Passive Heat Stress Affects Decision-Making, but not Situational Awareness and Executive Functioning in Virtual...

Decision-making in military occupations is vital for operational success and personnel safety and relies on situational awareness, executive control, and strategic alignment of operational goals. This study examined the effects of acute operational and passive heat stress on cognitive performance in a randomized controlled trial with 68 service members. Participants were assigned to either a low- or high-stress group and completed two military scenarios using a desktop simulator. Passive heat stress was applied only to the high-stress group in a portable environmental facility. Decision-making and situational awareness were scored from scenario recordings, while executive functioning was assessed through a cognitive test battery. In addition to the group comparison, a heat index capturing individual variability in thermal strain was calculated. Contrary to expectations, heat stress did not impair cognitive performance across most domains. Decision-making performance actually improved over time in the high-stress group, with significantly better performance during the second assessment compared to the low-stress group. Cognitive flexibility also improved significantly within both groups. These changes are attributed primarily to learning effects rather than stress-induced performance. Situational awareness showed no significant differences between groups. Exploratory heat index analyses revealed that participants in the high heat index group exhibited increased situational awareness over time, suggesting a possible inverted U-shaped relationship between thermal strain and performance. In contrast, inhibition improved only in the low heat index group. Together, these findings emphasize that the heat stress protocol may not have been potent enough to generate the cortisol response needed to detrimentally affect higher-order cognition. Nevertheless, the findings highlight that thermal strain can interact with cognitive performance in complex, nonlinear ways. While passive heat stress remains a promising stressor for research, its effect may only become fully apparent under more intense or physiologically demanding conditions, warranting further investigation into its potential impact on higher-order cognitive functions in military contexts.