Effects of negative afterimages in visual illusions

We show that a broad class of visual illusions, including illusory motion, can be explained by the effects of negative afterimages. Two new illusions, illusory shading and illusory tilting, are devised on the basis of the proposed explanation. The general feature of these illusions is an alternation between a high-contrast (white or black) and a low-contrast (gray) local input signal, which can be caused either by eye motion over patterns of varied luminance or by a change in such patterns over time. A simple model of the local signal dynamics qualitatively reproduces the illusory effects by adding the negative afterimage to the original visual stimulus.