics accounted for much more of the variability and improvement in performance than did fixation duration. Increases in search speed were due primarily to subjects processing information from a greater area of the visual field, rather than processing information from a fixed area more quickly.”
Dyslexic children are confronted with unstable binocular fixation while reading
Stephanie Jainta, Zoï Kapoula Affiliations expand | https://pubmed.ncbi.nlm.nih.gov/21494641/
“We found that the binocular yoking of reading saccades was poor in dyslexic children (relative to non-dyslexics) resulting in vergence errors; their disconjugate drift during fixations was not correlated with the disconjugacy during their saccades, causing considerable variability of vergence angle from fixation to fixation. Due to such poor oculomotor adjustments during reading, the overall fixation disparity was larger for dyslexic children, putting larger demand on their sensory fusion processes. Moreover, for dyslexics the standard deviation of fixation disparity was larger particularly when reading at near distance. We conclude that besides documented phoneme processing disorders, visual/ocular motor imperfections may exist in dyslexics that lead to fixation instability and thus, to instability of the letters or words during reading; such instability may perturb fusional processes and might—in part—complicate letter/word identification.”
Speed of processing of the visual-orthographic and auditory-phonological systems in adult dyslexics: the contribution of “asynchrony” to word recognition deficits
Zvia Breznitz, Maya Misra | https://pubmed.ncbi.nlm.nih.gov/12744959/
“Our data support and extend previous work that found SOP asynchrony to be an underlying factor of childhood dyslexia. The present data suggests, however, that among adult dyslexics the between modalities asynchrony occurs at later processing stages than in children. ”
Speed of lower-level auditory and visual processing as a basic factor in dyslexia: electrophysiological evidence
Zvia Breznitz, Ann Meyler | https://pubmed.ncbi.nlm.nih.gov/12735934/
“This study investigated speed of processing (SOP) among college-level adult dyslexic and normal readers in nonlinguistic and sublexical linguistic auditory and visual oddball tasks, and a nonlinguistic cross-modal choice reaction task. Behavioral and electrophysiological (ERP) measures were obtained. The results revealed that between both groups, reaction times (RT) were longer and the latencies of P2 and P3 components occurred later in the visual as compared to auditory oddball tasks.“
Reduced Structural Connectivity Between Left Auditory Thalamus and the Motion-Sensitive Planum Temporale in Developmental Dyslexia
Nadja Tschentscher, Anja Ruisinger, Helen Blank, Begoña Díaz and Katharina von Kriegstein | https://www.jneurosci.org/content/39/9/1720.abstract
“Developmental dyslexia is one of the most widespread learning disabilities. Although previous neuroimaging research mainly focused on pathomechanisms of dyslexia at the cerebral cortex level, several lines of evidence suggest an atypical functioning of subcortical sensory structures. By means of diffusion tensor imaging, we here show that dyslexic male adults have reduced white matter connectivity in a cortico-thalamic auditory pathway between the left auditory motion sensitive planum temporale and the left medial geniculate body. Connectivity strength of this pathway was associated with measures of reading fluency in neurotypical readers. This is novel evidence on the neurocognitive correlates of reading proficiency, highlighting the importance of cortico-subcortical interactions between regions involved in the processing of spectrotemporally complex sound.“
From Auditory Rhythm Processing to Grapheme-to-Phoneme Conversion: How Neural Oscillations Can Shed Light on Developmental Dyslexia
Marie Lallier, Mikel Lizarazu, Nicola Molinaro, Mathieu Bourguignon, Paula Ríos-López & Manuel Carreiras | https://link.springer.com/chapter/10.1007/978-3-319-90805-2_8
“Here, we review evidence showing that a high sensitivity to auditory rhythmic cues may be critical for phonological and reading development. Moreover, the brain signature of prosodic and rhythmic processing difficulties in dyslexia may reside in atypical right hemisphere synchronization to slow frequency auditory modulations, that would then generate left hemisphere-based dyslexic reading symptoms. Overall, the data presented in this chapter suggests that interventions aimed at facilitating the extraction of rhythmic and temporally regular patterns in auditory sequences could improve reading in dyslexia through the enhancement of phonological skills.“
Developmental trajectories of white matter structure in children with and without reading impairments
Catherine Lebel, Alina Benischek, Bryce Geeraert, John Holahan, Sally Shaywitz, Kirran Bakhshi, Bennett Shaywitz | https://doi.org/10.1016/j.dcn.2019.100633
“We found typical age-related increases of fractional anisotropy (FA) in bilateral temporal-parietal areas in non-impaired readers, but a lack of similar changes in dysfluent readers. We also found steeper decreases of mean diffusivity (MD) in the right corona radiata and left uncinate fasciculus in dysfluent inaccurate readers compared to dysfluent accurate readers. Changes in diffusion parameters were correlated with changes in reading scores over time.“
Disruption of Functional Networks in Dyslexia: A Whole-Brain, Data-Driven Analysis of Connectivity
Emily S Finn, Xilin Shen, John M Holahan, Dustin Scheinost | https://www.researchgate.net/publication/257812764_Disruption_of_Functional_Networks_in_Dyslexia_A_Whole-Brain_DataDriven_Analysis_of_Connectivity
