Cognitive Processing Speed, Working Memory, and the ...

Cognitive processing speed (CPS) is the rate at which relatively simple perceptual and automatic cognitive operations can be carried out; ... DownloadArticle DownloadPDF ReadCube EPUB XML(NLM) totalviews ViewArticleImpact SHAREON ClaudiaRepetto CatholicUniversityoftheSacredHeart,Italy PietroSpataro MercatorumUniversity,Italy ChristianDesloovere UniversityHospitalsLeuven,Belgium Theeditorandreviewer'saffiliationsarethelatestprovidedontheirLoopresearchprofilesandmaynotreflecttheirsituationatthetimeofreview. Abstract Introduction MaterialsandMethods Results Discussion Conclusion EthicsStatement AuthorContributions Funding ConflictofInterestStatement Acknowledgments References Checkforupdates Peoplealsolookedat ORIGINALRESEARCHarticle Front.Psychol.,15August2017Sec.Cognition https://doi.org/10.3389/fpsyg.2017.01308 CognitiveProcessingSpeed,WorkingMemory,andtheIntelligibilityofHearingAid-ProcessedSpeechinPersonswithHearingImpairment WycliffeKabayweYumba1,2* 1DepartmentofBehavioralSciencesandLearning,LinköpingUniversity,Linköping,Sweden 2LinnaeusCentreHEAD,SwedishInstituteforDisabilityResearch,LinköpingUniversity,Linköping,Sweden Previousstudieshavedemonstratedthatsuccessfullisteningwithadvancedsignalprocessingindigitalhearingaidsisassociatedwithindividualcognitivecapacity,particularlyworkingmemorycapacity(WMC).Thisstudyaimedtoexaminetherelationshipbetweencognitiveabilities(cognitiveprocessingspeedandWMC)andindividuallisteners’responsestodigitalsignalprocessingsettingsinadverselisteningconditions.Atotalof194nativeSwedishspeakers(83womenand111men),aged33–80years(mean=60.75years,SD=8.89),withbilateral,symmetricalmildtomoderatesensorineuralhearinglosswhohadcompletedalexicaldecisionspeedtest(measuringcognitiveprocessingspeed)andsemanticword-pairspantest(SWPST,capturingWMC)participatedinthisstudy.TheHagermantest(capturingspeechrecognitioninnoise)wasconductedusinganexperimentalhearingaidwiththreedigitalsignalprocessingsettings:(1)linearamplificationwithoutnoisereduction(NoP),(2)linearamplificationwithnoisereduction(NR),and(3)non-linearamplificationwithoutNR(“fast-actingcompression”).Theresultsshowedthatcognitiveprocessingspeedwasabetterpredictorofspeechintelligibilityinnoise,regardlessofthetypesofsignalprocessingalgorithmsused.Thatis,therewasastrongerassociationbetweencognitiveprocessingspeedandNRoutcomesandfast-actingcompressionoutcomes(insteadystatenoise).WeobservedaweakerrelationshipbetweenworkingmemoryandNR,butWMCdidnotrelatetofast-actingcompression.WMCwasarelativelyweakerpredictorofspeechintelligibilityinnoise.Thesefindingsmighthavebeendifferentiftheparticipantshadbeenprovidedwithtrainingandorallowedtoacclimatizetobinarymaskingnoisereductionorfast-actingcompression. Introduction Hearing-impairedindividualsoftenshowincreaseddifficultiesrecognizingspeechunderadverselisteningconditions,includingnoiseandreverberantordistortedspeech,evenwhenwearinghearingaids(CommitteeonHearing,Bioacoustics,andBiomechanics[CHABA],1988;Akeroyd,2008;Larsbyetal.,2008;SouzaandArehart,2015).Previousstudieshaveindicatedthatolderadulthearingaidusersmayhavedifficultieshandlingtheconsequencesofhearingaidsignalprocessing,whetherinregardtothedistortionscausedbytheeffectsofbackgroundnoiseortheunwantedartifactsfromcertaindigitalsignalprocessingalgorithms(e.g.,fast-actingcompression;Lunner,2003;SouzaandArehart,2015).Theseconsequencesmayleadtobenefitsofsignalprocessinginthehearingaidthatarelessthanexpected.Itmaybepossiblethatthesignalprocessingimplementedinthehearingaiditselfmaybecognitivelydemandingforhearing-impairedhearingaidwearers(Lunner,2003).Othersstudieshaveattributedspeechrecognitiondifficultiesamonghearing-impairedhearingaiduserstotheslow-downofcognitivespeed.Thisdeclineincognitiveprocessingspeedmayarisefromageneralizedslowinginbrainfunctioningduetoadvancementinage,whichcouldberesponsibleformost,ifnotall,age-relateddeclinesinproblem-solving,memory,andlanguagecomprehension(Salthouse,1996;Pichora-Fuller,2003;Schneideretal.,2005). Workingmemoryreferstoacognitivesystemresponsibleforprocessingandtemporarystorageofinformationduringcomplexcognitivetasks,suchascomprehension,learningandreasoning(BaddeleyandHitch,1974;DanemanandCarpenter,1980;Baddeley,1986).Thismemorysystemisassumedtohavealimitedcapacitythatneedbesharedbetweentheworkandthememory,betweentheprocessingandstoragedemandsofthetasktowhichtheworkingmemoryisapplied(DanemanandCarpenter,1980;Baddeley,2012).Workingmemorycapacity(WMC)isgenerallyassessedwithspantests,suchasreadingspantest(DanemanandCarpenter,1980),semanticword-pairspantest(Rönnbergetal.,2016).Cognitiveprocessingspeed(CPS)istherateatwhichrelativelysimpleperceptualandautomaticcognitiveoperationscanbecarriedout;usuallythisismeasuredundertimepressureinsuchthatadegreeoffocusedattentionisinvolved(Salthouse,1996,2000).Severaltypesoftasksareusedtomeasurecognitiveprocessingspeedability,includinglexicaldecisionspeedtest(LDT),rapidautomatizednamingtest(RAN),physicalmatchingtest(PMT),Rhymejudgmenttest,thedigitalsymbolsubstitutiontest(DSST),theflankertask,etc.(Wingfieldetal.,1985;Rönnberg,1990;Salthouse,1996;Wiigetal.,2002).Forexample,LDTisconsideredasoneofthemostoftenusedtasksinthefieldofvisualwordrecognition.Inthistask,participantshavetojudgeasquicklyandaccuratelyaspossiblewhetheradisplayedletterstringisarealwordoranon-word(Rönnberg,1990).TheoverallassumptionthatunderliestheuseofLDTisthattherateandtheaccuracyofreactingtowordstimulishowstheeffectivenesswithwhichwordrepresentationsareactivatedorretrievedfromlong-termlexicalmemory(Rönnberg,1990).Previousstudiessuggestedthatcognitiveprocessingspeedmaybeaffectedbyindividuals’knowledgebaseandexperience.Thatis,themoreanindividualknowsaboutsomethingand/ortheexperienceshe/hehaswithit,thegreatertheprobabilitythather/hiscognitiveprocessingspeedontasksrelatedtothisinformationwillbeincreased(Lunner,2003;Pichora-Fuller,2003;DesjardinsandDoherty,2014). AcomprehensivewayofviewingtherelationshipbetweenworkingmemoryandspeechrecognitionisviatheEaseofLanguageUnderstanding(ELU)model(Rönnbergetal.,2008,2013).TheELUmodelconsiderslanguageinputasconsistingofphonological,syntacticprosodic,andsemanticinformation.Thatis,whenspeechsignalinputisdegradedoralteredfromitsordinaryform,itcanbemoredifficulttomatchthoseacousticpatternstophonologicalrepresentationsstoredinthelongtermmemory,andworkingmemorymaybeexplicitlyengagedtoagreaterextenttoreconcileamatch(mismatch,Rönnbergetal.,2008).However,underfavorableconditions,theincomingspeechsignalinputarenotdegraded(audibleorundistorted),itcanbeeasilymatchedtoaphonologicalrepresentationstoredinlong-termmemory);andWMCmaybeengagedtoalesserextent(Rönnbergetal.,2013).Inthecontextofthismodel,signaldegradationreferstowhatevermaysubstantiallymodifytheavailableacousticsignalcuesofthetargetsignal(Rönnbergetal.,2008).Thesourcesofsignaldegradationmaybesingle(e.g.,noise)ormultiple(e.g.,combinedhearingaidsignalprocessingandnoiseforolderpersonswithhearingloss).Otherstudiessuggestthatforlistenerswithhearingloss,varioussignalprocessingalgorithmsimplementedinhearingaidsmaybeapotentialsourceofspeechsignaldegradations(Gatehouseetal.,2003,2006;Fooetal.,2007;SouzaandArehart,2015). Moderndigitalhearingaidsaretypicallyequippedwithawiderangeofsignalprocessingalgorithms,includingwidedynamicrangecompressionspeed,noisereduction,anddirectionalmicrophones(Dillon,1996,2001,2012;Kates,2008).Althoughmanyhearing-impairedpersonsmaybenefitfromsuchsignalprocessingalgorithms,theymayintroducedistortionsthatmaycounteractorreducetheintendedbenefitsforsomelisteners(Lunner,2003).Fast-actingwidedynamicrangecompression(fast-actingWDRC)isintendedtosimultaneouslyimprovetheaudibilityofweaksoundsandmaintainloudnessandcomfortforhigher-intensitysounds(Dillon,2001,2012).Moreover,improvedaudibilityrequiressignalmodification,andagreatermodificationoftheexpectedacousticsignalmayplacegreaterdemandonWMC(Rönnbergetal.,2008,2013).Fast-actingcompressionmaymodifythespeechamplitudeenvelope,whichmaycauseachallenginglisteningsituationforhearing-impairedpersonswhorelyonenvelopecues(Kates,2008;Dillon,2012).Inaddition,otherstudiessuggestthatfast-actingcompressionmayintroduceunwantedartifacts,whichmaycreategreatersignalmodification(Dillon,2001;Lunner,2003).Anumberofstudiesfoundarelationshipbetweencognitiveabilitiesandtheabilitytorecognizespeechinnoiseusingdifferenttypesofhearingaidsignalprocessingalgorithms.Inparticular,thesestudiesshowedthatWMCwasassociatedwithspeechrecognitioninnoiseperformancewhenspokensentenceswereamplifiedbyfast-actingwidedynamicrangecompression(Gatehouseetal.,2003,2006;Fooetal.,2007;LunnerandSundewall-Thorén,2007;Akeroyd,2008;Ohlenforstetal.,2015;SouzaandArehart,2015).OtherstudiesindicatedthatWMC,executivefunctionandcognitivespeedwererelatedtowidedynamicrangecompression(Schwartzetal.,2008;SouzaandArehart,2015)andtofrequencycompression(Arhartetal.,2013;SouzaandArehart,2015).Rudneretal.(2011)foundthathearingimpairedlistenerswithlowerWMCdemonstratedpoorbenefitwithfast-actingcompressionthanslow-actingcompression,comparedwithlistenerswithhigherworkingmemorywhobenefitedmorewithfast-actingcompression(seealsoFooetal.,2007).AstudybyGatehouseetal.(2003)indicatedthatcognitivecapacitywasassociatedwithspeechrecognitioninnoisewithfast-actingcompression.Thatis,therewasagreaterbenefitfromfast-actingcompressionforlistenerswithgreatercognitivecapacitythanthosewithpoorercognitiveabilityinmodulatednoisebackground.Infurtherstudy,thesameauthors(Gatehouseetal.,2006)reportedthatcognitivecapacityrelatedtospeechrecognitioninnoiseperformancedifferently(bothwithfastandslowactingcompression),suggestingthatfast-actingcompressionprovidedgreaterbenefitforlistenerswithlargercognitivecapacity,whileslow-actingprovidedbetterbenefitforlistenerswithsmallercognitivecapacity. Therationalefornoisereductionalgorithmsistoidentifyandsuppresstheadverseeffectsofbackgroundnoiseonspeechrecognitionandsoundqualitybyimprovingthesignal-to-noiseratios(SNRs)forlistenerswithhearingloss(Kates,2008;Dillon,2012).Although,noisereductionsystemsareintendedtoimprovespeechintelligibility,theymayalsoaffectspeechqualityandeaseoflisteningbyintroducingsignaldistortions(Kates,2008;Wangetal.,2009;SouzaandArehart,2015).AfewstudiesfoundarelationshipbetweenWMCandspokensentencesamplifiedbydigitalnoisereduction(Ngetal.,2013,2015;Arhartetal.,2015).Recently,Ngetal.(2013)conductedastudywheretheyexaminedtheeffectsofWMC,noiseandbinarymask-basednoisereductiononspeechrecognitionandrecall.TheyfoundthatlistenerswithlargerWMCwerebetteratrecallingmorewordsthanlistenerswithsmallerWMC,asaresultofnoisereductionprocessing.TheresultsshowedthatnoisereductioneffectivelysuppressedtheadverseeffectsofbackgroundnoiseonspeechrecallperformanceoflistenerswithlargerWMC.Inanotherrecentstudy,Ngetal.(2015)carriedoutaresearchwheretheytestedtheNon-idealversionofnoisereductioninafollow-upexperimentalbasedonessentiallythesameset-upwithelderlyhearingaidusers.Arhartetal.(2015)investigatedtheeffectsofidealbinarymask-basednoisereductionprocessingandseveralnon-idealversionsresultingfromthesystematicmanipulationsoftwoalgorithmicparameters.TheresultsshowedthatWMCwasapotentialpredictoroftheoverallspeechintelligibilityperformance;however,therewasnointeractionbetweenWMCandthelevelofsignaldistortionsinexplainingtheperformance.RelatedtoWMC,recentstudybyNeher(2014)examinedtheeffectsofWMCandhearinglossonresponsetonoisereductionforthethreelevelsofabinauralcoherencealgorithms(i.e.,none,moderate,andstrong).Theyfoundthatspeechrecognitionperformancewaspoorwhenspeechwasamplifiedwithnoisereduction,andtherewasnosignificantdifferencebetweenlistenerswithlargerWMCandthosewithsmallerWMC.Nevertheless,workingmemoryappearedtobeimportantforthefactthatparticipantswithsmallerWMCpreferredmoreaggressive(strong)noisereductionthanmoderatenoisereduction(intermsofspeechquality). Anumberofstudiessuggestedthattheassociationbetweenworkingmemoryandnoisereductionislikelytobestrongerforspeechrecognitionperformanceunderlow-contextspeechmaterialinmodulatedbackgroundnoiseandrelativelyweakerunderunmodulatedbackgroundnoise(Rudneretal.,2011;Ngetal.,2013).Afewstudiessupportingthisviewsuggestedthatsentencematerialmayplayanimportantrole.Forexample,shorterspeechsegmentsinrelativelyfavorablesignal-to-noiseratiosmayreducetheactivationforengagementforWMCcomparedwithlongerspeechsegmentswhichactivatethedeploymentofworkingmemorytoagreaterextent(Rudneretal.,2009;SouzaandArehart,2015).Previousstudieshavesuggestedthatprocessingspeed,WMCandselectiveattentionareessentialforlinguisticanalysisforspeechinchallenginglisteningsituations(Lunner,2003;Rönnbergetal.,2013). Thepresentstudyinvestigatedtherelationshipbetweencognitiveabilities(cognitiveprocessingspeed,WMC)andindividuallisteners’responsestodigitalsignalprocessingsettingsinnoise.Here,wemanipulatedhearingaidsignalprocessingandbackgroundnoise,resultinginsixconditions(seeTable1)inwhichHagermansentenceswerepresented.WehypothesizedthatcognitiveabilitieswouldbecorrelatedwithHagermansentenceintelligibilityinnoise.WewouldexpectstrongerassociationsbetweenWMCandspeechrecognitionwhenspeechisacousticallydegradedandweakerassociationswhenspeechisaudible.Numerousstudieshavesupportedthisview,showingstrongerrelationshipbetweenWMCandspeechcomprehensioninadverselisteningconditionsinhearing-impairedparticipants(Fooetal.,2007;Akeroyd,2008;Rudneretal.,2011;Rönnbergetal.,2013;Ohlenforstetal.,2015;SouzaandArehart,2015). TABLE1 TABLE1.Means(M)andStandardDeviations(SD)forspeechrecognitioninnoise,age,andcognitivemeasures. MaterialsandMethods Participants Atotalof194nativeSwedishspeakers(83womenand111men),aged33–80years(mean=60.75years,SD=8.89),withbilateral,symmetricalmildtomoderatesensorineuralhearinglosswhohadcompletedaLDTandsemanticword-pairspantest,andtheHagermanmatrixsentencetest(HagermanandKinnefors,1995)wereincludedinthisstudy.Thepure-toneaveragehearingthresholdforbothearsatfrequencies0.5,1,2,and4kHz(PTA4)was39.23dBHL(SD=19.64).TheparticipantswererandomlyselectedfromthehearingclinicpatientregistryattheUniversityHospitalofLinköping,wherethetestingtookplace,andwereinvitedtoparticipatebyletter.Regardingtheinclusioncriteria,allparticipantswerebilaterallyfittedwithdigitalhearingaidswithcommonfeaturessuchasWDRC,noisereduction,anddirectionalmicrophones.Allparticipantshadusedthehearingaidsforaminimumof1yearatthetimeoftesting.TheparticipantswerehealthynativeSwedishspeakers,withnormalvisionorcorrected-to-normalvision(wearersofglasses).Theparticipantshadnohistoryofotologicalproblemsorpsychologicaldisorders.ThestudywasapprovedbytheLinköpingregionalethicscommittee(Dnr:55-09T122-09).Allparticipantsgavewritteninformedconsenttoparticipate. CognitiveTests SemanticWordPairSpanTest Asemanticword-pairspantask(Rönnbergetal.,2016)isavisualworkingmemorytestthatdoesnotcomparedtoreadingspantestincludeanysyntacticelementsintheprocessingandstoragecomponents.Thetestmaterialconsistsofaseriesofword-pairs(suchas“Bun,Hippo”).Thelistlengthvariedfrom2to5,withthreetrialsperlength.Thetaskwastocomprehendwordandtorecalleitherthefirstorthefinalwordsinthedisplayedseriesofpairwords(Baddeleyetal.,1985).Theword-pairsweredisplayedonacomputerscreenataspeedof800msperword.Halfoftheword-pairswerelivingthing(e.g.,“cat”),andhalfoftheword-pairswerenolivingthing(e.g.,“paper”).Theparticipantswereinstructedtoreadandidentifythewordsrepresentingthelivingthingonthescreen,thenpressthebuttonstatinginwhichpositionthewordrepresentingthelivingthingwaspresented(e.g.,Left–Right).Topresstheleftbutton(green)ifthelivingthingisattheleftside,andpresstherightbutton(red)ifthelivingthingisattherightside.Aftereachsequenceofword-pair,theparticipantswereaskedtorepeatorallyandloudlyallthewordsthatwererecentlypresentedeitheratleftorright,andshouldbeinthecorrectorderofpresentation.Theparticipants’responseswerescoredbytheexperimenterintermsoftotalnumberofwordscorrectlyrecalled.Themaximumtotalscoreis42points. LexicalDecisionSpeedTest TheLDT(Rönnberg,1990;Rönnbergetal.,2016)wasusedtomeasuretheparticipants’cognitiveprocessingspeed.IntheLDT,eightywordspresentedvisuallyoneitematatimeonthecomputerscreenwereusedastestmaterial,40ofwhichwererealSwedishwordsand40werenot.Inthistask,participantshavetodecideasquicklyandaccuratelyaspossiblewhethervisuallydisplayedcombinationsoflettersarerealwordsornot,bypressingthebutton“yes”forrealwordor“no”fornoword/pseudoword.Forexample,whentheword(e.g.,“SNÖ,snow”)wasdisplayed,theparticipantpressed“yes,”thisisarealSwedishword,butwhentheletters(e.g.,“NÄKK”)wasdisplayed,theparticipantpressed“NO”thisisnotarealSwedishword.Theresponsetimewassetat5s,andtheworddisappearedwhentheparticipantspressedthebutton.Accuracyandspeedofperformanceweremeasuredbasedonthereactiontimesforthecorrecttrials. TheHagermanTest SpeechrecognitionwasmeasuredusingtheHagermanmatrixsentencetest(HagermanandKinnefors,1995).Threelistsof10sentences,highlyconstrainedintheirnature,withlowsemanticredundancy,wereusedastestmaterial.ThesentencesallconsistedoffiveSwedishwords,andhadthefollowingstructure:propernoun,verb,number,adjective,andobject,inthatorder.Thesentenceswerepresentedintwotypesofbackgroundnoise,steadystatenoise(SSN)orfour-talkerbabble(4TB).Anexperimentalhearingaidwiththreedifferentsignalprocessingfeatures,includingthreesignalprocessingfeatures(1)linearamplificationwithoutnoisereduction(NoP,baseline),(2)linearamplificationwithnoisereduction(NR)and(3)non-linearamplificationwithfast-actingcompression(Fast,withoutnoisereduction),fittedbasedoneachparticipant’saudiogramwasemployed.4TBconsistedofrecordingsoftwomaleandtwofemalenativeSwedishspeakersreadingdifferentparagraphsofanewspapertextandSSN(i.e.,stationaryspeech-shapednoisewiththesamelong-termaveragespectrumasthespeechmaterial)wereused.Thesetwotypesofbackgroundnoisewerepresentedatequalrootmeansquare(RMS)levels(Larsbyetal.,2005). BackgroundNoise Twotypesofbackgroundnoiseswereusedinthisstudy:SSNand4TB.SSNisthestationarynoisespeech-shapednoise(i.e.,similarlong-termaveragespectrumasHINTsentences,Hällgrenetal.,2006).The4TBisatypeofcompetingspeech,consistingofrecordingsoftwomalesandtwofemales’nativeSwedishspeakersreadingdifferentparagraphsofanewspapertext(HagermanandKinnefors,1995).Thespeechbabblewasintroduced3sbeforetheonsetofsentencestimuliandended1saftersentenceoffset. SignalProcessingAlgorithmsSetting NoiseReduction TheprimarygoalofbinarymaskingnoisereductionsystemsistocounteracttheeffectsofnoiseonspeechrecognitionandsoundqualitybyimprovingtheSNRforhearingaidusers(Wangetal.,2009;Dillon,2012;SouzaandArehart,2015).Thetime-frequencyunitswererecordedusinga64-channelgammatonefilterbankandtime-windowing.Theideahereisthatforeachtime-frequencyunit(inbinarymatrix),thereisadecreaseof10dB;thelocalSNRofeachgiventime-frequencyunitislessthan0dB,whichmeansthatthesignalenergyisgreaterthanthenoiseenergy.Inthisway,thereisanoptimizationoftheSNRbenefitsprovidedbybinarymasking(LiandWang,2009).Thepresentstudyusedabinarymaskingnoisereductionalgorithmasaprocessingcondition(Boldtetal.,2008),ratherthananon-idealestimationofnoisereduction. LinearAmplificationandCompression Audibilitywasprovidedbysettingupthehearingaidinsuchawaythatlinearamplificationwasbasedonthehearingthresholdsofeachsubject,asafunctionofvoicealignedcompression.Thesettingswerethenmodifiedusingsoftwareprogrammedforalinear1:1compressionratiocorrespondingtopure-toneinputlevelsrangingfrom30to90dBSPL.Subsequently,allsignalsandnoisesweredistributedinsuchawaythatthenoiselevelcorrespondedtotheregionofthelinearcompressionratio,ensuringthattherewasnoeffectofanycompressionkneepointoroutputlimiting.Theprimarygoalofvoicealignedcompression,knownascurvilinearWDRC,istoreducecompressionatahighinputlevel,andtoincreasecompressionatlowinputlevels,byusinglowercompressionkneepoints(rangingfrom30to40dBSPL,dependingonthefrequencyregionaffectedandthedegreeofhearingloss).TheloudnessdataofBuusandFlorentine(2001)hascontributedinparttothiscompressionmodel,whichfocusesonprovidingbettersoundquality,whilemaintainingspeechintelligibility,ratherthanfocusingsolelyonloudness.Theattacktimeof10msandreleasetimeof40ms(withacompressionratioof2:1inallchannels)wereemployedinfast-actingmultichannelWDRCconditions. Procedure Thedatainthisstudywerecollectedaspartofalargerinvestigation(Rönnbergetal.,2016),whichinvolvedthreesessionsofapproximately3heach.Dataforthisstudywerecollectedduringthefirstsession(backgrounddataandpure-toneaveragehearingthresholddata)andthethirdsession(Hagermantest).Alltestingwasadministeredindividuallyduringa6-weekperiod.Visioncorrectionwasusedwhennecessary. TheHagermansentencestesttookplaceinasound-treatedtestbooth,andtheparticipantssatonachairatadistanceof1mfromasingleloudspeaker.Themasterhearingaidwasimplementedinananechoicbox(BrüëlandKjaer,type4232),containinganexperimentalwellcheckedhearingaid.Thisexperimentalhearingaidwasfittedbasedoneachparticipant’saudiogram.Thisenabledaudibility,andcontroloftargetsignalprocessingsettingssuchas:linearamplification(withoutnoisereduction,andwithnoisereduction(Wangetal.,2009;Ngetal.,2013)andfast-actingcompression(Dillon,2001,2012).TwotypesofbackgroundnoisewerepresentedatequalRMSlevels;thesewerethemodulatedspeech-shapednoisebasedonthemodulatedpatternof4TB(consistingofrecordingsoftwomaleandtwofemalenativespeakersofSwedishreadingdifferentparagraphsofanewspapertext)andthesteadystatespeech-shapednoise. Thesehearingaidfeaturesandthebackgroundnoiseweremanipulatedtoexaminethepredictionsofaidedspeechrecognitioninnoiseinwhichcognitionabilitiesarechallenged.Linearamplificationwithoutbinarynoisereductions(NoP)servedasabaselinetoclarifythedifferencebetweenlinearamplificationwithbinaryNRandnon-linearfast-actingcompression(withNR)intermsofbenefits. Aftercalibratingthesetup,foreachparticipant,abaselinemeasurewasperformedusinglinearamplificationwithoutbinarymaskingnoisereductionpriortoapplyinglinearamplificationwithbinarymaskingnoisereductionandthenon-linearamplificationfast-actingcompression(withoutnoisereduction)setting.Thetestingbeganwithtwolistsof10sentencesusedaspracticebeforethetestsession.Eachpracticesentencewaspresentedoneatatimeinarandomizedorderataconstant65dBSPLintwobackgroundnoiseconditions.Theorderinwhichtheconditionsweretestedwasfullyrandomizedacrossparticipantsandbetweentests.Eachparticipantwastestedindividually,andforeachtestandparticipant,aninitialSNRof0dBwasselectedtofacilitatethefamiliarizationperiodwithasomewhateasyrecognitiontask.Intheexperimentalsession,Hagermansentenceswerepresentedasdescribedinthepracticesession.Threelistsof10sentenceseachwerepresentedtoeachparticipantinarandomizedorderforeachcondition.Foreachsentence,theparticipantwasaskedtorepeatasmanyofthewordsaspossible.Thenumberofwordscorrectlyrepeatedwasrecordedonacomputerterminal.Onthebasisofwordscores,theSNRwasautomaticallyadaptedusingastandardalgorithmthatappliesaninterleavedtechniquetodetermineindividualSNRsfor50and80%correctlevelsofperformance,respectively(Brand,2000).The50%thresholdrepresents2.5wordscorrectoutoffive,and4wordscorrectoutoffivecorrespondsto80%threshold.TherandomizationprocesswasbeneficialbecauseitreducesthepossibilityofmemorizingorguessingthesentenceandreducestheoveralllearningeffectandthusincreasesthedegreeofreliabilityoftheHagermantest.Althoughthespeechsignalwasfixed,thenoiselevelwasadaptivelyadjustedtomatchtheappropriateSNR. DataAnalysis Dataanalysiswasconductedusinga3×2within-groupanalysisofvariancedesign,withdigitalsignalprocessingalgorithmsetting(noprocessing,noisereduction,andfast-actingcompression)andnoisetype(SSNand4TB)asindependentvariables,andspeechrecognitioninnoiseperformanceasthedependentvariable.Therelationshipbetweenthemeasuresofcognitivespeed,WMCandspeechrecognitioninnoiseperformancewasanalyzedusingPearsoncorrelations.Giventhatalargenumberofcorrelationswerecomputed,theBonferronicorrectionwasappliedinordertocontrolthechanceofcommittingaTypeIerrorswhichcouldincrease.ToobtaintheBonferronicorrected/adjustedp-value,theoriginalα-value[criticalvalueofp(0.05)wasdividedbythenumberofcomparisonsonthedependentvariable(i.e.,36].Thisyieldsanewp-value(0.0014)thatcontrolsforfamily-wiseTypeIerrorrate. Aseriesofhierarchicalmultiplelinearregressionanalyseswereconductedinaidedsixconditions,respectively,performanceonHagermansentencestest,underthefollowingtestconditions:(1)Linearamplificationwithoutnoisereduction(NoP)inanunmodulatednoisebackground;(2)Linearamplificationcombinedwithnoisereduction(NR)inanunmodulatednoisebackground;(3)Linearamplificationwithoutnoisereduction(NoP)inamulti-talkerbackground;(4)Linearamplificationcombinedwithnoisereduction(NR)inamulti-talkerbackground;(5)Fast-actingcompression(Fast)signalprocessinginanunmodulatednoisebackground(nonoisereduction);(6)Fast-actingcompression(Fast)signalprocessinginamulti-talkerbackground(nonoisereduction,Rönnbergetal.,2016),toexaminetheextenttowhichcognitivespeedandWMCmayrelatetoaidedspeechrecognitionperformanceinnoise.Allthesignificancelevelsweresetatp<0.05,andP<0.01(two-tailed).AllanalyseswereperformedusingSPSSstatisticalpackage23.0forwindows. Results