Improved X-ray baggage screening sensitivity with 'targetless' search training.

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.

Target templates specify visual, not semantic, features to guide search: A marked asymmetry between seeking and ignoring.

Top-down search templates specify targets' properties, either to guide attention toward the target or, independently, to accelerate the recognition of individual search items. Some previous studies have concluded that target templates can specify semantic categories to guide attention, though dissociating the effects of semantic versus visual features has proven difficult. In the present experiments, we examined the roles of target templates in search performance, by measuring the "two-template costs" incurred when observers did not know which of two types of targets would be presented. For target templates, these costs only varied with set size when a template could specify a target's features. Any semantic influences did not affect the guidance of attention, only the recognition of individual items. In contrast, templates for rejection-specifying the properties of irrelevant nontargets-do appear to specify semantic properties to guide attention away from those items, without affecting recognition. These qualitative differences between the two types of templates suggest that the processes of seeking and ignoring are fundamentally different.

Breakdowns of eye movement control toward smoking cues in young adult light smokers.

BACKGROUND: Many studies suggest that dependent smokers have a preference or attentional bias toward smoking cues. The purpose of this study was to test the ability of infrequent non-dependent light smokers to control their eye movements by look away from smoking cues. Poor control in the lightest of smokers would suggest nicotine cue-elicited behavior occurring even prior to nicotine dependency as measured by daily smoking. METHODS: 17 infrequent non-dependent light smokers and 17 lifetime non-smokers performed an antisaccade task (look away from suddenly appearing cue) on smoking, alcohol, neutral, and dot cues. RESULTS: The light smokers, who were confirmed light smokers and non-dependent (MFaegerström Dependency Score=0.35), were significantly worse at controlling their eye movements to smoking cues relative to both neutral cues (p<.04) and alcohol cues (p<.02). Light smokers made significantly more errors to smoking cues than non-smokers (p<.004). CONCLUSIONS: These data suggest that prior to developing clinical symptoms of severe dependence or progressing to heavier smoking (e.g., daily smoking), the lightest of smokers are showing a specific deficit in control of nicotine cue-elicited behavior.

Templates for rejection can specify semantic properties of nontargets in natural scenes.

In contrast to standard search templates that specify a target object's expected features, templates for rejection (TFR) may specify features of nontargets, biasing attention away from irrelevant objects. Little is known about TFR, and virtually nothing is known about their role in guiding search across natural scenes. In such scenes, targets and nontargets may not be easily distinguished on the basis of their visual features; it has been claimed that standard search templates may therefore specify target objects' semantic features to guide attention. Here, we ask whether TFR can do so. Noting a limitation of previous procedures used to study standard search templates, we trialed an alternative method to examine semantic templates for nontarget exclusion in natural scene search. We found that when nontargets belonged unpredictably to either of two physically distinct categories, search was less efficient than when targets belonged to one known category. This two-category cost, attributed to inefficient application of search templates, was absent for two physically dissimilar but semantically related categories. Adding a training phase to highlight semantic distinctiveness of two object categories reinstated the two-category cost, precluding stimulus-based accounts of the effect. These patterns were not observed for one-image displays or when observers searched for object categories rather than ignoring them, demonstrating their specificity to TFR, the inadequacy of search-and-destroy models to account for them, and likely basis in attentional guidance. TFR can specify semantic information to guide attention away from nontargets.