A very small number of people can drive safely while talking on the phone, University of Utah psychologists have found.
These individuals – described by the researchers as 'supertaskers' – constitute only 2.5 percent of the population.
The finding challenges current theories of multitasking.
"According to cognitive theory, these individuals ought not to exist. Yet, clearly they do, so we use the supertasker term as a convenient way to describe their exceptional multitasking ability," says psychologist Jason Watson.
"Given the number of individuals who routinely talk on the phone while driving, one would have hoped that there would be a greater percentage of supertaskers. And while we’d probably all like to think we are the exception to the rule, the odds are overwhelmingly against it."
The researchers assessed the performance of 200 participants over a single task - simulated freeway driving - and again with a cellphone conversation that involved memorizing words and solving math problems. Braking reaction time, following distance, memory, and math execution were all tested.
As expected, results showed that performance suffered across the board while driving and talking on a hands-free cell phone.
For most people, it took 20 percent longer to hit the brakes when needed and following distances increased 30 percent. Memory performance declined 11 percent, and the ability to do math problems fell 3 percent.
The results are in line with previous studies showing that talking on a cellphone impairs driving performance by a similar amount to drinking.
However, when supertaskers talked while driving, they displayed no change in their normal braking times, following distances or math ability, and their memory abilities actually improved by three percent.
The team is now studying expert fighter pilots, on the assumption that those who can pilot a jet aircraft are also likely to have extraordinary multitasking ability.
The study is available here.