driving an automobile is a primary means of mobility for many older adults , allowing them to access medical services and social contacts and participate in their communities .
driving is associated with independence , quality of life , and better health and , for many older adults , forms a central part of their identity .
research shows that , in canada , older adults use personal vehicles for almost 90 percent of their daily travel , serving as the driver in approximately 75 per cent of those trips .
driving is so important in the lives of older adults that it is often referred to as an instrumental activity of daily living ( iadl ) .
while it forms a central part of identity and contributes to quality of life , driving among older adults comes with an increased risk of motor vehicle collisions , injury , and mortality due to those collisions .
the increased injury risk among older drivers represents a significant public health issue and an economic burden which is particularly troublesome given that , in canada , drivers over 65 years are the fastest growing segment of the licensed population .
driving is a multifactorial behavior drawing upon multiple physical , cognitive , and sensory domains at the level of the driver . a large and significant body of research points to a relationship between deficits in attention and fitness to drive [ 68 ] .
age - associated changes in cognition , sensory function , and health increase older drivers ' risk of collision , and the identification of at - risk drivers is an important component in reducing traffic - related injuries and fatalities as well as in identifying remediation needs .
cognition is an essential function for safe driving and changes in cognition due to the onset of neurodegenerative conditions can increase older drivers ' risk of collision .
some reports suggest that the risk of motor vehicle collisions ( mvc ) among individuals with disorders that impair cognition has been shown to be comparative to the risk of driving a vehicle under the influence of alcohol . unlike intoxicated drivers , drivers with cognitive deficits are impaired 24 hours a day , 7 days a week [ 1012 ] .
dementia is not a normal part of aging ; however , estimates suggest that 480,600 canadians are impacted by dementia ( i.e. , 1.5% of the canadian population ) , a prevalence that is projected to increase to 1,125,200 individuals ( i.e. , 2.8% of the canadian population ) by 2038 .
drivers with dementia are not a homogenous group as they often start off with mild cognitive impairments and eventually experience more serious declines .
research has demonstrated that , on average , drivers with dementia continue to drive for approximately 4 years after the onset of their symptoms .
in addition , it has also been found that one in four canadians with serious cognitive impairments continue to have a valid driver 's license and continue to drive regularly . with the current demographic trends demonstrating an aging population and an associated projected increase in the prevalence of dementia , it is imperative to understand the driving abilities of individuals diagnosed with dementia .
alzheimer 's disease ( ad ) is the most common form of dementia , accounting 70% of the cases .
ad is characterized by impairments in reasoning , planning , language , attention , and memory .
the body of evidence examining driving performance among individuals with ad has grown in recent years ( e.g. , [ 9 , 11 , 1921 ] ) .
for example , our previous work examined simulated driving performance of drivers with mild alzheimer 's disease in comparison to neurologically normal drivers .
in particular , we found that mild ad drivers performed poorer in a portable driving simulator in comparison to controls .
we also observed that , within the sample of drivers with dementia , measures of attention and visual space perception predicted driving performance better than a test of general cognition ( i.e. , the mini - mental state exam ) . while there is a growing body of literature on the driving abilities of older adults diagnosed with ad ,
another prevalent form of dementia is dementia with lewy bodies ( dlb ) , accounting for 210% of all dementia cases [ 17 , 23 , 24 ] .
dlb is a neurodegenerative disease producing a combination of cognitive impairment , parkinsonism , and mental disturbances in the form of hallucinations .
the average age of onset of dlb is 67 years , with males being more affected than females .
the average duration of the illness is nine years , although estimates of speed and progression vary considerably from study to study .
the pathological hallmark of dlb is the presence of lewy bodies in neurons . in most dementias , such as ad and vad ,
however , in dlb , the most common presenting feature , in 3365% of all cases , are visual hallucinations . as with most dementias ,
it is postulated that the pattern of dementia is a mixed corticosubcortical dementia since patients have significant frontal - subcortical dysfunction ( i.e. , impairment of attention , visuospatial function , executive functions , thought , regulatory changes in praxis , and gnosis ) .
