Gutauskas A, Bertulis A, Bulatov A, 1998, "A quantitative measure of illusion of curvature" Perception 27 ECVP Abstract Supplement
A quantitative measure of illusion of curvature
A Gutauskas, A Bertulis, A Bulatov
An equilateral triangle or square inscribed in a circle were used as stimuli in psychophysical experiments. The stimuli were seen on a monitor as bright figures made of thin lines (0.7 min of arc). The triangles and squares had either straight sides or curved ones of various radii that made the internal angles of the figures vary in appearance. For subjects, the arcs of the circumscribed circles appeared to be puffy owing to perceptual distortions. Viewing the stimulus monocularly and by manipulating the panel keys, subjects adjusted the curvature of the arcs to reduce the illusion to zero. The corrections of the subjects were considered as a measure of the illusion strength. Ten subjects showed approximately the same results . The illusion increased gradually with the size of the stimulus (diameter of the circle, 7 - 70 min of arc): 2 - 11 min of arc for triangles, and 2 - 20 min of arc for squares of the right-sided type. Also the illusion increased with the internal angle (10 - 80 deg) of the figures: 12 - 20 min of arc for triangles and 20 - 35 min of arc for squares of the stimuli up to 1 deg in diameter. The results obtained can be interpreted in terms of spatial filtering. A neurophysiological filter model with dynamic characteristics (Bulatov et al, 1997 Biological Cybernetics 77 395 - 406) has been applied to the experimental data. A quantitative and qualitative correspondence between the data and predictions of the model have been found in the study.
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