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Accident Analysis and Prevention 50 (2013) 895– 904

Contents lists available at SciVerse ScienceDirect

Accident Analysis and Prevention

j ourna l h o mepage: www.elsev ier .com/ locate /aap

erformance of a cognitive, but not visual, secondary task interacts withlcohol-induced balance impairment in novice and experiencedotorcycle riders

hristina M. Rudin-Brown ∗, Ashleigh J. Filtness, Amy R. Allen, Christine M. Mulvihilluman Factors Team, Monash University Accident Research Centre (MUARC), Monash Injury Research Institute (MIRI), Building 70, Wellington Road, Clayton, VIC 3800, Australia

r t i c l e i n f o

rticle history:eceived 9 March 2012eceived in revised form 28 May 2012ccepted 17 July 2012

eywords:tatic balanceual-task paradigmivided attentionoad safetyody sway

a b s t r a c t

The appropriateness of applying drink driving legislation to motorcycle riding has been questioned asthere may be fundamental differences in the effects of alcohol on driving and motorcycling. It has beensuggested that alcohol may redirect riders’ focus from higher-order cognitive skills such as cornering,judgement and hazard perception, to more physical skills such as maintaining balance. To test this hypoth-esis, the effects of low doses of alcohol on balance ability were investigated in a laboratory setting. Thestatic balance of twenty experienced and twenty novice riders was measured while they performed eitherno secondary task, a visual (search) task, or a cognitive (arithmetic) task following the administration ofalcohol (0%, 0.02%, and 0.05% BAC). Subjective ratings of intoxication and balance impairment increasedin a dose-dependent manner in both novice and experienced motorcycle riders, while a BAC of 0.05%,but not 0.02%, was associated with impairments in static balance ability. This balance impairment was

ostural sway exacerbated when riders performed a cognitive, but not a visual, secondary task. Likewise, 0.05% BACwas associated with impairments in novice and experienced riders’ performance of a cognitive, but nota visual, secondary task, suggesting that interactive processes underlie balance and cognitive task per-formance. There were no observed differences between novice vs. experienced riders on static balanceand secondary task performance, either alone or in combination. Implications for road safety and future

derat

‘drink riding’ policy consi

. Introduction

The high crash involvement of motorcyclists is well known.hile motorcycles account for only 4.5% of all Australian passen-

er vehicle registrations and 1.4% of vehicle-kilometres travelled,otorcycle riders account for approximately 16% of all road fatal-

ties and a higher proportion of serious injuries (BITRE, 2010; ABS,011a, 2011b; Johnston et al., 2008). Riding a motorcycle is muchore likely to result in death or serious injury than is travelling

n a car. In Australia, the rate of motorcycle rider deaths per dis-ance travelled is approximately 30 times the rate for occupantsf passenger vehicles, and the rate for serious injuries is approxi-ately 41 times greater (Johnston et al., 2008). These patterns are

ot unique to Australia—similar estimates have been reported forther developed countries, including the United Kingdom (Jamson

nd Chorlton, 2009) and the United States (NHTSA, 2007).

There is much evidence relating alcohol consumption to motorehicle crashes, including motorcycle crashes (Colburn et al., 1993;

∗ Corresponding author. Tel.: +61 3 998 1947; fax: +61 3 990 0682.E-mail address: christina.rudin-brown@tc.gc.ca (C.M. Rudin-Brown).

001-4575/$ – see front matter © 2012 Elsevier Ltd. All rights reserved.ttp://dx.doi.org/10.1016/j.aap.2012.07.018

ions are discussed.© 2012 Elsevier Ltd. All rights reserved.

Compton and Berning, 2009; Kasantikul et al., 2005; Lin and Kraus,2009; Mau-Roung and Kraus, 2009; Soderstrom et al., 1993, 1995;Sun et al., 1998). Alcohol is implicated more frequently in the fatalcrashes of motorcycle riders than in the fatal crashes of car drivers(NHTSA, 1989), a finding that may be attributed to the impor-tance of coordination and balance in motorcycle riding. A recentempirical test track study (Creaser et al., 2009) demonstrated sig-nificant decrements in riding performance in experienced ridersfollowing low levels of alcohol intoxication (0.02%, 0.05% and 0.08%blood alcohol content, BAC). In that study, participants at 0.05%and 0.08% BAC responded more slowly (compared to a baseline, 0%BAC condition) on a hazard avoidance task, which led to more taskperformance errors. The authors postulate that the decrements inresponse times may have resulted from the effect of alcohol onrelevant functions such as riders’ ability to attend to their environ-ment or their attempts to compensate for impaired balance whileperforming the complex, multi-task activity of motorcycle riding.

1.1. Rider balance and the potential interaction with alcohol

Motorcycles are inherently unstable vehicles. At low speeds,stabilisation is attained through movement of the handle bar andby the rider adjusting their body position (Seiniger et al., 2012).

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ow doses of alcohol (i.e., ≤0.05% BAC) may affect riders’ abilityo maintain their balance, which may consequently impair overallike stability. Body sway is a sensitive measure of the depressantffects of alcohol on the central nervous system (Franks et al., 1976),ith the sensitivity to detect changes at alcohol doses (0.043% BAC)

hat are too low to significantly affect fine motor activity (Mangoldt al., 1996). Body sway parameters are used in the context of clini-al, sports and research settings to measure an individual’s ability toaintain a balanced body posture to prevent falling (Sarabon et al.,

010; Winter, 1995). Static balance tasks involve quiet standingn one or both legs and are generally easy for healthy individualsKitabayashi et al., 2004). A simple method to measure body swayuring static balance involves the use of a device known as the LordSwaymeter”, which is attached at waist level and records body dis-lacement in the anterior–posterior and the lateral directions (Lordt al., 1991).

