Abstract
Over et al. (2007) reported that when participants are searching in complex displays, they use a course-to-fine search strategy in which, as search progresses, the duration of fixations increases and the distance between fixations decreases. In the current study we examined the extent to which participants employed a course-to-fine search strategy while searching for an elevation marker in aeronautical charts of varying amounts of visual clutter. Our previous work demonstrated that search time increased as the amount of clutter in the chart increased (Beck et al., 2010). Search may be faster in less cluttered charts because attention within each fixation can be spread over a larger region of the chart (evidenced by longer saccades) and/or because the information within the attended region of each fixation can be processed more quickly (evidenced by shorter fixation durations). Replicating previous research, we found that reaction time increased as chart clutter increased. Examination of eye movements during search revealed that participants were using a coarse-to-fine search strategy in charts of all levels of clutter; as search progressed, the duration of each fixation increased and the distance between two fixations decreased. However, this effect was weakest in the least cluttered charts. Interestingly, the amount of global clutter (i.e., average clutter of the entire chart) affected fixation durations more than the distance between fixations. When global clutter was low, fixation durations were shorter, but the distance between fixations was similar to that in more cluttered charts. This suggests that higher levels of global clutter increase the time needed to process information within a given region, but do not change the size of the region attended during the fixation. In conclusion, a coarse-to-fine search strategy was found for maps of all levels of clutter, and less cluttered maps did not lead to a broader focus of attention.
This research was funded by Naval Research Laboratory (NRL): Broad Agency Announcement Grant to the first author.