Altering Mueller–Lyer illusion magnitude using figural additions at the wing–shaft intersections

ALAN SEARLEMAN
St. Lawrence University

CLARE PORAC
Pennsylvania State University, Erie

COLETTE DAFOE AND BRIAN HETZEL
St. Lawrence University

The Mueller–Lyer (ML) illusion has been used to study the way in which perceived length is affected by processes of information extraction when a visual target of interest (the ML shaft) is surrounded by other nontarget figural elements (inward- or outward-turning wings). It is argued that the perception of length is computed in terms of the center of gravity or centroid of figural elements at the wing–shaft intersection. The outward-turning wings shift the computational centroid away from the shaft end, giving rise to an erroneous overestimation of shaft length, while the inward-turning wings have the opposite effect. In three experiments, we observed that figural changes, which theoretically shifted the center of gravity of figural elements at the wing-shaft intersection, also increased or decreased the magnitude of the ML illusion.