A phenomenal observation on transparency and layer of depth

Brightness differences between an overlapping area of two figures and a surrounding area as a background effected to bring apparent transparency at the area. Regarding this phenomenon of a sense of transparency, there were two kinds of a sense being related to either depth or interposition. In this paper we analyzed conditions of a figure-background brightness relation in terms of contrast and assimilation evoked these two senses of transparency at the area. A sense of transparency of the area located apparently in a space of three dimensions produced a sense of depth by a brightness contrast effect between the crossing area of two figures and its surrounding background. On the other hand a sense of transparency of the crossing area of two figures as seen in a space of two dimensions produced a sense of interposition when assimilation occurred between the area and its surrounding background.