a comparison of the benefit provided by well-fit linear hearing aids and instruments with automatic...

666 JSLHR, Volume 40, 666–685, June 1997

Journal of Speech, Language, and Hearing Research

Larry E. HumesDepartment of Speechand Hearing Sciences

Indiana UniversityBloomington

Laurel A. ChristensenDepartment of

Communication DisordersLSU Medical Center

New Orleans, LA

Fred H. BessAndrea Hedley-Williams

Division of Hearing andSpeech Sciences

Vanderbilt UniversitySchool of Medicine

Nashville, TN

In this clinical study, 110 patients seen at three different clinical facilities were fitbinaurally with linear, in-the-canal (ITC) hearing aids. All patients were new hearingaid users. Each of the hearing aids was equipped with an adjustable control thatcould be set by one of the audiologists (Audiologist A) at each site to convert it froma linear instrument to an experimental nonlinear one with automatic reduction oflow-frequency gain at high input levels (or base increase at low levels, BILL). Both thepatient and the audiologist performing the outcome testing at each site (AudiologistB) were blind as to the present setting of the hearing aid. Each participant wasenrolled in the study for a total of 12 weeks, with the hearing aid set to either thelinear or BILL-processing mode of operation for the first 8 weeks and the oppositesetting for a subsequent 4-week period. In summary, this was a prospective, double-blind, crossover study of 110 new hearing-aid users. Outcome measures focused onhearing-aid benefit and included both objective and subjective measures. Objectivemeasures were derived from scores on the Northwestern University Auditory TestNo. 6 (NU-6) and the Connected Speech Test (CST) obtained for all possiblecombinations of two speech presentation levels (60 and 75 dB SPL), two types ofbackground noise (cafeteria noise and multitalker babble), and two signal-to-noiseratios (+5 and +10 dB). Subjective outcome measures included magnitude estima-tion of listening effort (MELE), the abbreviated form of the Hearing Aid PerformanceInventory (HAPI), and estimations of hearing-aid usage based on daily-use logs keptby the participants. All of these measures were used to evaluate the benefit providedby linear amplification and the benefit resulting from the experimental BILL process-ing. Participant preferences for the experimental BILL-processing scheme or linearprocessing were also examined by using a paired-comparison task at the end of thestudy. Results were analyzed separately for three subgroups of patients (mild,moderate, severe) formed on the basis of their average hearing loss at 500, 1000,2000, and 4000 Hz. In all three subgroups, significant improvement in performancewas observed for linear amplification and for BILL processing when compared tounaided performance. There were no significant differences in aided performance,however, between linear processing and the experimental BILL processing.

KEY WORDS: hearing aids, benefit, linear processing, BILL-processing, speechunderstanding in noise

A Comparison of the BenefitProvided by Well-Fit LinearHearing Aids and InstrumentsWith Automatic Reductions ofLow-Frequency Gain

JSLHR, Volume 40, 666–685, June 1997

O ther than the obvious effect of reduced audibility of conversa-tional level speech, it has long been observed that sensorineuralhearing loss interferes with communication in noisy backgrounds.

666 Journal of Speech, Language, and Hearing Research 1092-4388/97/4003-0666 ©1997, American Speech-Language-Hearing Association

Humes: Benefit From Linear Hearing Aids 667


the past several decades, there have been no compre-hensive, large-scale, prospective clinical studies of thebenefits provided by such instruments. Such informa-tion is critically important as alternatives to linear am-plification, such as BILL-processing, multichannel com-pression, and wide-dynamic-range compression, aredeveloped and evaluated. When studies have been con-ducted comparing linear and nonlinear systems, it hastypically been the case that the hearing aids under in-vestigation differ in more than just their linearity. Inview of the foregoing, the purpose of this study was toevaluate the clinical performance of a linear ITC hear-ing aid with and without activation of an experimentalBILL-based processing option. The hearing aid, with andwithout the BILL processing activated, was evaluatedusing objective and subjective tests of device perfor-mance and measures of participant preference. As de-scribed in more detail below, a total of 110 persons withsensorineural hearing loss participated in this prospec-tive study conducted at three different clinical sites.

ProtocolOverview of Design

This was a prospective, double-blind, crossover, con-trolled study. The study population was divided intothree groups according to their hearing loss: (1) mild,defined as a four-frequency (500, 1000, 2000, and 4000Hz) pure tone average (4PTA) of 25–40 dB HL; (2) mod-erate, 4PTA of 41–60 dB HL; and (3) severe, 4PTA of61–85 dB HL. Each of the participants was tested withthe same hearing aid in two different circuit configura-tions: BILL option and linear. Randomly, one-half of theparticipants were dispensed the BILL circuit active first,and the other one-half received the linear circuit activefirst. After an appropriate adjustment period (discussedbelow), the participant’s performance with the first cir-cuit configuration was assessed. After that assessment,the participant was switched to the second circuit con-figuration and was given an appropriate adjustmentperiod. The participant then returned for an assessmentof performance with the second circuit configuration.

Assignment of initial aided condition (BILL vs. lin-ear) was randomized such that an equal number of par-ticipants was included in each group. Further, the studywas double blind. The participants did not know whichcircuit type was being tested first. At each test site, oneaudiologist (A) was responsible for fitting the hearing aids.A second audiologist (B), without knowledge of which cir-cuit type a participant was using for any given test ses-sion, performed the performance testing. The participantsand Audiologist B were also blind regarding the hearingaid’s manufacturer. This was accomplished by having nomanufacturer’s labeling or markings on the hearing aid

For the vast majority of listeners with sensorineural hear-ing loss seen by audiologists and hearing instrument spe-cialists over the past few decades, the conventional ap-proach to rehabilitation has been to fit the person havingsensorineural hearing loss with a linear, head-worn hear-ing aid with output limiting accomplished via peak clip-ping (Bess & Humes, 1995; Hawkins & Naidoo, 1993). Toimprove the communication performance of persons wear-ing such instruments in noise a variety of modificationsto the basic linear, peak-clipping instrument has beeninvestigated. High-pass filtering in a hearing aid has beenadvanced as one technique to minimize the effect of back-ground noise on speech communication.

High-pass filtering can be accomplished in a hear-ing aid in two ways. First, the hearing aid can be set tohave a static high-pass response. At all times, the hear-ing aid’s frequency response is set to minimize low-fre-quency gain and to maximize high-frequency gain. Theprincipal drawback to this approach is that many lis-teners do not like the sound quality of such an amplify-ing system in quieter environments (Punch & Beck,1986). Further, there is useful speech information in thelower frequencies that should be provided to the listener,if at all possible. This low-frequency information shouldbe restricted only if there is a drawback to its presence(such as excessive upward spread of masking or unde-sirable sound quality).

The second manner in which low-frequency energycan be attenuated is via adaptive high-pass filtering(Fabry & Walden, 1990). In this approach, the hearingaid is set to have a relatively broad response in quieterenvironments. As the overall sound level in the envi-ronment increases above a certain threshold level, thehearing aid automatically shifts to a more high-passresponse. The assumption behind such an approach isthat the listener is likely to prefer a broader response ifthere is a minimal amount of noise present. If the over-all level of the listening environment rises, there is ahigh likelihood that a significant amount of this energyis low-frequency noise (Ono, Kanzaki, & Mizoi, 1983).Therefore, the hearing aid automatically reduces gainfor this undesirable low-frequency sound and concen-trates the response of the hearing aid to the more im-portant high-frequency region. This automatic low-fre-quency reduction in gain at high input levels isimplemented through different methods in several mod-els of commercially available hearing aids. It has beenvariously termed “automatic signal processing (ASP),”“adaptive frequency response (AFR),” and “bass increaseat low levels (BILL).” Some commercial devices incor-porate adaptive high-pass filtering in single-channelanalog devices, whereas others make use of single- ormultichannel compression to realize BILL processing.

