Hearing Aid Frequency Response Research Articles

Characterization and Prediction of Speech Intelligibility at the Output of Hearing Aids in a Noisy Working Environment.

Hearing aids are more and more technically advanced, but do not necessarily guarantee the reproduction of useful signals in all working environments. This is particularly the case for speech intelligibility. This study focuses on the prediction of hearing aid performance in the case of a moderate deafness setting, in service and industrial work environments. To improve intelligibility, hearing aids propose signal processing options such as noise reduction and compression. These processes can transform hearing aids into nonlinear systems. The aim of this study is to develop a nonlinear method for the characterization of hearing aids. The method is based on the synchronized swept sine (SSS) signal method.[16] The SSS method is applied for determining hearing aid frequency responses fitted according to the present methodology and several processing options. The characterization of hearing aid's program containing the noise reduction function is specifically analyzed. Indeed, to be fully active and efficient, the hearing aid, with the noise reduction feature activated, needs to be immersed in a noisy environment which does not allow nonlinear characterization. A linear approach is taken to study this feature. Three hearing aids commonly sold by hearing care professionals are studied here; all of them have three different programs. The characterization for each program is discussed. The statistical study showed that the intelligibility, assessed using the speech transmission index in these sound environments, is well estimated for every program, although certain differences are observed when the compression effect is too high in the service work sector. The characterizations of hearing aids using the programs studied did not highlight the presence of frequency nonlinearities. The characterization method could not take into account amplitude nonlinearities when there is too much gain compression in the hearing process. Globally, all the hearing aid programs provided a very significant improvement in intelligibility in service and industrial work contexts.

Rethinking the Audiogram for Hearing Aid Selection

Rethinking the Audiogram for Hearing Aid Selection

Clinical Significance or Statistical Significance: Which One Should Be Considered for Analyzing the Gain- Frequency Responses of Hearing Aids?

Background and Aim: When analyzing the gain-frequency response of a hearing aid, data can be analyzed both clinically and statistically. This study aimed to investigate and compare the gain-frequency responses using statistical and clinical analyses under active digital noise reduction (DNR-on) and inactive digital noise reduction (DNR-off) conditions.
 Methods: The gain-frequency responses of a hearing aid for one of the most well-known commercial digital hearing aid manufacturers were measured using the FP35 hearing aid analyzer (Frye Electronics Inc., USA) by presenting two types of signals (digital speech and composite noise) at input levels of 65 and 80 dB SPL under the DNR-on and DNR-off conditions. Data analysis was performed both statistically (using Wilcoxon signed rank test) and clinically (using 3 dB difference criterion).
 Results: A statistically significant difference was found in the gain-frequency responses for all speech and noise input levels between the two conditions; while a clinically significant difference was observed only at noise input levels of 65 and 80 dB SPL.
 Conclusion: For analyzing the hearing aid performance, both clinical and statistical analyses should be considered.
 
 Keywords: Digital noise reduction; gain-frequency response; clinical analysis

Extended High Frequency Hearing, but Not Tinnitus, Is Associated With Every-Day Cognitive Performance.

Research into the potential associations between tinnitus and cognition has investigated specific cognitive domains in laboratory settings despite adults with tinnitus reporting broad cognitive difficulties in every-day life. To address this limitation, the present study compared performance and perceived exertion on a visual office-like task in 38 adults with tinnitus (19 with normal hearing and 19 with hearing loss) and 38 adults without tinnitus (19 with normal hearing and 19 with hearing loss) matched for age, sex and educational background. All participants were also assessed for hearing, anxiety and depression, and participants with tinnitus were also assessed for tinnitus handicap. No associations were found between presence of tinnitus and cognitive performance (mean total rate correct score on the visual office-like task being 2.9 for the tinnitus group, 2.8 for the control group, p = 0.612) and perceived exertion (mean ratings of perceived exertion on the Borg CR10-scale being 5.8 for the tinnitus group, 6.5 for the control group, p = 0.063) on the visual office-like task when corrected for standard (0.125 to 8 kHz) and extended high frequency (10 to 16 kHz) hearing thresholds, anxiety, and depression. The correction for extended high frequency average (10, 12.5, 14, and 16 kHz) hearing threshold was significant for performance (p = 0.009) but not perceived exertion on the visual office-like task. Overall, the results showed extended high frequency hearing, but not tinnitus, was associated with every-day cognitive performance. This indicates clinical testing of hearing thresholds above 8 kHz could support clinicians’ identification and management of cognitive difficulties. One management method suggested by the current findings would include provision of auditory stimulation at frequencies exceeding the frequency response of many current hearing aids.

