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Jessica L Peters, Alyse Brown, Edith L Bavin, Sheila Crewther; Both Low and High Contrast Flicker Fusion Sensitivity Differentiate Dyslexic and Typically Developing Children. Journal of Vision 2019;19(10):207d. doi: https://doi.org/10.1167/19.10.207d.
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Evidence over the last 30 years indicates that individuals with dyslexia may demonstrate reduced magnocellular-dorsal stream efficiency in regard to high temporal frequency and low contrast as compared to typically developing individuals. Although this area of research remains controversial, it could substantially alter the way that dyslexia is understood, diagnosed and treated. Hence, we aimed to investigate magnocellular processing sensitivity in dyslexic (n =40) and typically developing (n =40) children aged 7;06 - 12;11 years. Participants were individually matched on age (with 1 year) and nonverbal intelligence (Ravens Coloured Progressive Matrices; within 0.67 SD). Participant’s processing thresholds were assessed using a four-option forced-choice flicker fusion task at 5% and 75% contrast. The high motion and low contrast components of the flicker fusion task are known to maximally activate magnocells, while higher levels of contrast increase parvocellular activity. Participants’ phonological awareness (elision task) and text reading skills (York Analysis of Reading Comprehension) were also assessed. Results demonstrate that children with dyslexia show lower flicker sensitivity at both 5% and 75% contrast, and as expected, performed significantly worse on tests of text reading and phonological awareness as compared to typically developing children. Within group correlational analyses indicated that flicker fusion sensitivity at 5% contrast significantly and positively correlated with better reading comprehension in dyslexic children, while higher flicker fusion sensitivity at 75% contrast correlated with better nonverbal intelligence and phonological awareness in typically developing children. These findings suggest that primary school aged children with dyslexia show temporal processing impairments and low contrast deficits indicative of an attentional system that is slower to activate. Findings also suggest that contrast sensitivity thresholds of dyslexic and typical children show a different pattern of association with reading skills.
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