Despite the prevailing use of linear hearing aids over



casing or accompanying hardcopy materials, as well asby channeling all communications between the manufac-turer and test site through Audiologist A.

This study was carried out at three independentaudiology research facilities: (1) the Division of Hear-ing and Speech Sciences, Vanderbilt University Schoolof Medicine, Nashville, Tennessee; (2) the Departmentof Communication Disorders, Louisiana State Univer-sity Medical Center, New Orleans, Louisiana; and (3)the Department of Otolaryngology, University of IowaHospitals and Clinics, Iowa City, Iowa. These facilitieswere all in close physical and administrative proximityto an active clinical hearing aid dispensing program.Investigators at all research facilities obtained the ap-propriate Institutional Review Board approval for theuse of human participants at their facilities.

ParticipantsThe participant was eligible for entry into the study

if the participant: (a) was at least 18 years of age or older;(b) had a flat or gently sloping sensorineural hearing loss(slope 0–15 dB/octave from 250 Hz to 4000 Hz, no inter-octave change of greater than 20 dB), consistent with thefitting guidelines of the hearing aid; (c) had a hearing lossthat was symmetrical (within 10 dB at octave and half-octave frequencies from 250 Hz to 4000 Hz); (d) had thresh-olds that ranged between 25 and 85 dB HL at octave andinter-octave intervals from 250 Hz to 4000 Hz, inclusively;(e) had received medical clearance by a physician to usehearing aids binaurally; (f) had read, understood, andsigned the Informed Consent form; (g) had normaltympanograms bilaterally; and (h) resided within a rea-sonable distance of the test facility.

The participant was ineligible for entry into thestudy if the participant: (a) was a prior hearing aid user,although the participant could have participated in aprior 30-day trial of amplification (but not within theprevious 6 months); (b) had any indication of a medi-cally or surgically treatable ear disorder; (c) had an ex-ternal auditory canal with a size and shape that wasinconsistent with an appropriately sized device; (d) hadknown fluctuating or rapidly progressive hearing loss;(e) had any cognitive, medical, or language-based con-dition that limited his/her ability to complete all testprocedures; (f) was currently participating in any otherclinical trials; (g) had any known disease or condition,other than sensorineural hearing loss, that might affecthearing or cognition; or (h) was taking any medication(s)that could affect hearing or cognition.

Participants could also be discontinued from thestudy for one of the following reasons: (a) development ofany of the exclusion criteria during the course of the study,such as medical/surgical ear condition, fluctuating hear-

ing loss, disease/condition affecting hearing/cognition, orVIII-nerve tumor; (b) inability or unwillingness to main-tain wearing schedule; (c) inability or unwillingness tomake or keep clinic appointments during study; (d) deathor disability; (e) relocation of participant; (f) over 3 weekscumulative off-the-ear time; (g) change in participant’sthresholds at two or more test frequencies by more than10 dB, as compared to the initial baseline audiogram; or(h) a missed evaluation visit.

For their participation in the study, the participantsreceived their hearing aids at no charge. All clinical ser-vices provided during the study were also provided atno charge to the participant.

The mean air-conduction audiograms for the left(squares) and right (circles) ears for each of the threehearing-loss subgroups are provided in Figure 1. Stan-dard deviations are also given in the upper portion of Fig-ure 1. The mean audiogram for each subgroup shows abilaterally symmetrical, gently sloping configuration thatvaries in severity across subgroups. Table 1 shows thedistribution of participants by site, severity of hearingloss, and gender. Age ranges are also provided. As canbe seen, most of the participants with severe hearingloss were tested at the University of Iowa and weremostly men, whereas those with mild hearing loss werefairly evenly distributed across all three sites and weremostly women.

Figure 1. Mean right (circles) and left (squares) air-conductionthresholds (ANSI, 1989) for the mild, moderate, and severehearing-loss participant groups. N indicates the number ofparticipants in each group. Corresponding standard deviations foreach group are plotted at the top of the audiogram.



Hearing AidAll participants were fit with binaural, custom, in-

the-canal (ITC) hearing aids manufactured by Dahlberg,Inc. The shells of the hearing aids were unvented (whichwas considered to be generally appropriate given thedegree and configuration of the hearing losses) and werefabricated from standard materials and with medium-length canals. The test hearing aids included an experi-mental BILL circuit that reduced the amount of gain inthe low frequencies as the input intensity increased. Amanually adjustable potentiometer on the device, ac-cessible only to the audiologist, allowed the BILL cir-cuit to be deactivated. When the circuit was deactivated,the device acted as a linear amplifier—the most com-mon circuit currently used on the hearing aid market.This particular linear circuit, however, made use of apatented Class AB output stage that, according to themanufacturer, incorporated low-distortion peak clipping,reduced low-frequency circuit noise, and low currentdrain. When the BILL circuit was active, the thresholdfor activation of the BILL processing was set at the low-est possible level (about 60 dB SPL). This was essen-tially a single-channel analog device with adaptive high-pass filtering with a variable threshold for activation ofthe adaptive filtering. When the potentiometer was ad-justed to one extreme position, inputs as low as 60 dBSPL would activate the adaptive high-pass filtering andmaximum reduction of low frequencies occurred,whereas adjustment to the other extreme position re-sulted in deactivation of the adaptive filtering (linearprocessing). Figure 2 illustrates the effect of these twoextreme potentiometer settings on the frequency re-sponse of the hearing aid as a function of input level.The biggest reductions in low-frequency gain are ob-tained for the BILL circuit for inputs of 70 and 80 dB.Note that activation of the BILL circuit actually reducesthe gain in the mid and high frequencies by about 8–10dB, compared to the linear setting at an input level of

Table 1. Detailed descriptions of study participants by clinical site,participant hearing loss severity, and participant gender.

Hearing loss Site # Males # Females Age range (y)

Mild LSU 3 11 27–85Vanderbilt 3 7 44–84Iowa 3 14 48–83

Moderate LSU 8 12 34–83Vanderbilt 8 9 45–83Iowa 7 9 25–87

Severe LSU 1 1 54–66Vanderbilt 0 1 90Iowa 12 1 47–85

Figure 2. Illustration of the effects of hearing-aid circuit setting(linear vs. BILL) on the frequency response measured in accordancewith ANSI S3.22-1987. Frequency responses are shown for boththe linear (solid lines) and BILL (dashed lines) settings. Each paneldepicts the frequency responses for each setting obtained for adifferent input level (50–90 dB SPL). Results shown are for thehighest gain linear circuit included in this study.



used to listening to an amplified signal. It may not beuntil several weeks after being fit with a new hearingaid that some users can make maximal use of the newauditory information. Therefore, in order to increasethe likelihood of achieving optimal performance withthe hearing aids in this study, the user was allowed toadapt to its use. A longer period of acclimitization (8weeks) was implemented for the trial with the first cir-cuit because it was anticipated that there would be agreater need for adjustment to the use of amplificationinitially that included familiarization with the insertion/removal of the device, operation of controls, replacementof batteries, and adjustment to the new sound quality.

