Effects of training in design on magnitude of the Müller-Lyer illusion

The Müller-Lyer illusion was measured for 10 design and 10 optometry students. The illusion was smaller for design students and they improved significantly with practice. The results are discussed in relation to size-constancy, according to which part of the figure corresponding to a distant object is overestimated and to the aptitude of design students to draw according to their retinal image.