divided attention and driving: a pilot study using virtual ...sg94g745/pubs/jhtr.divided...

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Aspen Pub./JHTR AS107-03 January 2, 2002 8:58 Char Count= 0

Divided Attention and Driving:A Pilot Study Using VirtualReality Technology

Background: Virtual reality (VR) was used to investigate the influence of divided attention (simple versuscomplex) on driving performance (speed control). Design: Three individuals with traumatic brain injury(TBI) and three healthy controls (HC), matched for age, education, and gender, were examined. Results:Preliminary results revealed no differences on driving speed between TBI and HC. In contrast, TBI subjectsdemonstrated a greater number of errors on a secondary task performed while driving. Conclusion:The findings suggest that VR may provide an innovative medium for direct evaluation of basic cognitivefunctions (ie, divided attention) and its impact on everyday tasks (ie, driving) not previously availablethrough traditional neuropsychological measures. Key words: brain injured, divided attention, driving,virtual reality

Jean Lengenfelder, PhD ∗

Maria T. Schultheis, PhD ∗

Talal Al-Shihabi, MS †

Ronald Mourant, PhD †

John DeLuca, PhD ∗

∗Neuropsychology and Neuroscience Laboratory,Kessler Medical Rehabilitation Research and Educa-tion Corporation, West Orange, New Jersey, Depart-ment of Physical Medicine and Rehabilitation, Univer-sity of Medicine and Dentistry of NJ-NJ Medical School,Newark, New Jersey.†Virtual Environments Laboratory, Northeastern

University, Boston, Massachusetts.

TRAUMATIC BRAIN INJURY (TBI) can re-sult in a range of cognitive, behavioral,

and physical impairments that can contributeto a decline in the ability to carry out everydayactivities. The ability to drive an automobileis one activity that can be affected by thesedisabilities and one that is critical to maintain-ing independence. Prior studies have demon-strated that impairments on such cognitiveskills as visual scanning, attention, informa-tion processing speed, visuospatial skills, andvarious executive functions can result in im-paired driving skills and abilities.1–5 The pres-ence of deficits within these cognitive do-mains has been well documented in TBI.6,7

Address correspondence and requests for reprints toMaria T. Schultheis, PhD, Neuropsychology and Neuro-science Laboratory, Kessler Medical Rehabilitation Re-search & Education Corporation, 1199 Pleasant Val-ley Way, West Orange, NJ 07052. Telephone: (973) 324–3528. E-mail: [email protected]

Preparation of this article and research presentedwas supported in part by grant H133G000073 of theNational Institute on Disability and RehabilitationResearch and by grants HD08589–01 and HD7522–01from the National Institute of Child Health and HumanDevelopment.

J Head Trauma Rehabil 2002;17(1):26–37c© 2002 Aspen Publishers, Inc.

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Divided Attention and Driving 27

As such, it is important to understand howspecific cognitive impairments affect drivingcapacity.

The driver’s lack of attention has been fre-quently cited as a major cause of motor vehi-cle accidents.8,9 Although it should be notedthat attention encompasses a wide variety ofdefinitions, generally it can be broadly definedas the ability of the individual to process in-formation from the environment or the ca-pability of receiving and processing stimuli.Various aspects of attention have been identi-fied in the literature, including immediate at-tention span, selective or focused attention,sustained attention or vigilance, divided atten-tion, and alternating attention or attentionalcontrol.10,11

In particular, divided attention, whichspecifically requires the ability to processand/or respond to information while simul-taneously conducting more than one task ata time, has been commonly deemed as rele-vant to driving capacity. In TBI, impaired per-formance on tasks requiring divided attentionhas been documented.11–13

Early studies with healthy individuals de-fined the ability to simultaneously processinformation from more than one source asa requirement for driving.14,15 Functionally,driving demands that the individual is re-quired to focus on multiple tasks at the sametime. Examples of “real-life” divided atten-tion demands while driving can include con-tinuously monitoring information from theroad scene while being able to scan theenvironment for potential hazards, attendingto multiple elements of information, and shift-ing attention back and forth as needed (ie,monitoring information from the dashboardwhile attending to road conditions).

The relationship between impairment ofdivided attention and decreased driving ca-pacity has been documented in a varietyof clinical populations, including driverswith Alzheimer’s disease,16,17 stroke,18 and

TBI.19–22 In such studies, a correlation be-tween impaired performance on neuropsy-chological measures, such as the Trail MakingTest, WAIS-R Digit Span and Digit Symbol, andPass/Fail performance on behind-the-wheelevaluations have been observed.23 However,as is the case with many neuropsycho-logical measures, these traditional measureshave both poor face validity and ecologicalvalidity.24 Little work has been done to di-rectly measure specific driving performancerequiring divided attention with traditionalneuropsychological measures of divided at-tention. A direct examination of divided atten-tion and driving remains to be conducted.

