The earliest writings in history report the damaging and extreme impact of the thermal environment on human performance. The Bible has documented the death of a young son from exposure to sun when harvesting in his father’s fields in about 1000 BC : he “went out to … the reapers, said unto his father, ‘my head, my head,’” and died in his mother’s lap .
Air quality – characterized by temperature, humidity, pollution, etc. – affects human health, satisfaction, and performance. Sustaining and managing physical and cognitive performance under extreme temperatures is of critical importance to professional athletes (e.g., skiers), military personnel, and industrial workers.
During the winter Olympics, for example, cold causes an increase in shivering and muscle coactivation, and a decrease in muscle contraction velocity, nerve conduction velocity, and stretch-reflex response . These conditions could affect fine psychomotor control, postural control, balance, and proprioception in alpine skiers . Military operations are particularly likely to produce large numbers of heat problems including death due to heatstroke. In manufacturing and food processing, the ambient temperature could be as low as 0 °C. These examples show that studying extreme temperatures is important because humans do not always work under thermoneutral conditions.
What do we already know?
Although much is known about this topic, many researchers still study – albeit in more details – the impacts of cold or heat stress on humans, particularly in contexts where a high proportion of accidents are caused by human errors. The effects of indoor air temperature on thermal comfort in residential and office environments and work-related performance have been extensively explored. However, due to the variety of factors involved, there is still no single formula to accurately describe the correlation of air temperature and cognitive performance.
Cognitive performance typically refers to the quality of human information processing and is measured by speed, accuracy, and attentional demand. Individual studies often ask participants to perform cognitive tasks in thermoneutral (control) and hot or cold (experiment) environments and measure the differences in performance results between the two conditions. However, the results of such individual studies are usually heterogeneous, leading to inconsistent or statistically insignificant results.
There are theoretical models of cognitive performance under stress, such as Yerkes-Dodson, that have been criticized for methodological shortcomings and flawed interpretations. The Maximal Adaptability Model (Fig. 1) is a widely cited theoretical development, which emphasizes the role of attentional resources in cognitive responses to stress .
What does the correlation look like?
The objective of the current study  is to estimate the correlation between ambient air temperature and cognitive performance through a systematic literature review and meta-analysis. This widely-used methodology gathers evidence and develops research theories by synthesizing the findings of several individual studies through a process of using systematic, explicit, and accountable methods.
This study included 28 laboratory experiments published between 1980 and 2018 in a single analysis conducted by the use of the Comprehensive Meta-Analysis software. The study finds that the estimated temperature-performance correlation follows a bell-shaped curve centered around the average control temperature.
Under laboratory conditions with fixed clothing values, studies with the weighted mean of 4.34 °C, 10.04 °C, and 26.68 °C increase in the control air temperature, which is close to thermoneutral conditions, show about % 0.40, % 5.37, and % 7.97 reductions in cognitive performance, respectively. The results of the current research suggest that, regardless of participant characteristics, temperature, task type, task measure, and exposure time affect the correlation between heat and cognitive performance.
More attention-demanding tasks (e.g., math, reading comprehension, etc.) are more vulnerable to temperature variations than less attention-demanding tasks (e.g., inspection) in the heat but not necessarily in cold. Such declines in attention-demanding tasks can be attributed to a reduction in cognitive resources, which could result in less systematic and more heuristic information processing. In terms of accuracy and speed, the results show more decline in accuracy measures. Also, longer pre-task and task exposures cause significantly more decline in performance.
Implications for future studies
This study suggests that individual experiments on the effects of environmental factors on human performance could become more conclusive through improved study methods and by providing more detailed study statistics for meta-analysis, generalization, and model building. In both control and experiment conditions, individual studies with human subjects should identify, control, and report all primary factors that affect thermal sensation (e.g., air temperature, mean radiant temperature, relative humidity, air velocity, metabolic rate, fixed or free to adjust clothing insulation, etc.) and common sources of heterogeneity (e.g., acclimatization, learning effects, bonus, etc.), which can restrict the generalizability of findings and models.
Many studies report the experiments’ locations but very few provide information about outdoor air conditions, such as the average outdoor temperature, relative humidity, or the time during which the study is performed. In addition, thermal characteristics, such as global temperature, which are needed to calculate the apparent temperature (e.g., WBGT), should be measured by the use of standard instruments and specifications set by organizations such as ISO or NIOSH.
Essential statistics needed for a meta-analysis, such as standard deviation and pre-post correlation values, are often omitted from individual studies. Also, some studies fail to sufficiently describe experimental procedures (i.e., schedule, task duration, etc.).
The results of the current analysis were obtained from laboratory environments, in which participants were asked to maintain fixed clothing insulation values. In reality, office and industry workers are often free to adjust their metabolic rate and the actual transfer of heat through clothing to improve the heat balance equation and maintain thermal comfort.
Simple changes in clothing color, insulation, coverage, and ventilation along with changes in human posture and activity – also known as behavioral responses – significantly impact human thermoregulation and thermal sensation. The results of this study help inform policy and design decisions concerned with thermal comfort and upper limits for occupational exposure to cold and heat. For detailed guidance, see Ref. .
These findings are described in the article entitled Correlation of ambient air temperature and cognitive performance: A systematic review and meta-analysis, recently published in the journal Building and Environment. This work was conducted by Armin Jeddi Yeganeh, Georg Reichard, Andrew P. McCoy, Tanyel Bulbul, and Farrokh Jazizadeh from Virginia Tech.
- II Kings 4:18–20. In: The Holy Scriptures According to the Masoretic Text. A New Translation: With the Aid of Previous Versions and With Constant Consultation of Jewish Authorities. Philadelphia, Pa: The Jewish Publication Society of America; 5677–1917.
- Goldman, R. F. (2001). Introduction to heat-related problems in military operations. Medical aspects of harsh environments, 1, 3-49.
- Racinais, S., Gaoua, N., Mtibaa, K., Whiteley, R., Hautier, C., & Alhammoud, M. (2017). Effect of cold on proprioception and cognitive function in elite alpine skiers. International journal of sports physiology and performance, 12(1), 69-74.
- Hancock, P. A., & Vasmatzidis, I. (2003). Effects of heat stress on cognitive performance: the current state of knowledge. International Journal of Hyperthermia, 19(3), 355-372.
- Yeganeh, A. J., Reichard, G., McCoy, A. P., Bulbul, T., & Jazizadeh, F. (2018). Correlation of ambient air temperature and cognitive performance: A systematic review and meta-analysis. Building and Environment.