Interruption of a Monotonous Activity with Complex Tasks: Effects of Individual Differences

The fluctuations of vigilance and performance for operators working in monotonous conditions were studied in laboratory. Three experimental designs were achieved on 20 subjects: — one reference condition with a vigilance task of 3 hours 30 during day time, — one experimental condition with interruptions of monotony during the vigilance task by a sustained task, during the same day time period, — the same experimental condition during night time. The purpose was to analyse the effect of breakdown in monotony on arousal and human performance and to look for individual differences in human performance. Physiological data were collected in order to study the variation of arousal. Response times and omissions were used as performance index. Individual differences can be observed for performance and vigilance. Two kinds of behavior are defined: stable subjects and subjects characterized by fluctuations both for arousal and performance during the task. During day time period, breakdown of monotony has a positive effect on performance especially for subjects with fluctuations of arousal. Night time condition creates a sleep deprivation and the consequence is that the efficiency of the reactivation due to breakdown by sustained task is not demonstrated. Results are discussed in regard of the theory of Fisk and Schneider on automated and controlled mental processing during monotonous activities.