Assessment of mental workload on older workers during performance of a calculating task.

Twenty-four healthy male clerical workers (50-59 years of age) in an automobile manufacturing plant performed as accurately as they could a calculating task consisting of the addition or subtraction of two 2-digit numbers at five grades of task load for 5 min each. The workers' work capacities were inferior in speed but not in precision to those of male students determined previously. The resting levels of occipital midline beta-2 (Oz beta 2) amplitude were significantly lower for the workers than for the students. The workers' mental workloads were objectively shown to be lighter than the students' based on a significant difference between the percent increases in Oz beta 2 amplitude over resting levels. The workers' subjective mental workloads assessed by subjective rating of task difficulty (SRTD) were lighter than the students' at higher task loads. From the trend that there was no undue rise in either SRTD or percent increase in Oz beta 2 amplitude, it was judged that no task load could induce excessive mental workload on workers.