Surface completion affected by luminance contrast polarity and common motion.

Our visual system ably integrates the visible parts of a partially occluded surface with the occluded parts (amodal surface completion), mainly by relying on the surface boundary contours of the image. Less known, is whether the visual system also utilizes surface feature information, such as luminance contrast polarity, for surface completion. We conducted three experiments to investigate this issue. Experiment 1 found that when visible segments of a partially occluded rectangle with the same luminance contrast polarity move behind an occluding surface, observers perceive the visible segments as part of the occluded rectangle moving cohesively behind the occluding surface. However, when the visible segments have opposite luminance contrast polarity, the global motion of the segments is barely perceived, suggesting a failure of amodal surface integration. Experiment 2 revealed that this same luminance contrast polarity constraint applies to amodal surface integration of a display without an explicit occluding surface image. Experiment 3 showed that both the shape and luminance contrast polarity of the visible segments of the partially occluded rectangle affect amodal surface completion. Together, these findings demonstrate that luminance contrast polarity, along with surface boundary contour, are important cues for amodal surface integration.