Abstract
BACKGROUND:
Virtual reality (VR) offers an innovative method to assess the impact of neurocognitive deficits on daily activities like driving.
OBJECTIVE:
This study sought to evaluate the reliability of a VR driving simulator (VRDS) in assessing driving behaviors.
METHODS:
Participants included 91 individuals with a neurological condition (e.g., acquired brain injury, multiple sclerosis) and 59 participants with no history of neurological disorder. Internal consistency and split half reliability were examined from data for all participants for driving speed, lane positioning, and steering on a rural segment of the virtual reality driving simulator route. Test-retest reliability was examined for data from the 22 drivers who completed the same route sections across two time periods.
RESULTS:
Internal consistency and split half reliability were excellent (alphas
CONCLUSIONS:
Findings suggest that VRDS is a generally reliable instrument for measuring speed, lane positioning, and steering in a virtual basic rural driving environment. Reliability of repeated testing is not consistent, likely due to practice effects, highlighting the importance of using a comparison group in VRDS studies.
Introduction
Virtual reality (VR) technology offers new opportunities for the development of innovative neuropsychological assessment and clinical tools that can explore cognition in ecologically valid environments [1, 2, 3, 4, 5, 6, 7, 8, 9]. One application of VR is in the use of driving simulation for examining driving capacity in individuals with neurological disorders. An emerging body of research suggests that virtual reality driving simulation (VRDS) is a promising approach for examining the cognitive demands of driving in individuals with neurological impairments [10, 11, 12, 13, 14].
VRDS offers unique advantages for evaluation of driving performance, which can be important for functional independence following neurological compromise. Specifically, VRDS 1) allows for safe assessment of challenging driving scenarios, which are often difficult to capture with traditional behind the wheel assessments; 2) utilizes realistic scenarios that involve complex (i.e., dual-task) behaviors, which allows for nuanced assessment of performance variables not available in current clinical approaches for evaluation of driving; and 3) offers a systematic and objective approach to measuring driving performance in contrast to traditional neuropsychological testing or behind the wheel assessments, which are often subjective and difficult to control [10, 15, 16].
Despite its potential utility and growing research base, clinical use of VRDS remains limited. This may be partially due to the paucity of research regarding the feasibility, validity, and reliability of VRDS as a tool for informing clinical decisions. Discriminant validity, or the ability of VRDS to discriminate between healthy drivers and those with neurological disorders, is the most commonly investigated metric within the current literature [17, 18, 19, 20]. Discriminant validity has also been investigated when comparing performance between healthy drivers and those with visual deficits [21, 22], varying levels of prior driving experience [23], sleep deprivation [24], and among aging populations [17, 25, 26]. Research has also pointed to the external validity of VRDS [27] while studies examining other validity metrics (e.g. internal validity) remain limited.
In addition to validity, it is important to evaluate consistency and reliability of this clinical instrument. VRDS can allow clinicians to examine specific abilities that contribute to the complexity of driving that are captured with several novel variables (e.g. average speed, variability in speed, change in lane position). Establishing internal consistency of VRDS can ensure clinicians that these variables will consistently and equally assess driving performance. VRDS is also clinically beneficial in that it allows for standardized repeated assessment. Establishing test-retest reliability of VRDS would allow for a standardized comparison of baseline and follow-up assessment of the same individual, thereby allowing the use of VRDS for repeated assessment of driving skills including monitoring of change in performance (particularly relevant in studying impaired performance in progressive disorders) and assessment of driver retraining.
The Applied Neuro-technologies VRDS has been used in several research studies to evaluate driving skills in a variety of neurological disorders including multiple sclerosis, acquired brain injuries, attention deficit/hyperactivity disorder, autism spectrum disorder, and post-traumatic stress disorder, as well as typically developing individuals across a wide age range [11, 12, 13, 14, 28, 29]. The current study sought to evaluate the reliability of that VRDS in assessing basic driving behaviors of neurologically compromised and healthy participants.
Methods
Participants
Data for this study were pulled from three separate existing studies that examined simulated driving abilities in individuals with neurological conditions (concussion, acquired brain injury, or multiple sclerosis) compared with neurologically healthy individuals [29, 30]. Specifically, these data were pooled to create a larger sample size given predefined criteria and consistent driving methodologies across the three studies [29]. All three studies included a training session, baseline drive, and drive with secondary tasks on a VRDS, along with completion of neuropsychological tests. Participant demographic information is shown in Table 1. Participants included 46 individuals diagnosed with a mild to severe traumatic brain injury, 2 individuals diagnosed with a brain tumor, 1 individual who sustained a stroke, 42 individuals diagnosed with multiple sclerosis, and 59 individuals with no history of neurological disorder. Diagnoses were corroborated by medical reports and/or physicians who referred individuals to the study. All studies were approved by the Drexel University Institutional Review Board.
