Binocular rivalry occurs when incompatible monocular images are displayed at the same retinal location in the two eyes: perception oscillates between the two alternative interpretations, rather than yielding a stable intermingled percept. As the perceptual epiphenomenon keeps changing over time whereas the physical stimulus remains invariant, binocular rivalry can be usefully employed as a tool to explore the dynamical features of visual awareness and how they vary with the state of the observer. Indeed, binocular rivalry can be influenced by a number of cognitive, motivational and affective factors. Stable characteristics of the observers, such as their past experience and even their sociocultural context can affect rivalry dominance: Upright pictures of human faces prevail over inverted ones (Engel,
1956; Hastorf & Myro,
1959), familiar images dominate over novel ones (Goryo,
1960), and emotional facial expressions dominate over neutral expressions (Alpers & Gerdes,
2007); Jewish and Catholic religious images dominate for respectively Jewish and Catholic observers (LoSciuto & Hartley,
1963), pictures depicting violent acts (e.g., rape or murder) are perceived more often than are neutral control pictures by policemen and institutionalized offenders than by control observers (Shelley & Toch,
1962; Toch & Schulte,
1961). Binocular rivalry can also be affected by more volatile cognitive factors: Voluntary intention and attention are known to affect observers' ability to increase alternation rate during rivalry (Lack,
1971; Meng & Tong,
2004; van Ee, van Dam, & Brouwer,
2005). However, their effect on rivalry dominance is more controversial (Chong & Blake,
2006; Chong, Tadin, & Blake,
2005; Lack,
1978; Meng & Tong,
2004; Ooi & He,
1999; van Ee et al.,
2005). Furthermore, diverting the observer's attention to a concurrent task during rivalry has been shown to slow down alternation rate (Paffen, Alais, & Verstraten,
2006). Finally, Pearson, Clifford, and Tong (
2008) found that endogenously generated mental images can exert facilitatory effects on binocular rivalry stabilization: In case of intermittent presentation of rivalry displays, perceptual dominance tends to stick to the same stimulus that appeared dominant on the preceding trial. When observers are required to imagine one of the rivalry stimuli during the blank period between presentations, perception is biased in favor of the imagined stimulus.