Sentence recognition in noise and perceived

Sentence recognition in noise and perceived
Washington University School of Medicine
Digital [email protected]
Publications
Division of Adult Audiology
2013
Sentence recognition in noise and perceived benefit
of noise reduction on the receiver and transmitter
sides of a BICROS hearing aid
Michael Valente
Washington University School of Medicine in St. Louis
Kristi M. Oeding
Washington University School of Medicine in St. Louis
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Recommended Citation
Valente, Michael and Oeding, Kristi M., "Sentence recognition in noise and perceived benefit of noise reduction on the receiver and
transmitter sides of a BICROS hearing aid" (2013). Publications. Paper 26.
http://digitalcommons.wustl.edu/audio_hapubs/26
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J Am Acad Audiol 24:980–991 (2013)
Sentence Recognition in Noise and Perceived Benefit
of Noise Reduction on the Receiver and Transmitter
Sides of a BICROS Hearing Aid
DOI: 10.3766/jaaa.24.10.9
Kristi Oeding*
Michael Valente*
Abstract
Background: In the past, bilateral contralateral routing of signals (BICROS) amplification incorporated
omnidirectional microphones on the transmitter and receiver sides and some models utilized noise reduction (NR) on the receiver side. Little research has examined the performance of BICROS amplification in
background noise. However, previous studies examining contralateral routing of signals (CROS) amplification have reported that the presence of background noise on the transmitter side negatively affected
speech recognition. Recently, NR was introduced as a feature on the receiver and transmitter sides of
BICROS amplification, which has the potential to decrease the impact of noise on the wanted speech
signal by decreasing unwanted noise directed to the transmitter side.
Purpose: The primary goal of this study was to examine differences in the reception threshold for sentences (RTS in dB) using the Hearing in Noise Test (HINT) in a diffuse listening environment between
unaided and three aided BICROS conditions (no NR, mild NR, and maximum NR) in the Tandem 16
BICROS. A secondary goal was to examine real-world subjective impressions of the Tandem 16 BICROS
compared to unaided.
Research Design: A randomized block repeated measures single blind design was used to assess differences between no NR, mild NR, and maximum NR listening conditions.
Study Sample: Twenty-one adult participants with asymmetric sensorineural hearing loss (ASNHL) and experience with BICROS amplification were recruited from Washington University in St. Louis School of Medicine.
Data Collection and Analysis: Participants were fit with the National Acoustic Laboratories’ Nonlinear
version 1 prescriptive target (NAL-NL1) with the Tandem 16 BICROS at the initial visit and then verified
using real-ear insertion gain (REIG) measures. Participants acclimatized to the Tandem 16 BICROS for
4 wk before returning for final testing. Participants were tested utilizing HINT sentences examining differences in RTS between unaided and three aided listening conditions. Subjective benefit was determined
via the Abbreviated Profile of Hearing Aid Benefit (APHAB) questionnaire between the Tandem 16
BICROS and unaided. A repeated measures analysis of variance (ANOVA) was utilized to analyze
the results of the HINT and APHAB.
Results: Results revealed no significant differences in the RTS between unaided, no NR, mild NR, and
maximum NR. Subjective impressions using the APHAB revealed statistically and clinically significant
benefit with the Tandem 16 BICROS compared to unaided for the Ease of Communication (EC), Background Noise (BN), and Reverberation (RV) subscales.
Conclusions: The RTS was not significantly different between unaided, no NR, mild NR, and maximum
NR. None of the three aided listening conditions were significantly different from unaided performance as
has been reported for previous studies examining CROS hearing aids. Further, based on comments from
*Department of Otolaryngology—Head and Neck Surgery, Division of Adult Audiology, Washington University in St. Louis School of Medicine
Kristi Oeding, 4566 Scott Ave., Campus Box 8115, St. Louis, MO 63110; Phone: 314-362-7496; Fax: 314-747-5593; E-mail: [email protected]
Portions of this manuscript were presented at a poster session at the Annual Meeting of the American Auditory Society, March 2012, Scottsdale, AZ.
The Hearing Aid Research Laboratory received funding from Unitron to offset some of the direct and indirect costs associated with completing this
study. In addition, Unitron provided hearing aids, earmolds, and reimbursement of $100 or the study hearing aids to each participant at a significantly
reduced cost upon completion of the study.
980
Noise Reduction in BICROS/Oeding and Valente
participants and previous research studies with conventional hearing aids, manufacturers of BICROS
amplification should consider incorporating directional microphones and independent volume controls
on the receiver and transmitter sides to potentially provide further improvement in signal-to-noise ratio
(SNR) for patients with ASNHL.
Key Words: Asymmetric sensorineural hearing loss, bilateral contralateral routing of signals (BICROS),
hearing aid, noise reduction, reception threshold for sentences (RTS)
Abbreviations: APHAB 5 Abbreviated Profile of Hearing Aid Benefit; ASNHL 5 asymmetric
sensorineural hearing loss; AV 5 Aversiveness of Sounds; BICROS 5 bilateral contralateral routing
of signals; BN 5 Background Noise; CROS 5 contralateral routing of signals; EC 5 Ease of
Communication; HINT 5 Hearing in Noise Test; HRPO 5 Human Research Protection Office; MIL 5
most intelligible level; NAL-NL1 5 National Acoustic Laboratories’ Nonlinear version 1 prescriptive
target; NR 5 noise reduction; REIG 5 real-ear insertion gain; RTS 5 reception threshold for
sentences; RV 5 Reverberation; SNR 5 signal-to-noise ratio; SRT 5 speech reception threshold;
SSQ 5 Speech, Spatial, and Qualities of Hearing Questionnaire; USNHL 5 unilateral sensorineural
hearing loss; WRS 5 word recognition score
P
atients with unilateral sensorineural hearing
loss (USNHL), which is defined as unaidable
hearing loss in one ear and normal hearing in
the opposite ear, and asymmetric sensorineural hearing
loss (ASNHL), which is defined as unaidable hearing
loss in one ear and aidable hearing loss in the opposite
ear, have unique disadvantages communicating compared to patients with normal hearing or bilateral symmetrical hearing loss. Patients with USNHL or ASNHL
do not have the advantages that binaural hearing provides, which include eliminating the head shadow effect
(Tillman et al, 1963), maintaining the squelch effect
(Markides, 1977; Gulick et al, 1989), binaural summation, and improved localization. Patients with USNHL
and ASNHL have great difficulty recognizing speech
when the signal arrives to the poorer ear, recognizing
speech in background noise when noise arrives to the
better ear, and localizing sound.
