Recently concern about aviation security has focused on the work of airport security
screeners who detect threat items in passengers' luggage. An effective method of training
and screening is required for improving screeners' detection abilities and performance to
cope with the unreliable human performance of screening. The overall aim of this thesis is
to understand and define the potential visual and cognitive factors in the task of
inspecting airport passengers' X-ray luggage images, examine usability of perceptual
feedback in this demanding task and develop a new method of salient regions which
assist screeners to detect targets. The result of this work would obtain knowledge and
skills of X-ray luggage images examination, provide insight into the design of training
system and develop a method to significantly enhance screeners' detection ability.
A questionnaire was developed for screeners to extract the expertise of the screening
task and investigate the effect of image features on visual attention. A series of
experiments were designed to understand the screening task and explore how
knowledge and skills are developed with practice. Results indicated that training under
time stressed conditions is recommended for ensuring adequate high detection ability in
real life situation as screeners have to balance accuracy and speed in time pressure. The
advantages of screeners are better detection ability and search skills which were gained
by experience of the search task. Hit rate of naive people was improved with the
perceptual exposure of images of threat items. However, scanning did not become
efficient. It has demonstrated that detection performance and search skills are improved
by the practice of frequency exposure targets in the search task and such ability partly
transfer to novel targets. Learning in visual search of threat items is stimuli specific such
that familiarity with stimulus and task is the source of performance enhancement. Threat
items should be updated constantly and massive amount of X-ray threat objects should
be employed for airport security screeners training so as to enlarge object knowledge and
enhance recognition ability.
Perceptual feedback of circling areas with dwell duration longer than 1000ms does not
Significantly improve observers' detection ability in the airport screening task. Features of
bags and threat items influence initial attention and attention allocation in the search
process. Salient regions, based on the pure stimulus properties, not only contain most of
targets in X-ray images but also improve observers' detection performance of high hit rate
by forcing observers to scrutinize these areas carefully.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.