| The escalation of the global warming has led to the high outbreak of extreme climate events in recent years(e.g.,heat waves).As a result,the hot and humid environments/climates appear with greater frequency and affect people’s everyday work and lives,bringing about the health problems such as heat stroke.Most importantly,the hot and humid climate could reduce people’s cognitive functions,thus increase the working risks and bring safety and health issues.However,sometimes people have to work under hot and humid environments,especially for jobs with high cognitive demands,such as the outdoor maintanance of the precision instrument/equipment in summer,and the modern military maneuvers and operations in hot and humid climate zones,etc.Therefore,in order to ensure the health and safety of workers in humid and hot environment,the high productivity as well,it is necessary to conduct a study on the changes in human cognitive performances under humid and hot environment.To scrutinize the mechanisms behind the human cognitive performance reduction under hot-humid exposure experimentally,a total of 14 male right-handed participants were recruited.And a 180-minute exposure was conducted at 32,35,38,and 41°C respectively,with the relative humidity of 70%.During each exposure,the skin temperature,core temperature,and sweating were measured,and ECG data were recorded continuously for heart rate variability analysis.In addition,the subjects were asked to complete 5 sets of cognitive tests and 5 sets of questionnaires(30 min/set)at each temperature.Each cognitive test contained 5 different types of subtasks corresponding to different cognitive functions of the human body,and the order of the sub-tasks followed the Latin Square Design.The 5questionnaires included subjective evaluations of human fatigue,effort and emotion.Based on the experimental results,the mechanism of the human cognitive performance reduction under hot-humid exposure were analyzed in terms of the physiological and psychological aspects,and the evaluation model was also established.The main findings of this study are as follows.(1)The difference between core temperature and mean skin temperatureΔt could reflect the human body’s tolerance to the hot-humid environments.Δt = 1°C might be the threshold for human tolerance to a hot-humid environment.When Δt was less than 1°C,the human body was unable to tolerate the hot and humid environment.(2)The mean accuracy of cognitive tasks reduced with the air temperature,and a "quasi-U-shaped" relationship was observed between the mean accuracy and the exposure time under the same hot and humid environment.In addition,the mean reaction time increased with the air temperature,and a "quasi-inverted U" relationship was observed between the mean reaction time and the exposure time under the same hot and humid environment.Finally,the mean cognitive performance decreased with the air temperature,and a "quasi-U-shaped" relationship was observed between the cognitive performance and the exposure time under the same hot-humid exposure.(3)This study verified that the human cognitive performance was affected by the physiological and psychological factors during the hot-humid exposure.Consequently,by analyzing the relationship between the relative cognitive performance and the physiological parameters,subjective questionnaire results of the participants under hot-humid exposure,the mechanism of the psychological and physiological compensations on cognitive reduction was acquired.Therefore,the hypothesis of this study was well verified.Based on the findings above,a phased evaluation model of the human cognitive performance under hot-humid exposure was established,in which the psychological compensation model(RCPPANAS)was a linear function,while the physiological compensation model(RCP-LF/HF)was a third-order function,and the phased reduction features could be well expressed. |
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