www.bjorl.org
Brazilian
Journal
of
OTORHINOLARYNGOLOGY
ORIGINAL
ARTICLE
Relative
contributions
of
auditory
and
cognitive
functions
on
speech
recognition
in
quiet
and
in
noise
among
older
adults
夽
Siti
Zamratol
Mai
Sarah
Mukari
a,∗,
Yusmeera
Yusof
b,c,
Wan
Syafira
Ishak
b,
Nashrah
Maamor
b,
Kalaivani
Chellapan
d,
Mariam
Adawiah
Dzulkifli
eaUniversitiKebangsaanMalaysia,InstituteofEar,HearingandSpeech,KualaLumpur,Malaysia bUniversitiKebangsaanMalaysia,FacultyofHeathSciences,KualaLumpur,Malaysia
cMinistryofHealth,Putrajaya,Malaysia
dUniversitiKebangsaanMalaysia,FacultyofEngineering&BuiltEnvironment,Bangi,Malaysia
eInternationalIslamicUniversity,KuliyyahofIslamicRevealedKnowledgeandHumanSciences,KualaLumpur,Malaysia
Received11July2018;accepted23October2018 Availableonline10December2018
KEYWORDS Speechrecognition; Hearingthreshold; Auditory; Cognition; Elderly Abstract
Introduction:Hearingacuity,centralauditoryprocessingandcognitioncontributetothespeech recognitiondifficultyexperiencedbyolderadults.Therefore,quantifyingthecontributionof thesefactorsonspeechrecognitionproblemisimportantinordertoformulateaholisticand effectiverehabilitation.
Objective: Toexaminetherelativecontributionsofauditoryfunctioningandcognitionstatus tospeechrecognitioninquietandinnoise.
Methods:We measuredspeech recognition inquietandincompositenoise using theMalay Hearinginnoiseteston72nativeMalayspeakers (60---82years)olderadultswithnormalto mildhearingloss.Auditoryfunctionincludedpuretoneaudiogram,gaps-in-noise,anddichotic digittests.CognitivefunctionwasassessedusingtheMalayMontrealcognitiveassessment.
Results:Linearregressionanalysesusingbackwardeliminationtechniquerevealedthathadthe betterearfourfrequencyaverage(0.5---4kHz)(4FA),highfrequencyaverageandMalayMontreal cognitiveassessmentattributedtospeechperceptioninquiet(totalr2=0.499).Ontheother hand, highfrequencyaverage, Malay Montrealcognitiveassessmentanddichoticdigittests contributedsignificantlytospeechrecognitioninnoise(totalr2=0.307).Whereasthebetter earhighfrequencyaverageprimarily measuredthespeechrecognition inquiet,thespeech recognitioninnoisewasmainlymeasuredbycognitivefunction.
夽 Pleasecitethisarticleas:MukariSZ,YusofY,IshakWS,MaamorN,ChellapanK,DzulkifliMA.Relativecontributionsofauditoryand cognitivefunctionsonspeechrecognitioninquietandinnoiseamongolderadults.BrazJOtorhinolaryngol.2020;86:149---56.
∗Correspondingauthor.
E-mail:zamratol@ukm.edu.my(S.Z.Mukari).
PeerReviewundertheresponsibilityofAssociac¸ãoBrasileiradeOtorrinolaringologiaeCirurgiaCérvico-Facial.
https://doi.org/10.1016/j.bjorl.2018.10.010
1808-8694/©2018Associac¸˜aoBrasileiradeOtorrinolaringologiaeCirurgiaC´ervico-Facial.PublishedbyElsevierEditoraLtda.Thisisanopen accessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).
Conclusions:Thesefindingshighlightthefactthatbesideshearingsensitivity,cognitionplays animportantroleinspeechrecognitionabilityamongolderadults,especiallyinnoisy environ-ments.Therefore,inadditiontohearingaids,rehabilitation,whichtrainscognition,mayhave aroleinimprovingspeechrecognitioninnoiseabilityofolderadults.