When alcohol is consumed, the degree of body sway whentanding is increased in both males and females in a significantinear relationship with dose (Lipscomb and Nathan, 1980; Millsnd Bisgrove, 1983). Stance stability is most affected at peak BACevels and, because of the involvement of the vestibular and ocu-omotor systems (both important in the maintenance of posturaltability), continues to be impacted even as alcohol is cleared fromhe system and BAC decreases (Lukas et al., 1989).

If balance during riding is affected by low doses of alcohol, ridersay adapt their riding behaviour to compensate for this psychomo-

or impairment by focusing more on maintaining bike stability. Thisdaptation may consequently decrease the level of attention, oresources, available to perform other, higher-order tasks (Creasert al., 2009). Higher-order skills, such as cornering, judgement andazard perception ability, are necessary for safely riding a motorcy-le while navigating the shared road environment. Therefore, anyalance impairment would be of concern. A dual-task paradigmhat includes the assessment of balance in conjunction with per-ormance of a concurrent, higher-order secondary task can be usedo investigate these possibilities.

.2. Higher-order skills and safe riding

Higher-order skills that are critical for safe riding rely primarilyn cognitive and/or visual faculties (Underwood, 2007; Groeger,000). Cognitive-motor, dual-task design commonly involves theomparison of a motor task performed alone vs. when performedoncurrently with an additional (secondary) cognitive task. Theesultant comparison allows for a determination of dual-task costsi.e., single- minus dual-task performance), which thereby indicatehe degree of interference, or interdependency, between the twoasks. The dual-task paradigm reliably demonstrates a clear inter-ction between balance and cognitive processing (Andersson et al.,002; Ferrara et al., 2011; Hyndman et al., 2009; Li et al., 2009;eilly et al., 2008; Weeks et al., 2003). The paradigm can also besed effectively to assess the effects of psychoactive compoundsn balance and secondary task performance in healthy individualsHegeman et al., 2011). This indicates that the dual-task paradigms suitable to investigate the psychomotor and balance impairmentffects of alcohol. To the authors’ knowledge, no research to-dateas used a dual-task (balance vs. cognitive task) methodology to

nvestigate the contribution of alcohol’s balance impairment effectso riders’ performance of higher-order cognitive tasks.

.3. Potential contribution of riding experience

The high crash risk of young and novice car drivers at lower<0.08%) BAC levels indicates that these drivers are more vulner-ble to the effects of alcohol than older, experienced drivers, anding that may relate to their cognitive immaturity (Peck et al.,

and Prevention 50 (2013) 895– 904

2008). Similarly, riding experience may influence how well a ridercan effectively divide their attention between the requirement tomaintain balance and their ability to engage in higher-order tasks.Indeed, previous research has found impairments in the hazardperception ability of novice compared to experienced motorcycleriders (Liu et al., 2009). Riding inexperience is not only associatedwith slower hazard response times, but also with less flexible visualscanning patterns (Hosking et al., 2010). It has been suggestedthat experience may interact with alcohol to more significantlyaffect the riding performance of novice riders (Creaser et al., 2009)through such a mechanism. If so, novice riders’ ability to maintainstatic balance following the ingestion of low doses of alcohol maysimilarly be impaired.

1.4. Study rationale

Test-track and riding simulator research paradigms can be usedto empirically evaluate some aspects of motorcycle riders’ perfor-mance. Use of a test-track allows for riders’ maintenance of balanceto be taken into account, but it may expose participants to unac-ceptably high potential injury risk. On the other hand, limitations inthe functionality of present-day motorcycle riding simulators gen-erally do not allow the investigation of riders’ balance-related andother vehicle handling skills. To overcome these limitations, thecurrent laboratory study used a dual-task paradigm to investigatethe effects of alcohol on static balance both alone and in conjunctionwith performance of either a visual (search) or a purely cognitive(arithmetic) secondary task. It was hypothesised that subjectiveratings of intoxication and balance impairment would increase, andobjective measures of static balance would decrease, in a dose-dependent manner following the ingestion of low doses (≤0.05%BAC) of alcohol. A second study hypothesis was that maintenanceof static balance following alcohol ingestion would be more affectedwhen participants were required to concurrently perform the sec-ondary tasks than when balancing alone. At the same time, lowdoses of alcohol were predicted to impair performance on the sec-ondary tasks, and to do so significantly more when participantswere required to maintain their balance than when not balancing.Finally, it was predicted that the effects of alcohol on static balanceand/or secondary task performance would be more pronounced innovice riders compared to more experienced riders.

2. Method

2.1. Design

A three-way (3 × 3 × 2) mixed design with ‘BAC’ (within-subjects; 0%, 0.02% and 0.05% BAC), secondary ‘Task’ (within-subjects; no task, cognitive task, visual task) and riding ‘Experience’(between-subjects; experienced, novice) as independent variableswas used to investigate the effects of low (≤0.05% BAC) dosesof alcohol on dependent measures of static balance and sec-ondary task performance in a dual-task paradigm. The researchwas approved by the Monash University Human Research EthicsCommittee.

