Mental Fatigue Monitoring Using a Wearable Transparent Eye Detection System

Abstract

We propose mental fatigue measurement using a wearable eye detection system. The system is capable of acquiring movement of the pupil and blinking from the light reflected from the eye. The reflection is detected by dye-sensitized photovoltaic cells. Since these cells are patterned onto the eyeglass and do not require external input power, the system is notable for its lightweight and low power consumption and can be combined with other wearable devices, such as a head mounted display. We performed experiments to correlate information obtained by the eye detection system with the mental fatigue of the user. Since it is quite difficult to evaluate mental fatigue objectively and quantitatively, we assumed that the National Aeronautics and Space Administration Task Load Index (NASA-TLX) had a strong correlation with te mental fatigue. While a subject was requested to conduct calculation tasks, the eye detection system collected his/her information that included position, velocity and total movement of the eye, and amount and frequency of blinking. Multiple regression analyses revealed the correlation between NASA-TLX and the information obtained for 3 out of 5 subjects.

Anti-fatigue Performance in SSVEP-Based Visual Acuity Assessment: A Comparison of Six Stimulus Paradigms

“…Here we used NASA-TLX to assess mental fatigue subjectively as a psychological measurement. We assumed that workload deduced by the NASA-TLX represented the mental fatigue of the subjects (Sampei et al, 2016).…”

“…Next, after all the runs were completed, the subjects were asked to complete a pairwise comparison method of the six defined sources. The weights a, b, c, d, e, and f were assigned to each of the six workload sources from the pairwise comparison results, with weight integers ranging from 0 to 5, and their combinations were C(6, 2) = 15 (Sampei et al, 2016). Finally, the individual NASA-TLX of each run for each subject was derived from a weighted average of the ratings of these six factors:…”

“…Moreover, pupil diameter can also be an index to evaluate mental fatigue, and the increase of mental fatigue coincides with a decrease in pupil diameter (Hopstaken et al, 2015b;Koo et al, 2018). Besides that, the National Aeronautics and Space Administration Task Load Index (NASA-TLX) is also used as a subjective and quantitative estimation of mental fatigue (Hart and Staveland, 1988;Sampei et al, 2016).…”

Fatigue Assessment by Blink Detected with Attachable Optical Sensors of Dye-Sensitized Photovoltaic Cells

“…In our prior work, we investigated the successful detection of the eye blinks with respect to the threshold. Based on the experimental results, we set the threshold to be 70% of the maximum voltage change rate [ 14 , 15 ], as illustrated in Figure 1 b. The optimal position of the cells to have the most reliable detection was experimentally deduced.…”

“…Information acquired from eyes, including movement of the eye and eye blinks, provides the state of the subjects [ 11 , 12 , 13 ]. In order to obtain the information with minimal physical and mental stress, we used a wearable, see-through eyeglass-type eye-tracking system [ 14 , 15 ]. The system had an array of transparent optical sensors, which were dye-sensitized photovoltaic devices [ 16 , 17 , 18 ].…”