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`International Journal of Audiology
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` ISSN: 1499-2027 (Print) 1708-8186 (Online) Journal homepage: http://www.tandfonline.com/loi/iija20
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`Variation in preferred gain with experience for
`(cid:36)(cid:8)(cid:10)(cid:9)(cid:11)(cid:6)(cid:19)(cid:4)(cid:10)(cid:11)(cid:18)(cid:3)(cid:15)(cid:46)(cid:8)(cid:9)(cid:46)
`hearing-aid users
`
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`Gitte Keidser, Anna O'Brien, Lyndal Carter, Margot McLelland & Ingrid Yeend
`
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`To cite this article: Gitte Keidser, Anna O'Brien, Lyndal Carter, Margot McLelland & Ingrid
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`Yeend (2008) Variation in preferred gain with experience for hearing-aid users, International
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`Journal of Audiology, 47:10, 621-635, DOI: 10.1080/149920208021 78722
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`To link to this article: http://dx.doi.org/10.1080/14992020802178722
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`ati Published online: 07 Jul 2009.
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`HIMPP 1013
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`

`

`Original Article
`
`International Journal of Audiology 2008; 47:621 635
`
`Variation in preferred gain with experience for
`hearing-aid users
`
`Abstract
`This study aimed to determine whether gain adaptation
`occurs, and at which frequency bands, among new
`hearing aid (HA) users. Fifty new and 26 experienced
`HA users were fitted with three listening programs (NAL-
`NL1 and NAL-NL1 with low- and high-frequency cuts)
`in the same hearing instrument family. Real-life gain
`preferences and comfortable loudness levels were mea-
`sured one, four, and 13 months post-fitting for the new
`HA users, and one month post-fitting for the experienced
`HA users. Relative to experienced HA users, new HA
`users preferred progressively less overall gain than pre-
`scribed as the hearing loss became more severe. Gain
`adaptation occurred in new HA users with greater
`hearing loss, but was not complete 13 months post-
`fitting, and was not explained by changes in loudness
`perception. Preferences for a high-frequency gain cut by
`half of all study participants could not be predicted from
`audiological data. Gain adaptation management is re-
`commended for new HA users with more than a mild
`hearing loss.
`
`Sumario
`El propo´ sito del estudio fue determinar si es que ocurre la
`adaptacio´ n a la ganancia y en cua´les bandas de frecuen-
`cia, entre usuarios nuevos de un auxiliar auditivo (HA).
`Cincuenta nuevos usuarios de HA y 26 con experiencia
`fueron adaptados con tres programas diferentes (NAL,
`NL1 y NAL-NL1 con cortes de frecuencia altos y bajos)
`con aparatos de la misma familia. Se midieron las
`preferencias de ganancia en la vida real y los niveles de
`confortabilidad a los cuatro y a los 13 meses despue´s de la
`adaptacio´ n en los nuevos usuarios de HA y un mes
`despue´s de la adaptacio´ n en los usuarios experimentados.
`Con respecto a los usuarios experimentados, los nuevos
`usuarios prefirieron progresivamente una ganancia menor
`que la prescrita conforme la hipoacusia era ma´s severa.
`La adaptacio´ n a la ganancia ocurrio´ en los nuevos
`usuarios de HA con mayor hipoacusia, pero aun no era
`completa a los 13 meses despue´s de la adaptacio´ n y no se
`explicaba a partir de los cambios en la percepcio´ n de la
`intensidad. No fue posible predecir a partir de los datos
`audiolo´gicos, la preferencia por un corte de alta frecuen-
`cia que tuvieron la mitad de los participantes del estudio.
`El manejo de la adaptacio´ n de la ganancia es recomen-
`dado para nuevos usuarios de HA con una pe´rdida
`auditiva mayor a la hipoacusia leve.
