This U.S. study was conducted to examine the combined effects of visual and cognitive distraction on driver behavior. A total of 16 participants took part in the study and their ages ranged from 35 to 55 years, with a mean age of 45. The simulator road task in this study involved a straight, five-lane suburban roadway comprised of two lanes in each direction separated by a center turning lane. Participants were instructed to drive 45 mph and a cruise control was activated automatically when drivers reached the designated speed. Participants could deactivate the cruise control by using the brake. During the drive, distraction was manipulated using three in-vehicle secondary tasks. A visual task consisted of participants looking at a map display and selecting an arrow to match the target on top of the display. A cognitive task required participants to listen to audio clips that described the path of a person and then verbally identify which cardinal direction (e.g., east, north, and southwest) that this person faced at the end of the path. Finally, the combined visual-cognitive task required participants to listen to an audio clip similar to the one in the cognitive task and identify the orientation of the person using the touch screen display.
Results of the visual and combined task revealed that reaction time to the events increased. This suggested that visual distraction degrades hazard detection. When examining steering neglect and over-compensation, these events occurred most frequently during the visual and combined secondary tasks (visual: 90%; combined: 80%), but accounted for only 40% of the lane departures during the cognitive task. In contrast, the cognitive task actually reduced off-road glances and improved lane-keeping performance, but made steering more abrupt.
Liang, Y., & Lee, J. D. (2010). Combining cognitive and visual distraction: less than the sum of its parts. Accident Analysis & Prevention, 42(3), 881-890.