-
Dept. for Speech, Music and Hearing
Quarterly Progress andStatus Report
Analysis of different speechperformance in patients with
multi-channel cochlearimplants
Agelfors, E. and Beidestam, G. and Rollvén,B. and Vainio, M.
and Lindström, B. and
Bredberg, G.
journal: TMH-QPSRvolume: 37number: 4year: 1996pages: 097-110
http://www.speech.kth.se/qpsr
http://www.speech.kth.sehttp://www.speech.kth.se/qpsr
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TMH-QPSR 4/1996
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Analysis of different speech performance inpatients with
multi-channel cochlear implantsEva Agelfors2, Gunnar Beidestam1,
Birgitta Rollvén1, Marja Vainio1, Bo Lindström1 and Göran
Bredberg1
1. Department of Audiology, Söder Hospital, Stockholm, Sweden2.
Department of Speech, Music and Hearing, KTH, Stockholm, Sweden
AbstractTotally 41 postlingually deafened adult patients who
have received multi -channelcochlear implants at Stockholm Söder
Hospital have participated in this study. Allpatients have followed
the CI-programme at the clinic and have been tested 0, 6,12, and 24
months postoperatively. The test-battery consisted of vowels (cVc)
andconsonants (vCv), Everyday Sentences(ES), and Connected
Discourse Tracking(CDT) presented in two modaliti es: cochlear
implant plus lip-reading and implantalone. Results for the 41
patients from the speech tests showed an improvement, onaverage,
within the first 6 months of implant use. Some patients, however,
get highscores from the beginning, while others gradually improved
over a 2-year period.The patients have been divided into three
groups POOR (11), AVERAGE (13) andGOOD (17) based on their
performance auditory alone on Connected DiscourseTracking test.
Group mean results on consonants, showed that for patients
withAVERAGE and GOOD speech understanding, errors in recognition of
voicingwere rare but nasals were poorly perceived. For the
POOR-group, envelope cuesseem to dominate the consonant
recognition. The fricative [
� ] was well i dentified
by all patients in the three groups. Results are discussed in
relation to etiology ofdeafness, years of deafness and other
factors.
IntroductionNowadays, cochlear implantation is a
generallyaccepted alternative for patients with a severe toprofound
hearing loss who derive li ttle or nobenefit from a conventional
hearing aid.Published results, however, show a wide varia-tion in
performance with the same type of coch-lear implant and the
possibili ties to predict theseresults from preoperative data and
measurementsare limited (Tyler, 1991; Dorman, 1993; Dowell ,1995).
In Sweden, cochlear implants have beenused for 12 years and 114
patients have beenimplanted at Söder Hospital, Stockholm. From
thebeginning, a single-channel extracochlear implantwas used,
Vienna/3M, but today multi-channelcochlear implants are used.
Some researchers suggest that the per-formance with a cochlear
implant stabili sesduring the first year, whereas others note
thatperformance continues to improve after 1 year.Waltzman &
Hochberg (1990) found that SpeechPattern Contrast (SPAC) scores of
six subjectswearing the Nucleus were similar at 3, 12 and 24months
after cochlear implant connection. Tye-Murray et al. (1992)
reported about resultsobtained over time by 13 Nucleus and 14
Ineraid subjects. On average, the abilit y of thesubjects to
recognise words and phonemes in anaudition-only condition improved
during thefirst 9 months, but the phoneme scorescontinued to
improve during the next 9 months.About 50% of the subjects, who
demonstratedpoor word recognition at 1 month, showedsignificantly
improved percent word correctscores by 18 months. They also
reported that theNucleus and Ineraid subjects did not differ
intheir pattern of change over time. Tyler &Summerfield (1996)
reported that 80% of theadult patients implanted in Iowa
showsignificant performance improvement over time.On average,
performance reached asymptoteafter 30 to 40 months of implant use,
althoughindividual differences in the rate and amount ofimprovement
are large. Many patients had greatbenefit from their aids and have
some open-setspeech understanding, others had li ttle benefitand
performed less well on speech perceptiontests.
