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The effect of inner elements of the context figures on the Ebbinghaus illusion
Milena Vuk & Anja Podlesek
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Written in English. | Published: March 5, 2006
Abstract: In the Ebbinghaus illusion, the size of a figure is overestimated when it is surrounded by smaller figures and underestimated when it is surrounded by larger figures. The present study examined whether the illusion is also influenced by the additional inner parts of the inducing context figures. A central square was surrounded by two types of context figures: larger and smaller figures. Each type of context figures had either square or circular shape, or was absent from the display. When both larger and smaller figures were presented, smaller figures were added inside the large ones. Data was gathered with the adjustment method. When the Ebbinghaus display was presented to the left of the probe figure, the perceived size of the central square was larger than in conditions with the display presented to the right of the probe figure. Larger context figures alone induced size underestimation and smaller figures induced size overestimation. A clear similarity effect was observed – squares induced larger illusion than circles, so the size contrast effect was most likely the predominant factor of the illusion. When the smaller context figures were added to the larger ones, the underestimation of the size of the central figure was reduced. Although the effects of the larger and smaller context figures were not completely additive, the results showed that the visual system takes into consideration both similar and dissimilar context figures when making size comparisons.
Keywords: Ebbinghaus illusion, visual perception, size perception, contextual effects, method of adjustment, illusions
