The experiment research of pupil change for the evaluation of mental workload

To investigate whether the motivation or interesting can take effect on the change of pupil size and whether pupil size reflect mental workload differences in a situation with different task difficulties. Twelve subjects participated in the experiment and they were asked to make target search task of three different difficulty level. The task difficulty levels were controlled through searching different number of differences between pictures. The experiment was done in two different conditions: the subject did the searching task only with basic rewards without time limited; the subjects received different additional rewards according their performance. The pupil size was recorded with eye movement tracking system. The results of the pupil size change showed the common characteristic and also difference for all the subjects. The same characteristic of pupil size change for all subjects was that the pupil size was larger in the second experiment condition than of the first corresponding condition. The difference were reflected on that some subjects pupil size first dilated and then constricted, and some first constricted and then dilated, while some others continuously constricted. Conclusions can be made from the results: the increasing of task difficulty will make pupil dilate, the positive motivation or interesting also dilate the pupil size, while the visual fatigue constrict the pupil size.