2.2. Participants

Forty paid participants (20 experienced, 20 novice) ranging inage from 18 to 54 years were recruited from the university and thelocal community by means of advertisements. Experienced riders

(two female) were required to have a full (unrestricted) motorcyclelicence and to have ridden regularly in the past five years, coveringat least 5000 km per year. Novice riders (two female) were requiredto have three years’ or less riding experience and to also have a car

C.M. Rudin-Brown et al. / Accident Analysis and Prevention 50 (2013) 895– 904 897

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ig. 1. Measurement of postural sway using the Lord “Swaymeter” (Lord et al.,991).

river’s licence (Hosking et al., 2010; Liu et al., 2009). All partici-ants were required to be social drinkers (i.e., consume, on average,pproximately two to three alcoholic drinks per week).

.3. Equipment

.3.1. Balance assessmentBalance assessment was conducted with participants standing

n a wooden beam (80 cm long × 7 cm wide × 4.5 cm high) withheir eyes open, with the toes of the back foot touching the heelf the front foot. The decision to use this stance was based on aonsideration of face validity (in terms of motorcycle riding) as wells results of a pilot study of six participants tested in 19 differenttances that showed it to be the most sensitive to perturbations inalance. Postural sway was measured using the Lord “Swaymeter”o record body displacement at waist level (Lord et al., 1991; Fig. 1).his device consists of a firm belt attached around the waist and

40 cm metal rod extending horizontally behind the participantith a vertically mounted pen at the end of the rod. Behind thearticipant, graph paper (with a 1 mm square grid) is placed on topf a height-adjustable table so that the pen records movement ofhe participant onto the paper.

.3.2. Measurement of BACA Lion Alcolmeter SD-400 unit (Lion Laboratories, Glamorgan,

K) was used to measure alcohol exhaled in the breath and to con-ert it to a BAC reading using a 1:2100 partition coefficient. Tonsure accurate performance, the breathalyser was calibrated byictoria Police prior to study commencement.

.3.3. Secondary tasks

.3.3.1. Cognitive task. The Serial Sevens Subtraction Test (SSST;ayman, 1942) has been widely used in neurological examina-

ions of mental function as a measure of concentration (Karzmark,000; Smith, 1967). It involves a person performing mental cal-

ulations to successively subtract the number seven from a giventarting number, usually 100 (Karzmark, 2000). For the currenttudy, instructions were given as such: “Start immediately from theumber I give you and continue to subtract the number seven out

Fig. 2. Screen shot of the visual search task (Surrogate Reference Task; SuRT).

loud. You can go as slow as you like and remember that maintainingyour balance is the primary task”. The starting number was stated(using a different starting number for successive trials) at the sametime as the 30-s balance assessment began. Verbal responses wererecorded using a digital voice recorder and later scored accordingto the number of correct subtractions. If the participant made anerror by subtracting an amount other than seven, any subsequentsubtractions could be scored as correct so long as they involvedthe subtraction of the number seven from the previously statednumber.

2.3.3.2. Visual search task. The Surrogate Reference Task (SuRT; ©2004 DaimlerChrysler AG) was used as the visual search task. TheSuRT was presented on a laptop computer positioned within easyview in front of the participant on a height-adjustable table. Theparticipant was required to visually search for a slightly largertarget circle among visually similar distracter circles and statealoud whether the target circle appeared on the left or the rightof the screen (Fig. 2). The experimenter keyed in the participant’sresponse and the software automatically presented the next cir-cle display. Performance on the SuRT was scored on the basis ofthe number of circle presentations correctly solved within the 30-stime period.

2.4. Procedure

All testing took place between 9:00 am and 6:00 pm. Partici-pants were required to attend three test sessions, each separatedby at least one day. Participants were instructed not to drink alco-hol the night before testing and not to eat for at least two hoursprior to arriving at the test session.

2.4.1. Alcohol administrationAlcohol doses for each BAC condition were calculated using a

BAC calculator that estimates total body water based on height,weight and gender to determine the volume of alcohol required toreach a desired peak BAC level (Hume and Weyers, 1971). Doseswere prepared to achieve the target BAC of either 0.02% or 0.05%using a vodka (37.5% alcohol) and chilled orange juice mixturemade up to a total of 480 ml and presented to participants in anacrylic tumbler.

All participants were tested under each of the three BAC condi-tions (0%, 0.02% and 0.05%) and the order of alcohol administrationwas counterbalanced across test days. Participants were ‘blind’ to

which dose of alcohol they received on each occasion. For the zeroBAC condition, a nominal amount (1 ml) of alcohol was floated atopthe beverage using an eye dropper. Participants were instructed toconsume a sip (approximately 30 ml) of the beverage every minute

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or 16 min. After dosing, participants were given a glass of waternd instructed to rinse their mouth of any residual alcohol. Thisrocedure is a common approach to administering alcohol, includ-

ng a zero alcohol condition, in studies where participants are keptblind’ to the alcohol dose (e.g., Oxley et al., 2006). To allow peak BACevels to be reached, a 20-min period elapsed before BAC measure-

ent using a breathalyser. The BAC that was attained following the0-min waiting period was that at which a participant was tested;o adjustments, in terms of added time or dosing to achieve the tar-et BAC, were made. Balance testing was conducted immediatelyollowing the breathalyser measurement.

