Effects of frequency compression and frequency transposition on fricative and affricate perception in listeners with normal hearing and mild to moderate hearing loss

Effect of frequency compression on fricative perception between normal-hearing English and Mandarin listeners

High-frequency speech information is susceptible to inaccurate perception in even mild to moderate forms of hearing loss. Some hearing aids employ frequency-lowering methods such as nonlinear frequency compression (NFC) to help hearing-impaired individuals access high-frequency speech information in more accessible lower-frequency regions. As such techniques cause significant spectral distortion, tests such as the S-Sh Confusion Test help optimize NFC settings to provide high-frequency audibility with the least distortion. Such tests have been traditionally based on speech contrasts pertinent to English. Here, the effects of NFC processing on fricative perception between English and Mandarin listeners are assessed. Small but significant differences in fricative discrimination were observed between the groups. The study demonstrates possible need for language-specific clinical fitting procedures for NFC.

Frequency importance functions in simulated bimodal cochlear-implant users with spectral holes

Frequency importance functions (FIFs) for simulated bimodal hearing were derived using sentence perception scores measured in quiet and noise. Acoustic hearing was simulated using low-pass filtering. Electric hearing was simulated using a six-channel vocoder with three input frequency ranges, resulting in overlap, meet, and gap maps, relative to the acoustic cutoff frequency. Spectral holes present in the speech spectra were created within electric stimulation by setting amplitude(s) of channels to zero. FIFs were significantly different between frequency maps. In quiet, the three FIFs were similar with gradually increasing weights with channels 5 and 6 compared to the first three channels. However, the most and least weighted channels slightly varied depending on the maps. In noise, the patterns of the three FIFs were similar to those in quiet, with steeper increasing weights with channels 5 and 6 compared to the first four channels. Thus, channels 5 and 6 contributed to speech perception the most, while channels 1 and 2 contributed the least, regardless of frequency maps. Results suggest that the contribution of cochlear implant frequency bands for bimodal speech perception depends on the degree of frequency overlap between acoustic and electric stimulation and if noise is absent or present.

The Importance of High-Frequency Bandwidth on Speech and Language Development in Children: A Review of Patricia Stelmachowicz's Contributions to Pediatric Audiology

We review the literature related to Patricia Stelmachowicz's research in pediatric audiology, specifically focusing on the influence of audibility in language development and acquisition of linguistic rules. Pat Stelmachowicz spent her career increasing our awareness and understanding of children with mild to severe hearing loss who use hearing aids. Using a variety of novel experiments and stimuli, Pat and her colleagues produced a robust body of evidence to support the hypothesis that development moderates the role of frequency bandwidth on speech perception, particularly for fricative sounds. The prolific research that came out of Pat's lab had several important implications for clinical practice. First, her work highlighted that children require access to more high-frequency speech information than adults in the detection and identification of fricatives such as /s/ and /z/. These high-frequency speech sounds are important for morphological and phonological development. Consequently, the limited bandwidth of conventional hearing aids may delay the formation of linguistic rules in these two domains for children with hearing loss. Second, it emphasized the importance of not merely applying adult findings to the clinical decision-making process in pediatric amplification. Clinicians should use evidence-based practices to verify and provide maximum audibility for children who use hearing aids to acquire spoken language.

Preference for Combinations of Hearing Aid Signal Processing

PURPOSE

The purpose of this study was to determine how multiple types of signal processing activated together influence listeners' preferences.

METHOD

Participants were adults with mild to moderately severe sensorineural hearing loss. Stimuli were spatialized low-context sentences mixed with six-talker babble at 3 and 8 dB signal-to-noise ratios (SNRs). Stimuli were processed with three common hearing aid processing algorithms: wide dynamic range compression (WDRC), frequency compression (FC), and digital noise reduction (DNR). A full-factorial design with two levels for each algorithm (WDRC & DNR: mild versus strong; FC: ON versus OFF; clinically relevant ranges) was evaluated. Preference was measured using a paired-comparison task within a choice-based conjoint analysis framework. Remote data collection methods were used. A signal fidelity metric quantified the acoustic effects across conditions.

RESULTS

At 3 dB SNR, participants preferred a combination of Slow WDRC and Mild DNR, although the mean preference was small (odds ratio close to 1). At both SNRs when Strong DNR was used, Fast WDRC was preferred over Slow WDRC. This may be related to signal fidelity, which was lower for the combination of Fast WDRC and Mild DNR and higher for the combination of Slow WDRC and either Mild DNR or Strong DNR. There was no effect of FC on preference or signal fidelity.

CONCLUSIONS

WDRC and DNR together influenced both listeners' preferences and signal fidelity in the investigated listening conditions. On average, the small effect sizes suggest that minor fine-tuning adjustments to hearing aid algorithms may not result in a substantial change in clinical outcomes.