Effects of Sound-Induced Hearing Loss and Hearing Aids on the Perception of Music

Exposure to high-level music produces several physiological changes in the auditory system that lead to a variety of perceptual effects. Damage to the outer hair cells within the cochlea leads to a loss of sensitivity to weak sounds, loudness recruitment (a more rapid than normal growth of loudness with increasing sound level), and reduced frequency selectivity. Damage to inner hair cells and/or synapses leads to degeneration of neurons in the auditory nerve and to a reduced flow of information to the brain. This leads to poorer auditory discrimination and may contribute to reduced sensitivity to the temporal fine structure of sounds and to poor pitch perception. Hearing aids compensate for the effects of threshold elevation and loudness recruitment via multichannel amplitude compression, but they do not compensate for reduced frequency selectivity or loss of inner hair cells/synapses/neurons. Multichannel compression can impair some aspects of the perception of music, such as the ability to hear out one instrument or voice from a mixture. The limited frequency range and irregular frequency response of most hearing aids is associated with poor sound quality for music. Finally, systems for reducing acoustic feedback can have undesirable side effects when listening to music.

Fitting recommendations and clinical benefit associated with use of the NAL-NL2 hearing-aid prescription in Nucleus cochlear implant recipients

Objective: For a group of cochlear implant recipients, who use hearing aids in the contralateral ear, the benefit of NAL-NL2 relative to a recipients’ own prescription was assessed. Whether there was a preferred frequency response and/or gain deviation from NAL-NL2 was then investigated. Design: Speech recognition and self-reported ratings of benefit were examined for the recipients’ own prescription compared to the NAL-NL2 prescription, in the bimodal and hearing-aid alone conditions. Paired-comparison of hearing-aid frequency response was conducted with default NAL-NL2 and two variants, a low frequency boost or cut. Using a loudness balancing procedure, the hearing-aid gain required to achieve equal loudness between the devices was measured. Study sample: Sixteen adults with post-lingual hearing loss. Results: A 22% increase in group median word score in quiet with use of NAL-NL2 in the hearing-aid alone condition. In the bimodal condition there was no improvement with NAL-NL2. Default NAL-NL2 frequency response was preferred by 67% of participants. For 56% of participants, the preferred gain to achieve loudness balance across bimodal devices was within 5-dB of prescribed values. Conclusions: The NAL-NL2 prescription provides a high level of clinical performance, and an acceptable frequency response and gain for most participants.

Evaluation of hearing aid frequency response fittings in pediatric and young adult bimodal recipients.

