Abstract
INTRODUCTION. Our visual system typically constructs an unambiguous representation of objects we see, even when the retinal stimulus is consistent with several different perceptual interpretations. Neural populations representing the alternative percepts compete for perceptual dominance to resolve ambiguity. When two such objects in view require perceptual resolution, recent evidence shows that the two may be resolved simultaneously to be identical (that is, similarity enhanced) or, in some conditions, maximally dissimilar (difference enhanced; Peiso & Shevell, 2020). Experiments here address how chromatic context influences whether the percepts are similarity-enhanced or difference-enhanced and whether a neural divisive normalization model can account for this effect. METHODS. Two circular regions of diameter 1.5 degrees, above and below fixation, were made ambiguous using chromatic interocular-switch rivalry (CISR). Dichoptic isoluminant (15 cd/m2) stimuli were swapped between the eyes at 3.75 Hz (Christiansen et al., 2017). Dichoptic chromatic backgrounds were varied between trials to be either identical (dichoptically stable and non-rivalrous) or presented using CISR. The rivaling chromaticities were set at [L/(L+M), S/(L+M)] values of [0.62, 1.00], called “green,” and [0.71, 1.00], called “red.” The background varied between rivalrous (red/green), stable red, or stable green. Observers used a gamepad to report the perceived disc and background colors simultaneously. RESULTS. All five observers resolved two chromatically rivalrous discs as different in color from the stable background (e.g., two green perceived discs on a red background) more often than the same rivalrous discs on a chromatically rivalrous background. Additionally, all observers perceived significantly more identical (similarity-enhanced) disc percepts with rivalrous backgrounds than with identical backgrounds. CONCLUSION. Chromatic background context can alter the perceptual resolution of ambiguous regions from similarity enhancement to dissimilarity enhancement. Moreover, this change is consistent with the divisive normalization of competing neural signals, with the normalization acting on the most common chromatic signal.