The size of eye movements across text was measured under conditions in which the text was illuminated by fluorescent light or was displayed on the screen of a cathode-ray tube. Under these conditions of intermittent illumination the high-velocity saccadic eye movements were enlarged. The extent to which they were enlarged depended on the frequency of intermittency, but was generally equivalent to the width of one letter. This disturbance of ocular motor control by intermittent illumination might help to explain why reading is generally slower on computer display terminals than with printed text.
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