Distortions on Length Perception in a Combination of Illusionary Figures

Abstract

In psychophysiological experiments, subjects were asked to compare the lengths of the test and control parts of stimuli constructed of two variants of superimposed illusionary figures: (1) two Muller–Lyer figures of the same body length but different in contrast, wing lengths, or tilt angles or (2) Muller–Lyer and Oppel–Kundt figures. Experiments with superimposed Muller–Lyer figures showed that the strength of illusion is determined by differences in the wing lengths and tilts, as well as the difference in the absolute contrast levels of the figures. Similar dependences were also found in experiments with stimuli formed by superimposing the Muller–Lyer and Oppel–Kundt figures. The data showed that simultaneous presentation of superimposed figures causes an illusion, which cannot be decomposed into parts, and the results of these experiments cannot be explained by summation of the effects of the figures. It is suggested that illusions caused by figures with different spatial organizations, such as Muller–Lyer and Oppel–Kundt figures, have common mechanisms. Calculations based on our model are fully consistent with experimental data and support the hypothesis based on the principles of spatial–frequency filtration of the image at the level of the primary visual cortex.