Abstract
The Oppel-Kundt illusion was examined in the psychophysical experiments with the classical two-part stimuli and modified three-part figures. The modified versions comprised either one filled medial interval and two empty flanking intervals or one empty space situated in between two fillings. The illusion was measured as a function of the number of filling elements in the referential parts of the figures. The curves obtained by two modified figures and by the original two-part stimulus were quite similar in shape, but the magnitudes of the illusions differed significantly. The figure with two filled intervals yielded about twice-stronger illusory effect than the contrasting figure with a single filled and two empty intervals. The two-part stimulus showed the illusion magnitudes in the midst. Our assumption suggests the illusory effect being related particularly to over estimations of the filled interval when compared with the empty interval displayed side-to-side. The unfilled interval might not contribute to the illusion.
Highlights
The OppelKundt illusory pattern reshaped into the stimulus formed of vertical stripes with two contiguous spatial extents: one filled up with a regular sequence of stripes having the same size as the terminal ones, and the other extent empty
The orientation anisotropy of the visual field appeared to be a separate distortion in perception, but it might add algebraically to the strength of the filled-space illusion in a simultaneous manifestation [2, 3]
Such an explanation failed for the illusory pattern with the infinite number of the filling elements, which convert into a continuous segment
Summary
An analogous illusory figure formed of spots instead of stripes has emerged Both for stripes and spots, the strength of the illusion was similar and varied with an increase in the stimulus length, number of the filling elements, and changes of the stimulus orientation in the visual field. The model was shown to be valid for the experimental data without any exception There was another attempt to explain the Oppel-Kundt phenomenon by the difference of the averaged contour density in the two halves of the figure [5]. Contour density may correspond to zero-crossing numbers within a range of spatial scales contributing quantitatively to the illusory effect [6]. The illusion is likely to originate at higher functional levels gene-
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