Meansandstandarddeviationsforthepredictor(cognitivespeedandworkingmemory)andthemeanSNR(dB)forspeechrecognitioninnoiseinthevariousconditionsareshowninTable1.LowerSNRscoresmeansbetterspeechrecognitionperformancebecauselowSNRshowsthattheparticipantscorrectlyidentifiedthespeechsignaldespiteahighlevelofbackgroundnoise,whilehighSNRscoresindicatethatthesentencescouldonlybecorrectlyrepeatedatlownoiselevels(HagermanandKinnefors,1995).ThescoringmethodfortheHagermansentencesboostedalevelofperformancewhere80%(i.e.,fouroutoffive)ofthewordsinanyparticularsentencewererecognizedcorrectly.Thatis,optimalperformancecanbefoundevenifonewordineachsentenceismeaninglessduetounder-amplificationormasking.Nevertheless,theSNRatwhich50%ofwordscorrectlyrecognized(or2.5wordsoutof5words)wasappliedforthecalculationofthethresholdsinaccordancewithPlompandMimpen(1979). SpeechRecognitioninNoisePerformance Atwo-way,within-participantanalysisofvariance,whichincludedthedigitalsignalprocessingalgorithm(noprocessing,noisereduction,andfast-actingcompression)andnoisetype(SSNand4TB),wasconducted.Theresultsrevealedamaineffectofthedigitalsignalprocessingalgorithm,F(2,386)=2137.82,p<0.001,ηp2=0.91,inwhichthemeanSNRforthenoisereductioncondition(-6.81dB,SE=0.13)waslowerthanthatforthenoprocessingcondition(-1.33dB,SE=0.13)andthefast-actingcompressioncondition(-0.47dBSNR,SE=0.14).Posthoct-tests(Bonferroniadjustedformultiplecomparisons)showedthatthetestperformanceinthelinearamplificationwithnoisereductionconditionwasbetter(i.e.,withaloweraverageSNR)thanthatinthelinearamplificationwithoutnoisereductioncondition(p<0.001)(Wangetal.,2009;Ngetal.,2013).Inaddition,performanceinthelinearamplificationwithnoisereductionconditionwasbetterthanthatinthenon-linearamplificationwithfast-actingcompressioncondition(p<0.001).Thissuggeststhatlinearamplificationresultedinabetterspeechrecognitionperformancethannon-linearamplificationwithfast-actingcompression.Therewasalsoasignificantmaineffectofthenoisetype,F(1,193)=3637.09,p<0.001,ηp2=0.95,inwhichthemeanSNRintheSSNcondition(-5.25dBSNR,SE=0.13)waslowerthanthatinthe4TBcondition(-0.48dBSNR,SE=0.12).Thisindicatesthatcompetingspeechnoisehasastrongermaskingeffectthanstationarynoise. Interestingly,asignificanttwo-wayinteractioneffectbetweenthedigitalsignalprocessingalgorithmandthenoisetypewasfound,F(2,386)=122.00,p<0.001,ηp2=0.38(Figure1).Furtherinvestigationoftheinteractionusingposthoct-testingwithBonferroniadjustmentformultiplecomparisonsshowedthatthedifferencebetweenspeechrecognitionperformanceinSSNandin4TBwasrelativelynotsignificant(p>0.05)whenbinarymaskingnoisereductionwasapplied.Thatis,whenNRwasapplied,thepresenceofnoiseeffectwasnolongersignificant,possiblyduetotheeffectivenessofNRatreducingthemaskingeffectofnoise(Ngetal.,2013),comparedtowhenfast-actingcompressionwasapplied,wherethedifferencebetweenSSNand4TBwassignificant(p<0.05,relativetoNoPbaseline).AsobservedinFigures1,2,thisinteractionhasbeendrivenbythefactthatthebackgroundnoisehasalargereffectinthenoprocessingcondition(differenceof-5.5)andthefast-actingcompression(difference-5.48)comparedtotheinthenoisereductioncondition(differenceof-3.32).Thismaysuggestthatbackgroundnoiseratherthancognitiveabilityisthekeyfactorinfluencingtheinteraction(Larsbyetal.,2005).Wemaysuggestthattherewasarelativelysmallerdependenceoncognitiveabilitiesinthenoisereductionconditionandarelativelylargerdependenceoncognitiveabilitiesinfast-actingcompressionduetothedetrimentalmaskingeffectsofthe4TBcondition(e.g.,Ngetal.,2013). FIGURE1 FIGURE1.Significanttwo-wayinteractionbetweenhearingaidsignalprocessingsetting(noisereductionandfast-actingcompression)andnoisetype[steadystatenoise(SSN),four-talkerbabble(4TB)]inaidedconditionswithHagermantest(relativetoNoPbaseline,errorbarsrepresentstandarderrors). FIGURE2 FIGURE2.Atwo-wayinteractioneffectbetweenhearingaidsignalprocessingsetting(linearamplificationwithoutnoisereduction,linearamplificationwithnoisereductionandfast-actingcompression)andnoisetype(SSN,4TB)inaidedconditionswithHagermantestareshown.TherewasasignificantdifferencebetweenSSNand4TB(i.e.,indB,intermsofspeechrecognitionperformance)inlinearamplificationwithoutnoisereduction,andinnon-linearamplificationfast-actingcompressioncondition.However,therewasnosignificantdifferencebetweenSSNand4TBinlinearamplificationwithnoisereductioncondition. Thenegativemaskingeffectsof4TBmighthavedisruptedanddelayedtheamplificationeffectivenessoffast-actingcompression(e.g.,thecompressorspeed:attacktimeorreleasetime)comparedtonoisereduction.ThisstudyindicatesthatperformancewasbetterwhenspokensentenceswerepresentedinSSNwithanoisereductionalgorithm.Noisereductionappearstobeeffectiveinreducingstablebackgroundnoise.ThisisinlinewithrecentstudiesthatsuggestthatnoisereductionprovidesgreaterbenefitsinSSNconditions(Ngetal.,2013;Arhartetal.,2015). Correlations Pearson’scorrelationscoefficientwascalculatedtoexaminetherelationshipbetweenage,scoresontheLDTandtheSWPST,andperformanceontheHagermansentencestestforthesixconditions.AgesignificantlycorrelatedwiththeLDTscores(r=0.19,p<0.05)andtheSWPSTscores(r=-0.30,p<0.01).Thecorrelationsbetweenageandthecognitivetestssuggestthataspeoplebecomeolder,cognitiveperformancebecomesworse(e.g.,Salthouse,1996).Thatis,advancedagecorrespondstolongerreactiontimesandlowerWMC(Rönnbergetal.,1989;Rönnberg,1990;Larsbyetal.,2005).AgealsosignificantlycorrelatedwiththeHagermansentencestestperformanceunderallsixaidedconditions.Thisisinlinepreviousstudies(e.g.,Larsbyetal.,2005).TheLDTscoresalsosignificantlycorrelatedwiththeHagermansentencestestperformanceunderallconditionswhenNoP,NR,andfast-actingcompressionwereused.Thisfindingindicatesthatcognitiveprocessingspeedmayberelativelyassociatedwithbothnoisereductionandfast-actingactingcompressionintermsofspeechrecognitioninnoiseperformance.Thispatternofcorrelationsdemonstratestheimportanceofcognitivespeedintheabilityofhearingaiduserstorecognizespeechinnoise. Theperformanceonthesemanticword-pairspanscoresnegativelyandsignificantlycorrelatedwiththeHagermansentencestestperformanceunderonly5outof6aidedconditions,thatis,whenNoP,NR,andfast-actingcompressionwereused.ThisisinlinewithpreviousstudiesthatsuggestedthatWMCwasrelatedtospeechrecognitioninnoiseperformancewithNR(Ngetal.,2013;Arhartetal.,2015)andfast-actingcompression(LunnerandSundewall-Thorén,2007;Rudneretal.,2011).However,thefactthatthesemanticword-pairspandidnotsignificantlycorrelatewiththeHagermansentencestestperformancewhentherewasnoprocessingandinSSNwithfast-actingcompressioncontrastswiththefindingsofGatehouseetal.