NoteInvestigating the functional integrity of the dorsal visual pathway in autism and dyslexia
Section snippets
Methods
We present novel analyses of combined data which were collected using the same procedures (including task scripts) in the same laboratory, and under similar experimental conditions. The autism data were reported previously by Pellicano et al. (2005) and the dyslexia data were reported by Gibson, Hogben, and Fletcher (2006).
Results
Initial data screening identified several outliers within each group. To reduce the impact of these outlying cases, scores more than 3 S.D.s above/below the group mean for any task (7% of data) were replaced with the value representing 2.5 S.D.s above/below their group mean (Tabachnick & Fidell, 2007). Split-half reliability analysis (Spearman–Brown correction) on the two blocks of each psychophysical task yielded moderately high reliability coefficients (FCS: r = .80; GDM: r = .79). The mean of
Discussion
Contrary to Braddick et al.'s (2003) proposal, the present results demonstrate that autism and dyslexia can be dissociated at a perceptual level: children with autism, on average, showed a sparing of early (magnocellular) levels, but a deficit in higher-level global motion perception, while children with dyslexia, on average, demonstrated atypicalities at both lower and higher levels of the dorsal visual stream. Furthermore, these deficits were present only in a minority of children within each
Acknowledgments
We are very grateful to all the children and families who participated in this research and to Oliver Braddick, Elizabeth Milne, Kate Nation, Marc Stears, and an anonymous reviewer for comments on a previous draft.
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