Braz. j. . vol.82 número1

www.bjorl.org

Brazilian

Journal

of

OTORHINOLARYNGOLOGY

ORIGINAL

ARTICLE

The

effects

of

concurrent

cognitive

tasks

on

postural

sway

in

healthy

subjects

夽

,

夽夽

Banu

Mujdeci

,

Didem

Turkyilmaz

,

Suha

Yagcioglu

,

Songul

Aksoy

a_{DepartmentofAudiology,FacultyofHealthSciences,YıldırımBeyazıtUniversity,Ankara,Turkey} b_{DepartmentofAudiology,InstituteofHealthScience,HacettepeUniversity,Ankara,Turkey} c_{DepartmentofBiophysics,FacultyofMedicine,HacettepeUniversity,Ankara,Turkey}

Received8November2012;accepted9December2014 Availableonline21November2015

KEYWORDS

Posturalbalance; Taskperformanceand analysis;

Memory,short-term; Attention

Abstract

Introduction:Keepingbalanceoftheuprightstanceisahighlypracticeddailytaskforhealthy adultsandiseffectivelyperformedwithoutovertattentionalcontrolinmost.

Objective: Thepurposeofthisstudywastoexaminetheinfluenceofconcurrentcognitivetasks onposturalswayinhealthyparticipants.

Methods:Thiswasaprospectivestudy.20healthyvolunteersubjectswereincluded.The cog-nitiveandbalancetaskswereperformedseparatelyandthen,concurrently.Posturalcontrol taskconsistedof6conditions(C)oftheSensoryOrganizationTest.Thecognitivetaskconsisted ofdigitrehearsaltaskofvaryingpresentationandvaryinglevelsofdifficulty.

Results:AstatisticallysignificantdifferencewasnotedbetweendualtaskandnotaskforC1, C2,C3andC4SensoryOrganizationTestscores(p<0.05).Therewasnostatisticallysignificant differencebetweendualtaskversusnon-taskforC5,C6andcombinedSensoryOrganization Testscores(p>0.05).

Conclusion: Duringdualtask,increasehasbeendeterminedinposturalswayforC1,C2,C3and C4forallpresentationmodesanddifficultylevelsofthecognitivetasks.

© 2015Associac¸ãoBrasileira de Otorrinolaringologiae CirurgiaCérvico-Facial. Publishedby ElsevierEditoraLtda.Allrightsreserved.

夽 _{Pleasecitethisarticleas:MujdeciB,TurkyilmazD,YagciogluS,AksoyS.Theeffectsofconcurrentcognitivetasksonposturalswayin} healthysubjects.BrazJOtorhinolaryngol.2016;82:3---10.

夽夽

Institution:YıldırımBeyazıtUniversity,FacultyofHealthSciences.Ankara,Turkey.

∗_{Correspondingauthor.}

E-mail:banumujdeci@yahoo.com(B.Mujdeci). http://dx.doi.org/10.1016/j.bjorl.2015.10.011

PALAVRAS-CHAVE

Equilíbriopostural; Realizac¸ãoeanálise detarefas;

Memóriadecurto prazo;

Atenc¸ão

Efeitosdetarefascognitivassimultâneasnoequilíbrioposturalemindivíduos saudáveis

Resumo

Introduc¸ão:Mantero equilíbrio naposturavertical éuma tarefa cotidianaconstantemente praticadaporadultossaudáveis,eéefetivamenterealizadapelamaioriasemanecessidadede umcontroleatencional.

Objetivo:A finalidadedesteestudofoiexaminarainfluênciadetarefascognitivas concomi-tantesnoequilíbrioposturaldeindivíduossaudáveis.

Método: Trata-sede um estudo prospectivo em queparticiparam 20 voluntários saudáveis. As tarefas cognitivase de equilíbrio foram realizadas separadamente; e em seguida, real-izadas simultaneamente. A tarefa de controle postural consistiu em seis condic¸ões (C) do TestedeOrganizac¸ãoSensorial(TOS).Atarefacognitivaconsistiunarepetic¸ãodedígitoscom apresentac¸õesvariadaseváriosníveisdedificuldade.

Resultados: Houve diferenc¸a estatisticamentesignificante entre os escores do TOS para as condic¸õesC1,C2,C3eC4para‘‘duplatarefa’’vs.‘‘nãotarefa’’(p<0,05).Nãohouvediferenc¸a estatisticamente significanteentre os escores do TOS para as condic¸ões C5 e C6 e para a combinac¸ãodosescoresdoTOSpara‘‘duplatarefa’’vs.‘‘nãotarefa’’(p>0,05).