(2006)andLunnerandSundewall-Thorén(2007;seealsoNgetal.,2013).Thelexicaldecisionspeedandsemanticword-pairspansignificantlycorrelated,showingthatalongerreactiontimeonspeechrecognitionperformanceisassociatedwithlowerWMC. ResultsafterBonferroniCorrectionWasApplied WhenBonferronicorrectionwasapplied,anewp-valuewasobtained(0.0014),andtodeterminewhetheranyofthecorrectionswassignificant,thep-valuemustbep≤0.001.Thecorrelationsbetweenage,theLDTscores,theSWPSTscoresandtheHagermansentencestestscoreswhenBonferronicorrectionwasusedareshowninTable2.Surprisingly,agedidnotsignificantlycorrelatewiththeLDTscores(r=0.19,p>0.05)butcorrelatedwiththeSWPSTscores(r=-0.30,p<0.05)atthevergeofsignificance.However,agesignificantlycorrelatedwiththeHagermansentencestestperformanceunderallsixaidedconditions(p<0.05,seeTable2).Thisisconsistentwithpreviousstudiesthatindicatethattherewasanage-relateddeclineinspeechrecognitioninadverselisteninginolderadultscomparedtoyoungerlisteners(Larsbyetal.,2008;Gordon-SalantandCole,2016).Interestingly,theLDTscoressignificantlycorrelatedwiththeHagermansentencestestperformanceunder5outof6aidedconditions(p<0.05)whenNoP,NR,andfast-actingcompression(inSSN)wereused.TheSWPSTscoressignificantlycorrelatedwiththeHagermansentencestestperformancein3outof6aidedconditions.Inaddition,thecorrelationbetweentheLDTscoresandtheSWPSTscoresdidnotsignificantlycorrelate(p>0.05),whichcontrastswithpreviousstudies(Larsbyetal.,2005).Insummary,verbalinformationprocessingspeed(LDTscores)wasassociatedwithalargebenefitfrombinarymaskingNRandfromfast-actingWDRC(inSSN).WMC(SWPSTscores)wasrelatedtoalargerbenefitfrombinarymaskingNRbutnotrelatedtofast-actingWDRCoutcomes. TABLE2 TABLE2.Correlationmatrixofselectedpredictorvariablesandspeechrecognitionperformancemeasures(Hagermantest)afterapplyingBonferronicorrections. Inthepresentstudy,thefocuswasontheinvestigationofhowcognitiveabilities(i.e.,cognitivespeed,WMC)mayrelatetoaidedspeechrecognitionperformanceinadverselisteningconditions.ToperformamorerobusttestofthepredictionconcerningtherelativeinvolvementofcognitivespeedandWMCaspredictorsofaidedspeechrecognitioninnoiseundersixaidedconditions,weperformedaseriesofhierarchicalmultipleregressionanalyses. HierarchicalMultipleRegressionAnalysis ToinvestigatetherelativeroleofcognitivespeedandWMCinexplainingthevarianceinaidedspeechrecognitioninnoiseperformanceundersixaidedconditions,agewascontrolledtoeliminateitsconfoundingeffects.Aftercontrollingforage,aseriesofhierarchicalregressionswasappliedundersixaidedconditions,andineachregression,agewasenteredinstep1,andtheLDTandSWPSTwereenteredinstep2.TheresultsofthesehierarchicalregressionsareshowninTables3,4.AsshowninTables3,4,theLDTscorespredictedspeechrecognitionin5outof6aidedconditionsaftercontrollingforage,thatis,in(1)SSNwithNoP,(2)4TBwithNoP,(3)SSNwithNR,(4)4TBwithNR,and(5)SSNwithfast-actingcompression.However,theLDTscoresdidnotpredictspeechrecognitionin4TBwithfast-actingcompression(p>0.05).TheSWPSTscorespredictedspeechrecognitionperformanceinonly1aidedcondition(p<0.05),beyondageandtheLDT.Thiscontrastswithpreviousstudiesthatfoundthatworkingmemorypredictedalargeportionofvariancewhensentenceswerepresentedinmodulatednoise(Gatehouseetal.,2003;Akeroyd,2008;Rudneretal.,2011;SouzaandArehart,2015).However,agesignificantlypredictedthedeclineinspeechrecognitioninallsixconditionsandexplainedalargepartofthevariancewhentheHagermansentenceswerepresentedinsteadystateand4TBnoisebackgroundregardlessofthehearingaidsignalprocessingalgorithmsapplied. TABLE3 TABLE3.HierarchicalregressionspredictingspeechrecognitionperformanceinSSN,4TBconditionswithandwithoutnoisereductionprocessing. TABLE4 TABLE4.HierarchicalregressionspredictingspeechrecognitionperformanceinSSN,4TBconditions,withfast-actingcompression. Discussion Thepurposeofthepresentstudywastoexaminetheextenttowhichcognitiveabilities(cognitivespeed,andWMC)mayrelatetoindividuallisteners’responsestodigitalsignalprocessingsettingsinadverselisteningconditions.Weconsideradverselisteningconditionsverygenerallytomeananybackgroundnoise(e.g.,4TB)and/ormodificationsoftheacousticsignal(inthisstudy,bynoisereductionandfast-actingcompression)thatmayoffsetthelistener’sperformance(Larsbyetal.,2005;Souzaetal.,2015a,b).Overall,ourfindingsareinlinewithpreviousstudiesinshowingthatcognitiveabilitiessuchasWMCandcognitiveprocessingspeedplayanimportantroleineffectivespeechrecognitionindifficultlisteningenvironments(Akeroyd,2008;Rönnbergetal.,2008,2013,2016;Rudneretal.,2011;SouzaandArehart,2015)anddeclinewithage(Salthouse,1996,2000).Arecentinformationprocessingmodel(ELU;Rönnbergetal.,2013)providesatheoreticalbackgroundforabetterunderstandingoftherelationshipobservedbetweencognitiveabilitiesandspeechrecognitioninnoise.Thismodelsuggeststhatwhenthespeechsignalispresentedclearlywithoutdistortion,thelistenerwillrapidlyandeffectivelyperformalexicalmatchwiththeengagementofcognitiveresourcestoalesserextent(i.e.,WMC,processingspeed).Incontrast,ifthespeechsignalisdistorted(causedbyeitherbackgroundnoiseorunwantedsignalprocessingartifacts),thenlexicalmatchingmaybemoredifficult,andthelistenermayhavetoengagehisorhercognitiveabilitytoagreaterextenttounlockthemeaningofthemessageortofillinthemissingacousticinformation.OurresultsareconsistentwiththeassumptionsoftheELUmodel. TheEffectsofHearingAidSignalProcessingandBackgroundNoise