Voyeurism
Hitchcock instructed cinematographer John Russell to shoot Psycho using 50 mm lenses, which "give the closest approximation to human vision technically possible. 'He wanted the camera, being the eyes of the audience all the time, to let them [view the action] as if they were seeing it with their own eyes....'" (Rebello 93).
Hitchcock introduces the visual theme of voyeurism from the very first shot of Psycho - he invites the viewer behind the drawn blinds and through the window of Sam and Marion's hotel room. Later, when Norman is watching Marion undress in her cabin at the Bates Motel, Hitchcock uses point-of-view shots to implicate the audience in Norman's spying.
Narratively, the theme of voyeurism in the film indicates that human sexual urges can fester and go sour when suppressed for too long. Marion's desire to stop hiding her relationship with Sam drives her to steal Cassidy's money; Norman's secret yearning for Marion drives his "mother" to kill. By placing the audience in the place of the spy and not the object of his/her gaze, Hitchcock warns his viewer about the dangerous effects of our own hidden desires.
The Destruction of the American Dream
Psycho dismantles a number of tenets that (still) are important to American society. Most prominently, Hitchcock unravels the role of the mother through Norman and Mrs. Bates. Not only does the film imply a past incestuous relationship between mother and son, but Norman's sexual urges are what bring out his "mother" side.
Meanwhile, Marion's crime disrupts many commonly accepted images of American society. First, she steals from her boss, a man who trusts her implicitly with his money and kindly allows her to go home early when she complains of a headache. Later, Marion is so eager to get out of the used car lot that California Charlie, unable to accept Marion's unorthodox behavior, practically begs her to bargain with him. The Bates Motel itself, a failing family business, is a visual symbol of the corruptive power of the American Dream. It is the shell of a livelihood where conventional relationships (like mother and son, or husband and wife) can only exist on the surface, and beneath which lie the rotten reality.
Internal Darkness
Nothing in Psycho is what it seems; everyone has something to hide. Marion and Sam fool around in hotels during her lunch hour, Marion's co-worker, Caroline, has a purse full of tranquilizers, Cassidy doesn't pay taxes, Lowery has a secret stash of liquor, Marion steals and lies, and charming Norman has the most shocking secret of all. "Arbogast sums it up neatly when he says of the Bates Motel: 'This is the first place that looks like it's hiding from the world" (Spoto).
Even as this darkness starts to ooze out onto the surface, Hitchcock's characters are desperate to hide it. As Marion is running away, she lies time and time again to conceal the true nature of her trip; she even trades in her black car for a white one, trying to maintain the image of innocence. At the Bates Motel, when Marion suggests that Norman put his mother in a home, he starts to become angry - but manages to pull "mother" back just in time; he manages to avoid arousing Marion's suspicion. Later, after Marion's murder, Norman works hard to restore the clean, white bathroom before burying all the physical evidence in an endless black swamp. Then, the final shot in the film is of a chain pulling Marion's white car out of the grimy darkness; now, everyone's secrets are out, but the world is no happier for it.
Duality
The theme of duality is an important one in Psycho, most visibly in the form of Norman's bifurcated psyche. Furthermore, Hitchcock frequently uses mirrors to underline the dual nature of all human beings. For example, he places Marion in the frame with her reflection a number of times. She actually looks in the mirror when she's with Sam in the hotel room and at home. However, after she has stolen the money, Marion does not consider her own image, even though she is in front of a mirror in the used car lot bathroom, in the Bates Motel office, and in Cabin 1. This signifies that Marion, in the throes of madness, is unable to take responsibility for her actions or to extricate herself; it takes meeting Norman for her to be able to realize the ramifications of what she's done. By contrast, when Lila is exploring the Bates house, she not only sees her reflection in the mirror, but she is scared of it.
Hitchcock's decision to cast Vera Miles, Janet Leigh, John Gavin, and Norman Bates also emphasizes the idea of duality; the male and female pairs resemble each other closely. Marion and Norman are the versions of Sam and Lila who have succumbed to madness.
Isolation
Throughout Psycho, Hitchcock prefers to isolate his characters in the frame, using mostly alternating close-ups even during close conversations and/or intimate encounters. Raymond Durgnat writes, "the close-up both enlarges (intensifies) and isolates (blots out the rest of the world). While each character is speaking, the spectator sees, feels, becomes him and only him" (Kolker 96).
The most notable example of Hitchcock cross-cutting one-shots is during Marion and Norman's conversation in the parlor of the Bates Motel, in which they are appropriately discussing being stuck in their own private traps. As Marion learns more about Norman's life, Hitchcock increasingly highlights the stuffed birds around him in his one-shots. Like he has done with Mrs. Bates, Norman has treated, maintained, and displayed the birds as if they are still alive. They alone know his secrets, while he will never be able to have a normal relationship with Marion, a living person with whom he strikes up an immediate kinship.
Filial piety
Hitchcock seems to take a great deal of pleasure in subverting the universal value of filial piety, and not just with Norman and Mrs. Bates. In the very first scene, Sam suggests to Marion that once they're alone in her home, they might "turn mother's picture to the wall," thus corrupting the respectable familial scene that Marion has just been describing. Meanwhile, Sam himself is burdened by his father's debt. In Lowery's office, Cassidy speaks of his soon-to-be married daughter as his "baby," boasting about how his money has prevented her from ever suffering. However, Jean Douchet writes of Cassidy's unseen daughter: "she will probably be better without the $40,000 house, which is clearly a symbol of her father's power over her" (Kolker 76).
Ultimately, the parents in Psycho are not nurturers or guides. Rather, they callously exert power over their children and repay their offspring's devotion with pain and suffering.
