The effect of the stimulus shape on tilt judgment T Ueda, T Yasuda, K Shiina |
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Faculty of Education and Integrated Arts, Waseda Univeristy, Japan
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| The Okuma illusion [Yasuda, et al, 2012, Perception, 41(10),1277–1280] is a visual illusion in which the tilt of two objects in an image is perceived differently when the image is rotated. The difference of object shapes, geometric or not above all, would be a primary factor of the illusion. In this study, we tested the effect of the object shapes in a tilt judgment task by measuring the difference threshold of the tilt. Forty-six participants were first required to adjust upright the several geometric or non-geometric figures. Then in a randomized series of presentation, they were asked to judge if a stimulus was shown tilted as fast and accurate as possible. The result of the experiment showed that non-geometric stimuli, which were complex and had less vertical and horizontal components in shape, had a wider difference threshold. The result suggested that the difference of the sensitivity in tilt perception was a cause of the Okuma illusion. |
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