The picture above is an X-ray computed tomography (CT) scan of a human lung. Go ahead and take a few seconds to look at it carefully.

How long did it take you to spot the gorilla?

The image takes a starring role in a fun study in press at Psychological Science. Trafton Drew and colleagues at the Brigham and Women’s Hospital showed that when people focus on searching these images for bright white cancer nodules, they never notice the gorilla. More shocking, radiologists — who are trained to read CT scans — usually miss it, too.

“It’s a vivid example that looking at something and seeing it are different,” says Drew, a postdoctoral fellow in Jeremy Wolf’s lab. “You can put your eyes on