.4.2. Balance assessmentAll participants completed three 30-s trials of the balance

ssessment across each secondary task condition (none, visual, andognitive) and under each BAC level. Trials were conducted witharticipants standing (dominant foot in front) on the wooden beamn the floor with their eyes open. Participants were asked to removeheir shoes and stand as still as possible with arms hanging looselyy their side. They were permitted to raise their arms slightly toegain their balance, if necessary. Instructions specified that thearticipant should keep their eyes open and fixated on a pointowards a laptop computer positioned in front of them. All trialsere completed across three repetitions and the average body sway

mm2) recorded. If a participant was not able to remain standingor a 30-s trial period, their test score was extrapolated as per the

ethod used by Lord et al. (1991). For example, if they were able toaintain their balance for only 15 s and the product of the maximal

nterior–posterior and lateral sway in this period was 100 mm2,hen the balance score was 200 mm2 during that particular trial.

.4.3. Secondary task performanceTo assess the effects of BAC and of the requirement to maintain

alance on secondary task performance, participants were requiredo perform three 30-s repetitions of each secondary task (totalf nine) at each dose of alcohol while standing comfortably andhile performing the balance test. The order of presentation of

he balance test vs. standing comfortably for each participant wasounterbalanced across participants. Within each stance configu-ation, participants always completed the cognitive task, followedy the no task condition, and then the visual search task. The num-er of correct items during a 30-s trial was used as the dependenteasure.

.4.4. Subjective ratingsIn all BAC conditions, subjective ratings of intoxication and

redicted balance impairment were collected 20 min followingonsumption of the beverage. Participants were asked to circle aumber from 0 to 10 to indicate how intoxicated they felt and howuch they thought their balance would be impaired, with the num-

er 0 on the left being “completely sober/not affected at all” and theumber 10 on the right being “extremely intoxicated”. At the con-lusion of testing, participants were asked to rate, on a scale from 1easy) to 10 (difficult), how difficult they found balancing across thehree secondary task conditions (no task, cognitive task and visualask).

.5. Statistical analyses

Each of the dependent variables was analysed using a mixedesign repeated-measures ANOVA, with the within-subjects fac-ors of BAC (0%, 0.02%, 0.05% BAC) and Task (no task, cognitive task,

isual task), and the between-subjects factor of Experience (expe-ienced, novice). Degrees of freedom (d.f.) were corrected usinguynh–Feldt estimates of sphericity where Mauchley’s test indi-ated that the assumption of sphericity had been violated; epsilon

and Prevention 50 (2013) 895– 904

(ε) values are listed accordingly. Square root transformations wereconducted on subjective intoxication and predicted balance impair-ment data, as well as postural sway and stance duration data, dueto non-normal distribution of data. Effect size is listed as partial Etasquared (partial �2), demonstrating the proportion of the total vari-ance explained by a variable that is not explained by other variables(.01 is considered a small effect size, .06 a medium effect and .14 alarge effect; Cohen, 1988). Observed power is reported as a decimalranging from 0 to 1 demonstrating the ability to detect an effectif there is one. Power of .80 is considered acceptable (Shavelson,1988). All statistical analyses were conducted using the SPSS sta-tistical program (PASW v.18.0). Pairwise comparisons assessed thesignificance of any differences among conditions. An alpha (˛) levelof .05 was used to determine statistical significance, and pairwisecomparisons conducted using Bonferroni correction.

3. Results

3.1. Participant characteristics

To investigate whether there were any differences in participantcharacteristics between the two experience groups, independentgroups t-tests were performed on the data. The experienced par-ticipants were, on average, significantly older than the noviceparticipants, with significantly more driving and riding experienceboth in terms of years they had held a licence and average numberof riding hours and riding trips per month (Table 1).

3.2. BAC readings

BAC readings were taken immediately prior to balance testingto ensure that participants’ BAC levels had reached the target BACfor each condition. Mean observed BAC for the three BAC condi-tions were 0 (±0)%, 0.023 (±0.006)%, and 0.054 (±0.009)% BAC,respectively.

To investigate whether there were differences in observed BAClevel between the two experience groups, an independent groupst-test was carried out on the BAC data. There was no significantdifference in BAC readings between the two experience groups inany BAC condition.

3.3. Subjective ratings of intoxication and balance impairment

Twenty minutes after consuming each beverage, participantswere asked to rate, on a scale from 0 to 10, how intoxicated they feltand how much they expected their balance to be impaired. Mixedmeasures ANOVA revealed a significant main effect of BAC on sub-jective ratings of intoxication, F(1.7, 64.9) = 133.70, p < .001, partial�2 = 0.78, ε = 0.854, observed power = 1.0, and on ratings of pre-dicted balance impairment, F(1.79, 68.13) = 109.74, p < .001, partial�2 = 0.74, ε = 0.896, observed power = 1.0. Alcohol was associatedwith a dose-dependent increase in ratings on both measures, withpairwise comparisons revealing the 0.02% BAC condition to be asso-ciated with significantly higher ratings of intoxication and balanceimpairment than the sober condition, and the 0.05% BAC conditionbeing associated with significantly higher ratings of intoxicationand balance impairment than the 0.02% BAC condition (Fig. 3).There was no effect of riding experience on either measure.

3.4. Static balance

Participants’ static balance ability was evaluated using measuresof postural sway and stance duration. One experienced participantelected not to perform the balance test at the 0.05% BAC dose, andso balance data from only 39 participants were analysed.

C.M. Rudin-Brown et al. / Accident Analysis and Prevention 50 (2013) 895– 904 899

Table 1Participant characteristics.

