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Tadas Surkys, Algis Bertulis, Arunas Bielevicius, Aleksandr Bulatov; Oppel-Kundt illusion weakens with shortening of the time presentations. Journal of Vision 2010;10(7):1401. doi: https://doi.org/10.1167/10.7.1401.
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© ARVO (1962-2015); The Authors (2016-present)
The magnitude of the Oppel-Kundt illusion was measured at various durations of presentation followed by the masking stimulus. The referential part of the Oppel-Kundt figure was of 70 arc min length and comprised 7 stripes, height of which was 28 arc min and width 1 arc min. The empty test part of the stimulus was terminated by a single stripe. The figure luminance was 52cd/m2 and background luminance was 0 cd/m2. The masking stimulus 130×200 arc min in size consisted of randomly distributed stripes equivalent to illusory figure elements but brighter twice (100 cd/m2). The stimulus display duration varied from 60 ms to 1.3 s. Each presentation consisted of three parts: the blank fixation point exposed for 700 ms on the screen, the Oppel-Kundt figure itself, and the masking stimulus appearing immediately after the figure offset and lasting 2s. Two alternative forced choice constant stimulus procedures were used to measure illusion strength. Psychometric functions were obtained for all display durations of the stimulus. Six subjects participated in the experiments. The Oppel-Kundt illusion weakened gradually from the maximum strength (of about 20% overestimation) within the 700 – 1300 ms interval to 2 – 3 times less strength at about 100 ms and showed tendency to decrease further at shorter times. The results suggest that an extra time is required to establish the spatial misperception of the Oppel-Kundt type compared to the time used in the length estimation procedure. The results obtained also denote that the Oppel-Kundt and Müller-Lyer illusions may be of different origin, as previous experiments with the Müller-Lyer illusory figure didn't show substantial strength variations with duration of presentations.
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