Participant demographics
Participant demographics
Data were collected as part of several studies examining driving performance in individuals with neurological disorders compared with neurologically healthy controls, all administered in the span of 7 years. Across studies, participants completed several driving tasks on the same VRDS. The simulator displayed a pre-programmed driving environment across three monitors to help provide a deep level of immersion and a believable driving experience. Driver input was provided via a modified steering column and foot pedals adapted from an actual vehicle, and digital sensors tracked the motion inputs. The simulator simultaneously tracked and stored multiple events, including vehicle position, speed, lane deviation, target object distances, raw steering input, steering angle, accelerator position, brake pedal position, turn signal position, and auxiliary data such as key position, gearshift position, and car stereo operation. The simulator’s rendering engine utilized medium resolution geometry and high-resolution textures to provide high quality visuals.
Across studies, all participants completed the following tasks on the Applied Neuro-technologies VRDS:
Training: Participants completed two training sessions: one for practicing basic speed and lane management and another for practicing making turns and stops-which included feedback and coaching regarding driving at posted speed limits, using turn signals, and making complete stops at stop signs. Basic rural route: Participants completed a basic 8-mile route consisting of a 2-lane highway with few cars or other distractions. The speed limit was 40 mph throughout the route and participants were not required to change lanes or navigate environmental challenges. Highway: Participants drove on a divided highway with frequent curves and oncoming traffic in the opposite lane. The speed limit increased to 55 mph. Residential/commercial zone: Participants exited the highway and drove through a residential area where the speed limit reduced to 25 smph. Participants were required to make several turns through a neighborhood that included houses, cars, and pedestrians. They then entered a commercial zone, which included oncoming traffic in the opposite lane, commercial buildings (e.g. restaurants), and parked cars. The speed limit increased from 25 to 35 mph.
For 22 participants with no history of neurological impairment, data to examine test-retest reliability were available from one study in which participants completed a second session 2 to 8 weeks after the first session. During the second session, participants again completed the basic rural drive, highway, and residential/commercial zone. There were several confounding factors limiting the available data for use. First, the data included participants who had sustained concussions as well as neurologically healthy participants. Given that a change in driving performance in patients who were recovering from concussion was expected and therefore likely to produce poor data for examining test-retest reliability, only data from neurologically healthy participants (
Driving behaviors of interest included speed, deviation from the center of the driver’s lane, and steering wheel movement. Parameters utilized in this study were derived from previous similar driving studies conducted by our group in addition to existing literature indicating specific parameter for differentiating driving performance.
Internal consistency for baseline rural drive
Internal consistency for baseline rural drive
Note. Demographic information was not available for all participants. Sample sizes for different types of demographic information are displayed.
Split-half reliability
Note. The neurological group included participants with history of traumatic brain injury, brain tumor, stroke, or multiple sclerosis.
These behaviors were recorded by the VRDS 16 times per second. These data were then summarized for each quarter mile section of the driving route to create the following variables: mean speed, mean variability in speed (standard deviation), mean variability in lane position (standard deviation of distance from center lane position), and mean variability in steering (standard deviation of steering wheel position).
Internal consistency and split half reliability were calculated from data for all participants on the basic rural drive, using averaged data from quarter mile segments. In other words, driving behavior (speed, variability in speed, variability in lane position, and variability in steering) during each quarter mile section was treated as a separate data point numbered in order of completion (e.g., quarter mile 1, quarter mile 2, etc.). Internal consistency was measured by calculating Cronbach’s alpha. Split-half reliability was attained by placing every other quarter mile segment into one of two group. Because split-half reliability was based on half the trials, a Spearman-Brown correction was applied.
Test-retest reliability was calculated using Pearson’s
Test-retest reliability for whole rural route baseline drive in non-neurological sample (
Note.
Test-retest reliability for select portions of highway, residential, and commercial drives in non-neurological sample (
Note.
Internal consistency, split-half reliability, and test-retest reliability for the full sample and each neurological group are displayed in Tables 2 through 4. Internal consistency and split-half reliability of driving variables during the basic rural route were excellent with coefficients between 0.8 and 0.9. All driving variables assessed, including mean speed, variability in speed, variability in lane positioning, and variability in steering, had excellent consistency and reliability. Findings held across neurological conditions, as well as with patients with no history of neurological impairment.
Test-retest reliability was more variable. For the baseline drive on the basic rural route, reliability of variability in lane positioning and steering were adequate to good. Although test-retest reliability of variability in speed was statistically significant, it was less than adequate. Reliability of mean speed was not statistically significant. On select portions of the highway, residential, and commercial drives (i.e., portions that did not vary from session 1 to session 2), test-retest reliability was excellent for mean speed, variability in speed, and variability in steering. Test-retest reliability for variability in lane positioning was statistically significant but less than adequate.
