Recognition of nonsensesyllables by hearing-impaired listeners
and by noise-maskednormal hearers
LarryE. Hurries
a)
Division
ofHearingandSpeech
Sciences,
Vanderbilt
University
School
ofMedicine,
Nashville,
Tennessee
3 7232
Donald D. Dirks, Theodore S. Bell, and Gail E. Kincaid
Division
ofHeadandNeckSurgery,
U.C.L.,4.School
ofMedicine,
Los.4ngeles,
California90024
(Received
4 February
1986;accepted
forpublication
15October
1986)
In thepresent
study,speech-recognition
performance
wasmeasured
in fourhearing-impaired
subjects
andtwelvenormalhearers.
Thenormalhearers
weredividedintofourgroups
of three
subjects
each.Speech-recognition
testing
forthenormalhearers
wasaccomplished
in a
background
ofspectrally
shaped
noisein whichthenoise
wasshaped
to produce
masked
thresholds
identicalto thequietthresholds
of oneof thehearing-impaired
subjects.
The
question
addressed
in thisstudyiswhether
normalhearers
witha hearing
losssimulated
througha shaped
masking
noisedemonstrate
speech-recognition
difficulties
similarto thoseof
listeners
withactualhearingimpairment.
Regarding
overallpercent-correct
scores,
theresults
indicated'
thattwoof thefourhearing-impaired
subjects
performed
betterthantheir
corresponding
subgroup
of noise-masked
normalhearers,
whereas
theothertwoimpaired
listeners
performed
likethenoise-masked
normallisteners.
A grossanalysis
of thetypesof
errorsmadesuggested
thatsubjects
withactualandsimulated
losses
frequentlymadedifferent
typesof errors.
PACS numbers:43.71.Ky, 43.71.Es,43.66.Dc
conductive
pathologythanwith sensorineural
impairment.
Both filteringand conductivepathologyappearto simply
The psychoacoustic
and speech-recognition
perforattenuate
incoming
signalenergypriorto stimulation
of the
manceof listenerswith sensorineural
hearinglosshasbeen
cochlea.It hasbeensuggested
previously
(Milner, 1982;Destudiedby severalinvestigators
in recentyears(for recent
Gennaroetal., 1981;Humes,1982)thatthemostapproprireviews,seeIesteadt,1978;Scharfand Florentine,1982;
atecontrolconditionfor comparison
to sensorineural
hearHumes,1982;andMoore,1983).It hasbeenfrequentlysugingimpairment
is the introduction
of broadband
masking
gested
thatthespeech•recognition
difficulties
experienced noiseshapedto producemaskedthresholdsin the normal
by listeners
havingsensorineural
hearinglossaretheresult
hearersthat are identicalto thoseof the impairedears.The
ofpsychoacoustic
abnormalities
accompanying
thecochlear maskingprocessresponsible
for thresholdelevationis bepathology
andnotsimplythethreshold
elevation
(Bonding, lieved to be predominantlyof cochlearorigin (Fletcher,
1979;Tyleretal., 1980;Patterson
etal., 1982).Appearing
to
1953;Zwicker and Feldtkeller, 1967;Zwicker, 1975, 1982).
INTRODUCTION
support
thisconclusion
isthefrequent
observation
thatnormalhearerslisteningto filteredspeech
performbetterthan
hearing-impaired
subjects
havingcomparable
hearingloss.
'Such an outcome has been observed in several studies
(Wanget al., 1978;Waldenet al., 1981;Kiukaanniemi,
In addition, noise-maskednormal listeners demonstrate
loudnessrecruitmentcomparableto that observedin ears
with sensorineural
pathology(Lochnerand Burger,1961;
Stevens,1966).
The presentstudysoughtto evaluatehow accurately
1979, 1980). It is reasonedthat if the filteringeffectsof
noise-masked normal listeners simulate sensorineural listenthreshold
elevation
wereresponsible
for thespeech-recogniers in their speech-recognition
performance.
If somephetion performance
of hearing-impaired
listeners,
thenthe nomenonother than thresholdelevationof cochlearorigin
normals
shouldalsoperformpoorlywhenlistening
to approandaccompanying
loudness
recruitmentisat leastpartially
priatelyfilteredspeech.
Althoughtheperformance
of norresponsible
for thespeech-recognition
difficulties
of listeners
mal hearersis reducedby filteringthe signal,the normal
with sensorineural
impairment,thenonewouldexpectthe
hearers
listening
to filteredspeech
typicallyoutperform
the
sensorineural
listeners
to performmorepoorlythanthenorimpaired
subjects.
It isfrequently
suggested
thatsome
addi- mal hearerslisteningin noise.If, however,similarperfortionalabnormality
beyondthe thresholdelevationmaybe
manceis observed
for bothgroupsor theimpairedsubjects
operating
in theimpairedearsto account
for thisdifference performbetterthanthenoise-masked
normallisteners,
then
in performance
betweengroups.
no additional abnormality, beyond threshold elevation of
Filtered signalspresentedto normal hearers,however,
cochlearorigin and accompanying
loudnessrecruitment,
providea bettersimulation
of hearinglossassociated
with
needbe invokedto explainthe speech-recognition
perfor-
a•Present
address:
Department'
ofSpeech
andHearing
Sciences,
Indiana manceof the impairedlisteners.Superiorperformanceby
University,.Bloomington,
IN 47405.
