Reversal of the Müller-Lyer Illusion with Changes in the Length of the Inter-Fins Line

Abstract

Subjects were asked to judge the relative lengths of lines placed between the ingoing and the outgoing fins of a Müller-Lyer figure. It was found that with the gap between the fins constant at 160 mm. there was a reversal of the normal Müller-Lyer illusion when the inter-fins line was between 40 and 100 mm. long. This effect was maximal when the line was 80 mm. The normal illusion returned when the line was increased in length to 120 mm. These findings do not support Gregory's inappropriate constancy scaling theory. They seem to suggest the operation of two distinct illusory forces in the Müller-Lyer situation. The reverse illusion may be due to the greater expansion effect upon the line between the ingoing fins, caused by the greater “enclosing” nature of these fins.