Benham’s Top unrolled

from Michael’s Visual Phenomena & Optical Illusions


What to see

On the right you see some (rather irritating) pattern flicker. Inspect the top grating row – does it look a little reddish? The row below a little greenish (very little)? The third row a little blueish?

The colours a just a little stronger (more saturated) if you speed up to zero frame delay between each flicker step.

What to do

Slow down the flicker with the stepper at bottom left –  e.g. delay to 10. Then you see that there is only black and white in the display no colour. The sequence is full black, full white with upper grating row, second grating row, third grating row, and full white alone. The colours are illusory.

Another parameter to change is the number of stripes, technically the spatial frequency of the grating. For me, the colours are present without difference from 1 stripe to ≈50 stripes.


Maybe you already saw Benham’s Top on the preceding page. There I had strived to imitate an actual spinning top. But the rotation is not necessary – the local flicker & pattern is the relevant stimulus. So I “unrolled” the Benham Top into the present demonstration. It is just as strong (or weak, as the case may be for you).

What was unexpected for me: the spatial frequency of the grating seems irrelevant. This is in direct contradiction to the explanation (“pattern induced flicker colors”) that there is center-surround opponency in retinal colour-specific cells at play – when the bars are wide, they certainly cover center + surround.


See Benham’s Top