Effect of adaptive opportunity on cognitive performance in warm environments

This study investigates the hypothesis that thermal adaptive opportunities available to building occupants affect their cognitive performance and mental workload. The change rate of cerebral blood flow (Δtotal Hb) was measured by Near Infra-Red Spectroscopy (NIRS) and interpreted as the metric of mental workload in subjects while performing cognitive tasks (n-back tests) with, or without access to thermal adaptive opportunities such as regulable fan-induced air flow and clothing insulation adjustment. Participants underwent three experimental conditions: Condition 22 (operative temperature t_o = 22 °C without adaptive opportunities), Condition 28 (t_o = 28 °C without adaptive opportunities), and Condition 28w (t_o = 28 °C with adaptive opportunities. Under Condition 28w, thermal sensations were neutral, while thermal satisfaction and comfort levels were higher than those reported for Condition 28, and the same as those reported under Condition 22. The subjects' mean skin temperature under Condition 22 was the lowest at 32.1 °C, followed by Condition 28w at 33.6 °C, while the highest, 34.5 °C was recorded in Condition 28. No significant differences were observed in accuracy and reaction time of n-back tests between the three different environmental conditions. Under Condition 28w, mental fatigue levels and the left side Δ total Hb results were lowest out of all three conditions, although the differences failed to reach statistical significance. Availability of adaptive opportunities plays a role in expanding the range of thermal environmental conditions for optimal cognitive task performance in a moderately warm environment (t_o = 28 °C). This finding cannot be fully explained by the direct effect of adaptive behaviours on human heat balance and associated physiological responses, but the unexplained component may potentially be attributed to the psychological dimension of human adaptive response. These findings and their interpretation within an adaptive comfort framework are consistent with the extended-U hypothesis of cognitive performance.