The primary aim of this study was to evaluatethe test results
obtained by all postlinguallydeafened adults, who had received a
multi-channel cochlear implant at Söder Hospital,Stockholm, and
used their implant for at least 2
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Agelfors et al.: Analysis of different speech performance
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98
years. All patients followed the CI-programme atthe clinic and
were tested at 0, 6, 12 and 24months postoperatively. The second
aim was toevaluate what effects residual hearing, durationof
deafness, age at onset of deafness and etiologycould have on the
obtained results with theimplant.
MethodPatientsTotally 41 postlingually deafened adults,
allSwedish, participated in this study and all havereceived
multi-channel cochlear implants at SöderHospital, Stockholm,
operated by the samesurgeon (G Bredberg). They had no benefit froma
conventional hearing aid at the time ofimplantation. All have
followed the CI-programme at the clinic and have been tested at0,
6, 12 and 24 months postoperatively. Somedata for the patients is
shown in Table 1.
Table 1. Some patient data
Patients: 41 (19 females, 22 males)Age: mean 54.5 years (range
24-78)Years of deafness: mean 14 years (range 1-41)
Etiology N=Unknown, progressive loss 11Otosclerosis 7Meningitis
6Unknown, sudden deafness 5Ototoxicity 5Skull trauma 3Meniérè 1Rem.
Artrit 1Sarkoidos 1Unknown 1
CI-systemsTwo different systems have been used: Nucleusand
Ineraid. Thirty-nine patients have beenimplanted with the Nucleus
22-channel cochlearimplant (Clark et al., 1981) and two
patientshave been implanted with the Ineraid (Eddington,1980). The
most important difference betweenthe two processors is that the
Nucleus design is a22-channel feature extraction device, whereas
theIneraid processor is a simultaneous, analog four-channel
implant. The Ineraid processor does notperform feature extraction,
but presents thebroadband speech waveform in four fil terchannels
(Dorman et al., 1990).
Two different processing strategies in theNucleus device have
been used, F0/F1/F2 andMultipeak (MPEAK). Both of these
strategiesextract frequency and ampli tude information
concerning the first and second formantfrequencies (F1 and F2).
In addition to F1 andF2, the MPEAK strategy extracts and
codesinformation in three high-frequency bandsbetween 2-6 kHz. Both
strategies use non-simultaneous pulsatile stimulation and
codefundamental frequency as the rate of stimulation.Table 2 shows
the number of patients that usedthe different coding strategies.
Stimuli mode BP= bipolar; the active and reference electrodes
areadjacent to each other. The spread of current isconfirmed to a
relatively small area. BP+1 = theactive and reference electrodes
are separated byone nonactive electrode. The further the activeand
reference electrodes are spaced, the greater isthe spread of
current. CG = common ground; oneelectrode is active all the others
are connectedtogether to constitute a single reference
electrode.The spread of current is more diffuse.
Table 2. Characteristics of the CI-systems andnumber of
patients.
1. Nucleus Mini system 22Strategy: F0/F1/F2 (N = 9)
MPEAK (N = 30)Stim.mode: BP+1 (N = 38)
CG (N = 1)Number of active electrodes: mean 19 (range14-20)
2. IneraidAnalog 4 band-pass filters (N = 2)
Test batteryThe test battery that was used consisted ofvowels
(cVc) and consonants (vCv), EverydaySentences (ES), and Connected
DiscourseTracking (CDT) presented in two modali ties:cochlear
implant plus lipreading and cochlearimplant alone. All subjects
have been tested at 0,6, 12 and 24 months postoperatively. The
firsttest session “0“ means results obtained after oneweek of the
speech processor´s connection to theimplant. The patients have also
been testedauditory alone at the clinic in a soundfieldsituation on
closed-set tests; 3-digits span testand 12-choice spondees, and on
open-set speech;PB-words and spondees. The results from thesetests
are not discussed here.
1) Connected Discourse Tracking (CDT)The tracking technique
developed by De Fili ppoand Scott (1978) has been used by many
groupsto train and to evaluate the reception ofconnected speech via
lipreading alone and incombination with various types of sensory
aids.The speaker reads from a book, phrase by
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phrase, and the speechreader (the subject) isrequired to repeat
the text verbatim. If the phraseis not correctly repeated, the
speaker employs ahierarchy of strategies to assist the subject
inrepeating every word correctly. The score iscalculated according
to the number of words inthe text conveyed in a given time.
