Sustained attention and serial responding in heat: mental effort in the control of performance.

The effects of heat (40 degrees C) on sustained attention and serial responding were studied in a simple reaction time task and a serial four choice reaction time task, respectively. Core temperature (Tc), heart rate variability (HV) and subjective reactions were monitored during the 80 min of exposure time. Simple reaction time performance and accuracy in the serial choice reaction time task deteriorated significantly in heat. In the serial choice reaction time task, the effects of heat on response times and on HV were correlated. Performance and level of Tc were not correlated, but a relationship was found between performance and rate of Tc change. Results are discussed in relation to the thermophysiological status of the subjects and the compensatory mechanism of effort allocation. It is proposed that task characteristics regulate the degree of activity of this compensatory mechanism.