Ehrenstein Illusion

The Ehrenstein illusion is an optical illusion of brightness or color perception studied by the German psychologist Walter H. Ehrenstein, who lived from 1899 to 1961. Ehrenstein originally set out to test and modify existing theories of the related Hermann grid illusion, and in the course of that work he found that a grating pattern made of straight lines that each stop short of meeting at a central point produces the appearance of a brighter center compared with the surrounding background, even though no actual brightness difference exists there. Ehrenstein published his findings in a book titled Modifications of the Brightness Phenomenon of L. Hermann, in which he argued against Ludimar Hermann's original explanation of grid-based brightness illusions, contending instead that the effect he found was better explained as a distinct brightness phenomenon in its own right, rather than as an ordinary contrast effect, a claim that called for further investigation into how the visual system perceives illusory brightness and illusory contours.