TheEffectsofHearingLossonBinauralFunction

SteveColburn

BostonUniversity

colburn@bu.edu

•Outline

Whatarethemajoradvantagesoftwoears?

Howdotheleftandrightsignalsdiffer?Howdoweusethisinformationphysiologically?

Howwellcanweexploitourtwoearsforimportanttasks?LocalizationofsoundsourcesAttendingtosourceofinterestincomplexsituations

Effectsofhearingimpairmentinbinauralprocessing...Interauralparametersensitivityandspeechwithspeechmaskers.(astudybyNathanSpencerinmylab).

Whatlimitsperformancewithimpairments/aids/implants?

Whatarethemajoradvantagesoftwoears?

Redundancy

Localizationofsources

Identifyingroomcharacteristics(size,shape,wallreflectivity,and???)

TheCocktailPartyEffect…Renoir's“LuncheonoftheBoatingParty”

•LocalizationCues:

•ITD:fareardelayed•ILD:farearattenuated•SpectralShapes

Differentsignalsatthetwoears

InterauralTimeDelay(ITD)•versusazimuthθ

•DurlachandColburn, 1978

•InterauralLevelDifference(ILD)•ILDversusazimuthfortwofrequencies•Measurementsandspherecalculations

SpectralShapeInformationasalocalizationcue

Outer Ear (beige), Middle Ear (pink), Inner Ear (Blue, cochlea)

•

lConsiderstimuluscodingandbinauralprocessinginphysiologicalstructures.

lQuickreviewofperipheralphysiology

lAuditoryNerveResponsesandTimingInformation

lSuperiorOlivaryNucleicompareleftandrightresponseswithsensitivitytoITDorILD

PhysiologicalMechanisms

Middle Ear bones

Cochlear spiral

Vestibular and Auditory Nerves

Semicircular Canals

Stapedius muscle attaches to third bone (stapes) and contracts to decrease transmission

May respond in anticipation of loud sounds

RecordingsfromthreeindividualauditorynervefiberswithNOACOUSTICSTIMULUS

•Primary Auditory Nerve Patterns (Kiang, 1965)

•Note the stochastic nature of the response

Rate-intensityfunctionforauditorynervefiber

AuditoryNerveTuningCurves:Levelrequiredfordetectableresponse

Histogramsofresponsestotonesatvariouslevels

Notethathistogramsherecovertwoperiodsofthetonalstimulus

Synchronizationtotonecycles

•JeffressmodelofITDprocessing

•Howdoprocessthistiminginformationtocomparerightandlefttimings

•JeffresspostulatedCoincidenceDetectorNetworkin1948.

•Internaldelaysthataredifferentforeachcellinanarray

•Fixedtimedelayoninputpatternswouldexcitecompensatingdelaycellmoststrongly

•Coincidence Network of Jeffress (1948)

ITD-sensitive neuron in MSO

•MechanismsofITDProcessing

•CodingoftimestructuretoneuralpatternlPrimary auditory nerve coding

•Maintenance/sharpening of temporal structurelSharpening in cochlear nucleus (Bushy Cells of CN)

•Sensitivity to delays of left and right inputslSingle neuron processing in MSO

•Preservation to higher neural levelslMaintenance of “spatial code” for ITD

From Stern and Trahiotis, 1997

Binaural Display: (f,τ)-plane

Narrowband Cross-correlation function for each f

Internal delay limiting function

Resulting distribution of activityITD from ridge

•Interaurallevel(ILD)representation

•LSOneurons(ILDandonset-ITDsensitive)

•Excitatoryinputfromipsilateralside

•Inhibitoryinputfromcontralateralside

•ArrayofILDprocessorsversusfrequency

•DiraniehandColburn,1994•(MODEL)

•LSONeuronandILDsensitivity

•ILD,farrayofLSOneurons

•LSOneuronsareeachILDsensitive

•LSOneuronsaretunedinfrequency(likeauditorynervefibersandMSOcells)

•ProvideinformationaboutILDforeachfrequencyband

•Maybeparticularlyimportantinreverberantenvironments(Hartmann,1999)

InterauralDifference(ITDorILD)ResolutionforHumanSubjects

•Howsmallatimedelaybetweentheearsisreliablydetectablebyahumanlistener?

•CalledaJust-NoticeableDifferenceinITDorILD

•Bestlistenerscandobetterthan10µs −− on the order of ten millionths of a second!

