White’s Illusion

What is happening

The fragment on the left replaces a black stripe; the fragment on the right replaces a white stripe. Both fragments are the same size and the same gray. Rather than just counting the black and white touching each side, pay attention to what each fragment looks like a continuation of.

Why it looks that way

Whether a gray fragment reads as a continuation of the white stripes or the black stripes changes the impression of its brightness. It’s not just the difference with adjacent colors — how regions group together and the direction of the lines both matter. This is a case that simple lateral inhibition alone can’t fully predict.

How to check

Hide the black-and-white stripes and only the two columns of fragments remain. Revealing the answer adds a horizontal band, also in the same gray as the fragments. Look at the stripes above and below, then move your eyes to the band, and compare the brightness impression with and without that context.

Try a related illusion

For reference: Michael Bach’s explanation. The figure here is an original implementation for this site.

First described

After Michael White, 1979

An example showing brightness is not determined by "contrast with the immediate neighbour" alone.

See it in the timeline