Alfred Hitchcock, arguably the most influential director of all time, used many recurring themes in his films. Staircases, birds, trains, sexuality, brandy, the perfect murder, and tennis are just some of the motifs and symbols explored by the master of suspense. Hitchcock was fond of using plot techniques which at the time were revolutionary but since have become commonplace in films, such as the wrong man or innocent man being placed in a dangerous situation (e.g. The Wrong Man, Strangers on a Train, North by Northwest) or the use of a MacGuffin, a technique popularized by this Hitchcock and found in many of his films (e.g. Vertigo, Notorious, The Man Who Knew Too Much).
The domineering mother figure presents itself in such Hitchcock films as Notorious, Strangers on a Train, North by Northwest, Rope, Marnie, The Birds, and Shadow of a Doubt. Many of his most famous films, these movies all contain some form of mother figure that control their sons. In Notorious, the character of Sebastian’s mother is stronger of the two, the one who pushes for him to poison Alicia because of her intentions. This was the first of Hitchcock’s films in which the aggressive mother figure was addressed head-on.
Psycho has been analysed by modern Freudian psychologists, saying that the Bates mansion is symbolic of the three levels of the psyche, the superego, ego and the id. This would explain the deeply rooted connection between Norman and his mother. In the Freudian sense, Hitchcock’s characters also occasionally blend sexuality and motherhood in a disturbing take on the Oedipus complex. Hitchcock famously explored many levels of insanity through his sociopathic characters, and many aspects of psychology can be found in his films.
Sources:
http://neurophilosophy.wordpress.com/2006/10/17/the-psychology-of-alfred-hitchcock/
http://en.wikipedia.org/wiki/Themes_and_plot_devices_in_the_films_of_Alfred_Hitchcock