During the adjustment period, no changes in theresponse or casing of the hearing aid were allowed, ex-cept in cases of reported physical or loudness discom-fort or acoustic feedback. In typical clinical practice, theaudiologist may make fine-tuning adjustments in theparticipant’s hearing aid during the first several weeks.These adjustments are typically due to sound-qualitypreferences on the part of the participant. However,these adjustments are not predictable and will vary fromparticipant to participant depending on factors that arenot fully understood. The NAL-R prescriptive rules arewell developed, well supported in the literature, and gen-erally accepted by audiologists. Therefore, in an attemptto provide consistent responses from participant to par-ticipant, variations from the NAL-R prescribed hearingaid responses were not permitted during the study.

The first evaluation session took place no more than2 weeks after the end of the 2-month adjustment period.After the first circuit had been evaluated, the participant’shearing aids were changed to the alternative circuit. Theparticipant was then given a 1-month adjustment periodwith the second circuit. The second evaluation sessiontook place no more than 2 weeks after the end of this 1-month adjustment period. Follow-up phone and mail con-tacts were made in cases in which participants did notkeep scheduled evaluation sessions.

Speech levels vary across a broad range in typicalcommunicative environments (Pearsons, Bennett, &Fidell, 1977). In this study, testing was performed attwo different speech levels, 60 and 75 dB SPL, whichrepresent normal and raised speech (Pearsons et al.,1977). Further, the degree of low-frequency amplifica-tion in the experimental BILL circuit varies inverselywith the overall input level. Evaluating nonlinear cir-cuits at more than one level has been recommended byothers (e.g., French-St. George, Engebretsen, &O’Connell, 1992). By testing at these two levels, we wereable to assess BILL-circuit performance aspects andaided benefit across a range of typical input levels.

A variety of background noise types has been usedin past evaluations of automatic low-frequency reduc-

60 dB and, to a lesser extent, at 70 dB. Although resultsshown in Figure 2 are only for the hearing aid circuitwith the highest gain, identical patterns of results wereobserved for the circuit with lowest gain, although thereduction of gain in the mid- and high-frequency regionswas less pronounced (4–6 dB) for this circuit. The rela-tive effects of BILL processing shown in this figure, more-over, are independent of volume-control setting.

During the study, the hearing aids were marked onlywith a serial number—no brand identification informa-tion. At study completion, they were returned to themanufacturer for proper labeling before they were re-turned to the participants. All hearing aids were testedelectroacoustically in accordance with ANSI S3.22-1987before dispensing and at all post-fit evaluations.

The gain, frequency response, and maximum out-put of each hearing aid was individually selected by themanufacturer on the basis of audiometric characteris-tics of each test ear. The gain and frequency responsewere selected to meet the targets prescribed by the re-vised National Acoustics Laboratory (NAL-R) fitting pro-cedure (Byrne & Dillon, 1986) when set for the linearmode of operation. The desired frequency response wasconfirmed via probe-tube measurement techniques athearing-aid delivery. Consistent with the recommenda-tions of Mueller (1992), the real-ear insertion gain ofthe hearing aid was within 10 dB at all octave frequen-cies below 4000 Hz and within 15 dB at 4000 Hz. Themean target gain curves based on the NAL-R formulaand the mean real-ear insertion responses for the lin-ear setting obtained from the participants for a 60-dB-SPL input are shown for each ear and hearing-loss sub-group in Figure 3. There is excellent agreement betweenthe prescribed (target) gain and the measured insertiongain in all cases from 250 Hz to 4000 Hz, but a consis-tent underamplification of about 8–12 dB at 6000 Hz.

SSPL90 targets were derived from loudness discom-fort levels (LDLs) measured using procedures describedby Hawkins, Walden, Montgomery, and Prosek (1987).The maximum output of the device was selected to beno more than 10 dB below the SSPL90 target maximumat octave frequencies from 500 Hz though 4000 Hz.

Hearing Aid EvaluationsNo evaluation of hearing aid benefit took place until

after a 2-month adjustment period with the first circuit.This adjustment period is consistent with recent evi-dence of the maturation of hearing aid benefit or“acclimitization” (Cox & Alexander, 1992; Gatehouse,1992, 1993), allowing for plateau performance, al-though there is some debate about the size and sig-nificance of this effect (Turner, Humes, Bentler, & Cox,1996). Nonetheless, it was assumed that it takes somefinite amount of time for a new hearing aid user to get



tion amplification. The performance of automatic low-frequency reduction amplification has been demon-strated to vary with background noise type (Fabry, 1991).Specifically, as the noise shifts from predominantly low-frequency energy to more broadband energy, the benefi-cial effects of the circuit tend to diminish. Also, the use

of steady-state narrow-band, speech, or white noise doesnot replicate real-world listening environments. There-fore, in this study, two noise types were used: cafeterianoise (Auditec) and multitalker speech babble (Auditec).Spectrally, cafeteria noise tends to be dominated by low-frequency energy, but continues to have some higher

Figure 3. Mean target real-ear insertion gain generated by the NAL-R formula (squares) compared to themean real-ear insertion gain measured (circles) for a 60-dB input. Vertical bars above and below circlesrepresent one standard deviation above and below the mean. Left-hand panels and unfilled symbols are forleft ear, whereas right-hand panels and filled symbols are for right ear. Top panels present data for groupwith mild hearing loss, middle panels contain data for group with moderate hearing loss, and bottompanels present data for group with severe hearing loss.



frequency content because of the presence of some com-peting speech. Babble tends to have the same long-termcharacteristics as test speech material. By using both caf-eteria noise and speech babble, we assessed the effects ofthe BILL circuit and the benefit provided by both BILL-processing and linear hearing aids in realistic, yet spec-trally different, background conditions.

ProceduresBefore the beginning of this study, investigators from

each clinical site met with the study sponsor (the manu-facturer) to review the protocol and data-handling is-sues. Identical materials, protocols, and forms were usedat all sites. An independent study monitor familiar withmedical-device clinical field studies was retained by thestudy sponsor to monitor the study procedures at eachsite; this person made several visits to the sites through-out the duration of the study to assure uniformity andadherence to the protocol.

At the patient’s first visit to the facility, referred toas the recruitment visit, information on the participant’shistory, demographics, eligibility, unaided hearing per-formance, and hearing-aid fit was collected and evalu-ated. Ear impressions were obtained at this visit, andthe hearing aids were ordered. The investigator also ex-plained the Physician Release Form and the InformedConsent Form to the participant during this visit.

The second visit, the dispensing visit, took placewithin 3 weeks of the recruitment visit. At this visit,the participant returned the signed Informed Consentand Physician Release Forms, and before the hearingaids were dispensed Audiologist B confirmed theparticipant’s hearing thresholds measured previously.Next, Audiologist A evaluated the hearing aids in thetestbox, measured the real-ear performance, and gave ahearing-aid-use log to the participant with an explana-tion of its use. Participants were instructed to wear theirhearing aids at least 5 hours per day, 5 days per week.Audiologist B then obtained unaided speech-recognitionscores, along with magnitude estimates of listening ef-fort (see below), from the participant.

The third visit to the facility represented the first aidedevaluation of performance and took place no more than 2weeks after the 2-month “acclimatization” period (time fromdispensing visit to the first aided evaluation visit). At thisvisit, hearing sensitivity was again measured by Audiolo-gist B to confirm the stability of hearing thresholds. Audi-ologist A evaluated the hearing aids in the testbox andcollected the hearing-aid-use log from the participant. Inaddition, the Hearing Aid Performance Inventory (HAPI;Walden, Demorest, & Hepler, 1984) was administered inits abbreviated form (Schum, 1993) using a pencil-and-paper format, and a new hearing-aid-use log was given

to the participant. Audiologist B then obtained aidedspeech-recognition and listening-effort scores. Oncethese measures were completed, the hearing aid wasswitched to the alternate setting (linear or BILL) byAudiologist A.