A coordinated fitting of a cochlear implant (CI) and contralateral hearing aid (HA) for bimodal device use should emphasize balanced audibility and loudness across devices. However, guidelines for allocating frequency information to the CI and HA are not well established for the growing population of bimodal recipients. The study aim was to compare the effects of three different HA frequency responses, when fitting a CI and an HA for bimodal use, on speech recognition and localization in children/young adults. Specifically, the three frequency responses were wideband, restricted high frequency, and nonlinear frequency compression (NLFC), which were compared with measures of word recognition in quiet, sentence recognition in noise, talker discrimination, and sound localization. The HA frequency responses were evaluated using an A B₁ A B₂ test design: wideband frequency response (baseline-A), restricted high-frequency response (experimental-B₁), and NLFC-activated (experimental-B2). All participants were allowed 3-4 weeks between each test session for acclimatization to each new HA setting. Bimodal benefit was determined by comparing the bimodal score to the CI-alone score. Participants were 14 children and young adults (ages 7-21 yr) who were experienced users of bimodal devices. All had been unilaterally implanted with a Nucleus CI24 internal system and used either a Freedom or CP810 speech processor. All received a Phonak Naida IX UP behind-the-ear HA at the beginning of the study. Group results for the three bimodal conditions (HA frequency response with wideband, restricted high frequency, and NLFC) on each outcome measure were analyzed using a repeated measures analysis of variance. Group results using the individual "best bimodal" score were analyzed and confirmed using a resampling procedure. Correlation analyses examined the effects of audibility (aided and unaided hearing) in each bimodal condition for each outcome measure. Individual data were analyzed for word recognition in quiet, sentence recognition in noise, and localization. Individual preference for the three bimodal conditions was also assessed. Group data revealed no significant difference between the three bimodal conditions for word recognition in quiet, sentence recognition in noise, and talker discrimination. However, group data for the localization measure revealed that both wideband and NLFC resulted in significantly improved bimodal performance. The condition that yielded the "best bimodal" score varied across participants. Because of this individual variability, the "best bimodal" score was chosen for each participant to reassess group data within word recognition in quiet, sentence recognition in noise, and talker discrimination. This method revealed a bimodal benefit for word recognition in quiet after a randomization test was used to confirm significance. The majority of the participants preferred NLFC at the conclusion of the study, although a few preferred a restricted high-frequency response or reported no preference. These results support consideration of restricted high-frequency and NLFC HA responses in addition to traditional wideband response for bimodal device users.

The relationship between hearing aid frequency response and acceptable noise level in patients with sensorineural hearing loss.

Background:When fitting hearing aid as a compensatory device for an impaired cochlea in a patient with sensorineural hearing loss (HL), it is needed to the effective and efficient frequency response would be selected regarding providing the patient's perfect speech perception. There is not any research about the effects of frequency modifications on speech perception in patients with HL regarding the cochlear desensitization. The effect (s) of modifications in frequency response of hearing aid amplification on the results of acceptable noise level (ANL) test is the main aim of this study.Materials and Methods:The amounts of ANL in two conditions of linear amplification (high frequency emphasis [HFE] and mid frequency emphasis [MFE]) were measured. Thirty-two male subjects who participated in this study had the moderate to severe sensorineural HL.Results:There was not any significant difference between ANL in linear amplification of hearing aid with HFE frequency response and ANL in linear amplification of hearing aid with MFE frequency response.Conclusion:The gain modification of frequency response not only does not affect the patient's performance of speech intelligibility in ANL test. This indicates that we need to note to the cochlear desensitization phenomenon when fitting hearing aid as a compensatory device for an impaired cochlea in a patient. The cochlear desensitization has not been considered properly in hearing aid fitting formula which is needed to be explored more about the bio-mechanisms of impaired cochlea.

Perceptual Effects of Noise Reduction With Respect to Personal Preference, Speech Intelligibility, and Listening Effort