VIRTUAL REALITY TECHNOLOGY

Virtual reality (VR) is an emerging tech-nology that allows individuals to “inter-act” with and become “immersed” in athree-dimensional computer-generated envi-ronment. Through its capacity to createdynamic, multisensory, “real-life” stimulus en-vironments, within which all behavioral re-sponding can be recorded, VR potentiallyoffers clinical tools that are not available us-ing traditional neuropsychological methods.To date, VR has been successfully integratedinto several aspects of medicine, including thetreatment of phobias,25 pain distraction,26 thetraining of surgeons,27 and the education ofpatients.28 Not surprisingly, within rehabilita-tion medicine, clinicians and researchers arealso beginning to recognize VR’s potential asa new tool for the study, assessment, and reha-bilitation of cognitive processes.29–32 In addi-tion, a number of researchers have advocatedfor using VR for the evaluation and retrain-ing of functional activities of daily living, suchas the use of public transportation,33 mealpreparation,34 and driving an automobile.32

Results from these initial studies indicatethat the use of VR has several advantages

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28 JOURNAL OF HEAD TRAUMA REHABILITATION/FEBRUARY 2002

over traditional neuropsychological assess-ment and retraining protocols, including thedirect evaluation of complex behaviors in eco-logically valid environments, objective evalu-ation of complex behaviors, and the opportu-nity to present challenging conditions whilemaintaining the safety of both the clinicianand patient.

Given these advantages, VR can providea new mechanism for objectively quantify-ing driving skills and more directly examiningthe impact of specific cognitive functions (ie,divided attention) on driving performance.The purpose of this pilot study was to beginto examine the benefits offered through VRto investigate the purported relationship be-tween divided attention and driving perfor-mance among persons with cognitive impair-ment. Specifically, using a VR-based drivingenvironment, the influence of various aspectsof divided attention (ie, simple v complex) ondriving performance (ie, speed control) wasevaluated among adults with TBI and healthycontrols.

METHOD

Subjects

The subjects consisted of three individu-als with moderate to severe TBI and threeage-, gender-, and education-matched healthycontrols (HC). All subjects were right-handedmen. Two of the individuals with TBI werecurrently driving at the time of testing; oneindividual had been driving for 18 years be-fore his injury and 1 year after his injury;and the other individual had been driving for3 years after his injury. The third individualwith TBI had been driving for 13 years be-fore his injury and was in the process of re-ceiving a driving evaluation to reinstate hisdriver’s license at the time of testing. Noneof the subjects required any type of adaptiveequipment to assist with driving, and none

had any gross physical limitations that wouldaffect their ability to drive a vehicle.

TBI subjects were recruited from a databaseof individuals who had previously partici-pated in other research studies. The mean in-terval between onset of TBI and time of test-ing was 12.67 years (SD= 9.29; range, 5–23years). The mean age of the TBI group was38 years (SD= 3.46; range, 34–40 years), andthe mean years of education was 13.3 years(SD= 1.53; range, 12–15 years).

HC subjects were recruited from hospitalstaff or individuals from the community whohad previously participated in other researchstudies. The mean age of the HC group was38 years (SD= 3.61; range, 34–41 years), andthe mean years of education was 16 years(SD= 2.00; range, 14–18 years).

The TBI and HC groups were matchedfor age, education, and gender (all subjectswere men). All subjects with a history of anyneurological disease, drug or alcohol abuse,or significant psychiatric disorders were ex-cluded from study participation.

Procedures

All subjects completed an institutional re-view board-approved consent form at the be-ginning of the testing session. Subjects com-pleted the protocol in one testing sessionlasting approximately 2 to 3 hours. Duringthis session, subjects completed neuropsy-chological measures, as well as two comput-erized measures, the Useful Field of View(UFOV)35 and a Driving Divided AttentionTask.

Neuropsychological measures

Subjects were administered the AuditoryConsonant Trigrams36 and the Paced AuditorySerial Addition Test (PASAT) to assess dividedattention, working memory, and informationprocessing.37 Tests were administered accord-ing to standardized protocols.

