Time on task effect on tracking performance under heat stress.

Abstract

The time on task effect on human tracking performance under three levels of ambient temperature, namely; 20, 26 and 30°C wet-bulb globe temperature (WBGT) and under two different work/rest ratios (2/1 and 3/1) was investigated. Total exposure time in each session for the three temperature levels was 120 min while the time on task was 90 min. The work cycle time was kept constant at 30 min and each work session contained three cycles. The subjects in the experiment were six fit, acclimatized, undergraduate male students aged 20-23 years and the task need was a compensatory one-dimensional vertical tracking task. The statistical analysis of the results indicated that time on task had a significant detrimental effect ( p< 0.01) on tracking performance. As the time on task increased, the tracking performance decreased. The detrimental time on task effect on the tracking performance appeared to be greater in hot environments as demonstrated by the significant effect ( p< 0.1) of the time on task/ambient temperature interaction on tracking performance. A significant deterioration in tracking performance occurred after 25 min on task. When performing the task under hot environments, this effect was more pronounced. Ambient temperature was found to deteriorate the tracking performance significantly (p<0.01). By raising the ambient temperature from 20 to 26°C WBGT, the tracking error score was approximately doubled, while the rise of ambient temperature from 26 to 30°C WBGTdid not produce as great a deterioration in the tracking performance. Neither work/rest ratio nor its interaction with time on task or ambient temperature showed any significant effect on tracking performance. Finally, the results demonstrated that environmental siresses affect the homogeneity of a group of subjects. A group which was homogeneous for performance under comfort environment (20°C WBGT), became heterogeneous when worked under hot environments.