Electrical stimulation rate effects on speech perception in cochlear implants.

Abstract

The objective of this study was to explore cochlear implant users' speech perception performance in quiet and in noise for low to moderate stimulation rates. Eight postlingually deaf adult users of the Nucleus CI24 cochlear implant (contour electrode array) using the ESPrit 3G speech processor participated in this study. Monosyllabic word recognition in quiet and sentence perception in noise was evaluated for low to moderate stimulation rates of 275, 350, 500, and 900 pulses-per-second/channel (pps/ch). All four stimulation rate programs were balanced for loudness. A repeated ABCD experimental design was employed. Take home practice was provided with each stimulation rate. Subjects also responded to a comparative questionnaire to examine their rate preference for a variety of listening situations. Results for six of the eight subjects showed no significant effect of rate for monosyllables in quiet. However, results for the sentence test in noise demonstrated improvements with 500 or 900 pps/ch stimulation rates in seven out of the eight subjects. Although there was not a close relationship between each subject's subjective preference and the rate program that provided best speech perception, most subjects indicated a preference for 500 pps/ch rate in noise.

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Komal Arora*
Pam Dawson§
Richard Dowell*
Andrew Vandali§
*Department of Otolaryngology, The
University of Melbourne, Australia
§The HEARing Cooperative Research
Centre (CRC), East Melbourne,
Australia
Key Words
Cochlear implant
Electrical stimulation rate
Speech perception
Abbreviations
ACE: Advanced combination
encoder
CIS: Continuous interleaved
sampling
pps/ch: Pulses-per-second/channel
SIT: Speech intelligibility test
Original Article
International Journal of Audiology 2009; 48:561?567
Electrical stimulation rate effects on speech
perception in cochlear implants
Abstract
The objective of this study was to explore cochlear
implant users’ speech perception performance in quiet
and in noise for low to moderate stimulation rates. Eight
postlingually deaf adult users of the Nucleus CI24
cochlear implant (contour electrode array) using the
ESPrit 3G speech processor participated in this study.
Monosyllabic word recognition in quiet and sentence
perception in noise was evaluated for low to mode-
rate stimulation rates of 275, 350, 500, and 900 pulses-
per-second/channel (pps/ch). All four stimulation rate
programs were balanced for loudness. A repeated ABCD
experimental design was employed. Take home practice
was provided with each stimulation rate. Subjects also
responded to a comparative questionnaire to examine
their rate preference for a variety of listening situations.
Results for six of the eight subjects showed no significant
effect of rate for monosyllables in quiet. However, results
for the sentence test in noise demonstrated improvements
with 500 or 900 pps/ch stimulation rates in seven out of
the eight subjects. Although there was not a close
relationship between each subject’s subjective preference
and the rate program that provided best speech percep-
tion, most subjects indicated a preference for 500 pps/ch
rate in noise.
Sumario
El objetivo de este estudio fue explorar el desempen ˜o en la
percepcio ´n del lenguaje en silencio y en ruido utilizando
tasas de estimulacio ´n bajas y medias en usuarios de
implante coclear. Participaron en este estudio ocho
adultos sordos post-linguı ´sticos usuarios del implante
coclear Nucleus C124 (punta de electrodos contour) con
procesados ESPrit 3G. Se evaluo ´ el reconocimiento de
monosı ´labos en silencio y la percepcio ´n de frases en ruido
con tasas de estimulacio ´n con un rango de 275, 350, 500 y
900 pulsaciones/segundo/canal (pps/ch). Los cuatro pro-
gramas de tasa de estimulacio ´n fueron balanceados en
intensidad.Se utilizo ´ un disen ˜o experimental ABCD
repetido. Se proporciono ´ una pra ´ctica para llevar a casa
con cada tasa de estimulacio ´n.
respondieron a un cuestionario comparativo para exam-
inar su tasa preferida en una variedad de situaciones de
escucha. Los resultados en seis de los ocho sujetos no
mostraron efectos significativos para los monosila ´bicos en
silencio. Sin embargo, la prueba de frases en ruido mostro ´
mejorı ´a con la tasa de estimulacio ´n de 500 y 900 pps/ch en
siete de los ocho sujetos. Aun cuando no hubo una clara
relacio ´n entre la preferencia subjetiva de cada sujeto y el
programa de cada tasa que proporcionaba la mejor
percepcio ´n del lenguaje, la mayorı ´a de los sujetos indicar-
on que preferı ´an la tasa de 500 pps/ch en ruido.
