Jane's worsening migraine headaches over several months brought her to the doctor's office.

The moment the medical student walked into the examination room, she noticed Jane had a large, black and brown irregular spot the size of a half-dollar on her arm just above the wrist. The student was quick to consider the skin cancer.

Why hadn't she come in sooner, wondered the student, particularly given the large and rapidly expanding size of the mole? The student guessed Jane must have looked at the mole a dozen times every day.

One explanation for Jane's lack of action to seek advice about the spot might be denial – a powerful and often dangerous method of dealing with fear.

Another explanation might be what has been called "inattentional blindness" – we don't see things that we are not expecting.

A recent example of inattentional blindness involved a study of 24 expert radiologists – physician experts trained at reading imaging studies such as X-rays, CT scans, MRIs.

Each radiologist was asked to look at five lung CT scans, each of which had multiple areas of lung cancer. The radiologists were told to use a mouse and click on every area of the CT scan where cancer was visible.

Researchers modified the fifth CT and inserted a picture into the CT scan of what they thought was a very obvious gorilla that was nearly 50 times larger than any of the cancer nodules.

After they finished reading the CT scans, the radiologists were asked if they noticed anything different about the fifth X-ray. If they responded no, they were then asked point-blank: "Did you see a gorilla?"

Twenty of the 24 did not see the gorilla when reading the CTs. Of course, they all saw the gorilla immediately when ask to look for it a second time.

These were not bad radiologists, but 83 percent of them missed a large abnormality on the CT scan. The study shows that when we are paying attention to one thing we often fail to notice other very obvious things happening at the same time.

In this case the radiologists were looking for lung cancer so they ignored everything else – even a dancing gorilla that any 5-year-old would easily spot.

But this is more than just interesting social science. It can have significant implications as it did for Jane, who ended up with serious skin cancer.

Most of us can think of examples in our own everyday lives when we fail to see the obvious because our attention is focused on details. This is particularly true with a failure to notice other people's emotions and well-being. It may be wise to force ourselves to regularly take a step back and consider the big picture and those we touch.

The goal would be to make sure we aren't missing anything important before we return again to focus on details that seem so important to us at the time.

Michael Wilkes, M.D., is a professor of medicine at the University of California, Davis. Identifying characteristics of patients mentioned in his column are changed to protect their confidentiality. Reach him at drwilkes@sacbee.com.

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