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Veronica T. Edwards, John H Hogben; Colour effects on metacontrast masking and reading. Journal of Vision 2002;2(7):149. doi: 10.1167/2.7.149.
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Temporal processing in individuals with dyslexia is often found to be abnormal. In vision, there are continual reports of deficits in dyslexic individuals on measures of magnocellular- (M-) system function. The nature of the relationship between deficits in M-system functioning and reading development is, however, unclear. That is, whether a deficit in M-system functioning is causally related to the reading failure of those with dyslexia is not known. This research explored the issue of causality using metacontrast masking. Initial studies on adults revealed that the wavelength of the background field on which metacontrast stimuli are presented influences the magnitude of the masking effect. Based on a two-component interpretation of metacontrast, this suggested that variations in background wavelength might be used to manipulate the degree of activation within the M-system. This provided a means to test whether degree of M-system activation influences reading performance. Accordingly, 36 children with dyslexia and 36 children with average reading ability were assessed on metacontrast masking and on three reading measures (passage reading, single word reading, and nonword reading). The masking and reading tasks were completed in four background wavelength conditions. Manipulating the wavelength of the background field affected metacontrast outcomes, which in the long wavelength condition could plausibly be explained as an effect on M-system function; however, the long wavelength background resulted in no observable effects on reading performance. The lack of co-variation in degree of M-system activation and reading performance suggests that a deficit in M-system function either affects reading at the acquisition stage, or is simply a non-causal correlate of dyslexia.
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