Monday, June 29, 2009 - Posts
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And all along, the secret was right there in the stochastic gradient descent. On Friday, a team called “BellKor’s Pragmatic Chaos” declared itself the winner of the $1 million Netflix Prize, the contest to improve the site’s existing movie recommendations formula by 10 percent. We don’t yet know exactly how the likely winners did it—the winning team is keeping quiet, since other contestants still have a month to beat their entry, according to the contest rules. We do know this: The contest probably wasn’t won thanks to a revolutionary idea about how we form our taste in movies.
While such a concept may still be out there, the Netflix Prize champs appear to have notched a major victory for computer science over psychology. That seems like a safe conclusion based on progress reports team members have published over the years. For a taste, try this sentence: “The values of the parameters are learnt by stochastic gradient descent with weight decay on the Probe data.”
I’m sure BellKor’s final paper will contain some insights into the psychology of taste, so long as you’re willing to ponder the math and computing behind it. A 2008 paper (PDF), for example, outlines how to represent the ebb and flow of a movie’s popularity over time, as well as a model for how an individual’s rating technique evolves. (Cinematch, the model that Netflix uses today, is a simpler formula that correlates lots of data to predict your preferences based on your past ratings.)
As the Times noted over the weekend, the tentative winners are a fusion of four previously independent teams “made up of statisticians, machine learning experts and computer engineers.” The fact that it took the combined powers of four teams to crack the 10 percent ceiling is another telling sign that the Netflix contest won’t produce some elegant, easy-to-parse theory of movie-watching. That shouldn’t diminish the accomplishment. Even if we won’t understand why it works, we should expect real results—that is, smarter recommendations—as soon as the BellKor et al. solution is implemented. The Netflix Prize is a good reminder that the human brain is an extremely powerful computer capable of juggling hundreds of variables, even when it’s thinking about how much it likes Weekend at Bernie’s II.
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If we are what we Google, then Google Hot Trends—an hourly rundown of search terms "that experience sudden surges in popularity"—is the Web's best cultural barometer. Here's a sampling of today's top searches. (Rankings on Hot Trends list current as of 11 a.m.)
No. 8: "Don Cornelius." Google Trends today are full of searches relating to Sunday's BET Awards, which were retooled at the last minute as a Michael Jackson tribute. Soul Train creator Don Cornelius was just one of dozens of black entertainers who honored Jackson. Over the weekend, Cornelius told Time about the first time he saw Jackson perform in the mid-1960s: "He's only 4 ft. tall and you're looking at a small person who can do anything he wanted to do onstage—with his feet or his voice. To get to that level ... you're talking about James Brown as a performer. Michael was like that as a kid."
No. 40: "8 st 1 oz." The results of Michael Jackson's autopsy were released today, and according to reports in the British press he was bald, needle-pricked and "severely emaciated," weighing just "8 st 1 oz." That's short for 8 stone 1 ounce, or about 112 pounds. Metric is the official system for measuring weight in England, but the stone (14 pounds), is commonly used to express body weight.
No. 45: "Lynndie England." The Associated Press has interviewed former Army reservist Lynddie England, the subject of some of the most iconic pictures in the 2004 Abu Ghraib prisoner abuse scandal. Today, England lives in West Virginia, where she's unemployed and spends most of her time in her house for fear of being recognized and harassed. England granted the interview to promote a new biography of her: Tortured: Lynndie England, Abu Ghraib and the Photographs that Shocked the World.
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In 1915, D.W. Griffith, a Kentucky-born director who'd shot the first-ever movie in Hollywood, Calif., released The Birth of a Nation, a 190-minute film that imported old American horrors into a new medium. The movie is an extraordinarily elaborate piece of Ku Klux Klan propaganda, recasting the Civil War in order to blame secession and the ailments of Reconstruction on black people. Despite its heinous content (and because of it), Griffith's production is regarded even today as a cinematic milestone, the first feature-length film ever to use careful montage—crosscuts, jump-cuts, deep focus—to weave a contrapuntal story on the screen.
In a piece just screened at New York's MoMA, Paul D. Miller (nom de guerre: DJ Spooky) "remixes" Griffith's movie to expose the undergirding of its racism and to explore its success as agitprop. Rebirth of a Nation (also recently released on DVD), introduces what Miller calls "DJ as director"—the idea that a film, like a remixed song, can be composed through a director's selective use of source material.
Miller's version plays with the atmospherics of Griffith's reels—inserting "PDM"-initialed title cards in place of Griffith's notorious "DWG" originals, backing scenes with a contemporary soundtrack (ranging from harmonica blues to light techno), and recutting the film to tighten the story and highlight Griffith's devious art. The shot in which Robert E. Lee surrenders to Ulysses S. Grant, for instance—a passing moment in the original—becomes, in Miller's remix, sinister: A roving viewfinder zooms in on the generals' handshake as the tobacco tip of Grant's cigar glows red against the sepia projection, signifying not so much peace as a realignment of white interests.
It's easy to regard Miller's remix as the YouTube sensibility gone conceptual—or more conceptual than usual—in the name of historical justice. Yet it's also an effort to beat Griffith at his own game. The Birth of a Nation was itself a project in historical revision, one that also bore the burnish of a new medium. What surprised me most about Rebirth wasn't the way Miller applied today's technology to the prewar film. It was how little was actually remixed. For all the cosmetic revisions and minor structural changes, the arc of Griffith's story (and the raw force of its propaganda) is left intact, even helped along. In doing so, Miller blurs the line between his artistic choices and those of the original, drawing our attention to Griffith's own DJ-like selectiveness. What was The Birth of a Nation, after all, if not a loathsome remix of the history books?
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