`
`Gitte Keidser
`Anna O’Brien
`Lyndal Carter
`Margot McLelland
`Ingrid Yeend
`
`National Acoustic Laboratories,
`Chatswood, Australia
`
`Key Words
`Gain adaptation
`Acclimatization
`Gain preference
`Hearing aid
`Amplification
`Experience
`Loudness
`
`Abbreviations
`4FA: Four-frequency-average
`ABR: Auditory brainstem response
`BTE: Behind-the-ear
`DLI: Discrimination limen for
`intensity
`DSL[i/o]: Desired sensation level
`(input/output)
`EN: Environmental noise
`FAAF: Four-alternative auditory
`feature
`FF: Free field
`HA: Hearing aid
`HFA: High-frequency average
`HFC: High-frequency cut
`HL: Hearing level
`HTL: Hearing threshold level
`ITC: In-the-canal
`ITE: In-the-ear
`LFA: Low-frequency average
`LFC: Low-frequency cut
`NAL: National Acoustic
`Laboratories
`NAL-NL1: National Acoustic
`Laboratories non-linear version 1
`NAL-R: National Acoustic
`Laboratories revised
`PHAP: Profile of hearing-aid
`performance
`REIG: Real-ear insertion gain
`SD: Standard deviation
`SE: Standard error
`SLM: Sound-level meter
`SPL: Sound pressure level
`
`ISSN 1499-2027 print/ISSN 1708-8186 online
`DOI: 10.1080/14992020802178722
`# 2008 British Society of Audiology, International
`Society of Audiology, and Nordic Audiological Society
`
`Received:
`January 16, 2008
`Accepted:
`May 1, 2008
`
`Gitte Keidser
`National Acoustic Laboratories, 126 Greville Street, Chatswood, NSW 2067,
`Australia.
`E-mail: gitte.keidser@nal.gov.au
`
`

`

`VAD: Voice activity detection
`VC: Volume control
`WDRC: Wide dynamic range
`compression
`
`According to clinical anecdotes, new hearing aid (HA) users
`prefer less gain than experienced HA users (e.g. Mueller &
`Powers, 2001; Convery et al, 2005). If this is true, the implication
`is that new HA users will prefer gradually increasing gain after
`fitting. The notion appears plausible given that the onset of a
`hearing loss in many adults happens gradually over time, hence
`the unaided hearing-impaired person has become accustomed to
`listening to surrounding sounds at softer levels than normal.
`When first fitted with a hearing aid, the new user may therefore
`need time to adapt to the higher output levels presented by the
`device.
`In response to the belief that new HA users need time to adapt
`to prescribed gain levels, gain adaptation tools have been
`implemented in some hearing-aid manufacturers’ fitting soft-
`ware. Such tools allow the clinician to select reduced gain levels
`relative to a target before the fitting is verified and validated (e.g.
`Eberwein et al, 2001; Schum, 2001). Over time, the clinician will
`then increase gain in a gradual fashion until the target is reached.
`More recently, hearing devices have been introduced that contain
`a feature that will automatically increase gain over a predeter-
`mined period of time (e.g. Robinson & Verberne, 2003; Schum &
`Beck, 2006).
`(2005) on gain
`A literature review by Convery et al
`preference by new and experienced HA users over time,
`however, found very little support for gain adaptation in new
`HA users. Specifically, data from three studies
`(Cox &
`Alexander, 1992; Horwitz & Turner, 1997; Humes et al,
`2002), that provided gain preferences relative to the NAL-R
`prescription (Byrne & Dillon, 1986) for a total of 98 new and
`77 experienced HA users, suggested that the average difference
`in preferred gain between new and experienced users was no
`more than 2 dB, with new users preferring less gain than
`experienced users. This difference was not statistically signifi-
`cant, nor did it appear to change over a period of up to 12
`months. The trend for new users to prefer slightly less gain
`than experienced HA users was also found by Byrne & Cotton
`(1988) and Marriage et al (2004), both of whom investigated
`the acceptance of prescribed gain among new and experienced
`HA users. In Marriage et al (2004), the 2.6 dB lower gain
`required by new users relative to experienced users to accept
`the hearing-aid fitting was statistically significant. However, it
`should be noted that adjustments to the hearing-aid settings
`were restricted to those necessary for the participants to accept,
`rather than prefer, the fitting. It should also be noted that the
`observed differences in gain preferred by new and experienced
`HA users in the above studies are smaller than the typical gain
`reductions of 5 10 dB introduced in the adaptation managers
`implemented in various fitting software. More recently, a study
`by Smeds et al (2006a, 2006b) compared loudness perception
`and gain preferences of normal-hearing listeners and new and
`experienced HA users in the laboratory and in the field. The
`study found no significant difference in loudness ratings or gain
`preferences between new and experienced HA users.
