Radiologists struggle to ID gorilla on a CT lung scan

"You couldn't see a dancing gorilla if it was right in front of you."

What might be a way of sarcastically questioning someone's eyesight apparently turns out to be true when it comes to most radiologists. At least, that's what an upcoming study in Psychological Science has determined.

In that study researchers, led by Harvard University post-doctoral fellow Trafton Drew, tested 24 credentialed radiologists by asking them to look at five lung CT scans, each of which had about 10 nodules or abnormalities. For each scan, the radiologists were asked to click on anything strange. On the last scan, a dancing gorilla roughly 48 times the typical size of a nodule was placed in the upper right quadrant. 

The radiologists were able to find the correct nodules 55 percent of the time, but 20 out of the 24 said they were unable to see the gorilla, even though they scrolled past it 4.3 times on average. The researchers found that the radiologists spent 5.8 seconds looking at the scan with the gorilla, and, through the use of eye-tracking, determined that half of the radiologists actually looked directly at the gorilla.

The researchers also tested the scans on a group of 25 subjects with no medical background, who were each given 10 minutes of training on how to identify nodules. None of the non-radiologist subjects saw the gorilla, either. In addition, they were able to identify only 12 percent of the nodules.

In order to determine how easy it was to spot the gorilla if its presence was known, the researchers tested another 12 non-medical subjects by asking them specifically if they could spot the gorilla. Eighty-eight percent saw the gorilla even thought they were given less time to look at the scans.

Radiologists are "in a different world when it comes to finding this very, very hard-to-find thing" like a nodule," Drew said in an interview with National Public Radio.

The radiologists, Drew said, were so intent on looking for cancer nodules, and not gorillas, that what they were focusing on so aggressively shaped what they saw--a phenomenon known as inattentional blindness.

"They look right at [the gorilla], but because they're not looking for a gorilla, they don't see that it's a gorilla," he said.

"The larger point of the paper is that even these expert searchers miss things if they are not looking for them," Drew told CBS News. "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.

"The consequence of focusing your attention really tightly is that you may be prone to missing things which may be pretty obvious in retrospect."

To learn more:
- here's the study
- read the interview on NPR
- see the CBS News article


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