although memory impairments are not usually found in the beginning stages of dlb , they become marked once the disease has fully developed .
one of the most impaired cognitive abilities present in dlb is visuoperceptual and spatial functions . within this domain ,
it is theorized that this impairment may cause their visual hallucinations , which is a hallmark of the disease .
in addition , patients with dlb have difficulty with visual construction and spatial functions , which can be seen through difficulty putting things together ( i.e. , blocks ) or navigating in an environment .
in addition to visuoperceptual and spatial impairments , patients with dlb also suffer from attentional deficits .
ballard and colleagues   demonstrated that patients with dlb had slowed processing speed , attentional impairments , and fluctuations in attentional impairments .
given that dlb accounts for approximately 10% of all dementia diagnoses , it is critically important to better understand the driving behaviour of this clinical population as a first step in promoting road safety and reducing the occurrence of costly collisions .
interestingly , carr and o'neill   note that there are currently no studies that have examined driving behaviour among individuals with dlb .
thus , the purpose of the present study was to examine the simulated driving performance of individuals diagnosed with dlb . it was hypothesized in addition to exhibiting poorer performance in the driving simulator that dlb drivers ' deficits in visuospatial skills would emerge as a significant predictor of simulated driving performance .
a group of individuals diagnosed with mild dementia with lewy bodies ( dlb ) ( n = 15 ) and a group of neurologically healthy older adult controls ( n = 21 ) participated in the present study .
all participants were over the age of 65 years , english speaking , and held a valid driver 's license .
the mean age of the mild dlb group was 76.4 years ( sd = 6.59 ) with a range of 68 to 88 years , the mean years of education was 14.20 ( sd = 4.55 ) , and the group was comprised of 6 women and 9 men .
the mean age of the control group was 77 years ( sd = 5.86 ) with a range of 68 to 86 years , the mean years of education was 13.14 ( sd = 3.18 ) , and the group was comprised of 10 women and 11 men .
the participants diagnosed with mild dlb were recruited from the memory disorders clinic at the bruyre continuing care center ( i.e. , a tertiary care facility ) in ottawa , on ( canada ) .
the patients were assessed for severity using the global deterioration rating scale and only participants in the mild stage of dlb were included in this study ( i.e. , stage 3 ) .
patients taking psychoactive medications , such as acetylcholinesterase inhibitors , were included in the dlb group .
the exclusion criteria included serious visual or hearing impairments left uncorrected ( e.g. , cataracts ) , serious health problems aside from dementia ( e.g. , mental illnesses , history of head injury , epilepsy , apoplexy , heart attacks , hypertension , and sleep apnea ) , any history of substance abuse , and any history of learning disabilities . the convenience sample of neurologically healthy older drivers ( control group ) was recruited through announcements placed in a local community newspaper .
none of the control participants had abnormal mini - mental state exam ( mmse ) scores of less than 25 . 

the mmse is one of the most widely used brief screening instruments in dementia . 

the drs-2 assesses attention , memory , visuospatial construction , conceptualization , and initiation / perseveration .
the test was administered according to the discontinue rules as outlined in the test protocol . 
 visual object and space perception ( vosp ) test .
this is a measure of visuoperceptual and spatial abilities that specifically assesses object and space perception .
was calculated by adding the first four subtests and a vosp space perception composite score was calculated by adding the last four subtests .
these calculations were extracted from the user manual and were found to be valid and reliable measures of object perception and space perception . 

evidence has shown that the factor structure of the tea aligns with contemporary research supporting several attentional circuits in the brain .
the scores from the eight subtests in the tea were aggregated so that they matched the three factors outlined in robertson et al . .
standard scores ( i.e. , z - scores ) were first computed for each subtest and , subsequently , variables corresponding to each of the three factors were summed . 

