Abstract
There are two standpoints of view for the measurement of mental work load (MWL). One deals with the task demand and the other measures the subject's mental fatigue as an after effect. We focused on the task demand and expanded the concept to the task difficulty and duration. A dual task that is composed of pursuit tracking task as a primary task and memory retrieval task as secondary one was carried out using a computer display and a hand-made controller over 3 blocks (one block is about 10 minutes). The level of task difficulty stood at three (low, mid, and high) based on the stability of control dynamics. The reaction patterns to each task condition was examined in terms of the following indexes; performance on the task, subjective evaluations of the task load, emotional state, and physiological indexes (event related potentials: ERP, and heart rate). The results indicated that the Japanese version of the NASA-task load index score for the primary task was increased and P300 amplitude of ERP for the secondary task was decreased as the task difficulty increased. On the other hand, the interaction between work duration and task difficulty was reflected in the following points; 1) decreasing awareness in low and middle difficulty level, and 2) decreasing feeling of relaxation and increasing irritability in high difficulty level. Subjective fatigue increased only according to the work duration. These results suggested the necessity to separate task difficulty from work duration in the sensitivity on measures of MWL.
