The Full Monty is a cultural artifact. Titanic, almost despite its soggy pretensions and boffo box-office, is a cultural artifact. Most anything Steven Spielberg even looks at transmutes, de facto, into a cultural artefact. Which is to say, films that transcend cinema, video, DVD or what have you - that transcend their very filmness - to enter the public consciousness at an altogether more subliminal level. They are hard to argue: defence is inbuilt.

Alfred Hitchcock made several films that could be so classified, but only one that is literally certifiable. Everyone knows Psycho. It doesn't matter if you've seen it - seeing it, like seeing, say, The Texas Chainsaw Massacre or Natural Born Killers, is really beside the point. It's a trace memory.

Douglas Gordon understood that. That's why the Turner Prize winner was able to create his 1993 installation 24 Hour Psycho. Shown three years later as part of Spellbound at the Hayward, it takes the 1960 classic and projects it at two frames per second instead of the usual 24. Dynamics shift radically as the film stretches to a day in length: shock effects take tens of minutes; the commonplace acquires new tension; dialogue scenes (the film is projected silently) expand to the point of monotony. Hitchcock is redefined. The effect is at once bizarre, tedious and positively hypnotic. Gus Van Sant's remake operates in a similar arena.

The announcement of this Psycho resulted in collective head-scratching. Subsequent rumours - publicity was shunned - that the gay indie wünderkind was not only using Joseph Stefano's original script and Bernard Herrmann's marvellous score (rejigged by Danny Elfman), but was aiming at a shot-for-shot remake, were met with incredulity. And yet here it is. And far from shoddy, money-grabbing grave-robbery, Gus Van Sant's Psycho is as fascinating an artistic endeavour as either that of Gordon or even Hitchcock himself.

Van Sant's picture is not a film about the similarities between the two extant versions but their differences; sneaking a big budget art movie out to a mass audience. It's a game as surely as any Peter Greenaway plays: we are supposed to know. Seeing this new one without benefit of re-viewing the original is to be purposefully perverse. The shocks and jolts come not from the same source as Hitchcock, but from those points that signal that, no, this is not quite the film of collective memory.

Indeed, for a movie that has been so precisely modelled to resemble its forebear, you have to ask why, from time to time, Van Sant makes changes. Why, at the car dealership, does Marion Crane walk in the opposite direction to pick up the newspaper? Why is it not the same exterior of the Bates house, when the interior so clearly is? What is the significance of the two, surreal, split-second visions Arbogast sees as he dies on the stairs? Why were shots of roiling clouds and Marion's eye dilating added to the murder? (Paradoxically, the infamous shower scene is perhaps the most radically altered of any in the film.)

The film is equally intriguing for the ways in which it plays with the big book of thriller convention - much of which, of course, Hitchcock wrote in the first place. Julianne Moore's searching of the house at the end is remarkable. We already understand the dynamics of the sequence - the film has hammered the point sufficiently: she will search upstairs before, eventually, descending into the fruit cellar to confront both Mothers. And yet, despite - even because - of that, Van Sant is able to invest his film with real tension. He is playing our intelligence off against itself. It's very smart, the one time he really becomes Hitchcock, using our own sense against itself.

If anything, this is the real tribute. We cannot but help recall Hitchcock's maxim that dread follows more completely if we already appreciate the outcome - famously, showing the bomb under the table, then allowing the participants to discuss baseball, ignorant of impending doom. Van Sant has made to extend this lore across his entire picture: not only do we understand, we have already seen. He then tosses the occasional curveball and we fumble the catch. For example, the original cellar is now where Norman stuffs his birds, and feels (and looks) more like that in Demme's Silence of The Lambs than the dank original. It's no accident. Likewise, when Norman is given the blanket at the police station, we expect Hannibal Lector not Mother, who "wouldn't hurt a fly." Not doing something is worse that doing anything.

Anne Heche takes the female lead from Janet Leigh and plays much of the picture with a wry smile - the mirror opposite of the terrific, nervy original. Where that Marion was guilt-ridden (as much by sex as her theft), Heche seems untroubled, even joyful. It's a necessary change - a 90s audience would never accept the same restrictions.

And in replicating Perkins' nervous laugh, Vince Vaughn seems now to be laughing with us. His line, on showing Marion her cabin and indicating the bathroom - "And here's the, er..." - assumes the mantle of post-modern joke. If he winked to the camera we wouldn't be surprised. And he does, later. When Moore and Viggo Mortensen (as Marion's sister and lover, respectively) check into the Bates Motel, she winks at him and he winks back. We are all complicit in their game.

Moore is arguably the only one to give anything like a performance. Vaughn and Heche are in no position to do much, while William H. Macy's Arbogast is a note-perfect delight. Perhaps because Lila was so ill-defined the first time around, it's possible for Moore to bring her own baggage. It has been suggested that she is actually a lesbian (her dress, her rebuffs to Sam) which would certainly complicate the film's sexual orthodoxies: Heche is famously Hollywood's most out gay actress; Norman Bates' sexuality always was debatable, especially as played out by the bisexual Perkins; and Mortensen is given the always rather colourless part of Sam to play as a real heterosexual oaf.

Using the original screenplay - simply updated - is inspired. Now you read the film totally differently. Why would her boss just let Marion walk out of the building with that amount of cash ($400,000 in the new one) in her handbag? Why would she stop at an isolated motel where there are no other guests and a proprietor clearly two sandwiches short of a picnic? Even with historical distance, Robert Bloch's original plot looks bizarre to say the least.

The end is odd too. The very last shot. You get Marion's car being dragged from the swamp, but it goes on and on after the original. They drag it, then we watch them tow it away and the authorities leave. It plays under the credits, then the shot is held over the swamp for several seconds. It makes for a disconcerting, oddly troubling climax and emphasises that Australian cinematographer Chris Doyle (who made his name photographing Hong Kong so hypnotically for Wong Kar-Wai) has done much more than simply reshoot in colour.

Gus Van Sant's Psycho, then, is a curious and contradictory beast. For the uninitiated it will serve as an efficient but (given almost 40 years distance) unremarkable suspense thriller. For many the concept will be so deeply flawed from the outset that they will have set their caps against it even before a frame was shot. But for the more open-minded, prepared to invest the patience and understanding Van Sant requires, this new Psycho is one of the eeriest experiences cinema has offered in a while. Whether you accept Van Sant's challenge as farce or gamesmanship, it's tempting to suggest that, while you will undoubtedly see many better films this year, you won't see a more intelligent one.