Post by misty on Dec 9, 2008 9:04:52 GMT -5
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Driving in Adults with ADHD Mimics Intoxicated Drivers
Although considerable research on the adverse impact of ADHD on adults has focused on employment issues, another important issue concerns the possibility that attention deficits associated with ADHD might lead to impaired driving performance. Studies indicating that adults with ADHD are more likely to engage in illegal driving behavior such as speeding, to have their license revoked, and to be involved in accidents has promoted efforts to better understand the nature of their driving difficulties.
These efforts have utilized sophisticated driving simulators which allow for objective assessments of driving skills under controlled test conditions. Although the use of driving simulators enables precise comparisons of driving behavior in adults with and without ADHD to be made, understanding the 'real world' importance of significant differences that emerge in these studies is not always clear. An interesting solution to this issue implemented in the studies described below was to compare the simulated driving performance in adults with ADHD with the performance of adults who 'drove' while intoxicated [Weafer et.al., (2008). Simulated driving performance of ADHD with ADHD: Comparisons with alcohol intoxication. Experimental and Clinical Psychopharmacology, 16, 251-263.]
- Study 1 -
Participants were 15 adults with a confirmed diagnosis of ADHD (5 men and 10 women) with an average age of 21.5 year and 23 control participants (13 men and 10 women) of similar age. Their driving behavior was tested using a sophisticated computerized driving simulator that allows for precise measurements of critical driving parameters during a simulated test drive. During the test, which simulated a 20-minute drive in a rural wooded area, participants were instructed to remain in their 'lane' and maintain a 55 mph speed. Three important aspects of driving behavior were measured during the simulated drive. These were:
Deviation of lane position - This refers to the degree of adjustment a driver implements to maintain a desired position within the lane. Greater within-lane deviation indicates he driver is having difficulty maintaining the desired position and is seen in individuals whose driving is impaired by fatigue or alcohol intoxication.
Steering rate - This is a measure of the average speed with which a driver turns the steering wheel to maintain position on the road. Sober drivers typically use continuous smooth steering to maintain their position; in contrast, intoxicated drivers are often slow to initiate steering adjustments and more likely to make abrupt steering movements, a more dangerous way to steer.
Driving speed variation - This refers to participants' ability to maintain a constant driving speed; difficulty doing so is also characteristic of drivers who are intoxicated.
Adults with ADHD were tested when they had been off medication for 24 hours. Comparison adults were tested in 2 conditions - when sober and after ingesting sufficient alcohol to attain a blood alcohol level of 80 mg/kg, the legal threshold to be considered driving while intoxicated.
- Results -
As expected, the driving of non-ADHD adults deteriorated markedly when they were intoxicated. When intoxicated they had greater difficulty maintaining lane position, they made more frequent quick and abrupt steering moves, and their driving speed showed greater variability. This driving profile is typical for intoxicated drivers and increase the risk for motor vehicle accidents. Within both groups, however, there were very few actual crashes recorded during the simulation.
Although adults with ADHD did not show greater driving speed variability than sober controls, they had greater difficulty maintaining the proper lane position and also made more quick and abrupt steering maneuvers. In fact, their driving performance was surprisingly similar to how control participants drove while intoxicated.
- Study 2 -
The goal of study 2 was to investigate the impact of alcohol use on the driving of adults with ADHD as well as their ability to evaluate their driving ability. Eight adults with a confirmed ADHD diagnosis and 8 control adults served as participants. These subjects completed a simulated driving test identical to that used in study one in 3 different conditions: when sober, after a low dose of alcohol that did not raise blood alcohol level to the legal limit, and after a higher dose that brought them to the legal threshold for intoxication.
In addition to measuring simulated driving performance, participants also rated their perceived intoxication level and their present ability to drive. These ratings were completed to learn whether adults with and without ADHD differed in their ability to monitor their intoxication level and their ability to drive.