the ufov task is a computerized measure of attention that examines three test variables and is composed of three subtests , entitled processing speed , divided attention , and selective attention .
each subtest presents participants with stimuli for increasingly shorter durations and , after each presentation , participants are asked to indicate what they had seen .
performance on the ufov is often cited as being related to performance on functional activities requiring sustained attention , such as driving .
participants were asked to complete a simulated driving scenario mimicking an on - road evaluation .
the stisim drive software ( version 2.08.004 ; systems tech , california ) was implemented on a dell precision m6300 laptop computer ( intel core 2 duo processor , 2.10  ghz/2.0  gb ram ) with a 17-inch display running windows xp .
the laptop was equipped with a logitech brake / throttle and steering wheel ( model g25 ) .
instructions to the drivers ( e.g. , turn left / right , lane changes , and speed maintenance , etc . ) were given through laptop speakers .
the driving simulator had a 60-degree horizontal field of view and a 75-degree vertical field of view and the frame rate of the simulator was 30 frames per second ( 30  hz ) ( see   for more information ) . before beginning , participants completed a comprehensive training session including a thorough explanation of the task , an accommodation phase during which they practiced operating the pedals and steering wheel , followed by a training course that took approximately 20 minutes to complete ( see   for a detailed description ) .
the assessment course employed was programmed to mimic a driving assessment by a provincial regulatory body in canada and is described by weaver et al . .
it was 12.3 kilometers long , based on a real segment of road found in thunder bay , ontario , and included driving in residential , highway , and urban environments .
notably , given that the course is utilized by a provincial licensing body to differentiate between safe and unsafe drivers , it was found to exhibit high face validity .
similarly , the evaluation course allowed for the collection of two aggregate measures of driving performance : the total number of errors recorded by the simulator and a structured rater score .
the course presented participants with a wide variety of typical driving situations allowing for generalizability .
most importantly , previous research examining driving behavior among drivers from across the driving lifespan ( ages 1883 years ) shows that scores on the simulated assessment course correlate highly with those on the real - world driving course .
measurements of the simulated driving task were generated both from driving performance as recorded by the computer and from a demerit point assessment .
driving errors and parameters were recorded ( e.g. , speed exceedances , stops sign violations , and traffic light violations ) by the simulator .
all simulated drives were recorded and scored by two blind independent raters using a structured demerit point assessment .
interrater reliability was found to exceed r = .9 and as such the mean of both scores was used in the analysis .
none of the participants in this study reported any symptoms associated with using the driving simulator , a condition known as simulator adaptation syndrome ( sas ) .
patients at the tertiary care facility with a diagnosis of mild dlb were contacted in order to verify whether they were willing to participate in the present study and verify that they met the inclusion criteria . following this screening , testing commenced immediately .
all participants underwent cognitive and computerized assessment including a test of general cognitive functioning ( drs-2 ) , visuospatial / perceptual abilities ( vosp ) , attention ( tea and ufov ) , and processing speed ( ufov ) .
all cognitive and computerized testing was completed according to the protocol specified by each test .
the cognitive and computerized testing was administered in the presence of the participant and the investigator only .
following data collection , each drive was rated independently by two raters using the playback feature of the stisim drive .
the two groups of participants were compared using a series of between groups anovas with group ( dlb and control group ) as the primary independent variable .
comparison of the driving variables ( table 1 ) revealed that dlb drivers consistently performed poorer in comparison to neurologically healthy older drivers .
the composite measures of driving performance offer a global indication of participants ' driving behaviour in the context of the simulated assessment course .
the results revealed that the number of errors accrued by the driving simulator was significantly higher among dlb drivers ( m = 57.07 ) than among controls ( m = 27.86 ) [ f(1,34 ) = 57.61 ,  p < .001 ] .
similarly , dlb drivers were assigned over four times the number of demerit points ( m = 284.00 ) in comparison to the control group ( m = 59.64 ) during the simulated driving assessment , a difference that also reached statistical significance [ f(1,36 ) = 57.61 , p < .001 ] . to better understand the composite results , types of driving errors
the results showed that dlb drivers exceeded the posted speed limit significantly more often in comparison to controls [ f(1,34 ) = 7.53 , p = .01 ] and spent an average of 24% of the time driving over the speed limit , a significantly higher proportion than controls who spent an average of 12% of the time over the speed limit [ f(1,34 ) = 6.82 , p = .01 ] . in terms of lateral control of the vehicle , dlb drivers crossed the centerline [ f(1,34 ) = 30.39 , p < .001 ] more frequently than controls and were found to spend an average of 13% out of their own lane , significantly higher than controls who spent an average of 3% out of their own lane [ f(1,34 ) = 9.01 , p = .01 ] .
