What are you hiding in your holiday luggage?

06 July 2011

The snake-like queue in the security hall at the airports is probably the least appealing part of embarking on any holiday. The ritual of emptying pockets of loose change, stripping off jackets, placing luggage on the X-ray conveyer belt and padding barefoot through the body-scanners brings frustration for most travellers. Spare a thought, however, for the screeners who spend their days surveying X-ray images of the contents of our rucksacks – according to research being presented at this year’s Royal Society Summer Science Exhibition their task is probably more difficult than one might think.

In airport security search, screeners search X-ray images of baggage for multiple types of weapons: guns, knives and explosives. In these X-ray images, colour is often used to represent different types of materials. However, the fact that different types of materials (e.g. metals, organics) lead to different colours creates a potential challenge for the brain’s visual system.

Dr. Tamaryn Menneer and colleagues from the Centre for Visual Cognition, University of Southampton, together with researchers from the Visual Cognition and Attention Laboratory, University of Massachusetts, have shown that the visual system finds searching for one of two colours (e.g. orange or blue) much more difficult than searching for single specific colours (e.g. orange). By monitoring eye-movements during visual searches, they have found that when looking for two colours, people look at a disproportionately large number of objects that are unlike both targets.

This fundamental limitation on visual search has implications for any situation involving search for multiple items. For example, might security screening be enhanced if screeners conducted two separate searches for threat items, e.g. one for metal threats (guns and knives) followed by one for improvised explosive devices (IEDs)?  The research was supported by the Human Factors Program of the U.S. Department of Homeland Security, Science & Technology Directorate’s Transportation Security Laboratory.

Future research from the Centre for Visual Cognition and Durham University’s Visualization Laboratory will assess the usefulness of 3D images in training participants to interpret X-ray images. 3D displays will allow layered images, such as baggage X-rays, to be seen as separate layers at different depths. It is expected that experience with 3D X-ray images will facilitate search of 2D X-ray images.

Visitors to the Exhibition will be able to experience the state-of-the-art eye tracking technology that scientists are using in this research. They’ll also get to play a range of games comparing 2D versus 3D, and see how having two eyes is important for depth perception in three dimensions.

Talking about the exhibit, which is supported by the Wellcome Trust, Dr. Tamaryn Menneer said:

“Standing in the queue at airport security waiting to have our belongings scanned is a familiar experience for many people. I think visitors to the exhibition will find it interesting to stop and think about what X-ray screeners are actually seeing and how the human brain makes sense of it. We live in times where heightened security and terrorist threats are a part of everyday life. If science can come up with ways of making this task easier then I think it’s important that the public gets a chance to learn about them.”