Visual half-field contrast sensitivity in children with dyslexia

We address the question whether left-hemispheric and/or right-hemispheric c ontrast thresholds differ between children with dyslexia and controls, and whether there are interhemispheric differences. In order to answer these qu estions we examined [1] thresholds for the detection of Contrast-Defined (C D) forms to left and right half-field stimulation, and [2] half-field patte rn onset Evoked Potentials (EPs) as a function of stimulus contrast in 21 c hildren with dyslexia of 8-15 years of age and in 17 age-matched healthy co ntrols. It was found that (A) children with dyslexia were less sensitive to CD forms than controls irrespective of half field of stimulation. In child ren with dyslexia as well as controls the forms were more easily detected i n the right visual half-field than in the left one; (B) Peak latencies of t he pattern onset EPs to contrast levels above 20% were up to 10 ms longer i n children with dyslexia than in controls irrespective of half field of sti mulation, and (C) children with dyslexia had smaller mean amplitudes for al l contrast levels used. (D) Neither children with dyslexia nor controls sho wed hemispheric differences in the pattern onset EPs.