title: The role of first- and second-order stimulus features for human overt attention.
abstract: When processing complex visual input, human observers sequentially allocate their attention to different subsets of the stimulus. What are the mechanisms and strategies that guide this selection process? We investigated the influence of various stimulus features on human overt attention--that is, attention related to shifts of gaze with natural color images and modified versions thereof. Our experimental modifications, systematic changes of hue across the entire image, influenced only the global appearance of the stimuli, leaving the local features under investigation unaffected. We demonstrated that these modifications consistently reduce the subjective interpretation of a stimulus as "natural" across observers. By analyzing fixations, we found that first-order features, such as luminance contrast, saturation, and color contrast along either of the cardinal axes, correlated to overt attention in the modified images. In contrast, no such correlation was found in unmodified outdoor images. Second-order luminance contrast ("texture contrast") correlated to overt attention in all conditions. However, although none of the second-order color contrasts were correlated to overt attention in unmodified images, one of the second-order color contrasts did exhibit a significant correlation in the modified images. These findings imply, on the one hand, that higher-order bottom-up effects--namely, those of second-order luminance contrast--may partially account for human overt attention. On the other hand, these results also demonstrate that global image properties, which correlate to the subjective impression of a scene being "natural," affect the guidance of human overt attention.
authors.affiliation: Institute of Cognitive Science, Department of Neurobiopsychology, University of Osnabrück, Osnabrück, Germany. hfrey@uos.de
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Frey
authors.forename: Peter
authors.initials: P
authors.lastname: König
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Einhäuser
mesh_terms: D001288:Attention; D003118:Color Perception; D005403:Fixation, Ocular; D006801:Humans; D008027:Light; D014796:Visual Perception