83% Of Radiologists Didn't Spot The Gorilla Hiding In This CT Scan

You've almost certainly seen the dancing gorilla video, which demonstrates the theory of change blindness — a phenomenon which means we don't see changes we're not expecting. Now, an updated experiment shows that the same may be true of radiologists analysing CT images.

A team of psychological scientists from Brigham and Women's Hospital in Boston wanted to work out if the previous dancing gorilla experiment only worked because test subjects were naive, untrained and thus less aware. So they thought they would see if radiologists — the physicians who analyse medical images like MRIs, X-rays and CT scans — would fall for a similar trick. The Association for Psychological Science explains:

They recruited 24 experienced and credentialed radiologists-and a comparable group of naïve volunteers. They tracked their eye movements as they examined five patients' CT scans, each made up of hundreds of images of lung tissue. Each case had about 10 nodules [minuscule signs of lung cancer] hiding somewhere in the scans, and the radiologists were instructed to click on these nodules with a mouse. On the final case, the scientists inserted a tiny image of a gorilla (an homage to the original work) into the lung. They wanted to see if the radiologists, focused on the telltale nodules, would be blind to the easily detectable and highly anomalous gorilla... The gorilla was minuscule, but huge compared to the nodules. It was about the size of a box of matches-or 48 times the size of a typical nodule.

After they were done scrolling through the images as much as they wanted, the scientists asked them: Did that last trial seem any different? Did you notice anything unusual on the final trial? And finally: Did you see a gorilla on the final trial? 20 of the 24 radiologists failed to see the gorilla, despite scrolling past it more than four times on average. And this was not because it was difficult to see: When shown the image again after the experiment, all of them saw the gorilla. What's more, the eye-tracking data showed clearly that most of those who did not see the gorilla did in fact look right at it.

What can we learn from the experiment? Well, the point isn't to admonish radiologists. Rather, the test was designed to investigate whether being highly trained made people less susceptible to the phenomenon of change blindness. Clearly, it doesn't.

It is, however, hard to get round the fact that 83 per cent of highly trained physicians missed what could have been a life-threatening anomaly. If that had been a tumour, not a gorilla, it may never have been spotted — and that's certainly something worth worrying about. [Psychological Science]

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Comments

    If that had been a tumour, not a gorilla, it may never have been spotted — and that’s certainly something worth worrying about.

    But wasn't the point to see if they could spot something they weren't expecting? Presumably radiologists are used to looking for and spotting cancer.

    I wonder how many nodules they spotted...

      I'm going to bet they spotted all of them, but only because they knew exactly what they were looking for and how about how many on each slide. Given random slides that might or might not have something unspecified wrong with them, they might miss a lot more.

    "It is, however, hard to get round the fact that 83 per cent of highly trained physicians missed what could have been a life-threatening anomaly."

    When Gorilla in the Lung would certainly be a life threatening condition. When it becomes widespread, or some risk factors are identified I'll start to worry.

    Researcher here:

    "...hard to get round the fact that 83 per cent of highly trained physicians missed what could have been a life-threatening anomaly. If that had been a tumour, not a gorilla, it may never have been spotted — and that’s certainly something worth worrying about."

    Is a profound misinterpretation of the research. They missed the gorilla BECAUSE they've trained themselves to focus ONLY on life threatening anomalies. The fact is, the gorilla is just an irrelevant distraction, so its actually better if they don't pay it any attention - which uses up other cognitive resources.

      My post below was meant to be a reply to this. :p

      How do I internets?

        Yeah - we're actually on the same wave-length really. In my field what your describing is selective attention. You'd pay attention to the gorilla if it was relevant to the task.

    I want to see a similar experiment done on top detectives. grab the top guys (or girls) from the FBI, Scotland Yard, Interpol, doesn't matter where, and give them the same test. I want to see if people who are trained to notice every detail, do in fact, notice every detail.

    Doctor here:

    This test in no way represents a real life scenario. A CT scan is an investigation that must be analysed and interpreted within the context of the patient's history and physical exam just like any other test. From what I can see in this article and in the link, it looks like the subjects were just given scans to look at and told to click on the nodules. So they just looked for nodules.

    If they had been given the story, "This man came into hospital after his child put a hand grenade in his toy box," I bet they'd have found the foreign body.

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