Fowler (1960) initially introduced contralateral routing of signals (CROS) and bilateral contralateral routing
of signals (BICROS) amplification to help alleviate the
problems associated with the head shadow effect and listening in background noise. CROS was developed for
patients with USNHL, while BICROS was developed
for patients with ASNHL. This study focuses on patients
with ASNHL and the potential benefit provided by
BICROS for these patients. The original purpose of
BICROS was to improve the ability of patients with
ASNHL to hear sounds originating on the poorer ear side
(i.e., eliminate the head shadow effect). This was accomplished by placing a microphone in or over the poorer ear
(transmitter side), which then transmits and amplifies
the signal from the poorer ear to a hearing aid with a
microphone, amplifier, and receiver on the better ear
(receiver side) (Harford, 1966). This allows patients with
ASNHL to achieve improved speech recognition regardless of which side the speech signal originates.
Patients with ASNHL often develop strategies to
situate themselves so the “wanted” signal is on the side
of the better ear, and when able to do so, the patient
typically performs quite well while also avoiding situations where noise is on the side of the better ear and the
signal is on the side of the poorer ear. Constantly having
to scan the listening environment so the better ear is
toward the signal and the poorer ear is toward the noise,
however, can be fatiguing. BICROS amplification can
assist a patient in regaining the speech signal missing
from the poorer ear side (i.e., eliminate the head shadow
effect). When noise is on the transmitter side, however,
the noise is amplified and transferred to the better ear,
which could interfere with the wanted signal.
Unfortunately, few peer-reviewed studies are available examining the efficacy and effectiveness of speech
recognition with BICROS amplification in background
noise. In one study, Del Dot et al (1992) examined
whether significant differences exist in speech recognition
with the BICROS transmitter turned on or off with speech
from 0° and four-talker babble noise from 135° and 225°.
Differences in the speech reception threshold (SRT),
which is the signal-to-noise ratio (SNR) at which sentences can be repeated correctly in noise 50% of the time,
were examined with input levels of the noise at 40 and
60 dB SPL. Results revealed a mean improvement in
SRT with the transmitter turned on, compared to off,
by 4.3 dB (p < 0.01) and 3.4 dB (p < 0.001) when the background noise levels were at 40 and 60 dB SPL, respectively. This result indicates that the presence of the
BICROS transmitter can provide significant benefit when
the transmitter is on versus off in background noise when
speech arrives from the front and noise from behind.
Although studies on the effectiveness of BICROS
amplification are limited, numerous studies have examined the efficacy and effectiveness of CROS amplification. Results from studies on CROS amplification
would be expected to be similar to BICROS amplification because the primary purpose of both amplification
strategies is to eliminate the head shadow effect. Studies examining CROS amplification have utilized a variety of loudspeaker arrays, including speech and noise
from 0° (Niparko et al, 2003; Wazen et al, 2003;
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Journal of the American Academy of Audiology/Volume 24, Number 10, 2013
Hol et al, 2004; Lin et al, 2006), noise from 0° and speech
from ±90° (Bosman et al, 2003; Hol et al, 2004, 2005),
speech from 0° and noise from ±90° (Niparko et al,
2003; Wazen et al, 2003; Hol et al, 2004, 2005; Lin
et al, 2006), or speech to the better ear and noise to
the poorer ear or vice versa (Lotterman and Kasten,
1971). These studies report that CROS amplification performed better than unaided when noise was presented to
the side of the better ear and speech was presented to the
side of the poorer ear. When noise, however, was presented to the side of the poorer ear and speech to the side
of the better ear, CROS consistently performed poorer
than unaided. Poorer performance occurs because the
transmitter transfers the unwanted amplified noise to
the hearing aid on the better ear, which amplifies the
noise and results in interference with the unamplified
wanted speech signal. While CROS amplification effectively eliminates the head shadow effect, speech recognition
in noise remains problematic.
Harford and Dodds (1974) recognized this drawback
of CROS amplification and recommended incorporating
an on-off switch on the transmitter side to allow patients
to turn off the transmitter in difficult listening environments. Other options include incorporating independent
volume controls on the receiver and transmitter sides or a
remote control to reduce the gain or turn off the transmitter. These options, however, require the patient to auditorily scan the environment and remember to make the
appropriate decision. Another solution could be the presence of noise reduction (NR) on the receiver and transmitter sides to assist in attenuating amplification if an
unmodulated signal (noise) is detected. This feature could
resolve the problem addressed above because the offside
transmitting microphone would provide greater gain if
the processor detected a modulated signal (speech) and
reduced gain if an unmodulated signal (noise) is detected.
Until recently, BICROS amplification has only
been available with an omnidirectional microphone
and/or NR on the receiver side. The only option for
the listener to improve performance in noise was a volume control, if available, or turning off the transmitter
so a directional microphone could be activated on the
receiver side (i.e., a monaural fit). To address this problem, Unitron (Plymouth, MN) introduced a CROS/
BICROS hearing aid (Tandem 16) where programmable
multichannel NR is available on the receiver and transmitter sides in 16 frequency channels. While most previous studies have reported no significant improvement
in speech recognition in noise for conventional hearing
aids when NR is activated (Boymans and Dreschler,
2000; Alcantara et al, 2003; Nordrum et al, 2006;
Bentler et al, 2008), the Tandem 16 BICROS presents
a unique application. Unlike these previous studies, all
speech and noise signals are being processed by one ear,
and one hearing aid serves to transfer the signal from
one ear to the other. As mentioned earlier, the primary
982
purpose of the transmitter is to transfer the wanted
speech signal from the side of the poorer ear to the side
of the better ear. When noise, however, is present alone
or combined with speech on the transmitter side, the
noise is amplified and transferred to the side of the better ear and may degrade the audibility of the wanted
speech signal. The addition of NR on the transmitter
side could provide an improvement in speech recognition by attenuating the noise transferred from the side
of the poorer ear that interferes with the wanted speech
signal, which could improve the SNR at the better ear.