dlb drivers exceeded the road edge more often than did neurologically healthy drivers [ f(1,34 ) = 9.17 , p = .01 ] .
comparison of performance between dlb and controls revealed that dlb drivers failed to stop at traffic lights significantly more often than controls [ f(1,34 ) = 2.47 , p < .001 ] .
dlb drivers were also found to have difficulty in interacting safely with other road users in the driving simulator as evidenced by significantly more crashes compared to controls [ f(1,34 ) = 19.83 , p < .001 ] .
prior to calculating the degree of association between the cognitive measures with indicators of driving performance , the cognitive measures were first compared between the two groups . to this end
, anovas were again computed for all cognitive measures with group ( dlb and control group ) as the primary factor . in comparison to controls ,
dlb drivers were found to have poorer performance on all measures of cognitive function administered in this study .
one goal of this study was to assess the contribution of cognitive tests of global cognition , attention , and space processing in assessing driving outcomes among individuals with dlb . to meet this goal
, pearson correlation coefficients were calculated between each of the cognitive test scores and key indicators of overall driving performance for the dlb group only . 

table 3 summarizes the correlations between cognitive tests and driving outcomes among individuals with dlb . in terms of global measures of cognitive function , the results indicated statistically significant relationships between the mmse and the total number of errors in the simulator ( r = .529 , p = .043 ) and the rater score ( r = .622 , p = .013 ) .
when associations between the mmse and types of errors were examined , it is clear that this relationship derives primarily from its association with the percentage of time spent over the speed limit ( r = .656 , p = .008 ) and the percentage spent out of the lane ( r = .792 , p < .001 ) . in particular ,
dlb drivers with lower mmse scores were associated with more driving time over the speed limit and more time spent outside of the driver 's lane .
the drs , however , was not significantly correlated with simulated driving outcomes among dlb participants . in terms of visual processing ,
a statistically significant correlation was observed between the vosp space scores and the rater score ( r = .624 ,  p = .013 ) .
the associations between measures of attention and simulated driving indicated a statistically significant association between the first subtest of the ufov ( i.e. , processing speed ) and the rater score ( r = .548 , p
the third subtest of the ufov ( i.e. , selective attention ) was also significantly related to the number of speed exceedances in the driving simulator ( r = .588 , p = .021 ) .
the purpose of the current study was to examine the driving behaviour among older drivers with mild dlb in comparison to neurologically healthy older drivers . to our knowledge , this is the first empirical study to examine the driving behaviour of drivers diagnosed with dlb .
our results indicated clearly that when variables related to simulated driving performance were contrasted between groups , dlb drivers were found to perform significantly worse on all measures .
thus , the simulated driving performance of mild dlb drivers was found to be significantly impaired , which is a noteworthy result considering that most drivers diagnosed with dementia continue to drive for 4 years following diagnosis . when performance on the cognitive tests was contrasted between groups , drivers with mild dlb
this finding aligns with the existing literature indicating that attention , visuospatial and perceptual skills , and global cognition are impacted within this patient group .
however , what is most interesting in our results is the degree of association between scores on cognitive tests and simulated driving performance . in particular
, a strong association was found between the mmse and the total number of errors in the simulator , as well as with the rater score . when examining mmse scores in relation to specific errors in the simulator , it was found that mild dlb drivers with lower mmse scores were associated with driving over the speed limit and outside of the driver 's lane .
in addition , measures of attention , including processing speed and selective attention , significantly correlated with rater score and speed exceedances , respectively .
these results are of particular relevance in that they demonstrate that impaired cognitive abilities , namely , global cognition , attention , and visuospatial functioning , are predictive of poor simulated driving performance among mild dlb drivers .
these findings support the existing literature examining driving performance of individuals with dementia , showing that , in comparison to neurologically healthy controls , ad drivers perform poorer in the driving simulator ( for a detailed summary of the existing literature , see ) .