765
J.Acoust.
Soc.Am.81 (3),March1987
the hearing-impairedlistenersover that of noise-masked
0001-4966/87/030765-09500.80@ 1987Acoustical
Society
ofAmerica
765
normalscloselymatchedfor signalaudibility, however,
while not suggestive
of additionalprocessing
difficultiesin
the impairedlisteners,couldcompromisethe utility of noisemaskednormal hearersas a modelof sensorineural
hearing
loss.
It shouldbe notedthat thisapproachhasbeenpursued
by othersin recentyears,althoughonlya limitednumberof
subjects
or a limitedrangeof speech
stimulihavetypically
beenemployed(Miller, 1982;Braidaetal.,1985;Zurekand
Delhorne, 1986;Fabry and Van Tasell, 1986). All possible
outcomes, moreover, have been observed in these earlier
studies.
Some
noise-masked
normal
hearers
performed
better thanimpairedlisteners,
someperformedthesame,while
still othersperformedmorepoorly.
!. METHODS
A. Subjects
A total of 16 subjects
participatedin the presentstudy.
Four subjectshad bilaterally symmetricalsensorineural
hearinglossof presumed
cochlearorigin.All fourhadmoderate-to-severe
high-frequency
hearinglosswith varyingdegreesof impairmentin thelowandmidfrequencies.
Threeof
the four subjects
had their hearinglosssincebirth or early
childhoodwhile one (HI-02) had suddenonsetof hearing
lossapproximately
4 yearspriorto thepresenttesting.Subjectageswere32, 56, 17,and36yearsforsubjects
HI-01, HI02, HI-03, and HI-04, respectively.
All impairedsubjects
had normaltympanograms.
Three normal hearers were selected for each of the hear-
ing-impairedsubjects
to serveas noise-masked
normallisteners.By usingthreenoise-masked
normalhearersfor each
impaired subject,interindividualvariability in the performanceof normallistenerswith identicalmaskedaudiograms
couldbe takeninto considerationwhen comparingthe performanceof the hearing-impaired
to the noise-masked
nor-
nontestearofall subjects
toassurethatlisteningwasrestricted to the test ear.
For thenoise-masked
normalhearersit wasnecessary
to
mix the testsignalwith a shapedmaskingnoise.The latter
wasproducedby a random-noisegenerator(G-edRad1390B ) which,followingattenuation( Hewlett-Packard350D),
was shapedby a 1/3 octave-bandmultifilter (GenRad
1925). The outputof the multifilterwasthenroutedto the
secondchannelof the GS-162speechaudiometerusedfor
the testsignal.The outputof this channelwassetto maximum attenuationwhen testingthe hearing-impaired
subjeers.
For speech-recognition
testing,the C.U.N.Y. Nonsense
SyllableTest (NST; Resnicket al., 1975) was employed.
This testis comprisedof vowel-consonant
and consonantvowel nonsensesyllablesspokenby a male talker and arrangedin 11 subtests.
Within eachsubtest,consonantposition (syllableinitial or syllablefinal), consonantvoicing
(voiced or voiceless),and vowel environment (/a,u,i/)
are
constantwhile consonantplaceand/or mannerof articulation vary. Nine of the original subtestswere usedin this
investigation(subtests1, 2, 3, 6, 7, 8, 9, 10, and 11). These
stimulihad beenpreviouslydigitized(Kamm et al.,. 1985).
The NST stimuliwereroutedthroughequipmentidentical
to thatof thepure-tonesignalsfollowingoutputthroughthe
digital-to-analog
converter.A 400-Hz calibrationtonedigitizedfromthemastertapeof theNST materialswasusedfor
calibrationandspecification
of presentation
levels.All stimuluslevelsfor puretones,speechsignals,and noisestimuli
are referencedto the soundpressurelevelgeneratedin an
NBS-9A6-era3coupler.
c. Procedures
Pure-tonethresholdsfor all subjectswereobtainedusinga two-alternativeforced-choice
paradigmdesigned
to estimate
the
79.6
percent-correct
point
on
the
psychometric
real-hearing
subjects.
Differences
between*
impairedand
functionrelatingpercent-correct
signaldetectionto stimumasked-normal
listeners
couldthenbeevaluatedin light of
lus
level
(Levitt,
1971
).
Three
successive
correctresponses
theobserved
between-subject
variabilityof thenoise-masked
were
followed
by
a
decrease
in
signal
level
while incorrect
normalhearers.All 12 subjectsin this grouphad pure-tone
responses
were
followed
by
an
increase
in
the
level of the
thresholdsfrom 125-8000 Hz< 15 dB HL (ANSI, 1969).
signal.
A
total
of
15
reversals
in
signal
level
were
employed
Tympanogramswere normal and acousticreflexeswere
for
a
single
threshold
estimate.
Signal
increments
or decrepresentat 100dB HL at 1000Hz. Normal hearersrangedin
ments were 10 dB for the first five reversals and 2 dB for the
agefrom 19-32 years.
last ten. Of the last ten reversals,the first two were discarded
For measurement
of pure-tonethreshold,stimuliwere
generateddigitallyby a PDP-11/23 laboratoryminicomputersoasto havea 350-msduration(from onsetto offset)
with the midpointof the last eight representingthreshold.
