  Visual search is an important strategy of the human visual system for fast
scene perception. The guided search theory suggests that the global layout or
other top-down sources of scenes play a crucial role in guiding object
searching. In order to verify the specific roles of scene layout and regional
cues in guiding visual attention, we executed a psychophysical experiment to
record the human fixations on line drawings of natural scenes with an
eye-tracking system in this work. We collected the human fixations of ten
subjects from 498 natural images and of another ten subjects from the
corresponding 996 human-marked line drawings of boundaries (two boundary maps
per image) under free-viewing condition. The experimental results show that
with the absence of some basic features like color and luminance, the
distribution of the fixations on the line drawings has a high correlation with
that on the natural images. Moreover, compared to the basic cues of regions,
subjects pay more attention to the closed regions of line drawings which are
usually related to the dominant objects of the scenes. Finally, we built a
computational model to demonstrate that the fixation information on the line
drawings can be used to significantly improve the performances of classical
bottom-up models for fixation prediction in natural scenes. These results
support that Gestalt features and scene layout are important cues for guiding
fast visual object searching.
