WASHINGTON (American Psychological Association) -- Keeping your eyes on the road is obvious advice to drivers. Now, new research published in the March issue of the American Psychological Association's (APA) Journal of Experimental Psychology: Applied, has demonstrated that keeping one's mind on the road is important as well.

While research has tried to demonstrate the potential danger of external distractions (looking at road signs or a map while driving), previous studies have not focused on internal distractions such as one's thoughts. In their study, psychologists M.A. Recarte, Ph.D., and L.M. Nunes, Ph.D., of the Universidad Complutense, in Madrid, Spain, examined whether a driver's eye movements would be affected by additional verbal and visual tasks to the point where the driver's ability to pay attention to his or her surroundings is sacrificed.

Twelve drivers between the ages of 21 and 37 drove 43 km on two highways and 40.6 km on two secondary roads (a total of 83.6 km). Their eye movements were recorded while they performed verbal and spatial-visual tasks. On each route they performed two verbal tasks (repeating words starting with a certain letter) and two spatial-imagery tasks (imagining the letters of the alphabet, one by one, from A to Z and describing the letters as far as which letters were "open" or "closed").

Pupil size and amount of time spent viewing a particular object were used as indicators of how much visual attention was directed at a particular object. The researchers also measured how often each driver checked his or her side and rear mirrors and the speedometer on the dashboard.

The authors found that during spatial-imagery tasks, drivers fixated on certain points longer and, therefore, glanced at their mirrors and dashboard less. The driver's attention was affected more by the spatial-imagery tasks than by the verbal tasks. "It seems that during the visual tasks, a person's eye freezes up, and the eye's visual inspection window decreases, which impairs perception of the environment, " said Dr. Recarte.

"When a person's visual inspection window is reduced," said Dr. Recarte, "peripheral visual capacity can be affected. Mirror use to evaluate the surrounding traffic can also be diminished, and this can make it more difficult to detect changes in traffic."

"The potential hazard of using a cellular phone is one thing," said Dr. Nunes. "But add in-depth conversation that requires a considerable amount of mental effort, like recalling a route on a map, performing a mathematical computation or discussing an emotional charged subject, and you compound an already risky behavior."

"Our research shows for the first time that doing mental calculations while driving," said the authors, "may make some people pay less attention to the road ahead and put themselves more at risk for an accident. On the other hand, some secondary activity (listening to music) can have beneficial effects. Drivers need to know how much they can do or think while driving and know when to stop the activity to concentrate on the road."

"With our research," said Dr. Nunes, "we are trying to help people know a little more about themselves to give them the opportunity to learn better criteria to decide how much they want to use their minds while driving."