Pure-tonethresholdsweremeasuredfor frequencies
at 1/3octaveintervalsfrom 125-8000Hz. The 19 testfrequencies
weredividedintotwosubgroups
by selecting
everyothertest
frequencyfrom 125-8000 Hz. Test orderwithin a subgroup
with a 25-ms raised-cosine rise-fall time. The stimuli were
was randomized.
outputthrougha 12-bitdigital-to-analog
converterat a rate
of 25 kHz and low-passfilteredat 10kHz. The stimuliwere
then routedthrougha programmableattenuatorthat was
controlledby the computerand sent to one channelof a
speechaudiometer(Grason-Stadlermodel 162, GS-162)
priorto transduction
by a TDH-49 earphonemountedin an
MX-41/AR cushion.A secondGS-162speechaudiometer
wasusedto producea speech-shaped
noiseat an overall
soundpressure
levelof 65 dB. This noisewasroutedto the
subgroupsthe procedure was repeated a second time.
Thresholdsreportedare the meansof thesetwo estimates.
Identical psychophysicalprocedureswere employed
with the hearing-impairedand normal-hearingsubjects.
Oncethe quietthresholdsfor the hearing-impaired
subjects
had beenestablished,
the pure-tonetestingfor the normal
B. Apparatus and stimulus generation
766
J. Acoust.Sec. Am., Vol. 81, No. 3, March 1987
After
thresholds
were obtained
for both
hearersproceeded.Initial multifilter settingsrequiredto
shapethenoisesoasto producemaskedthresholds
identical
to the quiet thresholdsof the corresponding
hearing-imHumeseta/.: Recognitionof nonsensesyllables
766
pairedsubject
wereestablished
fromcalculations.
Thecalcu-
patedfor 8-12 h. All subjects
werepaidfor theirparticipa-
lations made use of the critical ratio and the l/3-octave-band
tion.
noiselevels
measured
fora flatmultifilter
setting?
Withthe
exception
of onegroupof subjects,
thosesimulating
HI-03,
theseinitial settingsrequiredonly minoradjustments
to
achieve
thedesiredgoalthat maskedthreshold
bewithin3
dBoftheimpaired
subject's
quietthreshold
foratleast17of
II. RESULTS
A. Pure-tone
thresholds
Figure I displaysthe meanpure-tonethresholdsobtainedfromthefourhearing-impaired
subjects
of thisstudy.
For comparison,
a setof reference
datafromnormal-heating
subjectsis alsoprovided(filled circles).The latter values
the end of three 2-h sessions,then the last set of multi filter
represent
meant_hresholds
from12normal-hearing
subjects
adjustments
Wereconsidered
final.
testedpreviously
in thesamelaboratory
withidenticalpsySpeech-recognition
testingproceeded
identicallyfor the
procedures.
As indicatedin thisfigure,all imhearing4mpaired
and noise-masked
normal-hearingsub- ehophysical
paired
subjects
in
the
present
studyhadmoderate-to-severe
jects.The testitemsfor a givenrandomlyselectedsubtest
high-frequency
hearing
loss
with
varyingamounts
of hearwereadministered
six timesin completelyrandomfashion
ing
loss
in
the
low
and
mid
frequencies.
beforeproceeding
to anothersubtest.All subtests
werepreTable I providesthe root-mean-square
(rms) error
sentedinitially at 86 dB SPL for practice.Testingwasthen
between
the
quiet
thresholds
of
the
impaired
listenerand
performedat 66, 76, and 86 dB for threesubjectgroups(HI01, HI-02, HI-04, and those noise-maskednormals simulateachof the threecorresponding
noise-masked
normallisteners. Figure 2 illustratesthe agreementbetweenthe-threshing theseconfigurations)and 56, 66, and 76 dB for the renormals
mainingsubjectgroup(HI-03 andassociated
noise-masked oldsof the poorestmatchof the threenoise-masked
hearing-imnormals). Presentationlevelswere selectedto encompass and the thresholdsfrom the corresponding
These
the linear portion of the performance-intensity
function pairedsubjectfor eachof the four impairedsubjects.
data,togetherwith the rms-errorvaluesappearingin Table
whileattempingto maintainuniformityacrosssubjects.
OrI, indicatethat a dose match was achievedbetweenthe imder of testingfor the threetestlevelswas randomizedfor
paired
subjects
andthenoise-masked
normalhearers.
The
eachsubject.
poorest
match
overall
was
observed
in
the
subgroup
simulatThe speech-recognition
testingconcluded
with a retest
ingimpairedsubjectHI-03 (lowerleftpanelof Fig. 2). This
of severalsubtests
administeredat oneof the lowertwo preimpaired
subjecthad the steepest
slopein audiometricconsentationlevels.Generally,thosesubtestsfor which the subfiguration.
The
difference
between
maximumand minimum
jectsrecognizedbetween20% and 50% of the itemscorrecthearing
loss
for
this
subject
exceeded
the workingrangeof
ly were retested.This typically amountedto four or five
the
multifilter.