© 2018 Associac¸˜ao Brasileira de Otorrinolaringologia e Cirurgia C´ervico-Facial. Published by Elsevier Editora Ltda. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/). PALAVRAS-CHAVE Reconhecimentode fala; Limiarauditivo; Auditivo; Cognic¸ão; Idoso
Contribuic¸õesrelativasdasfunc¸õesauditivasecognitivasnoreconhecimentodafala nosilêncioenoruídoentreidosos
Resumo
Introduc¸ão: Aalterac¸ãodaacuidadeauditiva,doprocessamentoauditivocentraledacognic¸ão sãofatoresquecontribuemparaadificuldadedereconhecimentodafalaemidosos.Portanto, quantificaracontribuic¸ãodessesfatoresnoproblemadereconhecimentodafalaéimportante paraaformulac¸ãodeumareabilitac¸ãoholísticaeefetiva.
Objetivo:Examinarascontribuic¸õesrelativasdofuncionamentoauditivoedoestadocognitivo paraoreconhecimentodafalanosilêncioenoruído.
Método: Nósmedimosoreconhecimentodefalanosilêncioenoruídocompostocomoteste
Malayhearinginnoisetestem 72idososmalaiosnativosfalantes(60-82anos)comaudic¸ão normalaperdaauditivadegrauleve. Aavaliac¸ãodafunc¸ãoauditivaincluiuaudiogramade tonspuros,testegaps-in-noiseetestesdicóticodedígitos.Afunc¸ãocognitivafoiavaliadapelo testeMalayMontrealcognitiveassessment.
Resultados: Análisesderegressãolinearcomtécnicasdeeliminac¸ãobackwardnaorelhamelhor revelarammédiadequatrofrequências(0,5---4kHz) (4AF),médiadealtafrequênciaeteste
MalayMontrealcognitiveassessmentnaorelhamelhor,mensuradapelapercepc¸ãodafalano silêncio(r2total=0,499).Poroutrolado,amédiadealtafrequência,MalayMontrealcognitive assessmenteotestedicóticodedígitoscontribuíramsignificativamenteparaoreconhecimento dafalanoruído(r2total=0,307).Enquantoamédiadealtafrequênciadamelhororelhamediu principalmenteoreconhecimentodafalanosilêncio,oreconhecimentodafalanoruídofoi mensuradoprincipalmentepelafunc¸ãocognitiva.
Conclusões:Essesachadosdestacamofatodeque,alémdasensibilidadeauditiva,acognic¸ão desempenhaumpapelimportantenacapacidadedereconhecimentodafalaemidosos, prin-cipalmenteemambientesruidosos.Portanto,alémdeaparelhosauditivos,areabilitac¸ão,que treinaacognic¸ão,podeterumpapelnamelhoriadacapacidadedoreconhecimentodafalano ruídoentreosidosos.
© 2018 Associac¸˜ao Brasileira de Otorrinolaringologia e Cirurgia C´ervico-Facial. Publicado por Elsevier Editora Ltda. Este ´e um artigo Open Access sob uma licenc¸a CC BY (http:// creativecommons.org/licenses/by/4.0/).
Introduction
Following a speech conversation in a noisy environment is hard, especially among older adults with and without hearing impairment.1 Three hypotheses have been pro-posed to explain the speech understanding difficulties in older adults; they are peripheral auditory, central audi-toryandcognitiveprocesses.2Althoughthecontributionsof centralauditoryandcognitiveprocessesonspeech recogni-tionperformanceinadverselisteningconditionshavebeen documented,3,4 management of hearing impairment has beenmostly focusedtowards improvingaudibility through the use of hearing amplification devices. A more holistic rehabilitation approachaddressing the processes involved in speech recognition difficulties is necessary in order to provideamoresatisfactoryresult.
In addition to peripheral hearing loss, ageing is often accompaniedbyreducedsoundprocessingefficiencydueto degenerationofcentralauditorypathway5andadeclinein cognitivefunction.6 Ofthethreefactors,peripheral hear-inglosshasbeenextensivelystudiedastheunderlyingfactor forspeech-in-noisedifficultiesexperiencedbyolderadults.7 Althoughthosestudiessuggestthatperipheralhearingloss playsaprimaryroleinspeechunderstandingdifficultiesin noise, the fact that older listeners, despite normal hear-ing, tend to have greater difficulties than young ones,8,9 indicatesthatprocessesotherthanperipheralhearingalso contributetothesespeechrecognitiondifficulties.
