Investigating training and transfer effects resulting from recurrent CBT of x-ray image interpretation.

Investigating Training and Transfer Effects Resulting from Recurrent CBT of X-Ray Image Interpretation Saskia M. Koller (s.koller@psychologie.unizh.ch) University of Zurich, Department of Psychology, Binzmuhlestrasse 14, 8050 Zurich, Switzerland Diana Hardmeier (d.hardmeier@psychologie.unizh.ch) University of Zurich, Department of Psychology, Binzmuhlestrasse 14, 8050 Zurich, Switzerland Stefan Michel (s.michel@psychologie.unizh.ch) University of Zurich, Department of Psychology, Binzmuhlestrasse 14, 8050 Zurich, Switzerland, and Max Planck Institute for Biological Cybernetics, Dept. Bulthoff, Spemannstrase 38, 72076 Tubingen, Germany Adrian Schwaninger (a.schwaninger@psychologie.unizh.ch) University of Zurich, Department of Psychology, Binzmuhlestrasse 14, 8050 Zurich, Switzerland, and Max Planck Institute for Biological Cybernetics, Dept. Bulthoff, Spemannstrase 38, 72076 Tubingen, Germany Abstract The importance of airport security has increased dramatically in the last years. Large investments into x-ray screening technology have been made in order to cope with the changed terrorist threat situation. However, the most expensive equipment is of limited value if the humans who operate it are not trained well enough to detect threat objects in x-ray images of passenger bags quickly and reliably. In this study we investigated whether adaptive computer based training (CBT) can be used to increase x-ray image interpretation competency of airport security screeners. To this end, we tested screeners before and after six months of weekly recurrent CBT using X-Ray Tutor (XRT). A control group of screeners was tested as well but this group did not receive training with XRT. Large increases in detection performance were found for the training group, which did also generalize to new threat objects that were not shown during training. The results of this study indicate that recurrent CBT can be a powerful tool to increase the x-ray image interpretation competency of screeners. Keywords: Object recognition; perceptual learning; x-ray screening; human-computer interaction; airport security human factors. Introduction In recent years, x-ray screening of passenger bags has become an essential component of airport security. Large investments were made into state-of-the art x-ray screening equipment. However, well trained human screeners are needed to operate the equipment appropriately in order to detect threat objects in passenger luggage within few seconds of inspection time. Object shapes that are not similar to ones stored in visual memory are difficult to recognize (e.g., Graf, Schwaninger, Wallraven, & Bulthoff, 2002; Schwaninger, 2004, 2005). Thus, a prerequisite for good threat detection performance is knowledge about which objects are prohibited and what they look like in x- ray images. Schwaninger, Hardmeier, and Hofer (2005) have shown that x-ray screener performance depends on knowledge-based and image-based factors. Image-based factors refer to image difficulty resulting from viewpoint variation of threat objects, superposition of threat objects by other objects in a bag, and bag complexity depending on the number and type of objects in the bag. The ability to cope with image-based factors is related to individual visual- cognitive abilities rather than a mere result of training. In contrast, knowledge-based factors refer to knowing which items are prohibited and what they look like in x-ray images of passenger bags. Because objects look quite different in x- ray images than in reality and because many threat objects are not known from everyday experience, computer-based and on the job training are important determinants of x-ray detection performance. Schwaninger et al. (2005) compared detection performance of novices with the one of trained aviation security screeners. A rather poor recognition of unfamiliar object shapes (e.g. self-defense gas spray, electric shock device etc.) in x-ray images was found for novices. For trained aviation security personnel, a much higher recognition performance was shown. Schwaninger and Hofer (2004) showed that adaptive computer-based training (CBT) can be very effective to increase the detection of improvised explosive devices (IEDs) in x-ray images of passenger bags. McCarley, Kramer, Wickens, Vidoni, and Boot (2004) reported a better performance after training for the detection of knives in x-ray images. The purpose of this study was to investigate to what extent the previous findings can be expanded to other threat categories (e.g., guns and other prohibited items) and to examine transfer effects. The training group conducted weekly recurrent CBT using X-Ray Tutor (Schwaninger, 2004). The control group did not receive this type of training and conducted recurrent classroom training including another CBT system. Both groups of screeners were tested before and after 6 months using the X-Ray Competency Assessment Test (X-Ray CAT, Koller & Schwaninger, 2006). This test shows different kinds of prohibited items in x-ray images of passenger bags. Half of