`
`While the literature on the gain preferred by new and
`experienced HA users shows inconsistent support
`for gain
`adaptation in new HA users, there are strong suggestions that
`some changes do happen in the auditory system as a result of
`wearing hearing aids. Such changes may be referred to as
`acclimatization, of which gain adaptation is one aspect. The
`mechanism of acclimatization may be explained by neural
`plasticity (i.e. a reorganization of the neural maps following
`damage at the peripheral level) in the auditory system. Auditory
`plasticity may occur as a result of the hearing loss, and again
`through rehabilitation with hearing aids when acoustic cues that
`were lost through the acquired hearing loss are reintroduced.
`This theory is based on numerous studies that have demon-
`strated that the representation of acoustic stimuli along the
`auditory pathway can be remodelled by various hearing
`experiences in both animals and humans (e.g. Palmer et al,
`1998; Philibert et al, 2005; Willott, 1996).
`Auditory acclimatization as a result of hearing-aid usage has
`been discussed widely in the literature since Gatehouse (1989)
`reported that unilaterally-fitted listeners, with symmetric bilat-
`eral hearing loss, performed better in a word recognition task
`with their aided ear (tested unaided) at a high intensity level
`(95 dB SPL), and performed better with their unaided ear at a
`lower intensity level (65 dB SPL). Subsequently, the acclimatiza-
`tion effect after hearing-aid fitting has been studied by means of
`changes in (1) speech recognition performance over time
`(e.g. Bentler et al, 1993a; Cox et al, 1996; Gatehouse, 1992,
`1993; Munro & Lutman, 2003; Reber & Kompis, 2005; Saunders
`& Cienkowski, 1997; Silman et al, 1993); (2) subjective ratings of
`benefit or sound quality over time (e.g. Bentler et al, 1993b;
`Ovegard et al, 1997); (3) rated loudness perception or intensity
`discrimination over time (e.g. Olsen et al, 1999; Philibert et al,
`2002; Philibert et al, 2005; Robinson & Gatehouse, 1995, 1996);
`or (4) a combination of some of the above measures (Amorim &
`Almeida, 2007; Cox & Alexander, 1992; Horwitz & Turner, 1997;
`Humes & Wilson, 2003; Humes et al, 2002; Lindley et al, 2000;
`Prates & Iorio, 2006; Yund et al, 2006). Excellent reviews of the
`literature published before 1998 that presented inconsistent
`conclusions, presumably due to procedural variations, are found
`in Turner et al (1996) and Palmer et al (1998). Among the post-
`1998 literature, the findings continue to be inconsistent. How-
`ever, across all the literature acclimatization appears to be more
`evident in objective than subjective measurements of benefit.
`Further, the more recent studies that show evidence of acclima-
`tization seem to lend support to a theory that acclimatization to
`high-level, high-frequency sounds may occur after fitting with
`hearing aids.
`For example, Munro and Lutman (2003) obtained speech
`recognition scores from 16 unilaterally fitted, first-time HA users
`at zero, six, and 12 weeks post-fitting. At each test, speech scores
`were obtained aided and unaided for both ears using three
`presentation levels of speech (55, 62, and 69 dB SPL), and a
`benefit score was calculated by subtracting the unaided score
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`from the aided score. There was a significant improvement in
`benefit score over time for the highest presentation level and for
`the fitted ear that resulted from improved aided scores. It is
`noted that the four-alternative auditory feature (FAAF) test
`(Foster & Haggard, 1987)
`that was used in this study is
`particularly sensitive to high-frequency auditory capabilities. In
`Olsen et al (1999), a categorical
`loudness scaling test was
`administered to 18 full-time HA users (eight fitted unilaterally
`and 10 fitted bilaterally) and 18 non-users. The test was
`administered for each ear unaided at four frequencies (0.5, 1,
`2, and 4 kHz). However, for each listener, only the response for
`one ear and frequency was included in the analysis. The main
`criterion for inclusion in the analysis was that the hearing loss
`was in the range of 50 to 75 dB HL for that frequency. Another
`aim was to balance the frequencies included across the two
`listener groups. A majority of data (75%) included in the analysis
`was measured at the two higher frequencies (2 and 4 kHz) and
`showed that the mean level rated ‘loud’ was significantly higher
`(by 4.5 dB) for the HA users than for the non-users. Data were
`incomplete for the ‘very loud’ category, but the available data
`showed the same tendency as the data for the ‘loud’ category.
