Drivers have constrained cognitive resources under cognitive and visual distraction: Safety implications for transitions of control from vehicle automation.

The objective of this study was to evaluate the effect of both cognitive and visual distraction on drivers' gaze behaviour and takeover performance during an SAE Level 2 automated drive. A driving simulator study was conducted where drivers needed to take over control during a safety critical scenario i) while engaged in an auditory version of the 2-back task (cognitive distraction), ii) during ambient occlusion of the driving scene (visual distraction) or iii) a combination of both. In line with previous studies, results showed that, under the 2-back task, drivers showed a lower horizontal dispersion of gaze for scanning the environment. In the ambient occlusion condition, drivers compensated for the temporary absence of the driving scene by dispersing their gaze vertically and towards offroad areas of the environment. In terms of their takeover performance, the results found no significant differences between cognitive and visual distraction manipulations alone. However, drivers' performance was significantly worse, when both manipulations were combined. The findings suggest that both visual and cognitive distraction may tax drivers' cognitive resources and consequently impact their takeover performance. This finding is relevant for future development of driver monitoring systems, which should consider the impact of cognitive load on drivers' performance, even if their eyes are facing towards the road.