Curvature discontinuities are cues for rapid shape analysis

Using the visual search method, we show that stimuli that contain curvature discontinuities (i.e., points where the second derivative along an image contour is not defined) are easily found among stimuli containing only smooth changes in curvature. Curved stimuli that lack curvature discontinuities, however, are difficult to find among distractors that have them. These results suggest that the visual system detects and analyzes abrupt changes in curvature in the image quickly to extract vital information about the 3-D structure of the visual environment.