Los sujetos tambie ´n
The stimulus signals delivered in existing CI systems are generally
derived by sampling the temporal envelope of each channel at
some constant (analysis) rate and using its intensity to control the
stimulation current level delivered to the corresponding electrode
site (again at a constant stimulation rate which is typically equal
to the analysis rate). The range of stimulation rates employed
in devices varies extensively amongst systems from low
(B500 pps/ch), to moderate (500?1000 pps/ch), through to high
(?1000 pps/ch). When considering the appropriate rate to
employ for coding of F0 temporal information, Nyquist’s
theorem states that the rate must be at least twice the highest
frequency to be represented. However, according to McKay et al
(1994), the stimulation rate for CI systems should be at least four
times the highest frequency to be represented. This suggests that
rates of ?1200 pps per channel are needed to effectively code the
voice pitch range up to 300 Hz. On the other hand studies
examining neural responses to electrical stimulation in animals
have shown that at rates above ?800 pps/ch, there is poorer
phase locking and less effective entrainment of neurons due to
refractory effects being more dominant (Parkins, 1989; Dynes &
Delgutte, 1992). It is therefore simplistic to assume that a higher
stimulation rate alone will necessarily result in more effective
transfer of temporal information in the auditory system.
A number of studies explored the effect of stimulation rate on
speech perception in CI users. Results for some of the previous
studies using the continuous interleaved sampling (CIS) speech
coding strategy and the MED-El implant showed benefits for
moderate and high stimulation rates (Loizou et al, 2000; Keifer
et al, 2000; Verchuur, 2005; Nie et al, 2006). However, other
studies using the CIS strategy did not show a benefit for high
rates (Plant et al, 2002; Friesen et al, 2005). The comparison of
these studies is complicated by the use of different implant
systems. Studies using the Nucleus devices with 22 intracochlear
electrodes and the advanced combination encoder (ACE)
strategy did not show a conclusive benefit for higher rates
(Vandali et al, 2000; Holden et al, 2002; Weber et al, 2007; Plant
et al, 2007). Again, there are some limitations in these studies
due to the specific hardware used. The higher stimulation rates
tested by Vandali et al (2000) and Holden et al (2002) probably
did not add any extra temporal information due to the limited
analysis rate of 760 Hz employed in the SPRINT processor used
in those studies.
Many of these studies reported large individual variability
among subjects. Although the recent study by Plant et al (2007)
found no significant group mean differences between higher rate
and lower rate programs, five of the 15 subjects obtained
significantly better scores with higher rates (2400 pps/ch & 10
maxima, or 3500 pps/ch & 9 maxima) compared to lower rates
(1200 pps/ch & 10 maxima, or 1200 pps/ch & 12 maxima) for
speech tests conducted in quiet or noise. Only two subjects
ISSN 1499-2027 print/ISSN 1708-8186 online
DOI: 10.1080/14992020902858967
# 2009 British Society of Audiology, International
Society of Audiology, and Nordic Audiological Society
Komal Arora
Department of Otolaryngology, The University of Melbourne, 384?388 Albert
Street, East Melbourne, 3002, Australia.
E-mail: karora@bionicear.org
Received:
November 10, 2008
Accepted:
March 1, 2009

Page 2

obtained significant benefits in both tests using the higher set of
rates, and the results were not conclusive because significant
learning effects were observed in the study. Likewise, in the
study by Weber et al (2007), group speech perception scores in
quiet and noise did not demonstrate a significant difference
between stimulation rates of 500, 1200, and 3500 pps/ch using
the ACE strategy. However, some variability in individual scores
was observed for six of the 12 subjects for the sentences in
noise test.