Unable
to
match
both
the maximum and
subtests
per subgroup.This expandedsetof data wasto be
the 19 test frequencies.In most instancesthis goal was
achieved.If, however,the desiredgoal wasnot achievedat
used
forsubsequent
analysis
ofconfusion
patterns,
ananaly- minimum thresholds,it wasdecidedto match the maximum
sisthat isnotreportedhere.Thesedata,however,areusedin
thepresentstudyto evaluatethetest-retestreliabilityof the
individual subtest scores.
Subjects
wereseatedin a sound-treated
roomfor testing.
A response
box, undercomputercontrol,was usedto activate appropriatelightsand buttonsfor both the pure-tone
andspeech-recognition
testing.The 2AFC pure-tonethreshold paradigmutilizeda 500-mswarninglight followedby a
500-msdelay.Eachintervalwasthenmarkedby a light activatedfor 350 ms with a 500-msdelaybetweenintervals.A
response
light followedthe secondintervaland indicated
that the computerwas readyto receivethe subject'sresponse.The subject'sresponseterminatedthe trial.
The same warning light parameterswere used for
speech-recognition
testing.For thistesting,however,no intervallightwasrequired.In addition,oncetheresponse
light
wasactivated,the subjectwasrequiredto pressthe button
corresponding
to the syllableheard.A removablelabel,containingorthographicrepresentations
of the nonsense
sylla-
blesin a particularsubtest,waspositioned
abovean arrayof
buttons.Eachbuttoncorresponded
to one of the possible
items on that subtest.
Trial-to-trial feedbackregardingcorrectresponses
was
providedonly for the pure-tonetesting.The hearing-impairedsubjectsrequired6-8 h of testingto completethe
study.The noise-masked
normal-hearinglistenerspartici767
J. Acoust. Sec. Am., VoL 81, No. 3, March 1987
thresholdsascloselyaspossibleat the expenseof the minimum thresholds.The poormatchis apparentin the region
between400 and 1000Hz for thedatafromsubjectMN-03B
shownin the lowerleft panelof Fig. 2. The maskedthresholds for the other two noise-masked normal listeners of this
subgroupalsovariedfrom thoseof the impairedsubjectin
this frequencyregion.
I
98
o
I
I
HT-81
I
I
I Ill
I
I
I
I
I
I
I
A
n H•-82 X HT-04
70
x--X-_ X
.j 6•
3•
2o
le
I
2m•
i
J
i
S00
Illll
I
100•
FREQUENCY
28•
i
•;000
(Hz)
FIG. 1. Mean pure-tonethresholds
for the four hearing-impaired
subjects
in this study. For comparison,the filled circles show mean pure-tone
thresholdsfor normalhearers()V= 12) testedwith identicalprocedures.
Humos eta/.: Recognitionof nonsensesyllables
767
TABLE 1.The tanserrorbetweenmaskedthresholds
of a normal-hearing
subject
andquietthresholds
ofthecorresponding
hearing-impaired
subject.
Subject
rms error (dB)
MN-01A
MN-01B
4.5
4.2
MN-01C
4.0
MN-02A
3.5
MN-02B
3.8
MN-02C
2.2
MN-03A
4.9
MN-O3B
6.1
MN-03C
5.1
MN-04A
3.2
3.1
2.9
MN-O4B
MN-04C
presentation
levels
employed
appear
tohaveadequately
defined the linear portion of the performance-intensity
func-
tion.Floorandceilingeffects
arenota,pparentandthelevels
havedefineda wide rangeof performancefor eachsubject
(at least a 35% differencebetweenthe minimum and maxi-
mumperformance).
Regarding overall speech-recognitionpeformanee,
comparisonbetweenthe data from the hearing-impaired
subjectand the corresponding
noise-masked
normalsfor
each of the four subgroupssuggestedthe following outcomes: (1) Hearing-impaired subjectsperformed better
than noise-masked
normalhearers;or (2) hearing-impaired
subjectsperformedthe sameas noise-maskednormals. An
exampleof the firstoutcomeis depictedin Fig. 4. This figure
providesperformance-intensity
functionsfor each subtest
and for the overall (NST)
B. Speech-recognitionperformance
Figure3 illustrates
theperformance-intensity
functions
for eachof the four hearing-impairedsubjects.Each data
pointrepresents
the meanoverallpercentcorrectfor 438
syllablepresentations
(73 syllables
presented
sixtimes).The
I
g8
J
ß
I
I
i
I
Ill&
i
i
represented
by the filled circlesconnected
by solidlines
whiletheothersymbols
represent
datafromeachof thethree
corresponding
noise-masked
normalsubjects.
Asthedatain
the lowerright panellabeled"ALL" indicate,the overall
NST scoreof this impairedsubjectwasbetterthan that of
everynoise-masked
normalhearerat all presentation
levels.
For the datain eachpanelof Fig. 4, aswell asFigs.5, 6, and
7, the followingcriterionwasusedto defineequalityof per-
I
I
HT-O I
score. The data for HI-01 are
I
I
I
I t I I I
I
I
I
I
I I I I
gO
ß HI-02
• MN-•
IA
- eooHN-025
7½}
u•5½}
- '-o.
