Vol.7 No.4 2015
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Research paper : Mental fatigue measurement as application software on consumer devices (S. IWAKI et al.)−215−Synthesiology - English edition Vol.7 No.4 (2015) quantitative evaluation of the chronic changes in fatigue. While it is not certain what kind of information can be extracted from the chronic fatigue data that are measured daily and continuously, it may be possible to use this technology effectively in various scenes in our society from health management at a personal level and improvement of our living environment to optimization of resource distribution and task efficiency in companies, based on the temporal change of mental fatigue conditions. We are starting to collect data to clarify the significance of conducting fatigue measurement continuously over a long term in the real living environment. Figure 9 shows an example where an engineer who works at a R&D division of a private company continuously measured the flicker perception threshold for five weeks including the summer vacation period using the Android smart phone app that we developed. While this is still in the preliminary stage, we are obtaining results that the changes in the daily fatigue level are related to the work and off-day patterns.6 Summary and future developmentWe developed a low-cost, practical mental fatigue monitoring system to be used in daily life based on the measurement of flicker perception threshold (flicker test) which has been used conventionally for academic purposes in a laboratory setting. Our prototype system showed promise in implementing such a system just by installing the software in the general purpose personal devices, e.g. smart phones and PCs, which are readily available in daily life.The remaining issue is to deal with the dependency of the flicker perception threshold on the changes in surrounding lighting environment and visual distance. Although the basic idea has been submitted for correcting the measurement result based on the lighting condition and visual distance using the camera function installed in the device (Japanese Patent # 4406705), verification based on real data has not yet been done. For now, we instruct the users to conduct measurement under the same lighting and viewing conditions as much as possible, however, it is necessary to develop an additional technique for robust fatigue measurement in changing surrounding environments for further diffusion.The flicker perception threshold is also affected by age and eyesight of the user as well as the display performance of the information device. In the laboratory setting, the variation by examinees can be standardized by using the results of the reference measurements conducted at the start of the experiment or before applying workload (standard value), but it is expected that the standard value cannot be obtained accurately for continuous measurements in daily life. We are developing an algorithm to determine the standard value appropriately from the previously acquired data.For the future application of the proposed technique to the screening of fatigue related diseases as well as for multifaceted understanding of mental fatigue conditions, it is also necessary to clarify the correlation between FPT and the biochemical indices such as the changes in various biomarkers obtained from blood or saliva samples. We are working with the Health Research Institute, AIST to collect blood and saliva samples simultaneously as the flicker test during overnight work load. The current results indicate that there is a significant correlation between the changes in FPT and the oxidative stress marker in the blood samples.[21] Since there have not been any methods to evaluate long-term changes in fatigue condition quantitatively in daily life, it is not certain what information is embedded in the fatigue data acquired over several months or years. The future topics include the development of a health management system that combines our fatigue measurement technique and time-series data processing algorithms to extract useful healthcare information, as well as application to enhance work efficiency through appropriate management of fatigue SunSatFriThuWedTueMonSunSatFriThuWedTueMonSunSatFriThuWedTueMonSunSatFriThuWedTueMonSunSatFriThuWedTueTueMon0.940.960.981Flicker perception threshold normalized by the maximum value obtained during experimental periodFig. 9 Preliminary data to show relationship between changes in the flicker perception threshold and work/off-day pattern obtained by continuous measurements over five weeks for an office worker (at a R&D division of a private company). Broken lines denote off-days.

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