The speech material chosen had a relativelyconsistent level of
reading diff iculty from sessionto session. During each test
session tracking wasperformed for ten minutes under each
condition:lipreading plus aid and auditory alone with thedevice.
All patients were tested in conditionauditory alone but testing was
interrupted assoon as it was evident that this situation was
toodiff icult and the patient was given a score ofzero. The
CDT-test was presented live by a maleor a female habili tationist.
The tracking rateachieved by a normal-hearing subject, who usesthe
same method with the same speaker and thesame text material, is
85-95 words per minute.
2) Everyday Sentences (ES)Two different test lists with 20
sentences each atvarying length (2 - 14 words) were used. Afemale
speaker was video-taped and thesentences were presented on a
TV-screen in theaudiovisual test situation. A tape-recorder wasused
in the test condition auditory alone. Thecorrect sentences were not
given to the patients.The results are scored based on the number
ofwords correctly identified.
3) Vowels (cVc)Nine Swedish vowels /i:, y:, � :, e:, � :, � :,
u:, o:,� :/ were presented in a /bVb/-context. The voweltest was
video taped, and each vowel waspresented 3 times in a random order
by a femalespeaker on a TV-screen in the audiovisualsituation. In
the test situation auditory alone,only one of each vowel was
presented. Theconfusion matrices were analysed.
4) Consonants (vCv)Sixteen Swedish consonants were presented in
an/aCa/-context. The following consonantphonemes were used /p, b,
m, t, d, n, k, g, � , f, v,s, � , r, l, j/. The consonants sampled
a variety ofdistinctions in voicing, place of articulation,
andmanner of articulation. The consonant test wasvideo taped and
each consonant was presentedtwice in a random order by a female
speaker on aTV-screen in the audiovisual test situation. In thetest
situation auditory alone, only one of eachconsonant was presented.
The confusion matriceswere analysed.
All speech tests were presented at thepatient´s most comfortable
listening level
adjusted by themselves. All tests were conductedin a special
test room at the clinic.
Results and discussionIndividual results obtained 24 months
post-operatively from the CDT-test presented in thetwo situations,
audiovisual and auditory alone,are shown in Figure 1. There was a
largevariation in abili ty to perceive speech in the testsituation
auditory alone among the cochlearimplantees. Some patients had no
abili ty at all ,others achieved a score of more than 60 wordsper
minute auditory alone. All patients obtainedsome improvement with
their aids in theaudiovisual situation. The correlation betweenthe
results from two test situations was r = 0.81.
Some patients derived li ttle benefit from theircochlear
implants and if, in addition, they arepoor lipreaders, they have
severe problems indaily communication situations. By experiencewe
know that a tracking speed around 40 wordsper minute is a minimum
speed required for anacceptable communication. Results over 60words
per minute indicate a good communicationabili ty and these patients
are able tocommunicate nearly as well as normal-hearingpersons in
this particular test situation.
The analysis showed that the mainimprovement on the CDT-test in
the two testsituations were obtained during the first sixmonths of
CI-use (Fig. 2). There were no signi-ficant differences in the mean
scores obtained bythe CI-users over time after the first six
monthsof CI-use. The average results at 6, 12 and 24months varied
from 22, 24 to 25 words perminute auditory alone. In the combined
situation,the average results varied from 56, 57 to 56words per
minute.To obtain more information about the differentlevels of
performance among the patients theywere divided into three
subgroups which arelabelled POOR (11 patients), AVERAGE
(13patients) and GOOD (17 patients) based on theirmean score with
the implant on CDT-testauditory alone at 6, 12 and 24
monthspostoperatively. POOR = 30 words/minute. Individual results
(mean scoreat 6, 12 and 24 months postoperatively),obtained by
patients on the CDT- test auditoryalone, are shown in Figure 3.
There was a largevariation in the result across the patients
onCDT-test, from 0 to 64 words per minute.
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Agelfors et al.: Analysis of different speech performance
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100
Fig. 1. Individual results obtained by the CI-users on Connected
Discourse Tracking in test situationsaudiovisual and auditory alone
with the implant at 24 months postoperatively.