Conclusão:Durantearealizac¸ãodeduplatarefa,foramdeterminadosaumentosnaoscilac¸ão posturalparaascondic¸õesC1,C2,C3eC4paratodososmodosdeapresentac¸ãoeníveisde dificuldadedastarefascognitivas.

©2015Associac¸ãoBrasileira deOtorrinolaringologiaeCirurgiaCérvico-Facial.Publicadopor ElsevierEditoraLtda.Todososdireitosreservados.

Introduction

Stancebalancecontrolisacomplexmotorskillthatrelies ontheinteractionsamongthreemajorsensorycomponents: thevisual,somatosensory,andvestibularsystems.1_The

inte-grationofvisual,vestibular,andsomatosensorycomponents isusedtomaintainone’sposturalbalance.Posturalcontrol representsacomplexinterplaybetweenthesensorysystems whichinvolvesperceivingenvironmentalstimuli,responding toalterations,andmaintainingthebody’scenterofgravity withinthebaseofsupport.2_{Keepingbalanceoftheupright}

stanceisahighlypracticeddailytaskforhealthyadultsand iseffectivelyperformedwithoutovertattentionalcontrolin mostcircumstances.3

Thenatureoftherelationbetweenposturalcontroland cognitionremainsunclear.4_{Themainquestionsarewhether}

the postural challenge will have an effect on cognitive performance,andconversely,whetherperformanceofthe cognitivetaskdecreasesposturalstability.5_Several

investi-gatorshavesuggestedthatcontrolofstanceandcontrolof locomotionrequiresomelevelofhighercognitiveprocessing despitetheir highlypracticednature.6---8 _{The methodology}

for experimental testing using a dual-task paradigm with motorskills is describedin a classicpaperby Abernethy.9

Oneof two tasks is designated the primary task.Primary taskperformanceismaintainedatthebaselinelevelduring the dual task condition.10 _{The dual task paradigm}

pro-vides information on the automaticity, hemispheric locus andstructuralindependence ofprocesseshypothesized to underlietheproductionofskilledperformance.9

Common real-word observations of people convers-ing while walking or listening to music while running

illustrate this statement. In those situations, the atten-tionalresourcesmustbedividedtoproperlyperformboth tasks.11 _{If,inthedualtaskcondition,performanceonthe}

secondarytaskisreducedfromthebaselinelevel,itreflects highattentionaldemandsoftheprimarytaskandsuggests insufficientreservecapacitytoperformthesecondarytask atthebaselinelevel.10 _{Acommonlyaccepted approachto}

understanding dual-task interference between motor and cognitivetasksisgroundedinlimitedresourceorcapacity theories of attention. According to those theories, the brain’s information-processingcapacityor resources avail-ableforprocessingarelimited.12_{Amultiple-resourcetheory}

wouldpredictdual-taskinterferenceonlywhenconcurrent tasksemployaspectsofthesamecognitiveresource.13_The

combineddifficulty of the tasks requires excessive atten-tion,theninterferencebetweentaskscouldoccur.Thatis, thequalityofperformanceofbothtaskscoulddecrease,or onetaskbeperformedinpreferencetotheother.8,14

Thepurposeofthisstudywastoexaminetheinfluence of different concurrent cognitive tasks on postural sway in healthy subjects. We hypothesized that postural sway wouldbemodulatedbythepresenceanddifficultyofdigit rehearsaltask.

Methods

Participants

history of neurological disease, hearing impairments, visual impairments not correctable with lenses, muscu-loskeletal impairments and injuries or disordersaffecting balance.

Tests

All measurements were carried out in one experimental session for each subject. At first, the cognitive and bal-ancetaskswereperformedseparately(singletask);thenthe cognitive andbalance tasks were performed concurrently (dual task). The study wasapproved by the Ethical Com-mitteeoftheinstitution.Afterthescopeandobjectiveof theresearchhadbeenexplainedtothesubjectswho par-ticipatedintheresearch,theirwritten consentswerealso obtained.