The roles of central auditory and cognitive factors in understandingspeechinnoisehavebeen extensively stud-ied in the past decades.10,11 Most of those studies have includedmeasuresofauditorytemporalresolution.7,8,11The
effectsoftemporalprocessingdeficitsonspeechrecognition remainunclear.Forexample,Besseretal.11 whoexamined thecontributionsofauditory,cognitiveandlinguistic abili-tiestothelisteninginspatializednoise-sentences(LISN-S) outcomesinnormalhearingyoungandolder groupsfound that measures of temporal processing, linguistic abilities and hearing level did not predict LISN-S outcomesin the olderagegroup.IncontrastaretheresultsofTyleretal.12 who reported significant correlation between gap thresh-oldsandwordrecognitioninnoiseaftercombiningthedata of the young and older adults. It should be noted, how-ever, thatacross studies,differencesin theranges ofage and hearing level of the study participants, measures of temporalprocessingaswellasvariancesinthespeech recog-nitionmaterialsmayhavecontributedtothedifferencein results.
Another central auditory processing function which declines with age is dichotic listening. Dichotic listen-ing is a challenging task in that a listener is required to copewithcompetingsoundsignalspresented toboth ears simultaneously. A study investigated the influence of age attentional control of bottom-up, stimulus driven lateral effectin youngerand older adults.13 Study subjects were testedusingfreerecall,forcedrightandforcedleft listen-ingparadigms. Theirresultsrevealed thatbothyoung and older groups showed better performance in the right ear (rightearadvantage)infreerecallandforcedright listen-ingparadigms.However,inforcedleftlistening paradigm, whiletheyoungergroupdemonstratedleftearadvantage, thisphenomenonwasnotobservedinoldergroup, suggest-ingthatageingreducestheabilityfortop-downattentional controlofabottomuplateralityeffect.Sinceattentionis knowntoreducewithage14andisexpectedtobegenerally importantforspeechinnoiseperformance,15 itispossible thatdichoticlisteninginfluencesspeechrecognition perfor-mancein noise. Additionally, studies ondichotic listening usingspeechstimulihave shown that ageingis associated withanoverallreductiononbothrightandleftearscores, withtheleftearscoreshowingmorerapidreduction resul-tinginagreaterrightearadvantage.16Itissuggestedthat rightearadvantageinlinguisticallybaseddichoticlistening mayhaveconsiderableimpactinbinauralsignalprocessing, whichmayinterferewiththeabilityrecognizingspeechin noise.17 Despitethepossibleinfluenceofdichoticlistening onspeechrecognitioninnoise,areviewoftherelevant liter-aturerevealsverylimitedstudieswhichincludedadichotic test.
The influence of cognition onspeech understanding in noise has been vastly studied and established.10,18 Among thecommonlystudiedcognitivemeasuresincludedworking memory capacity, attention and speed of processing.19---21 A meta-analysis,which involved 25 articles that included attention, memory, executive function, intelligence quo-tient andprocessingspeed revealed a generalassociation between cognition and speech-in-noise performance.22 Whilemoststudiesexaminingtheinfluenceofcognitionon speech performance in noise used domain-specific cogni-tiveassessment, afew studies suchasBesseretal.11 and Zhanetal.23haveusedascreeningtestforglobalcognitive status suchas theMontreal cognitive assessment (MoCA). TheirstudiesdemonstratedasignificantinfluenceofMoCA onspeechperformanceinnoise.
