Nasal visual field of origin contributes to interocular competition strength

During binocular rivalry (BR), perceptual dominance alternates between the inputs of the eyes, meaning that (at any time) the non-dominating input is suppressed, despite being projected on a retina. It has been proposed that BR is the result of interocular competition (IOC), where the input that ‘wins’ the competition becomes the dominant percept. Both top-down factors (e.g., attention, working memory content) and bottom-up factors (e.g., saliency, eye dominance) have been shown to affect IOC. One factor has remained largely disregarded, however: the input’s visual field of origin. The lack of attention to this factor is surprising, since the visual field of origin is known to affect performance in various contexts outside of BR. Exploratory analyses on previously gathered data using a breaking continuous flash suppression (b-CFS) paradigm suggested that nasally presented targets (i.e., presented in the nasal visual hemifield (VHF)) broke through suppression faster than temporally presented targets. We confirmed this exploratory observation in a reanalysis of five independent b-CFS datasets. Strikingly, we found that the effect of VHF was even larger (by 25%) than the well-established effect of eye dominance, as measured by response time differences in the b-CFS paradigm. Importantly, the magnitude of the VHF effect depended on the strength of IOC, both within-observers (recessive > dominant eye), and across-observers (weak > strong eye-dominance). These findings show that the VHF effect reported here is specific to IOC, rather than reflecting a generic visual field anisotropy. Lastly, we simulated 10.000 datasets to show that our findings did not spuriously emerge from our analysis pipeline. Taken together, we demonstrate a substantial advantage for visual input from the nasal VHF during IOC. These findings have broad implications for augmented/virtual reality applications and yield important methodological considerations for researchers utilizing IOC-based paradigms to investigate the contents and functions of human consciousness.