Relationship between EEG amplitude and subjective rating of task strain during performance of a calculating task.

With the use of a calculating work tester, a paced calculating task consisting of addition or subtraction of two 2-digit numbers was imposed for five minutes at each of eight grades of workload upon 24 healthy male students. The subject's scalp EEG was recorded for 10 s at the occipital midline (Oz) during rest and task performance, and the average amplitude was obtained for each of the five spectral bands. The subjective rating of the hardness of each task was adopted as a subjective measure of mental task strain. The logarithm of percentage of errors, the amplitudes of the alpha, beta 1, and beta 2 bands and the subjective ratings of hardness of the task increased in linear proportion to the workloads of the task. The highest correlation was found between the subjective ratings and the percentage increases of the Oz beta 2 amplitude over the resting level. It was suggested that these two measures would be useful for the measurement of mental task strain. In addition, it was judged that workloads of more than 90% of capacity induce excessive mental task strain in the subject.