Alignment errors in Poggendorff-like displays when the variable segment is a dot, a dot series, or a line

In the standard Poggendorff figure, the abutting tip of the upper right transversal appears more misaligned than its distal tip. This appears paradoxical, since dot alignment errors increase with line-to-dot separation. To attempt a resolution of the paradox, four experiments were conducted in which single dots, series of dots, and lines were adjusted to be apparently collinear with a standard line segment, with neither, one, or both vertical inducing lines present. The results, taken together, suggested an explanation of the paradox and also that the standard Poggendorff display may result in alignment errors which represent a compromise judgment, based on conflicting cues to collinearity. In particular, the fourth experiment showed that line-to-line alignment errors could be made to resemble dot-to-line alignment errors by instructional variables. It was suggested that the effect was produced by forcing observers to process asymmetrically rather than symmetrically (Krantz & Weintraub, 1973).