'"
-
-•6½}
•"ø'"ø•ø'
•4•
RHS ERROR -
28
I
20½}
i
i I I lilt
I
see
! eaa
2aao
FREQUENCY (Hz)
I
4.$
dB
200
-1 •
'
RH$ ERROR = 3.8
I
seca
i
i i i Illl
I
s½}½} t oea
2gee
FREQUENCY (Ha)
I
I I 11tl
s½}oo
ß H[-04
IIIIIIIIIIIIIIIJlJ
f iII•IIIIIIIIIiill
oMN-O3B
7½}
--0'
20
J i i Ill
ß HI-C3
"O.
q e½} oMN-•4A
78
•.1_.
6½}
_-
,t
/ 0
-o.
o•
2½}½}
See}
! OZ½}
2e½}a
FREQUENCY (Hz)
i 2½}
S½}½}e
20½}
RI'•
ERROR
see
iees
FREQUENCY
:'eoe
FIG. 2..Comparison
of meanquietthresholds
of eachimpairedsubject(filledcircles) to themeanmaskedthresholds
of the mostpoorlymatchednoisemaskednormallistenerin eachsubgroup(opencircles).Eachpaneldisplaysthedatafor a differentheating-impaired
subject.
768
J. Acoust.Sec. Am.,VoL81, No. 3, March1987
Humeseta/.: Recognition
of nonsense}
syllables
768
• 7e
_
bJ
n,
n,
z
66
bJ
o
4e
• 3e
•o
lee
2o
• 70
I
I
I
n,
LI
L2
L•
o
SPL
i-
SPEECH
LEVEL
dB
i,i
FIG. 3.Performance-intensity
functions
relatingoverallpercent
correcton
theNSTtospeech
level.
L1---56dBforHI-03and66dBfortheother
three
impaired
subjects.
L2= LI 4- 10dBandL3= L1+ 20dB.Circles:
HI-01;
• 3e
•8
Squares:
HI-02;Triangles:
HI-03; Xs: HI-04.
•
7E
•9
•
•
7•
•10
•
SPEECH
•
7B
L•¾EL
x •11
88
86
7B
ALL TM
•8
e6
76
I•
½cJB SPL•
formance
between
thehearing-impaired
listenerandthecor- FIG. 5.SameasFig.4 butforHI-04 andcorresponding
subgroup
ofnoiseresponding
noise-masked
normalhearers.
If thescores
ofthe masked normal listeners.
hearing-impaired
subject
ona particular
subtest
werewithin
therangeofscores
observed
forthethreenoise-masked
norlistening
in noise.On a fewoccasions,
the
malhearersonthatsamesubtest
at twoor morepresentation normalhearers
oftheimpaired
subject
relative
tothatof the
levels,
thenperformance
oftheimpaired
subject
wasconsid- performance
group
ofnoise-masked
normal
hearers
varied
withpresentaered to be the same as that of the noise-maskednormal
one
hearers.
Otherwise,
performance
of the impairedlistener tionlevelsuchthatonelevelyieldedequalperformance,
levelyielded
superior
performance
bythehearing-impaired
was consideredto be either better or worse than that of the
subject,
andtheremaining
levelrevealed
superior
performancebythenoise-masked
normalhearers.
In theseeases,
theperformance
ofthenoise-masked
normal
hearers
andthe
hearing-impaired
subjects
wasconsidered
tobeequal.
Using
thisdefinition
of equalityof performance,
examination
of
40
3e•
20•
a
•
tee
?e -
•
x
SPEECH
LEVEL
(dB
SPL•
FIG. 4. Percent-correct
performance
oneachof theninesubtests
of the
NSTplottedversus
speech
level.Eachpanelshows
theresults
fora separate
subtest
withthenumber
ineachpanelcorresponding
tothesubtest
number.
SPEECH LEVEL
CdB SPL)
"ALL" in thelowerrightpanelreferstotheoverallNSTscore.
Theconneeted
filledcircles
represent
thedatafromhearing-impaired
subject
HI-01
whiletheothersymbols
represent
theperformance
of thecorresponding FIG. 6. SameasFi•. 4 butforHI-03 and•ndin•
noise-masked
normallistenersin this subgroup.
769
J.ACOuSt.
Sec.Am.,Vol.81,No.3,Marciq
1987
m•k•
no•=l
sub•oupofnoise-
listeners.
Humes
eta/.:Recognition
ofnonsense
syllables
769
individual NST subtest scores obtained from individual lis-
•
.o
x
x
x x
teners(Dubno and Dirks, 1982). Subtest-score
reliability
measuredpreviously,moreover,wasassessed
usingrepetitionsof a singlesubtestcomprisedof 7-9 testitems.In the
presentstudy,a singlesubtestscorewasbasedonbetween42
and 54 testitems.Recall that in the presentstudy,subtest
scoresobtainedfrom hearing-impairedsubjectsthat fell
eo
• 46
2•-
between 20% and 50% correct were fetested. These same
o
subtestswere subsequentlyretestedfor the corresponding
noise-masked
normalhearers.As mentionedpreviously,this
wasdoneto increasethe samplesizefor subsequent
analysis
of confusionpatterns,an analysisthat will not be reviewed
• ee
here. In addition, somesubtestscoresoutsidetheselimits for
the lowesttwo presentationlevelswere arbitrarily selected
for retest.Thesedata, therefore,affordedan opportunityto
examinethe reliability of the individual subtestscoresobtainedin this study.Figure 8 showsthe test-retestscoresfor
the varioussubtests,
eachrepresented
by a differentsymbol.