Giventhat difficultieslisteninginnoise iscommonand continuetodeclineamongolderadults,andthefactthat hearinglossalonedoesnotalwaysexplaintheseproblems, itisimportantthatwe examinetherelativecontributions ofperipheralauditory, centralauditoryandcognitive pro-cesses to speech recognition. Knowing the magnitude of the effects of these processes is crucial in developing a more comprehensive management plan of hearing loss in olderadults. Therefore,this study is aimed todetermine the relative contribution of auditory and cognitive func-tions on speech recognition in older adults with normal tomild hearing loss.This study is novel in a way.Firstly, whilemanystudieshaveexaminedthecontributionof cen-tralauditoryprocessingonspeechrecognitionperformance amongolderadults,veryfewhaveincludeddichotic listen-ingtest. We included gaps-in-noise and dichotic listening testasmeasuresofcentralauditoryprocessinginthisstudy. Specifically,weviewtheinclusionofdichoticlisteningtest asimportantbecausesomestudiessuggestthepotentialof dichoticlisteningtraininginimprovingspeechrecognition.24 Wehypothesizedthatspeechrecognitionreliesonhearing level,centralauditoryprocessingand cognitivefunctions, andthateachofthefactorscontributedifferentlyinvaried HINTconditions.
Methods
Participants
Atotalof72 participantsparticipatedin thisstudy.Tobe includedparticipants must be60 yearsoldor more, right handed,nativeMalayspeakershadnohistoryofstroke,head injury,earsurgery,psychiatricproblemordementia. Addi-tionally,participantsmusthavenormalmiddleearfunction basedontympanometryandsymmetricalhearinglevelwith normalhearingormildhearinglossasindicatedbyPureTone Average(PTA)for0.5,1,2and4kHzof40dBHLorlessin thebetterear.Symmetricalhearingthresholdwasdefined asdifferencebetweenthePTA(0.5---4.0kHz)ofbothearsof nogreaterthan10dB.Thetestswerespreadintotwo ses-sions,whichlastedaboutonehoureach.Theexperimental protocolandproceduresinthisstudywereapprovedbythe UniversitiKebangsaanMalaysiaResearchEthicsCommittee (approvaln◦.NN-050-2015).Informedconsentwasobtained beforedatacollection.
Peripheralhearingtests
Puretoneaudiogram
Pure-Tone Audiometry (PTA) was conducted by a trained audiologistinasoundtreatedbooth,usingstandardTDH-39 earphonesandaMadsen OB822audiometer (Madsen Elec-tronics Itera 2). Air conduction (AC) thresholds for each earwere measured for frequencies of 0.5, 1.0, 2.0, 4.0, and8.0kHz.BoneConduction(BC)wasevaluatedwhenever AC thresholds were greater than 20dB HL for frequen-ciesof 0.5, 1.0,2.0 and4.0Hz.Masking for airand bone conductionthresholdswereperformedwhenindicated.The four-frequencypuretoneaverage (4FA)wascalculatedfor frequencies of 0.5, 1.0, 2.0 and 4.0kHz. High frequency average(HFA)wasbasedonfrequencies4and8kHz.Normal
andmild hearing losswere definedasfollows: no impair-ment, PTA ≤25dB HL and mild, PTA 26---40dB HL.25 The betterear(BE)4FAandBEHFAwereusedintheanalyses. Tympanometry
Tympanometrywasconductedonbothearsusingan Inter-acousticTitan tympanometer.Anormaltympanogram was definedasstaticadmittanceof 0.2---1.5mmhoand tympa-nometricwidthof35---125dapa.26
Centralauditorytests
Dichoticdigitstest(DDT)
DDTwasconductedusingtheMalay doubledichotic digits test.27 Pairs ofdifferent digitswere presented simultane-ouslytoeachofthetwoearsat35dBsensationlevel(dBSL). TheDDTwasconductedusingfreerecalltestcondition,in whichthesubjectwasinstructedtorepeatallthefourdigits thattheyheardinnospecificorder.Thetestwascarriedout using20stimulusitems;eachitemconsistsoffourdifferent digits.Acorrectresponsewasallocatedtoeachdigitthat wasrepeatedcorrectly.Thepossibletotalcorrectscorewas 40foreachear.TheRightEarScore(RES)andtheLeftEar Score(LES)werecalculatedaspercentcorrect.TheRight EarAdvantage(REA),determinedbydeductingtheleftear scorefromtherightearscorewasusedintheanalysis. Gaps-in-noisetest(GIN)
TheGINtestwasadministeredandscoredaccordingtothe setcriteriabyMusieketal.28TheGINcontainsaseriesof36 different6-swhitenoisesegments.Eachofthewhitenoise segmentscontainbetween0 and3silencegapsofsilence rangingfrom2to20ms.The GINcontains60gapsandthe orderofthegapdurationsisrandomized.A5-sgapofsilence separateseach6-snoisesegment.Thetestwasconducted binaurally through a headphone at 35dB SL. The subject was asked to listen and respond to the silence gap that occur withineach noise burst.GIN threshold wasdefined bytheshortestsilencegapthatwascorrectlydetectedby thesubjectatleastfouroutofsixtimes.
