SourcePerception, 34, , (2005), pp. S166
Article / Letter to editor
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SW OZ DCC CO
SW OZ NICI CO
SubjectAction, intention, and motor control
We have created patterns in which illusory Kanizsa squares are positioned on top of a background grid of bars. When the illusory contours and physical contours are misaligned, the resulting percept appears to be rather confusing (van Lier et al, 2004 Perception 33 Supplement, 77). Observers often perceive a shift of the part of the grid that falls inside the illusory square, leaving the impression that the physical grid is indented at the positions of the illusory contours. All in all, these displays have a remarkably unstable and restless appearance. We have performed two experiments to study the strength and the direction of the illusory shifts. In the first experiment, an illusory square, induced by a pacmen configuration, was positioned at various positions on a grid of straight bars. After briefly flashing these stimuli, observers frequently reported illusory shifts (or indentations) of the background bars for those cases in which physical and illusory contours were slightly misaligned. In a control condition, the pacmen were replaced by crosses (that did not induce an illusory square). As expected, this time, no illusory shifts were reported. In the second experiment, observers had to judge the direction of the illusory shift. The results show that the perceived shifts, in fact, reflect a tendency to cancel the misalignment between physical and illusory contours in the display. We argue that these temporary relocations of physical and illusory contours reflect both competition and cooperation between the underlying contour mechanisms.
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