Reports on subjects’ preferences for particular stimulation
rates with Nucleus devices have shown results in favor of low to
moderate stimulation rates. In the study done by Vandali et al
(2000), 250 and 807 pps/ch rateswere preferred over 1615 pps/ch.
Similarly, Balkany et al (2007) reported preferences for slower set
of rates (500 to 1200 pps/ch, ACE strategy) for 37 of the 55
subjects, compared to faster set of rates (1800 to 3500 pps/ ch,
ACE RE strategy). Authors also reported that the rate preference
by individual subjects tended towards the slower rates within
each of the two sets of stimulation rates. Similarly, in a recent
clinical trial conducted in North America and Europe by
Cochlear Ltd (2007) on subject selection of stimulation rate
with the Nucleus Freedom system, there was a preference for
stimulation rates of 1200 pps/ch or lower. Speech perception test
results also showed improved performance with stimulation rates
of 1200 pps/ch or lower compared to a higher set of rates (1800,
2400, and 3500 pps/ch).
If low to moderate stimulation rates in Nucleus devices do
indeed provide equivalent or better speech perception, then
recipients may also benefit from reductions in system power
consumption and processor/device size and complexity. So far,
low to moderate rates have not been explored well in CI24
implants with the ACE strategy, especially in the range of
250?900 pps/ch, in spite of the fact that this range of rates is
most commonly used in clinical settings with Nucleus devices
(which worldwide are the most used devices so far among CI
recipients). We chose to examine rates of 275, 350, 500, and
900 pps/ch in this study.
In this study, care was taken to loudness balance all four rate
programs so as to minimize any adverse effects of loudness on
comparative outcomes between rate conditions. Thresholds and
comfortable levels were measured for all electrodes as each new
stimulation rate was introduced. The experimental design
provided take home practice with each stimulation rate program.
Learning effects were assessed by using a repeated ABCD
design. The study was specifically designed to determine:
. Whether rates of stimulation (between 275 and 900 pps/ch)
have an effect on the speech perception in quiet and noise for
the group of adult CI subjects.
. Whether optimal rate varies among various subjects.
. Whether there is a relation between the subjective preference
measured with comparative questionnaire and the speech
perception scores.
Methods
Subjects
Eight postlingually deaf adult subjects using the CI24 cochlear
implant (Contour electrode array) and ESPrit 3G speech
processor participated in the study. They had a moderate level
of open set speech perception ability (over 50% CUNY sentence
perception score in quiet). Table 1 shows the demographic data
for the subjects. The use of human subjects in this study was
approved by the Human Research and Ethics Committee, Royal
Victorian Eye and Ear Hospital.
Study design
A repeated ABCD experimental design for the four rate
conditions was employed. Evaluation order for rate conditions
was balanced amongst the subjects, and learning effects were
assessed by employing a repeated design model. Four weeks of
take home practice was provided with each stimulation rate
condition during the initial phase of the study. Only one rate
condition was taken home at a time. After practice with each
stimulation rate, speech perception outcomes were measured.
The same procedure was repeated in the second phase of the
study, except that two weeks instead of four weeks take home
practice was provided with each stimulation rate program. At
the end of this second phase, subjects took home all four rate
programs in two ESPrit 3G processors for a period of two
weeks. They were asked to directly compare each of the four
programs in a variety of listening situations.
Speech processor programs
The ACE (advanced combination encoders) strategy was used
for all stimulation rates. The stimulation rates tested were: 275,
350, 500, and 900 pps/ch. For the 275 pps/ch case, the stimula-
tion rate was jittered in time by approximately 10% which tends
to lower the rate to approximately 250 pps/ch. This was done to
minimize the audibility of the constant stimulation rate. The
Table 1. Subject details
SubjectAgeCause of deafness
Duration of implant
use (years)
Everyday stimulation rate
and strategy*
1
2
3
4
5
6
7
8
58
67
64
64
74
75
62
68
Hereditary
Otosclerosis
Unknown
Unknown
Unknown
Otosclerosis
Unknown
Unknown
4
5
5
5
4
8
8
6
900 pps/ch, ACE
720 pps/ch, ACE
900 pps/ch, ACE
250 pps/ch, SPEAK
1200 pps/ch, ACE
250 pps/ch, SPEAK
250 pps/ch, SPEAK
250 pps/ch, ACE
*Prior to commencement of the study. Each of the everyday program used monopolar mode of stimulation (MP1?2).