The fourth visit to the facility represented the secondand final aided evaluation of performance and took place nomore than 2 weeks after the 1-month adjustment period(time from the first aided evaluation visit to the second aidedevaluation visit). At this visit, hearing sensitivity was againmeasured by Audiologist B to confirm the stability of hear-ing thresholds. Audiologist A evaluated the hearing aids inthe testbox and collected the hearing-aid-use log from theparticipant. In addition, the abbreviated HAPI was againadministered. Audiologist B then obtained aided speech-rec-ognition and listening-effort scores. Finally, a series of paired-comparison measurements was performed by the partici-pant with the assistance of Audiologist A.

Table 2 provides a summary of the sequence of mea-surements peformed during this study. It also indicateswhich audiologist (A [not blind] or B [blind]) at each sitewas involved in the measurements. Explanations ofhearing-aid function, use, care, and communicationstrategies were provided by Audiologist A.

Outcome MeasuresTaped speech-recognition tests (NU-6; Tillman &

Carhart, 1966 / Connected Speech Test, CST; Cox,Alexander, Gilmore, & Pusakulich, 1988) were admin-istered at +5 and +10 dB signal-to-noise ratios (S/N) inbabble and cafeteria noise at speech presentation levelsof 60 and 75 dB SPL. Oral responses were used for bothtests. All scores for both the NU-6 and CST tests werebased on 50 items. Speech and noise were presented froma single loudspeaker located at zero-degrees azimuth andone meter from the center of the participant’s head. Allsound pressure levels refer to those measured in the soundfield using the method of substitution (Skinner, 1988).

A magnitude-estimate of listening effort (MELE) wasalso developed and used in this study. In this task, thelistener rated the difficulty of listening to speech in caf-eteria noise and babble backgrounds. The listener hearda 10-sentence encyclopedia-style passage from the CST.Four passages were presented at 60 and 75 dB SPL inboth noise backgrounds at +5 and +10 dB S/N (32 totalpassages). After each passage, the listener rated “ease oflistening” on a 0–100 scale, with 100 representing ex-tremely easy listening. In each listening condition, theratings from the last three passages were averaged andthe first in each condition was discarded as practice.

After completion of the second round of objectiveand subjective measures of performance, the participantwas then placed in the sound field and presented with

https://www.researchgate.net/publication/14775789_Test-retest_reliability_of_a_shortened_version_of_the_hearing_aid_performance_inventory?el=1_x_8&enrichId=rgreq-6c8d7c1f-a49e-41f0-b29a-c3b022a74a69&enrichSource=Y292ZXJQYWdlOzE0MDA5NTcwO0FTOjExMjA1MzM4MTUwNTAyNEAxNDAzNzI3MDE3MDU4



continuous discourse (the Rainbow Passage recordingavailable on the Q/MASS Speech Audiometry, Volume 1compact disk) at the same levels and signal-to-noise ra-tios described above. The audiologist then switched thecircuit back and forth from the BILL to the linear set-ting. The participant heard a 15- to 20-second passagein one circuit setting, followed by a second 15- to 20-second passage with the other circuit active. The orderof which circuit was active first was randomly varied.The participant then chose which circuit he/she preferredto use in that noise condition.

The participant used the following rating scale toindicate preference: (1) Circuit A significantly better thancircuit B; (2) Circuit A moderately better than circuit B;

(3) Circuit A slightly better than circuit B; (4) Circuit Bslightly better than circuit A; (5) Circuit B moderatelybetter than circuit A; (6) Circuit B significantly betterthan circuit A. The participant made one practice, thenthree test ratings, at each speech level, in both noisebackgrounds and at each signal-to-noise ratio. The re-sults from the three test ratings were averaged in eachlistening condition.

ResultA total of 115 participants was enrolled in the

study, but 1 was not dispensed a hearing aid and 4

Table 2. Summary of visits and forms used in the study.

Session Form/Data description Audiologist

1st visit: Recruitment Participant History Form BOrder Form

Pure tone thresholds BLoudness discomfort levels BSpeech discrimination BTympanometry BHearing aid order information A

Impressions AEligibility Criteria (reviewed participant eligibility) APhysician Release (explained & gave to participant) AInformed Consent (explained and gave to participant) A

2nd visit: Dispensing Eligibility Criteria (reconfirmed eligibility and signed) APerformance Testing form B

Pure tone thresholds BNU-6 monosyllabic word list scorea BConnected Speech Test scorea BListening Effort Test scorea B

Hearing Inventory (HHIE) AHearing Aid ANSI Performance AHearing Aid Use Log (explained & gave to participant) A

3rd visit: 1st Evaluation Performance Testing form BPure tone thresholds BNU-6 monosyllabic word list scoresa BConnected Speech Test scoresa BListening Effort Test scoresa B

Hearing Aid Performance Inventory (HAPI) AHearing Aid ANSI Performance AHearing Aid Use Log (explained & gave to participant) A

4th visit: 2nd Evaluation Performance Testing form BPure tone thresholds BNU-6 monosyllabic word list scoresa BConnected Speech Test scoresa BListening Effort Test scoresa B

Hearing Aid Performance Inventory (HAPI) AHearing Aid ANSI Performance APaired Comparison Testinga A

aThese tests were performed at +5 and +10 dB S/N; at 60 and 75dB SPL; and in cafeteria and babble noise.



were discontinued. Of the 4 discontinued participants,1 was discontinued because closer evaluation revealedthat the participant did not meet all of the inclusioncriteria and should not have been enrolled, whereasthe other 3 were lost to follow-up (did not return andcould not be reached). Of the 110 remaining partici-pants, none missed a scheduled visit. The results de-scribed below are for the 110 who were enrolled andcompleted the entire study.

Group Data—Linear vs. BILL-ProcessingNU-6 Test

Recall that the NU-6 test was performed at severalsignal-to-noise ratios, speech levels, and in two differ-ent types of noise background at the dispensing visit(unaided) and the first and second evaluations (aided).Figure 4 provides a summary of the mean aided NU-6percent-correct data for the 110 participants with mild,moderate, or severe hearing loss, respectively. Table 3provides the corresponding standard deviations for themean values appearing in Figure 4.

Connected Speech TestThe Connected Speech Test (CST) was also per-

formed for the same combinations of signal-to-noise ra-tio, speech level, and types of background noise usedwith the NU-6 at the dispensing visit (unaided) and atthe first and second evaluations (aided). Figure 5 pro-vides a summary of the mean aided CST percent-cor-rect data for the 110 participants with mild, moderate,or severe hearing loss, respectively. Table 4 provides thecorresponding standard deviations for the mean CSTvalues appearing in Figure 5.

