Detection Measures for Visual Inspection of X-ray Images of Passenger Baggage

Abstract

Researchers often use the detection measures d' and A' to analyze detection performance in X-ray image inspection task. We investigated whether detection measures (d', A', and da) are truly independent of response tendency. In a first experiment, response tendency was manipulated directly through instruction and resulted in a decrease of d' and A', whereas da with a slope parameter of 0.6 remained constant. Eye-tracking data indicated that manipulating response tendency affected the decision component of the inspection task rather than search errors. Receiver operating characteristic (ROC) curves based on confidence ratings from a second experiment also supported da. Consistent with previous findings, our results imply that d' and A' are not always valid measures of detection performance in X-ray image inspection. We recommend calculating da with a slope parameter of 0.5 in addition to d' to avoid wrong conclusions if ROC curves are not available.