362 J. Cosmet. Sci., 73, 362–376 (November/December 2022) Address all correspondence to Ken Nishino, Nishino.ken@kao.com Differential Effects of Eyeliner Color and Thickness Applications on the Perceived Color of the Eye Sclera KEN NISHINO AND NATSUKO OKIYAMA Makeup Product Research Laboratory, Kao Corporation, Odawara, Japan (K.N., N.O.) Accepted for publication February 14, 2023. Synopsis The most widely studied influence of eye makeup on perception is the eye enlargement effect. There are limited studies on other influences on visual perception. This study aimed to demonstrate the influence of eyeliner color and thickness on the perceptual color of sclera, the white part of the eyes, and to understand the relationship between them. A psychophysical experimental method, the staircase method, was employed to evaluate the influence of eyeliners on perception. The first experiment showed that thicker eyeliners resulted in perceptually larger eyes and a white sclera. The second experiment revealed that eyeliner colors that were significantly different from skin color, such as blue and green, made the perceptual sclera color whiter. The third experiment confirmed that the hue of the eyeliner color considerably affected perceptual sclera whiteness, whereas the lightness of the eyeliner affected perceptual eye size. An influence on sclera whiteness perception by cosmetic eyeliners was demonstrated, and the relationship between the influence on perception and the characteristics of the applied eyeliner was clarified. This effect may be one of the mechanisms behind the impressive eyes obtained by eye makeup, and the results will provide important scientific evidence for improving makeup products and techniques. INTRODUCTION Cosmetics such as foundations, lip rouges, and eye makeup can notably enhance female facial attractiveness by changing the appearance of facial features in several ways. In particular, eye makeup products such as mascaras, eyeliners, and eye shadows significantly influence facial attractiveness (1). Among the various beautification mechanisms, the perceptual eye enlargement effect is the most widely studied effect. Childlike features such as full lips and large eyes are considered attractive (2). Matsushita et al. quantitatively demonstrated that all three eye makeup products cited above perceptually enlarged eye size by approximately 5% (3). Other mechanisms may also influence attractiveness, but they have rarely been studied (4). Although various products have been created based on sensory evaluations, advances in mechanistic understanding can help develop more effective products. Studies on the basic mechanism for determining a new phenomenon are limited. Detailed analyses and research in the fields of vision, optics, and physics are important for the development of product design.

363 EFFECT OF EYELINER ON THE PERCEIVED SCLERA COLOR The contrast between facial features such as the eyes, eyebrows, and mouth and the surrounding skin, called facial contrast, has a significant influence on beauty. Porcheron et al. demonstrated that facial contrast decreases with age, and the aspects of facial contrast are also significantly correlated with perceived age (5). This effect has also been observed in cross-cultural studies (6). This work thoroughly elaborates the beautification mechanism of makeup, as almost all point makeup products, such as mascara, lipstick, and eyeliner, enhance facial contrast. Facial features, especially the color of the sclera, the white part of the eye, considerably change with aging and strongly affect visual impressions of age, health, and beauty (7). Eye makeup products increase eye contrast by darkening and coloring the skin around the eyes. The sclera color does not change directly, but its perceptual color can be changed by visual color illusion effects such as the lightness–contrast illusion. Perceptual color change of the sclera is one of the primary beautification mechanisms of eye makeup. The enhancement of color, texture, and the application region to maximize the change of perceptual sclera color can help improve eye makeup products. According to earlier research on the lightness–contrast illusion, the illusion effect on a test field (a central field with lightness affected by the surrounding inducing field) increases with an increase in the area of the inducing field and the difference in lightness between the inducing and test field (8–11). Therefore, applying a dark color around the eyes is the simplest way to change the sclera’s color perceptually, but it may appear to be unnatural. Alternatively, popular makeup products, such as mascara and eyeliner, make the eyes more impressive by defining the boundary of the eyes. Boundary is a very important factor for lightness perception and illusion (e.g., gradient illusion, figure–ground separation, watercolor illusion, etc. 12–14). Traditional eye makeup methods that define boundaries may also induce color illusions in the sclera through a mechanism different from the lightness–contrast illusion. In the present study, eyeliners were selected as the research target. The relationship between eyeliner designs (thicknesses and colors) and their influence on perception of average Japanese female faces was studied. The mechanisms for the influence of eyeliner color and thickness on eye perception were compared with the above-described visual illusions in the field of vision science. In the first experiment, the influence on perceptual sclera color induced by black eyeliner (the most popular color) was analyzed using a psychophysical experimental method, and the relationship between the influence on perceptual color and eyeliner thickness was elucidated. If the mechanism of the perceptual sclera color change is not the lightness–contrast illusion, the influence on perceptual color should not increase with the thickness. The most popular effect of eye makeup, the eye enlargement effect, was also studied and compared with the influence of perceptual color. In the second experiment, the hue of the eyeliner color was varied, and the effect on perception was measured to explore the relationship between the effects and line chromaticity. Finally, the effects of lightness and hue of an eyeliner for the two influences on perception, color of the sclera and eye size, were studied in the third experiment. MATERIALS AND METHODS MEASUREMENT OF THE SCLERA COLOR CHANGE WITH AGE In the present work, the change in perceptual sclera color was studied along with the sclera color change with age in Japanese females. The measurements provided the direction of color change for the comparison stimuli.