ANOVAs on NU-6 and CST ScoresPercent-correct scores for the NU-6 test and the CST

were arcsine transformed to stabilize the error variance(Kirk, 1968), and the difference scores between the linearand BILL settings were computed. An analysis of variance(ANOVA) with a between-subject factor of hearing-lossgroup and four bivalent repeated-measures or within-sub-ject variables (test materials, signal-to-noise ratio, noisetype, and speech level) was performed first and showed nostatistically significant (p < .05) effects of hearing-loss group(either main effects or interactions). Consequently, a sec-ond ANOVA was performed on the difference scores (lin-ear vs. BILL) for all 110 participants and the four re-peated-measures, within-participant variables withoutregard to hearing-loss group. The results of this ANOVAare summarized in Table 5 and indicate that there wasno difference in performance between the linear andBILL settings (i.e., the linear-minus-BILL differencescores did not differ significantly from zero). Moreover,

Figure 4. Mean percent-correct scores on the NU-6 test for thelinear (cross-hatched bars) and BILL (unfilled bars) settings of thehearing aid. Panels are organized from top to bottom according tohearing loss group such that participants with mild hearing loss arein the top two panels, those with moderate hearing loss are in themiddle two panels, and those with severe hearing loss are in thebottom two panels. All left-hand panels contain data for the 60-dB-SPL presentation level, whereas all right-hand panels contain datafor the 75-dB-SPL presentation level. Within each panel, results forbabble background at +5 and +10 dB signal-to-noise ratio,followed by cafeteria-noise background at +5 and +10 dB signal-to-noise ratio, are plotted along the x-axis as one moves from leftto right.



none of the other variables (test materials, noise type,signal-to-noise ratio, or speech level) significantly af-fected the linear-minus-BILL difference scores, eitherindividually or in combination.

Magnitude Estimation of Listening EffortTest (MELE)

The MELE test required the listener to rate, from 0to 100, the ease of listening to speech in cafeteria noiseand in babble backgrounds. The same connected-speechpassages used in the CST served as the speech stimu-lus. As with the NU-6 and CST tests, the MELE testwas performed at +5 and +10 dB S/N in babble and caf-eteria noise, with the speech signal presented at 60 and75 dB SPL at the dispensing visit (unaided) and the firstand second evaluation visits (aided).

Figure 6 provides a summary of the MELE data forthe 110 participants in this study with mild, moderate,or severe hearing loss, respectively. Table 6 provides thestandard deviations corresponding to the mean MELEdata appearing in Figure 6. Ratings, which ranged from0 to 100, were repeated a total of four times per condi-tion, with the first rating discarded and the remainingthree averaged for each subject. Preliminary analysesconducted on the linear-minus-BILL difference scores,as used in the analysis of the NU-6 and CST results,found significant heterogeneity of variance for the MELEdifference scores. Consequently, analyses of variancewere performed on the raw scores rather than differ-ence measures for the MELE test (variances of rawscores were found to be homogeneous across conditions).

An analysis of variance performed on the MELE rat-ings, with hearing-aid setting (linear vs. BILL) as a vari-able, is summarized in Table 7. For the most part, thisanalysis indicated that there was no significant effect ofthe hearing-aid setting on MELE ratings. That is, themain effect of circuit setting (linear vs. BILL) was notsignificant and only one of the 15 interactions involvingthis variable was significant (hearing loss group x noisetype x setting). The presence of this significant interac-tion involving hearing loss group, however, confounds asimple interpretation of the effect of hearing-aid setting.From visual inspection of the data in Figure 6, this three-way interaction involving the hearing-aid setting appearsto be due to the higher MELE scores for the subjects withsevere hearing loss listening in babble for the BILL hear-ing-aid setting and the reversal of this trend under thesame conditions for the listeners with mild hearing loss.The presence of several significant two-way interactions(noise type x signal-to-noise ratio, noise type x presenta-tion level, and signal-to-noise ratio x presentation level),none involving the hearing-aid setting variable, illustratesthe importance of assessing MELE across a range of lis-tening conditions.

Figure 5. Mean percent-correct scores on the CST for the linear(cross-hatched bars) and BILL (unfilled bars) settings of the hearingaid. Panels are organized from top to bottom according to hearingloss group such that participants with mild hearing loss are in thetop two panels, those with moderate hearing loss are in the middletwo panels, and those with severe hearing loss are in the bottomtwo panels. All left-hand panels contain data for the 60-dB-SPLpresentation level, whereas all right-hand panels contain data forthe 75-dB-SPL presentation level. Within each panel, results forbabble background at +5 and +10 dB signal-to-noise ratio,followed by cafeteria-noise background at +5 and +10 dB signal-to-noise ratio, are plotted along the x-axis as one moves from leftto right.



Table 3. Standard deviations for NU-6 percent-correct scores for participants with mild, moderate, orsevere hearing loss.

Processing condition and presentation level

BILL Linear

Stimulus condition 60 dB SPL 75 dB SPL 60 dB SPL 75 dB SPL

Mild hearing loss group

+5 dB S/N in Babble 15.75 15.84 14.71 15.51+10 dB S/N in Babble 20.16 18.08 18.77 14.52+5 dB S/N in Cafeteria Noise 17.81 16.07 16.15 17.22+10 dB S/N in Cafeteria Noise 19.66 16.64 19.86 13.67

Moderate hearing loss group


Severe hearing loss group


Table 4. Standard deviations for CST percent-correct scores for participants with mild, moderate, andsevere hearing loss.


BILL Linear








Order EffectThe results were analyzed for effects of the order in

which the hearing-aid setting was first dispensed to aparticipant. One might hypothesize that participants will

perform best with the hearing-aid setting (linear vs. BILL)to which they first became accustomed, in part because itwas their first experience, but also because they worethe hearing aid with that setting for 8 weeks, versus 4



weeks for the second setting. To address this issue, sixseparate ANOVAs were performed: one for each of thethree benefit measures (NU6, CST, and MELE) in eachof two noise types (cafeteria and babble). A significant (p<. 01) main effect of the initial hearing-aid setting wasnot observed, and no significant interactions with theinitial setting were obtained in any of these ANOVAs.

Hearing Aid Performance Inventory(HAPI)

The HAPI questionnaire was used to identify theeffect of the hearing aids on the participant’s communi-cation abilities in daily life. Each participant completedthis questionnaire at the first and second evaluationvisits, ranking the benefit provided by the hearing aidfrom Very Helpful (1) to Hinders Performance (5).

Table 8 provides a summary of the observed HAPIscores (means and standard deviations) for all hearingloss groups. Analyses using Wilcoxon Signed Ranks Testsfor each participant group showed no significant differ-ence in HAPI scores for linear or BILL settings (WilcoxonZ = –1.10, p = 0.27; Z = –1.59, p = 0.11; Z = –1.53, p =0.12; for mild, moderate, and severe hearing-loss groups,respectively). The grand mean scores across all hearingloss groups were 2.10 for the BILL setting and 2.02 forthe linear setting, indicating that both circuits were gen-erally considered to be “helpful” to the participants. (Onthe HAPI, a rating of 1 is associated with a label of “veryhelpful” and a rating of 2 with a label of “helpful.”) Thedifference in grand mean HAPI scores for the linear andBILL settings, collapsed across all three subject groups,however, approached statistical significance (Z = –2.36,p = 0.02).

Table 5. Summary of ANOVA results for BILL-linear differences forall 110 participants combined (all p values > .05).

Effect F value (df = 1, 109)

Constant (BILL-linear difference > or < 0) 1.07Material (NU-6, CST) 0.30Noise (cafeteria noise or babble) 0.10SNR (signal-to-noise ratio, +5 or +10 dB) 0.66Sound level (sound level, 60 or 75 dB SPL) 0.14Material by noise 0.09Material by SNR 0.48Material by sound level 0.22Noise by SNR 0.55Noise by sound level 0.20SNR by sound level 0.06Material by noise by SNR 0.41Material by noise by sound level 3.52Material by SNR by sound level 1.43Noise by SNR by sound level 0.86Material by noise by SNR by sound level 0.02

Figure 6. Mean ratings on the MELE test for the linear (cross-hatchedbars) and BILL (unfilled bars) settings of the hearing aid. Panels areorganized from top to bottom according to hearing loss group suchthat participants with mild hearing loss are in the top two panels,those with moderate hearing loss are in the middle two panels, andthose with severe hearing loss are in the bottom two panels. All left-hand panels contain data for the 60-dB-SPL presentation level,whereas all right-hand panels contain data for the 75-dB-SPLpresentation level. Within each panel, results for babble backgroundat +5 and +10 dB signal-to-noise ratio, followed by cafeteria-noisebackground at +5 and +10 dB signal-to-noise ratio, are plottedalong the x-axis as one moves from left to right.



