Inattentional blindness or "What's that gorilla doing there?"

There has been much media attention recently on the fact that radiologists are unable to spot gorillas. For most people, the first encounter with this gorilla will have been the "passing the ball" video which demonstrates a study by Daniel Simons and Christopher Chabris in 1999 at Harvard University. This video shows the limits of human attention.

All of us will have experienced inattentional blindness in our everyday lives, perhaps while driving a car or watching TV. Things which are occurring within our field of vision (and therefore are being picked up by the retina) are being ignored in preference to something else.

What does the study about radiologists add to our understanding about this phenomenon? 83% of radiologists failed to detect an image of a dancing gorilla on a CT scan when they were asked to look for nodules. 100% of untrained observers failed to spot the gorilla. The authors admit that if the radiologists had been told to look for something unusual then they would probably have spotted more gorillas. What the study doesn't tell us is the difference between those radiologists who did or did not spot the gorillas. Did those who spotted the gorillas spot fewer lung nodules because they were less focused on their primary task?

In terms of clinical practice and understanding of human factors, the study adds to the evidence that if you are focused on one task you cannot also focus on something else. This would suggest that a team leader does not get involved in a task. It also suggests that one should be precise when asking someone else to perform a task. For example if you ask someone to keep an eye on a patient's saturations then don't be surprised if they fail to pick up the ectopics on the ECG... you didn't ask them to look at the ECG trace.

Inattentional blindness is a side-effect of our amazing ability to focus on something and stay focused on it. The best defences against are to be aware of its existence and to have another background mental process running which is asking you whether there is something else you are missing while you are focusing on a given task.