Ebenbreite (Morinaga 1941) is a powerful factor of figure/ground organization. Regions bounded by parallel contours are perceived as figures more easily than regions bounded by non-parallel contours (Metzger 1953). Despite its power to generate elegant demonstrations, the crucial stimulus feature involved in Ebenbreite is unclear. Vertically-oriented stripes used in Morinaga-like patterns can involve two different transformations: (a) translation of a curved contour along a horizontal direction; (b) reflection relative to a curved axis, under a smoothness constraint. At small curvatures the stripes generated by the two transformations are similar; whereas they differ substantially at large curvatures. We performed two experiments to study the possible superiority of reflection over translation, following the general intuition that figural organization based on reflection Ebenbreite might be easier because of its compatibility with a simpler 3D percept. In the first experiment observers judged if a target stripe was present/absent in a pattern made of several stripes, which could be either translatory or reflective, depending on trial. In the second experiment observers searched for a stripe with translation Ebenbreite among distractors with reflection Ebenbreite, or viceversa. In both conditions we found a superiority of reflection over translation, despite the fact that also translation Ebenbreite is compatible with a 3D percept. Such a superiority might depend on the projective compatibility of reflection Ebenbreite with rotational symmetry around an elongation axis.
ASJC Scopus subject areas
- Sensory Systems