- Results -
For lane deviation and steering speed, adults with ADHD showed impaired driving performance compared to controls in all 3 conditions. For speed deviation, differences were found only after ingesting alcohol and group differences were strongest for the lower dose.
Results from the self-perception ratings were also interesting. Compared to controls, adults with ADHD reported significantly lower ratings of perceived intoxication after ingesting the higher dose of alcohol. In addition, in all 3 conditions, adults with ADHD perceived themselves as more able to drive than control participants.
- Summary and Implications -
Results indicate that young adults with ADHD have significantly poorer driving skills than other adults. On a simulated driving test, they had greater difficulty maintaining the proper lane position and were more likely to adjust their course with quicker and more abrupt steering maneuvers. On these dimensions, which have important associations with driving safety, their performance was similar to that of comparison adults driving at the legal threshold for alcohol intoxication.
Results from study 2 indicate that preexisting driving deficits associated with ADHD are further exacerbated by alcohol. A noteworthy finding from this study was that the one area where adults with ADHD did not show impaired driving relative to sober controls, i.e., the ability to maintain a constant speed, showed significant deterioration even after a relatively small amount of alcohol was ingested. Thus, drinking and driving is even more dangerous for young adults with ADHD than for other young adults. The authors suggest that because alcohol disrupts the ability to divide attention between different driving requirements, i.e., stay in one's lane, check one's speed, it may create particular problems for adults who already have attentional difficulties.
Another important finding from study 2 was that adults with ADHD overestimated their driving abilities and underestimated their degree of intoxication. This is similar to studies in children with ADHD who have been found to consistently overestimate their abilities in academic and social domains. Unfortunately, overestimating one's ability to drive while intoxicated is far more dangerous.
While these results are concerning, it should be noted that not all adults with ADHD demonstrated the driving difficulties reported by the authors. It is always important to remember that when significant group differences are found it does not mean that everyone in one group performed poorer than everyone in the other group. Thus, many adults with ADHD are likely to drive as safely as anyone on the road and one definitely cannot assume that just because an adult has ADHD, he/she must be a risky driver.
The authors raise several important limitations of their study. First, the sample was small which raises questions about the robustness of the findings. While this is true, it should also be noted that results from the 2 studies were highly consistent, and that this replication allows one to have greater confidence in the findings. It should also be noted, however, that the average age of their sample was roughly 21. Thus, they were working with very young adults and whether similar results would be found in older adults with ADHD is unknown. In fact, this would be an important follow up to this research.
It is also important to recognize that the simulated driving tests occurred when adults were off their medication. The results therefore say nothing about how young adults with ADHD drive while appropriately medicated. The authors chose this strategy because many adults with ADHD do not take medication, do not take it regularly, or may take it during the work day but not while driving on evenings and weekends, and they wanted to assess driving performance in the absence of benefits that medication may provide. Examining whether medication treatment eliminates the driving difficulties reported in this study would thus be another important question to pursue.
Finally, one might question whether simulated driving performance - no matter how technologically sophisticated the simulator - provides an accurate assessment of real world driving. As the authors note, perhaps simulated driving may overestimate poor or reckless driver behavior "...because it does not engender the same degree of driver motivation as actual driving because there is no actual risk of personal injury." However, it may also be argued that the simulator over states drivers' ability - especially for adults with ADHD - because the distractions typically encountered in real-life driving, e.g., talking with passengers, cell phones, listening to music, are not present. These distractions would seem to enhance the need for divided attention, something that adult drivers with ADHD are more likely to struggle with.
These limitations not withstanding, findings from this study demonstrate the potentially serious driving deficiencies in young adults with ADHD. Research that follows from this study should seek to replicate the findings with a larger and more diverse sample that includes older adults; the degree to which medication treatment reduces the problems reported here should also be examined. Given the seriousness of concerns raised by these results, however, it is worth considering whether specialized driver training programs for individuals with ADHD could be developed that would promote safe driving skills in adolescents that would continue into young adulthood. I am not aware of any such programs that are underway or being developed, but it seems like a potentially important area to pursue.
