Guest post by Caroline Drucker

A screenshot of the Airport Scanner game, with a suitcase containing two dynamite sticks. Courtesy of the Mitroff Lab and the Kedlin Company.

A screenshot of the Airport Scanner game, with a suitcase containing two dynamite sticks. Courtesy of the Mitroff Lab and the Kedlin Company.

You’re at the airport waiting to pass through security and board your flight. The security agent stops the person in line ahead of you: there was a full water bottle in his carry-on bag. He throws out the bottle and proceeds through the airport. Later that evening, you see that person’s face on the news, for having pulled out dynamite on their flight. Why did the TSA agent overlook the dynamite?

A team of researchers at Duke led by Dr. Stephen Mitroff is using a cell phone game to provide answers to this and other questions about airport baggage screenings. Last year, they reported that luggage screeners are likely to miss extremely rare illegal items. In a new study which will appear in the Journal of Experimental Psychology: Human Perception and Performance, Dr. Mitroff’s team once again leverages the power of big data to address a different issue: what happens when a carry-on suitcase contains multiple illicit items?

Baggage screening is an example of what cognitive scientists refer to as visual search: attempting to locate a target among a crowded visual display. Many laboratory studies have demonstrated that when more than one target is present in the display, people are less likely to find additional targets once they have spotted a first target. One possible reason for this “subsequent search misses” phenomenon is that people become biased toward searching for targets that match the first target. That is, a baggage screener who finds a water bottle might enter “water bottle” mode and be unprepared to see dynamite. This theory is most likely to hold in situations with large and unpredictable sets of targets – which is precisely why it has been difficult to test in the lab, where the relatively small amount of trials that subjects can perform has limited the possible target numbers and frequencies.

A smartphone game called Airport Scanner circumvents this problem. In the game, players act as TSA agents and view X-ray images of carry-on luggage, earning points for correctly tapping illegal items. More than 200 possible illegal items can appear, and each bag can contain between zero and three illegal items among up to twenty legal items. The game is available as a free download from the Kedlin Company, who share the data with the Mitroff lab. They have now collected close to two billion trials (bags searched) from over seven million people, which would take centuries to collect in the lab.

Using these data, Dr. Mitroff and his colleagues were able to make an important discovery about subsequent search misses. When two identical targets are present in a bag, it is more likely that both will be found than when two different targets are present. In other words, if someone first spots a water bottle, it is more likely that they will also find a second item if it is a water bottle than if it is dynamite.

This result supports the theory that finding a visual target biases a person’s perceptions. We become better prepared to find another instance of the same item, rather than a different item. According to Dr. Mitroff, “Knowing this fact can help create search environments and standard operating procedures to overcome this priming effect.”