A QUANTITATIVE-ANALYSIS OF ILLUSION MAGNITUDE PREDICTED BY SEVERAL AVERAGING THEORIES OF THE MULLER-LYER-ILLUSION

This article describes a quantitative method to evaluate several avera ging (i.e., confusion and assimilation) theories by comparing predicti ons of the absolute magnitude of the Muller-Lyer (ML) illusion with re sults of previous studies of the composite ML figure. The magnitude of illusion was best predicted by Davies and Spencer's (1977) theory and by integrative field theory (Pressey & Pressey, 1992). Furthermore, w hen the ML figure was at the point of subject equality, the average of shaft and intertip distances, and the configural dimensions proposed by Davies and Spencer, were most frequently closest to being equal in the apex-in ML and apex-out ML. Results indicate that a comparison of predicted and reported absolute magnitudes of the ML illusion can prov ide quantitative criteria to distinguish and evaluate averaging theori es of the ML illusion.