Driving in Adults with ADHD Mimics Intoxicated Drivers
Although considerable research on the adverse impact of ADHD on adults has focused on employment issues, another important issue concerns the possibility that attention deficits associated with ADHD might lead to impaired driving performance. Studies indicating that adults with ADHD are more likely to engage in illegal driving behavior such as speeding, to have their license revoked, and to be involved in accidents has promoted efforts to better understand the nature of their driving difficulties.
These efforts have utilized sophisticated driving simulators which allow for objective assessments of driving skills under controlled test conditions. Although the use of driving simulators enables precise comparisons of driving behavior in adults with and without ADHD to be made, understanding the 'real world' importance of significant differences that emerge in these studies is not always clear. An interesting solution to this issue implemented in the studies described below was to compare the simulated driving performance in adults with ADHD with the performance of adults who 'drove' while intoxicated [Weafer et.al., (2008). Simulated driving performance of ADHD with ADHD: Comparisons with alcohol intoxication. Experimental and Clinical Psychopharmacology, 16, 251-263.]
- Study 1 -
Participants were 15 adults with a confirmed diagnosis of ADHD (5 men and 10 women) with an average age of 21.5 year and 23 control participants (13 men and 10 women) of similar age. Their driving behavior was tested using a sophisticated computerized driving simulator that allows for precise measurements of critical driving parameters during a simulated test drive. During the test, which simulated a 20-minute drive in a rural wooded area, participants were instructed to remain in their 'lane' and maintain a 55 mph speed. Three important aspects of driving behavior were measured during the simulated drive. These were:
Deviation of lane position - This refers to the degree of adjustment a driver implements to maintain a desired position within the lane. Greater within-lane deviation indicates he driver is having difficulty maintaining the desired position and is seen in individuals whose driving is impaired by fatigue or alcohol intoxication.
Steering rate - This is a measure of the average speed with which a driver turns the steering wheel to maintain position on the road. Sober drivers typically use continuous smooth steering to maintain their position; in contrast, intoxicated drivers are often slow to initiate steering adjustments and more likely to make abrupt steering movements, a more dangerous way to steer.
Driving speed variation - This refers to participants' ability to maintain a constant driving speed; difficulty doing so is also characteristic of drivers who are intoxicated.
Adults with ADHD were tested when they had been off medication for 24 hours. Comparison adults were tested in 2 conditions - when sober and after ingesting sufficient alcohol to attain a blood alcohol level of 80 mg/kg, the legal threshold to be considered driving while intoxicated.
- Results -
As expected, the driving of non-ADHD adults deteriorated markedly when they were intoxicated. When intoxicated they had greater difficulty maintaining lane position, they made more frequent quick and abrupt steering moves, and their driving speed showed greater variability. This driving profile is typical for intoxicated drivers and increase the risk for motor vehicle accidents. Within both groups, however, there were very few actual crashes recorded during the simulation.
Although adults with ADHD did not show greater driving speed variability than sober controls, they had greater difficulty maintaining the proper lane position and also made more quick and abrupt steering maneuvers. In fact, their driving performance was surprisingly similar to how control participants drove while intoxicated.
- Study 2 -
The goal of study 2 was to investigate the impact of alcohol use on the driving of adults with ADHD as well as their ability to evaluate their driving ability. Eight adults with a confirmed ADHD diagnosis and 8 control adults served as participants. These subjects completed a simulated driving test identical to that used in study one in 3 different conditions: when sober, after a low dose of alcohol that did not raise blood alcohol level to the legal limit, and after a higher dose that brought them to the legal threshold for intoxication.
In addition to measuring simulated driving performance, participants also rated their perceived intoxication level and their present ability to drive. These ratings were completed to learn whether adults with and without ADHD differed in their ability to monitor their intoxication level and their ability to drive.
- Results -
For lane deviation and steering speed, adults with ADHD showed impaired driving performance compared to controls in all 3 conditions. For speed deviation, differences were found only after ingesting alcohol and group differences were strongest for the lower dose.
