It has long been accepted in ergonomics research on mental workload that overload and underload are equally detrimental to performance (see e.g.,Young and Stanton, 2002). UnderMalleableAttentional ResourcesTheory (MART;Young and Stanton, 2002), underload is explained by a shrinkage of attentional capacity in conditions of excessively low mental workload. Consequently, any sudden increase in workload will be beyond the capacity limit of the operator – even if such a level of demand would ordinarily have been within their ability to cope.