Balancetest

All subjects were evaluatedin a study of postural stabil-ityusingComputerizedDynamicPosturography.TheSensory Organization Test (SOT) was conducted with a Neuro-Com SmartBalance Master(NeuroCom International,Inc., Clackamas,OR).TheSOTwasperformedinaclinically rou-tinemanner.Sixtestconditionsweredevelopedforbalance assessment:eyesopen fixed supportsurfaceandsurround (fixed---fixed) (C1), eyes closed fixed support surface and surround(fixed---absent)(C2),eyesopen fixedsupport sur-faceandsway-referencedsurround(fixed---sway)(C3),eyes open sway-referenced support surface and fixed surround (sway---fixed)(C4),eyesclosedswayreferencedsupport sur-faceandfixedsurround(sway---absent)(C5),eyesopensway referencedsupportsurfaceandsurround(sway---sway)(C6). Sway gainwassetat 1.0,exactly matchingsway referen-cingtosubject’sswayasdescribedintheNeuroComSystem Operator’sManual.15_{Thelengthofeachtrialwasextended}

to20s.Thesubjectsthencompletedeachofthesix condi-tionsthreetimes.

Cognitivetest

Beforebeginningthebalancetask,participantscompleted thedigitmemorytestsothatwecoulddetermineeach par-ticipant’sdigit string.Thedigitswere givenusingE-Prime 2.0Professional(PsychologySoftwareToolsInc.,Pittsburgh, PA, USA). The digits were given at the rate of one per secondonacomputerof NeuroComBalanceMastervia E-Prime2.0Professionalusing144-pointTimesfontpositioned at eye level in front of the participant.The participants weregivenatest ofdigit stringusingauditory, visualand auditory---visualmixedpresentation,andtheywereaskedto repeattheorder.Speakerswereusedforauditory presenta-tion.Whenasubjectfailedatbothattemptsatonelevel, thetest ceased.The maximum numberof digitscorrectly recalledinthesameorderaspresentedservedasthe num-berofdigitsdisplayedinthedifficultexperimentalcondition ofthecognitivetask.Wedeterminedthenumberofdigits displayedintheeasyconditionbytakinghalfofthe maxi-mumnumberofdigitsrecalled.Afterarelaxationbreakof tenminutes,dualtaskorderwasappliedtothesubjects.

Procedures

The dual task session began with instructions. After con-firming that the participant understood the procedure, testingbegan.Theparticipantwastheninstructedtostand ontheNeuroComBalanceMasterplatformandtoperform thecognitivetestwhilemaintainingbalanceundersixtest conditions(Fig.1).Eachtrialwasrandomizedtominimize practiceeffects.

The participantswere givena test ofdigit stringusing auditory,visualandauditory---visualmixedpresentation.The orderofpresentationoftrialsineachoftheexperimental conditions(no-task, easy, difficult) was fully randomized. ThreetrialsineachofthesixSOTconditionswerepresented inrandomorder.Oneachtrialinthedigit-taskconditions, digitstring wasdisplayedon acomputer. The digitswere given at the rate of one per second. Participants were instructedtorehearsethedigit stringuntilitdisappeared

6

SOT

Digit span test

Participant

Clinicion Computerised dynamic

posturography

Cognitive task

6

+

Verbal recall

Data analyzed Rehearsal

20 second

Figure2 Illustrationofthedualtaskprocedure.

andabluescreenappeared.Meanwhileparticipantshadto encodethisdigitstringuntildisappeared.Atthatpoint,the 20sposturalswaymeasurementperiodbegan.Forthe eyes-closed trials, participants were instructed to close their eyes; for eyes-open position participants kept their eyes open,and wereinstructed tosimplylookahead butwere nottoldtofixateonanygivenobjectorlocation.Subjects hadtomentallyrepeatthestringduringthe20sduration. At the end of this 20s maintenance period, participants repeateddigitstring(Fig.2).Participants’responseswere recorded for each trial. The number of errors(intrusion, order error and omission) in the response was recorded bytheexperimenter.Allofthescoresrecordedwithinthe 20s SOT test were used in the statistical analyses. The subjects were allowed to take a relaxation break of ten minutesaftereachdualtaskstage,whichsumsuptoatotal time of fifty minutes. During the relaxation breaks, the subjects were offered refreshments. Although it changed depending on the cognitive performance of the subject, theduration of all tests, includingthe relaxation breaks, rangedbetween130and150min.

