Sleep-Inducing Factors in Mechanical Environments

In running cars or trains, passengers are often getting sleepy. We focus on this physiological phenomenon. If a machine can reproduce this phenomenon, it is feasible to put insomnia patients or infants to sleep without any harmful effects. This will bring extreme benefit for insomnia patients or parents of babies. The purpose of this study is to elucidate the sleep-inducing factors of running cars or trains, and the final goal is to develop a sleep inducing machine which reproduces the mechanical environment for sleep. For the first step, this study investigated the relationship between sleepiness and vibrations on several trains. The sleepability of each train is discussed by the ratio of sleeping passengers (RSP). High RSP trains can be recognized as comfortable to sleep. The acceleration profile of trains is analyzed by FFT and jerks. The results suggest that the comfortable train has mainly low-frequency (under 2.0 Hz) vibrations with particular fluctuation. Small jerk also contributes the sleepability. A prototype sleep inducing machine is tested with several subjects. The questionnaire survey indicates that near 1.0 Hz excitation is the most comfortable vibration for sleep. This result supports our hypothesis.