Almost all individuals exhibit sensory eye dominance, one neural basis of which is unequal interocular inhibition. Sensory eye dominance can impair binocular functions that depend on both excitatory and inhibitory mechanisms. We developed a 'push-pull' perceptual learning protocol that simultaneously affects the excitatory and inhibitory networks to reduce sensory eye dominance and improve stereopsis in adults with otherwise normal vision. The push-pull protocol provides a promising clinical paradigm for treating the extreme sensory eye dominance in amblyopia ('lazy eye'). The prevailing standard of care does not directly treat sensory eye dominance; instead, selected excitatory functions in the amblyopic eye are stimulated while the strong eye is patched, on the assumption that recovery of the weak eye's excitatory functions rebalances the eyes. Patching the strong eye does not directly address interocular inhibition; in contrast, the push-pull protocol by design excites the weak eye, while completely inhibiting the strong eye's perception to recalibrate the interocular balance of excitatory and inhibitory interactions. Here, we show that three adult amblyopes who trained on the push-pull protocol gained longstanding improvements in interocular balance and stereopsis. Our findings provide a proof-of-concept and evidence that push-pull learning leads to long-term plasticity.

The visual system relies on both the integration and interocular inhibitory processes to achieve single vision from different images in the two eyes. It is generally assumed that the integration process first searches for matching local features between the two eyes. If the matching fails, an interocular inhibitory process is triggered to suppress the image representation of one eye, leading to visual perception that is essentially contributed by the other eye. Here, using a stimulus comprising of binocularly corresponding features (vertical gratings) but incompatible surface border information, we found evidence to the contrary. In one half-image, a circular patch of vertical grating was phase-shifted relative to the surrounding vertical grating to create a circular, monocular boundary contour (MBC), while the other half-image had a similar vertical grating. The two half-images had a binocular disparity at the circular grating patch area, leading to the percept of a disc in depth. Concurrent with the stereo percept, threshold for detecting a Gabor probe on the half-image without the MBC was higher than that on the corresponding area with the grating disc, indicating binocular suppression. These findings reveal that when we perceive depth, which requires the integration process to obtain binocular disparity from the two eyes, one eye's image could simultaneously be suppressed from visual awareness by the interocular inhibitory process. Our study also presents a provocative example of where the brain selectively binds some, but not all, features of the images from the two eyes for visual perception.awareness ͉ binocular fusion ͉ boundary contours ͉ contrast threshold ͉ stereopsis

Two experiments were conducted to reveal that the human visual system represents grating texture surface using a border-to-interior strategy. This strategy dictates that the visual system first registers the surface boundary contour and then sequentially spreads texture from the border to the interior of the image. Our experiments measured the perceived grating texture surface at various stimulus durations after the onset of a grating texture image. We found that the grating texture is initially seen near the boundary contours, with eventual spreading inward to the center of the image. To quantify the observation, the extent of the texture spreading from the boundary contour is measured as a function of the stimulus duration (30-500 ms). This allows us to analyze the texture spreading in retinal and cortical distances, based on human fMRI studies of the cortical magnification factor in cortical areas V1-V4, and to derive the spreading speed. We found that the spreading speed is constant when scaled according to the cortical distance. Similar findings are obtained no matter whether the grating texture image is presented monocularly or dichoptically, suggesting the generality of the border-to-interior strategy for representing surfaces.