Mental fatigue is a decrease in cognitive performance resulting from prolonged periods of cognitive activity. It is a subjective feeling reported by the subject, rather than an objective one that can be observed by others. Our goal is quantification of the subjective mental fatigue by measuring eye movement, and solves the neural circuit about mental fatigue.
In our study, we focus on measuring small fixational eye movements. When we try to fixate our gaze, our eyes move constantly. Especially, microsaccade that is the fastest and largest fixational eye movements has important roles in visual perception. Previous studies suggested that the microsaccades are sensitive to volitional action preparation, such that the microsaccade rate gradually decreased toward stimulus appearance in successfully completed pro- and anti-saccade trials, but increased in erroneous trials. Thus, here we recorded fixational eye movements of healthy subjects by using a high-speed video camera and analyzed the time dependent changes in the microsaccade parameters to examine the effect of mental fatigue.
We found that the microsaccade rate gradually increased depending on time sequence. It might reflect a lack of motor preparatory process depending on mental fatigue. On the other hand, microsaccade dynamics didn't change significantly during the time sequence. These findings suggest that mental fatigue affects the specific neural circuit concerned with generation of microsaccade.