Most modern hearing aids use noise reduction to increase listening comfort in noisy environments. However, it is unclear whether perceptual effects (e.g., intelligibility, listening effort, and preference) of noise reduction differ among hearing aids and among listeners. The authors compared perceptual scores across different hearing aid noise-reduction systems to determine (1) whether noise-reduction systems differ perceptually and (2) which factors underlie the overall preference of individual listeners. The authors recorded hearing aid noise-reduction outputs and used these signals in a laboratory experiment. The recording method allowed the evaluation of noise reduction in an isolated form, without the dominant effects of hearing aid frequency response and interactions with dynamic-range compression. Ten normal-hearing subjects listened to speech in babble noise processed by noise reduction from four different hearing aids. The subjects performed (1) speech-intelligibility tests, (2) listening-effort ratings, and (3) paired-comparison ratings with respect to noise annoyance, speech naturalness, and overall preference. Noise-reduction systems from different hearing aids differed in the degree to which they influenced the noise annoyance and speech naturalness perceived by the normal-hearing listeners. Small differences in intelligibility and effort scores were found among different noise-reduction systems but not between having noise reduction on and off. Subjects differed in whether their overall preference was more strongly related to noise annoyance or to speech naturalness. The authors conclude that noise annoyance and speech naturalness are determining factors for the overall preference of normal-hearing listeners for a specific noise-reduction condition, and found individual differences in the preferred weighting of these factors even in a homogeneous group of normal-hearing listeners. Subsequent experiments should include hearing-impaired subjects to determine whether these conclusions also hold for a more heterogeneous group of listeners. If these results can be extrapolated to hearing-impaired listeners, the fitting and fine-tuning of noise reduction in hearing aids needs considerable revision.

TEST COUPLER FOR HEARING INSTRUMENTS EMPLOYING OPEN-FIT EAR CANAL TIPS

In a system and method for open fitting hearing aid frequency response sound measurements, a test space is provided having located therein a sound source, a hearing aid with a microphone, and an open fit receiver. An acoustic shield is provided and within the acoustic shield an ear simulator coupler is provided having an ear extension attached thereto, the ear extension having mounted thereto at least a portion of the open fit receiver. A measurement unit receives sound signals from the ear simulator coupler.

Comparison of the frequency response of acoustic and implantable hearing aids

Comparison of the frequency response of acoustic and implantable hearing aids

Results reported from two clinical trials of a real-ear system within a hearing aid

Results reported from two clinical trials of a real-ear system within a hearing aid

Hearing aids plus cochlear implants: Optimizing the bimodal pediatric fitting

Hearing aids plus cochlear implants: Optimizing the bimodal pediatric fitting

Hearing Aid Low Frequency Cut: Effect on Mandarin Tone and Vowel Perception in Normal-Hearing Listeners

Objective: To investigate the impact of low frequency cuts (LCs) in hearing aid frequency response on Mandarin tone and vowel perception at varying signal-to-noise ratios (S/N ratios). Patients and Methods: Four LC conditions were reviewed, using a programmable, behind-the-ear hearing aid: no LC (NoLC), a 6-dB/octave LC (LC6), a 12-dB/octave LC (LC12), and an 18-dB/octave LC (LC18). Five S/N ratios for speech to white noise were selected: +10 dB, +5 dB, 0 dB, –5 dB and –10 dB. Speech and noise stimuli were presented to 25 normal-hearing, native Mandarin-speaking listeners monaurally. Results: Tone and vowel recognition scores were high for subjects in all experimental conditions except for LC18 and S/N –10 dB. The LCs had minimal impact on tone perception in the positive S/N and S/N 0 conditions. Significant differences for tone recognition were found between the NoLC and LC6, and the LC6 and LC18 conditions with negative S/N ratios. Significant differences in vowel recognition were observed between the LC12 and LC18 settings, at all S/N conditions. Conclusion: LC hearing aid settings may negatively impact on vowel recognition, and may adversely affect Mandarin tone recognition in adverse noise conditions, in normal-hearing listeners.

Effect of variations in hearing-aid frequency response on real-life functional performance of children with severe or profound hearing loss

This study examined the effect of variations in hearing-aid frequency response on real-life functional performance of children with severe to profound hearing loss. A cross-over design was used in a double-blind comparison of the NAL prescription with alternatives that produced either a BOOST or a CUT (6dB/octave from 0.5 to 2kHz), relative to the NAL response. The functional performance of 30 children (aged 7 months to 16 years) when wearing hearing aids adjusted to each response over two to four weeks was assessed by using parents’ and teachers’ observations (PEACH and TEACH scales). Intelligibility judgments and self-reports were also obtained from school-aged children. Results indicated that on average, variations in frequency response resulted in differences in functional performance in real life. There were significant correlations between PEACH and TEACH, and also between children's intelligibility judgments and subjective reports from children and their parents and teachers. The findings support the use of the NAL response for initial fitting, and the evaluation of children's amplification needs by a systematic use of parents’ and teachers’ observations.

Temporal Intraspeech Masking of Plosive Bursts: Effects of Hearing Loss and Frequency Shaping

The purposes were (a) to compare masking of consonant bursts by adjacent vowels for listeners with and without hearing loss and (b) to determine the extent to which the temporal intraspeech masking can be reduced by a simulated hearing-aid frequency-response shaping. Fourteen adults with sensorineural hearing loss and 10 with normal hearing participated. Seven of the participants with hearing loss had flat or gradually sloping audiograms, and 7 had steeply sloping losses. Stimuli consisted of 3 consonant bursts (/t/, /p/, /k/) presented in isolation and in vowel-consonant-vowel combinations using the vowel /a/ with formant transition information removed. Normal-hearing listeners were tested using unfiltered stimuli. Listeners with hearing loss were tested using unfiltered stimuli and stimuli filtered to approximate a hearing aid frequency response prescribed by NAL-R. All listeners were tested under earphones at the most comfortable level for the vowel stimulus. Temporal intraspeech masking was quantified as the threshold shift produced by the adjacent vowels. Average intraspeech masking for listeners with steeply sloping hearing loss was significantly higher than that of normal-hearing listeners and those with flat/gradually sloping losses. Greater intraspeech masking was observed for /t/ and /p/ than for /k/. On average, frequency shaping significantly reduced the amount of intraspeech masking for listeners with steeply sloping hearing losses. Even with appropriate amplification/spectral shaping, however, temporal intraspeech masking remained greater than normal for several individuals. Findings suggest that some individuals with steeply sloping losses may need additional signal processing to supplement frequency shaping to overcome the effect of temporal intraspeech masking.

Identification of Cantonese tones by children with sensory hearing impairment: effects of noise and hearing aid frequency response

The present study examined the tonal identification abilities of a control group (n = 23 normal hearing children, mean age = 13.6 years; SD = 1.9) and two experimental groups: a mild to moderate hearing-impaired group (n = 11, mean age = 15.8 years, SD = 1.9); and, a moderately severe hearing-impaired group (n = 11, mean age = 14.3 years, SD = 3.7). The two experimental groups were tested monaurally in a sound field under two different hearing aid frequency responses and two noise conditions (quiet/noise). All participants in the experimental group were of normal intelligence and free from other disabilities except hearing impairment. The results revealed that tonal identification ability was impeded as the degree of hearing impairment increased. A noise effect was found, showing a significant lower tone identification score in noise than in quiet. The hearing aid frequency response effect, however, did not reach significance. The most common tonal identification errors, made by the hearing-impaired groups, were tone 6/tone 4 and tone 5/tone 2 confusions, with their reciprocals. These results highlight the difficulty of hearing-impaired children in identifying Cantonese tones, particularly in noisy environments.

A novel method of improving sound quality and reducing acoustic feedback in hearing aids

Most current hearing aids have relatively narrow bandwidths, when compared to high-fidelity equipment, and exhibit undamped peaks because the peaks are considered less troublesome than the problem of wax-clogged dampers. Attempting to make hearing aids wider band has typically resulted in increased acoustic feedback problems. The recent availability of an off-the-shelf digital hearing aid integrated circuit amplifier, which contains several biquad filters, when used with special software, automatically detects and suppresses peaks. The filters then further flatten and extend the hearing aid frequency response to 16 kHz, while the appropriate CORFIG correction is added to the frequency response, producing a transparent sound. Open ear versus aided KEMAR recordings were produced using a live jazz trio and a string quartet. The sound quality ratings for eight commercially available digital hearing aids were obtained from several different listening panels. The new response equalization proved advantageous in all cases. The effects of eliminating the peaks in the response on maximum real ear gain achievable before onset of acoustic feedback oscillation will be reported.

