Is that a gun? The influence and features of bags and threat items on detection performance

An experiment is reported where naïve observers searched 50 X-ray images of air passenger luggage for potential terrorist threat items. For each image their eye movements were recorded remotely and they had to rate their confidence in whether or not a potential threat item was present. The images were separately rated by other naïve observers in terms of; visual complexity of bags, the familiarity and visual conspicuity of threat items. The visual angle subtended by guns and the familiarity of threat items influenced the detection rate. Eye movement data revealed that the complexity of bags and the conspicuity of threat items also influenced visual search and attention