Wertheimer-Koffka Ring
Warning: this is a subtle effect.
Compare the two halves of the ring. The left half looks subtly darker than the right
one. Now move the mouse over them…
You may need to change your observation distance to see a sizable effect.
Comment.
In the presence of the bar, the brightness difference without luminance difference
is a standard case of simultaneous contrast. This is probably due to retinal mechanisms.
Without the bar, filling-in (a cortical phenomenon) ‘wins’.
Source
Koffka (1935) Principles of Gestalt Psychology. Lund Humphries, London [Chapter 1]
New
demo from Ted Adelson's site
Created: 1997-04-13
Last update: 2013-10-04