Spin this disk - What color do you see?

Spin this disk - What color do you see?

Benham's top, also called Benham's disk, is named after the English newspaper-man, amateur scientist, and toymaker Charles Benham, who in 1895 sold a top painted with the pattern shown. When the disk is spun, arcs of pale color, called Fechner colors or pattern-induced flicker colors (PIFCs), are visible at different places on the disk. Not everyone sees the same colors. Benham was inspired to propagate the Fechner color effect through his top after his correspondence with Dr. Gustav Theodor Fechner, who had observed and demonstrated the said effect. Benham's top made it possible for speakers of the English language to learn of the Fechner color effect, about which Fechner's original reports were written in German.

The phenomenon is not entirely understood. One possible reason people see colors may be that the color receptors in the human eye respond at different rates to red, green, and blue. More specifically, the latencies of the center and the surrounding mechanisms differ for the different types of color-specific ganglion cells.

The phenomenon originates from neural activity in the retina and spatial interactions in the primary visual cortex, which plays a role in encoding low-level image features, such as edges and spatiotemporal frequency components. Research indicates that the blue-yellow opponent process accounts for all the different PIFCs.

Benham's top and other PIFCs are being researched for use as a diagnostic tool for diseases of the eye and the visual track. It has shown particular promise in detecting optic neuritis.