Alfred Hitchcock's "Psycho" is the grandaddy of all horror thrillers - the penultimate textbook statement on thrills and suspense. There has never been a greater Master of Suspense, and this is surely Hitch's greatest suspense thriller. Even after 40 years, it has not lost the power to shock or surprise.

"Psycho" changed movie history forever after its release in 1960 - in a sense, the innocence of the 1950's was forever crushed by Hitchcock's atmospheric pull and sinful characters. Here we had Janet Leigh as Marion Crane, the bank clerk who has embezzled 40,000 dollars and leaves the town of Phoenix, Arizona in the hopes of starting a new life with her beau, Sam Loomis (John Gavin). Along the way, she runs into ominous policemen, suspicious used car dealers, and a nice, callow motel owner, Norman Bates (Anthony Perkins) who rents a room to her, and offers a meal ("just sandwiches and milk") in his parlor. We are itching for Marion to get away, but she decides to go back to Phoenix - her "private trap" as she calls it. Her conversation with Norman almost turns awry as she suggests keeping his invalid mother in a home. "In an institution," asks Norman, while in the background we see stuffed birds. We begin to think that Marion will get away the next day, and hope that Norman will not get in the way. She calmly takes a shower, and suddenly a silhouetted figure opens the shower curtain and kills her! A major shock to the senses in one of the infamous montage sequences in film history. This is the section that most people recall when "Psycho" is brought up. It is also the most misunderstood.

The shower sequence occurs barely halfway through "Psycho" and Hitchcock still has a lot of tricks up his sleeve. The trick is that we were following Marion Crane all through the story, assuming all along that the film is about Marion and the money she stole. Hitchcock makes it very subjective, we see this story through her eyes. Credit Janet Leigh for making Marion into one of the most sympathetic, humane female protagonists of all time. It is precisely for this reason why we are so shocked by her murder - a life has been taking away from us and we are left helpless like those stuffed birds in Norman's parlor. It is not a matter of punishment considering that Mother does not kill Marion for her money - we, the audience, only see it as punishment. Suddenly, the subjectivity shifts to poor Norman Bates since we assume that his mother killed Marion because he was attracted to her, and perhaps wanted her sexually.

This is the second act of the film, now focusing on Norman and Marion's tempermental sister, Lila Crane (Vera Miles). She comes to Sam Loomis asking where Marion might be, and there is also a private investigator, Arbogast (Martin Balsam), making inquiries. Arbogast eventually discovers that Marion (having used her alias Marie Samuels) had stayed at the Bates Motel. This sets up a brilliantly tense and comical scene where Arbogast asks Norman questions, realizing Norman is lying about the situation, and is curious about his mother sitting in the upstairs window of the house next door.

"Psycho" has one clever sequence after another, building its tension through surprises and mounting suspense. Who is Mother anyway? How come she has to be carried out of the house by Norman yet somehow moves at lightning speed when she attacks with the kitchen knife? The secret to the tension is in how Hitch switches from subjectivity to objectivity. For example, the Arbogast murder starst subjectively as he walks up to the house and enters through the front door - every shot is seen from his point-of-view. Then he walks up the stairs, and Hitchcock cuts to a shot of a door opening. Who is it? Could it be Mother? We are aware someone is up there but Arbogast does not know, thus the tension builds with acute dexterity. Low-angle shots to a high-angle shot of Mother steadfastly attacking Arbogast.

Subjectivity has always been Hitchcock's secret to suspense and unparalleled tension, and never before did it make such an impression as in "Psycho." It is a film that changed our perceptions of what a film could be, and it sired a genre rooted in gratuitous gore and cheap shocks - the slasher genre. The countless rip-offs and remakes never did any justice to "Psycho," with the exception of the cleverly Hitchcockian suspense thriller, "The Stepfather," and Scorsese's lone thriller, "Cape Fear." In terms of slasher fare, there is John Carpenter's influential "Halloween," which borrows from Hitch freely as well as Brian De Palma's early thrillers.

What most slasher films forget is that Hitchcock never intended on featuring the sole two murders in "Psycho" without any rhyme or reason - his sole purpose was not just to shock or titillate. The justification comes from the screenplay by Joseph Stephano, who wisely spent time investing humanity and dimension in these characters. Most of today's thrillers or slasher films spend an inordinate amount of time lopping off characters whom we could care less about - witness the execrable "I Know What You Did Last Summer." The latter cared more about the killing methods than about the thin characters.

"Psycho" is nearly a perfect thriller, though the ending where a psychiatrist (Simon Oakland) explains Norman's condition is still trite and unnecessary - sometimes nobody can acutely pinpoint a murderer's motives. But then Hitchcock has a brilliant finish where Norman is in his cell and we hear Mother in a voice-over spreading a sense of optimism about her confinement - "Why she would never harm a fly!" says Norman. The final shot is a superimposition of Mother's skull over Norman's smiling face while there is yet another superimposition of a car being drained from a swamp containing Marion's body.

"Psycho" is dated in certain respects, but it retains the potency it has in its thrills and excitement. A visceral experience like no other, it shows Hitchcock at the height of his powers. The late Anthony Perkins might have become miscast, but his empathetic, almost too human look at Norman Bates will always enthrall precisely because he does not seem so evil. "Psycho" will never be forgotten, and stands as the standard thriller by which all others thrillers have and will be measured.