Differential effects of hot-humid and hot-dry environments on mental functions.

Twenty five subjects acclimatised to heat artificially were exposed to "basic effective temperatures" (BET) of 25.0 degrees, 29.6 degrees, 32.2 degrees, 33.3 degrees and 35.0 degrees C BET under conditions of both humid and dry heat. The object of the investigation was to ascertain the nature of effects of varying degrees of heat stress on mental alertness, associative learning, reasoning ability and dual-performance efficiency. A further aim was to determine the temperature levels at which impairment of psychological functions was severe enough to be of practical concern. The duration of each exposure was four hours, during which subjects performed physical exercise followed by rest every 30 min. It was found that all the psychological functions tested were adversely affected under extreme heat, and that a significant drop in various psychological functions was seen at effective temperatures of 32.2 degrees C and 33.3 degrees C in hot-humid and hot-dry conditions respectively. It is concluded that at the same effective temperatures the magnitude of the overall effect on psychological functions under humid conditions is relatively greater than that under dry conditions.