`Data for softer loudness categories showed no significant
`differences between groups. Similar results were observed by
`Philibert and colleagues (Philibert et al, 2002, 2005). In both
`studies, listeners completed a categorical loudness scaling test
`and a discrimination limen for intensity (DLI) test using 0.5 and
`2 kHz tones. The DLI test was performed at two intensity levels
`(75 and 95 dB SPL). In the 2002 study, the performance by nine
`long-term bilateral HA users was compared to that of nine non-
`users. The two listener groups were balanced for age, gender, and
`hearing thresholds. Non-users assigned lower intensity levels to
`the same loudness categories than did long-term HA users and
`showed poorer DLI performance. However, significant differ-
`ences between groups were only found for the loudness percep-
`tion task at 2 kHz and the differences were more prominent for
`the category ‘OK’ and louder. In the 2005 study, eight new
`bilaterally fitted HA users were tested at one, three, and six
`months post-fitting. The authors found changes in loudness
`perception over time for the highest level and highest frequency.
`In addition, the auditory brainstem responses (ABRs) were
`measured on the eight participants in the 2005 study, and over
`time there was a shortening of the wave V latency in the right ear,
`suggesting that a peripheral auditory system modification was
`induced by the hearing aid. According to Yund et al (2006),
`acclimatization is more likely in new HA users after fitting with
`multichannel wide dynamic range compression (WDRC) than
`linear amplification. Over a period of 32 weeks, new HA users
`fitted with WDRC showed a significant improvement in benefit
`scores obtained with a nonsense syllable test whether tested with
`WDRC or linear amplification, while new HA users fitted with
`linear amplification showed no change in benefit with either
`signal processing strategy relative to unaided performance. After
`32 weeks, the two listener groups switched signal processing
`strategies. Although there was a small but significant improve-
`ment in aided performance from week 32 to week 40 for both
`listener groups, the magnitude of the improvements was much
`smaller than that seen for the initial WDRC experience. The
`authors suggest that the difference in performance is caused by
`
`multichannel WDRC processing more effectively bringing the
`range of speech frequencies and intensities into the reduced
`dynamic range of the impaired ear.
`In contrast, an investigation of the acclimatization effect in
`twenty-three first-time HA users who were bilaterally fitted using
`one of three different fitting protocols found an improvement
`over time in both unaided and aided speech recognition scores
`for a presentation level of 50 dB SPL (Reber & Kompis, 2005).
`Interpretation of data obtained at two higher presentation levels
`(65 and 80 dB SPL) were complicated by ceiling effects in both
`the aided and unaided data. Data were collected at zero weeks,
`two weeks, and six months post-fitting, during which time there
`was little variation in the listeners’ selected insertion gain. A
`training effect was also ruled out by the authors because the
`improvement was greater in the aided than in the unaided
`condition. Three case reports presented by Lindley et al (2000)
`demonstrated different levels of acclimatization to hearing-aid
`settings according to categorical loudness ratings and profile of
`hearing-aid performance (PHAP) subscale scores for environ-
`mental noise (EN) measured over a two-month period. While the
`participant who demonstrated the greatest and most systematic
`amount of acclimatization (i.e. the need for a louder level to
`reach the same loudness category and the demonstration of
`reduced handicap over time) had a mild to moderate, flat
`hearing loss, many of the participants who demonstrated little or
`no acclimatization had moderate to moderately severe high-
`frequency hearing loss (2 kHz). Finally, in a longitudinal study
`(Humes et al, 2002; Humes & Wilson, 2003), little evidence for
`acclimatization was found in bilaterally fitted HA users based on
`subjective and objective measurements of benefit obtained from
`outcome measures and speech recognition scores after one, two,
`and three years of hearing-aid usage. The trend for acclimatiza-
`tion, however, varied greatly among individual participants.
