Jonathan Caouette and his mother Renee talk to Donald Clarke about breaking all the rules with Tarnation, Caouette's ultra-low-budget, home-made movie about madness

"People see this film and then think that they know me," Jonathan Caouette, the sole progenitor of Tarnation, says. "Which is amazing, because I never thought the film would ever be shown anywhere other than a hole-in-the-wall coffee shop on a video projector. But suddenly all these people think that I am this dark, afflicted, affected person. And I'm not really."

I take his point. Tarnation, a harrowing memoir told through blissfully disorienting multi-media collage, puts a grim tale before us. The tragedies started even before Caouette's birth in 1973. His mother, Renee Leblanc, was, while still a child, subjected to severe electro-shock therapy following a fall from a tree. The doctors were trying to jolt her out of what they believed was psychosomatic paralysis, but, Caouette maintains, merely managed to disturb a functioning brain and condemn Renee, once a cherubic child model, to a lifetime of mental illness.

The film weaves Renee's misfortunes together with her son's. Jonathan was abused by foster parents. He was present when his mother was raped at knife-point. Later, after smoking a PCP-laced joint with one of Renee's boyfriends, he came down with a chronic psychological disorder that still lingers today. And, as if all that weren't enough, he had to face the challenge of growing up gay in, of all places, Texas. "Oh yeah, I don't recommend that to anybody," he laughs. "It's a horrible place. I really don't recommend it to anybody."

Yet, as that response suggests, he seems to have emerged from his traumas with good humour intact. Throughout Tarnation - put together from footage Jonathan has been shooting since the age of 11 - he often comes across as desperate, nervous or troubled. It is a pleasure to relate that the now-lauded director has filled out physically and carries himself with relaxed confidence. Renee, still, sadly, grappling with her condition, is not quite so together.

"I know where I am!" she says. "A beautiful place." "But you're in Belfast," I say, genuinely aghast. (It is, in fact, the closing night of the Belfast Film Festival.) "I know it. I love it. This is the best place we've been so far." Actually, the business of trying to interview Caouette in the packed, cacophonous cafe of the Queen's Film Theatre - dignitaries are brought over to shake his hand, a photographer asks him to pose while he is refilling his coffee, the charming Renee adds puzzling footnotes to arguments concluded minutes earlier - nicely replicates the experience of watching Tarnation. Like the film, our conversation moves forward in disconcerting jolts and surges. I wonder if the rhythms Caouette achieves with his synthesis of pop songs, video diary and contemporaneous TV footage might help us understand the depersonalisation syndrome he was saddled with following that brush with PCP.

("It all just happened to him in five minutes. Like that," Renee, dark hair pulled tightly back, eyes darting behind square-framed sunglasses, says some time later. I think she means the onset of her son's condition.) "It was supposed to be an emulation of my thought processes, but also to match the music I was inspired by," Caouette says. "I would always start with the song. What would evoke this period, this moment? I would then just cut rhythmically to the film." The effect is striking. Using songs by artists such as Glen Campbell, the Red House Painters and the Magnetic Fields as an aural backdrop, Caouette tells his story through striking images and the display of stark blocks of text.

Edited using Apple's iMovie programme, the film could only have emerged in this century, but, nonetheless, owes much to earlier American experimentalists such as Andy Warhol and Kenneth Anger. Yet, for many years, the director did not even know he was making a feature film. He was just doodling with a camera. "I really didn't know I was making a documentary," he confirms. "I was mainly trying to emulate all the horror films I loved." It was James Cameron Mitchell, director of Hedwig and the Angry Inch, who urged Caouette, then a struggling actor in New York, to put some footage together for the city's Experimental Mix film festival. Juiced up on cigarettes and coffee, Jonathan worked flat out for three weeks and eventually produced a cut that lasted two hours and 40 minutes. I would guess that the pressure he was under - not to mention the nicotine and caffeine - probably added to the jumpy energy of that first version.

"Oh, I think so. But you know if somebody hadn't said 'I really think there's a possibility that you are a film-maker', then that might never have happened for me. 'You are a film-maker. Do this!'"

Gus Van Sant, the director of Elephant and Drugstore Cowboy, subsequently came on board as an executive producer and, after cutting the film down to its current, taut 88 minutes, Caouette progressed to the Sundance Film Festival, where he received a 10-minute standing ovation. Much of that goodwill was probably directed towards Renee, who, despite her confusion, emerges as a brave, witty figure.

But is the story entirely reliable? Do we know for certain that the shock therapy caused her psychological decline? "I am definitely sure about that," Caouette says. "And I have to blame my grandparents for that. But shock treatment was very big in the 1960s and 1970s. It was just done casually." When I ask Renee if she has anything to say on the matter she demurs and then, just as Jonathan has begun talking again, blurts out: "It really wasn't fair on me." As is the case whenever she interrupts his flow, he stops and listens patiently, before calmly picking up the threads of his argument again. It is a touching exchange.

