ADJUSTMENT OF FIXATION DURATION IN VISUAL-SEARCH

To investigate whether fixation durations are adjusted to the duration of a foveal analysis task, we designed a search task in which each st imulus element yielded information about the position of the target. W e asked subjects to look for the target by making eye movements in the direction indicated by each stimulus element, We explicitly asked the subjects to make the eye movements in the correct direction, but they did not always do this. They made only 65-80% of the eye movements in directions indicated by the stimulus elements, From these results we conclude that fixation durations are not solely determined by the imme diate visual stimulus and that subjects encounter difficulties when tr ying to increase fixation durations to values that would enable them t o direct saccades accurately. In a second experiment we shortened the presentation time in order to provide an incentive for the subjects to speed up search. Shortening the presentation time did not affect fixa tion duration. Therefore, we suggest that fixation duration is control led by a mechanism that uses estimations of the foveal analysis time o f previous fixated stimulus elements. (C) 1998 Elsevier Science Ltd. A ll rights reserved.