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Research paper−210−Synthesiology - English edition Vol.7 No.4 pp.210-217 (Mar. 2015) during work[3]Changes in movement and posture unrelated to required task[4]− Physiological index:Respiration, pulse rate, sweating,[5] Electroencephalography (EEG),[6] etc.− Perception and cognition index:Flicker perception threshold of visual stimulus[7]Spatial discrimination threshold of tactile stimulus[8]− Biochemical index:Metabolites in saliva, urine, or blood; genetic expression; etc.[9]-[11]In the measurement of fatigue based on above objective indices, the measurement and analysis of data or samples were conducted using special equipment under supervision of the test administrator, and the data were interpreted as part of the research activity. Therefore, it was impossible for ordinary users to use them readily in their daily lives. For example: (i) for the measurement of behavioral index, the performance evaluation specialized for particular tasks must be conducted, and it is necessary to record the subject’s actions from a third-party viewpoint using cameras as well as conduct advanced image processing; (ii) to use the physiological signals such as respiration or pulse rate, a transducer is necessary to convert such signals into digital data that can be handled on portable information terminals; and (iii) to use the biochemical index, it is necessary to have specialized equipment for collecting and analyzing biological samples. Hence, the realization of a system that can be used by general users in the course of their daily lives was difficult. In contrast, for the sensory and cognitive indices, 1 Objective of research and background of related technologiesThe accumulation of mental fatigue in daily living is not only an issue of health management where overwork may negatively affect health, but also is a serious social and economic issue where such fatigue may link directly to decreased work efficiency or traffic accidents caused by reduced wakefulness. Particularly, drowsy driving and reduced attention due to overwork have been indicated as some of the major factors of serious traffic accidents in commercial vehicles such as freight trucks,[1] and the realization of technology that allows evaluation of daily fatigue condition without excessive economic cost has been highly in demand. Therefore, our objective was to quickly develop a technology that allows objective and quantitative monitoring of mental fatigue level at low cost, easily done on a daily basis, using the information device that are commonly available.Meanwhile, there have been several indices developed for the quantitative evaluation of mental fatigue condition, and these were used mainly for research purposes. The major methods can be listed as follows:A. Subjective index− Self-conscious index:Subjective symptoms of fatigue (QA sheets and questionnaires)[2]B. Objective index− Behavioral index:For the required task, workload and frequency of error - Introducing reliable fatigue index to daily life-Monitoring mental fatigue is critical for traffic safety and health care. Various indexes of mental fatigue have been developed and used in the fields of ergonomics and industrial hygiene. One such index is the flicker-perception frequency threshold: the frequency at which the perception of flickering lights disappears for human observers. This index has a long history as a reliable indicator of mental fatigue in the laboratory setting. We have developed low-cost technologies for measuring mental fatigue objectively with widely available consumer devices such as personal computers and smartphones.Mental fatigue measurement as application software on consumer devicesKeywords : Mental fatigue, flicker perception threshold, personal mobile device, traffic safety [Translation from Synthesiology, Vol.7, No.4, p.220-227 (2014)]Sunao Iwaki1* and Nobuyoshi Harada21. Human Technology Research Institute, AIST Tsukuba Central 6, 1-1-1 Higashi, Tsukuba 305-8566, Japan *E-mail:, 2. Flicker Health Management Corp. AIST Kansai, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, JapanOriginal manuscript received January 14, 2014, Revisions received June 20, 2014, Accepted August 5, 2014

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