Perception psychologists come to the aid of airport security screeners

matter how easy an object is to spot, they found, it is harder to spot if it is extremely uncommon. Wolfe and his colleagues found that people were much better at spotting objects that occurred half the time than in spotting the exact same object if it occurred only 1 in 50 times. This may be a quirk of psychology with evolutionary roots, Wolfe suggests: If you were hunting prey it would make sense that your brain devote more attention to the species that comes along more often. In the security scenario, however, in which the most important threats occur very infrequently, it backfires. Wolfe and his Brigham and Women’s Hospital team, In a paper now under review by the Journal of Experimental Psychology, offer one way around the perceptual glitch: If test subjects are “primed” for two minutes on tests in which knives and guns appear frequently, their high success rate continues when they switch over to a scenario in which the frequency drops. The priming effect lasts at least twenty minutes — probably long enough to get through a typical X-ray scanner shift (officers are rotated every half hour, to keep them from zoning out). Another reason baggage screening is hard is that people’s visual acuity is stimulated when objects move (think hunting). Yet on an X-ray screen, the target objects are stationary against their background. So Josh Rubinstein, head of the “human factors” program at the DHS’s Transportation Security Lab, is working on modifying current X-ray machines to produce simulated motion. Images taken from slightly different angles can be presented in sequence, “animating” them enough to make screeners more effective at picking out the potential weapons. Based on the work of a British psychologist, Paul Evans of Nottingham Trent University, and amounting to an inexpensive tweak of old technology, the approach has been shown to improve threat detection by 15 percent, Rubinstein says. The Halo 3 theory comes from a simple observation made by researchers at Duke University: Frequent video-game players seem to be better at picking out threats quickly.

Shea writes that Stephen Mitroff, a Duke professor, and Mathias Fleck, a graduate student, had been following the growing research on the effect of video games on cognitive abilities. They compared the performance of gamers with nongamers, defining gamers as people who had spent at least five hours a week for the past six months playing “first-person shooters” — video games that show a world through the player’s eyes, moving through a series of threat-filled hallways and landscapes. In one test of people’s ability to identify low-frequency threats, gamers had an error rate of 15 percent, compared with 25 percent for nongamers. The reason for the advantage was unclear, though gamers have obvious experience both in scanning a screen quickly for threats and in improving their visual detection in new arenas. This work has not yet been published, but is under consideration by the journal Psychonomic Bulletin and Review, and Fleck says it “could potentially shift hiring practices or training procedures.” Rubinstein says his lab is keeping an eye on such studies, but there are no real-world tests planned. Shea notes that, as befitting a true academic field, security-screening studies now has its warring camps and intramural squabbles. In the November issue of Psychological Science (see below), Mitroff and Fleck argue that Wolfe’s “prevalence” theory may be wrong. This is not to palce to elaborate on their argument and the test that support it, but in essence they say that Wolfe’s “prevalence effect” was not a fundamental perceptual error, in other words, but rather that the hand was just quicker than the eye: Visual recognition did kick in, but a microsecond after the finger made the wrong call (the finger clicking the computer mouse in lab tests). Wolfe, for his part, takes issue with technical details of the Duke tests and stands by his original findings. The Duke team is now working on other failures of human observation, such as the “satisfaction of search” problem. This refers to the well-established human tendency to end a search after one potential problem has been identified. Radiologists who detect a problem spot on an X-ray, for example, have a notably high rate of failure in identifying a second problem spot if it appears on the same X-ray.

-read more in Mathias S. Fleck Stephen R. Mitroff, “Rare Targets Are Rarely Missed in Correctable Search,” Psychological Science 18, no. 11 (November 2007): 943