Dataanalysis

StatisticalanalyseswereperformedusingtheSPSSsoftware version 18. The Wilcoxon test was used to assess differ-ences between mean balance scores obtained under the no-task and dual-task conditions (easy, difficult) for each ofthesixbalanceconditionsandeachpresentation (audi-tory, visual, auditory---visual mixed). Descriptive analyses werepresentedusingmediansandinterquartilerange(IQR) forthenon-normallydistributedandordinalvariables.Ap -valueoflessthan0.05wasconsideredtoshowastatistically significantresult.

Results

TheSOTscoresobtainedfromthedualtaskconditionswere compared separately with the no-task SOT scores. There was statistically significant difference between dual task andno-taskC1,C2,C3andC4SOTscores(p<0.05).There wasnostatisticallysignificantdifferencebetweendualtask andno-taskSOTscoresforC5,C6andcombinedSOTscores (p>0.05)(Table1).

Withintheconditionsofdualtaskofthesamedifficulty degree,asaresultof doublecomparisonaccording tothe presentation manner of the stimulus (e.g. auditory easy

and visual easy) nostatistically significant differencewas obtainedwithinalldualtaskconditionSOTscores(p>0.05). Inthedualtaskorder,asaresultofdoublecomparison accordingtothedifficultylevelofthecognitivetasks hav-ingthesamepresentation manner(e.g.auditoryeasy and auditorydifficult)nostatisticallysignificantdifferencewas obtainedwithinalldualtaskconditionSOTscores(p>.05). Nostatisticalanalyseswerecarriedoutforthemistakes ofthesubjectsinthesixSOTconditionsthatweredonewith threerepetitiveinthedualtaskorder;onlytheiraverage wascalculated.Sixerrorsweremadeintheauditoryeasy condition,six intheauditorydifficult condition,12in the visualeasycondition,98inthevisualdifficultcondition,five intheauditory---visualmixedeasycondition,and117errors weremadeintheauditory---visualmixeddifficultcondition.

Discussion

The purpose of this study was to examine the influence of concurrent cognitivetasks on postural sway in healthy participants. Our short-termmemory taskfocused on the process of rehearsal. In dual task studies, visual and/or auditory cognitive tasks generally have been used simul-taneouslywithposturaltask,16---18 _{buttherearenostudies}

using auditory---visual mixed cognitive task. Therefore, in thisstudy,auditory---visualmixedtask,inadditiontovisual and/or auditory cognitive tasks with concurrent postural taskhasbeenalsousedduringdualtask.No-taskscoresand dualtaskscoreswereobtainedseparatelyandcompared.

Inthisstudy,anterior---posteriorswayincreasedfor C1, C2, C3, C4 SOT scores but was not affected for C5, C6 andcombinedSOTscorescomparedtono-taskscores. Dur-ing dualtask,togetherwithadding thecognitive tasksto postural control task, statisticallysignificant increase has been determined in the postural sway for relatively easy posturalconditionsC1,C2(theplatformisstable),C3and C4 (only one of the proprioceptive and visual perception inputdistortedorabsent)forallofthepresentation man-nersanddifficultylevelsofthecognitivetasks.Thisfinding isconsistentwiththeresultsofPellecchiaetal.19_reporting

that posturalsway increasedwhendualtaskwasapplied. Otherinvestigators8,20---22_{havealsofounddeficitsinpostural}

control followingthe additionofa cognitivetask.Several reasonscan beofferedfor thisfinding. Increasedpostural sway under dual task in this study can be explained by divided attention.23 _{It is known that when one needs to}

Table1 Thecomparisonoftheno-taskSOTscoresandSOTscoresobtainedsimultaneouslywithcognitivetask.

Task SOT Scores

C1 C2 C3 C4 C5 C6 Composite

Notask

Median 94.50 93.00 92.33 87.50 68.66 70.83 81.00

IQR 1.83 3.17 5.17 6.00 12.75 17.25 7.00

Auditoryeasy

Median 89.33 89.16 90.00 80.83 72.83 68.83 80.50

IQR 7.25 4.50 6.58 12.42 12.67 21.33 6.50

p 0.001a _0.001a _0.005a _0.002a _{0.355 0.601 0.256}

Notask

Median 94.50 93.00 92.33 87.50 68.66 70.83 81.00 IQR 1.83 3.17 5.17 6.00 12.75 17.25 7.00

Auditorydifficult

Median 92.16 91.00 89.83 81.66 71.00 71.66 82.00 IQR 6.25 6.25 7.92 11.75 11.00 20.92 8.00

p 0.001a _0.003a _0.016a _0.003a _{0.588 0.679 0.615} Notask

Median 94.50 93.00 92.33 87.50 68.66 70.83 81.00 IQR 1.83 3.17 5.17 6.00 12.75 17.25 7.00