Experienced mean (s.d.) Novice mean (s.d.) t (degrees of freedom) p

Age (yrs) 37.1 (9.9) 27.2 (10.8) 3.02 (38) .004*

Years held a motorcycle licence 14.2 (10.3) 1.7 (3) 5.21 (22.3) <.001*

Years held a car licence 18.6 (10.3) 9.1 (10.4) 2.91 (38) .006*

Hours ridden per week 8.2 (6.7) 3.4 (2.4) 3.06 (23.9) .005*

Times ridden per month 21.6 (13.5) 12.2 (12.8) 2.23 (37) .032*

Number of standard drinks consumed per week 5.4 (2.32) 6.2 (2.8) 1.04 (38) .303

* Statistical significance at the p < .05 level.

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The degree of postural sway in each trial was measuredsing the log of the product of maximal sway in the lateral andnterior–posterior directions (Lord et al., 1991). The average pos-ural sway across three trials was used in the analysis. Mixed

easures ANOVA on postural sway data revealed a significantAC by Task interaction, F(3.3, 123.1) = 3.64, p < .05, partial �2 = .09,

= .83, observed power = .82 (Fig. 4; left panel). Paired contrastsevealed that participants at 0.02% BAC demonstrated less posturalway when they performed the visual secondary task than whenhey performed either no task (p < .05) or the cognitive task (p < .05).articipants at 0.05% BAC demonstrated more postural sway whenhey performed the cognitive task than when they performed theisual task or no task (p < .05), and less postural sway when theyerformed the visual task compared to when they performed noask (p < .01). The main effects of BAC, F(1.41, 52.6) = 12.81, p < .01,artial �2 = .257, ε = .92, observed power = .94, and Task, F(1.8,8.3) = 12.80, p < .01, partial �2 = .257, ε = .92, observed power = .44,

ere also significant.

Mixed measures ANOVA on mean stance duration data alsoevealed an interaction between BAC and Task, F(3.5, 129.5) = 2.79,

< .05, partial �2 = .07, ε = .88, observed power = .71 (Fig. 4, right

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panel). Paired contrasts revealed differences among the three tasksonly at the 0.05% BAC dose. Participants at 0.05% BAC demon-strated significantly shorter stance durations when they performedeither the cognitive task or no task than when they performed thevisual task (p < .01). The main effects of BAC, F(1.42, 52.7) = 9.58,p < .01, partial �2 = .206, ε = .71, observed power = .93, and Task, F(2,74) = 9.99, p < .001, partial �2 = .213, observed power = .98, were alsosignificant.

3.5. Secondary task performance

Participants’ performance on the two secondary tasks (cog-nitive, visual) while balancing vs. not balancing (standingcomfortably) was measured using the number of correct responsesper trial. Due to a technical malfunction, secondary task data fromone experienced participant failed to record, and so data from only38 participants were included in the analysis.

Mixed measures ANOVAs on secondary task data were con-ducted to investigate whether the requirement to maintainbalance, BAC, task type, or a combination of the three factors, hadany effect on secondary task performance. The ANOVA revealed a

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ance duration (right) (bars represent standard error of the mean).

900 C.M. Rudin-Brown et al. / Accident Analysis and Prevention 50 (2013) 895– 904

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Fig. 5. Interaction between BAC and Task (left panel) and

ignificant interaction between BAC and Task, F(2, 72) = 4.66, p < .05,artial �2 = .115, observed power = .77, with participants makingignificantly fewer correct responses on the cognitive, but not theisual, secondary task in the 0.05% BAC condition compared to thewo lower BACs (p < .01) (Fig. 5, left panel). The interaction betweenask and Balance approached statistical significance, F(1, 36) = 3.19,

= .082, partial �2 = .081, observed power = .41, with participantsaking fewer correct responses on the cognitive task, but not the

isual task, when they were required to balance compared to whenhey stood comfortably on the floor (p < .01) (Fig. 5, right panel).lthough the interaction only approached statistical significance,

he main effect of Balance on secondary task performance (bothecondary tasks combined) was significant, F(1, 36) = 5.2, p < .05,artial �2 = .126, observed power = .60, with participants makingignificantly fewer correct responses when they were required toalance than when they stood comfortably on the floor.

.6. Subjective ratings of ‘ease of balancing’

Immediately following the balance test, participants were askedo rate, on a scale from 1 (easy) to 10 (difficult), how difficulthey found balancing across the three secondary task condi-ions (no task, cognitive task and visual task). Mixed measuresNOVA revealed a significant BAC by Experience interaction F(2,2) = 5.913, p = .004, partial �2 = .141, observed power = .86 (Fig. 6,

eft panel). While both Experience groups rated balancing as moreifficult when at 0.05% BAC compared to when sober, the expe-ienced riders rated balancing as significantly less difficult whent 0.02% BAC compared to when sober and at 0.05% BAC. Theain effect of BAC on subjective ‘ease of balancing’ ratings was

lso significant, F(2, 72) = 16.49, p < .001, partial �2 = .314, observedower = 1.0.

Finally, there was a significant main effect of Task on subjectiveatings of ‘ease of balancing’, F(1.75, 63.1) = 8.43, p = .001, partial2 = 0.19, ε = 0.88, observed power = .94 (Fig. 6, right panel), withairwise comparison showing ease of balancing ratings when com-leting the cognitive task to be significantly higher (more difficult)han when completing either no task or the visual task (p < .01), buto differences between the visual task and the ‘no task’ conditions.

. Discussion

The current study used a dual-task laboratory paradigm toxamine the effects of low dose alcohol on static balance in

otorcycle riders, both alone and in conjunction with two higher-

rder secondary tasks: a visual search task and a purely cognitivearithmetic) task. Subjective ratings of intoxication and balancempairment increased in a dose-dependent manner, while a BAC of

ement to balance (right) on secondary task performance.