Paired-Comparison TestAfter completion of the second round of objective

and subjective measures of performance at the secondevaluation visit, the participant was placed in the soundfield and presented with continuous discourse to deter-mine participant preference for either the BILL or lin-ear setting. The test was performed at +5 and +10 dBS/N in babble and cafeteria noise, with the speech sig-nal presented at 60 and 75 dB SPL. During this test theaudiologist switched the circuit back and forth fromthe BILL setting to the linear setting randomly. Foreach of the eight listening conditions (2 noise types x 2S/N values x 2 sound levels), the participant chose thecircuit he/she preferred. Each listening condition wasrepeated four times, and the mean preference ratingfor the final three ratings was computed (first ratingdiscarded as practice).

For this task, the hearing-aid settings were ratedon a scale of 1 to 6 by the participants, with ratings of 1,2, and 3 representing varying degrees of preference forthe BILL setting and ratings of 4, 5, and 6 representingvarying degrees of preference for the linear setting. Amean value of 3.49 or below, therefore, meant that theparticipant preferred the BILL setting, and a value of3.51 or above meant that the participant preferred thelinear setting. The overall mean result for the paired-comparison test (3.57) showed no group preference foreither the linear or BILL setting (z = 0.1472, p = 0.442).

Hearing-Aid UseTable 9 provides a summary of the average reported

hearing-aid wear times for participants with mild, mod-erate, and severe hearing loss. Participants with severehearing loss reported wearing their hearing aids longer(about 9 hours/day) than participants in the mild andmoderate groups (about 7 hours/day).

Group Data—Unaided vs. AidedPerformance

Figures 7 and 8 provide summaries of the mean datafor the NU-6 and CST with regard to unaided and aidedconditions for the 110 participants of this study with mild,moderate, or severe hearing loss, respectively. Table 10provides the standard deviations for the unaided scoresappearing in these two figures. Since aided performancewith the linear and BILL circuits was found to be equiva-lent in the previous analyses, the linear setting was se-lected arbitrarily to represent aided listening, and thestandard deviations for these data appeared previouslyin Tables 3 and 4. The less well-established MELE mea-sures are not considered in detail here as measures ofbenefit. Rather, the focus is on the more conventionalmeasures of benefit (NU-6, CST, and HAPI).

When a repeated-measures ANOVA was calculatedfor the aided-minus-unaided differences collapsed acrossall three subject groups (for arcsine-transformed NU-6and CST data), differences were found to be significantly

Table 6. Standard deviations for MELE ratings for completed participants with mild, moderate, and severehearing loss.


BILL Linear










greater than zero (F = 146.13, df = 1,109, p < .01). Inparticular, aided scores were higher than unaided scores,which led to statistically significant benefit. To analyzethe effects of each independent variable on the aided-minus-unaided difference scores, a second mixed-modelANOVA was performed. The results are summarized inTable 11. As can be seen in this table, main effects oftest material (NU-6, CST) and noise type (cafeteria,babble) were significant (p <. 01) and unconfounded by

any interactions with other independent variables. Aided-minus-unaided differences were greater in cafeteria noisethan in babble and for the CST than for the NU-6 test. Inaddition to these main effects, the three-way interactionof hearing-loss group, signal-to-noise ratio, and presen-tation level was also significant. From visual inspectionof Figures 7 and 8, this three-way interaction appears tobe attributable to the effect of signal-to-noise ratio on theaided-minus-unaided difference at various presentationlevels across the three groups. In particular, benefit onboth the NU-6 test (Figure 7) and the CST (Figure 8)increases as signal-to-noise ratio increases from +5 to +10dB, except for the groups with mild or moderate hearingloss at the highest presentation level (75 dB). Finally, itshould be noted that, given the lack of any significantdifferences in aided scores between the linear and BILLcircuits described previously, significant benefit (aidedscores minus unaided scores) exists for both circuits, eventhough the linear circuit was arbitrarily selected as thecircuit for the aided condition in these analyses of thebenefit provided by the hearing aid.

Individual DataFigure 9 provides scatterplots of the individual data

for all 110 participants on the NU-6 test. In the toppanel, percent-correct scores for the linear setting ofthe hearing aid are plotted against the correspondingpercent-correct score for the BILL setting. The solidlines represent the diagonal (equality of the two scores)and 95% critical-difference boundaries from Thorntonand Raffin (1978) for a test consisting of 50 items. Notethat the vast majority of the data points plotted fallwithin the 95% critical differences, with approximatelyequal numbers of points falling below the boundariesas above them.

In contrast, the bottom panel of Figure 9 shows theaided NU-6 scores for the linear condition plotted as afunction of the unaided scores. Notice that a much greaternumber of data points falls above the upper 95%-criti-cal-difference boundary than below the lower boundary.Thus, these individual data are consistent with the analy-ses of the group results in that little difference was ob-served between the linear and BILL settings (top panel),

Table 7. Summary of ANOVA for MELE results.

Effect F (df)

HL group (mild, moderate, severe) 2.22 (2,107)Noise (cafeteria noise, babble) 109.73 (1,107)*HL group by noise 0.33 (2,107)Setting (BILL, linear) 0.09 (1,107)HL group by setting 0.29 (2,107)Snr (+5, +10 dB) 234.66 (1,107)*HL group by snr 1.24 (2,107)Sndlev (60, 75 dB SPL) 5.92 (1,107)HL group by sndlev 3.84 (2,107)Noise by setting 1.44 (1,107)HL group by noise by setting 7.77 (2,107)*Noise by snr 38.66 (1,107)*HL group by noise by snr 0.62 (2,107)Noise by sndlev 16.50 (1,107)*HL group by noise by sndlev 1.06 (2,107)Setting by snr 0.01 (1,107)HL group by setting by snr 0.36 (2,107)Setting by sndlev 1.29 (1,107)HL group by setting by sndlev 0.98 (2,107)Snr by sndlev 9.45 (1,107)*HL group by snr by sndlev 1.90 (2,107)Noise by setting by snr 1.86 (1,107)HL group by noise by setting by snr 1.66 (2,107)Noise by setting by sndlev 1.51 (1,107)HL group by noise by setting by sndlev 0.56 (2,107)Noise by snr by sndlev 5.73 (1,107)HL group by noise by snr by sndlev 0.60 (2,107)Setting by snr by sndlev 3.94 (1,107)HL group by setting by snr by sndlev 1.80 (2, 107)Noise by setting by snr by sndlev 0.11 (1,107)HL group by noise by setting by snr by sndlev 0.18 (2,107)

*p < .01

Table 8. Summary of means and standard deviations (in parenthe-ses) for the Abbreviated Hearing Aid Performance Inventory (HAPI)for participants with mild, moderate, or severe hearing loss.

Hearing aid mode

Hearing-loss group BILL setting Linear setting

Mild 2.21 (0.56) 2.16 (0.55)Moderate 2.01 (0.53) 1.95 (0.47)Severe 2.11 (0.50) 1.88 (0.49)

Table 9. Mean reported wearing time (in hours per day) forparticipants by hearing loss group for BILL and linear hearing-aidsettings.