In this manner, what was “easier” in an unaided condition remains possibly easier in an aided condition (signal
on the better side; primarily noise on the poorer side) as
the activation of NR on the transmitter side may help
attenuate some of the unwanted noise. Currently, no
peer-reviewed studies have examined the effectiveness
or efficacy of NR in BICROS amplification to determine
if participants obtain improved speech recognition or
improved perceived listener benefit when listening in
noise. In addition, no study has examined the performance of BICROS amplification using a diffuse loudspeaker
array with 65 dB SPL “real-world” uncorrelated restaurant noise.
This study examined two null hypotheses:
1. No significant differences in the reception threshold
for sentences (RTS, in dB), which is the SNR at which
sentences can be repeated correctly in noise 50% of
the time, for Hearing in Noise Test (HINT) sentences
(Nilsson et al, 1994) presented in a diffuse listening
environment are present between unaided, no NR,
mild NR, or maximum NR on the receiver and transmitter sides of the Tandem 16 BICROS hearing aid.
2. No significant differences exist between unaided and
aided problem scores on the Ease of Communication
(EC), Background Noise (BN), and Reverberation (RV)
subscales of the Abbreviated Profile of Hearing Aid Benefit (APHAB) questionnaire (Cox and Alexander, 1995).
MATERIALS AND METHODS
Participants
Twenty-one participants were recruited from the
patient database of the Division of Adult Audiology at
Washington University in St. Louis School of Medicine
via personal communication in the clinic, telephone, or
a letter approved by the Human Research Protection
Office (HRPO). Each participant signed an Informed
Consent Form approved by HRPO either prior to or
at the initial visit. To qualify for entrance into the study,
each participant was required to (a) have worn BICROS
amplification for at least 4 wk, (b) have an ASNHL,
defined as unaidable hearing in the poorer ear (profound
Noise Reduction in BICROS/Oeding and Valente
sensorineural hearing loss, poor word recognition [less
than 40%], and/or an inability to tolerate amplified
sounds) and a word recognition score (WRS) of 60–
100% at the most intelligible level (MIL) in the better
ear, (c) be at least 18 yr of age, and (d) be a native English speaker. Participants were excluded if (a) they did
not meet the inclusion criteria, (b) were nonambulatory,
(c) had a history of chronic or terminal illness, and/or (d)
could not commit to the time requirements of the study.
Otoscopy, pure-tone audiometry (250 to 8000 Hz in
octave and midoctave frequencies), and WRS testing, utilizing the compact disc recording of the female version of
the Northwestern University Auditory Test No. 6 (NU-6)
(Tillman and Carhart, 1966) word lists presented at the
participant’s MIL were performed to determine if he/she
qualified for the study. The MIL was determined using
monitored live voice presentation (voice peaking at 0 dB
on the VU meter) by talking to the participant and asking the participant to indicate when the presentation
level was most intelligible and at a comfortably loud
level. An a priori power analysis utilizing G*Power
3.0.10 (http://www.psycho.uni-duesseldorf.de/abteilungen/
aap/gpower3) determined that 25 participants were
required to determine statistical significance using data
from Valente et al (2006), a two-tailed test, an alpha of
0.05, and power of 0.80. A concurrent sample size calculation after data were collected for 15 participants revealed
that 21 participants would be sufficient to determine statistical significance based on a two-tailed test, an alpha of
0.05, and power of 0.80.
Mean hearing thresholds (dB HL) in the better and
poorer ear and ±1 SD are reported in Figure 1. Ten participants had better hearing in the right ear and 11 in
the left ear. The average hearing thresholds revealed a
slight to severe sensorineural hearing loss in the better
ear and a severe to profound sensorineural hearing
loss in the poorer ear. The mean WRS was 88.0%
(SD = 7.5%) for the better ear and 5.7% (SD = 11.1%)
Figure 1. Audiogram reporting the mean and ±1 SD for hearing
thresholds (dB HL) in the better ear (♦) and poorer ear ( ). Arrows
indicate SDs beyond the limits of the audiogram.
•
for the poorer ear. Twelve participants were male and nine
were female with a mean age of 72.9 yr (SD = 8.4 yr). Etiology in the poorer ear included Ménière’s disease (n = 4),
acoustic neuroma (n = 4), congenital deafness (n = 4), sudden idiopathic sensorineural hearing loss (n = 6), noise
induced hearing loss (n = 2), and severe acute otitis media
(n = 1). The mean duration of hearing loss was 24.9 yr
(SD = 20.9 yr).
The participants’ mean years of experience with
BICROS amplification was 8.1 yr (SD = 5.5 yr). Table
1 reports the BICROS model and years of experience
with BICROS amplification. At the time of entrance into
the study, 18 participants wore BICROS amplification,
and three wore monaural amplification in the better
ear. All three participants wearing monaural amplification had worn BICROS amplification several years and
had experience with the advantages and disadvantages
of using BICROS amplification. One wore BICROS
amplification for 11.0 yr and decided to discontinue
use of the BICROS due to constant repairs to the receiver
and transmitter because of poor moisture resistance and
wore a monaural hearing aid for one year. The second
participant wore BICROS amplification for 15.3 yr and
had worn monaural amplification for nine months
because the transmitter was damaged and purchasing
another transmitter was prohibitive. The third participant wore BICROS amplification for 6.9 yr before using
monaural amplification for eight years because of a positive experience with a loaner monaural hearing aid during repair of the participant’s BICROS and improved
perceived benefit in noise with monaural amplification.
