Banned items can’t be spotted easily

WASHINGTON - Airport security employees may miss harder-to-spot prohibited items after identifying an easy-to-spot item such as a water bottle in scanners at security checks, research shows.

Missing items in a complex visual search is not a new idea; in the medical field, it has been known since the 1960s that radiologists tend to miss a second abnormality on an X-ray if they’ve found one already.

The concept, dubbed “satisfaction of search”, is that radiologists would find the first target, think they were finished, and move on to the next patient’s X-ray.

Does the principle apply to non-medical areas? That’s what Stephen Mitroff, assistant professor of psychology and neuroscience at Duke, and his colleagues set out to examine shortly after 2006, when the US Transportation Security Administration banned liquids and gels from all flights, drastically changing airport luggage screens.

“The liquids rule has introduced a whole lot of easy-to-spot targets,” Mitroff said.

In the new study, Mitroff and his group asked college students to identify specific targets on a computer display - in this case, two perpendicular lines that form the letter “T” amid distracters such as Ls and non-Ts.

In some cases, Ts were easy to spot, and in other cases more difficult because they blended in with the background.

When Mitroff’s group doubled the time allowed for each search, they saw that the students used barely a second of extra time but were significantly more accurate.

“It didn’t seem to do with time itself, but it seems to be the time pressure,” Mitroff said. “When you have the impending time pressure of going quickly, you are more likely to miss a second target,” he said.

In a new set of experiments, Mitroff’s group has plans to replace T-targets with multiple targets of different types, such as tools and bottles, a Duke University release said.

The findings were published in the Journal of Experimental Psychology: Applied.