No abstract

The effect of visibility on eye-movement parameters was investigated. As a measure of visibility, the notion of "visual span" was introduced. A first experiment, in which a simple letterrecognition task was used, directly measured the changes in visual span produced by changing viewing distance and character spacing. The results of this experiment were used as a reference for a second experiment in which the same visibility changes were made, but in which subjects read short texts while their eye movements were monitored. Saccade sizes were affected not primarily by visual span, but by other factors, possibly related to word boundary detection or linguistic processing. Fixation durations appeared to be strongly affected by the proximity of the letters to the subject's acuity threshold.