Hearinginnoisetest(HINT)
The speechin noisetest wasconducted in asound booth usingtheMalayversionofHearinginNoiseTest(MyHINT).29 MyHINT is an adaptive open-set speech recognition test, which is used to measure the Reception Threshold for Sentences(RTSs).HINTisequippedwithanaudiosound pro-cessingthatsimulatesthesource locationsforthe speech at0◦ andnoiseateither0◦,90◦,and270◦ azimuths.30 The My HINT consists of 12 phonemically balanced lists of 20 short4---6wordssimplesentences.ThenoiseusedinHINTis steady-statespeech-shapednoise.
TheHINTwasconductedinfourdifferentconditions:(1) Inquiet(HINTQ),(2)HINTNoiseFront(HINTNF),(3)HINT Noise Right (HINTNR), and HINTNoise Left (HINTNL). In alltestconditions,speechwaspresentedfromthefront.In noiseconditions,the noiselevelwasfixedat65dBA.RTS wascalculatedbasedontheaveragepresentationlevelof the5ththroughthe20thsentencesandthelevelatwhich the21stsentencewouldbepresented.
Table1 MeansandstandarddeviationsofMoCA,4FAand HFA(n=72). Variables Mean(SD) MoCA 17.7(4.5) RE4FA(dBHL) 26.5(8.0) LE4FA(dBHL) 26.6(7.6) BE4FA(dBHL) 24.9(7.5) REHFA(dBHL) 44.1(16.9) LEHFA(dBHL) 46.1(16.9) BEHFA(dBHL) 41.1(15.5)
In this study, HINT (Q) and HINT (composite),a score often used as a descriptor of noise conditions31 were analyzed. HINT (composite) was calculated based on the three RTS measures: RTS for HINT (Composite)=[2 HINT (NF)+HINT(NR)+HINT(NL)]/4.
Cognitiveassessment
TheglobalcognitivefunctionwasassessedusingtheMalay version of Montreal cognitive assessment,32 which was adapted from the original MoCA by Nasreddine et al.33 It consists of 16 items, which covers attention and concentration, executive functions, memory, language, visuo-constructional skills, conceptual thinking, calcula-tions,andorientation.MoCAhasthepossiblefull scoreof 30. Inthisstudy,raw scorewasused.The MoCAis only a screeningtestforcognitionanddoesnotprovideanindepth measureofcognition.
Statisticalanalysis
DatawasanalyzedusingtheStatisticalpackageforthesocial sciences version 22. Descriptive analyses wereperformed on demographic data, auditory function tests and MoCA. TheassociationsbetweenmeasuresonHINTtestwithage, peripheral auditory,centralauditory testsandMoCAwere assessed using Pearson Correlation test. Finally, multiple linearregressionanalyseswereusedtodeterminerelative contributionsofauditoryperformance,andglobalcognitive performanceandHINTmeasures.
Results
Atotalof72individuals,18malesand54femalesbetween 60and82yearsold(Min.67.4;SD=4.9years)participated. Table1showsthemeansandstandarddeviationsofMoCA, 4FAsandHFAsoftheparticipants.Fiftypercentofthe par-ticipants hadnormalhearing(4FA≤25dBHL)andanother 50% hadmild hearingloss. The BEHFA ranged from10to 80dBHL;lessthan25dBHL(18.1%),between26and40dB HL(30.6%),between41and70dBHL(48.6%)andmorethan 70dBHLin(2.8%)oftheparticipants.Fig.1showsthemean hearingthresholdsacrossthetestfrequenciesforbothears. The audiogram indicates a fairly flat configuration up to 2.0kHzandgentlyslopingathigherfrequencies,typicalof presbycusisaudiogram.