indeed , the authors of this study recently completed a similar investigation that examined the driving performance of drivers with mild ad , using an identical driving simulator protocol as the one described herein .
in particular , yamin , stinchcombe , and gagnon ( accepted with revision ) found that drivers with mild ad exhibited poorer performance in the simulator on all measures except for the number of road edge excursions . global cognition scores
( i.e. , mmse and drs ) , attention tests and visual perception results of ad drivers were also found to be lower than what was observed in the group of healthy controls .
moreover , among drivers with mild ad , strong associations were found with most measures of attention and a measure of visual perception but not with measures of global cognition . alongside our colleagues in the field of road safety , we cautioned against the use of measures of global cognition in isolation to identify unsafe drivers with dementia given our previous results with a sample of mild ad drivers [ 41 , 42 ] . however , in the present study , one of the stronger associations with driving performance that we found was with a measure of global cognition ( i.e. , mmse ) .
it is relevant to note that mild ad and mild dlb samples showed similar levels of decline as measured by the global deterioration scale ( gds ) ( i.e. , a score of 3 on the gds indicating mild dementia ) . considering this result as well as the pattern of findings that emerged when examining simulated driving performance among drivers with mild ad
, these data suggest that drivers with mild dlb exhibit some global cognitive decline that impacts driving performance . as indicated in introduction , driving is a multifactorial behaviour drawing upon multiple cognitive , sensory , and physical systems .
it follows that when patients experience global decline , driving performance will be negatively impacted . within the sample of mild dlb drivers , we observed that global cognition accounts for a substantial proportion of the variance in simulated driving performance . while we do not recommend that the mmse be used in isolation to predict driving performance , our results highlight the utility of this measure among mild dlb drivers .
first , driving in a simulator is less stressful than an on - road assessment for participants .
second , a small portable simulator reduces the risk of negative symptoms associated with using the driving simulator ( i.e. , simulator adaptation syndrome , sas ) .
third , driving simulators are considered to be a safe and economical means of presenting drivers with consistent situations and collecting behavioural data in real time .
finally , simulator performance has been shown to be reliable and a valid indication of on - road performance .
importantly , we used a scenario that was developed to assess the various components routinely assess in an on - road driving examination .
nevertheless , in this study , we did not collect on - road data and thus the generalizability of our findings to real - world driving and collision risk should be extrapolated with caution .
it would be of interest for future research to examine on - road driving performance among mild dlb drivers .
such an investigation would enhance the clinical relevance of our findings in order to inform policy and practice related to fitness to drive .
this study was the first to shed light on the driving behaviour of individuals diagnosed with mild dlb .
the results highlight the importance of cognitive functions , notably , global cognition , spatial and attentional abilities , in predicting driving ability . while a diagnosis of dementia does not automatically imply the immediate removal of driving privileges , it may alert professionals to the need for further in - depth assessment and regular monitoring . based on these data , global cognition , attention , and spatial abilities
future research directions should examine the clinical relevance of these findings with respect to on - road performance and crash risk .
 driving is a multifactorial behaviour drawing on multiple cognitive , sensory , and physical systems . 
 dementia is a progressive and degenerative neurological condition that impacts the cognitive processes necessary for safe driving . 
 while a number of studies have examined driving among individuals with alzheimer 's disease , less is known about the impact of dementia with lewy bodies ( dlb ) on driving safety . 
 the present study compared simulated driving performance of 15 older drivers with mild dlb with that of 21 neurologically healthy control drivers . 
 dlb drivers showed poorer performance on all indicators of simulated driving including an increased number of collisions in the simulator and poorer composite indicators of overall driving performance . 
 a measure of global cognitive function ( i.e. , the mini mental state exam ) was found to be related to the overall driving performance . 
 in addition , measures of attention ( i.e. , useful field of view , ufov ) and space processing ( visual object and space perception , vosp , test ) correlated significantly with a rater 's assessment of driving performance . 
1. Introduction
2. Materials and Methods
3. Results
4. Discussion
5. Conclusions