Recent 'tongue in cheek' research which has been reported in a Washington Post blog recently has caused a lot of questions to be raised concerning inattention blindness, which could cause concern unless you understand the underlying psychology.
Here's a CT scan:
During psychology lectures at Med School, you may have encountered the basketball bouncing students in front of a bank of elevators where you were asked to count the number of passes the basketball made from the player wearing the white T shirt, while a gorilla ran between the students. (Even if you did watch it before, you can re-watch the video on the Washington Post blog).
The recent study asked radiologists to identify and count how many nodules are present in the lungs on a regular CT thorax. If you look at the image you may see a gorilla waving his arms about. As a radiologist, I see the anatomy in the background, the chambers of the heart and mediastinum, but nothing there out of the ordinary.
As radiologists, we are looking for pathology, but also report pathological findings that are unexpected. The clinical history of a patient is very important for us in interpretation of imaging examinations, as we need to answer the question you are asking, but have to be careful we do not miss anything else of serious import. As we do not see any other pathology, we would not expect to find a gorilla in the chest, so our brains can pass over distracting findings.
The other psychological issue is the satisfaction of search, where we can see the expected pathology, but may miss the other cancer if we do not carefully and systematically look through the images.
So the main thing to learn from this is that your training should always keep you alert, not just to expected happening, but to not discount the unexpected, then many lives will be saved as a result of your attention to detail.