Hearing aid mode

Hearing-loss group BILL setting Linear setting

Mild 6.65 7.03Moderate 6.77 7.31Severe 8.84 9.59



Figure 7. Mean percent-correct scores on the NU-6 test for theunaided (unfilled bars) and aided (linear; cross-hatched bars)settings of the hearing aid. Panels are organized from top tobottom according to hearing loss group such that participants withmild hearing loss are in the top two panels, those with moderatehearing loss are in the middle two panels, and those with severehearing loss are in the bottom two panels. All left-hand panelscontain data for the 60-dB-SPL presentation level, whereas allright-hand panels contain data for the 75-dB-SPL presentationlevel. Within each panel, results for babble background at +5 and+10 dB signal-to-noise ratio, followed by cafeteria-noise back-ground at +5 and +10 dB signal-to-noise ratio, are plotted alongthe x-axis as one moves from left to right.

Figure 8. Mean percent-correct scores on the CST for the unaided(unfilled bars) and aided (linear; cross-hatched bars) settings of thehearing aid. Panels are organized from top to bottom according tohearing loss group such that participants with mild hearing loss arein the top two panels, those with moderate hearing loss are inmiddle the two panels, and those with severe hearing loss are inthe bottom two panels. All left-hand panels contain data for the60-dB-SPL presentation level, whereas all right-hand panelscontain data for the 75-dB-SPL presentation level. Within eachpanel, results for babble background at +5 and +10 dB signal-to-noise ratio, followed by cafeteria-noise background at +5 and +10dB signal-to-noise ratio, are plotted along the x-axis as one movesfrom left to right.



but many individuals demonstrated significantly higheraided scores than unaided scores (bottom panel). Thelatter conclusion appears to be particularly true for un-aided NU-6 scores less than or equal to 40%.

Figure 10 provides a comparable set of scatterplotsfor the CST percent-correct scores. The top panel againshows comparison of aided scores for the linear andBILL conditions, whereas the bottom panel comparesaided (linear) to unaided performance. Although thereis more scatter than in the NU-6 data, the same trendsare apparent. Specifically, the two aided conditions donot appear to differ systematically (top panel), whereasaided scores are frequently significantly greater thanunaided scores (bottom panel). Again, because therewere no significant differences between aided scoresfor the linear and BILL circuits, scatterplots equiva-lent to those in Figures 8 and 9 would have resulted ifthe results from the BILL circuit, rather than the lin-ear circuit, had been selected to represent aided lis-tening in these figures.

A voluminous amount of data was gathered in thecourse of this study—not only in terms of sample size,but in terms of the number of outcome measures ob-tained. Speech-recognition performance alone was mea-sured in 16 different conditions. How do these data com-pare with those in the literature? Unfortunately, thereare no norms available for these measures under thesame combinations of noise type, speech level, and sig-nal-to-noise ratio. To gain some insight into the valid-ity of these results, Speech Intelligibility Index (SII;

Table 10. Standard deviations for unaided NU-6 and unaided CST scores for participants with mild,moderate, and severe hearing loss.

Test material and presentation level

NU-6 NU-6 CST CST Stimulus condition 60 dB SPL 75 dB SPL 60 dB SPL 75 dB SPL







ANSI S3.79—draft V3.1) calculations were performed.The SII is essentially an updated version of the Articu-lation Index (AI) and is sensitive to factors manipu-lated in this study, including noise spectrum, noiselevel, speech level, hearing loss, and hearing-aid gain.SII calculations were performed only for the babblebackground—for which it could be reasonably assumedthat the speech and babble had the same long-termaverage spectrum. Moreover, it was assumed that theaverage speech spectrum and the normal vocal effortincluded in the SII standard were reasonably repre-sentative of the 60-dB SPL speech level for both theNU-6 and CST talkers. Figures 11 and 12 depict themean results from this study for the NU-6 test and theCST, respectively, plotted as a function of the SII. Best-fitting polynomials fit to the data in each figure (solidlines) indicate that the data are consistent with SII pre-dictions in that performance increases monotonicallywith the SII. In the absence of adequate norms, thisanalysis assists in establishing the validity of these data.

DiscussionNo statistically significant differences in perfor-

mance were found between the BILL-processing and lin-ear settings for any of the outcome measures used inthis clinical investigation. This is consistent with a num-ber of previous reports from smaller scale laboratory stud-ies (see review by Fabry, 1991). Essentially, in situationsin which the speech and noise are broadband stimuli, BILL



processing will provide level-dependent changes in gainthat affect both the speech and the noise equivalently anddo not improve the signal-to-noise ratio in any frequencyregion. Were the noise predominantly low-frequency innature, however, one might expect different results.

Perhaps of greater importance, however, is the con-sistent observation, across several outcome measures,that there was significant benefit provided by these hear-ing aids when operating in either the linear or BILL-processing mode compared to unaided listening. For boththe NU-6 and CST measures, for example, the differ-ence between unaided and aided scores was significantlygreater than zero. Moreover, the participants reportedusing their hearing aids 7–9 hours per day, on average,supporting a self-perceived benefit associated with theuse of their hearing aids. That is, they would probablynot wear the hearing aids much if they failed to per-ceive significant benefit. Recall, however, that partici-pants were instructed to wear their hearing aids at least5 hours per day, 5 days per week, as participants in this

Table 11. Summary of ANOVA on aided-unaided differences.

Effect F (df)

HL group (mild, moderate, severe) 8.42 (2,107)*Material (NU-6, CST) 14.07 (1,107)*HL group by material 0.73 (2,107)Noise (cafeteria noise, babble) 49.40 (1,107)*HL group by noise 4.17 (2,107)Snr (+5, +10 dB) 72.13 (1,107)*HL group by snr 1.18 (2,107)Sndlev (60, 75 dB SPL) 71.27 (1,107)*HL group by sndlev 12.80 (2,107)*Material by noise 0.28 (1,107)HL group by material by noise 0.84 (2,107)Material by snr 0.51 (1,107)HL group by material by snr 0.34 (2,107)Material by sndlev 0.83 (1,107)HL group by material by sndlev 2.62 (2,107)Noise by snr 4.35 (1,107)HL group by noise by snr 1.38 (2,107)Noise by sndlev 2.28 (1,107)HL group by noise by sndlev 4.45 (2,107)Snr by sndlev 9.31 (1,107)*HL group by snr by sndlev 10.80 (2,107)*Material by noise by snr 0.65 (1,107)HL group by material by noise by snr 0.10 (2,107)Material by noise by sndlev 1.68 (1,107)HL group by material by noise by sndlev 1.43 (2,107)Material by snr by sndlev 0.25 (1,107)HL group by material by snr by sndlev 0.48 (2,107)Noise by snr by sndlev 2.39 (1,107)HL group by noise by snr by sndlev 0.09 (2,107)Material by noise by snr by sndlev 0.30 (1,107)HL group by material by noise by snr by sndlev 1.12 (2,107)

*p < .01

Figure 9. Scatterplots of NU-6 percent-correct scores for individualparticipants. The top panel plots the aided score for the linear settingagainst the aided score for the BILL setting, whereas the bottompanel plots aided score for the linear setting against the unaidedscore. Triangles represent scores obtained in babble, whereassquares represent those obtained in cafeteria noise. There are a totalof 880 datapoints in each panel (440 for babble and 440 forcafeteria noise) for the 110 participants in the study. Solid lines ineach panel represent diagonal and 95% critical-difference bound-aries above and below the diagonal (Thornton & Raffin, 1978).