562International Journal of Audiology, Volume 48 Number 8

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number of maxima was fixed at eight for all the conditions.
Biphasic current pulses with pulse width of 25 microseconds
were used in a monopolar mode (MP1?2). Pulse width was
increased in cases where higher comfortable levels were needed.
Monopolar1?2 stimulation mode was used for all subjects.
Clinical default settings for frequency to electrode mapping
were employed. The speech processor was set at the client’s
preferred sensitivity and held constant throughout the study.
Speech processor programs were created for each rate condi-
tion. Thresholds (T-level) were measured by using a modified
Hughson-Westlake procedure with an ascending step size of two
current levels (CLs) and a descending step size of 4 CLs.
Comfortable listening levels (C-levels) were measured by an
ascending technique that slowly increases the levels from the
baseline T-levels until the client reported that the soundwas loud
but still comfortable. Loudness balancing was performed at C-
levels as well as at 50% level of the dynamic range, using a sweep
across four consecutive electrodes at a time. Subjects were asked
to make sure that stimulation of all four electrodes sounded
equally loud and if not, T- and C-levels were adjusted as
necessary. T- and C-levels were measured for all mapped
electrodes and for each rate condition. When testing the maps
in ‘live-mode’, any discomfort with the client’s own voice as well
as with the clinician’s voice was checked. Global C-level
modifications were made if necessary. In addition, speech like
noise ‘ICRA’ (International Collegium of Rehabilitative Audiol-
ogy) (Dreschler et al, 2001) was presented at 60 dB SPL RMS for
all programs to ensure that each were similar in loudness for
conversational speech. The comparison was conducted using a
paired-comparison procedure, in which all possible pairings of
conditions were compared twice. Adjustments were made to C-
levels if necessary to achieve similar loudness across all rate
programs.
Speech tests
Test material comprised of CNC words in quiet, and speech
intelligibility test (SIT) sentences presented in background noise.
Each CNC (Peterson & Lehiste, 1962) word list consists of 50
words recorded by a female Australian speaker. Four lists of
CNC words were presented in each session at a level of 60 dB
SPL RMS. The SIT sentences (Magner, 1972) consist of 40 lists
of 15 sentences of between three and eight key words recorded
by a male Australian speaker. A four-talker babble noise was
used for the sentence test in noise. The speech material was
presented at 0 degree azimuth with the subjects facing the
loudspeaker. Practice lists were provided for both the sentence
and word tests in the initial testing session.
An adaptive procedure was used to measure signal to noise
ratio (SNR) for the sentence test in noise. The procedure was
similar to the procedure used by Henshall and McKay (2001). At
the initial testing session, two lists of SIT sentences were
presented in quiet at 65 dB SPL RMS using the client’s regular
program. The percentage of key words repeated correctly was
recorded. A target score of 70% of the sentence score in quiet
was calculated for each subject. When measuring the SNR, the
SNR was initialized at 15 dB for the first two sentences.
Sentences were always presented at 65 dB SPL RMS; only the
noise levels were changed based on the subject’s responses. The
number of key words identified correctly in the pair of sentences
was compared to the target score. If the score was ?70%, the
noise level was increased, otherwise the noise level was
decreased. Noise levels were varied in 5-dB steps for the first
two reversals and in 3-dB steps for the next six reversals. The
final SNR was recorded as an average of the last six reversals.
Four such SNR estimates were recorded in each session.
Comparative performance questionnaire
A comparative questionnaire was provided to the CI subjects at
the end of the repeated ABCD protocol. Subjects were asked to
use all four rate programs for similar lengths of time over a
period of two weeks with a constant sensitivity setting for all
stimulation rates.