CDT
0
20
40
60
80
100
0 6 12 24
Months post implant
Auditory
Audiovisual
Words/min.
Fig. 2. Mean performance on CDT over time after implantation
presented in the conditions auditoryalone (CI) and audiovisual.
CDT / Auditory only (CI) (mean: 6,12, 24 months)
020406080
100
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39
41Patients
Words/min.
"AVERAGE" "GOOD"(N = 11) (N = 13) (N = 17 )
"POOR"
Fig. 3. Individual mean score obtained on CDT auditory alone
with the implant at 6, 12 and 24 mopostoperatively. The CI-users
were divided into three subgroups POOR, AVERAGE and GOOD basedon
their performance on the CDT-test.
Connected Discourse Tracking (CDT)(Postop. 24 mo)
0
20
40
60
80
100
0 20 40 60 80 100
Aud
iovi
sual
Words/min.
Auditory only (CI)
Goodcommunication
Acceptable communication
Words/min.
r = 0.81
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Fig. 4 a-b. Group-mean performance on number of correct words
perceived on CDT-test as afunction of time obtained by the three
groups of CI-users in the two test conditions: auditory alonewith
the implant and audiovisual.
Connected Discourse Tracking (CDT)The group-mean results
obtained on CDT areshown in Figures 4a and b. The performance onCDT
presented audiovisually showed a statisticalimprovement within the
groups (p
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Agelfors et al.: Analysis of different speech performance
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102
Fig. 6. Relationship between individual mean results at 6, 12
and 24 months on Connected DiscourseTracking and Everyday Sentences
tested audiovisually.
Everyday Sentences (ES)The results obtained on ES test showed
similartendencies as on the CDT, which can be seen inFigures 5a and
5b. The correlation between theresults from two speech tests is
shown in Figure6. The correlation coeff icient is r =
0.83.Individual results on ES showed a ceili ng-effectfor some of
the better CI-users already after 6 to12 months of CI-use.
The average performance on the ES for thesubgroups over time in
two test conditions areshown in Figures 5a-b. In the combined
situationall three groups of CI-users showed a
significantimprovement, on average, between the first andsecond
test sessions, but after six months ofimplant use no significant
improvement hadoccurred over time. As shown in Figures 4a-band
5a-b, performance stabili sed after about 6months for many of the
patients, but for thebetter performers it continued to
increasegradually over several years of implant use.Some patients
showed fluctuations inperformance, but some of the poorer
showedreductions in their performance over time. Themean score
obtained by the POOR groupdeteriorated between the first and second
yearwith the implant and the reason for this isunclear. There were
significant differences (p<0.01) on average between the groups
at the firstand second test sessions, but after 6 months of
CI-use the differences were negligible betweenthe two groups of
better performers. Theperformance in the combined condition
showedafter 6 months of CI-use an improvement around40% for all
three groups of CI-users compared tocochlear implant alone.
In the test situation auditory alone, significantdifferences
were obtained between the groupsafter 6 months of implant use, the
GOODperformers scored around 60% correct, theAVERAGE performers
around 30% and thePOOR performers perceived only a few
wordscorrectly. The improvement within the first 6months of CI-use
was for the GOOD and theAVERAGE groups around 20% compared to
noimprovement at all for the POOR group.
Analysis of vowel and consonant testFigure 7 shows the mean
results obtained by thethree subgroups on different speech tests at
6, 12and 24 months postoperatively. No significantimprovements were
noted over time from 6months until 24 months for any of the
subgroupson any of the tests. However, there are
significantdifferences in performance between thesubgroups on the
different speech tests. Toobtain a larger number of data for the
confusionmatrix analysis the vowel and consonant testresults at 6,
12 and 24 months were collapsed.
CDT /ES, Audiovisual (mean 6,12, 24)
0
20
40
60
80
100
0 20 40 60 80 100
CDT, words/min.
Eve
ryda
y S
ente
nces
, %
cor
rect
r = 0.83
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Fig. 7. Group-mean data on different speech tests obtained by
the three groups of CI-users at 6, 12and 24 months
postoperatively.
