Amodal completion in the absence of image tangent discontinuities.

It has been widely believed since Helmholtz that tangent discontinuities in image contours, such as T-junctions or L-junctions, will occur when one object occludes another. Here we describe a class of occlusion relationships where changes in 'border ownership' and amodal completion take place in the absence of tangent discontinuities in the image. We propose that even subtle curvature discontinuities can be a signal to potential changes in border ownership, and are valid ecological cues for occlusion in certain scenes.