s•
3•
x
Individual
SPEECH
L•EL
(rib
SPL)
FIG. 7. •mc • Fig.4 butforHI•2 •d •nding
;ubgmupo•nois•
data from noise-masked normal hearers and im-
pairedlistenersare presentedtogetherin thisfigure.Due to
the randomizationof presentation
level in this study,the
amountof practiceontheNST betweentestandretestvaried
between1 and 3 h. The datain thisfiguresuggest
that the
individual subtest scores are reliable. The Pearson-r correla-
individualsubtestscoresin the remainingpanelsof Fig. 4
indicates
that it is generallythe casethat the hearing-im-
tion coefficient between
test and retest score was 0.89
(p < 0.01). Again,eachsubtestscorein thisfigurewasbased
on
42 to 54 syllablepresentations(7-9 syllablesper subtest
paired subjectoutperforms
the noise-masked
normal
repeated
sixtimes).
hearers.
Theexceptions
aresubtests
1and6 (subtest
number
The
results
were analyzedfurther to providesomeinisindicated
bythenumbers
at thebottomofeachpanel).On
sight
into
the
types
of errorsmadeby hearing-impaired
and
these two subteststhere appearsto be little difference
noise-masked
normal-hearing
subjects.
This
was
accombetween
the performance
of the impairedsubjectandthe
plishedby examiningindividualsubtestscores.Subtests1-3
masked normals.
Figure5 displays
a similarsetof performance-intensitycontain syllable-initialconsonantspaired with the vowel
/o/. The remainingsixsubtests
incorporated
in thisstudyall
functions
foranotherhearing-impaired
subject(HI-04) that
contain
syllable-final
consonants,
two
paired
with/o/(subtendedtooutperform
thenoise-masked
normalhearers.
Altests
6
and
7),
two
paired
with/i/(subtests
8
and
9) andtwo
thoughtheoverallNST performance
of theimpairedlistenpaired
with/u/(subtests
10
and
11).
Comparison
of suber,shownin thelowerrightpanel,isconsistently
superiorto
test-score
profiles
between
the
hearing-impaired
subjects
thatof thenormalslistening
in noise,thisisnotthecasefor
normal-hearing
counterparts
would
all individualsubtests.Using the criterion of "sameness" andtheirnoise-masked
definedpreviously,
performance
of the impairedsubject
is
similar to that of the noise-maskednormals for subtests3, 7,
100 I I I I I I I I I/
11, and 2. In no case,however,doesthis impairedlistener
/-
perform
worse
thantheentiregroupofnoise-masked
normal
listeners.
Figures
6 and7 showcomparable
datafortheremaining
twohearing-impaired
subjects,
HI-03 andHI-02, respectively. In bothcases,the datain the lowerrightpanelindicate •"
that the hearing-impaired
and noise-masked
normal-hearing subjects
performequivalently
on the NST. This is also
generally
truefor individualsubtest
scores
for bothsubject
subgroups,
althoughthereareexceptions
(subtests
3, 8, 9,
and 10 in Fig. 6 andsubtests
1, 2, and 8 in Fig. 7). These
exceptions,
moreover,
arenotconsistently
inthesamedirection.On somesubtests
theimpairedsubjectperformedbetter
than the noise-masked normal hearers whereas on others
just theoppositeoutcomewasobserved.
Throughoutthisanalysisit hasbeenassumed
that indi-
L
" *•'"
-
I I I I I I IPERCENT
CORRECT--TEST
vidual subtestscoresfrom indiviual subjectsare reliable.
FIG. 8. Percent-correct
performance
on rctestis plottedasa functionof
performance
on theinitialtestfor individualsubtest
scores.
Data for impairedandnoise-masked
normallisteners
havebeencombined.
Eachsym-
Only limited data are availableregardingthe reliabilityof
bol represents
a differentsubtest.
770
J. Acoust.Soc. Am., VoL 81, No. 3, March 1987
Humosoral.: Recognitionof nonsensesyllables
770
providesomeinformationregardingdifferences
in thetypes
of errors made.
Toevaluate
thepatternoferrorsmadeacross
subtests
of
er. Figure9 displays
the meanAP(c) valuesobtained
for
eachofthefoursubgroups
ofsubjects,
witheachpanelrepresentingdatafrom a differentsubgroup.
The threesymbol
typesreflectthe threespeech
presentation
levelsemployed.
the NST, the subtestscoresin Figs. 4-7 were convertedto
differencescoresin whichthe scoreof a givennoise-masked The dashedlinein eachpanelat AP(c) = 0 (zero) indicates
normalhearerwasexpressed
relativeto that of the hearing- no differenceon averagebetweenthe performanceof the
hearing-impairedsubjectand noise-maskednormalscomimpaired subject. Specifically, AP(c),•= P(c),•i
prising that subgroup.Negative valuesof AP(c) indicate
--P(e)em, where P(e), = percent correct on subtesti,
MN$= masked
normal
j, andHI = hearing
impaired
listen- that the hearing-impairedsubjectoutperformedthe noisemaskednormalhearersin the samesubgroup,andconversely for positivevalues.From thedatain thefourpanelsof Fig.
9, it is apparentthat the majorityof AP(c) valuesfor sub-
x
¾
I
I
I
I
I
ß
I
ß
I
t
t
!
