| On the basis of investigation of some large chemical plants and oil refineries, two experiments were conducted to examine the efficiency of signal detection and its determinants in an instrument keep-watching task. The experiment one mainly studied the effects of the number of signal sources and the time length of sustained operation on operators' performance and reliability. In the experiment, the reaction times(RT) were used as the indicator of performance, the number of signal sources was 2, 4 and 8 instruments (3 ranks),The instrument keep-watching task lasted 80 minutes, it was divided into 4 periods, each period was about 20 minutes. The experiment two mainly examined the effects of dual tasks, and signal interval time on the efficiency of signal detection. in the experiment, the primary task was to monitor 4 instruments at a VDT for 60 minutes. the signal interval time was divided into 3 level(30-50 seconds, 4-6 minutes and 8-10 minutes),the secondary task was to make discrimination between a stable light and a flash light, the signal interval time was 4-7 seconds. The results showed : (1) In a visual monitoring task, the RT of signal detection increased over time on task. In thesame period, the number of signal sources had significant effects on the RT of signaldetection.(2)The signal interval time was an important factor affecting the RT of signal detection. The efficiency of signal detection decreased with an increase in signal interval. (3)The task characteristics had a significant effect on the efficiency of signal detection . TheRT of signal detection was markedly higher in the condition of dual tasks than in thecondition of single task. (4)The subjective fatigue increased significantly over the 1h monitoring period for both thesingle task and the dual task.
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