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Kelly Steelman, Jason McCarley; The effects of target foreknowledge on visual search performance and strategy. Journal of Vision 2007;7(9):1067. doi: 10.1167/7.9.1067.
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© ARVO (1962-2015); The Authors (2016-present)
Though target foreknowledge has generally been found to improve visual search performance (e.g., Vickery, et al., 2005), a study of one particularly difficult form of visual search, a simulated baggage x-ray screening task, found no benefit of familiarity to oculomotor scanning (McCarley et al., 2004). The present experiment investigated the role of target foreknowledge in a simulated baggage x-ray screening task more closely by 1) comparing performance under conditions of target certainty and uncertainty and 2) measuring the accuracy of predictive metacognitive ratings of the difficulty of target detection. After familiarizing themselves with the search task and stimuli, participants viewed target knives one at a time and rated the expected difficulty of finding each one if it was hidden in a baggage x-ray. Following this, participants performed 180 trials of the visual search task. On half of all trials, a cue informed the participant to search for a specific target knife. On the remaining trials, the participant was cued to search for any of the five potential targets. Eye movements, accuracy, and response time were recorded. Correlations between RTs and predictive metacognitive ratings of detection difficulty indicated that searchers used target foreknowledge to modify their stopping policy on target-absent trials, and oculomotor data revealed that target foreknowledge increased the detection rate of targets after they were foveated. However, the speed and likelihood with which observer's fixation landed on the target object were similar for cued and uncued trials, indicating that target foreknowledge did little to enable attentional guidance or otherwise improve oculomotor scanning. Data indicate that foreknowledge can improve target recognition and alter strategic components of visual search performance, but suggest that high levels of clutter may limit the capacity for top-down attentional guidance in some tasks.
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