Amodal completion as another perception of color-spreading stimuli

We made a solid three-dimensional object of the Redies-Spillmann figure and found two kinds of completely different phenomena. First, transparent color-spreading was observed in the empty space around the object. Second, another perceptual organization occurred: observers perceived a cross as a cross-shaped slit through which to see, and then they perceived spreading color disappear entirely. They reported an apparent opaque occluding surface which was localized at the same depth as the slit but was in fact the background. They also reported a colored circle which was mostly occluded by the surface with a cross-shaped slit. We interpreted the circle as being amodally completed in the sense described by Kanizsa in 1955. Even when the figure was drawn on a piece of paper, we observed these two perceptions. We examined whether other stimuli causing neon color-spreading lead to reports of the perception for the Redies-Spillmann figure and found that all the stimuli we examined led to reports of the same kind of perception. Interestingly, the shape of color-spreading was the same as that of the amodal completion.