In Tarnation, the grandparents come across as well-meaning, but confused. Yet Renee levels some pretty serious accusations against them.

"I feel they had their own idiosyncrasies and they were very prone to the power of suggestion. Particularly in regard to some bad advice a neighbour gave them," Jonathan says.

"They weren't intelligent," Renee says.

"No, they weren't very intelligent. But - and I know Renee won't like me saying this - I don't blame them. They were ignorant. They just didn't know any better."

Some critics have expressed concerns about the way Renee is represented in the film. If, they suggest, Jonathan wants to detail his exposure to punk rock and underground cinema as a youth, then fine. If he wants to tell us about his attempts to stage a musical based on David Lynch's Blue Velvet featuring the songs of Nancy Sinatra, well, that's all right too. But does he have the right to display the symptoms of his mother's condition in such detail? One scene, during which she serenades a pumpkin, does go on for a disturbingly long period of time.

Renee makes it very clear that she loves the film, but one might still argue that we are being invited to laugh at her illness here? "Well, in the context, it looks crazy, but we are actually having a really good time there. But I am trying to show her condition. At first the audience laugh uncomfortably - maybe because they think it is going to be over in a few moments - and then I think it transfixes them. They then begin to think maybe something quite serious is going on."

So he doesn't accept that the scene might be interpreted as exploitative? "This is my world. This is what I grew up with. I have a right to tell my story. I went through a whole lot more I didn't show. Look, exploitation is when somebody comes from outside and uses your life." Then Renee begins muttering - not angry exactly, more exasperated - about the picture's American distributors, Wellspring Films.

"Wellspring sold this film in about 30 territories. They have now sold it in every territory they can," Jonathan says. "I have yet to see any of that money. My mother has yet to see any of that money. We really got screwed here, but the representation I had back then didn't know what they were doing. Every other person I have talked to has said you have been swindled with this. It is an absolute travesty." This, it seems, is what Caouette understands as exploitation.

Wellspring did, however, fork out to get the film in a fit state for theatrical release. By calculating the amount of videotape he ran through over the years, Caouette has come up with an estimated budget of $218 for the initial cut of Tarnation. Sadly, the costs of clearing all the songs and footage in the film proved to be considerable and the final budget ended up being closer to $400,000. (Which, of course, is, in movie terms, still just a handful of bottle-tops.)

"I had about five Nick Drake tracks I couldn't get, because his sister, Gabrielle, who controls the rights, really didn't like the film. But I was able to preserve about 80 per cent of the pop songs and about 30 per cent of the underscore. But I was only able to keep about 20 per cent of the original video clips. The other stuff I had to emulate one way or another - very painstaking. I originally had clips from The Exorcist, and Warners' wanted $20,000 for about three seconds, which is what it costs. So we couldn't get that."

The same people who moaned about the representation of Renee's illness, had issues with those scenes that appear to have been dramatically restaged after the events depicted. This, for many documentary film-makers, is the greatest, most unspeakable of sins. One sequence in particular, where Jonathan hears about his mother's lithium overdose, has very clearly been reconstructed.

"I was watching this Judy Garland documentary on TV the other day and there was this actress who was playing Judy Garland and she was saying 'I ... I ... I ...' when she meant Judy Garland. It is sort of the same principle. But, at that stage, there was a very keen sense of urgency to get that story out there and I had to use anything available to get it out there. There was no way on earth I was going to have the camera on me when I heard that news."

To be fair, Tarnation is such a singular, unclassifiable piece of work it is barely possible - even if it were desirable - to apply the usual moral tenets of documentary film-making. The movie may, indeed, herald the advance of a whole new school of cinema. We have seen low-budget features edited on home computers before and even a few that have utilised domestic computer programmes such as iMovie, but the tone and form of Tarnation have, to a greater extent than those of any previous commercial release, been forcefully defined by these cheap, easy-to-use media. Of course, you could feed your favourite tunes into a professional editing system and then cut home movies to them, but somehow the results are bound to be different - more playful, more idiosyncratic - if you do such an operation at home over booze and fags.

"It is a very pure DIY thing," Caouette agrees. "And it is so cool that it is happening with my film. Eight years ago a friend and I were saying: in three years you will be able to make a movie in your house. And here I am. I think this new medium is going to transform the relationship between film-makers and film. I think there is going to be a renaissance on how films get out there. I hope Tarnation will inspire young film-makers to just get out there and make the fucking film."

Tarnation opens on April, 29th