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Angela H. Young, Johan Hulleman; Eye movement patterns underlying robustness against item motion in visual search. Journal of Vision 2011;11(11):1326. doi: https://doi.org/10.1167/11.11.1326.
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Hulleman (2010) found that item movement caused a decrease in search performance only for very difficult search tasks, whereas performance in easier tasks was not influenced by motion. Here, we investigate the relationship between eye movements and performance in search tasks of varying difficulty using static (0.0 deg/s) and moving (7.2 deg/s) items. The easy search task consisted of searching for a diagonal line amongst vertical lines, medium search was for a T amongst Ls and difficult search was for a square with a notch in the top left corner, amongst squares with a notch in one of the other corners. During present trials there was no effect of item speed on search performance for any difficulty level. During absent trials search performance was worse for moving items at all difficulty levels, perhaps the result of a more conservative stopping rule for moving items when the target is not found. Fixation durations, fixation counts and saccade amplitudes mainly depended on the level of difficulty rather than level of motion. However, there were some effects of speed, even for present trials. For moving items, at all difficulties, for both absent and present trials, there was a larger distance between the start point of a new saccade and the end point of the previous one. Moreover, for the medium task, gaze was closer to the target at the time of response for moving items. For difficult search, fixation durations on present trials were shorter for moving items. Even at the level of eye movements, search amongst static and amongst moving items is remarkably similar. This is consistent with the framework proposed by Hulleman (2010). One clear strategy emerged: moving items are tracked over short distances. This is probably to prolong processing times and provides the robustness of visual search against item motion.
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