0.05%, but not 0.02% was associated with impairments in static bal-ance ability in both novice and experienced motorcycle riders. Thisbalance impairment was more pronounced when riders performeda cognitive (arithmetic), but not a visual, secondary task. Likewise,0.05% BAC was associated with impairments in novice and experi-enced riders’ performance of a cognitive, but not a visual, secondarytask, suggesting that interactive processes underlie balance abilityand cognitive task performance. There were no observed differ-ences between novice vs. experienced riders on static balance orsecondary task performance. In contrast to the effects observedat 0.05% BAC, the lower 0.02% BAC was associated with balance-enhancing effects (over sober, baseline, measures of balance) whenparticipants performed the visual secondary task, but not whenthey performed the cognitive task. Performance of the visual taskwas associated with improved static balance ability compared tothe no task condition at both 0.02% and 0.05% BAC. Collectively,results may have important implications for motorcycle ridingsafety.

A dual-task paradigm with static balance and secondary taskwas selected based on a review of the scientific literature, as wellas discussions with a world expert in motorcycle simulation (S.Espié, personal communication). These discussions indicated thatthe currently available level of sophistication of motorcycle simu-lation technology would make the use of a motorcycle simulatorinadequate for the complete assessment of physical aspects ofmotorcycle riding, such as balance. The methodology used, there-fore, is considered an appropriate ‘surrogate’ means to test thehypothesis that low dose alcohol’s effects on balance impairmentinteract with higher-order cognitive abilities that likely play arole in hazard perception ability. Balance is a motor skill uniquelyinvolved in the operation of two-wheeled vehicles (Seiniger et al.,2012); any impairment of balance may, therefore, affect riding per-formance in a manner that would not be observed in car drivers.Previous research has reported motorcycle riders to feature withgreater prevalence in crash statistics at lower BAC than car drivers(Sun et al., 1998). As many of the higher-order skills (i.e., hazardperception) required for riding are the same as those required fordriving, it is possible that difficulties in maintaining balance mayaccount for the greater prevalence of crash involvement at lowerBAC level compared with car drivers.

Results provide some support for the first studyhypothesis—that subjective ratings of intoxication and bal-ance impairment would increase, and objective measures of staticbalance would decrease, in a dose-dependent manner following

the ingestion of low doses (≤0.05% BAC) of alcohol. Ingestionof alcohol was associated with a dose-dependent increase insubjective ratings of intoxication and predicted balance impair-ment. These ratings corresponded with decrements in objective

C.M. Rudin-Brown et al. / Accident Analysis and Prevention 50 (2013) 895– 904 901

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easures of static balance, including increases in body sway andhorter stance durations, at the 0.05% BAC dose. This is in accor-ance with previous research on the effects of low doses of alcoholn static balance (Mangold et al., 1996). Contrary to expectations,owever, 0.02% BAC was not associated with decrements in objec-ive measures of static balance, despite increases in subjectiveatings of intoxication and predicted balance impairment at thisevel of BAC. Previous studies of alcohol’s effects on balance haveound paradoxical results at 0.02% BAC (Moskowitz and Fiorentino,000). It is possible that the balance task used in the present studyas not sensitive enough to detect balance-impairing effects of

lcohol at this dose. Alternatively, it is possible that alcohol’sepressant effects on the central nervous system, which aressociated with relaxation and tension reduction at low (<0.05%AC) levels, resulted in participants’ balance being more stablet 0.02% BAC than when participants were sober (Pohorecky andrick, 1987). Interestingly, subjective ratings of ‘ease of balancing’esults support this possibility, especially among experiencediders, as subjective ratings were lower at the 0.02% BAC comparedo at both zero and 0.05% BAC.

The second study hypothesis—that maintenance of static bal-nce following alcohol ingestion would be more affected whenarticipants were required to concurrently perform the secondaryasks than when balancing alone—was supported by the findinghat BAC interacted with performance of the cognitive secondaryask to selectively impair balance. This was not the case for theisual secondary task, which showed no such interaction. In fact,erformance of the visual task resulted in improved static bal-nce at both the 0.02% and 0.05% BAC compared to the no tasknd cognitive task conditions. It is possible that the unimpairedfrom baseline) balance performance observed when participantserformed the visual task occurred because the visual task focusedarticipants’ attention more compellingly on the laptop in frontf them than either the cognitive task or no task. An attempt wasade to minimise this possibility by providing participants in all

onditions with identical instructions (to “keep their eyes open andxated on a point towards a laptop computer positioned in front ofhem”); however, it is possible that differences occurred regardless.lternatively, it is possible that the order of presentation of the sec-ndary tasks, in which the visual task was presented last, may haveesulted in the improved balance performance observed in thisondition. That a practice effect was at play is unlikely, however,s it would also mean that balance during the ‘no task’ conditionhould always have been better compared to balance when partici-ants performed the cognitive task, which was presented first. Thisas not the case. Similarly, with a practice effect, balance would

e expected to be most impaired when participants performedhe cognitive task (presented first) at 0% BAC, which also was nothe case. Another possible explanation for the selective effects ofhe cognitive task on alcohol-induced balance impairment is that

Task (right) on subjective ratings of ‘ease of balancing’ (out of 10).

the cognitive task exerted greater attentional demands on partici-pants than the visual task, which resulted in greater impairments inbalance. Previous research has found that attentional load of a sec-ondary task increases the degree of postural control interference(Reilly et al., 2008). The impact of cognitive secondary task per-formance on balance implies that there is an interaction betweenthese two processes that may compromise motorcycle riding per-formance.

