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Searching for the Presence and Absence of Features in Vigilance: The Decrement Persists

The present study was designed to reexamine the ability of individuals to look for the presence or absence of stimulus features in a vigilance setting. Forty individuals participated in a 40-min vigil where they were asked to monitor a display comprised of either two or five circles. Half of the participants were asked to respond when a 4 mm line was present in one of the circles, and the other half responded when the line was absent from one of the circles. The participants were given ample time to search the display and make their responses. The results showed that response times were longer for the larger displays and for the feature-absent search conditions. Also, response times increased over the course of the vigil irrespective of search condition. In addition, participants reported higher levels of subjective workload after the vigil, but there were no differences among conditions. These results are discussed with respect to the feature-integration theory and its applicability to vigilance.