Fechner color

When the top is spun, arcs of pale color are visible at different places on the disk that forms its upper surface.

The stable running speed of the fan does not (normally) produce colors, suggesting that it is not an interference effect with the frequency of the illumination flicker.

The effect was noted by Gustav Fechner and Hermann von Helmholtz and propagated to English-speakers through Charles Benham's invention of his top.

[citation needed] 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.

[4] Research has been done into the use of Benham's top and other PIFCs as diagnostic tools for diseases of the eye and the visual track.