“…Existing studies mainly used EEG and ECG sensors to measure drivers' physiological responses (Hong et al, 2014;Lee et al, 2010;Rogado et al, 2009), which may cause participants' repulsion on the sensor-attached location and the restrictions on participants' actions, due to sensor attachment. The PPG and respiration sensors are considered to be more easily embodied for actual use of a car system, compared to other bio signal sensors.…”