Brain Mechanisms Underlying Visuo-Orthographic Deficits in Children With Developmental Dyslexia

Abstract

Multiple hypotheses have been proposed to explain the reading difficulty caused by developmental dyslexia (DD). The current study examined visuo-orthographic processing in children with dyslexia to determine whether orthographic deficits are explainable based solely on visual deficits. To identify orthographic-specific, visual perception-specific, and overlapping deficits, we included two tasks (lexical and perceptual) in three Chinese subject groups: children with DD, age-matched controls (AC), and reading matched controls (RC) using functional magnetic resonance imaging (fMRI). We found that the left precuneus showed decreased activation across both tasks for the DD group compared to the two control groups, thus reflecting visual processing deficits in children with DD, which also affects orthographic processing. Furthermore, we found that the functional connectivity between left middle occipital gyrus (LMOG) and left inferior frontal gyrus (IFG) was decreased in the DD group compared to AC and RC for only the lexical task. This suggests a weaker association between orthography and phonology for children with DD. In addition, the children with DD showed decreased functional connectivity between the LMOG and right parahippocampal gyrus for only the visual perceptual task, thereby indicating a weaker association between visual regions for DD during visual symbol processing. Taken together, our findings suggest that the observed orthographic processing deficit in DD might be driven by both a basic visual deficit, and a linguistic deficit.

Children With Dyslexia and Familial Risk for Dyslexia Present Atypical Development of the Neuronal Phonological Network

“…In terms of BOLD activations as registered by fMRI, the pattern of differences observed between typical and dyslexic readers at the beginning of education was different depending on whether the analyses included the whole sample or only children with a familial risk for dyslexia. Reduced activation of the left visual cortex in dyslexics was present only when all children were included in the analysis (consistent with previous fMRI results in visual and orthographic processing tasks, e.g., Dehaene et al, 2010; Boros et al, 2016; Cao et al, 2018). It was no longer significant when the group was restricted to children with a familial history of dyslexia.…”

Processing speed in perceptual visual crowding

“…In the dyslexic subjects, less activation was found in the left precuneus and greater activation in the right pre/ postcentral gyrus compared to age-and readingmatched controls. These data suggest a shared mechanism of visual and orthographic deficits in dyslexia and shed new light on understanding visual processing problems in individuals with dyslexia (Cao, Yan, Spray, Liu, & Deng, 2018).…”

Reading Disability in Chinese Children Learning English as an L2

“…However, if those with RD are only different from age-matched controls and similar to reading-matched controls, this suggests a developmental delay that is a consequence of poor reading. Neuroimaging studies which have included a reading-matched control group in addition to an age-matched control group have investigated phonological (Hoeft et al, 2006(Hoeft et al, , 2007Quaglino et al, 2008;Schulz et al, 2009) and visuo-orthographic deficits (Cao, Yan, Spray, Liu, & Deng, 2018;Olulade, Napoliello, & Eden, 2013;Wang, Bi, Gao, & Wydell, 2010). In terms of phonological deficits, two studies have shown that alterations in the left IFG seem to represent a developmental delay, while the left temporo-parietal region may be a qualitative deviance (Hoeft et al, 2006(Hoeft et al, , 2007.…”