•Best listeners for ILD do about 0.5 decibels

InterauralDifferenceSensitivityversusfrequency

EnvelopecarriesITDatHF

• Temporalsynchronizationtotimingfallsoffathighfrequencies…

• MinimalsensitivitytofinestructureITDaboveabout1500Hzinhumans

• Buthighfrequenciescarryinterauraltiminginformationinsynchronizationtotheenvelopes.Thisisafactorinbinauralperformancebutitiscomplicated.

Envelopeonnoisebandprovidestimingcues

Neuralsynchronizationtotheenvelope(blackcurvewithfrequenciesrelatedtobandwidth)

Nosynchronizationtothefinestructure(i.e.,tothecarrier)athighfrequencies

Howdowehandlethecocktailparty?

• Combinedstimulimixedtogetherineachfrequencyband

• Wewanttousetheinternaldistributionsoverfrequencyandinterauralparameters…maybebasedoninterauraltimeandlevelormayinvolveprocessed,position-basedinformation

• Thesedisplayschangeovertimeasdifferentstimulifromdifferentdirectionsdominate.

• Thisisacomplexchallenge!

Sortingitallout

• Theinformationhastobethere.• Weneedtoignoredistractingsources

– Evidencethatmusicianscandothisbetter– Practicemakesusbetterinanycase– Calledinformationalmaskingversus“energetic”

• Weneedtoexploittheinterauraldifferencesaswellasthedynamictemporalvariations

• Weneedtouseourknowledgeofthesignals

InterauralSensitivitywithHearingLoss(NathanSpencerExperiments)

• Primaryinterestwaseffectsofhearingimpairmentsonbinauralprocessing.

• Measuredinteraural discriminationaswellasspatialreleaseinspeech-on-speechmasking.

• Hypothesizedthatinteraural discriminationability[just-noticeabledifferences(JNDs)ininteraural time,level,andcorrelation]wouldco-varywithspatialseparationbenefits.

NathanSpencerSubjects

• Tenyoungnormal-hearingsubjects,aged20-29

• Tenyounghearing-impairedsubjects.• HI1-HI8,HI10,HI11;aged19-38

• Oneolderhearing-impairedsubject• HI9aged70

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HI1 HI2 HI3

HI6HI5HI4

HI7 HI8 HI9

HI10 HI11

25yearsold,male

18,f 19,f

19,m 24,m

37,m 22,f

38,f

29,f29,m

70,m

AudiogramssymmetricinallcasesexceptforinHI10,anauthorinthiswork.

Interauraldifferencesensitivitytasks• Stimuli1/3octave,narrow-bandnoises,centeredateitherlowfrequency(500Hz)orhighfrequency(2kHzor4kHz).

• Measuredjust-noticeabledifferences(JNDs),relativetodioticreference(waveformssameinbothears)

§ Interauraltimedifference(ITD)discrimination§ Interauralleveldifference(ILD)discrimination§ Interauralcorrelationdifference(ICC)discrimination

Measuringinterauraldifferencesensitivitythresholds

• Acquiredadaptivetracksto(Levitt,1971)70.7%correct

• Keptmeasuringperformanceinalltasks,overmultipledays

• Calculatedthresholdsanderrorbarsbasedonlasttwelveadaptivetracks

ITDsensitivitymeasurements

• Ininterval2orinterval3,waveformwasdelayedinoneear,relativetoother…creatinganoff-centerimageinonlyoneinterval

• Presentedfourintervals

• Subjectaskedtoidentifywhichinterval(2or3)wasdifferent

• Providedwithfeedback

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Increasingaveragehearingloss

WilcoxonMedianTest…

p>0.05

ILDThresholds(Notelogscale)

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WilcoxonMedianTest…

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HearinglossasafunctionofinterauraldifferencesensitivitythresholdsforHI

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• Nocorrelationsfoundforeitherofthesubjectgroups,foranyinterauraldifferencesensitivitytask

• LackofcorrelationfoundforHIgroupinITDat500Hz

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r²=.73

r²=.79

r²=.88

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r²=.84 r²=.25

r²=.73

r²=.68

r²=.88

r²=.94

IDJNDmeasurementsweregenerallycorrelatedbetweenlowandhighfrequencies,consideredacrosssubjects

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Previousstudies:individualdifferencesininter-auraldifferencesensitivity,notinmonaurallevelsensitivity

