Distinguishing analysis on workload peak and overload under time pressure with pupil diameter

The main purpose of workload measurement is to identify conditions for overload so that they can be avoided by design. The operators´ workload peak is difficult to measure by subjective evaluation. Pupil diameter is widely used as a factor to measure workload sensitively, so it´s necessary to study the relationship between the workload peak and pupil diameter measurement. Eight trials were designed under different time pressure ranges from 0.5 to 1.5. The participants are required to press the corresponding letter key on the keyboard according to the letter on the screen randomly. In the experiments, the pupil diameter was measured by eye tracker. The relationship of pupil diameter, time pressure and correct rate was analyzed and established. Three change regions of the pupil diameter under different time pressure were found, which includes irregular change region, increasing linear region, decreasing linear region. When using pupil diameter to measure workload, the pupil diameter change irregularly in optimal performance region and task-related effort region. In overload region, there are two sub-regions: the pupil diameter is in linear increasing change and in linear decreasing change. The peak point of pupil diameter represents the most task-related effort, not the peak point of performance and workload. The change size of pupil diameter can represent the workload change, but the peak size of pupil diameter can´t be used directly to the quantitative analysis.