`The studies that have found evidence for acclimatization
`suggest that hearing-aid fitting may induce functional plasticity
`in the auditory system. One explanation for the varied outcomes
`may be the extent to which plasticity occurs in the individual and
`how quickly it occurs. For example, it has been speculated that
`neural plasticity in the auditory system is more likely to happen
`when the hearing loss is severe. This is because individuals with
`severe hearing loss are more likely to miss out on some acoustic
`information, such as portions of the speech signal, that is
`reintroduced when fitted with a hearing aid (Palmer et al, 1998).
`Speech recognition measurements obtained over
`time for
`listeners with severe or profound hearing loss after they switched
`from linear to non-linear amplification support this hypothesis
`(Flynn et al, 2004; Kuk et al, 2003).
`Overall, the issue of auditory acclimatization in hearing-aid
`rehabilitation has not been completely resolved. In terms of the
`overall negative outcome of past studies on the gain preferred by
`new and experienced HA users, it was noted by Convery et al
`(2005) that interpretation of the existing data was somewhat
`complicated. First, all but one of the reviewed studies did not
`directly aim to investigate the issue of gain adaptation in new
`HA users, and therefore the measured gain preferences were not
`well controlled for such confounding factors as degree of hearing
`loss and prescriptive target. Second, procedures differed greatly
`across the reviewed studies. In particular, the definition of ‘new’
`
`Variation in preferred gain with experience
`for hearing-aid users
`
`Keidser/O’Brien/Carter/McLelland/
`Yeend
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`

`and ‘experienced’ HA users and the goal of the fitting rationale
`varied. The use of different types of hearing aids within and
`across studies and the different audiological profiles of new and
`experienced HA users may also have had an effect on the
`findings. Convery et al (2005) therefore suggested that there was
`still a need for future studies that more specifically addressed the
`question about gain adaptation in new HA users, and that better
`controlled all relevant parameters. Further, gain preferences
`were often measured in terms of changes made to overall gain
`while data on auditory acclimatization suggest that the effect
`may be limited to high-frequency sounds.
`The aim of this study was to investigate gain preferences
`overall and across the low and high frequencies over time in a
`large clinical population of new HA users. All participants were
`fitted with hearing aids from the same family. The hearing aids
`contained three listening programs: the NAL-NL1 prescription
`(Dillon, 1999), the NAL-NL1 prescription with a high-frequency
`cut, and, where possible, the NAL-NL1 prescription with a low-
`frequency cut. Gain preferences in everyday listening situations
`were monitored about one month, four months, and 13 months
`post-fitting. At these appointments, loudness perception was
`also measured. A control group comprising HA users with at
`least three years of experience with amplification was fitted with
`the same test device with the same three programs. The control
`group was subjected to the same test battery one month post-
`fitting. These data served as a reference for the measurements
`obtained from the new HA users over time. The specific research
`questions addressed were:
`
`1. Do gain preferences for medium intensity levels of new and
`experienced HA users differ overall (averaged across 0.5, 1, 2,
`and 4 kHz), or only in the low (averaged across 0.25, 0.5, and
`1 kHz), or the high (averaged across 2, 3, and 4 kHz)
`frequencies?
`If gain preferences for medium intensity levels differ between
`new and experienced HA users, at what time post-fitting do
`the gain preferences of these groups converge?
`If preferred gain does change post-fitting, is it related to
`changes in perceived loudness?
`
`2.
`
`3.
`
`withdrew before the first test appointment after fitting, and three
`did not attend the final test appointment scheduled 13 months
`later. Reasons for withdrawal in the early stages of the study
`included dissatisfaction with amplification, poor health, and
`management problems. A further four new HA users were
`discarded from the data analysis. One of these participants had
`the test settings programmed in different orders in each ear,
`while another was fitted with unacceptably low gain relative to
`the prescribed target. The last two participants displayed shifts
`in the average threshold data measured across 0.5, 1, 2, and
`4 kHz of 10 dB, including a shift of 20 dB at a single frequency,
`between test appointments. All 26 recruited participants with
`hearing-aid experience completed the study.