• Four,highlytrainedNormal-Hearinglistenersat500Hz(Koehnke etal.1986)…

MONAURALdiscrimination

INTERAURALdiscrimination

InterauralDiscriminationConclusions

• Largeinter-subjectvariability

• Interauraldifferencesensitivitythresholdsdidnotcorrelatewithhearingloss

• ITDandILDthresholdshighlycorrelatedamongbothNHandHIsubjectgroups

• Consistentwithmyseeing“remarkablesubjects”whowereexcellentinbinauraltaskswithseverehearingloss

The famous psychologist George A.Miller once wrote:

"It is said that the best place to hide aleaf is in the forest, and presumably thebest place to hide a voice is among othervoices" (p. 118).

Miller,G.A.(1947) "Themaskingofspeech,"Psychol.Bulletin,44,105-129

Understanding speech in competition with other speechcan be challenging.

NowturntotheCocktailPartyProblem

•E.ColinCherry’s1953summary:

•“Howdowerecognizewhatonepersonissayingwhenothersarespeakingatthesametime(the‘cocktailpartyproblem')?”

•Factors:lVoices from different directionslLip-reading, gestures, and the likelDifferent speaking voices, pitches, speeds, …lAccents differinglTransition-probabilities (subject matter, voice dynamics, syntax, …)

ObtainingSRTs

• UsedproceduresdevelopedbyCarr(2010)(nowCarrLevy)• Adaptivealgorithmusedtodeterminethetarget/masker(T/M)

ratio(dB)for50%correct§ Maskerlevelsfixed

§ NormalhearingEachmaskersetto~45dBaboveSRTinquiet(65dBSPL)

§ HearingimpairedEachmaskerset~25dBaboveSRTinquietinHI,whenpossible

§ Targetlevelvaried

• ForHI11,discomfortthresholdslimitedmaskerlevel,sotargetcouldbelimitedbyaudibility(lessthan10dBabovequietthreshold,Duquesnoy,1983)

Colocated task

6m

10mDifficultcase,ingeneral…

• Alltalkersinthesameposition• Noseparation-relatedcues

~Infront

Sources~1.5mawayfromhead

Symmetricmaskerscondition

6m

10mModeratelydifficult…

• Interauraldifferences• Nolong-termbetterear

~Infront

~60⁰~60⁰

~1.5m

Anti-symmetricmaskerscondition

Expectedtobeeasierthancolocated…

• Long-termbetterear,contralateraltoearwithdominantmasker

• Interaural timedifferences• Interauralleveldifferences

~60⁰ ~Infront

Sources~1.5mfromhead

Measuredperformancebothright-earbetterandleft-earbetter

Colocated task

6m

10mDifficultcase,ingeneral…

• Alltalkersinthesameposition• Noseparation-relatedcues

~Infront

Sources~1.5mawayfromhead

Colocated SRTs

Limitedbyaudibilityp>0.05

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WilcoxonMedianTest…

Anti-symmetriccondition

Expectedtobeeasierthancolocated…

• Long-termbetterear,contralateraltoearwithdominantmasker

• Interaural timedifferences• Interauralleveldifferences

~60⁰ ~Infront

Sources~1.5mfromhead

Measuredperformancebothright-earbetterandleft-earbetter

Anti-symmetricSRTs

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• “Spatialreleasefrommasking”

• Individualdifferencesareevident

WilcoxonMedianTest…

†

• Monauralbenefit = Colocated – separatedmonaural

Determiningbenefitsofspatialseparation

• Binauralbenefit=Totalbenefit– monauralbenefit

• Totalbenefit=colocated - spatiallyseparated

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Monaural

Binaural

Separatedmonauralismeasuredatbetterear

Anti-symmetricbenefitsofspatialseparation

Largemonauralbenefit

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Anti-symmetricbinauralbenefit