The questionnaire involved rating the helpfulness of the
programs in 18 different listening situations. The rating scale
had five different levels ranging from 1 (no help) to 5 (extremely
helpful). The questions were grouped into four main listening
conditions: quiet (n?4), noise (n?6), media devices e.g. TV,
telephone, and stereo (n?4), and soft speech or listening at a
distance (n?4). After providing helpfulness ratings, subjects
were asked to indicate their first preferences in quiet, noise, and
overall. Subjects were also asked to indicate if their preferred
program was very similar/ slightly better/ moderately better/
much better than other programs.
Data analysis
Group performance for the speech tests was analysed with
repeated measures two-way analysis of variance (ANOVA) to
assess the factors ‘rate’ and ‘session’. Post hoc Tukey tests were
further performed to investigate any significant rate effects. One-
way independent analysis of variance (ANOVA) with post hoc
Tukey tests was used to analyse individual outcomes. The
Kruskal Wallis one-way ANOVA on ranks was employed if
the normality assumption was violated. The Friedman repeated
measures ANOVA on ranks was conducted for the group
average ratings across 18 listening conditions in the question-
naire and for the group average ratings across the four categories
(quiet, noise, media devices, and soft speech). Dunn’s tests were
further performed for the pair-wise multiple comparisons. A chi-
square analysis was conducted to determine whether there were
significant differences between the distribution of preferences for
the four rate programs in quiet, noise, and overall.
Results
CNC words
Figure 1 shows percentage correct CNC word scores for the
eight subjects using each stimulation rate program. The scores
were averaged across the two evaluation sessions. Analysis of
group results revealed no significant differences across the four
rate programs (F [3, 21]?1.87; p? 0.165). Furthermore, there
was no significant main effect for session (F [1, 21]?1.50;
p?0.25). However, the interaction between rate and session was
significant (F [3, 21]?4.08; p?0.02). Post hoc analysis revealed
a significant session effect for the 275 pps/ch stimulation rate
only.
In the individual analysis, subject 1 obtained significantly
better scores using the 500 and 900 pps/ch programs compared
to the 350 pps/ch program. There was no significant difference
between the 500 and 900 pps/ch programs. Subject 8 obtained
best CNC scores with the 500 pps/ch program but the 900 pps/ch
Electrical stimulation rate effects on speech
perception in cochlear implants
Arora/Dawson/Dowell/Vandali563

Page 4

program provided poorer performance compared to all other
programs.
Sentence test results
Figure 2 shows average SNRs obtained for each subject and the
group SNR on the SIT sentences for each stimulation rate
program. Lower SNRvalues indicate better speech perception in
noise. Repeated measures two-way analysis of variance revealed
a significant main effect for stimulation rate (F [3, 21]?5.95;
p?0.004). Group analysis showed significantly better SNRwith
the 500 pps/ch program (p?0.009) and the 900 pps/ch program
(p?0.01), compared to the 275 pps/ch rate program. The
majority of the subjects showed improved performance with
the 500 or 900 pps/ch rate programs. A small but significant
effect of session was observed for sentence in noise scores for all
four stimulation rate programs (F [1, 21]?6.88; p?0.034).
Mean SNR decreased by 0.7 dB during the second session.
There was no significant interaction effect between stimulation
rate and the session (F [3, 21]?1.53; p?0.234).
Individual data analysis revealed a significant rate effect for
the sentence test in seven out of eight subjects (pB0.001).
Subject 1 performed equally well with the 500 and 900 pps/ch
stimulation rate programs. Performance was significantly better
with both these programs compared to the 275 and 350 pps/ch
rate programs (pB0.05). Subject 2 showed improved perfor-
mance with the 900 pps/ch program. Pair-wise multiple compar-
isons with the Tukey test indicated significant differences
between the mean SNR obtained with the 275 pps/ch program
versus all other rate programs (pB0.05), and also between the
mean SNR obtained with the 350 and 900 pps/ch programs
(p?0.025). No significant differences were observed between the
SNRs for the 350 and 500 pps/ch programs and the SNRs for the
500 and 900 pps/ch programs.
