YOU text-editing induces contrast adaptation at the predominant spatial frequencies (periodicity) of the text page. Yisual contrast sensitivity was tested after 10and 60 min reading of YOU-displayed text of positive and negative contrast polarity. Contrast sensitivity impairments in'the order of 0·4 to O· 7 log unit change in contrast thresholds were observed. This contrast thresholdelevation after-effect decays as a power function of time, with time required to recover from adaptation

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... tely corresponding to the reading times. At low spatial frequencies (horizontal periodicity of rows), displays of negative polarity induce stronger contrast adaptation than displays of positive polarity, at medium spatial frequencies (vertical periodicity of characters) no effect ofcontrastpolarity was observed. The results are discussed in relation to VOUinduced visual fatique,