Time-Sharing of a Visual In-Vehicle Task while Driving: Effects of Four Key Constructs

Omer Tsimhoni, Paul Green

What affects time-sharing of a visual in-vehicle task while driving? Four key constructs are considered: (1) time pressure to complete the in-vehicle task, (2) interference of concurrent driving, (3) postponed processing while looking away from the display. and (4) the cost of task partitioning (due to forgetting and the need to reacquire last point of gaze). To examine these effects, 24 drivers were instructed to plan routes to destinations on an electronic map while driving a simulator at three levels of visual demand of the concurrent driving task, and then while parked. To force task partitioning while parked, the map was intermittently occluded. There were six combinations of viewing and occlusion time.

Total task time increased significantly from 11.0 s while parked to 19.5 s on a sharp curve. Total glance time at the display, however, remained unchanged in all 4 levels of visual demand (12.0+/-0.6 s). Thus, the time pressure imposed by driving resulted in shorter glances at the display, but subjects maintained constant total glance time. Interference from concurrent driving was not significant enough to negate this effect. With task occlusion of 1 s, when viewing time decreased from 2 to 1 s, total task time increased from 5.9 to 19.7 s. Total glance time, however, remained unchanged (10.4+/-0.4 s) in all 6 timing combinations. Thus, the costs of task partitioning and the benefits of postponed processing were either small or cancelled each other in this task. The task occlusion method, as described in this paper, provides a framework for understanding the effects of in-vehicle tasks on driving.

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