Benham's top

A sample of a Benham's disk.

Benham's top, also called Benham's disk, is named after the English toymaker Charles Benham, who sold a top painted with the pattern shown at right. When the disk is spun, arcs of pale color are visible at different places on the disk.

Although the cause of this illusion is not clearly understood, our discovery of and continued interest in such an effect reflect both the endless creativity and the appreciation for creativity that are to be found in human nature.

Discovery

The discovery of the phenomenon is generally attributed to C. E. Benham, although Gustav Fechner and Hermann von Helmholtz had experimented with similar disks many years earlier. The discovery was described in Nature, 52:113-144 in 1894, and in 1895 Benham invented the toy which he called the "Artificial Spectrum Top," which became more commonly known as a "Benham top/disk".

Description

The top of the disk is half black/half white, and the white side has a series of sets of concentric arcs. When the top is spun, the viewer sees a series of concentric circles of varying colors. Different people may not see the same set of colors, and the order of the colors is reversed if the disk is spun in the opposite direction.

Explanation

Scientists have long been puzzled over the phenomenon. The human retina is composed of both rods and cones; there are three types of cones that are sensitive to each of three colors of light (red, blue, and green). It is suggested that the colors in the Benham disk may be a result of the different response times of various cones. In this theory, the white part of the disk activates all three cones and the black half deactivates them. Because of the differing response times of the three types of cones, as well as the difference in time they remain activated, an imbalance of information is sent to the brain resulting in the perception of colors.

An alternate theory proposes that the spinning black and white areas activate neighboring areas of the retina differently, and the alternating response causes an interaction in the nervous system, generating the colors.

The generated colors have variously been referred to as "subjective colors," "Fechner-Benham colors," "polyphan colors," and "pattern-induced flicker colors" (PIFC's).

Despite these theories, the reason behind the illusion remains a scientific mystery, and no theory yet explains the colors of Benham's disk completely.

Applications

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.

References

ISBN links support NWE through referral fees

• Campenhausen, C. von and J. Schramme. "100 years of Benham's top in Colour Science." Perception, 24 (1995): 695-717.
• Falk, David R., Dieter R. Brill, and David G. Stork. "Seeing the Light: Optics in Nature, Photography, Color, Vision, and Holography." Wiley. 1986. ISBN 0471603856
• Hoffman, Donald David. "Visual Intelligence: How We Create What We See." W.W. Norton & Company. 2000. ISBN 0393319679
• Robinson, J. O. The Psychology of Visual Illusion. Dover Publications, 1998. ISBN 0486404498

External links

All links retrieved September 27, 2023.

• Benham’s Top – Colour from time & space From Michael’s “Visual Phenomena & Optical Illusions”.
• Benham's Top - an interactive demonstration
• Benham's Disk

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