This was more easily accomplished because I could always close my eyes to the stimulus around me and trust my fellow actors.
Tonight, Paul and I went to see "One Flew Over the Cuckoo's Nest" at CP and I was floored by Todd Kinder's performance. Throughout most of the play, except during scene breaks wherein he turned to the audience and recited the inner monologue of his character, he had to be mostly catatonic...not reacting to the stimulus around him. However, he had to do so while upright, walking, sometimes pushing a broom.
When he finally began to react to the things around him it was as much a surprise to this audience member as to the other characters on stage (I've never read the original novel nor this play that was based on it, nor have I seen the movie).
His one major scene of dialogue, between his character (Chief) and Russ' (McMurphy), in which he tells of his family, was one of the most moving I've seen on that stage or any stage.