Although previous studies have shown that Alzheimer's disease increases a person's risk for automobile accidents, not all individuals with mild dementia exhibit poor driving performance.
Investigators at Washington University School of Medicine in St. Louis have identified specific aspects of attention that may help in determining whether a demented individual can drive safely.
"A demented older adult's attentional capacity can sometimes be quite reduced, which makes it much more difficult for that person to deal with the complex environment that driving creates," says Janet Duchek, Ph.D., assistant professor of occupational therapy and lead author of a paper in the March 1998 issue of the Journal of Gerontology. John C. Morris, M.D., The Harvey A. and Dorismae Friedman Professor of Neurology, headed the research team.
The National Institute on Aging funded the study.
Alzheimer's disease affects about 4 million Americans, many of whom continue to drive throughout the early stages. A 1997 study of Alzheimer's and driving done by the same research team showed that 59 percent of individuals with mild dementia and 81 percent with very mild dementia passed their driving test and appeared to retain relatively safe driving skills.
In the current study, the researchers investigated aspects of attention to predict which individuals with Alzheimer's were still safe on the road.
Testing Driving Tasks
The investigators studied 136 participants recruited from the Washington University Alzheimer's Disease Research Center, which Morris co-directs. These individuals were still driving at the time of the study, had a valid driver's license, at least 10 years of driving experience and corrected visual acuity of at least 20/50. They were screened with the Clinical Dementia Rating scale, which was developed at Washington University and now is used worldwide. Some participants were healthy controls, whereas others had very mild or mild dementia.
The researchers administered various psychometric tests to access memory, intelligence and language levels and an on-road driving test, which also was developed at Washington University. They identified three visual tasks to test aspects of attentional processing that are important to driving. A visual search task, visual monitoring task and useful field of view task were presented on a computer that recorded each participant's response.
The visual search task measures selective attention by determining whether a person can detect a target letter in an array of distracting letters. The visual monitoring task measures the participant's ability to sustain attention by asking them to spot infrequent changes in a moving display. The useful field of view task tests the ability to localize target information in the periphery.
These tests were designed to simulate attentional capabilities that are important to driving, such as picking out a street sign amidst other distracting objects along the roadside or remaining vigilant enough, after traveling for a long time, to react to a deer suddenly jumping out in the road.
The results showed that participants who scored poorly on the attention tests also scored poorly on the driving tests, and those who did well on the attention tests, did well on their driving tests. Error rate in the visual search task was the best predictor of on-road driving performance. Poor drivers not only missed relevant target information in this task but also responded erroneously to target information that was not present in the array. These deficits in attentional control also were apparent in unsafe driving behaviors such as following the flow of traffic when making a left turn rather than attending to the oncoming traffic.
Focus On Screening And Intervention
Duchek believes that the results of the study could be used to design better screening batteries that can identify older adults who may be at risk for unsafe driving. Currently, static visual acuity is the only test elderly drivers are required to take in order to renew their license.
Morris says that even if visual acuity is relatively good, the brain's interpretation of the visual images may be impaired. "In order to drive safely, you must have the capacity to sort through many different kinds of visual information and concentrate on those stimuli that are most relevant for driving," he says.
Duchek also is working on developing an intervention program for older adults in an effort to optimize safe driving. "Most accidents of older adults occur at intersections, where there's a multitude of information to decipher," she says. "We want to design an intervention program that teaches older adults strategies for maximizing attentional processing and thus maintaining their driving skills as long as possible."
Morris explains that, though Alzheimer's patients may drive safely for a while, every person with the disease eventually will become an unsafe driver. "We do not wish to limit driving -- and hence an individual's independence -- too soon," he says. "The trick is to identify problems and intervene before a dangerous situation or actual crash occurs."
By Nicole Vines
Note: For more information, refer to: Duchek JM, Hunt L, Ball K, Buckles V, Morris JC. "Attention and Driving Performance in Alzheimer's Disease," Journal of Gerontology: Psychological Sciences, 53B, 130-141, March 1998.
Journal
Journal of Gerontology