20 Things You Didn't Know About Psycho
6. Norma Bates' Dialogue Was Recorded By Three Actresses
Further muddying the waters for Norma Bates' identity, Hitchcock decided to hire three actresses to record dialogue for Norman's mother, which were then mixed together until Hitchcock found the desired sound for a given scene.
The voices were recorded by Paul Jasmin, Virginia Gregg, and Jeanette Nolan, in an attempt to give Norma a vaguely uncanny, ambiguous voice which emphasised how haunting she sounded within Norman's own mind.
The exception is Norma's final speech to Norman, which was voiced entirely by Gregg, and who also returned to voice Norma in the next two sequels, before the part was recast with Olivia Hussey for a physical appearance in Psycho IV.