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.
Highlights
Developmental dyslexia (DD) is characterized as a specific and significant impairment in reading ability, which cannot be explained by deficits in general intelligence, motivation, or educational opportunity (Critchley, 1970)
For the brain activation analysis, we found less activation in the left precuneus and greater activation in the right pre/postcentral gyrus for the developmental dyslexia (DD) group compared to the age-matched controls (AC) and reading matched controls (RC) groups in both the lexical and perceptual tasks, suggesting a common mechanism for visual and orthographic deficits
The right pre/postcentral gyrus was less connected with the right anterior cingulate cortex (ACC) in the perceptual, but not the lexical task, for children with DD compared to both control groups
Summary
Developmental dyslexia (DD) is characterized as a specific and significant impairment in reading ability, which cannot be explained by deficits in general intelligence, motivation, or educational opportunity (Critchley, 1970). The phonological deficit hypothesis is one of the most commonly used theories to explain the etiology of dyslexia, and speculates that underspecified phoneme representations or the unsuccessful retrieval of phoneme representations are the core causes of. Reduced brain activation has been reported among left temporo-parietal areas during phonological processing in both the visual (Paulesu et al, 2001; Schulz et al, 2009; Van der Mark et al, 2009; Tanaka et al, 2011) and auditory modalities (Eden et al, 2004; Dufor et al, 2007; Kast et al, 2011). Reduced brain activation has been found in the left inferior frontal gyrus (IFG) (Hoeft et al, 2006; Richlan et al, 2011; Cao et al, 2017), which has been associated with phonological segmentation and manipulation during phonological awareness tasks (Pugh et al, 1996; Fiez, 1997; Tan et al, 2001)
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