Spotting a gun in someone's luggage is not as easy as it may seem, according to a paper in this week's Nature.
In a laboratory mock-up of airport baggage screening, Jeremy Wolfe, of Harvard medical school, and colleagues found that volunteers failed to notice up to 30% of the unusual items (such as guns, knives and bombs). By contrast, they were better at noticing items that occurred frequently, with only 7% of these objects going unnoticed. "We don't know exactly how this maps on to the real world, but it seems that we are well adapted to search for plentiful items (such as when picking raspberries), but that when things are rare, we tend to abandon searches inappropriately early," says Wolfe.
Baggage handlers are trained to spot unusual items, which may make them better than the volunteers in the survey, but Wolfe still believes that visual search tasks can be improved by understanding people's weaknesses. "Although it would be more expensive, it would probably reduce the error significantly if two people were to study the same scan," he says. "This is already used in medical screening."
The Harvard team is planning to repeat the experiment with real airport baggage handlers to see how many dangerous items might be making it onto aeroplanes.