Transparent surfaces defined by implicit X junctions.

An X junction is known to be a strong cue for transparency whereas a T junction typically indicates occlusion by an opaque surface. In this article, however, we will demonstrate two cases in which special T junctions (implicit X) can support the perception of a transparent surface. The T junction is perceived as having an additional illusory contour rendering it as an implicit X junction. There is physically realizable condition in which transparency can produce a T junction and the existence of this special case may explain why T junctions are not necessarily taken as cues for opaque surface. The similar processing for X junctions and implicit Xs to form transparent surfaces is suggested.