Decision making is one of the most vital processes we use every day, ranging from mundane decisions about what to eat to life-threatening choices such as how to avoid a car collision. Thus, the context in which our decisions are made is critical, and our physiology enables adaptive responses that account for how environmental stress influences our performance. The relationship between stress and decision making can additionally be affected by one's expertise in making decisions in high-threat environments, where experts can develop an adaptive response that mitigates the negative impacts of stress. In the present study, 26 male military personnel made friend/foe discriminations in an environment where we manipulated the level of stress. In the high-stress condition, participants received a shock when they incorrectly shot a friend or missed shooting a foe; in the low-stress condition, participants received a vibration for an incorrect decision. We characterized performance using signal detection theory to investigate whether a participant changed their decision criterion to avoid making an error. Results showed that under high-stress, participants made more false alarms, mistaking friends as foes, and this co-occurred with increased high frequency heart rate variability. Finally, we examined the relationship between decision making and physiology, and found that participants exhibited adaptive behavioral and physiological profiles under different stress levels. We interpret this adaptive profile as a marker of an expert's ingrained training that does not require top down control, suggesting a way that expert training in high-stress environments helps to buffer negative impacts of stress on performance.

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The report describes a field study designed to measure soldier performance of land navigation and other mission tasks using current navigational equipment and to compare these data with performance using navigational information integrated on a helmet-mounted display (HMD). Measures of stress, cognitive performance, and workload were also obtained. The results indicated that the soldiers traveled less distance between waypoints and experienced lower levels of mental workload using information presented on the HMD than they did using current navigational equipment. As might be expected, differences in time between manual and automatic map updates were significant, but no differences were found between current equipment and the HMD condition in object detection, determination of magnetic azimuth, or call for fire tasks. Differences between conditions in levels of stress and cognitive performance were not significant. Thanks to those at the Human Research and Engineering Directorate (HRED) of the U.S. Army Research Laboratory, particularly Jack Waugh for his assistance in defining the paths and object positions, to Mike Kosinski for the construction of the protractors with which our soldiers so accurately plotted coordinates, and to Dennis Hash and Nickey Keenan for their support in all phases and facets of this investigation. We would also like to express our appreciation to SFC Bobby King who assisted as pilot subject, trainer, and lane walker, and to SSG Brian James for the valuable extra set of hands he provided during training and testing. Last but never least, we are particularly grateful to the soldiers who participated in this investigation. We thank them for their enthusiasm, dedication, and opinions, and particularly their patience and sense of humor.

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