The human mind operates automatically in ways that often value identification more than perception. While we look with our eyes, we see with our mind … Our minds tend to make corrections …
If the goal is to paint what your retina sees and not what your mind knows … one useful strategy is to concentrate on painting the negative shapes (the shapes formed by background areas lying between the outlines of painted objects and figures). Because you don’t know the negative shapes conceptually, you will not be as prone to distortion of size or shape. Look and paint the shape of the air under and over the table, rather than painting the table itself.
“Painting as a Language”, by Jean Robertson & Craig McDaniel, page 18
A quick exercise in seeing negative space I like is to use a word as a starting point. Instead of writing the word, draw or paint the space around the letters. Such as this:
It’s something that gets easier with practise, but if you’re struggling to get your mind to ‘swap over’ to the negative space, you can ‘cheat’ the first few times by writing the letters down with pencil and then erasing them.