“Here, we improve upon previous methods by using a data-driven brain parcellation to compare connectivity profiles of dyslexic (DYS) versus non-impaired (NI) readers in the first whole-brain functional connectivity analysis of dyslexia. Whole-brain connectivity was assessed in children (n = 75; 43 NI, 32 DYS) and adult (n = 104; 64 NI, 40 DYS) readers. Compared to NI readers, DYS readers showed divergent connectivity within the visual pathway and between visual association areas and prefrontal attention areas; increased right-hemisphere connectivity; reduced connectivity in the visual word-form area (part of the left fusiform gyrus specialised for printed words); and persistent connectivity to anterior language regions around the inferior frontal gyrus. Together, findings suggest that NI readers are better able to integrate visual information and modulate their attention to visual stimuli, allowing them to recognize words on the basis of their visual properties, whereas DYS readers recruit altered reading circuits and rely on laborious phonology-based “sounding out” strategies into adulthood. These results deepen our understanding of the neural basis of dyslexia and highlight the importance of synchrony between diverse brain regions for successful reading.“
The current status of the magnocellular theory of developmental dyslexia
John Stein | https://www.sciencedirect.com/science/article/abs/pii/S0028393218301155?via%3Dihub
“Some people doubt that the concept of developmental dyslexia (DD) is useful at all because the phonological weaknesses seen in DD cannot be distinguished from those found in every person with poor reading skills, whatever their cause. Here I argue that true DD is characterised by poor temporal processing, hence impaired visual and auditory sequencing, that is caused by impaired development of transient/magnocellular (M-) systems throughout the brain. These deficits can be measured in order to distinguish the causes of the phonological weaknesses in DD from those causing similar deficits in other types of poor reading. Importantly this knowledge can be exploited to develop effective improvements in treatment. The evidence for impaired visual magnocellular function in many, if not all, people with dyslexia is now overwhelming; it is supported not only by psychophysical tests of M- function, but also by electrophysiological, eye movement, attentional, imaging, interventional and genetic findings. Analogously, auditory temporal processing is mediated by auditory transient, 'magnocellular', processing systems, and evidence is accumulating persuasively that this system is also impaired in dyslexics. I briefly introduce the idea that 'motor magnocellular systems' may also be impaired in dyslexia, then consider genetic, immunological and nutritional factors that interact to cause the impaired magnocellular phenotype.”
The magnocellular theory of developmental dyslexia
John Stein | https://pubmed.ncbi.nlm.nih.gov/11305228/
“The visual magnocellular system is responsible for timing visual events when reading. It therefore signals any visual motion that occurs if unintended movements lead to images moving off the fovea ('retinal slip'). These signals are then used to bring the eyes back on target. Thus, sensitivity to visual motion seems to help determine how well orthographic skill can develop in both good and bad readers. In dyslexics, the development of the visual magnocellular system is impaired: development of the magnocellular layers of the dyslexic lateral geniculate nucleus (LGN) is abnormal; their motion sensitivity is reduced; many dyslexics show unsteady binocular fixation; hence poor visual localization, particularly on the left side (left neglect). Dyslexics' binocular instability and visual perceptual instability, therefore, can cause the letters they are trying to read to appear to move around and cross over each other.”
Abrupt and ramped flicker-defined form shows evidence for a large magnocellular impairment in dyslexia
Robin Laycock , David P. Crewther , Sheila G. Crewther | https://www.sciencedirect.com/science/article/abs/pii/S002839321200214X
“Controversy still exists over whether there is a magnocellular deficit associated with developmental dyslexia. Here we utilised a magnocellular system-biased phantom contour form discrimination task defined by high temporal frequency contrast reversals to compare contrast sensitivity in a group of children with dyslexia and an age- and nonverbal intelligence-matched control group (9–14 years). Stimuli were either abruptly presented for 4 refresh frames (34 ms), or in two reduced transience conditions had contrast progressively ramped on and off over either 4 frames or 10 frames (86 ms). Children in the dyslexia group showed increased contrast thresholds compared with the control group in all three conditions, and thus strong evidence for a magnocellular deficit. Although the absolute size of the differences in threshold scores between control and dyslexic groups increased dramatically between the abrupt and the 4 and 10 frame ramped onset stimuli, the similar effect size across all tasks, and also the similar range of contrast change at the first frame of stimulus presentation across all tasks between groups suggests that a similar neural mechanism could provide the locus of the apparent magnocellular deficit in children with dyslexia for all tasks tested. These results suggest that threshold discrimination of stimuli with low contrast and high temporal frequencies designed to target the magnocellular system, and has great potential for early screening for children at risk of visually derived reading difficulties.”
