Müller-Lyer and Oppel-Kundt illusions compared

Abstract

Introduction. There are certain reasons to recognize the Müller-Lyer (M-L) and Oppel-Kundt (O-K) illusions as distinct phenomena. Firstly, the inducing stimuli differ in structure definitely: flanking wings in the M-L figures, and filled/unfilled intervals in the O-K patterns. Secondly, the two illusions may differ in their origin. Irrespective of the presence of numerous contraversial concepts, the M-L illusion tends to be related basically to the perceived positional shifting of the gravity centre of the excitation profile formed by stimulus terminals and distracters; the O-K illusion, presumably, arises due to the spatial and temporal integration along associated excitation path elicited by the filling. Moreover, the two illusions show different temporal dynamics: strengthening of the O-K illusion and weakening of the M-L illusion during the first 1000 ms of stimuli presentation. However, some affinity between these two phenomena can be recognized the illusions magnitude may reach 20-35% of the reference, both remain rather stable in a subject's reperative testing, and both vary among subjects due to the visual processing defferences. The aim of the present study is a further investigation of similarity and dissimilarity in the O-K and M-L illusions manifestation and variabilities. Materials and methods. The modified stimuli possessing three spatial intervals were taken for the psychophysical experiments. In the M-L figures (Fig 1A and Fig. 1B), four pairs of wings, designated the three intervals. The wings (length, 34 arc min; internal angle, 90°) were formed of spots or line segments. [...].