Illusory colors promote interocular grouping during binocular rivalry

When dissimilar monocular images are presented separately to each of a person’s eyes, these images compete for visual dominance, with dominance of one image or the other alternating over time. While this phenomenon, called binocular rivalry, transpires, local image features distributed over space and between the eyes can become visually dominant at the same time; the resulting global figure implicates interocular grouping. Previous studies have suggested that color tends to influence the incidence of global dominance; in this study, we assess whether illusory color can also influence interocular grouping. To test this, we exploited the McCollough effect, an orientation-contingent color aftereffect induced by prolonged adaptation to different colors paired with different orientations. Results show that during binocular rivalry, illusory colors induced by the McCollough adaptation enhance strong interocular grouping relative to preadaptation testing, to an extent comparable in strength with the enhancement induced by real colors. Thus, illusory colors that are present only in an observer’s mind are sufficiently potent to influence low-level visual processes such as binocular rivalry.