Abstract
Recent psychophysical studies investigate visual processings underlying the perception of homogeneously transparent, or translucent, materials such as glasses and milk (Fleming & Buelthoff, 2005; Motoyoshi, 2010). Here, we explored critical image features that support visual perception of a surface with multiple layers like human skin and foods, in which an opaque body is covered with a transparent material. We first created real objects that consisted of an opaque urethane body covered (vacuum-formed) by a transparent sheet of polyvinyl medium, and found that the transparent layer was perceived only when the object had sharp bumps or when the air was occasionally interleaved between the inner body and the superficial layer. We next used computer-generated images to systematically examine the effects of physical parameters including color, glossiness, transparency, refraction, and thickness of the superficial layer. Observations with these images revealed at least three parameters that might be important for perceiving the transparent layer; (1) visible separation between the outside edge of the superficial layer and that of the opaque body, (2) specular highlights on the outer layer, (3) color fluctuations within the object image. We speculate that appropriate relationships between them support visual impression of transparent layers.