The effect of contrast on reading speed in dyslexia

Contrast coding has been reported to differ between dyslexic and normal rea ders. Dyslexic readers require higher levels of contrast to detect sinewave gratings for certain spatiotemporal conditions, and dyslexic readers show faster visual search at low contrast. We investigated whether these differe nces in early contrast coding generalize to reading performance by measurin g reading speed as a function of text contrast for dyslexic children and ad ults and for age-matched controls. Contrast affected reading performance of dyslexic and normal readers similarly. For both groups, reading speed was relatively constant between 100 and 2% contrast, and decreased rapidly belo w 2% contrast. This pattern of results held true for both children and adul ts, for text with and without sentence context, across a range of character sizes, and for reading aloud and reading silently. We conclude that earlie r findings of group differences in contrast effects on grating detection or visual search tasks do not generalize to reading. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.