Sustained attention and hypovigilance: The effect of environmental monotony on continuous task performance and implications for road safety

While driver hypovigilance is often attributed to fatigue, it is more frequent in monotonous road environments, suggesting that monotony of task (requiring simple, under-demanding responses) and/or environment (containing highly repetitive, predictable stimuli) plays an important role. We report an experimental study designed to disentangle the characteristics and effects of monotony from those of time on task and fatigue, using a series of short vigilance tasks. Task monotony was manipulated through changes in target probability (p(monotonous) = 0.11 vs. p(non-monotonous) = 0.50), while environmental monotony was manipulated through stimulus variation. Results revealed that performance, as indexed by accuracy and response times (RTs), was significantly worse in a monotonous context versus non-monotonous context. Furthermore, performance decrements emerged early in the vigilance task (within 4.3mins) and were consistent over the course of the experiment, suggesting that monotony effects are independent of time on task and fatigue. Experimental manipulations of monotonous contexts revealed that both task demands and stimulus variability are independent moderating factors of sustained attention, with improved performance in conditions of increased task demands and stimulus variability. Implications for road safety are discussed.