Hearing Aid Fitting and Verification
In this study, the Unitron Tandem 16 BICROS hearing aid was investigated. This hearing aid features NR
that can be activated on the receiver and transmitter
sides and contains 16 frequency bands for programming
adjustments. The Tandem 16 has four settings of NR
that can be programmed for the receiver and transmitter. These settings include no NR and mild (z23 dB
SPL), moderate (z25 to 26 dB SPL), and maximum
NR (z28 to 29 dB SPL). The NR algorithm analyzes
the input signal in each of the 16 channels using three
criteria: (a) modulation depth, (b) modulation frequency, and (c) signal duration. The NR algorithm
has an overall sampling cycle of 320 times per second,
and when noise is the prominent signal in a channel,
gain/output is decreased in that specific frequency
channel(s). The attack time, when measured using
white noise with an input of 85 dB SPL, is approximately
2000 msec, and the release time is approximately
40 msec. These time constants can vary depending on
the input signal characteristics, level, and frequency.
The magnitude of NR does not change as input level
changes and is based upon the estimated SNR in a
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Journal of the American Academy of Audiology/Volume 24, Number 10, 2013
Table 1. Current or Previous BICROS Amplification Worn by Participants and Years of Experience
Participant
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Manufacturer
Model
Years of Experience
Phonak
Phonak
Phonak
Interton
Widex
Phonak
Phonak
Phonak
Phonak
Phonak
Phonak
Telex
Phonak
Unitron
Phonak
Phonak
Phonak
Phonak
Phonak
Phonak
Phonak
Eleva 311 BTE + CROSLink BTE
Savia 211 BTE + CROSLink BTE
Savia 211 BTE + CROSLink BTE
IQ Quantum CM WLXX ITE to ITE
Mind 440-9 BTE + Wired Satellite Side BTE
Versata M BTE + CROSLink BTE
Eleva 211 BTE + CROSLink BTE
Extra 211 BTE + CROSLink BTE
Valeo 211 BTE + CROSLink BTE
Eleva 211 BTE + CROSLink BTE
Savia 211 BTE + CROSLink BTE
Act II CR BTE to BTE
Eleva 211 BTE + CROSLink BTE
Conversa NT ITE + WiFi Mic ITE
Savia 211 BTE + CROSLink BTE
Nios Micro V BTE + CROSLink BTE
Savia 211 BTE + CROSLink BTE
Eleva 211 BTE + CROSLink BTE
Audeo S Smart V RIC + CROS BTE
Versata P BTE + CROSLink BTE
Audeo S Smart V RIC + CROS BTE
2.4
3.0
18.0
6.4
11.4
11.0
13.3
13.8
10.7
4.3
14.5
6.9
3.9
3.3
11.0
2.1
15.3
4.5
0.7
13.6
0.3
Note: BTE = behind-the-ear; ITE = in-the-ear; RIC = receiver-in-the-canal.
specific frequency channel, which significantly varies by the
spectrum of the noise and speech signal. (John Pumford,
pers. comm.).
Prior to the hearing aid fitting, performance of the
receiver to the ANSI S3.22-1996 standard (American
National Standards Institute [ANSI], 1996) was verified electroacoustically using a Frye© Fonix® 6500-CX
hearing aid analyzer. In addition, the transmitter side
was verified by placing the transmitter at the test point
inside the test box and connecting the receiver side to an
HA-2 coupler placed on top of the test box on a foam
cushion. Then a 70 dB SPL speech-weighted composite
signal was presented in the test box to confirm transmission between the two devices. In addition, the
receiver and transmitter were measured on the
Audioscan® Verifit® Model VF-1 hearing aid analyzer
to ensure that NR was operating correctly (see Fig. 2).
For this measure, the receiver was connected to an
HA-2 coupler and placed at the test point in the test
box. Then “air conditioner” noise was presented at 65 dB
SPL, and the NR settings were measured. For the transmitter side, the receiver was coupled to the HA-2 coupler and held outside, but near, the test box, and the
transmitter was placed at the test point inside the test
box. The air conditioner noise was again presented at
65 dB SPL, and each NR setting was verified. The overall root-mean-square level of NR was calculated from
these measures. As an example, in Figure 2A, the no
NR (upper curve), mild NR (middle curve), and maximum NR (lower curve) conditions overall had a reduction in noise of 0, 4, and 8 dB SPL (see NR box to the far
984
right), respectively, for the receiver, and in Figure 2B a
reduction in noise of 0, 2, and 6 dB SPL, respectively,
for the transmitter. The investigators tested the Tandem
16 BICROS using dual pink noise and the International
Speech Test Signal using a +9 dB SNR to determine that
NR was activated to determine how the presence of speech
affected the activation of NR after the study was complete.
NR was activated on the receiver and transmitter sides at
a +9 dB SNR. The NR decreased output more in the low
frequencies than in the high frequencies. Results revealed
a 0–1 dB SPL decrease in output for the mild and maximum NR compared to no NR and revealed a 1–3 dB SPL
decrease in output for mild NR and 2–5 dB SPL decrease
in output for maximum NR in the low to mid-frequencies
compared to no NR on the receiver and transmitter,
respectively, for a +9 dB SNR.
Each hearing aid was preprogrammed with three
programs in a randomized order with (a) no NR, (b) mild
NR, and (c) maximum NR to examine the effects of the
extreme ends of the available NR settings. The NR
“aggressiveness” of both the receiver and transmitter
sides of the Tandem 16 can only be programmed equally
(e.g., both have mild NR). The features of phase canceller (feedback manager) and datalogging remained
enabled, but Anti-Shock, Wind Noise Manager, AutoPro 3 (automatic program), and Speech Enhancement
LD were disabled. All three programs were programmed
the same and had the same features activated, with the
only difference being the magnitude of NR. If the participant qualified for the study after the audiometric
evaluation, he or she was fit with the Tandem 16
Noise Reduction in BICROS/Oeding and Valente
Figure 2. Example of NR testing using the Verifit hearing aid
analyzer on the receiver (A) and transmitter (B) sides using air
conditioner noise presented at 65 dB SPL. In both A and B, the
upper curve represents no NR, the middle curve mild NR, and
the lower curve maximum NR. Overall NR for each condition is
reported in the box to the right.
BICROS. If the participant’s earmolds provided a poor
fit, earmold impressions were made to order new earmolds, and the participant returned in 2 wk for the hearing
aid fitting. Otherwise, if the participant’s earmolds were
deemed appropriate, he or she was fit at the initial visit.
