Benham's Top

Benham's top is a visual illusion in which a disc patterned only in black and white, when spun at a moderate speed, produces the vivid appearance of faint colored bands, called Fechner colors or pattern-induced flicker colors, even though the spinning disc itself contains no color at all. The German physicist and psychologist Gustav Fechner first noted the general phenomenon of illusory color from a rotating black-and-white pattern in 1838, but the effect takes its common name from the British toymaker Charles Benham, who marketed a spinning top bearing a specific black-and-white pattern of concentric arcs in 1895, after which the toy quickly became a popular scientific curiosity. The accepted explanation holds that the human retina's different classes of color-sensitive cone cells respond to light and darken their response at slightly different speeds, so that a rapidly alternating black-and-white pattern drives these cone types out of their normal synchrony, and the brain interprets the resulting mismatch in neural signals as color even though no actual colored light is present. The particular colors a viewer perceives, and even the order in which they appear across the spinning pattern, vary somewhat between individuals and can shift depending on the disc's spin direction and speed, making the effect a long-standing subject of study for researchers investigating exactly how color perception is constructed by the visual system rather than simply read off the wavelength of incoming light.