HAIR APPEARANCE AND INTERNAL STRUCTURE 395 strictly, a color similar to the light source) reflection from the front surface and the colored reflection from the back surface (Figure 5a). On the other hand, the artificial nylon fibers without a cuticle structure show only a slightly colored single reflection (Figure 5b). The color of the human hair and the nylon fibers in Figure 5 was not matched precisely. The CIE L*a*b* values for each fiber were measured by a color meter as L* -- 27.18, a* = 6.44, b* = 10.25 for the human hair, and L* -- 30.17, a* = 4.85, b* = 12.13 for the nylon fiber. The nylon fibers were a little more yellowish in color (larger in b* value) and less reddish in color (smaller in a* value) than the human hair. Although the expression of the panel members on the hair appearance may be affected by this small color difference, the authors mainly discuss here the textures of the hair appearance, such as the impression of depth, along with transparency and a metallic or artificial impression. Further influence of color on hair appearance is considered in the Discussion section of this paper. The dynamic appearance of the poreless hair in Figures 4 and 5 was evaluated by professional panelists by moving the hair tresses. During the evaluation, the panelists observed changes in appearance when the shape of the hair tresses was repeatedly changed from a convex to a concave form, as in swinging hair. The opinions obtained from the panelists for the poreless hair compared to the porous hairs or the nylon tresses were: more dramatic and dynamic changes in colorfulness and the impression of depth along with a brilliant and vibrant impression. The changes in the appearance of the poreless hair as a function of curl curvature are shown in Figure 6. The relative position, size, and intensity of the double reflections of the poreless hair are dramatically changed in the course of the formational change. It is worth noting that the change in hair appearance is not symmetry at the curvature = 0 (flat shape), but symmetry at the curvature = -0.02 (concave shape), under the present geometrical condition of lighting and observation described in Figure 10b. Curl Radius (cm): -20, -33, -50, 0.00, 50, 33, 20, Curvature (cm4): -0.05, -0.03, -0.02, 0.00, 0.02, 0.03, 0.05, concave flat convex Figure 6. Photo images of a curled hair tress at several curl curvatures. The hair used in this figure is a human hair tress with a poreless structure and inclined cuticle structure and is characterized in Figure la. The curl radius and curvature of the hair tress are shown at the bottom of each image.

396 JOURNAL OF COSMETIC SCIENCE DISCUSSION INFLUENCE OF POROUS STRUCTURE IN HAIR FIBER ON VISUAL APPEARANCE The poreless hair in Figure 4 is evaluated as lustrous, colorful, and giving an impression of depth along with transparency, whereas the hair with a porous medulla is evaluated as lusterless, white-chalky, dull, dry, and fiat. In the goniophotometric data (Figure 3), the higher contrasts in lightness, saturation, and hue angle are observed in the poreless hair. The higher contrast in lightness simply causes a more lustrous impression, and the higher contrasts in saturation and hue angle cause a more colorful impression as well. Further appearance, the impression of depth along with transparency, is not explained only by the data obtained with the goniophotometer. In the visual perception, three-dimensional space is reconstructed from two-dimensional images on the retina with several cues to depth perception, such as perspective, binocular disparity, and motion parallax (11). The cues to depth included in the hair appearance were then considered, using a simple model. Figure 7 shows a plain plate model for understanding the light locus from a light source to viewpoint. With the plain plate model, two reflections are generally observed: reflection from the front surface (solid line) and that from the back surface (dotted line). The front surface reflection from the object is generally not colored when the color of the light source is white. On the other Light % View source Reflection from point ..% Front surface '""% \ "".% :•"'"' 'sua : . ' Angle Apparent De • , -- ? N Reflectiofrom Back surface Figure 7. Model illustration to understand light loci from light source to viewpoint via reflections at the front and back surfaces of an object. This model is a thick model with flat surface, compared with the models in Figure 8.