0 10 20 30 40 50 60 0. 25 0 .5 1 2 4 8 dBH L kHz
Right ear Left ear
Figure1 Themeanhearingthresholdsfortherightandleft ears.
Table2 MeansandstandarddeviationsofHINT(Q),HINT (composite),dichoticdigittestandgaps-in-noise.
Variables Mean(SD)
HINT(Q)(dBA) 28.7(5.9)
HINT(C)(dBSNR) −5.5(2.1)
DDT(REA)(%) 16.7(13.5)
Gaps-in-noise(ms) 13.7(4.2)
Hearinginnoisetestandcentralauditorytests
Table2 summarizesthe means andstandard deviationsof HINT(Q),HINT(composite),DDT(REA)andGIN.The inter-correlationsbetweenHINTtestsandthepredictorvariables wereshowninTable3.TheresultsindicatedthathigherBE 4FA,BE HFA and lower MoCAwere associated withworse HINT(Q)andHINT(composite).Inaddition,HINT (compo-site) was also positively correlated to GIN. There was a positive correlation between HINT (Q) and HINT (compo-site).
Contributionsofauditoryfunctionsandcognitive
functiontohearinginnoisetest
Weperformedmultiplelinearregressionanalysesto deter-minehowmuchhearingacuity, centralauditorytests and MoCAattributedtothevariationsofeachoftheHINT out-comes.Toexaminepotentialcasesofcollinearitybetween predictorvariables,weperformedadiagnosticcollinearity
testusingalinearregressionanalysis.Nocollinearitieswere observed,withvarianceinflationfactor valueslessthan2. Thus,allpredictorvariableswereincludedintheregression analyses.
Multiplelinearregressionanalyseswereperformedusing backwardeliminationmethod.Thepredictorvariableswere excludedstepwise,removingthevariablewiththehighestp
valueateachstep,untilonlyvariableswithp<0.1remained inthemodel.ThefinalmodelsareshowninTable4.
The resultsindicated thatHINT(Q)wasbestpredicted by BE 4FA, BE HFA and MoCA, F(4.67)=18.706, p<0.001. The three variables accounted to 49.9% of the variance. TheproportionofvarianceinRTS(Quiet)uniquelyexplained bythesevariables,asindexedbythesquaredsemi-partial correlations(partr2)were29.2% bytheBEHFA, 10.9%by
theBE4FA,and5.7%byMoCA.Thepositivebetacoefficient forthetwohearingaveragesandnegativebetacoefficient for MoCA indicate that HINT (Q) performance worsened asthe hearingaveragesincreasedandtheMoCAreduced. Individual differences in BE HFA, DDT (REA), and MoCA togetheraccountedfor30.7%oftheHINT(Composite) vari-ance,F(3.68)=11.467,p<0.001.MoCAuniquelyaccounted to18.5%ofthevariance,followedbyBEHFA(12.4%)andDDT (REA)(8.2%).LowerMoCA,greater BEHFA and DDT(REA) yieldedworseHINT(COMPOSITE)performance.
Discussion
ContributionsofaudiometricthresholdstoHINT
outcomes
Inthepresentstudy,whichinvolvedolderadultparticipants withnormalandwithmildhearinglossat4FA,hearingacuity atbothlowtomidfrequenciesaswellasathighfrequencies significantlycontributedtothe varianceof HINTin quiet. The4FAandHFAuniquelyaccountedfor10.9%and29.2%of thevarianceofHINT(Q),respectively.Theseresults corrob-oratedthefindingsofpreviousresearchwhichexplainedthe importanceofspeechspectrumaudibilityinspeech recog-nitionperformance.7,34
The importance of high frequency hearing acuity in speechrecognitioninquiet,especiallyinolderadults,has been well established. Articulation index theory predicts that individuals with sloping high frequency hearing loss suchasinpresbycusiswillexperiencedifficultylisteningto speechat conversational level due to inaudibility of high
Table3 CorrelationanalysisbetweenreceptionthresholdsofsentencesofHINTs,age,MoCA,peripheralandcentralauditory tests.