Visualeasy

Median 90.50 89.00 88.16 81.83 71.00 71.50 79.50 IQR 9.00 9.25 5.50 10.00 13.75 24.08 11.75

p 0.000a _0.006a _0.002a _0.007a _{0.904 0.478 0.055} Notask

Median 94.50 93.00 92.33 87.50 68.66 70.83 81.00 IQR 1.83 3.17 5.17 6.00 12.75 17.25 7.00

Visualdifficult

Median 90.33 90.33 90.16 79.33 75.66 68.00 78.50 IQR 6.17 8.08 7.67 9.83 16.00 17.75 8.50

p 0.000a _0.001a _0.017a _0.001a _{0.287 0.856 0.126} Notask

Median 94.50 93.00 92.33 87.50 68.66 70.83 81.00 IQR 1.83 3.17 5.17 6.00 12.75 17.25 7.00

Auditory---visual

Mixedeasy

Median 90.66 90.50 89.83 82.50 73.33 63.00 79.50 IQR 6.42 7.17 8.42 13.67 16.42 19.92 8.75

p 0.001a _0.001a _0.007a _0.015a _{0.370 0.185 0.055} Notask

Median 94.50 93.00 92.33 87.50 68.66 70.83 81.00 IQR 1.83 3.17 5.17 6.00 12.75 17.25 7.00

Auditory---visual

Mixeddifficult

Median 92.16 89.83 89.33 80.00 72.00 66.66 80.00 IQR 7.25 5.42 8.83 20.08 15.17 13.92 7.25

p 0.001a _0.000a _0.006a _0.013a _{0.411 0.411 0.204} SOT,SensoryOrganizationTest;C,condition;IQR,interquartilerange.

posturalandcognitivetasks.3 _{Duringadualtask,postural}

andcognitivetaskscan alsobeincompetition forcentral processingorattentionalresources,causing areductionin performanceofeither task.23,24 _{This mayalsoaccountfor}

increaseinposturalswayinthisstudy.

The possibility that participants might have employed a strategy that maintained cognitive performance at the expenseofposturalcontrolduringdualtask25_couldrelatea

possibleexplanationforposturalswayincreaseinthisstudy. Asanotherreasonforhigherposturalswayduringdualtask condition in relatively easy postural task conditions (C1, C2, C3, C4) compared tosingle task performance, it can be thoughtthat participants may have focused singularly onposturaltaskorhaveordinarilydirectedsomeamountof attentiontoposturalcontrol,butithasadetrimentaleffect. Itcanbeconcludedthatfocusingintentionallyonpostural controlduring dualtaskresulted in a less automatic con-trolof balance, thus disturbing the efficiencyof postural control.HunterandHoffman16_{havesuggestedthatfocusing}

solelyonabalancetaskcouldpossiblyleadtoanincreasein muscletension,leadingtoincreasedjointstiffnessand rigid-ityinthebody,thatinturnmayresultinincreasedpostural sway.Likewise,accordingtoconstrainedaction,26 _focusing

attentiononahighlyautomatizedbehaviorsuchaspostural controlinterferes,ratherthanhelps,theautomaticcontrol process.3

Whenhealthyhumansareperturbed,whilestandingon amovableplatform,acascadeofbalance-correcting mus-clereactions occurs.Some balancecorrectionshave been termed‘‘automatic’’,whereasothers,whichapproximate voluntary reactions. Balance corrections can be provided bykneemovementsasasecondarycontributionoraspart of the correctingstrategy itself.27 _{Knee proprioception is}

presumedto berequired for protection against excessive movements, stabilization during static posture and coor-dination of movements.28 _{We did not evaluate whether}

proprioceptivefeedback fromthe kneescontribute ornot to the triggering of balance corrections. Therefore, it is notpossibletomakeanexplanationaboutkneemovements onposturalcontrol.In astudy,Oude Nijhuisetal.29 _have

examinedtheeffectofbilateralkneeflexiononautomatic balance corrections generated by sudden perturbations. Theyhavefoundthathealthyadultscanincorporate volun-tarykneeflexionintotheirautomatic balancecorrections and that this depends on the direction of the postural perturbations.29_{Furtherstudiesevaluatingkneeflexionson}

posturalbalanceduringsecondarytaskcanbemade. The finding showing increase in postural sway during dual taskfor four of the six SOT conditions in this study wasin opposition with the previous researches using SOT evaluation.30---32_Broglioetal.30_{reportedsignificant}

improve-ments in SOT conditions 1, 3, 4. Resch et al.31 _found

decreasein posturalswayforSOT conditions1and2,and Teel et al.32 _{explained sway decrease for SOT condition}