Subjects 5 and 6 also obtained best SNRs with the 900 pps/ch
compared to 350 and 500 pps/ch stimulation rates (pB0.05).
Subjects 3, 4, and 8 performed best with the 500 pps/ch
stimulation rate. For subject 3, the results for the 500 pps/ch
condition were significantly better than the 275 pps/ch stimula-
tion rate (p?0.001). For subject 4 and subject 8, mean SNRs
with 500 pps/ch stimulation rate were significantly better than all
Significance
275 vs 350pps
275 vs 500pps
275 vs 900pps
350 vs 500pps
350 vs 900pps
500 vs 900pps
12345678
group
*
*
**
***
*
***
Subjects
12345678 group
CNC word score (%)
0
20
40
60
80
100
275pps/ch (A)
350pps/ch (B)
500pps/ch (C)
900pps/ch (D)
Preference
DCC B,CCCBC
(2) (2)(1) (3) (2)(1) (2)(1)
Figure 1. Individual patient’s percentage correct scores and
group mean percentage correct scores for CNC words in quiet.
Statistically significant differences (post hoc Tukey test) are
shown in the tables presented below each bar graph (*p50.05,
**p50.01, ***p50.001). The error bars indicate the standard
error. Each subject’s subjective preference in quiet along with the
degree of preference to other programs (1: very similar, 2:
slightly better, 3: moderately better, 4: much better) are shown
below the chart.
Preference
DCB B,CCCBC
(3)(4)(2)(3)(3) (1)(3)(1)
Subjects
12345678group
SNR (dB)
0
2
4
6
8
10
12
275pps/ch (A)
350pps/ch (B)
500pps/ch (C)
900pps/ch (D)
Significance
275 vs 350pps
275 vs 500pps
275 vs 900pps
350 vs 500pps
350 v s900pps
500 vs 900pps
12
**
***
**
345678 group
**
* ***
***
**
*
**** ** **
***
***
**
**
***
* **
* ***
Figure 2. Individual patient’s mean signal to noise ratio (SNR)
and group mean SNR for SIT sentences in competing noise.
Statistically significant differences (post hoc Tukey test) are
shown in the tables presented below each bar graph (*p50.05,
**p50.01, ***p50.001). The error bars indicate the standard
error. Each subject’s subjective preference in noise along with the
degree of preference to other programs (1: very similar, 2:
slightly better, 3: moderately better, 4: much better) are shown
below the chart.
564 International Journal of Audiology, Volume 48 Number 8

Page 5

other stimulation rates. Subject 7 did not show any significant
difference in performance when tested for sentences in noise for
all four stimulation rates.
Comparative performance questionnaire
Figure 3 shows group mean ratings of helpfulness for the four
questionnaire subcategories and averaged across these subcate-
gories for each stimulation rate program. Friedman repeated
measures ANOVA on ranks revealed no significant effect of
stimulation rate on subjects’ average helpfulness ratings across
the 18 listening situations (X2[3]?7.38, p?0.061). Further-
more, there was no significant effect of rate for the listening
categories: listening in quiet (X2[3]?1.70, p?0.63), listening to
media devices (X2[3]?7.55, p?0.056), and listening to soft
speech (X2[3]?6.9, p?0.074). Helpfulness ratings for listening
in noise showed a significant effect of stimulation rate (X2[3]?
9.0, p?0.029), however, pair-wise multiple comparisons using
Dunn’s method revealed no significant differences between any
pairs of rate programs.
After providing helpfulness ratings, subjects were asked to
indicate their first preferences in quiet, noise, and overall. Table 2
shows the number of subjects reporting their first preferences in
quiet, noise, and overall for the four rate programs. Chi-square
analyses revealed significant differences between the distribution
of preferences in quiet (X2[4]?9.5, p?0.049), but no significant
differences in noise and overall (X2[4]?5.75, p?0.218). Figures
1 and 2 indicate individual subjects’ preferred programs in quiet
and in noise respectively.
