'Hands free' isn't mind free: Performing even easy tasks impairs driving

March 10, 2006

Do you think using a hands-free device makes it okay to talk on a cell phone while driving? Despite the well-intended laws requiring the use of hands-free devices, a driver's performance is impaired when distracted by even the simplest tasks, whether or not both hands are on the steering wheel.

Until now, the slowing of reaction time under multitasking conditions, referred to as the psychological-refractory-period (PRP) effect, has been studied mainly with simple tasks in laboratory settings. But a new research study presents a unique perspective of how the PRP effect pertains to driving, perhaps the most ubiquitous real-world task where non-optimal performance can have serious consequences.

The study was conducted by University of California, San Diego scientists Jonathan Levy and Harold Pashler, along with Erwin Boer of ERB Consulting. Their research appears in the article "Central Interference in Driving: Is There Any Stopping the Psychological Refractory Period?" in the March issue of Psychological Science.

Forty students participated in the study, which involved driving a car simulator, composed of a large plasma screen, a steering wheel, and gas and brake pedals located on the floor. In the simulation, students followed a lead car and were instructed to brake as soon as they saw the illumination of the lead car's brake lights (they were instructed to avoid gradual slowing even if it was possible). While subjects performed the braking task, they occasionally were required to respond to a concurrent easy task, where a stimulus – either a light flash in the lead car's rear window or an auditory tone – was randomly presented once or twice. Participants indicated the stimulus' frequency, sometimes by pressing a key on the steering wheel once or twice and sometimes by saying aloud the words "one" or "two."

Subjects in the study braked more slowly when the easy task's stimulus was presented simultaneously or shortly before the brake lights, thereby demonstrating the PRP effect occurs with "real-world" tasks. Participants were 174 milliseconds slower at braking when the two tasks occurred at the same time than when they were presented 350 milliseconds apart. While 174 milliseconds may sound tiny, it translates to 16 feet in a car going 65 mph. Responses were just as slow with auditory stimuli (tones) and vocal responses compared to visual stimuli (light flashes) and manual responses, meaning that even tasks that do not have a visual or manual component (like hands-free talking) can still lower response times when driving.

"This study joins a growing body of research showing that 'freeing up the hands' does not result in faster brake response times," says Levy, the lead author on the project. He adds, "not everyone appreciates the processing cost while driving imposed by carrying out other tasks, even easy ones."

Source: Association for Psychological Science

Explore further: Tech disruption hangs over automakers at Frankfurt show

Related Stories

Amid China woes, European carmakers look to home market

September 15, 2015

European automakers are shrugging off the threat to sales from China's struggling economy and focusing instead on growing demand in their home market, where competition is getting increasingly fierce, particularly for mass ...

A flexible solution for secure IT in cars

August 3, 2015

Today, almost everything in your car is managed by an electronic control unit (ECU). The problem is that these minicomputers are increasingly coming under attack. Fraunhofer researchers have now developed a platform that ...

Recommended for you

Could 'The Day After Tomorrow' happen?

October 9, 2015

A researcher from the University of Southampton has produced a scientific study of the climate scenario featured in the disaster movie 'The Day After Tomorrow'.

Horn of Africa drying ever faster as climate warms

October 9, 2015

The Horn of Africa has become increasingly arid in sync with the global and regional warming of the last century and at a rate unprecedented in the last 2,000 years, according to new research led by a University of Arizona ...

A mission to a metal world—The Psyche mission

October 9, 2015

In their drive to set exploration goals for the future, NASA's Discovery Program put out the call for proposals for their thirteenth Discovery mission in February 2014. After reviewing the 27 initial proposals, a panel of ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.