First, a feedback test was performed followed by the
transmission optimization test, which was completed
using the fitting software per manufacturer’s instructions to ensure the receiver and transmitter communication was optimal. Prior to real-ear verification, the
National Acoustic Laboratories’ Nonlinear version 1
prescriptive target (NAL-NL1; Byrne et al, 2001) was
corrected for 16 channels and 0° loudspeaker placement
using the corrections available in the Frye 8000. This
corrected target was then manually entered into the
target menu on a Frye 6500 hearing aid analyzer.
The Tandem 16 BICROS was fit using a Frye 6500 hearing aid analyzer with real-ear insertion gain (REIG)
measures using the corrected NAL-NL1 prescriptive
target (Fig. 3). The features were left activated in the
hearing aid and the signal, 65 dB SPL speech-weighted
composite noise, was very quickly turned on and off to
prevent NR from attenuating the signal.
The goal of the fitting was to adjust the REIG to
match the NAL-NL1 target within ±5 dB to 2000 Hz
and ±10 dB to 4000 Hz. As can be seen in Figure 3, mean
measured REIG at seven discrete octave and interoctave frequencies from 500 to 8000 Hz were within ±5
dB, except for 6000 Hz, which was within ±10 dB.
The participant’s own BICROS or monaural hearing
aid (for three participants) REIG was also verified via
real-ear measures using the NAL-NL1 target corrected
for the number of channels in the respective hearing aid
(6 to 20 channels) and azimuth (0°) using a 65 dB SPL
speech-weighted composite noise (Fig. 4). This measure
was completed on 16 participants because two participants’ BICROS hearing aids were being repaired, and
three participants did not bring their own BICROS to
the clinic to complete testing. All features remained
activated, and the signal was again quickly turned on
and off to prevent an attenuation of the signal. The
mean participant’s own BICROS or monaural hearing
aid (#5 dB at 500, 2000, and 3000 Hz and #10 dB
at 1000 and 4000–8000 Hz) did not match the NALNL1 target as closely as the Tandem 16 (#5 dB at
500–4000 and at 8000 Hz and #10 dB at 6000 Hz).
The differences may be due to subtle decreases in hearing
thresholds over time and not compensating for these
changes in hearing levels or programming limitations
of the hearing aid. The mean measured REIG is, however,
within ±10 dB at all seven discrete octave and interoctave
test frequencies.
The performance of the transmitter microphone on
the Tandem 16 was verified by performing a real-ear
aided response (REAR) measurement using a 65 dB
SPL speech-weighted composite noise at 90° to the side
of the better ear. Then a second measure was completed
at 270° on the transmitter side to verify that sound was
being transmitted from the side of the poorer ear to the
side of the better ear (see Pumford, 2005, for more
details). Finally, loudness judgments were completed
for a speech-weighted composite noise at 50 (“soft”),
65 (“comfortable”), and 80 dB SPL (“loud, but OK”),
and adjustments, if necessary, were made to the overall
output based on participant report.
Each participant was counseled on how to use the volume controls on the receiver and transmitter sides, use
the program button, open and close the battery doors,
change batteries, and place the hearing aids in his or
her ears. Each participant was encouraged to press
the program button to change the three programs in
noisy listening environments to determine which program(s) he or she preferred. Datalogging was examined
at the final visit, and only a small number of participants switched between programs, while the majority
remained in Program 1 for the 4 wk. A follow-up phone
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Journal of the American Academy of Audiology/Volume 24, Number 10, 2013
Figure 3. Mean REIG and ±1 SD for the prescribed NAL-NL1
target, measured REIG, and difference for the Tandem 16
BICROS for a 65 dB SPL speech-weighted composite noise from
500 to 8000 Hz at seven discrete octave and interoctave frequencies. Note that the NAL-NL1 target was corrected for the number
of channels (16) in the hearing aid and azimuth (0°).
call was completed at 1 wk to ensure each participant
was performing well with the Tandem 16. If fine-tuning
was needed, the participant returned for fine-tuning
and wore the Tandem 16 for 4 wk before returning
for final testing; otherwise participants returned in
3 wk after the phone call for final testing. Prior to final
testing, the Tandem 16 BICROS was dehumidified, a
new battery was inserted in the receiver and transmitter, and electroacoustic analysis and NR performance
were measured and compared with initial analyses to
ensure the Tandem 16 BICROS was working properly.
R-Space System
The R-Space system consists of eight Boston Acoustics
CR-65 loudspeakers in a circular array, with each loudspeaker separated by 45° in a 1.97 × 2.54 × 2.73 m double-walled sound suite (volume = 14.05 m3) with a
reported reverberation time of 0.19 sec (Industrial Acoustics Company, pers. comm.). The radius of the circle was 2
ft plus the depth of the loudspeaker (200 mm) (see Oeding
et al, 2010, for a detailed description of the R-Space system, calibration, and recording of the uncorrelated restaurant noise). HINT sentences were presented from the
front loudspeaker, and uncorrelated Lou Malnati’s restaurant noise was presented from all eight loudspeakers to
create a diffuse noise sound field. A lavaliere microphone
was placed near the participant so the examiner could
hear the participant’s responses. The R-Space system
was calibrated each day prior to final testing.
Hearing in Noise Test (HINT)
The HINT consists of 250 sentences (25 lists of 10 sentences per list) read by a male speaker that are of approximately equal length (six to eight syllables) and difficulty
(first-grade reading level) and have been digitally
986
Figure 4. Mean REIG and ±1 SD for the prescribed NAL-NL1
target, measured REIG, and difference for the participant’s own
BICROS for a 65 dB SPL speech weighted composite noise from
500 to 8000 Hz at seven discrete octave and interoctave frequencies.
Note that the NAL-NL1 target was corrected for the number of
channels in the respective hearing aid (6 to 20 channels) and azimuth (0°), and this measure was only completed for 16 participants.
recorded for standardized presentation. The first 240
sentences (24 lists) were utilized in this study. The HINT
uses an adaptive step procedure to estimate the RTS at
which sentences, embedded in uncorrelated restaurant
noise, could be repeated correctly 50% of the time. The
administration of the HINT required presentation of four
lists (40 sentences) for each of the four experimental conditions (for a detailed description of the procedures for
administering the HINT, see Oeding et al, 2010).
