Complex Mental Tasks Can Reduce Driver Awareness

A study from researchers in Spain that tested actual highway drivers confirms that mental workload can interfere with the capacity to detect visual targets, discriminate among them and select a response. The study also found hands-free phone conversations to be as safe, or as risky, as talking to a passenger, depending on the demands of the conversation.

It probably comes as no surprise to many of us that higher-level mental tasks take attentional resources away from the road, resulting in those all-too-familiar post-accident reports of "I didn't expect it" or "I saw it too late." Already knowing that external distractions divert drivers, the authors, from Spain's Public Administration for Traffic Safety and the Universidad Complutense in Madrid, studied internal distractions produced by the driver's own thoughts or cognitive activity unrelated to the task of driving.

"It is easy to understand how one cannot see because of not looking," they explain in an article appearing in the Journal of Experimental Psychology: Applied, "but it is less obvious to explain how one looks but does not see."

The two-psychologist team studied 12 adults who drove for about four hours on the highway north from Madrid. They used a standard Citroen with an unobtrusive eye-tracking system that allowed them to study gaze and ocular fixation for signs of attention and distraction as drivers performed certain mental tasks. Drivers also were tested by an automatic system that periodically flashed spotlights in the driver's visual field, to which drivers responded using buttons placed ergonomically near the steering wheel.

The researchers analyzed how drivers scanned the road scene, including use of the speedometer and mirrors. Researchers also measured how often the drivers glanced at the flashing spotlights to identify them before they responded.

The effects of the performance of several mental tasks were compared with the effects of ordinary driving (the control condition). Drivers listened to recorded audio messages with either abstract or concrete information. Next, they were asked to repeat what they had just heard.

Although the more receptive tasks listening and learning had little or no effect on performance, there were significant differences in almost all of the measures of attention when drivers had to repeat the content of the audio message they had heard.

Drivers also performed other tasks, either live or by phone. One was mentally changing between Euros and Spanish pesetas, either with an researcher in the car, talking to the driver, or with the driver speaking by hands-free phone. Another was a memory task (giving detailed information about where they were and what they were doing at a given day and time). Both tasks produced remarkable distraction effects.

"When performing complex mental tasks," the authors say, "the percentages of detected targets and/or correct responses decreased significantly."

Researchers found drivers glanced at the targets less frequently, and gave a higher percentage of responses without directly looking in their direction. Also during these tasks, the targets (if looked at) were detected later and glanced at for less time, which would cause poorer identification.

In other words, say researchers, mentally distracted drivers still know how to drive, but don't see things well or fast enough to safely use their skills.

In the experimental variation that examined the impact of hands-free phone conversation, message complexity made the difference. The relative safety of low-demand phone conversation if hands-free and voice-operated appeared to be about the same as that of live conversation. Thus, the authors concluded, "Complex conversations, whether by phone or with a passenger, are dangerous for road safety."

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