The short-term effect of verbally assessing drivers’ state on vigilance indices during monotonous daytime driving

To investigate the effects of verbal assessment of subjective driver state on objective indicators of vigilance state during a monotonous daytime drive, a real road driving study was conducted. During a 4-h drive participants’ subjective state (sleepiness, inattention, monotony) was assessed every 20 min by an investigator accompanying the drive. The assessment procedure consisted of roughly 1 min of verbal interaction. Physiological indicators (EEG alpha spindle rate, blink duration, heart rate) revealed a significant improvement of vigilance state during the communication episode as compared to a pre-assessment baseline. The activation persisted for up to 2 min following the end of the verbal interaction. Reaction times supported these findings by indicating a significant decrease after the communication. The P3 amplitude of the auditory event-related potential did not show any consistent results. It can be concluded that a short verbal assessment has positive effects on drivers’ vigilance state. However, these effects persist only for a very limited time. The implications of these findings for the frequency of verbal assessment during experimental studies and for the use of verbal communication as a fatigue countermeasure are discussed.

Research highlights
► Monotonous real road driving study with 26 participants.
► Investigation of the effects of verbal state assessment on drivers’ vigilance.
► Application of physiological and performance measures.
► Improvement of vigilance state during and shortly after verbal assessment.