A randomized block repeated measures design was
utilized in which each participant was tested with each
of the four treatment levels of unaided, no NR, mild NR,
and maximum NR. The Tandem 16 BICROS was placed
in the respective program with the hearing aid off the
participant’s ear, blinding the participant to the current
program of use, and the volume control was rotated to
“three” on the receiver and transmitter sides. Two participants were evaluated with the volume control at
“two and a half” on the transmitter side and “three”
on the receiver side due to loudness discomfort. The four
treatment levels of unaided, no NR, mild NR, and maximum NR were counterbalanced to prevent order effects.
The participant was seated in the center of the R-Space
system facing the front (0°) loudspeaker, and head placement was level with the loudspeakers. Each participant
was instructed to face the dot in the center of the front
loudspeaker throughout the entire test session and told
that sentences would arrive from the front loudspeaker
and 65 dB SPL uncorrelated restaurant noise would
arrive from all eight loudspeakers. Participants were
asked to repeat the sentence exactly as heard and, if
unsure, take a guess. A HINT RTS (in dB) was measured
for each of the four treatment levels and HINT sentence
lists were counterbalanced for each participant. The test
session was approximately 45 min in length. At the end
of the study, participants were compensated $100 for
Noise Reduction in BICROS/Oeding and Valente
participation or had the option to purchase the Tandem
16 BICROS at a significantly reduced cost.
Abbreviated Profile of Hearing Aid
Benefit (APHAB)
Abbreviated Profile of Hearing Aid
Benefit (APHAB)
The mean unaided and aided Tandem 16 problem
scores, the resulting benefit scores, and ±1 SD are
reported in Figure 6 for the EC, BN, and RV subscales.
The results on the AV subscale were not included
because this subscale has been reported not to be as
clinically relevant as the EC, BN, and RV subscales
(Cox and Alexander, 1995). A repeated measures
ANOVA was performed for each subscale comparing
unaided and aided (Tandem 16) problem scores. Results
revealed significant differences between unaided and
aided problem scores for the EC (F(2, 40) = 30.6, p <
0.001), BN (F(2, 40) = 34.4, p < 0.001), and RV (F(2,
40) = 68.2, p < 0.001) subscales.
Participants’ perceived improved mean benefit with
the Tandem 16 for the EC (Mean = 30.9%; SD =
21.5%), BN (Mean = 32.4%; SD = 24.6%), and RV
(Mean = 40.7%; SD = 21.8%) subscales. Bonferroniadjusted pairwise comparisons revealed significant improved perceived performance with the Tandem 16 for
the EC (p < 0.001), BN (p < 0.001), and RV (p < 0.001)
subscales. Therefore, the null hypothesis stated previously was rejected and the alternative hypothesis that significant differences exist between unaided and aided
problem scores on the EC, BN, and RV subscales of the
APHAB was accepted. According to Cox and Alexander
(1995), the benefit scores are also clinically significant
for a 90% critical difference.
The APHAB is a questionnaire that measures a participant’s perception of how well he or she performs in
24 listening environments divided into four subscales
(six listening environments per subscale): EC, BN, RV,
and Aversiveness of Sounds (AV). A participant rates
how much difficulty he or she has in each environment
on a seven-point assessment scale when unaided and
aided. The resulting aided problem score (in %) is subtracted from the unaided problem score to determine
the magnitude of benefit the participant perceives from
the aided condition compared to unaided. The APHAB
was completed at the final visit via interview to prevent
confusion for the unaided and aided listening conditions.
RESULTS
Hearing in Noise Test (HINT)
The mean RTS (dB) and ±1 SD for each listening condition (unaided, no NR, mild NR, and maximum NR) is
reported in Figure 5. A higher RTS indicates poorer performance as the participant required a higher SNR to
repeat the sentences correctly 50% of the time. Minimal
differences in mean RTS were noted between the four listening conditions with a mean RTS of 8.0 dB (SD = 3.8 dB)
for the unaided condition, a mean of 9.4 dB (SD = 2.5 dB)
for no NR, a mean of 9.2 dB (SD = 3.0 dB) for mild NR, and
a mean of 8.6 dB (SD = 3.0 dB) for maximum NR.
A one-way repeated measures analysis of variance
(ANOVA) was completed to determine if significant differences were present between the four listening conditions.
Results revealed no significant differences between unaided, no NR, mild NR, and maximum NR (F(3, 60) =
2.5, p = 0.07). Therefore, the null hypothesis was accepted.
Figure 5. Mean RTS (in dB) and ±1 SD for each listening condition. Note that a higher RTS indicates poorer performance in background noise.
DISCUSSION
R
esults from the present study revealed no significant differences between unaided, no NR, mild NR,
and maximum NR. Unaided performance provided the
Figure 6. Mean problem scores and the resulting benefit scores
(%) and ±1 SD for the EC, BN, and RV APHAB subscales for the
unaided and aided listening conditions. A higher problem score
indicates more perceived problems, and a positive benefit score
indicates improved perceived benefit for the Tandem 16. Three
asterisks indicates p < 0.001.
987
Journal of the American Academy of Audiology/Volume 24, Number 10, 2013
lowest (best) RTS (Mean = 8.0 dB; SD = 3.8 dB), followed
by maximum NR (Mean = 8.6 dB; SD = 3.0 dB), mild NR
(Mean = 9.2 dB; SD = 3.0 dB), and no NR (Mean = 9.4 dB;
SD = 2.5 dB). Maximum NR resulted in a mean RTS
improvement of 0.8 dB compared to when NR was deactivated, which was not significant. This agrees with previous studies (Boymans and Dreschler, 2000; Alcantara
et al, 2003; Bentler, 2005; Ricketts and Hornsby, 2005;
Nordrum et al, 2006; Bentler et al, 2008) that examined
the effectiveness of NR in conventional hearing aids
using different NR algorithms in various loudspeaker
arrays. These arrays included speech and noise from
0° (Alcantara et al, 2003), speech from 0° and noise
from 180° (Bentler et al, 2008), speech from 0° and noise
from 90, 180, and 270° (Boymans and Dreschler, 2000;
Nordrum et al, 2006), and speech from 0° and noise from
60, 160, 180, and 300° (Ricketts and Hornsby, 2005).
