Electrophysiological evaluation of attention in drivers and passengers: Toward an understanding of drivers’ attentional state in autonomous vehicles

•Electrophysiological signals of drivers and passengers were compared.•Number of saccades, P1 amplitude of EFRP, and eye-blink duration were different.•These indices can be useful for evaluating drivers’ attention in autonomous vehicles. In order to safely use autonomous vehicle technologies, it is important to understand the state of drivers’ attention as they ride in Level 3 self-driving vehicles, because they might be required to take manual control of the vehicle in certain situations. We assumed that the attentional state of a driver who has perfect confidence in a self-driving system, and as a result, who is unready to take control of the vehicle is similar to that of a passenger riding in a vehicle driven by another person. Therefore, we compared electrophysiological signals from drivers and passengers that were riding a vehicle in real road environments. Results indicated the following differences: (1) The number of small saccadic eye-movements was greater in drivers than in passengers, whereas the number of large saccadic eye-movements was greater in passengers than in drivers, indicating that passengers tended to look at information irrelevant to safe driving. (2) The amplitude of the P1 component of eye-fixation-related brain potentials time-locked to the offset of large saccadic eye-movements was greater in drivers than in passengers, indicating that visual information processing load was lower in passengers. (3) The duration of eye-blinks was longer in passengers than in drivers, indicating that the arousal level of passengers was relatively low. These findings suggest that these electrophysiological indices can be useful measures for evaluating the attention of drivers while riding in Level 3 autonomous vehicles. Possible differences in the attentional state between drivers and passengers are discussed.