Effects of overnight military training and acute battle stress on the cognitive performance of soldiers in simulated urban combat.

Understanding the effect of stress, fatigue, and sleep deprivation on the ability to maintain an alert and attentive state in an ecologically valid setting is of importance as lapsing attention can, in many safety-critical professions, have devastating consequences. Here we studied the effect of close-quarters battle (CQ battle) exercise combined with overnight military training with sleep deprivation on cognitive performance, namely sustained attention and response inhibition. In addition, the effect of the CQ battle and overnight training on cardiac activity [heart rate and root mean square of the successive differences (RMSSD)] during the cognitive testing and the relationship between cardiac activity and cognitive performance were examined. Cognitive performance was measured with the psychomotor vigilance task (PVT) and the sustained attention to response task (SART). Altogether 45 conscripts participated in the study. The conscripts were divided into control (CON) and experimental (EXP) groups. The CON completed the training day after a night of sleep and the EXP after the overnight military training with no sleep. Results showed that the effect of the overnight training on cognitive performance and the between-group difference in heart rate (HR) and heart rate variability (HRV) depended on the cognitive test. Surprisingly, the cognitive performance was not largely affected by the CQ battle. However, as expected, the CQ battle resulted in a significant decrease in RMSSD and an increase in HR measured during the cognitive testing. Similarly, the HR parameters were related to cognitive performance, but the relationship was found only with the PVT. In conclusion, fatigue due to the overnight training impaired the ability to maintain sufficient alertness level. However, this impairment in arousal upregulation was counteracted by the arousing nature of the SART. Hence, the conscripts' cognitive performance was mainly preserved when performing a stimulating task, despite the fatigue from the sleep loss of the preceding night and physical activity.

Modeling the cardiac indices of stress and performance of nuclear power plant operators during simulated fault scenarios.

Acute stress can affect cognitive processing and decrease performance in demanding, stressful situations. Here, we recorded the cardiac indices of stress, that is, the heart rate and heart rate variability together with the physical activity of nuclear power plant operators, and examined their association with crew performance, while the operator crews were managing simulated incident and accident situations. Crew performance was evaluated both by the operator instructor and as the time taken to resolve the situation. In total, 64% of the variance in the information-seeking performance (adj-R2  = .64, p < .01), and 41% of variation in the performance time (adj-R2  = .41, p < .01) were explained by the psychophysiology. The cardiac measures indicated that increased stress was associated with poorer information-seeking performance and longer performance time. Increased physical activity was associated with poorer information seeking only. Otherwise, crew performance was robust, as the diagnosis and corrective actions, use of emergency operations procedures, and collaboration, were only weakly associated with the stress physiology. The association between information-seeking performance and stress might be explained by the larger requirement for cognitive processing at the information-gathering phase of the task. The results of the study show that psychophysiological measurements of stress and activity can provide valuable information on stress and its association with cognitive performance at work.

Cardiac measures of nuclear power plant operator stress during simulated incident and accident scenarios.

Maintaining optimal performance in demanding situations is challenged by stress-induced alterations in performance. Here, we quantified the stress of nuclear power plant (NPP) operators (N = 20) during a full-scale simulator training for incident and accident scenarios. We compared the ambulatory electrocardiography measurements of heart rate (HR) and heart rate variability (HRV), and self-reported stress during baselines and simulated scenarios. Perceived (scale 0-10) and physiologically measured stress were low during baseline after the scenarios and normal NPP operation (means 1.8-2.2, mean HR 75-80 bpm). During a cognitively challenging scenario simulating a sensor malfunction, the operators' stress was mild to moderate (mean 3.4; HR + 12% from baseline). During simulations of severe accidents of fire and radioactive steam leakage, the experienced stress and cardiac activity were on a moderate to high level (means 4.2 and 4.6; HR + 23% and + 14% from baseline, respectively). Cardiac activity paralleled the self-reported stress: correlation of self-reported stress to HR was 0.61 (p < .001) and to HRV features RMSSD, HF, LF/HF, SD1, and SD1/SD2 were -0.26, -0.28, 0.35, -0.40, and -0.39 (p < .01), respectively. The low shared variance (22%) between HR and physical activity further support the interpretation that the cardiac activity was strongly linked to the experience of stress and not accountable by operators' movement within the simulator. Cardiac measurements in naturalistic settings can thus reveal relevant information on acute stress with the benefit of not interrupting the primary task.

Field evaluation of a wearable multimodal soldier navigation system.

Challenging environments pose difficulties for terrain navigation, and therefore wearable and multimodal navigation systems have been proposed to overcome these difficulties. Few such navigation systems, however, have been evaluated in field conditions. We evaluated how a multimodal system can aid in navigating in a forest in the context of a military exercise. The system included a head-mounted display, headphones, and a tactile vibrating vest. Visual, auditory, and tactile modalities were tested and evaluated using unimodal, bimodal, and trimodal conditions. Questionnaires, interviews and observations were used to evaluate the advantages and disadvantages of each modality and their multimodal use. The guidance was considered easy to interpret and helpful in navigation. Simplicity of the displayed information was required, which was partially conflicting with the request for having both distance and directional information available.