Results revealed no significant differences when NR
was activated or deactivated (Boymans and Dreschler,
2000; Alcantara et al, 2003; Bentler, 2005; Ricketts and
Hornsby, 2005; Nordrum et al, 2006; Bentler et al,
2008). Results from studies that examined differences
in SNR when the NR was activated or deactivated
reported mean changes of approximately 22 to 2 dB,
with a negative SNR indicating better performance
with NR deactivated (Boymans and Dreschler, 2000;
Alcantara et al, 2003; Nordrum et al, 2006; Bentler
et al, 2008). The results from the current study are in
agreement with the middle of this range.
When the results of the current study are compared
to previous studies investigating CROS amplification, it
is interesting to note differences between CROS and
unaided performance compared to differences between
the Tandem 16 BICROS and unaided. Results from previous studies examining CROS and unaided with
speech from 0° and noise on the transmitter side reveal
better unaided performance compared to CROS by an
average of 2.5 to 4.1 dB SNR (Niparko et al, 2003;
Hol et al, 2004, 2005; Lin et al, 2006). In the current
study, however, participants, on average, performed
equally well in either of the three aided BICROS listening conditions relative to unaided listening, while using
a more difficult diffuse listening environment. That is,
participants in the current study performed better
when compared to previous studies using CROS amplification considering the listening environment in the
current study was considerably more difficult and
results of the three aided conditions were not significantly poorer than unaided.
The differences, however, between the results from
the current study and results from previous studies
are difficult to assess due to variations in methodology
(differences in speech materials, loudspeaker arrangements, etc.), but it can be hypothesized why the results
were different. One significant difference between the
current study and previous studies investigating CROS
988
amplification is the degree of hearing loss in the better
ear. That is, participants using CROS have normal or
near normal hearing in the better ear, while BICROS
participants have poorer hearing in the better ear. This
results in CROS participants having lower (better)
unaided SNRs than participants using BICROS. This
better SNR for CROS participants will result in greater
differences between unaided and aided performance
than BICROS participants who, due to the greater
hearing loss in the better ear, will result in a smaller
difference between unaided and aided performance.
Another difference involves the fitting and verification
of hearing aid performance. Past studies did not report
real-ear measures of CROS performance; therefore, the
validity of the hearing aid fit cannot be determined.
Another possibility are differences in hearing aid technology (ability to amplify soft speech; quality of signal
from transmitter; etc.) that were not examined in this
study.
While the findings of the current study did not reveal
objective benefit, subjective preference was reported.
The mean APHAB benefit score on the EC, BN, and
RV subscales revealed that the Tandem 16 was statistically and clinically better than unaided. Several studies
have examined APHAB problem and benefit scores of
CROS hearing aids (Bosman et al, 2003; Niparko
et al, 2003; Wazen et al, 2003; Hol et al, 2004, 2005).
These studies reported unaided problem scores of
16.7–29.0% for EC, 67.6–74.0% for BN, and 37.7–
50.0% for RV, and CROS aided problem scores of
12.0–20.0% for EC, 48.0–56.0% for BN, and 30.5–
40.0% for RV (Bosman et al, 2003; Hol et al, 2004,
2005). Unaided problem scores from the current study
were close to the high end of the range or greater for the
EC (46.0%), BN (71.8%), and RV (70.8%) subscales,
which is probably related to the greater difficulty due
to greater hearing loss in the better ear compared to
normal or near normal hearing for CROS users. Aided
problem scores for the Tandem 16 were 15.1% for EC,
38.7% for BN, and 30.1% for RV. Relative to past CROS
studies, the average aided EC problem score is similar
to the average problem score reported for CROS; the
average BN problem score is significantly lower than
the average problem score reported for CROS; and
the average RV problem score in the current study is
on the lower end reported for CROS. This indicates
that BICROS aided problem scores were similar to or
slightly better than previous CROS studies. This is
promising as this indicates that BICROS participants
achieve perceived performance in the real world that
is equal to or slightly better than CROS users that have
normal or near normal hearing in the better ear. Due to
the higher problem scores for unaided and essentially
equal or slightly improved aided problem scores, benefit scores were greater for BICROS participants in the
current study (EC = 32.4%; BN = 32.4%; RV = 40.7%)
Noise Reduction in BICROS/Oeding and Valente
than CROS users (EC = 0.6–7.6%; BN = 5.9–21.1%; RV =
2.5–9.6%) in past studies (Bosman et al, 2003; Niparko
et al, 2003; Wazen et al, 2003; Hol et al, 2004, 2005). One
reason for the slightly better benefit scores reported in
the current study (Fig. 6) may be related to the verification of the Tandem 16 BICROS, which may have led
to improved speech recognition because past studies
examining CROS amplification did not verify the fitting
using real-ear measures.
