Cyriaque Lamar writes on io9.com:
Looking for something you’re sure you won’t find? Even if the item you seek is close by, a doubtful attitude reduces your chances of finding it, claims a new study funded by the US Department of Homeland Security.Researchers simulated the conditions of an airport security checkpoint and instructed subjects to search for weapons. LiveScience reports that the monotony of the searches and increasing rarity of the weapons decreased subjects’ attention spans:
They asked subjects in the lab to look at X-ray scans of checked baggage, as if they were airport screeners. 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.
In another trial, the guns and knives appeared much more infrequently — in only 2 percent of bags. This time, subjects missed the weapon 30 percent of the time.