Fechner Color Effect

The Fechner color effect is an optical phenomenon, also called pattern-induced flicker colors, in which people perceive colors while viewing certain rapidly changing or moving black-and-white patterns that contain no color at all. The effect is most commonly demonstrated with Benham's top, also called Benham's disk, a spinning disk that shows pale arcs of color appearing at different places on its surface as it rotates; the same effect can also appear under stroboscopic lights at particular flash frequencies or with rotating fan blades as they accelerate or decelerate, though stable, constant fan speeds typically do not produce the colors. The phenomenon was first observed by Gustav Fechner and Hermann von Helmholtz, and later popularized among English-speaking scientists by Charles Benham's invention of his demonstration top, with Florence Winger Bagley conducting some of the earliest investigations into the effect; the illusory colors are thought to arise from neural activity in the retina combined with spatial interactions in the primary visual cortex, and research indicates that the blue-yellow opponent color process accounts for the different pattern-induced flicker colors observed. The effect has practical promise in ophthalmology, particularly as a tool for detecting optic neuritis and potentially other diseases of the visual system.