Using speed measures to predict performance in x-ray luggage screening tasks

The visual inspection of x-ray images of luggage items at airports is a challenging task, where detection rates suffer when threat item complexity increases. The relationship between threat-item types, aspects of image difficulty, and decision time are explored using a combination of Drury´s Two-Component Model and Signal Detection Theory. 67 professional screeners completed a 2048-image battery that manipulated various image-based difficulty factors. A strong linear relationship between hit rate and decision time was found (r² = 0.64), with the hardest images showing a marked increase in decision time and decrease in hit-rate. The search time was found to be relatively stable across the threat categories, but decision time increased in proportion to detection rate decreases. Decision time is shown to closely reflect changes in detection sensitivity caused by different threat and image difficulties.