HINT(Q) HINT(C) BE4FA BEHFA GIN DDT(REA) MoCA
HINT(Q) --- 0.505a 0.530a 0.621a 0.138c 0.137c −0.326b HINT(Composite) --- 0.235b 0.368a 0.234b 0.199c −0.436a BE4FA --- 0.413a 0.048c 0.061c −0.262b BEHFA 0.205c −0.067c −0.182c GIN --- 0.166c −0.206c DDT(REA) --- 0.065c MoCA ---ap<0.001;bp<0.05;cp>0.05.
Table4 Multiple regressionmodelsfor outcomemeasures.The lastcolumn indicatestheR2oftheregressionmodelsand relativecontribution(partr2)ofeachindependentvariabletothevariancesofdependentvariables.
Bcoefficient t p-Value PartR2 TotalR2
HINT(Q) 0.499 BE4FA 0.272 2.870 0.005 0.109 BEHFA 0.488 5.246 0.000 0.292 MoCA −0.177 −2.017 0.048 0.057 HINT(Composite) 0.307 BEHFA 0.312 3.097 0.003 0.124 DDT 0.245 2.473 0.016 0.082 MoCA −0.396 −3.393 0.000 0.185
frequencyspeechsounds.35 Apartfrombeingimportantfor detectingweakfricativessuchas/f/and/s/sounds,high frequency hearing acuity is also essential in differentiat-ing voiced versus voicelesscues and place-of-articulation cues.36 Furthermore,it is well knownthat hearingloss in a given frequency region affects not only audibility but mayalso affectssuprathreshold auditory processing abili-ties suchas intensity,frequency and temporalprocessing in the frequency region corresponding to hearing loss.37 Suprathreshold processing dysfunctionmay spread to fre-quencieslowerthan thataffected by hearingloss aswell causingan off-channelimpactonintensity,frequencyand temporalprocessing.38---40
The importance of high frequency hearing in speech intelligibilityinnoise hasalsobeenwell documented.For example,arecentstudyindicatedthatelderlylistenerswith betterhighfrequencyhearingintheregionbetween6and 10kHzhadgreaterspatialreleasefrommaskingresultingin betterspeechrecognitionwhenspeechandnoiseare spa-tially separated.11 Another study has shown that optimal speechrecognitioninnoise isobtainedbyextending audi-bilityupto7kHz.41 Thefindingofthepresentstudywhich indicateasignificantrelationshipbetweenBEHFAandHINT (Composite)areinlinewiththosestudies.
Althoughmostpriorstudieshaveobservedstrong corre-lationsbetweenspeechrecognitioninbothquietandnoise andhearingthresholdsupto4kHz,42,43itisnotthecasein thepresentstudy.Thisobservationcouldpartlybedueto thefactthatinthepresentstudy,theparticipants’BE4FA wasrelatively more homogenous ranging from 3 to 40dB HL compared to that of BE HFA which were remarkably morevaried, ranging from 5to90dB HL.Furthermore,it isalsopossiblethataveraging hearingthresholdsof2and 4kHz with the largely age-independent thresholds of 0.5 and1kHzweakenedtherelationshipbetweenthe4FAand speechrecognitionmeasure,especiallyinviewofthe slop-ingaudiogramconfigurationseeninthisstudy.
Contributionsofcentralauditoryprocessingto
HINToutcomes
GIN and DDT,were included as measures of central audi-toryprocessinginthepresentstudy.Generally,ourfindings revealed that GIN did not contribute to any of the HINT outcomes.Incontrast,theDDT(REA)contributed significan-tlytothevariancesofHINT(COMPOSITE),albeitminimally
(8.2%). The lack of significant influence of GIN on HINT outcomesfitswellwiththoseofthepreviousstudies10,44,45 whichalsofoundthatgapdetectionthresholddidnot influ-encespeechrecognitionperformanceinquietandinsteady state noise.The lack ofpronouncedtemporalfluctuations inlevelorspectrumofsteadystateasusedinHINTpartly explainedthisfinding.
