Abstract
Purpose:Dyslexia is one of the most common learning disabilities affecting millions of people worldwide. Although exact causes of dyslexia are not well-known, a deficit in the magnocellular pathway may play a role. We examined possible deficiency of magnocellular, as compared to parvocellular and koniocellular pathway function by measuring luminance and color perception.Methods:Visual stimuli consisted of a series of natural images, divided into layers of luminance, red-green and blue-yellow, which probed magnocellular, parvocellular, and koniocellular pathways, respectively. Thirteen children with dyslexia and 13 sex- and age- matched controls performed three psychophysical tasks. In the first task, subjects were instructed to match the contrast of luminance (magno) and red-green (parvo) images to that of the blue-yellow (konio) images. In the second task, subjects detected the isoluminant point of red-green images to probe parvocellular pathway. In the third task, temporal processing was assessed by measuring reaction time and percentage of correct responses in an identification task using four categories of images, activating all three pathways.Results:The dyslexic group had significantly elevated luminance and color contrast thresholds and higher isoluminant point ratio in comparison to the control group. Furthermore, they had significantly less correct responses than the control group for the blue-yellow images.Conclusion:We may suggest that dyslexic subjects might suffer from both magnocellular and parvocellular deficits. Moreover, our results show partial impairment of the koniocellular pathway. Thus, dyslexia might be associated with deficits in all three visual pathways.
Highlights
Dyslexia is a major neuro developmental disorder identified by noticeable difficulty in reading ability
The blue‐yellow layer of the image was shown on the left side of the screen, and the red‐green and luminance images were shown on the right [Figure 1]
The subjects were instructed to adjust the perceived contrast of the two images located on the right side of the screen to match the one on the left side.The contrast of the blue‐yellow image was fixed at a random value at the beginning of the trial
Summary
Dyslexia is a major neuro developmental disorder identified by noticeable difficulty in reading ability. Which is not correlated with intelligence, age, socioeconomic status or educational opportunities, and occurs in the absence of neurological disorders or sensory impairments.[1] Dyslexia is the most common learning. Accepted: 17-02-2015 disability affecting 4‐10% of school‐aged children[2,3] and is one of the most frequently diagnosed conditions in childhood in most countries.[4,5] The exact causes of dyslexia are controversial and poorly understood.[6] Even though some argue dysfunctional phonological processing as the main cause of deficit in dyslexia,[7,8] others have suggested other factors such as impaired. Journal of Ophthalmic and Vision Research 2015; Vol 10, No 4
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