I am now as clear minded as I ever was. Confusion Theory reigns.
Abstract
Used the method of reproduction to measure the illusion generated by that Muller-Lyer figure with obliques directed inward. In Exp. I, the angle between the obliques and the shaft of the figure was varied. The illusion decreased with increasing angle of the obliques. In Exp. II, length of obliques was concomitantly varied with angle size so as to keep distance between opposite obliques constant. 34 undergraduates were used in both experiments. Exp. II showed no effect of the angle of the obliques, indicating that the Muller-Lyer illusion results in part from confusion of the shaft length with the distance between the ends of obliques. In Exp. III with 44 undergraduates, the distance between ends of obliques was varied along with the angle size in a factorial design. The results indicate a strong effect of the distance and an interaction between the 2 variables. The latter effect is also explainable by the confusion hypothesis. (PsycINFO Database Record (c) 2016 APA, all rights reserved)