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Ann M. Skoczenski, Elizabeth F. Gramzow; Contour integration and hyperacuity in children with dyslexia. Journal of Vision 2005;5(8):472. doi: https://doi.org/10.1167/5.8.472.
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Children with dyslexia have reading deficits that may have a phonological, auditory or visual basis. Most studies of vision in dyslexia have examined disturbances in eye movements, in the latency of visual responses, or tasks that emphasize pattern detection, such as contrast sensitivity. We hypothesized that tests of visual discrimination and perceptual organization may identify visual deficits in dyslexia, since these tests tap the abilities needed to identify letters and words. We measured hyperacuity and contour integration in 92 children aged 6.5 to 16.5 years, 38 of whom were identified as dyslexic. Each child was administered two standardized tests designed to identify children at risk for dyslexia: the Dyslexia Screening Test and the Word Attack subtest of the Woodcock Johnson Reading Mastery Test. We then used visual evoked potentials (VEPs) to measure vernier acuity and contour integration thresholds. Vernier acuity was measured by sweeping the size of offsets embedded in square wave vertical gratings. Offsets appeared and disappeared at a fixed rate of 5 Hz. Contour thresholds were measured by sweeping the spacing of randomly oriented background Gabor elements that surrounded a closed circular contour formed by collinear Gabor elements. The contour appeared and disappeared as the target Gabor elements changed orientation (from noncolinear to collinear) at a rate of 3.6 Hz while the background Gabor elements modulated at rate of 3.2 Hz. Vernier acuity and contour integration both undergo some development in the age range that we tested. We did not find mean threshold differences between dyslexics and non-dyslexics when the dyslexics were considered as one group. However, a subgroup of older dyslexics (age 12–16), ironically those who were relatively faster readers according to one standardized test, had significantly poorer vernier acuity, compared to other dyslexics and to controls. This subgroup was not distinguished in the contour threshold data.
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