JOURNAL OF COSMETIC SCIENCE 172 and mascara. Thus, a possibility remains that application of eye shadow further enhances the eye size illusion caused by eyeliner and mascara. Future research should examine this aspect. Morikawa (31,32) suggested that illusions in the human face and body tend toward as- similation, rather than contrast. One reason for the predominance of assimilative illusions might be that spaces between facial parts or between body parts are fi lled with and con- nected to tissues such as skin, muscles, and bones, unlike the empty spaces between the lines that constitute classical geometric illusions (32). Moreover, the development of dif- ferent parts of an individual’s body is often governed and controlled by the same genetic and hormonal mechanisms. Therefore, if an individual’s eyebrows are drooping, his or her eyes are likely to droop as well. If one part of the body is thin, other parts are also likely to be thin (31,32). We hypothesize that visual perception is affected by these biological co-occurrences and natural correlations. Morikawa (31,32) also observed that, when geometric illusions in the human face and body are psychophysically measured, the maximum illusion magnitudes tend to be around 5%, a sort of a “magic number.” That is exactly what these experiments repli- cated. An illusion magnitude of 5% is small, as compared to well-known geometric illu- sions. Perhaps there exists a natural upper limit to visual illusions in the human face so that the illusions occur only to the extent that the resulting distortions do not appear unnatural. Notably, although a difference of 5% may be numerically small, the difference is perceptually conspicuous, perhaps because the human visual system is especially tuned to detecting fi ne differences in the human face. Identifying and recognizing faces is an extremely important skill in society. We are so sensitive to the confi guration of facial features that we can reliably perceive even a physically small difference (31,32). Historically, most researchers have studied visual illusions with very little relevance to or- dinary life. Most visual illusion stimuli have been highly contrived and unnatural fi gures created artifi cially in laboratories. The human visual system seldom encounters such stimuli in the natural environment or in daily life. However, illusions in natural objects, albeit much less dramatic than artifi cial ones, are far more prevalent in our daily lives than we may think. In fact, some illusions can be very relevant and useful in everyday life (31,32,39). This study investigated visual illusions in the human face, the most natural and socially important stimulus. The results indicated that one mechanism by which cosmetics and makeup alter facial appearances is by inducing visual illusions. Our results demonstrated that cosmetic illusions can be quantitatively measured using psychophysical methods. Russell (40) stated, “Though cosmetics are applied to the face of the wearer, they are de- signed to operate on the visual system of the perceiver.” Because the human visual system judges what is beautiful or attractive, we have to investigate cosmetics and makeup in terms of the perceiver’s visual system. Therefore, research on visual perception can be an important part of cosmetic science. We believe that measurement and analysis of cos- metic illusions will become a new and fruitful fi eld of cosmetic research in the future. CONCLUSIONS Our experiments examined whether eyes with makeup—eyeliner, mascara, and eye shadow—are perceived to be larger than they really are. To this end, we applied an ex- perimental paradigm used in visual illusion studies. Measurements revealed that

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