Forget the scene partners. Forget steeping yourself in the atmosphere of the set. In one sense, acting against one's own imagination is simply an extension of basic acting-school techniques. That's really what this is getting back to, those first exercises in which you create the cup, create the coffee, create the smell, the heat, the taste, and go at it that way.
Some actors find even simulated reality helpful in filling in the blanks.
It's not hard to make the imaginative leap into filling up the void, which is thin air, where there should be something big and scary. Neill admits to being less comfortable working on a green-screen stage, where not only the creatures have to be imagined but the entire set. And that's tricky. The irony is that as digital systems become sophisticated to the point where virtually anything can be simulated, filmmakers increasingly strive for physical reality. It was only difficult in that you don't have any kind of clue what to do next, it all has to be in your imagination and your memory.