Previous test-track research found that low doses of alcoholcontributed to higher-order deficits beyond vehicle handling skills(Creaser et al., 2009). This suggests that low levels of alcohol mayresult in riders adapting their attentional strategies to compensatefor psychomotor impairment, which may concomitantly detracttheir attention away from other, higher-order cognitive skills. Thethird study hypothesis predicted that, in addition to a synergis-tic impairing effect of alcohol and secondary task performance onstatic balance ability, low doses of alcohol would impair perfor-mance on the secondary tasks and that the impairing effect of lowdose alcohol on secondary task performance would be more sig-nificant when participants were required to maintain their staticbalance than when not balancing. This hypothesis was only par-tially supported, and once again, only for the cognitive task.

Decrements on the purely cognitive secondary task at the 0.05%BAC dose were observed when participants were required to main-tain balance. This combination of cognitive task and 0.05% BACalso resulted in significantly greater postural sway than the visualsearch task. These results suggest that if drinking riders were todevote significant cognitive resources to a non-visual secondarytask while riding, such as a mobile phone conversation, talkingon a headset to a pillion passenger, or inattention from the for-ward scene, then they would put themselves at a greater risk ofbeing involved in a collision due to impairments in their abilityto maintain motorcycle stability. This possibility is supported bycrash data showing that the majority of alcohol-related motorcy-cle crashes are single-vehicle, run-off-the-road crashes that occuron curves, at night, on weekends, and while riders are on theirway home—crash types that are attributed to alcohol-induced riderinattention (Kasantikul et al., 2005). Interestingly, results from sev-eral studies (Creaser et al., 2009; Kasantikul et al., 2005) suggestthat alcohol may have selective detrimental effects on attentionwhile riding. Based on the present data, though, it would seem thatthis may not be the case for all types of secondary tasks, as alcoholat the doses tested failed to impair performance on the visual task,which by its very nature involves attentional resources.

This study is one of the only attempts to use a dual-taskparadigm to investigate the contribution of alcohol’s balance-

impairing effects to higher-order, secondary task performance.Previous research has used the dual-task paradigm to investigateeffects of secondary task performance on sober static balance abil-ity in a variety of participant groups, however, and has found

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ixed results. The “posture first” principle has been put fortho explain observed decrements in cognitive task performance inual-task studies on cognition and balance (Shumway-Cook et al.,997). According to this theory, impairments in secondary taskerformance imply that participants are devoting more cognitiveesources to maintaining their balance than to their performancef a secondary (cognitive) task. For example, a recent study of 20ealthy, college-aged students using a purely cognitive (auditorywitch test) secondary task found improved balance under dual-ask conditions, but impaired performance on the secondary taskFerrara et al., 2011). Similarly, Andersson et al. (2002) found thaterformance of a mental task (silent backward counting in steps ofeven) while balancing was associated with decreases in posturalway in healthy volunteers but impairment on the secondary task.

While decrements in secondary task performance in dual-tasktudies can be interpreted as supporting the ‘posture first’ princi-le, it cannot explain decrements in balance ability observed inual-task conditions. For instance, the balance ability of strokeatients was found to worsen under dual-task conditions com-ared to balancing alone (Bensoussan et al., 2007). Another studyound impaired balance when healthy participants performed a

otor-based secondary task (finger-thumb pinch) but not a cogni-ive (mental arithmetic) secondary task, and no effect of increasedostural “demands” (electrical stimulation of the calf muscle) onerformance of either secondary task (Weeks et al., 2003). On thether hand, Hyndman et al. (2009) found stroke patients’ perfor-ance of a cognitive secondary task actually improved measures

f postural sway.Neither the ‘posture first’ principle nor its antipode can explain

he observed selective impairments in balance when participantsoncurrently performed the cognitive secondary task at the 0.05%AC. Instead, one might conclude from these data alone that moref a ‘cognition first’ phenomenon was at play. However, decrementsn secondary task performance were also observed at this BAC whilearticipants were required to maintain balance, indicating that nei-her interpretation would be adequate to fully explain the findings.t appears, therefore, that the relationship among alcohol, balance,nd cognitive higher-order task performance, is more complex thanhat which can be explained by ‘one- or the other’-type reason-ng. More research is needed to investigate the interactions amonghese variables, and their significance to motorcycle riding and roadafety.

The last study hypothesis, that the effects of alcohol on staticalance and/or secondary task performance would be more pro-ounced in novice riders compared to experienced riders, wasenerally not supported by the data and so can be rejected. Thenly observed difference between the two experience groups wasn subjective ratings of how easy participants found balancing to ben the 0.02% BAC condition, with experienced participants rating thectivity as significantly easier than the novice participants at thisAC. While the lack of an effect is always a challenge to explain, it isossible that the stance used in the balance assessment (standingn a wooden beam) was insensitive to differences in level of motor-ycle riding experience. All participants, regardless of their levelf motorcycle riding experience, would be expected to be ‘expe-ienced’ at maintaining their balance when standing upright. Onhe other hand, being seated on a motorcycle changes one’s cen-re of gravity, and may be more sensitive to differences in ridingxperience than maintaining balance while standing upright.

