Error Increase and Decrease in Minimal Form of Mueller-Lyer Illusion

Abstract

Based upon prior research showing that the error associated with the Sander parallelogram is maximal when the diagonal lines are physically omitted rather than physically present, an attempt was made to determine if a similar finding might result from eliminating the shaft in the Mueller-Lyer illusion. An interaction was found between shaft vs no-shaft condition and fins-in vs fins-out. Eliminating the shaft significantly increased error in the fins-in condition and significantly decreased error in the fins-out condition. The results were judged consonant with the previous study involving the Sander parallelogram.