Displacement of the edges of the filled intervals in the Oppel-Kundt illusion

Abstract

In the present study the possible role of the local positional shifts of the edges of the filled parts of the Oppel-Kundt figure was tested. The stimuli consisted of two filled (by spots) spatial intervals with an empty (referential) one between them. For length comparisons the separate test interval was employed.  It was demonstrated that the illusion strength increased with increasing of the density of filling and that the data for different length of the filled part of the stimulus do not differ significantly. The results support the suggestion that the perceptual positional shifts of the edges of the filled intervals may be considered as one of the main causes of emergence of the Oppel-Kundt illusion.