Recentstudieshavesuggestedthatadvancesinthehearingaidindustryareofgreatpotentialbenefittohearing-impairedpersonswhocommunicateusingtheauditorychannel(Dillon,2012;Ngetal.,2013;Souzaetal.,2015a,b).Insupportofthissuggestion,severalstudieshaveshownrelativebenefitsfromfast-actingcompression(Gatehouseetal.,2006;Fooetal.,2007;Akeroyd,2008;Rudneretal.,2011;Souzaetal.,2015a,b)andfrombinarymaskednoisereduction(Wangetal.,2009;Ngetal.,2013;Rönnbergetal.,2016;Souzaetal.,2015b)forpersonswithhearingimpairment.Theresultsofthepresentstudyshowedthatbinarymaskingnoisereductionprovidesagreaterbenefitthanfast-actingcompressioninadverselisteningconditions(Rönnbergetal.,2016).Noisereductionsignalprocessingreducedtheadverseeffectofmodulatednoiseonspeechrecognitionperformanceforlistenerswithgoodcognitiveability(SouzaandArehart,2015).Thismaysuggestthatthelexicalmatchingoftargetspeechinformationinlong-termmemorybecomeslessexplicitandlesscognitivelytaxing(Rönnbergetal.,2008).However,listenerswithpoorcognitiveabilitiesmaynotbenefitfromnoisereductiontoagreaterextentbecauseanysignificantbenefitsprovidedbythesignalprocessingmighthavebeencanceledoutbytheadditionalcognitivedemandexercisedbythedistortionscreatedbysignalprocessingartifacts(Lunner,2003;Rudneretal.,2011).Ontheotherhand,fast-actingcompressionpresentedlimitedbenefits(relativetotheNoPbaseline),insupportofpreviousstudiesthatsuggestedthatthefast-actingcompressionsettingmayintroducesignaldistortionsoralterthespeechenvelope,resultinginaphonologicalmismatchandhencedependenceonthelisteners’cognitivecapacities(Lunner,2003;Akeroyd,2008;SouzaandArehart,2015).Giventhatbinarymaskingnoisereductionismoreaggressiveatreducingtheeffectofbackgroundnoise,itmayhavelesserspeechsignalmodificationeffectsthanfast-actingcompressionintermsofspeechintelligibility(Wangetal.,2009). Asobservedinthetwo-wayinteraction,itshouldbenotedthatthisinteractionwasdrivenbythefactthatthebackgroundnoisehasastrongereffectinthenoprocessingconditionandthefast-actingcompressionconditioncomparedtonoisereductioncondition(seetheSNRdifferences;Figure2).Thismaysuggestthatbackgroundnoiseratherthancognitiveabilityisthekeyfactorinfluencingtheinteractioneffectofsignalprocessingandthenoisetypeonspeechrecognitionperformance(relativetotheNoPbaseline;Larsbyetal.,2005).Thepresentfindingsshowedthatwhennoisereductionwasapplied,speechrecognitionperformancewasnotsignificantlydifferentfromeitherthatinSSNorin4TB.Thatis,whennoisereductionwasused,themaineffectofnoisewasnolongersignificant.Itmaysuggestthattherewasrelativelylesserdependenceoncognitiveresourcesandmoredependenceonhearingaidsignalprocessing.Ontheotherhand,speechrecognitionperformancewassignificantlydifferentinSSNandin4TBwhenfast-actingcompressionwasapplied(relativetoNoPbaseline,Figures1,2).Thatis,whenfast-actingcompressionwasapplied,the4TBdisruptivemaskingeffectremainedrelativelysignificant,resultinginmoredependenceoncognitiveresourcestoagreaterextent(ELUmodel,Rönnbergetal.,2008,2013).Thefindingsalsoshowedthat4TBbackgroundnoisewasmoredisruptivethanSSN,affectingtheeasewithwhichalexicalmatchcanbemadeandtaxingcognitiveresources(Larsbyetal.,2005).Moreover,multiple-talkerbabbledelayedandsubstantiallyreducedthebenefitobtainedfromfast-actingcompressioncomparedtonoisereduction(relativetotheNoPbaseline;Ngetal.,2013).Ourresultsmayalsosuggestthat4TBmaybeoneofthemajorcontributorstoasourceofsignaldegradationinspeechrecognitionperformance(seeLarsbyetal.,2005;Rudneretal.,2011).Moreover,giventhatthe4TBbackgroundnoisealsoconsistedofwordsspokenbytwomaleandtwofemalenativeSwedishspeakersinthepresentstudy,theuseofnativespeakersmighthavestrongermaskingeffectsonspeechwithfast-actingcompressionthanwithnoisereduction.Ourresultsmaysuggestthatthecombinationoffast-actingcompressionand4TBnoisemayconstituteamajorsourceofdegradationthatcontributestoanimpoverishmentoftheperformanceonthespeechrecognitiontaskortothepoorbenefitfromthehearinginstrument.Thatis,thecombinationoffast-actingcompression-4TBmayinfluencetheengagementofexplicitcognitiveresourcestoagreaterextentthanthatofnoisereduction-SSNdoes.Thisfindingisinagreementwithpreviousstudies(Larsbyetal.,2005,2008;Akeroyd,2008;Ngetal.,2013).Nevertheless,thecombinationofbinarymaskingnoisereductionandSSNmayconstituteaminorsourceofspeechsignaldegradationforhearing-impairedpersons(Ngetal.,2013;Rönnbergetal.,2016).Wemaysuggestthatolderadulthearingaidusersmaybemorevulnerabletothesignaldegradationcreatedbyacombinationoftheunwantedeffectsoffast-actingcompressionand4TBnoise. TheEffectsofCognitiveSpeedandWorkingMemory Thecurrentfindingsareconsistentwiththeassumptionthatsignaldistortionfromthecombinationoffast-actingWDRCand4TBconstitutesamajorsourceofsignaldegradationthatresultsinanimpoverishedrepresentationattheauditoryperiphery.Inthecontextoftheinformationprocessingmodelsforspeechperception,listenersundergoingthesemultiplesourcesofsignaldegradationmustassignmoreprocessingresourcestopriorprocessingphases(Rönnbergetal.,2008;Lunneretal.,2009).Thisdistributionofresourcesmayimpoverishthesubsequentprocessesrequiredfortheidentificationofthelinguisticcontentofthesentencematerials.Then,alistenermayberequiredtodependonhis/herWMCforeffectiveprocessingofthedegradedspeechsignalandcomprehensionofthemeaningofthemessage.Nevertheless,whentheWMCislimited,thisprocessingmaybemoredifficultormayfail.OurfindingsshowthattheWMCscores(SWPST)andcognitiveprocessingspeedscores(LDT)didnotsignificantlycorrelatewithspeechintelligibilityonlyin4TBwithfast-actingWDRCafterusingBonferronicorrectionandthattheydidnotsignificantlypredicttheperformanceofspeechrecognitionin4TBwithfast-actingcompression.Inthecaseofworkingmemory,thisfindingcontrastswiththepreviouslyconfirmedrelationshipbetweenworkingmemoryandfast-actingcompressioninamodulatednoisebackground(Gatehouseetal.,2003,2006;Fooetal.,2007;Rudneretal.,2011).Thiscouldbebecausetheamountofresourcestobeallocatedtoprocessingandstoragemighthavebeenlimitedormighthaveexceededtheavailablecapacity,whichmayresultintaxerrors,lossofinformationorslowerprocessing.Ifwemaypostulatethatstrongerfast-actingWDRCprocessingresultsinagreatermodificationoftheinputsignal,thenwewillexpectarelationshipbetweenWMC(SWPSTscores)andbetterspeechintelligibility(greaterbenefit)withfast-actingWDRC(Rudneretal.,2011);however,thiswasnotthecaseinboththecorrelationsandtheregressionresults(seeTables2–4).Apossiblereasonforthiscouldbethatstrongerfast-actingWDRCprocessingmaybehavingconcurrenteffects:improvingtheaudibilityofthespeechsignalwhilemaintainingloudnesscomfort(byapplyinggainasafunctionofintensity,withalowergainappliedtohigherinputlevels)andintroducingunwantedprocessingartifactsthatmaycreatemoredistortionsratherthanlessaggressiveprocessing(Dillon,2001;Lunner,2003).PossiblytheneteffectoftheseopposingfactorscontributestotheweakassociationbetweentheSWPSTandfast-actingWDRC(Dillon,2012). Ontheotherhand,ourresultsindicatethattheeffectsofacombinationofnoisereductionandSSNmayconstituteaminorsourceofdegradation,contributingtoagreaterbenefitorbetterspeechintelligibility.Thatis,thereweresignificantassociationsbetweenWMC(SWPSTscores)andthebinarymaskingNRoutcomesandbetweenthecognitiveprocessingspeed(LDTscores)andthebinarymaskingNRoutcomes(seeTable2).ThismaybeviewedviatheELUmodel,whichassumesalargerinfluenceofcognitiveability(e.g.,WMC)whenthephonologicalformoftheperceivedlanguagesignaldoesnotmatchthephonologicalrepresentationsstoredinlong-termmemory.WemaypostulatethatstrongerbinarymaskingNRprocessingresultsinasignificantmodificationoftheinputsignal;wewouldexpectarelationshipbetweenworkingmemoryandbetterspeechintelligibility(orgreaterbenefitsfromNRprocessing),andthiswasthecaseinthepresentstudy.ApossibleexplanationforthiscouldbethatstrongerbinarymaskingNRprocessingmayhavetwobalancedeffects:improvingtheaudibilityofthespeechsignal(asaresultofaneffectivenoisesuppression),introducingrelativelylesserdistortionbutmoreaggressiveprocessing(relativelylessexplicitcognitiveresources;Neher,2014).Theresultsofthepresentstudyshowthatcognitiveabilityisanimportantfactorinaidedspeechrecognitioninadverselisteningconditionsforpersonswithhearingimpairment. EffectsofAge TherelationshipbetweenageandthemeasureofcognitiveprocessingspeedwasobservedbeforeapplyingBonferronicorrectionbutnotafter.Thepatternofthisrelationshipwascontrarytoourexpectations,insupportofpreviousstudiesthatindicatethatprocessingspeeddeclineswithage(Salthouse,1996;Lunner,2003;Larsbyetal.,2005).However,arelationshipbetweenageandthemeasuresofworkingmemorywasobservedbeforeandafterapplyingBonferronicorrection,suggestingadeclineinWMCwithage(Salthouse,1996).Asexpected,theeffectsofageonspeechrecognitioninnoiseperformancewereobservedbeforeandaftertheuseofBonferronicorrection.Thispatternoftherelationshipisinsupportofpreviousstudiesshowingpoorerperformanceforolderadultlistenerscomparedtoyoungerlisteners(Gordon-SalantandFitzgibbons,2001;Gordon-SalantandCole,2016).Theeffectofageonspeechrecognitioninnoiseperformanceisalsounderlinedbytheresultsofthehierarchicalregressionanalysis,whichshowedthatage,aboveandbeyondtheeffectsofthecognitiveprocessingspeedandworkingmemory,contributedtovarianceintheintelligibilityscores,suggestingthathearingaidusersmayhaveage-relateddegradationsinhigher-levelprocessingthatextendbeyondwhatiscapturedintheSWPSTandtheSDT.Thismaysuggestthatthereareotherfactorsassociatedwithagingotherthancognitivefunctioningthatmaybeinvolvedintheage-relateddeclineinspeechrecognitionamongolderhearingaidusers(BaltesandLindenberger,1997;WingfieldandTun,2001;Larsbyetal.,2008). Conclusion Thepresentstudyaddstopreviousstudiesanewwayofviewingtherelationshipbetweencognitiveabilitiesandbinarymaskingnoisereductionandfast-actingWDCforspeechrecognitioninnoiseforhearingaidusers(Lunner,2003;Akeroyd,2008;Ngetal.,2013;SouzaandArehart,2015).Theresultsshowedthataftercontrollingforage,cognitiveprocessingspeedwasabetterpredictorofspeechintelligibilityinnoise(inbothSSNand4TB),suggestingasignificantassociationbetweencognitiveprocessingspeed(measuredbyLDT)andbinarymaskingNRandfast-actingcompression(inSSN).However,therewereweakerassociationsbetweenWMC(measuredbytheSWPST)andspeechintelligibilityinnoisewithNR,andnoassociationwhenfast-actingWDRCwasused.Thatis,WMCwasaweakerpredictorofspeechintelligibilityinnoise.Thefindingsmighthavebeendifferentiftheparticipantshadbeenprovidedwithtrainingand/orallowedtoacclimatizetobinarymaskingnoisereductionorfast-actingcompression(Rudneretal.,2011).Takentogether,theresultssuggestthatassessingtheeffectsofcognitiveprocessingspeed,WMC,andhearingaidsignalprocessingsettingsinnoisemayprovideimportantinsightsintothesourceofhearingaidusers’complaintsofdifficultyrecognizingspeechinnoise. EthicsStatement Thesubjectswereinformedaboutthevoluntariness,confidentialityandtheywerefreetodeclineparticipationatanytime.Theyalsofilledupawritteninformedconsentforminwhichtheygivetheresearcherstherighttocollectandrestorepersonalinformationrelevanttothestudy.Personalinformationwascollectedandstoredinawaythatparticipant’sintegritywasmaximized(Breakwelletal.,2006). AuthorContributions WYhassubstantiallycontributedtothefollowingphasesofthepresentstudy:theconception,thedesign,theacquisition,analysis,andtheinterpretationofdata;thedraftandcriticalrevision;thefinalapprovaloftheversiontobepublished.Theauthorisaccountableforallaspectsofthiswork. Funding ThisworkwassupportedbyaLinnaeusCentreHearingandDeafness(grantnumber349-2007-8654)fromtheSwedishResearchCouncil. ConflictofInterestStatement Theauthordeclaresthattheresearchwasconductedintheabsenceofanycommercialorfinancialrelationshipsthatcouldbeconstruedasapotentialconflictofinterest. Acknowledgments TheauthorthanksJerkerRönnbergandHenrikDanielssonfortheirinsightfulcommentsonthismanuscript.MathiasHällgren(fromtheDepartmentofTechnicalAudiology,LinköpingUniversity)forhistechnicalsupport;TomasBjuvmarandHelenaTorlofson(fromtheHearingClinic,UniversityHospital,Linköping);ElaineNg(fromtheSwedishInstituteforDisabilityResearch,LinköpingUniversity)forherassistanceindatacollection;andThomasKarlsson,BjörnLidestam,ShahramMoradi,RachelJaneEllis,ÖrjanDahlström,andEmilHolmerfortheirsupport.Theauthorwouldliketothankthreereviewersfortheirhelpfulandinsightfulcommentsonthismanuscript. 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Editedby: ClaudiaRepetto,UniversitàCattolicadelSacroCuore,Italy Reviewedby: PietroSpataro,SapienzaUniversitàdiRoma,Italy ChristianDesloovere,UniversitaireZiekenhuizenLeuven,Belgium Copyright©2017Yumba.Thisisanopen-accessarticledistributedunderthetermsoftheCreativeCommonsAttributionLicense(CCBY).Theuse,distributionorreproductioninotherforumsispermitted,providedtheoriginalauthor(s)orlicensorarecreditedandthattheoriginalpublicationinthisjournaliscited,inaccordancewithacceptedacademicpractice.Nouse,distributionorreproductionispermittedwhichdoesnotcomplywiththeseterms. *Correspondence:WycliffeKabayweYumba,[email protected];[email protected] Peoplealsolookedat Download