Monitoring driving psychological fatigue through unconstrained heartbeat signal extraction by using pressure sensor array

The feasibility of monitoring driving psychological fatigue through unconstrained heartbeat extraction by using pressure sensors array was investigated. The pressure signals were obtained by close contact between subject's back and backrest of car seat. Correlation coefficients of electrocardiogram signals and pressure signals were used to select the optimal monitoring point due to the unavoidable adjustment of sitting posture during long times of driving. Lifting wavelet transform was applied for de-noising. J-J interval signals, which represent heartbeat signals, were extracted. The correlation dimension of heartbeat signals, reflecting the complicated degree and the chaotic level of a nonlinear dynamic system, was used as the indicator to determine the psychological fatigue. Its validity was verified by the consistency of correlation dimension with R-R interval (represents cardiac cycle). Finally, questionnaires during driving were administered. The effectiveness of this method to judge driver psychological fatigue was confirmed. This finding indicates that driving psychological fatigue can be monitored through unconstrained heartbeat signal extraction by using the pressure sensor array.