Depth propagation across an illusory surface.

We investigate the spatiotemporal dynamics of depth filling in on an illusory surface by measuring the temporal asynchrony of perceived depth between an illusory neon-colored surface and real contours. We temporally modulated the horizontal disparity at vertical edges of the illusory surface and measured the perceptual delay for the interpolated surface's depth under two different boundary conditions: disparity given at both sides, or disparity given at one side and a free boundary at the other side. The results showed that the amount of the delay depends on the spatial distance between the measured point and the edges where disparity was physically given. Importantly, the observed delay as a function of spatial distance was clearly different under the two boundary conditions. We found that this difference can be fairly well explained by a model based on a diffusion equation under different boundary conditions. These results support the existence of locally represented depth information and an interpolation process based on mutual interaction of this information.