Christian Bale has said that he finds it addictive obsessing over roles when he takes on new projects.
The former Batman appears in American Hustle, a film about con men, due out in January and said he loved the process of getting to know a new character.
He said: "Everybody dreams at night. They tend to go a little insane and that's acceptable. To me, acting's like dreaming in a waking state, as you get to study people, go a little insane and be obsessive about something, and it's expected. I find that very addictive."
American Hustle is directed by David O Russell, who also worked on The Fighter with Christian in 2010.
Christian said he was easily tempted to work with David again: "I'm always interested in what David's making. I always know it's going to be really fascinating and will hopefully become very, very memorable for many years to come."
American Hustle is due to be released in cinemas on January 1.