DOI:10.1068/p3016 The generic-viewpoint assumption and illusory contours

Illusory contours (ICs) are contours seen where there are no corresponding gradients in the stimulus. Although ICs were first reported around the turn of the century, interest in this phenomenon dramatically increased after Kanizsa (1955) presented his striking demonstrations. Since then ICs have received a great deal of attention both experimentally and theoretically (for reviews see Parks 1984; Purgheänd Coren 1992; Lesher 1995). Figure 1 is a typical example. Most observers see a rectangular illusory surface partially occluding the black inducers in the display. The illusory surface also appears brighter than the surround. Von der Heydt et al (1984) found that many cells in area 18 of monkey visual cortex respond to such illusory edges when they are placed in the cell's preferred position and orientation for ordinary luminance gradients.