TY - JOUR T1 - Humans perceive binocular rivalry and fusion in a tristable dynamic state JF - The Journal of Neuroscience JO - J. Neurosci. DO - 10.1523/JNEUROSCI.0713-19.2019 SP - 0713-19 AU - Guillaume Riesen AU - Anthony M. Norcia AU - Justin L. Gardner Y1 - 2019/09/13 UR - http://www.jneurosci.org/content/early/2019/09/11/JNEUROSCI.0713-19.2019.abstract N2 - Human vision combines inputs from the two eyes into one percept. Small differences ‘fuse’ together, while larger differences are seen ‘rivalrously’ from one eye at a time. These outcomes are typically treated as mutually exclusive processes, with paradigms targeting one or the other and fusion being unreported in most rivalry studies. Is fusion truly a default, stable state that only breaks into rivalry for non-fusible stimuli? Or are monocular and fused percepts three sub-states of one dynamical system? To determine whether fusion and rivalry are separate processes, we measured human perception of Gabor patches with a range of inter-ocular orientation disparities. Observers (10 female, 5 male) reported rivalrous, fused and uncertain percepts over time. We found a dynamic “tristable” zone spanning from ∼25-35 degrees of orientation disparity where fused, left- or right-eye dominant percepts could all occur. The temporal characteristics of fusion and non-fusion periods during tristability matched other bistable processes. We tested statistical models with fusion as a higher-level bistable process alternating with rivalry against our findings. None of these fit our data, but a simple bistable model extended to have three states reproduced many of our observations. We conclude that rivalry and fusion are multistable sub-states capable of direct competition, rather than separate bistable processes.SIGNIFICANCE STATEMENTWhen inputs to the two eyes differ, they can either fuse together or engage in binocular rivalry, where each eye's view is seen exclusively in turn. Visual stimuli have often been tailored to produce either fusion or rivalry, implicitly treating them as separate mutually-exclusive perceptual processes. We have found that some similar-but-different stimuli can result in both outcomes over time. Comparing various simple models with our results suggests that rivalry and fusion are not independent processes, but compete within a single multistable system. This conceptual shift is a step toward unifying fusion and rivalry, and understanding how they both contribute to the visual system's production of a unified interpretation of the conflicting images cast on the retina by real-world scenes. ER -