THE POGGENDORFF ILLUSION: THE PRESENCE OF ANOMALOUS FIGURE IN GENERATING THE EFFECT

  • D. Massidda
  • A. Bastianelli
  • R. Actis-Grosso
  • G. Vidotto

Abstract

In the classical version of the Poggendorff illusion the two ends of a straight line segmentpassing behind an obscuring rectangle appear offset when, in fact, they are aligned. Previousresearch (Tibber et al., 2008) showed that the illusion persists when the obscuring rectangleis replaced by Kanizsa-like subjective contours. Spoto et al. (2008) show that the illusion isstill present when both the obscuring rectangle and transversal segments consist of Pac-Mantokens generating Kanizsa-like subjective contours; in addition, the illusion persists evenwhen the Pac-Man tokens are arranged so that no illusory contours are generated. In thepresent research the role of Pac-Man tokens in generating the Poggendorff illusion isinvestigated. Twenty-four participants have been tested using the adjustment method on twoconditions including Pac-Man tokens in one condition and not in the other. The response biasin the direction of the classical effect is discussed.
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