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Author's profile photo Jonathan Becher

The Invisible Gorilla Effect

Remember the invisible gorilla video?

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 phenomenom called “inattentional 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 inattentional 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 inattentional 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 inattentional 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?

That’s one scary gorilla.

Follow me on Twitter: @jbecher

This blog was originally posted on Manage By Walking Around on February 10, 2013.

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      Author's profile photo Tim Clark
      Tim Clark

      Ok, that was weird, funny - and as you point out - kind of scary. I too failed with flying colors.

      Author's profile photo Tom Van Doorslaer
      Tom Van Doorslaer

      I guess this doesn't really come as a surprise. The idea of focussing on one task, is exactly to block everything else out, and look for patterns related to that one task.

      If the doctors would not be looking for nodules, but would be looking for anomalies in general, anything out of the ordinary, then I bet that they would notice the gorilla. (although I haven't tested that)

      If you're reading a book, you hardly notice the music in the background. When your kids are watching tv, how many times do you have to call "dinner is ready" before they notice (unless they're very hungry --> focused on food)?

      But the more general the task is, the harder it gets, because you can't focus on a single pattern anymore.

      Author's profile photo Tom Cenens
      Tom Cenens

      Hi Jonathan

      Nice writing. I actually know this very well 🙂 . I can get really focused on things which blocks me out from whatever is happening around me. Especially when I sit behind a computer 😎 .

      Is it scary? I don't think so. Things happen, we are all human in the end so neither of both options  "~too focused" vs "~not focused enough" can rule out human error.

      Best regards


      Author's profile photo Jonathan Becher
      Jonathan Becher
      Blog Post Author

      Hi Tom.

      The part I thought was scary was that training experts in doing one specific thing might get in the way of doing the job they should be doing. For example, looking for white nodules might miss other abnormalities.

      Author's profile photo Tom Cenens
      Tom Cenens

      Hi Jonathan

      I've been thinking about this yesterday when I was driving home 🙂 . This explains why inclusion & diversity are important. Or why the SAP Mentor program works, people come in with a different background, specialities & perspectives and they see / notice other things 😎 .

      Looking at tv shows on medical issues it shows very well how doctors can miss something and either direct people to other doctors or they go back to check historical data to see what they have missed. They miss especially when the disease is rare because symptoms are often written off as X or Y because that's what they have learned / seen before. It seems to be pretty common and in that sense I can understand that it can indeed be scary when you think it through 🙂 .

      Best regards


      Author's profile photo Derek Klobucher
      Derek Klobucher

      Very cool topic, Jonathan. I hadn't heard of invisible gorilla studies, but this video would only be the tip of an iceberg, I imagine.

      What if we'd been tracking the girls wearing black shirts? I suspect more people would have noticed the player walking off screen, as well as the similarly-colored benign gorilla.

      And what if the gorilla hadn't been so amiable? Or the curtain had changed colors more wildly -- or fallen?

      This seems to be as much about management setting proper parameters as it is about workers following instructions.

      Though I admit that the thought of radiologists missing the gorilla is kind of scary.


      Author's profile photo Tim Clark
      Tim Clark

      I think this discussion dovetails nicely into another taking place here on Business Trends:

      Does Analytics Make Us Smart or Stupid?

      Author's profile photo Iris Nagel-Martin
      Iris Nagel-Martin

      Thanks for sharing this interesting video. Do you know that this video is very often used in research for psychological disorders?

      They use it to test people with ADHD? Almost 100% of people who suffer from ADHD are able to recognise the gorilla, the color change, the leaving person. So appearently these people have ad different perception - sht that could be interesting for potential employers.