“[Studying driving] turns out to be an excellent way to look at the limits of our attentional abilities, especially as we get older and we start to show significant declines,” says David Strayer, a psychology professor at the University of Utah. “It’s one of the most direct ways to be able to look at how attention works, how multi-tasking works.”

The unresolved debate over how to monitor older drivers points to not only the difficulty of regulating an important social activity, but of the underappreciated complexity of driving itself. Getting behind the wheel of a car may be an everyday activity, but it’s also the most dangerous and cognitively assaultive thing most of us do, and the only realm in which most people are regularly confronted with split-second, life-or-death decisions. That also makes it a valuable laboratory for the study of human attention, perception, and concentration - an arena where brain science is turning seeming abstractions into hard knowledge about important life skills.

And yet it also emerges that, as a group, elderly drivers are in far fewer accidents per capita than those in any other age group. Older people, it turns out, have a second set of skills that helps them make up for the ones that have diminished. For many people, old age brings a growing awareness of their own limits, and they compensate by driving less and avoiding situations that overtax their abilities. They don’t drive fast, or at night, or on the freeway, or during rush hour. They certainly don’t text and drive. Consciously or not, older drivers become savvy at working with what they have.

The risk is real. While there is a wide variation, people for the most part grow measurably worse at driving as they age. They experience a steady erosion of physical capabilities like strength, eyesight, and hearing. And perhaps more importantly, they also lose the specific cognitive skills that driving requires. Even a healthy aging brain suffers a declining ability to respond quickly, to take in one’s surroundings and identify potential dangers, and to balance and coordinate all of the different tasks that merely backing out of a driveway can involve.

For all the indignities that the elderly suffer, they aren’t typically accused of being a menace to society. Until, that is, they get behind the wheel of a car. Here in Massachusetts, a spate of high-profile accidents involving older drivers - a 92-year-old man who killed his wife by backing over her in a parking lot, an 88-year-old woman who allegedly hit and killed a 4-year-old girl in a crosswalk in Stoughton last month, a 93-year-old man who mistook the gas pedal for the brake and drove through the entrance of a Danvers Wal-Mart - have triggered calls on Beacon Hill for measures that would take older drivers off the roads as their abilities decline. Within families, it has heightened anxieties about whether it may finally be time to take the car keys away from elderly parents or grandparents.

And driving is far more than looking ahead on the road: There’s the complicated choreography of steering wheel, gas and brake, plus the turn signal, headlights, and windshield wipers; there might be a clutch, or air conditioning, or a radio. Drivers have to remember directions, check the mirrors, gauge distances, maintain speed and, not insignificantly, keep in mind where they set out for in the first place.

This rationing works well enough, he points out, until the object in our peripheral vision is something critically important, like a truck running a stop sign - which the eyes might physically see, but the brain never registers. “The information about that truck just hits the brain and dissolves,” he says, and afterward the driver literally has no idea what hit him. Work by Karlene Ball, a psychologist at the University of Alabama at Birmingham, has found that visual information processing abilities, or the lack thereof, matches up neatly with the likelihood of future crashes.

As we age, we get worse at doing that. The processing power of the brain declines, and, unconsciously, we begin to ration it. So stimuli at the margins of vision - information that a younger brain could afford to lavish its ample processing power on - instead get ignored, and the brain’s energy is saved for the ostensibly more important items directly in front of the eyes.

That simple slowdown is just one part of the interlocked set of thoughts and instincts involved in driving. Since it is a highly visual activity, the problem of slowing reflexes is compounded by the decline of our powers of perception. The eyes themselves are partly to blame: age can bring cataracts, glaucoma, and retinal detachment. But “seeing” is mostly a process that takes place in the brain, which stitches tiny snapshots from our constantly roaming eyes into a coherent visual whole.

The human brain remains the most complex computer on earth, but as it gets older, it literally slows down. The speed at which neurons can convey impulses drops off, and as a result, so do our reflexes. An 80-year-old driver who sees a motorcycle dart in front of his car is going to take a potentially fatal split-second longer to hit the brakes than a 30-year-old driver.

Better understanding how older brains respond to the increasing challenge of driving offers the promise of effectively identifying those people most likely to be a menace, whether they’re the impaired elderly, or physically adept but heedless teens. And it offers, as well, an immensely valuable look at how all of us might better mitigate the mental diminishments of age.

Similar tests are starting to be enlisted in the effort to keep potentially dangerous older drivers off the road. Maryland now includes a battery of tests evaluating aspects of visual processing, executive attention, and working memory as part of its evaluation process for drivers who are reported for non-alcohol-related problem driving - and many of those drivers are elderly. In Massachusetts, several hospitals offer assessment programs for older drivers whose families are worried about their driving abilities. In one of the most influential, Beth Israel Deaconess Medical Center’s DriveWise, drivers not only take a road test and have their vision and reflexes examined, they also are given a series of tests covering judgment, insight, memory, attention, and information-processing speed.

