The effects of letter spacing and coloured overlays on reading speed and accuracy in adult dyslexia

Background Zorzi et al. (2012, Proc. Natl. Acad. Sci. U.S.A., 109, 11455) found evidence that extra-large letter spacing aids children with dyslexia, but the evidence for the coloured overlays is contradictory (e.g., Henderson et al., 2013, J. Res. Special Educ. Needs, 13, 57; Wilkins, 2002, Ophthalmic Physiol. Opt., 22, 448), and possible combined advantages have not been identified. Aims To investigate whether extra-large letter spacing or coloured overlays can alleviate reading problems in dyslexic adults. Sample The participants were 24 dyslexic and 24 non-dyslexic university students, matched for age and fluid intelligence. Methods The reading speed and the errors made by a dyslexic and a control group were measured in four conditions: with and without coloured overlays and with normally and largely spaced texts. Results Large letter spacing improves the reading speed in general, as well as improves the reading accuracy in dyslexic readers. Conclusions The results support the positive effect of letter spacing on reading performance.