Results from the self-perception ratings were also interesting. Compared to controls, adults with ADHD reported significantly lower ratings of perceived intoxication after ingesting the higher dose of alcohol. In addition, in all 3 conditions, adults with ADHD perceived themselves as more able to drive than control participants.
- Summary and Implications -
Results indicate that young adults with ADHD have significantly poorer driving skills than other adults. On a simulated driving test, they had greater difficulty maintaining the proper lane position and were more likely to adjust their course with quicker and more abrupt steering maneuvers. On these dimensions, which have important associations with driving safety, their performance was similar to that of comparison adults driving at the legal threshold for alcohol intoxication.
Results from study 2 indicate that preexisting driving deficits associated with ADHD are further exacerbated by alcohol. A noteworthy finding from this study was that the one area where adults with ADHD did not show impaired driving relative to sober controls, i.e., the ability to maintain a constant speed, showed significant deterioration even after a relatively small amount of alcohol was ingested. Thus, drinking and driving is even more dangerous for young adults with ADHD than for other young adults. The authors suggest that because alcohol disrupts the ability to divide attention between different driving requirements, i.e., stay in one's lane, check one's speed, it may create particular problems for adults who already have attentional difficulties.
Another important finding from study 2 was that adults with ADHD overestimated their driving abilities and underestimated their degree of intoxication. This is similar to studies in children with ADHD who have been found to consistently overestimate their abilities in academic and social domains. Unfortunately, overestimating one's ability to drive while intoxicated is far more dangerous.
While these results are concerning, it should be noted that not all adults with ADHD demonstrated the driving difficulties reported by the authors. It is always important to remember that when significant group differences are found it does not mean that everyone in one group performed poorer than everyone in the other group. Thus, many adults with ADHD are likely to drive as safely as anyone on the road and one definitely cannot assume that just because an adult has ADHD, he/she must be a risky driver.
The authors raise several important limitations of their study. First, the sample was small which raises questions about the robustness of the findings. While this is true, it should also be noted that results from the 2 studies were highly consistent, and that this replication allows one to have greater confidence in the findings. It should also be noted, however, that the average age of their sample was roughly 21. Thus, they were working with very young adults and whether similar results would be found in older adults with ADHD is unknown. In fact, this would be an important follow up to this research.
It is also important to recognize that the simulated driving tests occurred when adults were off their medication. The results therefore say nothing about how young adults with ADHD drive while appropriately medicated. The authors chose this strategy because many adults with ADHD do not take medication, do not take it regularly, or may take it during the work day but not while driving on evenings and weekends, and they wanted to assess driving performance in the absence of benefits that medication may provide. Examining whether medication treatment eliminates the driving difficulties reported in this study would thus be another important question to pursue.
Finally, one might question whether simulated driving performance - no matter how technologically sophisticated the simulator - provides an accurate assessment of real world driving. As the authors note, perhaps simulated driving may overestimate poor or reckless driver behavior "...because it does not engender the same degree of driver motivation as actual driving because there is no actual risk of personal injury." However, it may also be argued that the simulator over states drivers' ability - especially for adults with ADHD - because the distractions typically encountered in real-life driving, e.g., talking with passengers, cell phones, listening to music, are not present. These distractions would seem to enhance the need for divided attention, something that adult drivers with ADHD are more likely to struggle with.
These limitations not withstanding, findings from this study demonstrate the potentially serious driving deficiencies in young adults with ADHD. Research that follows from this study should seek to replicate the findings with a larger and more diverse sample that includes older adults; the degree to which medication treatment reduces the problems reported here should also be examined. Given the seriousness of concerns raised by these results, however, it is worth considering whether specialized driver training programs for individuals with ADHD could be developed that would promote safe driving skills in adolescents that would continue into young adulthood. I am not aware of any such programs that are underway or being developed, but it seems like a potentially important area to pursue.