2
3
8
7
8
0
19
II
hIST St,.•TEST
x
ß
x
•
--t ß
HZ-82
o x...... •--•-o
I
2
3
8
?
8
0
tO
II
NST SI,J•TEST
x
that the relative error rates across subtests were not the same
ß
.............
groupsHI-01 and HI-04 are negativewhilethoseof HI-02
and HI-03 vary aroundzero.
A separateanalysisof variancewith repeatedmeasures
havingwithin-subjectfactorsof presentationlevel (three
levels) and subtest(nine subtests)was performedon the
datain eachpanelof Fig. 9. For subgroups
HI-02 andHI-03,
the grandmeanAP(c) wasnot significantly
differentfrom
zero(p > 0.10). That is,collapsed
across
levelsandsubtests,
therewasno differencein performance
betweenthe noisemaskednormalsand the hearing-impaired
listenerin these
two subgroups.
For subgroups
HI-01 and HI-04, however,
therewasa significant
difference
betweenthe performance
of the impaired listener and the noise-maskednormal
hearers,with theimpairedsubjectoutperforming
thenormal
hearerslisteningin noise(p < 0.01). For all four subgroups,
therewasa significanteffectof subtest(p < 0.01) on AP(c),
whereas
presentation
levelwasnotsignificant
(p > 0.05). In
addition,the subtest-by-level
interactionwassignificantin
all foursubgroups
(p < 0.01). The significant
maineffectof
subtest
andthesignificant
subtest
x levelinteraction
suggest
x NX-83
for thenoise-masked
normalsandthe hearing-impaired
listenersandthat themannerin whichtheirperformance
differedacrosssubtestvariedwith presentation
level.
.........
IlL DISCUSSION
I
I
I
I
I
I
i
!
I
I
2
3
6
7
8
9
10
It
NST SUBTEST
HY-O4
x
I•
ß
normalhearersfor comparisonto hearing-impairedsubjects
havealsoreportedmixedoutcomes.Milner (1982), for example,presentsperformance-intensity
functionsfrom two
listenerswith sensorineural
heatinglosslisteningto uniiltered and filtered nonsensesyllables.Only the unfdtered
data are appropriatefor comparisonto the data from the
presentstudy. For subjectshaving unilateral sensorineural
impairment,comparisonwasmadeto two setsof data from
0
x
I
I
I
I
I
I
I
I
I
I
2
3
6
7
8
0
18
II
HST SOBTEST
FIG. 9. Mean deltaP(c), percentcorrectby noise-masked
normallesspercentcorrectby thecorresponding
impairedlistener,plottedversussubtest.
Eachsymbolrepresents
a differentspeechlevel (fOledcircles:Ll; untilled
circles:L2; and X s:L3). Eachpanelpresents
theresultsfor a separatesub-
noise-masked normal ears. In one case, the listener's own
normal ear servedas the noise-maskednormal ear, while in
the other casea secondsubjectwas the noise-maskednor-
group.
771
Regardingoverallnonsense-syllable
recognition,none
of the hearing-impaired
subjectsin this investigation
performedworsethanthe corresponding
noise-masked
normal
hearers.When there was a differencein performance,the
hearing-impaired
subjectsperformedbetterthan their normal-hearingcounterpartslisteningin noise.This outcome
occurredfor two of the four hearing-impaired
subjects
with
the othertwo subjectsperformingthe sameastheir respective subgroups
of maskednormals.
Prior studiesof speechrecognitionusingnoise-masked
J. Acoust.Soc. Am., VoL 81, No. 3, March 1987
Humosota/.: Recognitionof nonsensesyllables
771
real.For bothcomparisons,
thescores
obtainedfor thesimulated loss were 20%-25%
better than those obtained for the
actuallossat all presentation
levels.For the otherimpaired
subjectin Milner'sstudy,mixedresultswereobtainedwhen
comparedto the datafrom a noise-masked
normalhearer.
drawingconclusions
regardingthe accuracyof the match
obtained between3.
the speech-recognition
performanceof
maskednormalsandhearing-impairedlisteners.This would
alsoaddgreaterfacevalidityto the measureof"speechrecognition."
Theoutcome
ofthepresent
studyregarding
theutilityof
At speech
levelsbelow80dBSPL,performance
of thehearing-impaired
subject
exceeded
thatofthemaskednormalby the noise-masked normal car as a model of sensorineural
15%-20%, whereastheopposite
wastruefor levelsexceed- hearinglossis equivocal.For two of the four hearing-impairedsubjectsof thisstudy,overallspeech-recognition
pering 80 dB.
formanee
could
be
accurately
simulated
by
introducing
a
More recently,Braidaetal. ( 1985) andZurekandDelspectrally
shaped
masking
noise
into
a
normal
ear.
For
the
horne (1986) have reported good agreement between
thiswasnotthecase.It isimportant
speech-recognition
scores
of hearing-impaired
subjects
and remainingtwosubjects,
to
note,
however,
that
the four impairedsubjectsof this
comparable
datafromnoise-masked
normals.All subjects
in
study
neoer
performed
worse
thanthenoise-masked
normal
thesetwo studies,however,listenedto speechin a backhearers.