In recent years, as cognitive scientists have learned more about the driving brain, they’ve begun to create tests to monitor the particular mental skills driving demands. Over the past year and a half, Strayer has been running a study in which he gives subjects a memory and attention test meant to measure executive attention and other frontal cortex abilities. He then puts them through the paces in a driving simulator. In results that will be presented at this fall’s Psychonomic Society conference in Boston, Strayer found that elderly drivers do worse at both tests, and that the cognitive test results and driving results were strongly correlated - as were the test subjects’ real-world accident records.

To make matters worse, aging also shrinks the part of the brain responsible for “executive” functions like coordinating our working memory with our visual processing. Our frontal cortex, the bulging brain lobe between our temples that governs attention, planning and self-control, does not fully develop until we are in our twenties - that’s a big part of the reason teenagers (and teen drivers) can be so reckless and mercurial. But from the moment it’s mature, the frontal cortex begins to atrophy. According to Strayer, by age 70 it can be 20 percent smaller than it was at its peak, and as a result 70-year-olds can find it correspondingly harder to keep their minds from wandering. What can be a harmless and familiar attention gap around the house becomes a dangerous problem in the car.

Balancing all of these things is one of the hardest parts of driving, an unwieldy bundle of tasks that seems unmanageable when you first get behind the wheel, but eventually becomes second nature. But with old age they start to become hard again. The problem is, in part, simply one of memory. “Working memory” is the ability to mentally shuffle between several things without totally forgetting any one of them, a capacity that expands in late childhood. According to Earl Miller, a professor of neuroscience at MIT, young children can, on average, only keep two things in mind at any one time; for adults the number is usually four to five. After 65, however, working memory starts to shrink, settling eventually back around two. As a result, a 75-year-old driver is something like a highly preoccupied 40-year-old driver - someone simply less able to keep track of the myriad tasks driving entails. If he’s trying to remember the directions to a new grocery store along with what he’s supposed to buy there, it’s far harder to remember that the roads are icy.

Older drivers worry that such tests might pull them off the road prematurely, and even amount to a form of persecution against a demographic that, despite the headlines, causes relatively few accidents. But Strayer argues that a cognitive test in the driver’s license renewal process might actually help lift some of the stigma now attached to elderly drivers, and even move the debate away from age itself.

“There are going to be some people with good frontal cortex functioning who are 70 or 80 and are excellent drivers, and some people who are 60 whose frontal cortex is not functioning as well. We need to get away from age as the defining criterion,” he says.

A few psychologists have started to look at whether it’s possible to do more than just filter out problem drivers, and instead keep them on the road by honing their cognitive performance. Work by Arthur Kramer of the University of Illinois shows that the decline of abilities like working memory and executive attention can be slowed not only by cognitive exercises but even by moderate physical exercise. Ball, at the University of Alabama-Birmingham, found that a training program designed to sharpen visual processing cut in half the number of accidents those drivers had in the following six years; Posit Science, to which she is a scientific advisor, began selling a similar computer-based program earlier this month. Other researchers in the field are cautiously optimistic about such results.

The lessons we’re learning from older drivers have implications beyond road safety. Those who continue to drive into old age do so by adjusting to their limitations, carefully choosing when and where to drive. Some researchers suggest that such caution also means that fewer of the accidents that older drivers are in are serious, because they occur on smaller roads and at lower speeds. (Older drivers do have a high fatality rate, more likely because of their physical frailty than the violence of their crashes.)

Some of the measures that older drivers resort to would probably never even occur to a younger driver. Cindy Lustig, an assistant professor of psychology at the University of Michigan studying cognition and aging, says that many of her elderly test subjects will do a drive-by “dry run” in the days before they have an appointment at her lab. “They’ll say, ‘I drove by yesterday just to make sure I knew where it was at.’ That way they can establish the route for themselves in a low-pressure situation when they’re not worrying about the time and so on,” she says.

There is such a thing as too much caution, of course: driving too slowly on a highway can be as dangerous as driving too fast. But according to the researchers who study them, the wisdom of the elderly driver consists in treating driving as something dangerous - which, no matter how sharp our skills, it is.

And the lack of this sense, especially in younger drivers, is one of the most dangerous things on the road, as people ignore speed limits, fix their hair in the visor mirror, talk on the phone, or compose an iPod playlist as they drive. As a growing research literature makes clear, even people at the peak of their abilities are simply not as good at multitasking as they think. When their attention is siphoned away from the road, their likelihood of crashing jumps up. A road test published last month by Car & Driver Magazine found that texting behind the wheel degrades our reaction times more than being drunk.

What the brain tells us when tested in the crucible of driving is that even the sharpest thinkers have limits, and that husbanding mental resources is important. The skills that aging drivers learn are reflected in the rest of their lives as well - older people, for example, do better than younger ones when psychologists give them “real-world” prospective memory tests, such as remembering to call a phone number at a particular time on a particular day. That’s because older people, cognizant of the gaps in their memory, are more careful to do things like write a reminder in their calendar or put a note up on the refrigerator. Working within our capacities, it turns out, is an astute strategy no matter what we’re trying to get our brain to do. It’s a lesson that transcends the realm of neurology and starts to sound a lot like wisdom.

Drake Bennett is the staff writer for Ideas. E-mail drbennett@globe.com.

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