There have been limited studies which examined the relationshipbetweendichoticlisteningandspeech recogni-tionperformance.Astudywhichexaminedtherelationship between the two measures found a strong negative cor-relation betweendichoticscore andspeechrecognition in noise.46 It is important to note, however, that the rela-tionshipwasmeasuredusingbivariatecorrelation,without controlling for other possible confoundingfactors suchas hearing thresholds and cognitive function. In the present study,REAofdichoticlisteningtestwasfoundtocontribute to about 9.0% of the variance in HINT (COMPOSITE) after controllingforothertestedindependentvariables.This sig-nificantassociation couldbebecausebothmeasuresshare somecommonunderlyingprocessessuchasattention.
ContributionsofcognitivefunctiontoHINT
outcomes
The cognitive function as indexedby MoCA uniquely con-tributedto5.7%and18.5%ofthevariancesoftheHINT(Q) andHINT(Composite), respectively.The greater contribu-tionofMoCAonHINT(Composite)thanHINT(Q)isexpected becauselisteningtospeechinquietreliesmoreonspeech audibilityandislesscognitivelytaxing.Duringspeech recog-nitionprocess,speechinformationiscontinuouslycompared withtheinformationstoredinlong-termmemory.Ifthese informationmatch,speechprocessingandunderstandingon higher level will occur implicitly and effortlessly.47 How-ever, wheneverthe auditory input is degraded either due tohearinglossorduetonoise,additionalcognitive-control processesarenecessarytosupportspeechrecognition.48
Limitationsofthestudy
Thisstudyhasafewlimitations.First,theuseofMoCArather thanmorespecificneuropsychologicaltestbatterymakeit impossibletoascertainwhichcognitivedomainscontribute to the speechrecognition performance. MoCA asa single measure of cognitive function has, however, been use in
previousstudieswhichexaminedtheinfluenceofcognitive functionsonspeechunderstandingbyolderadults.11,23One of the studies which examined the contributions of audi-tory, cognitive and linguistic abilities on the listening in spatializednoise-sentences(LiSN-S)usedMoCAasameasure of cognition. Theirresults indicated that MoCApredicted threeoftheLiSN-Soutcomes.11Likewise,theuseofMyHINT whichusessteady-statespeechnoisedidnotreplicatethe most commonnoiseencountered ineveryday communica-tionwhichislargelymodulatedinnature.Despitethat,itis noteworthytohighlightthatthefactthatMoCAcontributed significantlytoMyHINTperformancessuggeststhatthetest is challengingenough totax thecognitivefunction during speechrecognitiontasksinolderadults.
Conclusions
Thisstudyexaminedthecontributionsofhearinglevel, mea-suresofcentralauditoryprocessing,andcognitivestatuson speechrecognitionperformanceinquietandinnoise.Our findingsrevealedthatBE4FA,BEHFAandcognitionwerethe significant predictors and accounted for about 50% of the variance of speechrecognition inquiet. In contrast,HFA, cognitivestatusasmeasuredbyMoCAandREAsignificantly predictedabout30%ofthevarianceofspeechrecognitionin noisecondition.Whilehighfrequency hearingwasthe pri-marypredictorforspeechrecognitioninquiet,MoCAscore contributedmorethanhigh frequencyhearingtothe vari-anceofspeechrecognitioninnoise.Thesefindingssuggest thatrehabilitationthatgearedtowardsimprovingcognitive functioncouldhelpin alleviatingsomeof speech recogni-tiondifficultiesexperiencedbyolder adults,especially,in noisyenvironment.Additionally,thefactthattheincluded predictorsexplainonlyabout20---40%ofHINTperformance, suggeststhatthereareotherrelevantpredictorsthathave notbeencoveredinthepresentstudy.
Funding
ThisstudywasfundedbytheMalaysianMinistryofEducation researchgrant(LRGS/BU/2012/UKM-UKM/K/02).
Conflicts
of
interest
Theauthorsdeclarenoconflictsofinterest.
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