Measurement of eye size illusion caused by eyeliner, mascara, and eye shadow

Do eyeliner, mascara, and eye shadow actually make the eyes appear larger than they really are? If so, by what percentage? To answer these questions, we used psychophysical experiments. Experiment 1 manipulated the degree of eyeliner (four levels) and mascara (five levels), and measured perceived eye size using a psychophysical procedure called the staircase method. The results showed that both eyeliner and mascara make the eyes appear larger than they really are by up to 6% (13% in area), but their effects are not additive. Eyeliner increased perceived eye size only in the absence of mascara. In the presence of mascara, however, eyeliner has no additional effect. Experiment 2 measured perceived eye size with or without eye shadow and demonstrated that eye shadow increases perceived eye size by about 5% (10% in area). These findings indicate that one mechanism by which makeup and cosmetics alter facial appearances involves inducing visual illusions. In addition, it is suggested that the eye size illusion caused by eyeliner, mascara, and eye shadow uses the same mechanism as that of the Delboeuf illusion, a geometric illusion of assimilation.