David Lynch has never been one to make his films easy on the audience, but though his groupies may find it fascinating, “Inland Empire” represents his eccentricity at its very worst. A three-hour practical joke without a punchline, it’s at once maddeningly obscure and infinitely boring—an experimental stream-of-unconsciousness epic that lacks any visual distinction that might relieve the narrative obfuscation.

It’s impossible to say what the movie’s about in any definitive way. Maybe it’s intended as some sort of commentary on the possibility of multiple dimensions of reality, or reincarnation. Or as a portrait of descent into madness. Or as an illustration of the illusory nature of film itself. Or perhaps it’s intended as nothing whatever beyond a smorgasbord of hallucinatory and incongruous images and sounds, tossed together on the basis of whim or a desire to antagonize or amuse. After sitting through it, one’s unlikely to care much what the motivation was.

Basically “Inland Empire” shuffles together a trio of narrative threads. One involves an actress named Nikki (Laura Dern) who wins the lead in a film to be directed by Kingsley (Jeremy Irons); indeed, before receiving word that she’d gotten the part she’d been told she’d do so by a strange visitor to her home, a half-crazed neighbor with an eastern European accent (Grace Zabriskie, in a playing-to-the-rafters cameo). On the first day of rehearsals Nikki and her co-star Devon (Justin Theroux) are informed by the silken, sallow Kingsley and his goofy assistant Freddie (Harry Dean Stanton) that their script has a curious history—it was filmed in part once before, but in the course of shooting the two stars were murdered. This is not a revelation designed to establish much confidence in the performers, but it might excite among viewers that a comprehensible plot might be afoot.

Unfortunately, from this point the film disintegrates, or perhaps deconstructs, into several lines, though they often overlap confusingly. One is the continuation of the making of the picture with Nikki and Devon and, apparently, the stars’ private lives. Another is apparently footage of the movie itself, in which Nikki plays Sue, who’s married to Devon’s Billy. A third consists of scenes in Poland, which perhaps represent the original unfinished version of the story, or the events on which the script is based. It’s often difficult to tell precisely what footage goes with which thread, or how the passages in each actually fit together, but that’s all presumably part of Lynch’s mind games with the audience. So’s another set of scenes, inserted periodically throughout, in which three actors dressed in human-sized rabbit suits (and voiced by Naomi Watts, Scott Coffey and Laura Harring) somberly recite nonsensical lines on a stage (two of them sitting on a sofa and the other ironing), with the dialogue punctuated by a laugh track. What this apparent sitcom parody has to do with anything else in the film is, like so much else going on here, totally unclear.

Dern, who’s onscreen almost constantly in her various guises, works up a dramatic lather over the long haul, but one can’t muster much interest in her gallery of quasi-heroines. Theroux strikes matinee-idol poses as Devon and looks suitably grubby as Billy, but that’s about it. Irons, on the other hand, brings an amusingly oily, smarmy quality to the director, and he plays nicely off Stanton’s inept, needy Freddie. There’s a raft of friends of Lynch in smaller parts—aside from Zabriskie, you can spy Julia Ormond, Diane Ladd, Mary Steenburgen, Natassja Kinski and William H. Macy along the way—but their presence seems just another pointless joke. Usually even in the most opaque Lynch efforts, there are at least striking visuals to compensate for the muddy content. But in the case of “Inland Empire” even that saving grace is lacking. It was shot (by Odd-Geir Saether) on digital video, which results in images that lack clarity and texture.

There’s a single moment in “Inland Empire” that briefly relieves the doldrums, when a group of hookers suddenly break into a song-and-dance routine to “The Locomotion.” But it only lasts about thirty seconds, and the other 10,710 or so are likely to strike you as both bizarre and boring, including another musical routine played along with the closing credits. Those who relish the opportunity for another visit to Lynch’s perverse unconscious will probably soon be producing elaborate explanations about this picture’s profundity, but don’t be misled. It’s an exercise in empty mystification, an endurance test there’s no reason to take.