Background & Objectives: Many studies were conducted to determine the effects of heat stress on human performance. However, they could not reach a decisive conclusion, mainly due to a large variation in experimental conditions and tests. This study investigated cognitive performance of university students exposed to different levels of heat stress under laboratory condition.

Methods: In this cross sectional study,33 students aged 23-35 years performed cognitive tests. Participants were exposed to four Wet Bulb Globe Temperature (WBGT) of 18, 22, 29 and 33 ºC under laboratory conditions while performing CPT tests to investigate attention and reaction time.

Results: The maximum percentage of continues attention (99.67%) belonged to WBGT of 22 º C, and at the upper and lower levels of exposure (WBGT of 18 and 33 º C) percentage of attention was reduced. Although the percentage of attention was changed in different levels of heat stress, statistical analysis did not show any significant differences in attention between levels of heat stress (P_value>0.05). In addition, increase in WBGT index from 22-33 º C increased the reaction time. At the WBGT of 33 º C, statistical analysis showed significant difference in reaction time compared to other heat stress levels(P_value<0.05).

Conclusion: The results revealed that in the CPT test, exposure to heat stress at levels of occupational exposure limit,wouldimprove performances, but exposure to higher levels of heat stress woulddecrease it.