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.

JOURNAL OF COSMETIC SCIENCE 162 perceived differently from real in terms of shape and/or size, then that can also be consid- ered a visual illusion. A good example is eye makeup that causes the eyes to appear larger than they really are. Although many previous psychological studies have investigated the impact of makeup on facial impressions (e.g., 2,9,10,15–18) and on gaze direction (19), virtually nothing is known about the illusory aspect of makeup. However, for at least three reasons, the eye size illusion induced by eye makeup merits scientifi c investigation. First, eyes are an important determinant of facial attractiveness. Previous facial identifi ca- tion experiments showed that information about the eye and eyebrow regions of facial stimuli was most clearly linked to observers’ ability to discriminate those faces (20–22). Moreover, large eyes are viewed as more attractive than small eyes. For example, Baudouin and Tiberghien (7) showed that wider eyes make female faces more attractive (also 23,24). Altering perception of eyes can cause a dramatic change in the overall facial impression, and most women emphasize their eyes above other features when applying makeup (25). Mulhern et al. (17) found that eye makeup is one of the most signifi cant contributors to the enhancement of female facial attractiveness. Second, although many makeup artists claim that eye makeup can make the eyes appear larger than they really are (e.g., 26–29), this claim has not yet been quantitatively dem- onstrated. One purpose of eye makeup is to make small eyes appear larger (e.g., 28–30). In fact, eye-enlarging makeup techniques are hugely popular among young Japanese women these days. However, so far, the effectiveness of these techniques has been sup- ported only by makeup artists’ experiences and subjective impressions. No scientifi c study has investigated such effects. The eye size illusion induced by eye makeup has yet to be quantitatively measured. Third, if experiments demonstrate to what extent eye makeup increases the perceived eye size, there are a number of practical implications. For example, quantitative as- sessment of eye makeup may facilitate comparing/evaluating different items of cos- metics and proposing effective makeup techniques to consumers. Quantitative assessment can also help develop new cosmetic products that are more effective in making eyes appear larger. Furthermore, including numeric data in advertising ren- ders more objectivity and credibility to an advertisement, thus increasing its appeal to consumers. Psychophysics is a branch of perceptual psychology and vision science. It specializes in quantitatively measuring the perceived intensity or quantity of stimuli as a function of the physical intensity or quantity of the stimuli. Psychophysical methods are particularly useful for measuring the magnitude of visual illusions. If eyes appear larger than they re- ally are as a result of eye makeup, it is a kind of illusion. Therefore, the effects of the makeup can be measured by psychophysical methods (31,32). One such psychophysical method is called the staircase method, also known as the up- and-down method. To measure visual illusions induced by eye makeup, we used a variant of the staircase method in which two faces are presented in each trial. An observer judges, which face appears to have larger eyes. One face is a standard stimulus with eye makeup, whereas the other is a comparison stimulus without eye makeup. If the observer judges that the comparison stimulus has larger eyes, then on the next trial, the comparison stimulus is replaced with another comparison stimulus. This comparison stimulus has eyes one step smaller than the previous eyes, and the same process is then repeated. When