Real and virtual borders in the Poggendorff illusion.
The strength of the Poggendorff illusion has been determined by a nulling method for the classical as well as other configurations of the central inducing region. Compared to a uniform field, an inducing rectangle with very low contrast produces a marked illusion, which saturates at a Michelson contrast of about 0.1. With virtual borders of the Kanizsa type there is a weak illusion and this effect is attenuated when the 'pacman' sectors are occluded. Texture borders without luminance contrast induce a stronger illusion. These results are discussed in relation to earlier data for contrast dependence of Vernier acuity and for the orientation discrimination and tilt illusion with real and virtual borders.
Westheimer
G
G
Division of Neurobiology, University of California, Berkeley 94720-3200, USA. gwest@socrates.berkeley.edu
Wehrhahn
C
C
D005556:Form Perception; D006801:Humans; D009903:Optical Illusions; D011581:Psychological Tests; D012858:Size Perception