Elsevier

Neuropsychologia

Volume 46, Issue 10, August 2008, Pages 2593-2596
Neuropsychologia

Note
Investigating the functional integrity of the dorsal visual pathway in autism and dyslexia

https://doi.org/10.1016/j.neuropsychologia.2008.04.008Get rights and content

Abstract

Numerous reports of elevated global motion thresholds across a variety of neurodevelopmental disorders have prompted researchers to suggest that abnormalities in global motion perception are a result of a general deficiency in the dorsal visual pathway. To test this hypothesis, we assessed the integrity of the dorsal visual pathway at lower subcortical (sensitivity to flicker contrast) and higher cortical (sensitivity to global motion) levels in children with autism, children with dyslexia, and typically developing children, of similar age and ability. While children with autism demonstrated intact lower-level, but impaired higher-level dorsal-stream functioning, children with dyslexia displayed abnormalities at both lower and higher levels of the dorsal visual stream. These findings suggest that these disorders can be dissociated according to the origin of the impairment along the dorsal-stream pathway. Implications for general cross-syndrome accounts are discussed.

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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