Figure 8 shows the confusion matrices for vowelspresented
auditory alone for the three groups ofCI-performers. The front
vowels /i:, y:, � :, e:, � :, :,/ and the back vowels / u:, o:, :/
are related totongue position from front to back of the oralcavity
and associated with distance between thefrequencies of the second
formant (F2) and thefirst formant (F1) of the vowels. There
weresignificant differences (p
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Agelfors et al.: Analysis of different speech performance
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104
(GOOD) (AVERAGE)R e s p o n s e R e s p o n s e
i y � � e � � u o � � i y � � e � � � � u o � �S i 43 26 21 S i
39 18 13 11t y 32 57 t y 55 34i � � 70 i � � 18 66
m e 66 19 m e 16 39 18u � � 13 57 28 u � � 21 32 37l � � 11 38
47 l � � 24 47u u 83 17 u u 61 32s o 26 72 s o 16 18 63� �
11 85� �
13 71
All correct: 64.0% All correct: 50.2%Front vowels: 98.6 % Front
vowels: 93.9%Back vowels: 99.3 % Back vowels: 87.7%
(POOR)R e s p o n s e
i y � � e � � � � u o � �S i 50 21t y 46 13 13 Figure 8.
Confusion matrices from i � � 38 21 vowel recognition test /bV:b/
in condition
m e 17 54 auditory alone obtained by three groupsu � � 13 25 25
25 of patients: GOOD, AVERAGE and POOR.l � � 17 29 13 29 Confusions
less than 10 % are not shownu u 17 42 13 in the matrices. Shading
indicates front s o 13 13 29 29 and back vowels.� �
17 17 50
All correct: 34.8%Front vowels: 79.9 %Back vowels: 68.1%
Table 3. Mean percentage scores (standard deviations are given
in parenthesis) obtained by the threegroups of CI-users on the
consonantal features in two conditions: auditory alone (A) and
audiovisual(AV). Signifi cant difference between the test
conditions within groups on consonantal feature* (p
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The consonantal features fricative and stopwere relatively well
perceived by the GOODperformers. The feature nasali ty was
poorlyperceived on average by all three groups ofimplantees. The
AVERAGE performers madealso more errors for stops and nasals, while
thePOOR performers were substantially poorer toidentify nasals and
fricatives with high frequencycomponents and often heard as /t/ and
/k/. In thecombined condition, all groups obtained animprovement on
average around 30% forconsonants overall . The group-mean scores
ofvoicing and nasali ty were not improvedstatistically as could be
expected in the combinedcondition compared to auditory alone for
any of
the groups, and the audiovisual characteristics ofthe stops were
not distinguishable for POORgroup of CI-users.
The confusion matrices for the consonants,Figures 9 and 10, were
analysed to obtaindetailed information about the most frequenterror
responses from the different groups of per-formers in the two test
situations. Figure 9 showsthe confusions of the consonants
presentedauditory alone. The GOOD performers weremuch better to
perceive voice/voicelessdistinction and manner information
andespecially the stops /b, g/ and /p, k/ were betterrecognised by
the better performers compared tothe poorer performers.
