Investigation of students' short-term memory performance and thermal sensation with heart rate variability under different environments in summer

An increase in temperature and change of correlated color temperature (CCT) would affect cognitive performance and human physiology. Moreover, the effect of CCT on thermal sensation at different temperatures is controversial and needs to be further explored. In order to study the effects of CCT variations on students' short-term memory performance and thermal sensation, 20 subjects were exposed to a “neutral temperature” (26 °C) and two “slightly warm temperature” (28 °C, 30 °C) in different periods. In each period, short-term memory tests were assessed under different CCT (3000 K, 4500 K, and 6000 K), and subsequently completed the questionnaire about their thermal sensation. Subjects’ short-term memory performance was assessed using the N-back memory tool, the thermal sensation was evaluated using a seven-point scale while undergoing electrocardiogram (ECG) continuous recording by PowerLab. Spectral analysis of ECG provided indices of heart rate variability (HRV). The results indicate the short-term memory performance was not significantly affected by temperature and CCT. In addition, the results indicate the short-term memory performance was not significantly affected by temperature and CCT. The effect of CCT over thermal sensation was weaker compared with the temperature effect. There was a significant negative correlation between CCT and thermal sensation at 26 °C and 28 °C. When the temperature difference is 2 °C, CCT would change the dominance of temperature on thermal sensation. When the temperature remained the same and the CCT difference reached 3000 K, there was a significant difference in thermal sensation. Moreover, the effect of CCT over thermal sensation was consistent with “Hue-heat” hypothesis. HRV could be used to evaluate short-term memory performance and thermal sensation. • The short-term memory is not affected by temperature and CCT within acceptable range. • A significant negative correlation exists between CCT and thermal sensation. • CCT could dominate the thermal sensation within comfort range (26 °C–28 °C). • HRV could be used to evaluate short-term memory performance and thermal sensation. • The thermal environment is accepted when the HRV value is close to 1.