Contrast sensitivity, ocular dominance and specific reading disability
Mason A., Cornelissen P., Fowler S., Stein J.
1. We have investigated the possibility that reduced flicker contrast sensitivity and unstable ocular dominance, which is revealed by failure in the Dunlop Test, may be associated in children with specific reading disability (SRD). We measured childrens' contrast sensitivity in two experiments. In Expt 1, we measured the flicker and static contrast sensitivity of 11 SRD children who passed the Dunlop Test, 11 SRD children who failed the Dunlop Test and 11 normal, control children, all of whom were matched for chronological age. We confirmed that, on average, all SRD children were less sensitive to flicker than normals at all spatial frequencies. But SRD children who failed the Dunlop Test were significantly less sensitive to the flickering gratings than those who passed it. 2. We wanted to be sure that these findings could not be attributed to systematic differences in chronological age, reading ability or intelligence. Therefore in Expt 2 we measured the flicker and static contrast sensitivities of two groups of children who differed only in their Dunlop Test performance. Thus the two groups were matched as closely as possible for age, reading age and IQ. Despite these more stringent controls, Dunlop Test failure was still significantly correlated with reduced flicker contrast sensitivity at all spatial frequencies. 3. Together these results suggest that flicker contrast sensitivity and the stability of ocular dominance may be linked in SRD children. Moreover, we suggest that the reduced flicker contrast sensitivities we observed could be caused by reduced magnocellular sensitivity. Finally, our findings support the idea that abnormal visual processing could affect how children read.