AuditoryaCa
(GOOD) R e s p o n s e (AVERAGE) R e s p o n s eb d g m n � � l
r j v f � � s p t k b d g m n � � l r j v f � � s p t k
b 66 14 b 27 11 19 8d 38 26 20 8 d 14 8 30 11 11 11g 8 20 42 10
8 g 16 11 8 14 24m 20 28 10 22 m 11 22 24 11 14
S n 12 50 18 8 S n 24 14 24 8 16t � � 32 36 14 t � � 22 30 16 8i
l 14 16 8 54 i l 21 34 13 13
m r 80 m r 8 79 8u j 10 10 10 44 10 u j 8 13 13 37 8l v 32 12 8
30 l v 8 11 8 14 11 16 8 8u f 44 14 14 12 u f 8 11 30 16 14s � � 86
8 s � � 74 16
s 30 46 20 s 16 51 19p 8 8 14 52 12 p 11 8 11 8 11 21 21t 12 28
32 14 t 11 21 35k 8 10 10 62 k 13 11 47
(POOR) R e s p o n s eb d g m n � � l r j v f � � s p t k
b 20 12 8 12 8 12d 20 12 8 8 8 12 8g 12 12 12 8 20 8m 8 28 8 20
8 Fig. 9. Consonant /vCv/ confusion matrices
S n 24 12 8 12 8 8 12 for the three groups of CI-users in
auditory testt � � 8 8 12 24 8 12 8 situation. Confusions less than
8% are not showni l 8 8 8 14 36 8 in the matrices. Shading
indicates manner and
m r 8 44 12 voice/voiceless categories.u j 8 8 12 12 12 44l v 8
8 20 8 8 8 8 0 8u f 20 14 24 12 20s � � 12 68
s 8 16 28 28p 8 8 8 16 12 28 12t 8 16 8 12 28 20k 8 8 24 32
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Agelfors et al.: Analysis of different speech performance
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106
AudiovisualaCa
(GOOD) R e s p o n s e (AVERAGE) R e s p o n s em p b f v n t d
r l s � � j k g m p b f v n t d r l s ! ! j k g
m 78 20 m 80 20p 84 16 p 68 30b 8 91 b 91f 99 f 96
S v 92 S v 17 74 8t n 62 15 9 t n 43 9 18 16i t 60 9 21 i t 24 8
24 9 25
m d 57 18 19 m d 22 36 12 14u r 65 29 u r 51 11 24l l 93 l l 12
86u s 65 31 u s 46 46s " " 98 s " " 8 91
j 8 86 j 88k 86 11 k 87 11g 94 g 9 24 58# #
19 16 56# #
11 11 28 11 38
(POOR) R e s p o n s em p b f v n t d r l s " " j k g # #
m 59 34p 72 24b 16 78 Fig. 10. Consonant /vCv/ confusion
matrices f 79 12 for the three groups of CI-users in
audiovisual
S v 36 50 9 test situation. Confusions less than 8% are not t n
26 10 31 12 shown in the matrices. Shading indicatesi t 28 24 33
visemes with the same place of articulation.
m d 24 9 22 18u r 36 19 19 10l l 95u s 43 45s " " 93
j 17 60k 81 12g 14 31 34# #
34 12 16 9 16
Nasals were heard predominantly as the /l/-soundor as voiced
consonants sharing the samecharacteristics. The /r/-sound was poor
recog-nised by the poorer performers and often heardas other voiced
consonants as /l and j/. Thefricatives /f, $ , s/ were often
confused with eachother and the intense fricative /s/
waspredominantly heard as / % /. The explanation forthis seems be
that they perceived all high-energyfricatives as / % /-sound. The
voiceless fricative /
% / is mostly generally characterised by aconcentration of
energy above 1.5 kHz andextending to above 4 kHz and /s/ is
characterisedby energy above 4.0 kHz. In the combinedsituation
(Fig. 10), the place feature was wellperceived by all three groups
of CI-users and theconfusions were often made within the
groups according to whether they are produced inthe front,
middle or back of the vocal tract.
Relationship between speech performanceand some back ground
variables of theCI-usersThe factors determining good performance
with acochlear implant have not yet been clearlyidentified. To get
some knowledge about thedifferences among the CI-users, the
resultsobtained by the three groups of performers werecompared with
respect to different backgrounddata; age at implantation, years of
deafness,number of active electrodes, etc. Some basic datais
presented in the following.
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1. Duration of deafness and age atimplantationYears of deafness
and maybe age at implantationare possible predictors for the
outcome. In Figure11, mean-group data and range min/max for ageat
implantation and duration of deafness arepresented from the
different groups of CI-users.The highest mean age was represented
in thePOOR group with a range of 54-78 years and amean age of 65
years. Younger persons wererepresented in the GOOD and
AVERAGEgroups and the mean ages were around 50 years.The widest
range of age, however, was found inthe group of GOOD performers
with a rangefrom 25 years of age up to 78 years at the time
ofimplantation.
Shorter durations of deafness was found inthe GOOD-group and
CI-users with longerdurations of deafness was represented in
thePOOR-group. The widest range of durations wasfound in the
POOR-group from about 10 yearsup to 40 years of deafness.
