How humans visually explore natural scenes depends on multiple factors. Eye movements are influenced by low level image properties (e.g., chromaticity, orientation, luminance, and color contrast; Itti, Koch, & Niebur,
1998; Le Meur, Le Callet, Barba, & Thoreau,
2006; Torralba,
2003) as well as higher level cognitive processes like the observers' scene understanding (Henderson, Weeks Jr., & Hollingworth,
1999; Loftus & Mackworth,
1978), task (Castelhano & Henderson,
2008; Yarbus, Haigh, & Rigss,
1967), or probability of reward (Hayhoe & Ballard,
2005; Tatler, Hayhoe, Land, & Ballard,
2011). Besides low-level image features and high-level cognition, systematic tendencies have a strong impact on how humans look at pictures (Le Meur & Liu,
2015; Tatler & Vincent,
2009). A dominant systematic tendency in natural scene viewing is the central fixation bias (CFB; Buswell,
1935; Tatler,
2007; Tseng, Carmi, Cameron, Munoz, & Itti,
2009). Regardless of stimulus material (Tatler,
2007; Tseng et al.,
2009), head position (Vitu, Kapoula, Lancelin, & Lavigne,
2004), initial fixation position (Bindemann, Scheepers, Ferguson, & Burton,
2010; Tatler,
2007), or image position (Bindemann,
2010), the eyes tend to initially fixate close to the center of an image when presented to a human observer on a computer screen. After several explanations of the CFB had been ruled out, two hypotheses remained.