New research now suggests that when airport screeners do not expect to find a gun in passengers’ bags, they more than likely won’t. This research suggests that when people do not think that they will find something, then they do not look as hard as if they think that they will find something.

Some call this the needle in the haystack effect. Apparently humans just are not adapted to finding “rare” things. Cognitive scientist Jeremy Wolfe said that people know that if they do not find things often, then they do not often find it. It’s due to this that the rare stuff gets missed.

Wolfe went on to say that this effect applies to any rare thing that people are hunting for. Unfortunately this includes looking for weapons in bags and tumors in radiology scans. The research was funded by the Department of Homeland Security.

The results come in at the same time as the announcement of a security breach at the Gallatin Field airport in Bozeman, Mont. on December 13^th. It was here that airport screeners failed to catch a gun that was packed in a man’s carry on luggage. The man turned himself in when he remembered he had packed it and was allowed to board the plane.

They asked subjects in the lab to look at X-ray scans of checked baggage as if they were airport scanners. In one trial, 50 percent of the scans showed a gun or knife in the bag. In this test, subjects did fairly well, only missing the weapons about 7 percent of the time. However, in another trial, the guns and knives appeared much more infrequently, in about 2 percent of the bags. This time subjects missed the weapons about 30 percent of the time. In other words, their accuracy went down, because what they were searching or was less prevalent.