Abstract
When searching for a known target, mental representations of target features, or templates, guide attention towards matching objects and facilitate recognition. When only distractor features are known, distractor templates allow irrelevant objects to be recognised and attention to be shifted away. This is particularly true in X-ray baggage search, a challenging real-world visual search task with implications for public safety, where targets may be unknown, difficult to predict and concealed by an adversary, but distractors are typically benign and easier to identify. In the present study, we draw on basic principles of distractor suppression and rejection to investigate a counterintuitive ‘targetless’ approach to training baggage search. In a simulated X-ray baggage search task, we observed significant benefits to target detection sensitivity (d′) for targetless relative to target-based training, but no effects of performance-contingent rewards or the inclusion of superordinate semantic categories during training. The benefits of targetless search training were most apparent for stimuli involving less spatial overlap (occlusion), which likely represents the difficulty and greater individual variation involved in searching more visually complex images. Together, these results demonstrate the effectiveness of a counterintuitive targetless approach to training target detection in X-ray baggage search, based on basic principles of distractor suppression and rejection, with potential for use as a real-world training tool.
Highlights
When searching for a known target, mental representations of target features, or templates, guide attention towards matching objects and facilitate recognition
Our analysis of criterion differences between the training groups revealed that both the target-based training group and the sTST group were biased towards responding to say that bags contained the type of item they had viewed during training
D′ and c scores for both training groups in Experiment 2 were similar to those of the sTST group in Experiment 1, which followed a training procedure that was similar but did not include superordinate grouping. These results suggest that participants did not develop broad distractor templates that could facilitate the rejection of multiple semantically-related object categories in response to training, or that they did, but that participants in the alphabetic condition grouped items in a similar way, contrary to their instructions
Summary
When searching for a known target, mental representations of target features, or templates, guide attention towards matching objects and facilitate recognition. When only distractor features are known, distractor templates allow irrelevant objects to be recognised and attention to be shifted away This is true in X-ray baggage search, a challenging real-world visual search task with implications for public safety, where targets may be unknown, difficult to predict and concealed by an adversary, but distractors are typically benign and easier to identify. The benefits of targetless search training were most apparent for stimuli involving less spatial overlap (occlusion), which likely represents the difficulty and greater individual variation involved in searching more visually complex images Together, these results demon‐ strate the effectiveness of a counterintuitive targetless approach to training target detection in X-ray baggage search, based on basic principles of distractor suppression and rejection, with potential for use as a real-world training tool. Developing a categorical template that will support guidance towards and recognition of this type of target is difficult (Hout et al, 2017) and may limit the effectiveness of target-based training procedures
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