What to observe
On the right you see a so-called luminance grating with 3 cycles. In the middle there is a horizontal grayish bar. Is the lightness (grey tone) constant when looking along it?
You may observe that the grey in the stripe is slightly darker and brighter along its length, in counterphase to the grating.
What to do
Click on the grating. A yellow cover will appear which you can drag over the grating. If it fully covers the grating, the horizontal gray stripe will be revealed as having the same lightness throughout.
The slider on the very right lets you change stripe width. The lightness modulation induced by the grating is strongest at fairly narrow stripe widths.
A classical case of lateral inhibition.
McCourt ME (1982) A spatial frequency dependent grating-induction effect. Vision Res 22:119–134
Foley JM, McCourt ME (1985) Visual grating induction. J Opt Soc Am 2:1220–1230
Created: 1999-Jun-28, major rework 2009-08-26