Perceptual Baggage

For airline passengers, airport security means saying goodbye to your jacket, carry-on and pocket change, being funneled through the metal detector, and being randomly herded into a roped-off pen where security guards wave wands around your armpits. It’s no cakewalk, but the security personnel are just doing their jobs.

It turns out that the searching that what the screeners do pushes the limits of human perception, raising serious questions about the effectiveness of current security efforts

That’s why a team of researchers from the University of Illinois at Urbana-Champaign, in an effort to aid training, investigated the cognitive processes used by security personnel. The study was conducted by Jason McCarley, Arthur Kramer, Christopher Wickens, Eric Vidoni, and Walter Boot of the University’s Beckman Institute and was published in the May issue of Psychological Science, a journal of the American Psychological Society.

The researchers asked subjects to perform the tasks of airport security screeners, looking for knives in colored X-ray images of bags. The subjects had to scan the images and decide whether each one was safe, while an eye tracker recorded their gaze. They looked at four sets of bags with similar knives in them before the researchers presented a fifth set of images with different knives.

Over the first four sets of bags, the subjects learned to search faster and more accurately. When the knives changed, though, their searching abilities dropped significantly, even though the subjects were warned to expect new targets. They were still better than when they started, but it’s apparent that when the search target changed, the task became harder.

As you might have imagined, it’s easier to find something in an image if it’s familiar. Security screeners can’t find every knife, gun, and nail file that comes their way if they only practice with the knives – they need to be familiar with every possible threat in order to find them reliably. As McCarley et al conclude, the ideal training for security screeners would involve as many different targets as possible.

For more information, contact McCarley at mccarley@uiuc.edu. To read the article, visit www.psychologicalscience.org/media.

Psychological Science is ranked among the top 10 general psychology journals for impact by the Institute for Scientific Information. The American Psychological Society represents psychologists advocating science-based research in the public's interest.

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