Feature Presence/Absence Modifies the Event Rate Effect and Cerebral Hemovelocity in Vigilance Performance

Abstract

Observers monitored displays of five circles for the presence or absence of a line in one of the circles during a 40-min vigil. Displays were updated 6, 12, or 24 times/min (event rate). Signal detections varied inversely with event rate when observers monitored for the absence of the distinguishing feature but not when monitoring for the presence of that feature and judged the workload of their assignment to be greater when monitoring for feature absence than presence. In addition, the availability of information processing resources, as indexed by transcranial Doppler sonography measurements of cerebral blood flow, was exhausted more rapidly when observers monitored for feature absence than for feature presence. This effect was limited to the right hemisphere. The results are consistent with the view that detecting feature absence is more capacity demanding than detecting feature presence and with previous brain imaging findings indicating right hemispheric control of vigilance.