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Home List of Titles Abrupt and ramped flicker-defined form shows evidence for a large magnocellular impairment in dyslexia
Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/228056
- Abrupt and ramped flicker-defined form shows evidence for a large magnocellular impairment in dyslexia
- Laycock, Robin; Crewther, David P.; Crewther, Sheila G.
- Controversy still exists over whether there is a magnocellular deficit associated with developmental dyslexia. Here we utilised a magnocellular system-biased phantom contour form discrimination task defined by high temporal frequency contrast reversals to compare contrast sensitivity in a group of children with dyslexia and an age- and nonverbal intelligence-matched control group (9-14 years). Stimuli were either abruptly presented for 4 refresh frames (34. ms), or in two reduced transience conditions had contrast progressively ramped on and off over either 4 frames or 10 frames (86. ms). Children in the dyslexia group showed increased contrast thresholds compared with the control group in all three conditions, and thus strong evidence for a magnocellular deficit. Although the absolute size of the differences in threshold scores between control and dyslexic groups increased dramatically between the abrupt and the 4 and 10 frame ramped onset stimuli, the similar effect size across all tasks, and also the similar range of contrast change at the first frame of stimulus presentation across all tasks between groups suggests that a similar neural mechanism could provide the locus of the apparent magnocellular deficit in children with dyslexia for all tasks tested. These results suggest that threshold discrimination of stimuli with low contrast and high temporal frequencies designed to target the magnocellular system, and has great potential for early screening for children at risk of visually derived reading difficulties.
- Publication type
- Journal article
- Research centre
- Swinburne University of Technology. Faculty of Life and Social Sciences. Brain Sciences Institute
- Neuropsychologia, Vol. 50, no. 8 (Jul 2012), pp. 2107-2113
- Publication year
- FOR Code(s)
- 1109 Neurosciences; 1701 Psychology; 1702 Cognitive Sciences
- Contrast sensitivity; Dyslexia; Flicker-defined form; Magnocellular
- Publisher URL
- Copyright © 2012 Elsevier Ltd. All rights reserved.
- Research Projects
- Peer reviewed