Death from overwork and severe accidents caused by mental fatigue and sleepiness are becoming one of the more pressing social problems of developed countries. Such mental fatigue and sleepiness often comes from declines and/or changes in wakefulness in our daily life. Recently, numerous researchers have focused on possible ways of utilising physiological signals to deduce alertness; however, the characteristic behaviours that can be used to deduce wakefulness are difficult to measure. To better understand the indices of change in wakefulness states, the authors fabricated a micro-optical sensor system that can measure physiological signals from eye and eyelid conditions without imposing stress on the user. Using the newly fabricated micro-optical sensor system, they have found and reproduced characteristic blink behaviours that are indicative of changes in a person's wakefulness. Herein, new indices are proposed that have potential for use in fatigue evaluation tests. The experimental results demonstrate that the sensor system can detect declines in and/or changes in wakefulness that indicate mental fatigue and sleepiness.
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