EVALUATING MULLER-LYER EFFECTS USING SINGLE FIN-SET CONFIGURATIONS

Four experiments were conducted to study the bias of perceived length for Muller-Lyer configurations that contained a single set of fins (i. e., two segments that join to form a vertex). The experiments manipula ted several factors that have been shown to be critical to the effect: (1) version (which way the apex pointed), (2) length of the stimulus span, (3) presence or absence of aline segment in the span being judge d, (4) fin length, (5) fm angle, and (6) the zone in which the respons e was rendered. Using percent error as the index of perceptual distort ion, the major finding was that the two versions show an opposite slop e for strength of effect as a function of span. When stimulus spans we re plotted against response means (not converting to percent error), a n almost perfect linear relation was found. These results indicate tha t the perceptual effects can be modeled as a linear system having two parameters through which the treatments exert their influence. The res ults are discussed in relation to major theories of mechanism for the Muller-Lyer illusion.