Wertheimer-Koffka Ring

Koffka Luminance Illusion

standard Koffka annulus

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 (or tap)…

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-Apr-13


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Last update 2014-09-21 by Michael Bach (G+)