Aviation Security Screeners Visual Abilities & Visual Knowledge Measurement

A central aspect of airport security is reliable detection of forbidden objects in passenger’s bags using X-ray screening equipment. Human recognition involves visual processing of the X-ray image and matching items with object representations stored in visual memory. Thus, without knowing which objects are forbidden and what they look like, prohibited items are difficult to recognize (aspect of visual knowledge). In order to measure whether a screener has acquired the necessary visual knowledge, we have applied the prohibited items test (PIT). This test contains different forbidden items according to international prohibited items lists. The items are placed in X-ray images of passenger bags so that the object shapes can be seen relatively well. Since all images can be inspected for 10 seconds, failing to recognize a threat item can be mainly attributed to a lack of visual knowledge. The object recognition test (ORT) is more related to visual processing and encoding. Three image-based factors can be distinguished that challenge different visual processing abilities. First, depending on the rotation within a bag, an object can be more or less difficult to recognize (effect of viewpoint). Second, prohibited items can be more or less superimposed by other objects, which can impair detection performance (effect of superposition). Third, the number and type of other objects in a bag can challenge visual search and processing capacity (effect of bag complexity). The ORT has been developed to measure how well screeners cope with these image-based factors. This test contains only guns and knives, placed into bags in different views with different superposition and complexity levels. Detection performance is determined by the ability of a screener to detect threat items despite rotation, superposition and bag complexity. Since the shapes of guns and knives are usually well-known even by novices, the aspect of visual threat object knowledge is of minor importance in this test. A total of 134 aviation security screeners and 134 novices participated in this study. Detection performance was measured using A’. The three image-based factors of the ORT were validated. The effect of view, superposition, and bag complexity were highly significant. The validity of the PIT was examined by comparing the two participant groups. Large differences were found in detection performance between screeners and novices for the PIT. This result is consistent with the assumption that the PIT measures aspects related to visual knowledge. Although screeners were also better than novices in the ORT, the relative difference was much smaller. This result is consistent with the assumption that the ORT measures image-based factors that are related to visual processing abilities; whereas the PIT is more related to visual knowledge. For both tests, large inter-individual differences were found. Reliability was high for both participant groups and tests, indicating that they can be used for measuring performance on an individual basis. The application of the ORT and PIT for screener certification and competency assessment are discussed.