Benham’s Top

from “Visual Phenomena & Optical Illusions”

What to do – On the right the “Benham Disk” spins, initially rahter slowly. Use the slider to adjust speed.

What not to observe – The higher the speed, the more stroboscopic artifacts occur due to the interaction of your monitor’s frame rate and the frame-wise display of the rotating wheel (think of the backwards rotating spike wheels in Western movies).

What to observe – For starters, go to highest speed. Then the arcs take on weak (desaturated) colours, for instance I see a red-brown in the centre three arcs. Clicking on reverse exchanges the colours. The effect is also present at slower speeds, the hues may change.
Fascinating: although the display is just black–grey–white, a suitable temporal modulation of local patterns makes us see colour. If you take a photograph or screen capture, the colours will not be there.

Comment — Benham’s top is a classic examples of subjective colours. Because of the interaction of space and time Campenhausen called them “pattern-induced flicker colours”. While nobody knows for certain why the colours appear, lateral inhibition and the different rates of stimulation for the colour-specific retinal ganglion cells clearly are involved. They code the pattern of light in space and time into patterns of nerve firings in space and time.
Fechner (1838) was the first to describe this phenomenon. In 1894, toy maker Charles E Benham discovered that a spinning disk with a particular pattern of black and white marks (more intricate than Fechner’s) could cause people to see colours. He called his disk an “Artificial Spectrum Top” and sold it through Messrs. Newton and Co. From this derives the name “Benham’s Top”.

I recently discovered Richard L. Gregory piece in the Oxford Companion to the Mind (1987): “Although generally called 'Benham's top', after C. E. Benham (1894), the basic effect goes back to a French monk, Benedict Prévost, who, in 1826, observed colours – like a heavenly light on his fingers – when he waved his hands about in the cloisters. Finding that this also happened with white cardboard, he realized that it has a physiological origin, in the eye, and attributed it to different rates of action of specific colour mechanisms of the retina. He was essentially correct. It is remarkable that Prévost's discovery was forgotten, and the effect was rediscovered no less than twelve times: by Gustav Fechner in 1838 and then by others. John Smith, in 1859, thought that the effects were 'objective' by changing the light itself, and so he (incorrectly) challenged Newton's account of light and colour. The third rediscovery was made by Sir David Brewster in 1861. (The history is given fully in Cohen and Gordon 1949.) Hermann von Helmholtz carried out systematic observations, noting that a white rotating sector is red on the leading edge and blue on the trailing edge, and in dim light the red becomes yellow and the blue violet. In very bright light the red becomes pinker and the blue greenish. … These subjective colours have been shown successfully on black and white television, but they are a little too weak for commercial uses. They are due to different time constants of the colour receptor systems of the eye, but they are rather too variable for precise measurements. The effects are interesting but not particularly useful.”

Sources

Adamczak W (1981) The amacrine cells as an important processing site of pattern-induced flicker colors. Vision Res 21:1639–1642

Benham CE (1895) The artificial spectrum top. Nature 2:321
Benham CE (1894) The artificial spectrum top. Nature 51:113-114
Benham CE (1894) The artificial spectrum top. Nature 51:200

“An "Artificial Spectrum Top", devised by Mr. C.E. Benham, and sold by Messrs. Newton and Co., furnishes an interesting phenomenon to students of physiology optics. The top consists of a disc, one half of which is black, while the other half has twelve arcs of concentric circles drawn upon it. Each arc subtends an angle of forty-five degrees. In the first quadrant there are three such concentric arcs, in the next three more, and so on ; the only difference being that the arcs are parts of circles of which the radii increase in arithmetical progression. Each quadrant thus contains a group of arcs differing in length from those of the other quadrants. The curious point is that when this disc is revolved, the impression of concentric circles of different colors is produced upon the retina. If the direction of rotation is reversed, the order of these tints is also reversed. The cause of these appearances does not appear to have been exactly worked out.” [source]

Cohen J, Gordon DA (1949) The Prevost-Fechner-Benham Subjective Colors. Psychol Bull 46:97–136

Festinger L, Allyn MR, White C W (1971) The Perception of Color with Achromatic Stimulation. Vision Res 11:591–612

Campenhausen von C, Schramme J (1995) 100 years of Benham’s top in colour science. Perception 24:695–717

Cohen J, Gordon DA (1949) The Prévost–Fechner–Benham subjective colours. Psychological Bulletin, 4:697–136

Fechner GT (1838) Ueber eine Scheibe zur Erzeugung subjectiver Farben. In: Poggendorff JC (ed.) Annalen der Physik und Chemie pp 227–232 · Verlag von Johann Ambrosius Barth, Leipzig

Fechner Illusion, Essex University

Le Rohellec J, Viénot F (2001) Interaction of luminance and spectral adaptation upon Benham subjective colours. COLOR research and application, 26:S174–S179

Kenyon GT, Hilla D, Theilerb J, Georgea JS, Marshak DW (2004) A theory of the Benham Top based on center-surround interactions in the parvocellular pathway. Neural Networks 17:773–786 [PDF]

Pilz J, Marre E (1993) Pattern-induced flicker colors. An ophthalmologic examination method (Article in German). Ophthalmologe 90: 148–154

Schramme J (1992) Changes in pattern induced flicker colors are mediated by the blue-yellow opponent process. Vision Research 32: 2129–2134