Abstract
When two images are presented dichoptically (that is, a different image is presented to each eye), one of them will temporarily dominate perception, leaving the other suppressed. This phenomenon is called binocular rivalry and is presumably caused by interocular competition (IOC). Although many stimulus attributes are known to affect IOC (e.g., stimulus contrast, luminance, and spatial frequency), it is less clear how IOC is affected by the visual field location of the images. We examined five independent datasets of breaking continuous flash suppression (b-CFS; a variant of binocular rivalry) experiments, to establish the role of visual hemifield (VHF) in IOC. B-CFS involves presenting a target of increasing intensity to one eye, and a dynamic mask to the other eye. Initially, the mask is perceived, but after some time the target ‘breaks’ into awareness. We investigated whether the time that observers needed to report an interocularly suppressed target depended on the VHF (nasal or temporal) to which the target was presented. We find that, across all datasets, targets presented in the nasal VHF broke suppression 23% faster than targets presented in the temporal VHF. Furthermore, we find that the nasal advantage was larger for the non-dominant eye (within-observers) and increased with increasing dominance of the dominant eye (between-observers). From these findings we conclude that targets in the nasal VHF enjoy a competitive advantage in IOC. Finally, we suggest that the reported nasal VHF advantage serves a functional role in everyday vision: When a distant fixated object is partly occluded by an object that is closer to the observer, the occluded part of the fixated object is in the nasal hemifield for one eye, while the occluding object is in the temporal hemifield of the other eye. Perception of the fixated object is facilitated by giving it a competitive advantage.