study. The extent to which these instructions could havebiased the participants’ estimates of hearing-aid use isunclear. The validity of the estimates of hearing-aid useis reinforced, however, by the fact that participants withsevere hearing loss reported greater daily usage than thosewith milder hearing loss and that many participants



reported daily usage that was either greater or less thanthe minimum usage targeted in the audiologist’s instruc-tions. Finally, the HAPI provided additional support forsignificant benefit in that, on average, participants ratedtheir hearing aids as being “helpful.” Thus, this large-scalestudy documents significant benefit provided by well-fit

Figure 10. Scatterplots of CST percent-correct scores for individualparticipants. The top panel plots the aided score for the linear settingagainst the aided score for the BILL setting, whereas the bottompanel plots the aided score for the linear setting against the unaidedscore. Triangles represent scores obtained in babble, whereassquares represent those obtained in cafeteria noise. There are a totalof 880 datapoints in each panel (440 for babble and 440 forcafeteria noise) for the 110 participants in this study. Solid lines ineach panel represent diagonal and 95% critical-difference bound-aries above and below the diagonal (Thornton & Raffin, 1978).

Figure 11. Scatterplot of mean NU-6 scores obtained in babble foreach hearing-loss subgroup plotted as a function of the SpeechIntelligibility Index (SII). All unfilled symbols represent unaidedlistening conditions, and filled symbols represent aided listening. Thesolid line represents the best-fitting 3rd-order polynomial, whereasthe dotted lines represent 95% prediction intervals, or populationconfidence intervals, above and below the best-fitting polynomial.The best-fitting polynomial accounts for 85.2% of the variance.

linear amplification, including significant improvementsin speech-recognition performance in noise. Moreover,equivalent benefit was measured for the linear and BILL-processing circuits. Although BILL processing did not re-sult in aided performance exceeding that achieved withwell-fit linear amplification, both circuits provided signifi-cant, measurable, and equivalent benefit across a widerange of measures and conditions.

It is important to recognize the importance of theterm well-fit in the preceding sentence. The real-ear gainmeasured in these participants was in close agreementwith that prescribed by the NAL-R procedure out to afrequency of 4000 Hz, thereby making a wide portion ofthe speech spectrum audible. The importance of the re-gion from 2000 to 4000 Hz to the understanding of speechin noise by hearing-impaired listeners has been empha-sized previously (e.g., Lee & Humes, 1993). Moreover,output limiting was adjusted so that SSPL90 was main-tained below an uncomfortable level for each patient.Although this may not have had a direct bearing on themeasures of objective benefit, it most likely had a sig-nificant impact on the amount of time the hearing aidswere worn by the participants.

A wide range of listening conditions was sampled inthis study: a total of 16 measures of speech recognitionin noise, resulting in 16 objective measures of benefit



per participant. When attempting to determine indi-vidual differences in the benefit provided by the hear-ing aids, the large number of measures poses some chal-lenges in defining benefit for individual participants. Forexample, should one consider a participant to have con-clusively demonstrated significant benefit only whenshowing significant benefit on all 16 speech-recognitionmeasures or is 8 out of 16 adequate? Perhaps one shouldonly care that the participant showed significant im-provement on any one condition of the 16 sampled. Thatone condition, for instance, could prove to be a highlyimportant and frequently encountered listening situa-tion for the participant.

Our approach to determining the number of individualparticipants who demonstrated significant benefit was thefollowing. First, the data were grouped by test material(NU-6, CST), hearing-loss category (mild, moderate, se-vere), and speech presentation level (60, 75 dB SPL). Foreach of these subgroups, a total of four listening condi-tions remained (two SNRs and two noise types). The per-centage of participants showing significant (p < .05) ben-efit on at least two of these four conditions was thendetermined. To evaluate significance, the individual scoreswere converted to rationalized arcsine units (RAUs;Studebaker, 1985), which enable the use of a constant-RAU difference score as a criterion for significance. For

the NU-6 test, a RAU difference of 18.1 was used to es-tablish significance (Studebaker, 1985), whereas Cox etal. (1988) recommend a 15.5 RAU difference-score crite-rion for the CST. Table 12 provides the results of this analy-sis. Each entry in the table represents the percentage ofparticipants showing significant improvements for two ofthe four conditions included in each subset of conditionsrepresented in the table. It is apparent from the values inthis table that about 60–80% of the participants showedsignificant improvement in at least half of the conditionswhen speech is presented at normal conversational levels(60 dB). This statement applies across test materials andhearing-loss categories, although there appear to be somesystematic variations in this percentage with hearing-losscategory. At the raised speech level (75 dB), a lower per-centage of each hearing-loss group demonstrated signifi-cant improvement than at normal conversational levels.At the higher speech level, moreover, the effects of speechmaterial (NU-6, CST) and hearing-loss category on theobserved percentages are more apparent. It is probablynot too surprising that fewer participants demonstratedsignificant benefit for raised speech levels than for nor-mal levels. Recall that benefit is the relative differencebetween unaided and aided performance. At higher speechlevels, listeners—especially those having milder impair-ments—will obtain higher unaided scores and conse-quently will have less room for improvement when thehearing aid is worn. Even so, approximately 20–60% oflisteners with moderate or severe hearing loss demon-strated significant benefit for speech recognition in noisein this study at the higher speech presentation level.

AcknowledgmentsThis work was supported, in part, by research contracts

provided by Dahlberg, Inc. to the investigators at each of theclinical sites. The first author was not one of the clinicalinvestigators for the study, but was hired by the study sponsoras a paid consultant while the study was underway to overseethe data collection, analyses, and internal reporting. Theauthors would like to express appreciation for their support toall those involved in this project at Dahlberg, Inc.—especiallyMelanie Raska and Tom Scheller (presently with anotherhearing-aid company); those at Bausch & Lomb Incorpo-rated—especially Eric Ankerud, Heather Bornemann, andTom Crescuillo; and those involved at the participatingclinical sites—especially Tara Thomas. In addition, twoindividuals at the University of Iowa deserve special mentionfor their significant contributions to this project. First, DonSchum, presently working for another hearing-aid manufac-turer, played a major role in the design and development ofthe clinical protocol used in this study. Second, AaronParkinson, who assumed Don’s on-site responsibilities at theUniversity of Iowa when Don left Iowa. Finally, preparation ofthis work for publication was supported, in part, by a grantfrom the National Institute on Aging to the first author and,in part, by the Retirement Research Foundation.

Figure 12. Scatterplot of mean CST scores obtained in babble foreach hearing-loss subgroup plotted as a function of the SpeechIntelligibility Index (SII). All unfilled symbols represent unaidedlistening conditions, and filled symbols represent aided listening. Thesolid line represents the best-fitting 2nd-order polynomial, whereasthe dotted lines represent 95% prediction intervals, or populationconfidence intervals, above and below the best-fitting polynomial.The best-fitting polynomial accounts for 80.6% of the variance.



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Received July 10, 1996

Accepted January 10, 1997

Contact author: Larry E. Humes, PhD, Department ofSpeech and Hearing Sciences, Indiana University,Bloomington, IN 47405

Table 12. Percentage of participants in each hearing-loss groupwho showed significant (p < .05) benefit (aided scores > unaidedscores) on at least half of the conditions (two of four) tested for thespecified test material and speech presentation level.

Presentation level

Hearing-loss group 60 dB SPL 75 dB SPL

NU-6 test material


CST test material


a comparison of the benefit provided by well-fit linear hearing aids and instruments with automatic...

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