`Table 1 shows an overview of the general profile of the two
`participant groups. The four-frequency-average (4FA) hearing
`threshold level (HTL) was measured across 0.5, 1, 2, and 4 kHz;
`the low-frequency-average (LFA) HTL was measured across
`0.25, 0.5, and 1 kHz; and the high-frequency-average (HFA)
`HTL was measured across 2, 3, and 4 kHz. The slope was
`calculated as the difference between the HFA and LFA HTL.
`Only data from the fitted ear are reported for unilaterally fitted
`participants. For bilaterally fitted participants, data were aver-
`aged across ears. It is apparent from Table 1 that, on average, the
`range of hearing loss was milder among the new than among the
`experienced HA users. Although the aim was to match the
`audiometric profile between the two participant groups,
`it
`proved too difficult to find experienced HA users with mild
`hearing loss similar to some of
`the new HA users. The
`distribution of participants in the two groups across degree
`and configuration of hearing loss
`is
`shown in Table 2.
`Specifically, new users had milder, flatter hearing loss than
`experienced HA users, and more experienced users had steeply
`sloping hearing loss. Apart from two new HA users (IP02,
`NA05) who displayed a mixed hearing loss, all the participants
`had a sensorineural hearing loss.
`There was a notable difference in the male/female ratio and
`age between the two groups; the experienced HA user group
`
`The study also addressed how the preferred gain levels for
`medium intensity levels compare with the NAL-NL1 prescrip-
`tion.
`
`Methodology
`
`Participants
`New HA users were recruited and tested at 13 hearing centres
`from the Australian Hearing network (government subsidized
`clients) and at the National Acoustic Laboratories (NAL), while
`all experienced HA users were recruited and tested at NAL.
`Experience was defined as consistent hearing-aid usage (at least
`four hours a day) for at least three years. One new HA user
`(NA02) had worn amplification for three years as a child, but
`not for 27 years prior to recruitment for this study. Another two
`new HA users briefly wore amplification 10 years prior to
`recruitment. One of these participants (NA05) stopped using the
`hearing aid following a tympanoplasty, and the other (NA07)
`stopped using hearing aids due to problems in background noise.
`In all, 76 new HA users were recruited. Nineteen of these
`
`Table 1. An overview of the general profile of the study
`participants.
`
`Parameter
`
`Average experience with
`amplification (years)
`and range
`Male/female ratio (%)
`Average age (years) and
`range
`Bilateral/unilateral
`fit ratio (%)
`Average 4FA HTL
`(dB HL) and range
`Average LFA HTL
`(dB HL) and range
`Average HFA HTL
`(dB HL) and range
`Slope (dB) and range
`
`New users
`(N50)
`
`Experienced users
`(N26)
`
`0
`
`11.2 [3.5, 26]
`
`50/50
`70.3 [33, 87]
`
`73/27
`74.6 [40, 91]
`
`72/28
`
`77/23
`
`39.6 [21.3, 55.0]
`
`46.1 [33.8, 63.1]
`
`28.6 [5.0, 58.3]
`
`33.6 [15.0, 58.3]
`
`49.3 [32.5, 67.5]
`
`57.7 [43.3, 75.0]
`
`20.7 [19.2, 43.3] 24.3 [0.0, 54.2]
`
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`

`Table 2. The percentage of experienced and new (shown in brackets) hearing aid users with various degrees and configurations of
`hearing loss.
`
`Configuration
`
`Flat loss
`(slopeB20 dB HL)
`
`Gently sloping loss
`(20 dB HL 5slopeB40 dB HL)
`
`Steeply sloping loss
`(slope ]40 dB HL)
`
`Degree
`Mild loss (20 dB HL54FAB40 dB HL)
`Moderate loss (40 dB HL54FAB60 dB HL)
`Severe loss (60 dB HL54FAB80 dB HL)
`
`
`(20%)
`35% (22%)
`4%
`
`19% (28%)
`27% (24%)
`
`
`
`
`(2%)
`15% (4%)
`
`
`
`consisted of more males and slightly older participants. In both
`listener groups, about 75% of participants were bilaterally fitted.
`
`Test devices and fitting
`All