 Seeing-in is a distinct kind of perception, and it is triggered by the presence within the field of vision of a differentiated surface. […] When the surface is right, then an experience with a certain phenomenology will occur, and it is this phenomenology that is distinctive about seeing-in. […] The distinctive phenomenological feature I call ‘twofoldness’, because, when seeing-in occurs, two things happen: I am visually aware of the surface I look at, and I discern something standing out in front of, or (in certain cases) receding behind, something else. (Wollheim 1987: 46)