When Alfred Hitchcock spoke to Francois Truffaut, the younger director revealed that he allowed all three actors to improvise one of the scenes in his film Jules & Jim. Hitchcock was surprised by this because he simply couldn’t imagine giving actors so much control over the material they were filming. Later in 1969, he also joked to The Montreal Gazette (via The Hitchcock Zone Wiki): “If an actor tries to change his lines or direct a scene, I tell him to do what he wants.” There’s always an editing room.” His films relied so heavily on precise, fluid camerawork that the director didn’t like loose dialogue and movement rules at all.
That doesn’t mean that all the improvisational material was left behind. On the “Notorious” set, Hitchcock surprised his staff when he took notes from star Ingrid Bergman on their scenes (via Vulture). And when Janet Leigh and Anthony Perkins were shooting Psycho, they were free to come up with actions that suited the characters as long as the camera didn’t need to be moved. Perkins even came up with the idea that his character Norman Bates would always eat candy corn on screen (via Bradenton Herald). “Hitch,” as he was known, was always in charge, but he didn’t always have to be in control.