Abstract
We investigated the neural interactions between binocular rivalry and perceptual filling-in of visual phantoms to elucidate the stages at which selective and constructive perceptual mechanisms operate in the visual pathway. Binocular rivalry leads to the selective perception of one of two competing monocular stimuli, whereas visual phantom formation leads to perceptual filling-in of a large gap between two collinearly aligned gratings. We devised a novel visual display to investigate interactions between rivalry and filling-in, and measured the resulting effects in human visual cortex. One eye was shown two vertically aligned gratings (positioned one above the other) that would normally lead to perception of a visual phantom in the gap, while the other eye viewed rivalrous horizontal gratings in corresponding locations, which if viewed alone would not lead to a visual phantom. Observers reported phantom filling-in only when the vertical gratings were dominant. This behavioral result suggests that rivalry can gate the formation of visual phantoms. We monitored fMRI activity while observers viewed this perceptually ambiguous display. When observers perceived the vertically aligned gratings as dominant, increased activity was observed in retinotopic regions corresponding to the phantom location in areas V1–V3. In contrast, when the horizontal gratings became dominant and observers failed to perceive a phantom, decreased activity was found. More strikingly, the modulations in early visual cortex during rivalry were just as strong as those evoked by the non-rivalrous stimulus alternation between the two monocular displays, suggesting that rivalry fully gates the neural filling-in of visual phantoms. These results show that rivalry occurs at an earlier stage of visual processing than perceptual filling-in, and that neural activity in V1–V3 closely reflects the observers' conscious perception of the visual phantom during moment-to-moment fluctuations in awareness.
Research supported by NIH grants R01-EY14202 and P50-MH62196 to FT