In Figures 12 a-b and 13 a-b are shown therelationship between
CDT presented in two testconditions and duration of deafness and
age atimplantation. The correlation coeff icient betweenage at
implantation and CDT auditory alone isweak (r = -0.24). There is a
tendency that manyof the older CI-users performed somewhat
poorlywith their implants which could be explained bya longer
deprivation of auditory input beforeimplantation. In the
audiovisual situation, wheretwo different modali ties are combined,
a higher
correlation coeff icient (r = -0.49) compared toauditory alone
was obtained.
Speech perception performance with theimplant and duration of
deafness are strongerassociated to each other compared to age
atimplantation, r = 0.60. Blamey (1995) hasgathered data for a
total group of 425 post-linguistic adult implant users and reported
aboutage at implantation and duration of deafness.When grouped by
both age at implantation andduration of deafness, the data showed
aconsistent effect of age at implantation only atshorter durations
of deafness. For durationslonger than 10 years, the effect of age
atimplantation was relatively small and did notshow an orderly
decrease from younger to olderages. Tyler & Summerfield (1996)
reported thatpartial correlations demonstrate that bothmeasures
have independent effects on outcomes.Many others have reported
significantassociations between performance with animplant and both
age at implantation andduration of deafness. However, some
otherstudies have not found this pattern (Summerfield& Marshall
, 1995). For example, among 119patients in United Kingdom who were
testedpreoperatively and 9 months postoperatively,there was no
significant association between ageand performance (r = 0.11),
whereas a significantcorrelation did exist between performance
andduration of deafness (r = -0.47, p
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Agelfors et al.: Analysis of different speech performance
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108
Fig. 12 a-b. Relationship between age at implantation and CDT
(mean value at 6, 12 and 24 months) intwo test situations: auditory
alone with the implant and audiovisual.
Fig. 13 a-b. Relationship between duration of deafness and CDT
(mean value at 6, 12 and 24 months)in two test situations: auditory
alone with the implant and audiovisual.
2. EtiologyThe cause of deafness varies among the im-plantees
(Table 4), and there would appear to beno particular etiology bias
in the three groups,except for otosclerosis which seems to be a
goodpredictor for good performance.
Table 4. Etiology represented in the differentgroups of
CI-users
GOOD AVERAGE POOREtiology: (N=17) (N=13) (N=11)
Unknown,progressive loss
3 3 5
Otosclerosis 5 2 -Meningitis 3 2 1Unknown,sudden deafness
2 1 2
Ototoxicity 3 1 1Skull trauma - 1 2Meniérè 1 - -Rem. artrit - 1
-Sarkoidos - 1 -Unknown - 1 -
3. Relationship between speech performanceand residual
hearingTable 5 shows group-mean data of audiometricthresholds and
range (min-max) at three differentfrequencies 250, 500 and 1000 Hz
measuredpreoperatively on the implanted ear for the threegroups.
There are great variations within eachgroup, but a majority of the
GOOD performershad some residual hearing, especially at the
lowerfrequencies, while most of the POOR performershad on average
poorer thresholds. Residualhearing means that there is still some
nerveactivity in the cochlea which could have a positiveeffect on
the results with the implants.
4. Processor strategyRelationship between speech performance and
CI-systems is presented in Table 6. Only twosubjects used Ineraid.
They were represented inthe GOOD and POOR groups. The twoprocessing
strategies available for the Nucleus
CDT/ Auditory (mean 6,12, 24)
0
20
40
60
80
100
20 30 40 50 60 70 80
Age at implantation (years)
r = - 0.24
Words/min. CDT/ Audiovisual (mean 6,12, 24 )
0
20
40
60
80
100
20 30 40 50 60 70 80
Age at implantation (years)
r = - 0.49
Words/min.
CDT/Auditory (mean 6,12,24)
0
20
40
60
80
100
0 10 20 30 40 50
Duration of deafness (years)
r = - 0.60
Words/min.CDT/ Audiovisual (mean 6,12,24)
0
20
40
60
80
100
0 10 20 30 40 50Duration of deafness (years)
r = - 0.64
Words/min.
-
TMH-QPSR 4/1996
109
Table 5. Group-mean data and range of audio-metric thresholds at
frequencies 250, 500 and1000 Hz at the implanted ear
preoperatively.