Should children who use cochlear implants wear hearing aids in the opposite ear?

The aim of this study was to investigate 1) whether a hearing aid needs to be adjusted differently depending on whether a child wears a cochlear implant or another hearing aid in the contralateral ear; 2) whether the use of a hearing aid and a cochlear implant in opposite ears leads to binaural interference; and 3) whether the use of a hearing aid and a cochlear implant in opposite ears leads to binaural benefits in speech perception, localization, and communicative functioning in real life. Sixteen children participated in this study. All children used a Nucleus 22 or Nucleus 24 cochlear implant system programmed with the SPEAK strategy in one ear. The hearing aid amplification requirements in the nonimplanted ear of these children were determined using two procedures. A paired comparison technique was used to identify the frequency response that was best for speech intelligibility in quiet, and a loudness balancing technique was used to match the loudness of speech in the ear with a hearing aid to that with a cochlear implant. Eleven of the 16 children participated in the investigation of binaural effects. Performance in speech perception, localization, and communicative functioning was assessed under four aided conditions: cochlear implant with hearing aid as worn, cochlear implant alone, hearing aid alone, and cochlear implant with hearing aid adjusted according to individual requirements. Fifteen of the 16 children whose amplification requirements were determined preferred a hearing aid frequency response that was within +/-6 dB/octave of the NAL-RP prescription. On average, the children required 6 dB more gain than prescribed to balance the loudness of the implanted ear for a speech signal presented at 65 dB SPL. For all 11 children whose performance was evaluated for investigating binaural effects, there was no indication of significantly poorer performance under bilaterally aided conditions compared with unilaterally aided conditions. On average, there were significant benefits in speech perception, localization, and aural/oral function when the children used cochlear implants with adjusted hearing aids than when they used cochlear implants alone. All individuals showed benefits in at least one of the measures. Hearing aids for children who also use cochlear implants can be selected using the NAL-RP prescription. Adjustment of hearing aid gain to match loudness in the implanted ear can facilitate integration of signals from both ears, leading to better speech perception. Given that there are binaural advantages from using cochlear implants with hearing aids in opposite ears, clinicians should advise parents and other professionals about these potential advantages, and facilitate bilateral amplification by adjusting hearing aids after stable cochlear implant MAPs are established.

Distortion product otoacoustic emission and auditory brain stem response measures of pediatric sensorineural hearing loss with islands of normal sensitivity.

To assess the accuracy of: 1) distortion product otoacoustic emission (DPOAE) measures for the identification of frequencies at which auditory sensitivity is normal or near normal; and 2) click and nonmasked tone burst-evoked auditory brain stem response (ABR) thresholds for behavioral threshold estimation for children with sensorineural hearing loss characterized by islands of normal sensitivity. DPOAEs and ABRs were recorded from five hearing-impaired and eight normal-hearing pediatric ears. The accuracy with which DPOAEs permitted identification of frequencies at which elevated hearing thresholds were present was examined. ABR and pure-tone threshold differences for the impaired ears were calculated. For three of the five hearing-impaired ears, significant impairments would have been missed based on click-evoked ABR thresholds. One of those hearing-impaired ears provided an essentially normal 500 Hz tone burst-evoked ABR threshold as well. Four of the hearing-impaired ears provided a 500 Hz tone burst-evoked ABR threshold within 10 dB of the respective pure-tone threshold. However, click-evoked ABR and 500 Hz tone burst-evoked ABR threshold data did not adequately delineate the hearing loss configuration for hearing aid frequency response selection. DPOAEs were present at three out of four frequencies from 1000 to 4000 Hz at which sensitivity was normal or near normal (< or =25 dB HL) and absent at 10 out of 11 frequencies at which sensitivity was impaired. The use of DPOAEs to identify frequencies at which sensitivity was normal and the use of tone burst ABR thresholds at frequencies where DPOAEs were absent provided a better estimate of these pure-tone audiograms than was provided by click-evoked and 500 Hz tone burst-evoked ABR thresholds.