Specific-Token Effects in Screening Tasks: Possible Implications for Aviation Security.

Abstract

Screeners at airport security checkpoints perform an important categorization task in which they search for threat items in complex x-ray images. But little is known about how the processes of categorization stand up to visual complexity. The authors filled this research gap with screening tasks in which participants searched for members of target categories in visual displays. The authors found that when targets were sampled with replacement and repetition, participant screeners relied on recognizing familiar targets and had great difficulty using category-general knowledge. The authors observed a "heartbeat" in detection performance--it improved while test images repeated but dropped sharply when unfamiliar targets from the same categories appeared. This reliance on familiarity illuminates the processes of categorization under conditions of visual complexity and suggests limits on those processes. This reliance also has implications for the training and evaluation of screeners in the field.

Low target prevalence is a stubborn source of errors in visual search tasks.

“…That is, all trials with a hammer target used the same hammer. There is evidence that observers learn specific targets and that this learning does not generalize well to other members of the same category (J. D. Smith, Redford, Washburn, & Taglialatela, 2005). Second, more critically, the three different targets were all from the "tools" category.…”

Diversity during training enhances detection of novel stimuli

“…Research has demonstrated support for the specificity of training in similar airport luggage screening tasks (Smith, Redford, Washburn, & Taglialatela, 2005). Specifically, researchers found that participants relied on the recognition of familiar targets and had great difficulty using category-general knowledge (Smith, Redford, Gent, & Washburn, 2005;Smith, Redford, Washburn, & Taglialatela, 2005). In those studies, performance improved when the transfer images were the same as the ones used during training.…”

“…So far, the visual search and categorisation literature are rarely brought together (cf. Smith et al, 2005;Wolfe et al, 2007) because categorisation often requires identifying targets presented in isolation, whereas visual search requires discriminating targets from simultaneously presented distractors. Presumably, if training variability improved the visual differentiation of targets within cluttered bags, a possibility is that the benefit of training variability would disappear in the absence of cluttered images.…”

“…This research report provides evidence of the benefits of training variability for the detection of novel targets in a visually complex cognitive task-luggage screening. Research has demonstrated support for the specificity of training in similar airport luggage screening tasks (Smith, Redford, Washburn, & Taglialatela, 2005). Specifically, researchers found that participants relied on the recognition of familiar targets and had great difficulty using category-general knowledge (Smith, Redford, Gent, & Washburn, 2005;Smith, Redford, Washburn, & Taglialatela, 2005).…”

“…Then individuals are asked to determine the presence of any of those weapons embedded in luggage X-ray images. Other studies have used similar luggage screening images to examine the visual search aspects of a screener's performance (McCarley et al, 2004), issues related to operator trust in automated decision support systems (Madhavan & Wiegmann, 2005), and categorisation and specificity of training (Smith, Redford, Gent, & Washburn, 2005). The task provides a compilation of the actual visual stimuli that screeners are subjected to and provides similar time pressures (our study's participants have a limited amount of time to inspect the bag).…”