A second reason for the higher (better) mean aided
problem scores may be the improved signal processing
of the Tandem 16 BICROS compared to past technology
that was not examined in this study (improved feedback
management, NR, amplification of soft speech, improved
programming capabilities, etc.). Hill et al (2006) evaluated participant satisfaction with recent CROS (wired)
and BICROS amplification (both wired and wireless
models) via a proprietary questionnaire investigating
satisfaction with the participant’s device. Of the 91 participants, 61 retained his or her device (67%). While Hill
et al (2006) did not specify the models of the newer technology or whether the devices were fit using real-ear
measures, the acceptance rate was higher than those
reported in the past (anecdotally, in the clinic of the
authors, the acceptance rate for CROS in the past was
z10%) (Valente, 2007). Another reason for perceived
improvement could be the participant’s ability to control
the volume independently on the receiver and transmitter sides, allowing the user to decrease unwanted noise
from the transmitter side, which was mentioned by several participants
While it is possible to conclude that the lack of agreement between the objective measure (i.e., no improvement in performance for the BICROS with NR on or
off) and the subjective measure (preference, as measured by the APHAB) is exclusively related to the Hawthorne or placebo effect (Bentler et al, 2003; Dawes et al,
2011), an alternative explanation might help explain
this seemingly contradictory finding. The lack of agreement between objective and subjective measures has a
long history when investigating hearing aid performance (Valente et al, 1998; Cord et al, 2000; Hallgren
et al, 2005; Ricketts and Hornsby, 2005; Oeding
and Valente, 2013). Consider for this study, for which
the participant wore the experimental hearing aid for
4 wk and the objective measures were completed in
approximately 1 hr, the average result revealed no significant differences in noise between NR on or off. As
stated earlier, this is not a novel finding and has been
reported numerous times in the past. The reader, however, needs to keep in mind that each participant wore
the experimental hearing aids for 4 wk. To globally conclude that the preference for the experimental device
was exclusively related to the placebo effect might, in
the opinion of the authors, be a little shortsighted. It
is possible that a participants’ subjective preference
for the experimental device was not at all related to performance in noise as these were experienced users and
probably already have grown to not expect improvement of recognizing speech in noise (Kochkin, 2000;
Kochkin, 2002a, 2002b). Rather, other untested factors
provided by the Tandem BICROS during the 4 wk in
which the participants used the aids may be of greater
importance to the participant. For example, it is possible that the Tandem 16 BICROS was less noisy; allowed
the participant to better hear his or her spouse, friends,
or grandchildren; had greater flexibility to control the
volume on each side; provided a smoother frequency
response, wider bandwidth, improved feedback management, improved sound quality, “naturalness” of sound,
greater audibility (Tandem providing improved REIG
of 5.4 dB at 1000 Hz, 4.5 dB at 3000 Hz, and 8.2 dB
at 4000 Hz) as reported in Figures 3 and 4, and improved
ease of listening; and so on. That is, it is possible that
the seemingly contradictory finding between objective
and subjective measures may not be exclusively related
to the dependent variable (differences in performance
for speech in noise) but may be related in part to other
subjective judgments not evaluated in this study. Also,
it is possible that the outcome measures used to assess
differences were not sufficiently sensitive to assess
additional factors that may be important to the typical
BICROS user.
Since the start of this study, another BICROS system was introduced that for the first time allows the
directional microphone to be activated when the hearing aid is in the BICROS mode. Williams et al (2012)
compared the new Phonak BICROS system to participants’ current BICROS using the Words-in-Noise
(WIN) test (Wilson, 2003) and the Speech, Spatial,
and Qualities of Hearing Questionnaire (SSQ) (Gatehouse and Noble, 2004). Unaided and both BICROS
systems were measured using monosyllabic words
from 0° and multitalker babble from 180° and with
the signal presented to the poorer ear and noise to
the better ear and vice versa for both BICROS systems.
A repeated measures ANOVA revealed a significant
main effect ( p < 0.001), but post hoc analysis did not
reveal any significant differences between the Phonak
and the participants’ BICROS ( p > 0.05). While the
Phonak BICROS had better SNR thresholds, Williams
et al (2012) attributes this to the investigators’ inability to match the NAL-NL1 target with the participants’
BICROS due to less programming ability compared to
the Phonak BICROS. The SSQ revealed significant
improvement for the Phonak BICROS for several subscales in the speech, spatial, and quality domains.
These results are similar to the current study as the
objective results were not significant, but the subjective results were. The speech recognition results also
contrast with past studies examining directional
microphones in conventional hearing aids.
989
Journal of the American Academy of Audiology/Volume 24, Number 10, 2013
When past research reporting the effectiveness of NR
upon speech recognition in noise is examined, studies
evaluating the efficacy of NR and directional microphones consistently report an improved SNR with the
use of a directional microphone alone compared to
NR alone with little added benefit when a directional
microphone and NR are combined (Boymans and
Dreschler, 2000; Ricketts and Hornsby, 2005; Nordrum
et al, 2006). In two studies, SNR differences between a
directional microphone alone, NR alone, and directional
microphone plus NR were examined (Boymans and
Dreschler, 2000; Nordrum et al, 2006) and reported
an average improved SNR of 3.3 to 4.0 dB for the directional microphone alone compared to NR alone and an
improvement of 20.2 to 0.2 dB for the directional microphone compared to the directional microphone plus NR
(a negative value indicates improved performance for
the directional microphone plus NR condition). Therefore, based on these previous studies, the addition of a
directional microphone could improve SNR, while the
addition of NR could improve perceived comfort in noise.
Based on the results of the current study and previous
studies, it is felt that manufacturers of CROS/BICROS
hearing aids should consider offering independent volume controls on the receiver and transmitter sides,
NR on both sides for potentially greater comfort in noisy
listening environments, and directional microphones on
the receiver and transmitter sides for potentially improved performance in noise.
CONCLUSIONS
R
esults from the present study did not reveal significant differences in RTS between unaided, no NR,
mild NR, or maximum NR on the receiver and transmitter sides for the Tandem 16 BICROS while measuring
speech recognition in diffuse noise. Participants, however,
perceived statistically and clinically significant benefit
with the Tandem 16 compared to unaided performance
on the EC, BN, and RV subscales of the APHAB. At
the final visit seven participants purchased the Tandem
16, three preferred the Tandem 16 but did not purchase
the Tandem 16 (major reasons cited were due to a recent
purchase of a new BICROS and cost of the Tandem 16),
and 11 participants preferred their current hearing aid.
Additional features, such as independent volume controls
on the receiver and transmitter sides, and directional
microphones included on the receiver and transmitter
sides need to be considered by hearing aid manufacturers
and evaluated to determine if adults with ASNHL can
obtain an improved SNR, similar to adults with bilateral
SNHL. BICROS technology has been shown to overcome
the head shadow effect and provide benefit for speech on
the side of the poorer ear. The next step is to investigate
solutions, such as those described above, to help patients
achieve greater speech recognition in noise.
990
Acknowledgments. Thanks to Brian Taylor, Au.D., and
John Pumford, Au.D., at Unitron for their support of this
research study and comments/suggestions on earlier drafts
of the manuscript, and to Michael Strube, Ph.D., professor
of psychology at Washington University in St. Louis, for completing the statistical analysis and providing advice on appropriate interpretation of the data.
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