Orientation-tuned surround-suppression is strongest within perceived 3D surfaces

Our perception of contrast is strongly affected by contextual factors. A well-known example is that of orientation-tuned surround suppression (OTSS). Surrounds have more suppressive effects on the perceived contrast of the center when they have the same orientation. This phenomenon has been linked to horizontal interactions within the early visual cortex. Here we show that the strength of suppression is modulated strongly by the perceived three-dimensional structure of the scene. Placing the surround at a different retinal disparity, and therefore perceived depth, decreased OTSS, regardless of whether the surround was placed behind or in front of the center. The difference in disparity was, however, not the key determinant of the strength of OTSS. Suppressive interactions were strongest when the surround formed a three-dimensional surface that was continuous with the center and weaker when the surround seemed to be part of a separate surface, even when the surround seemed to be closer to the center in perceived depth. The results suggest that visual features that are perceived to form part of the same surface can engage in stronger suppressive interactions than those perceived to lie on different surfaces. This raises questions about how the underlying neural interactions become restricted to surfaces and support the view that top-down information about perceptual organization can gate interactions occurring at lower levels in the visual system.