Koffka's Ring Effect Depends on Thickness, Not Continuity

Abstract

AbstractMore than 70 years ago Gestalt psychologist Kurt Koffka described a fascinating effect1,2: When a contiguous grey ring is placed on a background half of one shade of grey (different from the ring) and half of another shade of grey, the ring appears to be a homogenous. However, if the ring is slightly divided, now the two halves of the ring appear different shades of grey with the half of the ring on the darker background appearing lighter than the half of the ring on the darker background. The Gestalt principle of continuity in visual perception is invoked to explain this effect. Here we show that in fact when the ring is made thinner it appears heterogeneous even when contiguous. Furthermore, when viewing a thick ring after first viewing a thin ring, the thick ring now too appears heterogenous! These effects are also demonstrated with a colored background and backgrounds with more than two regions. We show that standard simultaneous brightness and color contrast weaken with larger test patches. Thus, Koffka's ring effect is due to vanishingly weak simultaneous contrast for a sufficiently thick ring, not continuity.