This
is
true
for
overall
speech-recognition
perforgroundof broadband
noise,whereasMilner (1982) tested
mance
sampled
with
a
wide
variety
of
speech
stimuli
and
his subjectsin quiet.
over
a
wide
range
of
speech
levels,
extending
from
conversaIn anotherrecentstudy,Fabry and Van Tasell(1986)
reporteddatafrom six unilaterally
impairedlisteners
in tional levelsto levelsapproachingthoseexperiencedwith
amplification.This is true,moreover,despitecloselymatchwhich the listener's own normal ear served as the noiseing
the impairedandnoise-masked
listenersfor audibilityof
maskednormalear for comparison.
All threepossible
outthe
speech
signal.
If
additional
secondary
psyehoacoustie
comeswere observedin this studywhen recognitionscores
processing
deficits
were
operating
in
the
four
impairedsubfrom the ears with simulatedand actual hearing losswere
jects
of
this
study,
one
would
have
expected
them
to perform
compared.
Thenoise-masked
normalearfora givensubject
worse
than
noise-masked
normal
hearers
listening
underthe
yieldedscores,
obtainedat twopresentation
levels,thatwere
same
test
conditions.
Again,
such
an
outcome
was
not obeitherbetterthan,the sameas,or worsethanthe scoresfrom
served
in
the
present
study,
suggesting
that
either
the
four
theimpairedear.Oneofthelevelsused(90 dBSPL) wasthe
impaired
subjects
of
this
study
did
not
have
such
secondary
samefor all subjects
andwascomparable
to thehighestlevel
deficitsor, if theydid, the deficitsexertedno inusedwith threeof the four subgroups
of this study(86 dB processing
performance.Not
SPL). For this high level presentation,
the differencein flueneeon overall speech-recognition
measures
from
overallpercentcorrectbetweenthe impairedear and the havingobtainedadditionalpsychoacoustie
maskedear in the Fabry and Van Tasellstudyhad a mean thesesubjects,it is not possibleto decidebetweenthesetwo
valueof -- 7.4% anda rangeof -- 1.3% to -- 23.3% with alternatives.
negative
valuesindicatingP(c)m < P(c}M•. Themeanperformaneedifference
at 86 dB in thepresentstudyfor subtests ACKNOWLEDGMEHTS
usingCV syllables
pairedwith/n/, asin theFabryandVan
This work wassupportedin part by an RCDA awarded
Tasell study, is --3.6% with a range of q-5.1% to to the firstauthorby the National Instituteof Neurological,
-- 26.3%. Thus, for similarstimuli,the resultsof both stud- Communicative Disorders and Stroke (NINCDS) and an
iesaresimilarwith noise-masked
normallistenerstendingto
NINCDS grant awarded to U.C.L.A. Preparationof the
outperformthe corresponding
hearing-impaired
listener. manuscriptwas also supported,in part, by a grant from
Milner (1982) reacheda similarconclusionusingCV items NINCDS to IndianaUniversity.The authorsthank Richard
pairedwith/a/,/u/, and/i/. Whenthedifference
in perfor- Tyler and Dianne Van Tasell for providinghelpful commancebetweenmaskedandimpairedearsat 86 dB isexam- mentson earlierversionsof thismanuscript.
inedacross
allsubtests
fromthepresent
study,
inel•ding
VC
syllables
pairedwith/o/,/u/, and/i/, themeandifference
becomesq- 6.3% and the rangeis q- 21% to -- 15%. For
thisbroaderrangeofstimuli,thetendency
isforthehearingimpairedsubject
to outperform
normalhearerslisteningin
'Withthemultifilter
setto0 dBateachl/3-octaveband(attenuation
range
is from + 25 to -- 25 dB at eachfrequency),the SPL outputwasmea-
suredat eachl/3-octavein a 6-era
3 coupler
fora broadband
noiseinput
noise.
signal.
Thel/3-octave
bands
areequal
toorgreater
thantheeritic.•l
band,
The findingsof thepresentstudyareconsistent
with the
limited data availablein the literature for comparabletest
therebyenablinguseof the critical ratio to producean estimatedmasked
thresholdat eachcenterfrequency.This was accomplishedby converting
theoverallsoundpressure
levelfor a given!/3-octavebandintonoisespectrum level,No [No in dB $PL = overalldB SPL-10 log ( 1/3-octavebandwidth). The critical ratio wasthen addedto N o. Thus, for a flat 0-dB setting of the multifilter,a predictedmaskedthresholdwasestimatedat each
l/3-octave centerfrequency.Adjustingthe overalllevelof the masking
noiseaffected.themaskedthresholdsuniformly acrossl/3-oetave bands,
while eachband could alsobe adjustedseparatelyover a 50-dB range
conditions.Becauseof the diversityof outcomesin the literature, however,virtually any findingwouldhavebeenconsistent with at leastsomeprior data. The diversityof previous
outcomesappearsto be due,in part, to the natureof the CV
or VC nonsensesyllablesselectedfor testing.The reasonsfor
thisdependence
of thegoodness
of thematchin performance
on the consonantlocationwithin the syllableare not immediatelyobvious.It is advisable,therefore,to includeasmany
vowel contextsand consonantpositionsas possiblebefore
772
J. Acoust.Soc. Am., Vol. 81, No. 3, March 1987
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