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A divided attention task, which involvedperforming two tasks concurrently, was ad-ministered. Various divided attention tasks(ie, dual tasks) have been reported in the lit-erature and have included tasks such as cardsorting with random item generation, back-ward counting with a cancellation task, digitrecall with a cancellation task, a simple visualreaction time task with random number gen-eration, and a visual reaction time task withcounting aloud.38–41 For this study a verbal flu-ency task and a cancellation task was chosenas the divided attention measure, because ithad previously been used in the literature andinvolved a verbal and visual component. Forthe single (ie, non-dual task condition) ver-bal fluency task, the letter “F” was adminis-tered alone using standard administration in-structions (ie, generate as many novel wordsin 60 seconds without repetitions or rule vio-lations). For the single cancellation task, sub-jects were given 60 seconds to cancel out thenumber “9” alone. For the divided attentiontask, the verbal fluency and cancellation taskswere administered concurrently. The letter“L” was administered with the number “6” asthe cancellation task. The letters “F” and “L”were chosen, because they have been shownin the literature to produce a similar numberof words per minute.42 Likewise, the number6 and 9 were chosen for the cancellation taskas these have been reported to provide equiv-alent scores.43

Useful field of view (UFOV)

The UFOV35 is a standardized and com-mercially available product that quantifies thevisual field area (useful field of view) overwhich a driver can process rapidly presentedvisual information. The UFOV is used to as-sess driving-related skills and is composed ofthree subtests: visual information processing,divided attention, and selective attention.

Fig 1. Sample road scene.

Driving divided attention task

The driving divided attention task consistedof a primary task (driving a VR route) and asecondary task (attending to numbers in thedriver’s visual field). The driving divided at-tention task was delivered using a VR-DrivingSimulator computer program based on thestudy by Levine and Mourant.44 Specifically,all subjects sat in front of a PC computerwith a 21-inch monitor screen equipped witha steering wheel and gas/brake pedals. Theprogram consisted of a simple VR drivingroute that included a 1.75-mile long, two-directional roadway containing four curves.The driving lane was approximately 12 feetwide. See Figure 1 for a sample scene of theroadway.

Primary task: VR driving task

Subjects were required to “drive” the ve-hicle through the VR driving route, usingthe steering wheel and foot pedals andkeeping in the center of the lane. Auto-matic recording of the subjects’ speed (mph)was logged through the computer every100 milliseconds. Upon the completion of theroute, an average speed was calculated andused as the dependent variable for drivingperformance.

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Fig 2. Study design.

Secondary task: Divided attention tasks

The secondary task involved the presen-tation of a four-digit number superimposedon the computer screen (“windshield”) whilethe subject drove the VR driving route. Eachfour-digit number was presented for approx-imately 300 ms and was randomly selectedby the computer from a database of pre-screened numbers. Subjects were required tosay the number out loud immediately after itappeared on the screen while they continueddriving. A tape recorder was used to recordresponses.

The present design consisted of five driv-ing divided attention conditions, a baselinecondition, and four divided attention condi-tions (see Figure 2). The four divided attentionconditions were counterbalanced to controlfor learning effects.

1. Baseline condition: The baseline condi-tion consisted of having the subjectscomplete the primary task one time (ie,drive the VR driving route) without thepresence of the secondary task (ie, num-bers were not presented).

2. Divided attention conditions: These con-ditions required subjects to drive the VRdriving route while attending to the sec-

ondary task (described previously). Thefour divided attention conditions were:

—Simple 2.4′′ condition: In this condi-tion, the four-digit number always ap-peared in a fixed central location onthe “windshield.” The numbers werepresented at 2.4′′ intervals.

—Simple 0.6′′ condition: The procedurefor this condition was identical to thesimple condition described previouslyexcept that the numbers were pre-sented at 0.6′′ intervals.

—Complex 2.4′′ condition: The proce-dure for this condition was similar tothe simple condition with the excep-tion that the numbers appeared ran-domly throughout the “windshield”rather than in one fixed central loca-tion. The numbers were presented at2.4′′ intervals.

—Complex 0.6′′ condition: The proce-dure for this condition was similar tothe preceding complex condition ex-cept that the numbers were presentedat 0.6′′ intervals.

For each of these conditions the total num-ber of errors in recalling the four-digit num-ber was recorded for each subject. Because

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total numbers presented varied between sub-jects (because of difference in speed andtime taken to complete the driving route), anoverall error percentage was calculated andused as the dependent variable for the drivingdivided attention task.

