Threat image projection (TIP) is a technology of current x-ray machines that allows exposing screeners to artificial but realistic x-ray images during the routine baggage x-ray screening operation. If a screener does not detect a TIP within a specified amount of time, a feedback message appears indicating that a projected image was missed. Feedback messages are also shown when a TIP image is detected or in the case of a non-TIP alarm, i.e. when the screener indicated that there was a threat but in fact no TIP was shown. TIP data is an interesting source for quality control, risk analysis and the assessment of individual screener performance. In two studies we examined the conditions for using TIP data for the latter purpose. Our results strongly suggest using aggregated data in order to have a large enough data sample as the basis for statistical analysis. Second, an appropriate TIP library containing a large number of threat items, which are representative for the prohibited items to be detected, is recommended. Furthermore, consideration should be given to image-based factors such as general threat item difficulty, viewpoint difficulty, superposition and bag complexity. Different methods to cope with these issues are discussed in order to achieve reliable, valid and standardized measurements of individual screener performance using TIP.

A central aspect of airport security is reliable detection of forbidden objects in passenger 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 can 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 known well even by novices, the aspect of visual threat object knowledge is of minor importance in this test. Abstract -A central aspect of airport security is reliable detection of forbidden objects in passenger bags using Xray 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 he 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 d...

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This paper investigates whether the greater accuracy of emotion identification for dynamic versus static expressions, as noted in previous research, can be explained through heightened levels of either component or configural processing. Using a paradigm by Young, Hellawell, and Hay (1987 ), we tested recognition performance of aligned and misaligned composite faces with six basic emotions (happiness, fear, disgust, surprise, anger, sadness). Stimuli were created using 3D computer graphics and were shown as static peak expressions (static condition) and 7 s video sequences (dynamic condition). The results revealed that, overall, moving stimuli were better recognized than static faces, although no interaction between motion and other factors was found. For happiness, sadness, and surprise, misaligned composites were better recognized than aligned composites, suggesting that aligned composites fuse to form a single expression, while the two halves of misaligned composites are perceived as two separate emotions. For anger, disgust, and fear, this was not the case. These results indicate that emotions are perceived on the basis of both configural and component-based information, with specific activation patterns for separate emotions, and that motion has a quality of its own and does not increase configural or component-based recognition separately.

Several previous studies have stressed the importance of processing configural information in face recognition. In this study the perception of configural information was investigated. Large overestimations were found when the eye-mouth distance and the inter-eye distance had to be estimated. Whereas configural processing is disrupted when inverted faces have to be recognized the perceptual overestimations persisted when faces were inverted. These results suggest that processing configural information is different in perceptual as opposed to recognition tasks.