Invisible Gorillas in Medicine

You may be familiar with the Invisible Gorilla phenomenon, a case for “inattentional blindness” when we are focusing on something intently and miss something else entirely. The most famous version is this video in which the narrator asks the viewer to count the number of basketball passes made, while a gorilla walks by in the background…

Now, a new study from psychological scientists at Brigham and Women’s Hospital in Boston showed that 83 percent of radiologists failed to spot the animal in a CT scan, even though they went past it four times on average:

Three psychological scientists at Brigham and Women’s Hospital in Boston—Trafton Drew, Melissa Vo and Jeremy Wolfe—wondered if expert observers are also subject to this perceptual blindness. The subjects in the classic study were “naïve”—untrained in any particular domain of expertise and performing a task nobody does in real life. But what about highly trained professionals who make their living doing specialized kinds of observations? The scientists set out to explore this, and in an area of great importance to many people—cancer diagnosis.

Radiologists are physicians with special advanced training in reading various pictures of the body—not just the one-shot X-rays of the past but complex MRI, CT and PET scans as well. In looking for signs of lung cancer, for example, radiologists examine hundreds of ultra-thin CT images of a single patient’s lungs, looking for tiny white nodules that warn of cancer. It’s these expert observers that the Brigham and Women’s scientists chose to study.

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 ten nodules 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 miniscule, 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. It faded in and out—becoming more, then less opaque—over a sequence of five images.  There was no mistaking the gorilla: If someone pointed it out on the lung scan and asked, What is that? – everyone would answer: That’s a gorilla.

The gorilla seems hard to miss (photo here).  I think the idea behind this experiment was to determine whether being highly trained made people less susceptible to the phenomenon of change blindness. Doesn’t seem to be the case based on the results of this study.