GOOD AVERAGE POOR
250 Hz, dBHLrange/ min-max
500 Hz, dBHLrange/ min-max
1000Hz, dBHLrange/ min-max
100(60-120)
102(75-120)
109(90-130)
103(75-120)
111(95-130)
121(105-130)
113(80-120)
118(95-30)
122(105-130)
users were MPEAK and F0/F1/F2. All subjectswho from the
beginning were equipped with theolder speech coding strategy have
had thepossibili ty to upgrade to MPEAK strategy.However, some of
the Nucleus users havepreferred their practised F0/F1/F2
strategy.MPEAK strategy was represented in all groupsbut F0/F1/F2
was represented only in theAVERAGE and POOR groups. There are
nodifferences between the groups regarding thenumber of active
electrodes.
Table 6. CI-systems, programming data andnumber af active
electrodes for the differentgroups of CI-users.
GOOD AVERAGE POOR(N =17) (N =13) (N =11)
CI-system Ineraid ( 1) - Ineraid ( 1)CI-system Nucleus (16)
Nucleus (13) Nucleus (10)Strategy MPEAK (16) MPEAK ( 9) MPEAK (
5)
F0/F1/F2 ( 4) F0/F1/F2 ( 5)
Stimuli mode BP+1 (15) BP+1 (13) BP+1 (10)CG ( 1)
No. of active electrodesmean 19 18 19range 15-20 15-20 14-20
Notes. Number in parentheses indicate number ofCI-users.
SummaryIn summary, 41 postlingually deafened adults whoreceived
a multichannel cochlear implant at SöderHospital, Stockholm,
equipped with second-generation devices have been evaluated in
thisstudy, all with daily experience with CI up to twoyears. The
abili ty to improve speech recognitionin different test situations
was confirmed bydifferent speech tests. There was, however, alarge
variation across the CI-users to understand
some open-set speech, without contextualinformation. Eleven
patients (27%) had no abili tyat all to understand connected speech
withoutsupport of lipreading on CDT-test. Oncomparison, the group
of GOOD performers(41%) perceived more than 30 words/minute,
andsome of them are very successful incommunication auditory alone
in a quietenvironment with a famili ar speaker. Theseresults show
that progress in speech perception isto be found within the first
six months, whichindicates that this period is of the
greatestimportance in terms of training and mapping,especially for
the POOR performers. Further-more, 50% of the POOR performers with
theNucleus device preferred the FO/F1/F2 to theMPEAK strategy which
is probably due to thefact that they were fitted with the former
strategyfirst and that they cannot utili se the moresophisticated
MPEAK strategy. The obtainedresults of consonants between the
better and thepoorer subjects could possibly be explained
bydifferent coding strategies Multipeak versusF0/F1/F2. On the
other hand, Skinner et al.(1991) report no difference in percent
correct foreither vowels or consonants for patients testedwith both
the F0/F1/F2 and Multipeak processor.
Many of the GOOD performers obtained openspeech from the very
first day of CI-use andcontinued to improve over these two years
oftesting. However, statistics showed that thehighest progression
was during the first sixmonths of implant use which was the
mostimportant period to predict the outcome for allgroups of
implantees. Many of the GOODperformers became profoundly deaf a
shorter timeprior to implantation compared to the POORperformers
and some of them possess someresidual hearing in the low frequency
range.Outcomes from CI vary widely among adultpatients even in a
homogeneous group of CI-userwho use similar devices.
Final remarksThe results in this study show that progress is
tobe found within the first six months, whichindicates that this
period is of the greatestimportance in terms of training and
mapping,especially for the POOR performers. The GOODperformers
continued to improve their abili ty toperceive open speech auditory
alone with thecochlear implants over time. The future
researchshould be focused on identifying the componentsof
individual variability among the CI-users.
-
Agelfors et al.: Analysis of different speech performance
.....
110
AcknowledgementThis study is a result of co-operation between
thedepartment of Audiology at Söder Hospital inStockholm and
Department of Speech, Music andHearing, KTH. This report is an
expanded versionof the paper presented at III rd
InternationalCongress on Cochlear Implant, Paris, April 27-29,
1995.
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