Key Points:

At the US premiere of David Lynch's Inland Empire, Laura Dern, his leading lady who had spent three years collaborating with the director on the movie, admitted she was still in the dark. "The truth is I didn't know what I was playing, and I still don't," she said candidly. "I look forward to seeing the film to learn more. I know there are several different characters that become one in their own way. And because it was done as a discovery along the way, I, too, was on the journey that David took me on, not knowing where we would turn next."

When we meet some time later, I confess I am also baffled by Lynch's three-hour opus. So what on earth has Lynch made? Hailed as a masterpiece by some, damned as an incoherent mess by others, Inland Empire is, by turns, familiar and alienating, accessible and impenetrable, stimulating and boring.

Apparently drifting back and forth in time, and perhaps even between different levels of consciousness, the film is held together by Dern's emotionally raw portrayal of a subtly delineated collection of women, who may emanate from her own battered wife character or from the mind of a woman seen tearfully watching a snowy television screen in some unnamed Baltic state.

There is a film-within-a-film, an allegedly cursed Polish folk tale, a murder, a surreal sitcom featuring actors dressed as rabbits, and an overlap between "real life" and role-playing. Inland Empire may make sense on some level - but on which level is anyone's guess.

"David's not really interested in clarity," says Dern, with considerable understatement. "He's not waiting for us to get the movie because he doesn't think the cinema is about 'getting it'."

Like one of his film-making inspirations, Federico Fellini, Lynch wants us to engage with his films in a way that allows our "subconscious to work and let something else take over," Dern suggests. "I think he believes - which I've found very rare in film-makers - in the intelligence of an audience, that they're intelligent enough to discover the film and what it means within themselves." In other words, Inland Empire is not just a movie, it is art.

A friend of Lynch, Dern recalls becoming angry when a journalist criticised the 60-year-old for not explaining Inland Empire after it was unveiled at the Venice Film Festival last September.

"I get so protective of David, like an older sister or something, which is so absurd," she says. "I thought, 'Oh my God, aren't we so fed up of the television telling us what we're supposed to feel?' "

The idea that film should do more than just entertain is ingrained in Dern. Born in Los Angeles in 1967, her parents are the actors Bruce Dern and Diane Ladd. At 6, Dern appeared with Burt Reynolds in White Lightning.

When she was 7, she appeared alongside her mother in Martin Scorsese's Alice Doesn't Live Here Any More. "Of course I was going to become an actor, and of course I would work with David Lynch," says Dern. "Who else could I work with? I mean, these were the guys I watched directing actors, so I defined film as that."

Her parents baulked at the idea of her acting, but Ladd eventually relented and enrolled her, aged 10, at the Lee Strasberg Theatre Institute.

Though she starred in Jurassic Park, Dern has generally steered clear of blockbusters, preferring the flawed characters more often found beyond the mainstream. She received plaudits for her performance as a glue-sniffing mum-to-be in Sideways, director Alexander Payne's controversial first feature, Citizen Ruth, and an Oscar nomination for her portrayal of a sweet-natured nymphomaniac in Rambling Rose.

From early on, she says, "I defined acting as risk-taking and playing protagonists who are complicated and dark and who force us as an audience to find empathy for someone intolerable. I don't think I saw a movie until probably in the last decade where nice people got together and had a romance.

"Those movies didn't even exist [when I was growing up]. Modern-day romances were love stories in Midnight Cowboy and Klute.

"Romantic scenes were those two men on the floor of the bank in Dog Day Afternoon who loved each other."

When she was 12, she watched A Clockwork Orange on cable while her father was out. "Never a good idea for a child," she laughs. "I was paralysed. But at the same time I fell in love with movies and where they could take you.

"So those are the people I saw growing up, those are the kinds of characters my parents played, and that's what I wanted to do for a living."

She was a senior in high school when she first worked with Lynch on his cult classic Blue Velvet. She reunited with the director four years later on Wild at Heart. He is the "closest person to me outside my mother that I collaborate with," says Dern.

Inland Empire was born out of mutual trust and respect. Lynch felt she could pull off multiple roles without knowing what the film was about; Dern had confidence in his ability to make it work.

"I don't think anybody else would have done this," says Dern. "I have friends who are actresses who stopped at, 'What do you mean, there's no makeup and hair?' "

Image, fame and celebrity seem of little concern to Dern, but this did not stop her from becoming the focus of tabloid interest when Billy Bob Thornton publicly ditched her for Angelina Jolie.

"I left our home to go and make a movie, and while I was away my boyfriend got married, and I never heard from him again," Dern said at the time.

"It isn't easy to be tabloid fodder," she reflects. "But it's not the invasion that's difficult, it's that you have to read things that hurt you, or be told things about someone you care about hurting you. That stuff sucks."

She has finally found romantic stability with the outspoken singer-songwriter Ben Harper. They married in 2005 and have two children together, Ellery Walker, 5, and Jaya, 2. Dern knows from experience that being the offspring of artists can sometimes be difficult.

The couple are determined to do things differently. "I would be a fool not to learn from previous mistakes by actors who were doing it for the first time," says Dern.

"Having a touring musician father and actress mother, we work diligently at keeping them together as much as possible. But they are gypsies."

There is excitement in her voice when she talks about Harper. "Being with a songwriter has been amazingly inspirational," she says.

"Every single day he sits down and writes. It doesn't matter if he's with our son at a play date, in nature, watching the news, discussing politics, he's examining the state of things. And that's incredible as an actor to be reminded of the wealth of opportunity to learn about human nature every single moment of the day."

Dern has also been busy. As well as Inland Empire she will be seen in Mike White's Year of the Dog, and Tenderness, opposite Russell Crowe.

Given that she and Harper have been outspoken opponents of the war in Iraq, would she like to do something overtly political?

Absolutely, she enthuses.

"My favourite movies as a teenager were political thrillers, politically based everything, films like Network, Three Days of the Condor, All The President's Men, The Candidate, and those were the kinds of films I dreamed of making.

"I would love to make a very specific political film right now about what's going on. And I am outspoken about my opinions.

"Whether we wanted to be before or not, now we have to be, which is why nonconformists like David are so essential."

Who: Laura Dern, muse to David Lynch; Partner to Ben Harper

Born: February 10 1967, Los Angeles

Key roles: Mask (1985), Blue Velvet (1986), Wild at Heart (1990), Rambling Rose (1991), Jurassic Park (1993),

Latest: Inland Empire screening at the Auckland International Film Festival on Wednesday July 25 at 10.15am and 8.30pm