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Anti-symmetricbinauralbenefitasafunctionofhearingloss

r2=.55

ILD500ILD4k

ITD500ITD4k

r2 shownintableRedmeansp<0.05

BinauralBenefitr2 <0.2r2 =0.67

r2=0.51r2 =0.39

Anti-symmetricbinauralbenefitasafunctionofinterauraldifferencesensitivity

NH

BinauralBenefitr2 <.2r2 <.2

r2 <.2r2 N/A

BinauralBenefitN=8r2 =.53N=6r2= 0.64

N=8 0.54N=4 r2 N/A

HI1-8(<70dBHL)HI1-10

Correlationformost interauraldifferencesensitivitythresholds

Correlationfornointerauraldifferencesensitivitythresholds

Correlationforsomeinterauraldifferencesensitivitythresholds

Symmetrictask

6m

10mModeratelydifficult…

• Interauraldifferences• Nolong-termbetterear

~Infront

~60⁰~60⁰

~1.5m

Symmetricbinauralbenefit

Highinter-subjectvariabilityamongeachsubjectgroup

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Symmetricbinauralbenefit

• Binauralbenefitdidnotcorrelatewithhearinglossineithergroup

• Binauralbenefitdidnotcorrelatewithinterauraldifferencesensitivitythresholdsineithergroups

DataConclusions

• Hearinglossakeyfactorinthebinauralbenefitfortheanti-symmetricconditionbutnotforthesymmetriccondition

• Inmostcases,hearing-impairedlistenersbenefitedfrombinaurallistening§ Binauralbenefitsmostlypositiveforanti-symmetric condition§ BinauralbenefitswerealwayspositiveforHIinthesymmetric condition

• Intheanti-symmetriccondition,binauralbenefitwascorrelatedwithsomeinterauraldifferencesensitivitythresholdsforbothnormal-hearingandsubsetofhearing-impairedlisteners

§ Inthesymmetriccondition,binauralbenefitnotcorrelatedwithinterauraldifferencesensitivitythresholds

Timewindowprocessingfactor?

• Inthesymmetriccase,withspeechmaskers,listenersbenefitfromselectivelylisteninginoptimaldirection(and/ortothebetterear)differentlyindifferenttimeintervals

• Thisfactorisdistinctfrominterauralresolutionfactorsandfromattenuationfactors

•Speech Spectrogram

lTime(about3.5seconds)

lFrequency (kHz)

EffectofECwindowlengthonSRT(1xJitter)

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Inconsistentbetter-ear

OverallConclusionsforthisstudy

• Binauralbenefitinanti-symmetricconditionforHIgroupdecreaseswithhearingloss

• Interauraldifferencesensitivityakeyfactorforbinauralbenefitforanti-symmetricspeechcondition§ Correlationswereobservedfornormalhearinggroupandfor

hearing-impairedsubgroupwithless-than-severeaveragehearingloss

§ Modelpredictionsshowlargeeffectofjitterstandarddeviation

• Interauraldifferencesensitivityandhearinglosseachunrelatedtobinauralbenefitforsymmetriccondition§ Neitherinterauraldifferencesensitivitynorhearinglosscorrelated

withbinauralbenefitinthesymmetriccondition§ Modelingresultsshowinfluenceofprocessingwindowduration§ Suggestindependentestimationofprocessingwindowlength

Takehomemessage?

• Theprocessinginmultiplespeechinterferencesituationsisverycomplex– Dependsonlocations,natureofsources,positionsofmaskers,individualabilitytousethemultiplecues,andpossiblyontemporalwindowfactors.

• Neithertheaudiogramnorabilitiestodosimplediscriminationtasksarepredictorsofabilitiesincomplexenvironments

• Teststobedonewithhearingaidsincomplexenvironmentsseemimportanttodevelop.

Ongoingworkonthistopic(withTheoGoverts atVUMC)

• Attempttocharacterizedifficultenvironments– Recording(binaurally)difficultenvironmentsasreportedbylistenerswithhearingimpairments

• Analysisofrecordingsandcomparisonswithsubjectiveimpressions

• Worktodevelopaspeech-in-complex-environmentstestthatcouldbeusedtoevaluatehearingaidsintheclinic.

Physical Acoustics

L(t)

R(t)

Current Model of Sources and Environment

ITD,f array

ILD,f array

freq spectra

ITD,f array

ILD,f array

freq spectra

Compare

Actual to

Hypothesis

Update Mechanism

Peripheral Physiology

Listener’s Learned Transformations

Non-auditory inputs

Real Sources in the real Environment

Fast (Add/Delete/Move Source)

Slow (Pinna)

Internal Representations

ColburnandKulkarni(2005)

StableWorldModel

Acknowledgements

• IRChearing-aidcompanyconsortium

• NationalInstitutesofHealthGrantsupport:– NIDCDR01DC00100

• ManyColleagues,especiallyGeraldKidd,TheoGoverts,SuzanneCarr Levy,NathanSpencer

TheEnd!!