Active vision and the identification of three-dimensional shape.

We examined the performance of human observers to identify three-dimensional (3D) shape from motion induced by exploratory head movements. Subjects categorized 3D quadratic surfaces with randomly chosen shape but with a fixed amount of curvature in one of eight shape categories. Human observers had their best performance with convex parabolic and concave parabolic shapes, but had more difficulties in identifying the hyperbolic shapes. The identification of 3D shape was not significantly influenced by the amount of curvature. This means that our description of 3D shape closely matches the intuitive notion of shape, and that its use in 3D shape perception tasks is justified.