Mental work-load has increased with technical innovation, while manual work-load has decreased. As a result, eye fatigue has become one of the complaints in the modern working environment. Heretofore, the evaluation of visual work-load was based mainly on observation of the refractive power and accommodative function of the eyes. The purpose of this study is to assess, through observation of eye movement, the work-load created by eye-tracking tasks.
The subjects were required to track, only by eye movement, a target oscillating between a distance of 35 cm in the horizontal or vertical direction for seven minutes. Mispursuit of the target, blinking and heart rate were recorded during the period of the experiment. The subjects were given eye-tracking tasks under nine conditions comprising angles 20°, 40° and 60° in the respective moving widths and 0.1 Hz, 0.3 Hz and 0.5 Hz in the moving frequency of the target. Four healthy male volunteers participated in the eye-tracking experiments involving the horizontally moving target and five healthy male volunteers participated in those involving the vertically moving target.
The task load condition of visual angle of 20° with target frequency of 0.1 Hz was employed as standard. The relative velocity of the target and the velocity of eye movement were obtained using various combinations of visual angles and target frequencies.
The following results were obtained:
1) The frequency of mispursuits increased significantly with the increase of relative target velocity. The degree of increase of mispursuit was especially remarkable at relative target velocities exceeding 1.0 Hz or at eye movement velocities exceeding 40°/s.
2) The frequency of repeated blinks decreased significantly under the task load condition of eye movement velocities exceeding 24°/s.
3) No significant changes in heart rate or sinus arrhythmia were observed with increase of relative target velocity.