I am not sure if everyone will know what I am talking about, but negative space was something taught to me in art class. It is all the objects which in a sense are the space behind the objects in a picture or painting. Some abstract artist use just the negative shapes to compose a picture. I was curious to the fact if in a lucid dream if you could train your mind to see just the negative shapes. Plus because your subconscious deals more in the abstract world. It would be quite a seen.