In any case, it's not clear to me why one depth cue might be deemed artificial and unnecessary, while others are just fine. After all, a regular old 2-D movie carries its own set of visual guidelines for understanding spatial relationships. Objects in the foreground block our vision of what's behind them. Shading and texture tell us about the three-dimensional shape of an object on the screen. Ebert would certainly agree that you don't need to watch the famous sequence from Dial M for Murder in its original 3-D to understand that Anthony Dawson is creeping up behind Grace Kelly, and that he's going to lift a stocking over her head to strangle her. Yet he's apoplectic over the thought of adding one more depth cue into the mix.
With 3-D cinema, we still have occlusion and shading and texture—and we're still missing motion parallax—but now we get the added benefit of binocular disparity. We don't need that extra information to see that Grace Kelly's killer is lurking behind her, but it adds, at the very least, clarity and precision to the scene. Exactly what part of that is "artificial"? As it happens, the 3-D version of Dial M also gives us something more: When Kelly falls across the desk, her hand reaches through the stereo window, as if imploring the audience for help. It doesn't make us jump out of the way like Ebert's Homo habilis. It draws us into the action.
Which brings me to Ebert's latest post, the one described as his final word on "why 3-D doesn't work and never will." To support this claim, he prints a letter from Walter Murch, a decorated film editor and sound designer most notable in this context for sharing Ebert's curmudgeonly disregard for stereo cinema. Like Ebert, Murch complains that 3-D is too dark, and then adds that it's too "small" on the screen. (I think he's referring to the medium's "puppet-theater effect," which tends to make everything and everyone appear shrunken down to the size of dolls.) These problems could be solved, he concedes, but "the biggest problem with 3-D … is the 'convergence/focus issue.' " A stereo film forces the viewers to hold their focus at one plane of depth, even while their eyeballs rotate inwards and outwards to follow the action. "It is like tapping your head and rubbing your stomach at the same time," he goes on. "And 600 million years of evolution has never presented this problem before." (Again with the cavemen …)
This is a reasonable point, and it may represent a real challenge for 3-D filmmakers. I've given my own accounting in Slate: In "The Problem With 3-D," I wondered if the unnatural eye movements provoked by stereo cinema might be the source of the bleary eyes, headache, and nausea that sometimes affect 3-D viewers. This wasn't an original idea, of course—the same concern had been laid out in the Atlantic (to pick just one instance) in 1953, not long after Ebert's dad took him to see Bwana Devil. All these years later, we still don't know whether the "convergence/focus issue" causes 3-D headaches, or if they arise from some other aspect of the experience. Either way, I proposed, the problem of visual discomfort would doom the new batch of digital 3-D films to the same fate as their analog forebears: The bubble will pop.
Thing is, I've changed my mind since I wrote that piece nearly two years ago. Or maybe 3-D movies changed my brain: After watching 10 or 20 of these films since then, I've grown accustomed to the ocular aerobics, and the same format that gave me splitting headaches back in 2009 hardly bothers me now. Meanwhile, certain technical innovations, especially in animated 3-D, have begun to eliminate some of the medium's most egregious visual quirks. And while, like Murch, I'm still distracted by the puppet-theater effect in live-action 3-D, that "problem," too, may diminish as we all get used to it.
If I'm right that it takes multiple viewings to understand and appreciate three-dimensional cinema, you might think Roger Ebert would eventually come around. But even before he'd decided the case was closed, Ebert seems to have sworn off any real engagement with the medium. Armed with his evolutionary theory of film, he's content to sit back and hurl the occasional spear of his own. A recent review of The Green Hornet contained only this note at the very bottom: "Yes, it was in 3-D. The more I see of the process, the more I think of it as a way to charge extra for a dim picture." And while he does commend the effect from time to time—it's "useful" in Tron: Legacy and "quite acceptable" in Megamind—he's rarely willing to acknowledge that 3-D might have anything substantive to offer on its own terms, that maybe it's not only a marketing gimmick (it is that, to be sure), but a new kind of filmmaking that brings along both limitations and opportunities.
Take Toy Story 3: I've gone on record with my admiration for the scene at Daisy's window, where Lotso finds he's been replaced by another toy. There's no sight gag there, no objects hurtling off the screen; instead, the image contorts visual space into a crisscrossing, emotional depth. If the scene were flat, Lotso and Daisy would be right next to each other on the screen; in 3-D, they're spread across a lonely chasm, separated by rain-streaked glass. Is this a fluke, or a sign of what three-dimensional cinema could be? Ebert's not interested. He sums up Pixar's innovative use of stereo with a one-line postscript to his review: "Just don't get me started about the 3-D." Don't get him started; the case is closed. Maybe that's for the best.