Abstract
<p>Time perception is a fundamental cognitive process supporting decision-making and task execution, particularly in extreme environments such as high altitude and spaceflight. Although neural and cognitive mechanisms of temporal estimation have been widely studied, the contribution of autonomic physiological activity under environmental stress remains less well understood. This study examined how heart rate, respiratory frequency, heart-rate variability, and their interrelationships relate to time-estimation accuracy under normoxic (0 m above sea level) and hypobaric hypoxic conditions (4500 m above sea level). Seventy-one healthy male participants aged 18-41 years completed auditory time-reproduction tasks across short (600-2000 ms), and long (2000-6000 ms) intervals. Participants were tested under normobaric sea-level conditions and, in the altitude cohort, during exposure to hypobaric hypoxia at high altitude. Resting respiratory frequency, rather than heart rate, significantly predicted short-interval reproduction accuracy, with higher respiratory frequency associated with greater underestimation of stimulus duration. High-altitude exposure was accompanied by significant shifts in autonomic activity, and respiratory frequency showed the strongest association with timing performance during the task. Whereas sea-level testing was characterized mainly by underestimation, high-altitude exposure was associated with more frequent overestimation, suggesting that hypobaric hypoxia may alter internal timing dynamics. These findings indicate that respiration-linked autonomic activity contributes to individual differences in subjective time estimation. They may have practical relevance for high-stakes environments, including aviation, high-altitude operations, and space missions, where monitoring or regulating respiratory dynamics could help reduce timing-related performance errors under physiological stress.</p>