Radiologists fail miserably on the "Invisible Gorilla Test" when screening for cancer

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Notice anything weird about this lung scan? If you look carefully you'll notice there's A FREAKIN' GORILLA SHAKING HIS FIST in the top right-hand corner! The scan is a play on the famous invisible gorilla experiment, where the most blatantly obvious of things — including those in plain sight — are simply ignored when our attention is directed elsewhere. And as this new study suggests, even radiologists — when screening for life-threatening cancerous nodules on lung scans— aren't immune to this phenomenon.

For those unfamiliar with the Invisible Gorilla Test, it goes like this: Participants are asked to watch a game in which members of two teams pass the ball to one another. The point, so they're told, is to count how many times the ball changes hands. But while the test is happening, a man wearing a gorilla suit walks in front of the camera, beats his chest, and then walks off.

What's astounding about this experiment is that 50% of participants fail to see the gorilla (I have to admit, I was one of them). It's crazy because when you watch the video knowing that the gorilla is going to show up, it's impossible to miss. The experiment reveals the power of our attention and how it overrides superflous detail — what's called "innattentional blindness."


But as the new study by Trafton Drew has revealed, sometimes these "superflous" details can be critical. Alix Spiegel from NPR explains:

Drew wondered if somehow being so well-trained in searching would make them immune to missing large, hairy gorillas. "You might expect that because they're experts, they would notice if something unusual was there," he says.

He took a picture of a man in a gorilla suit shaking his fist, and he superimposed that image on a series of slides that radiologists typically look at when they're searching for cancer. He then asked a bunch of radiologists to review the slides of lungs for cancerous nodules. He wanted to see if they would notice a gorilla the size of a matchbook glaring angrily at them from inside the slide.

But they didn't: 83 percent of the radiologists missed it, Drew says.

This wasn't because the eyes of the radiologists didn't happen to fall on the large, angry gorilla. Instead, the problem was in the way their brains had framed what they were doing. They were looking for cancer nodules, not gorillas, so "they look right at it, but because they're not looking for a gorilla, they don't see that it's a gorilla."

In other words, what we're thinking about — what we're focused on — filters the world around us so aggressively that it literally shapes what we see. So, Drew says, we need to think carefully about the instructions we give to professional searchers like radiologists or people looking for terrorist activity, because what we tell them to look for will in part determine what they see and don't see.


Moving forward, Drew hopes to develop techniques that will help radiologists see — both visually and cognitively — the things that hide in plain sight.

More at NPR.

Image: Trafton Drew and Jeremy Wolfe.