Some individuals with dyslexia demonstrate deficits in reading, visual attention, and visual processing which can be attributed to a functional failure of the magnocells in the visual system or in the dorsal visual pathway. The study examines the role of magno/dorsal function in dyslexic adults compared with normal, illiterate, and semi‐literate readers. Coherent motion and coherent form were used in Experiment 1, and the frequency doubling illusion and static‐gratings were used in Experiment 2. If a magno/dorsal deficit is demonstrated for dyslexic readers but not illiterate, semi‐literate, and normal reading adults, then the deficit cannot be attributed to reading experience. Illiterate adults performed the same as normal and semi‐literate readers in coherent motion and frequency doubling tasks, and all three groups performed better than the dyslexic readers. There was no difference between any of the groups in the coherent form or static grating tasks. Together, these studies show that illiterate and semi‐literate adults do not demonstrate a magno/dorsal deficit that is a characteristic of some sufferers of dyslexia. Therefore, magno/dorsal deficits in dyslexia are unlikely to be a consequence of failing to learn to read but rather provides evidence to suggest a causal role for reduced visual magno/dorsal processing.
Individuals with dyslexia have often been found to have deficits in coherent motion processing, an index of global dorsal stream functioning. In studies involving pre-literate children it has been demonstrated that there could be a relationship between dorsal stream functioning and poor reading ability, lending weight to the claim that dorsal stream deficits may contribute to reading failure. This research looks at coherent motion sensitivity in adult illiterate readers and matched literate and dyslexic readers. The coherent motion sensitivity of lliterate and literate adult readers from Papua New Guinea, and dyslexic readers from Australia were examined to see if research in adults could likewise illuminate the discussion on the role of dorsal stream functioning in reading ability. The results of this analysis will be discussed as well as possible areas for further investigating the relationship between dorsal stream function and reading ability.
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