The purpose of this research was to investigate the effects of varying the threshold of alarm systems and workload on human response to alarm signals and performance on a complex task. A receiver operating characteristic (ROC) curve was selected to reflect the sensitivity of the alarm system. The threshold of the alarm system was manipulated by changing the value of beta along the ROC curve. A total of 84 students participated in experiment 1 and 48 students participated in experiment 2. Participants performed a compensatory-tracking, a resource management and a monitoring task. As expected, results showed that participants responded significantly faster to true alarm signals when they were using the system with the highest threshold under low-workload conditions. Results also indicated that changing the threshold of the alarm system had a significant effect on overall performance and this effect was greater under high-workload conditions. However, contrary to expectations, the highest level of performance was achieved by setting the threshold at a low level. Results from both experiments revealed that the advantage of faster alarm reaction time as a result of increasing the system's threshold was lost because of its increased probability of missed events.

The present study examined how individuals detect critical patterns in maternal-fetal heart rate (MFHR) signals. Twenty-eight undergraduate students monitored simulated maternal-fetal heart rate signals for decelerations lasting either 30 or 44 seconds. They completed four 10-min sessions representing four different signal-to-noise S/N ratios (10, 4, 2, and 1), in which the S/N ratio represented the magnitude of the deceleration to background heart rate variability. The results showed that the introduction of any variability reduced the ability to detect signals and increased false alarms. Further, with S/N ratios of 2 and 1 participants made equivalent numbers of hits and false alarms. These results show that as the S/N ratio decreases, observers struggle to distinguish critical patterns from the background fetal heart activity. These findings highlight the source of one problem often observed when interpreting MFHR signals in clinical settings and underscore the need for auxiliary aids.

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Using a dual-task paradigm, we examined how alarm system detection threshold and task complexity affected human performance and perceived workload. We hypothesized that using an alarm system would improve task performance and lower perceived workload, particularly when task complexity was high and at the medium threshold level. Twenty-one students from Old Dominion University participated in this study. Results showed that alarm use improved performance during low task complexity. For high task complexity, improvement was accomplished only when alarm system threshold was low or intermediate. Results also indicated that changing the alarm system threshold affected performance only under high task load conditions. Optimal performance was achieved by setting the threshold of the alarm system at its lowest level. The use of alarms reduced workload under both low and high task complexity levels, but only when the threshold was high.

Interest in centralized monitoring in labor and delivery units is growing because it affords the opportunity to monitor multiple patients simultaneously. However, a long history of research on sustained attention reveals these types of monitoring tasks can be problematic. The goal of the present experiment was to examine the ability of individuals to detect critical signals in fetal heart rate (FHR) tracings in one or more displays over an extended period of time. Seventy-two participants monitored one, two, or four computer-simulated FHR tracings on a computer display for the appearance of late decelerations over a 48-minute vigil. Measures of subjective stress and workload were also obtained before and after the vigil. The results showed that detection accuracy decreased over time and also declined as the number of displays increased. The subjective reports indicated that participants found the task to be stressful and mentally demanding, effortful, and frustrating. The results suggest that centralized monitoring that allows many patients to be monitored simultaneously may impose a detrimental attentional burden on the observer. Furthermore, this seemingly benign task may impose an additional source of stress and mental workload above what is commonly found in labor and delivery units.