Subjects were asked to describe if their preferred rate program
sounded ‘very similar’, ‘slightly better’, ‘moderately better’, or
‘much better’ than the other programs. As shown in Figure 1,
four subjects reported their preferred program in quiet being
slightly better than other programs, one reported it moderately
better, and the remaining three subjects reported them as very
similar to other programs. For speech in noise (Figure 2), four
subjects rated their preferred program in noise as moderately
better than other programs, one subject rated it much better than
other programs, one subject rated it slightly better, and the
remaining two reported them as very similar to other programs.
Relationship between questionnaire results and speech
perception outcomes
The questionnaire results were described in terms of average
ratings of helpfulness and the subject’s first preferences in quiet,
noise, and overall. For seven out of the eight subjects there was
consistency in the average helpfulness ratings in noise and the
subjects’ first preferences in noise. There was no close relation
between the helpfulness ratings and the first preferences in quiet.
There does not appear to be a close relationship between each
subject’s subjective preference and the rate program that
provided best speech perception. Only two subjects (subject 1
and 8), who scored consistently better on a particular rate
program in quiet and noise, chose that program as the most
preferred. However, only subject 1 showed consistency between
speech test outcomes and helpfulness ratings in quiet and noise.
For two subjects (subjects 2 and 3) there was a partial
agreement between the speech perception scores in noise and
the subjective preference. Subject 2 performed best with
900 pps /ch for speech perception in noise, but there was no
significant difference in speech performance in noise for 500 and
900 pps /ch. This subject preferred the 500 pps/ch stimulation
rate in quiet and noise, and the average rating of helpfulness in
noise was also highest for the 500 pps/ch rate. Subject 3
performed best with 500 pps/ch for sentence perception in noise
and preferred this program when listening in quiet. This subject
preferred the 350 pps/ch rate in noise and overall, and the
average helpfulness rating in noise was highest with this rate
program.
Four subjects’ (subjects 4, 5, 6, and 7) speech test outcomes
did not agree with their subjective preferences. However,
the average helpfulness ratings were more or less similar to the
first preferences for these four subjects.
Attheconclusionofthestudy,fiveoftheeightsubjects(subjects
2,3,4,6,7)continuedtouseadifferentrateprogramcomparedto
their everyday rate program (used prior to the commencement of
the study). One of these five subjects (subject 6) preferred to
continue with the rate program with the best sentence in noise
perception score and the remaining four subjects continued with
the most preferred programm (overall) based on the questionaire
results.
Discussion
Speech perception in quiet and noise
The group averaged scores for monosyllables in quiet showed no
significant effect of rate. However, significantly better group
results for sentence perception in noise were observed with 500
and 900 pps/ch rates compared to 275 pps/ch stimulation rate.
Individual data analysis showed improvements with stimulation
rates of 500 or 900 pps/ch in seven out of eight subjects for
sentence perception in noise. Three out of these seven subjects
showed benefit with 500 pps/ch and another three showed
benefit with the 900 pps/ch rate. One subject showed improve-
ment with both 500 and 900 pps/ch stimulation rates.
Four out of eight subjects were using the 250 pps/ch stimula-
tion rate in their existing clinical-fitted processor before the
commencement of the study. Two out of these four subjects
obtained best speech perception in noise with 500 pps/ch, one
obtained best scores with 900 pps/ch, and the remaining subject
showed no effect of rate on speech perception. This suggests that
these subjects had enough time to become familiar with the
various rate conditions tested in this study and the results were
Table 2. The table shows the number of subjects reporting their first preferences in quiet, noise, and overall for the four rate
programs.
275 pps/ch350 pps/ch500 pps/ch900 pps/ch350?500 pps/ch
Quiet
Noise
Overall
0
0
0
1
2
2
5
4
4
1
1
1
1
1
1
Electrical stimulation rate effects on speech
perception in cochlear implants
Arora/Dawson/Dowell/Vandali 565