1.Otherinvestigators3,16---18,24,33 _{whodidnotuseSOT have}

alsoreported increasedpostural stability under dual task conditions.The discrepancies between our study and the other studies that have or have not used SOT conditions maybeexplainedbycognitivetaskdifferencesusedinthese studies.24_{Thedifferentcognitivetasksmayhavechallenged}

thebrain’sabilitytodivideattentiondifferently.Itisknown that some cognitive tasks may allow more allocation to

posturalcontrolmechanism,resultinginanincreasein equi-libriumbalancescore.32

Ourfindingsobtainedfromthisstudypartiallysupportthe studyhypothesis (forC1,C2,C3,C4),assuming that addi-tionofcognitivetasktoposturaltaskwillhaveaneffecton posturalstability.However,theydonotsupportthe hypoth-esisthatdifficultyof cognitivetaskwillhavean effecton posturalstabilityunderdualtask.

Inthe comparisonof the no-task SOT scores withdual task SOT scores C5, C6 in which both of the visual and proprioceptive perception inputs are absent or distorted, anterior---posterior sway has not been affected (p>0.05). C5 and C6 arethe most difficult postural conditions.The sameresultwasfoundforcombinedSOTscore.Thisresult is similar to that obtained by Barin et al.,34 _{who did}

not findasignificant differencein posturalsway in young adultswhenperformingsubtractiontasksunderaltered sen-sory conditions. Similarly, in dual task studies using SOT conditions postural stability did not change with sensory conditions.30---32,35_{Postural swaywasessentiallyunaffected}

byconcurrentcognitiveactivityforSOTscoresC2,C4,C5, C6,31 _{SOT scores C1, C3, C6,}32 _{SOT scores C6,}30 _{and SOT}

scoresC1toC6.35

One explanation for unaffected postural sway even in the mostdifficult posturalconditionswiththe additionof secondarycognitivetaskinthisstudymaybethat partici-pantshaveswitchedattentionfrominternalfocus(balance) toexternalfocus(cognitive).3,10 _{Releasingposturalcontrol}

from attentional focus when attention directed toward a concurrenttaskmighthaveallowedposturalcontroltowork inamoreautomatic,efficientmanner.16,18_Wulfetal.26_have

reportedthatanexternal focusofattentionpromotes the use of moreautomatic control processesin the brain, as opposed tovoluntary muscle control as withthe internal focustocorrectposturalperturbation.

Shumway-CookandWoollacott35 _{have explainedsimilar}

postural stability between single task and dual task, as attentional demands of maintaining balance stability are fairlyconstantacrosssensoryconditions.This explanation alsocanbevalidforunchangedposturalswayeveninthe mostdifficultsensorySOTconditions5and6inourstudy.

Another possible explanation for unaffected postural sway under dual task may be related to the conditions themselves.32_{UnderSOTconditions5and6,whichare,the}

participantmayhave alreadybeendividing his/her atten-tionbetweenbalanceandsurroundingduringthesingletask paradigmdue tothemovingplatform andsurroundingsas reportedbyTeeletal.32

Aphysiologicalexplanationofourfindingsisthatcerebral processingduringdual-task conditionsapparently modifies how the central nervous system controls postural stabil-ity. Under normal conditions, balance is controlled via integrationof sensoryinformationprovidedby the visual, vestibular, and somatosensory systems.30 _{Input based on}

limb positioning is transmitted to the basal ganglia. This signal isintegratedwithplannedactionsdevelopedin the premotor cortex and supplementary motor cortex in the cerebellum. The descending pathway continues via alpha motor neurons, which innervate skeletal muscle, allow-ingfor regulation of balance.30,36 _{Typically,thevisual and}

Postural sway during dual task conditions can be detectable usingdifferent testprotocolslikeBertec force platform,17 _{Kistler force platform}16 _{or AMTI Accusway}