.1. Limitations

A limitation of the present study is the laboratory setting andrtificial circumstances in which it was conducted. Participantsere required to sit by themselves in a windowless room while

onsuming a drink, and to perform prescribed balance tasks in the

and Prevention 50 (2013) 895– 904

presence of an experimenter. It is possible that the effects of alcoholon balance and higher-order cognitive processes would be differ-ent if they were evaluated under real world circumstances—forexample, in participants following an evening of drinks at thelocal pub. To more closely simulate real riding conditions, a motor-cycle riding simulator study has been conducted (Filtness et al.,in press); however, due to limitations of the simulator to mea-sure motorcycle handling skills (discussed above), it was notpossible to measure alcohol’s effects on balance using the simu-lator.

The static nature of the balance test, and the artificial nature ofthe secondary tasks, are also recognised as potential limitations tothe validity of the study paradigm to investigate motorcycle ridingperformance—a dynamic, real world activity. It is therefore unclearas to whether, and to what extent, the balance test used measuresthe type of balance used during motorcycle riding. Nevertheless,this study is one of the first to systematically investigate and test thehypothesis that the balance-impairing effects of alcohol cause rid-ers to adapt their riding behaviour by focusing more on maintainingbike stability at the expense of higher-order cognitive tasks, likehazard perception. As such, it represents a worthwhile contributionto the scientific literature.

Individual differences in tolerance to the effects of alcohol mayhave resulted in some participants’ balance ability being moreaffected than others by the doses of alcohol used in this study.That tolerances for alcohol were as similar as possible across par-ticipants, however, was made more likely by the requirement thatparticipants consider themselves to be ‘social’ drinkers (e.g., con-sume between 2 and 3 standard drinks, on average, per week).

The order of presentation of the secondary task conditions wasnot counterbalanced; this raises the possibility of a practice effectthat may have improved participants’ performance on the balancetest and/or the secondary tasks. On the other hand, it is similarlypossible that a fatigue effect may have impaired balance, secondarytask performance, or both. Regardless, it is unlikely that practice orfatigue effects contributed significantly to the results, as the totalduration of the balance testing was never longer than 4.5 min, andparticipants were provided with ample opportunity to rest andstretch their legs in between consecutive balance tests.

Finally, the balance task used in the present study was limited toa maximum duration of 30 s. This stance duration is much shorterthan the period of time required to maintain one’s balance andmotorcycle stability while riding. Regardless, impairment in bal-ance was identified at the 0.05% BAC dose during this, relativelyshort, balance task; impairment may be greater during the pro-longed task of real riding.

4.2. Future directions

Future research into alcohol’s effects on motorcycle ridingshould attempt to combine the balance aspect of alcohol inges-tion with motorcycle riding in order to quantify the magnitudeof impairment when experiencing the concurrent requirements ofbalancing and riding. While existing motorcycle riding simulatorsgenerally do not allow for investigation of riders’ balance-relatedand other handling skills, efforts should be made to improvethe functionality of future simulators so that these issues can beaddressed. In particular, the specific nature of balancing on a motor-cycle (or bicycle) could be investigated. Balancing on two-wheeledmodes of transport involves maintaining a unique posture. Abilityat such balancing may improve with experience.

A further consideration of any future study investigating the

effects of alcohol on motorcyclists’ balance should be the durationof the balance task. The current study used a 30-s balance durationlimit, which is in accordance with previous balance studies. How-ever, motorcyclists are required to maintain their balance for much

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onger periods of time. Allowing participants to maintain theiralance for a longer period would be expected to result in a greaterariety of results, which may be more sensitive to the effectsf alcohol and riding experience. An additional consideration ishe physical fatigue that may be experienced when riding longistances. It would be interesting to examine whether the effect oflcohol on postural sway is greater when participants have beenaintaining a stance for an extended period of time.Finally, positive BACs are more likely to be observed when

oadside breathalyser testing is conducted at night (Jama et al.,011; Kasantikul et al., 2005). Testing at night introduces fatigues another potential factor that was not considered in the currenttudy. Simulated driving impairment due to alcohol consumptionas been shown to be exacerbated by the added pressure of sleepestriction (Horne et al., 2003). In an effort to minimise any con-ounds associated with fatigue or time-of-day, the current studyas conducted during daylight hours. It is possible that effects of

ow doses of alcohol on balance and secondary task performanceould be more significant if a similar study was conducted duringeriods of usual sleepiness (e.g., at night).

. Conclusions

Results from the present study have implications for real worldotorcycle riding and related road safety policy. Increases in sub-

ective intoxication and balance impairment, as well as decreasesn objective measures of balance ability, at 0.05% BAC indicate thatven legal (i.e., <0.05% BAC) doses of alcohol may have adverseffects on riding performance and crash risk. These findings sug-est that a legal BAC limit for motorcycle riders of less than 0.05%AC would be appropriate. At the same time, the effects of 0.02%AC on these measures were paradoxical—although participantsated their subjective intoxication and balance impairment as sig-ificantly higher than when sober, there was no corresponding

mpairment in the objective measures of balance. Therefore, ridershould be advised to avoid drinking alcohol before riding or to limitheir alcohol intake to no more than one standard drink. Improve-

ents in objective measures of balance at both 0.02% and 0.05% BAChen participants performed the visual secondary task suggest that

iders who may have already ingested alcohol before riding wouldenefit from actively and continually scanning the forward visualcene while riding, rather than focusing on one point in the forwardcene. Finally, policy makers are encouraged to continue to supportesearch into the effects of legal (low) doses of alcohol on motor-ycle riding performance, with a view towards informing policyecisions using relevant, reliable, and robust empirical data.

cknowledgements

This research was performed under contract for Queensland’separtment of Transport and Main Roads. The views expressed are

hose of the authors and not necessarily of the study sponsor.

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