Viewing behavior and the impact of low-level image properties across repeated presentations of complex scenes.

Studies on bottom-up mechanisms in human overt attention support the significance of basic image features for fixation behavior on visual scenes. In this context, a decisive question has been neglected so far: How stable is the impact of basic image features on overt attention across repeated image observation? To answer this question, two eye-tracking studies were conducted in which 79 subjects were repeatedly exposed to several types of visual scenes differing in gist and complexity. Upon repeated presentations, viewing behavior changed significantly. Subjects neither performed independent scanning eye movements nor scrutinized complementary image regions but tended to view largely overlapping image regions, but this overlap significantly decreased over time. Importantly, subjects did not uncouple their scanning pathways substantially from basic image features. In contrast, the effect of image type on feature-fixation correlations was much bigger than the effect of memory-mediated scene familiarity. Moreover, feature-fixation correlations were moderated by actual saccade length, and this phenomenon remained constant across repeated viewings. We also demonstrated that this saccade length effect was not an exclusive within-subject phenomenon. We conclude that the present results bridge a substantial gap in attention research and are important for future research and modeling processes of human overt attention. Additionally, we advise considering interindividual differences in viewing behavior.