Poggendorff illusion with all-second-order contours

The classic Poggendorff illusion is typically drawn with an outline or filled horizontal or vertical rectangle intersected by two diagonal lines. Misperception of alignment between the latter persists when the rectangle is defined by subjective contours interpolated between Kanizsa-style pacmen, or is a borderless area filled with parallel stripes. Recently (Rose and Bressan, 2011 Perception 40 ECVP Supplement, 203) we reported that when the diagonals are defined by pacmen, the illusion reverses direction (for acute angles of intersection with the rectangle), for both outline and pacmen-defined rectangles. Here, we study the Poggendorff figure with the rectangle and its diagonals defined by stripe endings. To avoid the first-order luminance cues inherent in previous stimuli, we created a novel display with zero change in mean luminance across the entire display. The illusion was present with normal direction, indicating that the location cues presented by the first order stripe endings cannot be discounted and automatically participate in defining second-order contour locations at a stage preceding that at which the Poggendorff illusion itself is generated. In this respect, second-order contours defined by line endings are not equivalent to contours interpolated between pacmen.