Most people believe drivers' road attention falters when they grip cell phones or punch in phone numbers on keypads while cruising busy streets.

However, Manbir Sodhi, an industrial engineering professor at the University of Rhode Island, says, "The debate surrounding cell phone use in cars has been directed toward concerns over holding the phone. Holding the phone isn't the main issue. Thinking is," he adds.

Sodhi and colleague Jerry Cohen, a psychology professor, measured the distraction levels of 25 volunteer drivers while they were engaged in cognitive activities, such as memorizing lists and using a cell phone.

To do this, they fitted their subjects with a head-mounted device hooked up to two eye-tracking cameras -- one focused on the driver's eyes, the other on the road.

Two volunteer researchers accompanied the motorists as they drove from the University of Rhode Island to Interstate 95 and back, covering about 18 miles in 45 minutes.

During the ride, one researcher oversaw the equipment from the back seat while the second sat in the passenger seat and gave the driver various instructions. Besides memorizing lists and operating a cell phone, tasks included adding and subtracting numbers.

In their analysis, which has been presented at various engineering conferences, the researchers found that when the motorists puzzled over their tasks, their eye movements decreased, shrinking their field of view -- or peripheral vision.

The pupils of their eyes tended to focus almost exclusively on the road directly in front of them, not to the side, suggesting reduced peripheral vision, Sodhi says.

Since researchers believe that eye movement and attention are linked, fewer eye movements indicate the drivers were paying more attention to their thought processes than to the road, the researchers say.

Interestingly, when drivers glanced away from the road to adjust the radio, for instance, their wide-ranging eye movements implied they were more vigilant than when they were speaking on a cell phone.

"People are risk averse -- most of us are not out to put others at risk and the data we have shows the amount of time people look away (to tune a radio, for example) is only about one-and-a-half seconds," Sodhi explains.

In contrast, when drivers use cell phones, their "tunnel vision" continues well after the phone call ends. Sodhi speculates that's because they're probably still thinking about the conversation.

The data shows that hands-free does not mean risk-free when it comes to cell-phone use behind the wheel, he contends.

A similar study conducted by Transport Canada, that nation's agency charged with road safety, supports Sodhi's and Cohen's work. A research team, led by cognitive psychologist and lead author Joanne Harbluk, assessed 21 drivers' degree of distraction while they performed a series of mental tasks transmitted to them over cell phones.

Harbluk says her study revealed that the drivers' attention was diverted more by what they were thinking than by what they were doing.

As the motorists listened and responded to the different directives, they spent less time looking at their dashboards, their rear view mirrors or to their left and right sides.

What's more, says Harbluk, their vehicle control deteriorated. "We found that when they were doing a very demanding cognitive task, they tended to brake harder. They put more pressure on the brakes, and that's consistent with less control."

Sodhi acknowledges that more research is needed to establish the link between cell phone use and concentration. Nevertheless, he says, drivers should be aware that mental distractions could prove hazardous, especially in congested traffic, poor weather and on winding roads.

"I believe higher levels of safety can be achieved by establishing cell-free zones," he says.

SOURCES: Manbir Sodhi, Ph.D., professor, industrial engineering, graduate program director, University of Rhode Island, Kingston, R.I., Joanne Harbluk, Ph.D., cognitive psychologist and human factors specialist, Transport Canada

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