Hearing Pictures For decades, blind movie fans have relied on frame-by-frame audio description. Now, a blind scientist and a band of amateurs are questioning who decides what they see.

The Riviera Hotel & Casino, a vast, chiming monument to air conditioning and untrammeled tattoo artistry, was full of blind people last July. Thirteen hundred or so had come to Las Vegas for the American Council of the Blind’s 53rd annual conference; never had so many dogs roamed so many slot machines. In a small, windowless conference room on a Wednesday morning, though, just a dozen and a half people sat silently listening to a bird chirp.

It was totally a bird. But then came some faint … whirring? Water? Wind? Then … seagull cries? Next came human breathing, followed by grunting and a kind of labored scraping. The circumstances suggested by this recording were becoming hard to conceive. A chicken squawked. A chicken?

If you are blind or have low-vision, or if you’re pretending to be for a two-­minute exercise — most in the conference room were sighted — listening to a movie feels less like entertainment than a protracted aural grope. Or at least it did before audio description, a bland-sounding, life-changing tool that conveys what’s happening onscreen: a dubbed-in voice explaining that Han Solo is reaching for his blaster, or that Orson Welles has furrowed his brow.

Or that a child has found a fallen fledgling on a forest floor. After speculating about the chirping and whirring and grunting, the students of the three-day Audio Description Institute listened to the recording again — this time alongside its narration. The scene was a pivotal one in Majid Majidi’s The Color of Paradise (which happens to be about a blind 8-year-old Iranian boy). Those scraping sounds had come from the protagonist as he struggled to climb a tree. Following the cries of the bird’s siblings, we were told, the child returned it to its nest, and a smile spread across his face.

The exercise was striking, all the more so for occurring in the presence of a master. Joel Snyder is a round man with a booming voice that, if your vision is impaired, you might know intimately. In 1981, the young actor stumbled into the nascent field of audio description — he’d been volunteering with a Washington, D.C., group that was exploring ways to make local stage productions accessible to the blind. What began as an experiment grew into an industry, or at least a sub-industry, appended to Hollywood as well as live performances, museums, national parks, even cruises.

Snyder, meanwhile, grew into a godfather of description — a powerful voice, figuratively and literally, in how millions of Americans absorb a vast sweep of information. “Description is a literary art form,” he told the group. “A kind of poetry.”

If that sounds like a stretch, just watch a movie. Each scene presents an entire world to sift through, parse, and translate. Describers, then, must do the work of actors and also of set designers, choreographers, costumers, and the ominousness of those gathering clouds at the edge of the frame. They must do this without underexplaining or overexplaining or stepping on dialogue, or getting all that right but missing the tone. And no matter what, don’t say “close-up” — jargon, Snyder warned, punctures the suspension of disbelief.

Quick clarification: Blind people watch movies. Lots of them, plus TV and YouTube and all the other garbage and non-garbage we hunker down to each day. For the nation’s 20 million blind and low-vision citizens, these entertainments are just that. They are also a valuable cultural tether. Among adults reporting significant vision loss, less than 38 percent were employed in 2012. Isolation is huge.

Snyder wears his mantle of cultural authority with gusto. He’s a hammy guy (“I’m here all week, ladies and gentlemen”) who turns serious contemplating the impact that he and his colleagues have had. (After recording the first description of Sesame Street, he told the group, his company received a grateful letter from a blind mom who could finally follow along with her sighted child.) Snyder has been hired to describe everything from Mrs. Doubtfire to President Obama’s inaugurations. Along the way, he has helped elevate description to a genre all its own.

The Vegas workshop walked aspiring professionals through technical and philosophical challenges, but Snyder kept returning to the central pillar of his approach: objectivity. Instead of declaring a character furious, mention her clenched fists. A sunset isn’t beautiful, just deep orange. Qualitative judgments have no place, he insisted, and he rapped a table with his pen for emphasis. Later, Snyder told me that if he were God, he wouldn’t allow anyone to describe a movie without first taking his workshop. “I’ve seen blind people just pull their earbuds out,” he said. “I’d rather a film had no description than bad description.”

I pondered that remark. On its face, it reflected the authority of someone who has spent years refining a skill whose execution means a lot to a lot of people. But I also heard a drop of defensiveness. At that very moment, forces were gathering to disrupt Snyder’s carefully crafted fiefdom. Whether he was referring to them or not, I can’t say. That’s the thing about interpreting. It’s tricky sometimes.