Discussion
The current study sought to evaluate the reliability of the Applied-Neurotechnologies Virtual Reality driving simulator in assessing driving performance in individuals diagnosed with multiple sclerosis or acquired brain injuries, and individuals with no history of neurological impairment. Findings suggest that VRDS is a reliable tool for measuring driving behaviors. Internal consistency and split-half reliability were strong across a variety of driving variables and within both healthy and neurologically-impaired drivers. This lends additional confidence to findings from studies that have used this instrument [12, 29]. In addition, it suggests that this VRDS may be used as a reliable clinical and research tool for measuring driving behaviors consistently across various sections of the virtual route.
Despite good internal reliability, test-retest reliability in a sub-sample of 22 healthy participants was variable. Findings are likely due, at least in part, to participants habituating to specific sections of the routes over time. This was particularly true during the basic rural route, which is a much lengthier and basic, less complex driving segment than the highway, commercial, and residential routes. Interestingly, driving performance did not necessarily improve over time. For instance, mean speed increased and became more discrepant from the speed limit from session 1 to session 2. This may be due to participants adjusting to observer effects and therefore becoming less concerned about adhering to the speed limit. It may also suggest that mean speed is a less stable measure in driving simulation. Indeed, previous research has found mean speed to be faster when individuals are driving an instrumented car compared with driving a simulator [31]. Regarding lane positioning, changes between the first and second session varied, as participants demonstrated increased variability during the second session on the easier, basic rural route, and decreased variability during the second session on the more difficult highway and residential/commercial routes. This pattern suggests that driver engagement may have adjusted to the level of demand of the driving environment, leading to better performance during more engaging and difficult driving tasks. Taken together, test-retest results suggest that drivers’ behavior in the VRDS changes over time, which may be due to habituation, level of demand, or other factors. Inadequate test-retest reliability highlights the importance of using comparison groups to account for changes in driving behavior on the VRDS over time. Given that there is no clear standard of what constitutes “good” driving, samples of interest (e.g., individuals with acquired brain injuries) are typically compared to neurologically healthy or typically developing individuals. This study suggests that although driving across similar segments within a single session is quite reliable, session to session driving varies substantially even in neurologically healthy individuals. Although a variety of factors are likely contributing to these differences, practice effects are almost certainly impacting performance. To reduce practice effects bias, it is recommended that samples with neurological conditions continue to be compared to a control group who have completed the same number of driving sessions under similar conditions and driving environments.
Research has consistently pointed to the importance of utilizing ecologically valid tools to capture deficits in activities of daily living experienced by individuals with neurological disorders [32, 33, 34]. Research utilizing virtual reality for assessment of driving behaviors in individuals with neurological and neurocognitive impairments is growing. Virtual reality has also been used as a clinical tool in assessing fitness to drive and in training new or rehabilitating drivers [35, 36, 37, 38]. Establishing reliability and validity of the current study’s VRDS, which has previously been utilized in multiple studies improves confidence in interpretation of research and clinical findings stemming from this instrument. This study takes the first step by establishing internal consistency of rural segments of the VRDS route across several driving behaviors in a neurologically diverse sample.
Interpretation of findings is limited by a small sample size. In addition, reliability could not be tested for all driving environments and routes implemented by this VRDS because they were too varied to reasonably allow for consistent driving behaviors. Future research should aim to assess test-retest reliability in a larger and more diverse sample. Practice effects may be reduced by testing smaller sections of the route over repeated time frames and by allowing more time for habituation during the first session. Furthermore, research should investigate the reliability and utility of VRDS for measuring more complex driving behaviors, such as completion of turns, stops, and lane changes to further inform driver retraining and/or tailored interventions geared at complex activities of daily living, such as driving. Research is also needed to assess the validity of VRDS in predicting on-the-road performance. Specifically, though the VRDS is an important step towards measuring driving performance in an ecologically valid manner (i.e., utilizes realistic scenarios that involve complex behaviors and resemble daily driving), it still has limitations as it is conducted within a controlled environment that does not exactly mirror daily driving. In fact, incorporation of VRDS elements in an on-road performance test remains an important area of future research. Toward this end, this study provides the first step in establishing reliability of VRDS for clinical and research utility, which paves the way for future studies involving the VRDS and its potential predictive value over real-life driving-related behaviors and functional outcomes that may influence individuals with neurological disorders as well as healthy controls.
Footnotes
Conflict of interest
The authors do not have any conflicts of interest to report.
