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Why 83 Percent of Expert Radiologists Failed to See the Giant Dancing Gorilla in this CT Scan

Update Date: Feb 13, 2013 01:37 PM EST

Look at the scan above. Is there anything odd about this picture?

If you didn't see the gorilla dancing in the upper right hand corner, don't worry. In fact, researchers from Brigham and Women's Hospital found that 83 percent of radiologists trained to look at the scan above failed to spot the dancing gorilla even after closely examining the scan four times on average.

The latest study, expected to be published in the journal Psychological Science, involved 24 credentialed radiologists. Researchers said that nine of the radiologists were from Brigham and Women's Hospital and the other 15 were considered expert examiners at the American Board of Radiology.

Researchers asked the radiologists to look at lung CT scans from five different patients. Each of the five scans contained on average 10 nodules of abnormalities.

The first four patient CT scans did not show the dancing gorilla, which was 48 times larger than the average nodule, but the CT images from the fifth patient showed five consecutive scans showing the dancing gorilla. Researchers said that the CT scan gorilla was 50 percent transparent in the first scan, 75 percent visible in the second scan, fully visible in the third scan before fading back to 50 percent in the last two scans. The radiologists were asked to click on anything strange on the scans.

As a comparison, researchers tested the same scans on 25 participants who had no medical training. The regular participants were asked to practice for 10 minutes on how to look for nodules before they looked at the scans.

Researchers found that the radiologists were able to find the correct nodules 55 percent of the time, but only four of the 24 expert radiologists were able to see the gorilla. None of the participants in the control group with no previous medical training were able to see the gorilla. They were also only able to spot the nodules 12 percent of the time.

Researchers also used eye-tracking technology to see where all the participants had been looking and if their eyes passed over the gorilla on the CT scan.

"The majority of them looked directly at the gorilla for extended periods of time. They just don't see it," researcher Trafton Drew said, according to the Daily Mail.

The latest research was inspired by the "invisible gorilla" experiment from 1999, where researchers asked participants watching a video showing people passing a basketball to count the number of passes made by people wearing white.

Halfway through the video clip, a person wearing a gorilla suit walks past the basketball players and dose a dance. Researchers found that half of the participants watching the video did not see the gorilla until it was pointed out them the second time around.

Researchers explained that most people failed to see the gorilla in the video because of "inattentional blindness". In this case, they were so focused on counting the passes that they failed to process other superfluous information like the dancing gorilla.

According to Smithsonian Magazine, out brains only show us a specific part of what our eyes see if we are focused on certain tasks, therefore sometimes we fail to notice strange and unusual things right in front of us.

In the latest study, "inattentional blindness" also played a role because the radiologists were significantly better at identifying the nodules compared to the control group. However, they missed the giant dancing gorilla because they were focusing on looking for cancer in the CT scans.

Drew told CBS News that the "larger point" of the new study is that even "expert searchers" fail to see things if they are not looking for them.

"Radiologists are amazingly good at finding cancer, but that does not mean that they see everything. One reason that they are so good at detecting cancer might be that they are really tightly focusing their attention on the task at hand," he explained. "The consequence of focusing your attention really tightly is that you may be prone to missing things which may be pretty obvious in retrospect."

While the findings are certainly chilling, given that an overwhelming majority of radiologists failed to see a giant dancing gorilla that was 48 times the size of an average nodule in the CT scans, researchers say that patients could help doctors and health professionals by letting them know what exactly is ailing them to prevent mistakes caused by inattentional blindness.

Try Out the "Selective Attention Test" 

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