In an experiment popularized by the book of the same name, volunteers were told to keep track of how many times a basketball was passed between players. While the ball was being tossed, someone in a gorilla suit walked between them in plain view. Very few people noticed the gorilla because they were so focused on counting the passes.

The invisible gorilla study is the most famous example of a phenomenon called “inattention blindness.” When we pay close attention to one thing, we often fail to notice other things – even if they are obvious. The authors of the book modified the original video to reinforce the point. Watch the updated video to see if you notice anything unusual:

If you’re like most people – including me – you didn’t notice the person leaving the game or the background curtains change color. You had inattention blindness.

One thing has always bothered me about the gorilla experiment. Counting basketball passes is not a real-life task and the participants have no training in it. It’s possible they are easily fooled or just lazy. Would the same thing happen to experts?

A recent study from Brigham and Women’s Hospital confirms experts suffer from inattention blindness and raises some uncomfortable questions in the process. The scientists asked experienced radiologists to identify white nodules within five CT scans made up of hundreds of images of lung tissue – a process used to identify potential lung cancer. In one of the scans, the scientists inserted an image of a gorilla almost 50 times the size of a nodule.

Despite its relatively large size and its incongruous presence in the CT scans, only four of the 24 radiologists noticed the gorilla. It’s not that it was difficult to see; eye-tracking data showed clearly that the radiologists looked right at it. And when later told to look for a gorilla, nearly everyone found it.

The scientists repeated the experiment on untrained volunteers and none noticed the gorilla. Not surprisingly, the radiologists were also much better at spotting the warning signs of lung cancer.

The confirmation that expert observers suffer from inattention blindness raises some troubling questions. By training radiologists to identify white nodules, are they more likely to miss other life-threatening anomalies? Could the same issues pertain to other expert observers like MRI technicians, air traffic controllers, and police officers?

By multi-tasking in our day-to-day lives, are we missing more than the Gorilla?