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. Author manuscript; available in PMC: 2010 Feb 1.
Published in final edited form as: Atten Percept Psychophys. 2010 Jan;72(1):153–167. doi: 10.3758/72.1.153

Figure 2.

Figure 2

Top: Minima of curvature marked on a 2D cross shape. These minima of curvature correspond to minima that cut through the sides of a 3D convexity, but not to those of a 3D concavity, which are complementary. Middle: These minima of curvature marked on equivalent convex and concave 3D versions of the cross shape. There are twice as many minima cutting through the sides in the concave version. Bottom: Part structures (indicated by different image textures) based on the convex and concave minima and on the “shortcut rule” of Singh et al. (1999). It is unclear precisely how the concave image’s part boundaries radiate out past the cusp of the concavity. However, since the cusp itself is a maximum of curvature, the facets oriented in depth which form the sides of the concavity belong with regions of the surrounding plane, rather than with the surface forming the bottom of the hole.