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Classifying illusory contours: edges defined by "pacman" and monocular tokens
1Division of Neurobiology, University of California, Berkeley 94720-3200, USA.
Journal of Neurophysiology
|February 1, 1997
Summary
Illusory contours, like Kanizsa figures, are about twice as hard to discern orientation for compared to solid lines. These findings suggest illusory borders engage visual mechanisms differently than real edges.
Area of Science:
- Vision science
- Perceptual psychology
Background:
- Human foveal orientation discrimination thresholds were investigated.
- Comparison between solid line figures and illusory contours (Kanizsa figures, stereoscopic depth illusions) was performed.
Purpose of the Study:
- To quantify the orientation discrimination of illusory contours.
- To compare the performance with solid line contours.
- To investigate the relationship between border robustness and susceptibility to the tilt illusion.
Main Methods:
- Orientation discrimination thresholds were measured in the human fovea.
- Stimuli included solid lines, Kanizsa figures, and illusory contours from monocular depth tokens.
- Simultaneous orientation contrast (tilt illusion) was also assessed.
Main Results:
- Orientation discrimination for illusory contours was approximately twice as poor as for solid lines.
- Performance with illusory contours was only slightly better than with their supporting elements alone.
- More robust illusory borders showed less susceptibility to the tilt illusion.
Conclusions:
- Illusory borders do not activate "border" or "edge" mechanisms comparably to real lines.
- The robustness of illusory borders correlates inversely with their susceptibility to orientation contrast effects.