J. Cosmet. Sci., 66, 161–174 (May/June 2015) 161 Measurement of eye size illusion caused by eyeliner, mascara, and eye shadow SOYOGU MATSUSHITA, KAZUNORI MORIKAWA, and HARUNA YAMANAMI, School of Human Sciences, Osaka University, 1–2 Yamadaoka, Suita-shi, 565–0871 (S.M., K.M.), and Shiseido Research Center, Yokohama, 224–8558 (H.Y.), Japan. Accepted for publication March 1, 2015. Synopsis 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 ma- nipulated the degree of eyeliner (four levels) and mascara (fi ve 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 fi ndings indicate that one mechanism by which makeup and cosmetics alter facial ap- pearances 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 geo- metric illusion of assimilation. INTRODUCTION Cosmetics can enhance a woman’s facial appearance in multiple ways. They can empha- size healthy, youthful looks (1,2) accentuate femininity and sexual attractiveness (3–6) improve bilateral symmetry of the face, which leads to increased attractiveness (7,8) make the complexion appear clean and tidy (9) increase perceived competence and self- confi dence (2,10) and change the apparent shape and/or size of facial parts such as eyes, nose, and mouth (e.g., 11,12). When our perception of the shape and/or size of an object differ from reality, it is called a visual illusion. The Delboeuf illusion, for example, consists of two concentric circles. When the diameter ratio between the two circles is appropriate, the size of the inner circle appears larger than it really is. The Delboeuf illusion is considered an assimilation of the inner circle with the outer circle (13,14). If certain makeup causes the face to be Address all correspondence to Dr. Soyogu Matsushita at soyogu@hus.osaka-u.ac.jp.