Although the human experience is truly a unique one, it’s comforting to know that we all share some experiences and emotions. For example, we were all excited the day we were handed our very first motor vehicle driver’s license. You know, the one with the awkward smile and terrible lighting. When we first received our license, we vowed to be the most upstanding motor vehicle operator, following all required safety precautions.

However, with time, there is one thing we all became guilty of: Distracted driving! According to the U.S. National Highway Traffic Safety Administration, distracted driving refers to any activity that diverts attention away from driving. The CDC posits three main types of distraction: visual – activities that require taking your eyes off the road, manual – activities that require taking your hands off the steering wheel, and cognitive – activities that result in taking your mind off driving. Visit that National Traffic and Safety Administration for facts and figures on motor vehicle accidents involving distracted driving in the U.S. 

It may (or may not) be worth noting that not all distracted driving results from being intentionally irresponsible. For example, we might not post a tweet or read a digital content blog post while driving. However, we might look away from the road to check the navigation system directions on our smartphones or turn up the radio (eating that pack of cookies while in traffic after work counts too!). In these latter instances of distracted driving, we might assume that we still can perform critical driving functions such as monitoring other vehicles, checking for pedestrians, etc., while briefly looking away from the road to engage in another task.

An assumption like this raises an interesting and important question for cognitive research: What is the combined effect of looking away from the main road and performing a secondary (distracting) task on driving performance? More pointedly, for tasks that require drivers to look away from the road, to what extent does where drivers look compare with the difficulty of the distracting task account for driving failures? 

In a recent study published in the Psychonomic Society journal Attention, Perception, & Psychophysics, Benjamin Wolfe and colleagues sought to disentangle the contribution of perceptual (looking away from the main road) and attentional (performing another task) factors of distracted driving on driving performance. 

In their study, participants viewed dashboard camera footage of a vehicle driving along the highways and surface roads of Boston, Massachusetts. They were instructed to fixate on a specified location on the screen and indicate each time the car in the same lane as the car (from which the video was captured) pressed the brakes (i.e., each time the brake lights appeared).

To measure the impact of changes to the driver’s perception in terms of where they look, participants looked for brake lights (and performed an additional task) and fixated on the

• center of the screen to simulate attention during normal, forward driving conditions
• right or left of center to simulate using peripheral vision while driving (to mimic looking away from the main road to turn up the radio, for example), or 
• directly below the center to simulate the usual location of windshield-mounted smartphones. 

Figure 1a below shows an illustration of fixation points.

While detecting brake lights, participants took part in a secondary task that varied in levels of difficulty. For the secondary, distracting task, participants were shown green crosses at one of the four fixation locations described above. Intermittently, one of the cross’s four arms briefly turned white before returning to green. The participant’s task was to indicate which arm turned white. In the more challenging version of this task, participants were told to hold in memory which arm changed color, but only report the change when a second arm changed color. In other words, participants withheld reporting the arm that previously changed until a second change was observed. See the examples in Figures 1b and 1c below.

To measure brake light detection performance as a function of fixation location and secondary task difficulty, the researchers recorded the proportion of correct brake responses, the proportion of missed brake lights, and reaction time for detecting brake lights. 

The results of the task were quite surprising! As shown in the figure below, brake light detection was significantly better when fixating at the center of the roadway than the right of the center and bottom center (no significant difference between the center and the left). Also, brake light detection was significantly better for the easier version of the distracting task across all fixation locations. However, there was no combined effect of fixation location and task difficulty on brake light detection (a.k.a. no interaction).  

A similar pattern of results was observed for reaction times. Participants were faster at detecting brake lights at the center fixation location than all other locations, but there was no combined effect of fixation location and task difficulty. Lastly, missed brake lights were higher for all non-center locations than the center location, but again there was no effect of the secondary task’s difficulty. 

One possibility for these results was that the secondary task did not vary enough in difficultly to detect a difference. As a result, the researchers followed up with a second experiment where they used a more difficult secondary task. Although they found that overall brake light detection performance was better in Experiment 1 with the easier secondary task, there remained no combined effect of fixation and the more difficult secondary task in Experiment 2. 

Taken together, these results suggest that while the difficulty of a distracting task might not have a large effect on driving failures, shifting our gaze in any direction away from the main road will! 

An important take-home message of this work is that any task, regardless of its difficulty, runs the risk of shifting our fixation from the main road while driving. Even in simple laboratory tasks, this shift in fixation can have detrimental effects on driving-relevant tasks, such as detecting the brake lights of the cars in front of us. So do yourself and all of us a favor: Watch the road!

Featured Psychonomic Society article:

Wolfe, B., Sawyer, B. D., Kosovicheva, A., Reimer, B., & Rosenholtz, R. (2019). Detection of brake lights while distracted: Separating peripheral vision from cognitive load. Psychonomic Bulletin & Review, DOI 10.3758/s13414-019-01795-4.