Data analysis

The small sample size and preliminary na-ture of this investigation precluded a paramet-ric analysis of the data. Therefore, emphasiswas placed on descriptive analyses. After con-sultation with a statistician, nonparametricstatistics were used to assess any trends inperformance for both speed and errors. Dataon driving speed and percentage of errors onthe driving divided attention task were exam-

Fig 3. Average speed on driving task.

ined. The Mann-Whitney test was used to ex-amine preliminary differences in speed and er-rors between the TBI and HC group. Finally,Spearman’s correlations tests were used to ex-amine the relationship between standardizedneuropsychological tests of divided attentionand the driving divided attention task.

RESULTS

Driving divided attention task

Driving speed

The average speeds for both the TBI andHC groups on the baseline for each of the fourdivided attention conditions are depicted inFigure 3. To examine differences in speed on

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Fig 4. Speed and presentation rate of stimuli.

the driving divided attention task betweenthe TBI subjects and HC, a difference scorefor each subject was computed based ontheir baseline speed and speed on each of thefour divided attention task conditions (simple2.4′′, simple 0.6′′, complex 2.4′′, and complex0.6′′). Preliminary findings did not indicateany differences in relative speed between theTBI and HC on any of the four divided atten-tion conditions. In addition, TBI and HC didnot seem to differ when the secondary taskwas either simple (ie, presented in a centralfixed location) or complex (ie, presented inrandom locations).

In examining the data from the driving di-vided attention task, some preliminary trendsin speed performance could be identified.First, it was observed that speed increasesfor both groups when the secondary task (ie,divided attention task) is added to driving.That is, compared with the speed observed

during the baseline condition, five of the sixsubjects increased their speed during the di-vided attention conditions (see Figure 3). Thissuggests that the complexity of visual atten-tion (simple v complex) required for the sec-ondary task may not have an impact on driv-ing speed. In addition, subjects in both theTBI and HC group seemed to increase theirspeed when stimuli were presented at 0.6′′

compared with 2.4′′ (see Figure 4). Thesedata may suggest that how quickly one mustattend to stimuli may have an impact ontheir driving speed, for both TBI and HCsubjects.

Errors

The percentage of errors for both the TBIand HC group on each of the four divided at-tention conditions are depicted in Figure 5.The percentage of errors made across subjectswas examined for each of the four divided

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Fig 5. Percentage errors on number recognition task.

attention conditions (simple 2.4′′, simple 0.6′′,complex 2.4′′, and complex 0.6′′).

In examining the data from the driving di-vided attention task, some preliminary trendsin error performance can be identified. Nogroup differences in errors were observed be-tween whether stimuli were presented in afixed location (ie, simple) or random locations(ie, complex). This suggests that the complex-ity of visual attention (simple v complex) re-quired for a secondary task does not affecterror rate. However, it seems that the rateat which stimuli are presented (ie, 0.6′′ or2.4′′) affects error rate. In the simple condi-tion, both the TBI and HC subjects commit-ted a greater number of errors when stimuliwas presented at 0.6′′ compared with 2.4′′. Asimilar pattern was evidenced in the complexcondition. This suggests that how quickly onemust attend to stimuli may have an impact on

the ability to perform a divided attention taskcorrectly in both TBI and HC subjects. This issimilar to the pattern observed in the drivingperformance measure.

Neuropsychological measures

Neuropsychological divided attentiontask

Performance on the fluency and cancel-lation divided attention task was examinedbetween the TBI and HC groups. A differencescore between the number of words gener-ated when the fluency task was done alone(single task) and number of words generatedconcurrently with another task (divided at-tention task) was computed for each sub-ject. Preliminary analysis did not indicate anydifferences in the number of words gener-ated on the single fluency task compared

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Table 1. Average speed (mph) on driving divided attention task

Subject Baseline Simple 2.4′′ Simple 0.6′′ Complex 2.4′′ Complex 0.6′′

TBI #1 45.62 49.31 50.55 50.30 53.16TBI #2 29.72 35.34 39.32 35.01 39.09TBI #3 26.76 25.94 28.44 28.78 26.18HC #1 38.81 49.97 49.13 47.43 54.18HC #2 36.29 38.24 39.76 44.02 37.22HC #3 31.43 28.37 30.14 32.33 36.67

with fluency during the divided attentiontask for either the TBI (t= −.143; p= .89)or HC groups (t= 1.95; p= .19). A differencescore was also computed for the number ofcorrect responses on the cancellation taskwhen it was performed alone (single task)and concurrently with the fluency task (di-vided attention task). In contrast to the flu-ency data, cancellation task performance dur-ing the divided attention task was significantlyreduced compared with the single task condi-tion for both the TBI (t=−4.42; p< .05) andHC groups (t=−8.32; p< .05). These resultssuggest that during the divided attention task,performance on a secondary task decreases(ie, cancellation) as attention is allocated tothe primary task (ie, fluency).