System for Balance and Postural Sway Measurement.19

These tests quantify sway range and variability in both anterior---posterior direction and medial---lateral (side to side) direction. According to SOT protocol used in the present study, postural sway couldonly been detected in anterior---posterior direction like the other studies using SOT.21,30,35 _{Therefore, in this study, the effect of}

concur-rent cognitive tasks on postural sway in medial---lateral direction is not known and comparisons with the results of the other studies could not be made. In the study of Pellechia et al.19 _{postural sway in medial---lateral}

direc-tionhasnotbeenaffectedfromsecondarycognitivetasks; anterior---posterior sway hasincreased when the difficulty ofconcurrentcognitivetaskincreased.Rileyetal.17 _have

founddecreasedmedial---lateralposturalswayvariabilityas the cognitive load imposed by a shortterm memory task increased.Hunter andHofmann16 _{have explainedreduced}

level of medial---lateral center of pressure motion with a secondarycognitivetask.

In this study,no statistically significant differencewas observed between the presentation manners or difficulty levels of simultaneous cognitive tasks and postural sway (p>0.05).Thisresultmaysuggestthat thetypeof stimuli and difficulty of cognitive task are rather unspecific and independent of postural control.18 _{This result is different}

fromthoseof Rileyet al.,17 _{explaining thatauditory task}

affects postural sway more than visual task. Contrary to ourfinding,Pellecchiaetal.19_{reportedthemoreimpacted}

postural sway with the more difficult cognitive task. On theotherhand,inaccordancewithourresult,ithasbeen reportedthattherewasnoeffectof thedifficultyof cog-nitive task18 _{and similareffects of type of stimuli}16---18 _on

posturalsway.

In our study, when cognitive taskpaired with postural tasksimultaneously,it wasdeterminedthatthemost mis-takes were made withvisual difficult and auditory---visual mixeddifficultdualtaskconditions,whiletheleastmistakes weremade withauditorycognitivetask.This findingwith respect tovisual and auditory task is consistent with the studyof Penney,38 _{whichreportedalarge auditory}

modal-ityadvantageinserialrecallthatsuggestsacertaingreater robustnessorpersistenceofacousticmemorycomparedto visualmemory.However,Rileyetal.17_{foundmorecognitive}

performance errors during auditory task than visual task. Thereasonforthevisualandauditorycognitivetask perfor-manceerrorsseeninthisstudyisthoughttobeexplainedby themodalityeffect.Thetermmodalityeffectreferredto thefindingthat,inshort-termmemorytasks,auditory pre-sentation almostalways resulted inhigher recallthan did visualpresentation.38_{Sinceinformationabouttheeffectof}

auditory---visualmixedtaskconcurrentposturaltaskon pos-turalswayisnotavailableintheliterature,nocomparison canbemadeandapossibleexplanationforauditory---visual mixedtaskerrorsseeninourstudycannotbemade.Further studies are necessary todetect the reasonof increase in cognitiveerrorswithauditory---visualmixedtaskconcurrent posturaltaskonposturalsway.

The limitationsofourstudyare:thelimitednumberof subjectsthatparticipateinthestudy,thefactthatonlythe

rehearsalphaseisevaluatedandnotbeingabletoassessthe encodingphaseandresponsetimeforcognitivetask.

Conclusion

Asaresult,withinthedualtaskorder,togetherwithadding thecognitivetaskstopostural controltask,astatistically significant increase has been determined in the postural swayfor C1, C2, C3and C4, butno significant difference hasbeen observed withinthe sway for C5 and C6, which are the most difficult postural tasks. Under dual task, it isdeterminedthatthe presentationmanner anddifficulty level of the stimulus within the cognitive tasks have no effecton postural sway. When cognitive taskpaired with posturaltasksimultaneously,themostmistakeswerefound withvisualdifficultandauditory---visualmixeddifficultdual taskconditions,while theleast mistakes weremade with auditorycognitivetask.Vestibularimpairmentsincreasethe requirementofattentionforposturalcontrol.39_Inaddition,

attentional capacityin multi-tasking conditions decreases withaging.40 _{Older adults may be at risk for falls under}

concurrenttaskconditions.7_{Itisthoughtthatthedualtask}

model used in this study may provide useful information abouttheassessmentofthedualtaskcapacityamong geri-atricsubjectsandwithsubjectswithvestibulardisorders.

Conflicts

of

interest

Theauthorsdeclarenoconflictsofinterest.

Acknowledgments

TheauthorswouldliketothankGokhanAytekinand Saadet-tinKilic¸kapfordataanalyses.Theauthorswouldalsoliketo especiallythankErsinOrayforcontributions.

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