Driving divided attention task andneuropsychological measures

Given the preliminary nature of the study,it was important to examine the relationshipbetween the VR driving divided attention taskand more traditional measures of divided at-tention. To address this, correlational analysiscomparing the driving divided attention taskand standard neuropsychological measures ofdivided attention was conducted. Given thesmall sample size, the data must be viewed aspreliminary.

Correlations between the divided attentionsubtest of the UFOV, total number of correctresponses on the PASAT, and total number cor-

rect on Consonant Trigrams with two mea-sures from the driving divided attention task,driving speed and errors, were analyzed. Withrespect to driving speed, minimal to no corre-lations were initially present (UFOV, r = 0.08;p= .93; PASAT, r =−0.02; p= 1.0; Conso-nant Trigrams, r =−0.20; p= .72). In com-parison, higher correlations were seen whencomparing errors on the driving divided atten-tion task with neuropsychological measuresof divided attention. Errors were correlatedwith divided attention subtest of the UFOV(r = 0.79; p= .10), indicating that the greaterthe number of errors on the driving di-vided attention task, the longer the reactiontime on the UFOV divided attention subtest.Errors were also correlated with the PASAT(r =−.94; p= .01), indicating the more er-rors on the driving divided attention task, thelower total number of correct responses onthe PASAT. Errors were not found to be highlycorrelated with the total number correct onConsonant Trigrams (r =−.40; p= .44).

DISCUSSION

The purpose of this pilot study was tobegin to examine the potential benefitsoffered through VR to more closely inves-tigate the relationship between dividedattention and driving performance. Thefindings suggest that VR may provide a

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unique medium for direct evaluation of ba-sic cognitive functions (ie, divided atten-tion) and its impact on everyday tasks(ie, driving) not previously available throughtraditional neuropsychological measures.

Specifically, preliminary results from thispilot study suggest that when drivers are re-quired to attend to multiple elements of in-formation, there are increased errors on thesecondary task (ie, number recall), whereasperformance on the primary task (ie, driving)is less impacted. For this study, the resultssuggest that drivers with TBI demonstratedmore errors on the secondary task comparedwith HC drivers. This finding is consistentwith prior studies examining secondary tasksduring driving.14,45 The present findings alsosuggest that when drivers must divide theirattention to more than one task, speed of driv-ing seems to increase for both TBI and HCdrivers. Interestingly, initial results indicatethat the type of divided attention (ie, simplev complex task) did not seem to have the mostimpact on speed of driving, but rather, thespeed of stimulus presentation (ie, 2.4 s v 6 s)seemed to influence performance.

Although previous work has reported arelationship between divided attention anddriving, prior results are based on correla-tion analysis and used correlational compar-isons between psychometric test results andbehind-the-wheel driving observations ratherthan direct examination of driving behaviors.As such, the specific aspects of how driv-ing is affected (ie, speed increase, lane de-

viation) has not been delineated. This pilotstudy illustrates how VR can be used to ad-dress this limitation in prior studies and allowfor an objective and direct evaluation of therelationship between cognitive impairment(ie, divided attention) and functional perfor-mance (ie, driving). By use of a VR approach,the levels of divided attention tasks can be ma-nipulated, and actual driving measures suchas speed and lane position can be recorded.This type of evaluation may have implicationsfor the assessment and rehabilitation of driv-ing skills for cognitively impaired populations.

Although promising, the initial findings ofthis pilot study must be viewed as preliminaryand must await extension and replication. Thelimitations of this study to date include sub-jects not matched for driving experience. Inaddition, the small sample size of this pilotstudy requires nonparametric statistics andcautious interpretation of trends in perfor-mance. Our continued work is focusing on ob-taining larger samples, addressing questionsof validity and reliability, and comparing theVR divided attention task to traditional neu-ropsychological and driving measures.

Because the application of VR to neuropsy-chology is in early stages, future studies canprovide information about the use of VR toextend and enrich our neuropsychological as-sessments. VR seems to offer an innovativeand promising mechanism that can be usedfor objective and direct evaluation of the re-lationship between cognitive impairment andfunctional performance.

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divided attention and driving: a pilot study using virtual ...sg94g745/pubs/jhtr.divided...

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