Phoneme acquisition in French-speaking children with moderate hearing loss

The current study aims to provide a more precise understanding of phoneme acquisition by children with moderate hearing loss (MHL), since they have been an under-studied population among children with hearing loss. The acquisition of sounds by 15 children with MHL (mean: 3;11 year-old) was compared to that by six younger normal-hearing (YNH) children (mean: 2;8 year-old). All the children were video- and audio-recorded in interaction with one or both parents in two semi-spontaneous tasks, and during a naming task. All their productions were analysed in terms of percentage of accuracy and substitution patterns. Similarities and differences between the two populations were observed. Globally, the phoneme level of accuracy of children with MHL was similar to that of YNH, but with a general delay. The observation of substitution patterns revealed differences between the two populations, such as prevalent fortition of fricatives and /ʁ/ by children with MHL, which was unusual among YNH children. Another difference was the prevalent posteriorization of coronal fricatives by children with MHL, whereas anteriorization of post-alveolar fricatives was more common in YNH children. These findings highlight the role of perception and language experience in phonological acquisition, showing that an atypical hearing experience may not only cause a delay, but also the emergence of a specific developmental path.

A comparison of speech intelligibility and subjective quality with hearing-aid processing in older adults with hearing loss

OBJECTIVE

This study characterised the relationship between speech intelligibility and quality in listeners with hearing loss for a range of hearing-aid processing settings and acoustic conditions.

DESIGN

Binaural speech intelligibility scores and quality ratings were measured for sentences presented in babble noise and processed through a hearing-aid simulation. The intelligibility-quality relationship was investigated by (1) assessing the effects of experimental conditions on each task; (2) directly comparing intelligibility scores and quality ratings for each participant across the range of conditions; and (3) comparing the association between signal envelope fidelity (represented by a cepstral correlation metric) and intelligibility and quality.

STUDY SAMPLE

Participants were 15 adults (7 females; age range 59-81 years) with mild to moderately severe sensorineural hearing loss.

RESULTS

Intelligibility and quality showed a positive association both with each other and with changes to signal fidelity introduced by the entire acoustic and signal-processing system including the additive noise and the hearing-aid output. As signal fidelity decreased, quality ratings changed at a slower rate than intelligibility scores. Individual psychometric functions were more variable for quality compared to intelligibility.

CONCLUSIONS

Variability in the intelligibility-quality relationship reinforces the importance of measuring both intelligibility and quality in clinical hearing-aid fittings.

Effects of extended high frequency bandwidth in osseointegrated bone conduction device users

High-frequency hearing above 5000 Hz improves the detection and discrimination of high frequency phonemes. Improved access to high-frequency hearing may be particularly advantageous in unilaterally deafened listeners who experience reduced access to high frequency speech cues on their impaired side and decreased speech perception abilities in competing noise. This study aimed to investigate the effects of extended high-frequency bandwidth on speech perception in unilaterally deafened osseointegrated bone conduction hearing device recipients. To study the effect of extended high-frequency bandwidth, participants underwent aided testing in narrow bandwidth and extended high-frquency bandwidth BCD listening conditions. Aided word and phoneme recognition in quiet was assessed at soft and conversational speech levels with the better ear plugged. Aided thresholds and Ling 6 phoneme sounds were also assessed in quiet with the better ear plugged. Speech perception in noise was assessed at ± 90° and co-located at 0° using the adaptive Hearing in Noise Test. Findings demonstrate a significant improvement in speech perception outcomes when listening with extended high-frequency bandwidth. Extended high-frequency bandwidth significantly improved word and phoneme recognition for soft and average conversational speech. The largest effects were observed for voiceless phonemes. Results suggest use of bone conduction devices with extended high-frequency bandwidth result in improved hearing outcomes when compared with narrow bandwidth bone conduction devices.

Clinical Considerations for Routine Auditory and Vestibular Monitoring in Patients With Cystic Fibrosis

Purpose Specific classes of antibiotics, such as aminoglycosides, have well-established adverse events producing permanent hearing loss, tinnitus, and balance and/or vestibular problems (i.e., ototoxicity). Although these antibiotics are frequently used to treat pseudomonas and other bacterial infections in patients with cystic fibrosis (CF), there are no formalized recommendations describing approaches to implementation of guideline adherent ototoxicity monitoring as part of CF clinical care. Method This consensus statement was developed by the International Ototoxicity Management Working Group (IOMG) Ad Hoc Committee on Aminoglycoside Antibiotics to address the clinical need for ototoxicity management in CF patients treated with known ototoxic medications. These clinical protocol considerations were created using consensus opinion from a community of international experts and available evidence specific to patients with CF, as well as published national and international guidelines on ototoxicity monitoring. Results The IOMG advocates four clinical recommendations for implementing routine and guideline adherent ototoxicity management in patients with CF. These are (a) including questions about hearing, tinnitus, and balance/vestibular problems as part of the routine CF case history for all patients; (b) utilizing timely point-of-care measures; (c) establishing a baseline and conducting posttreatment evaluations for each course of intravenous ototoxic drug treatment; and (d) repeating annual hearing and vestibular evaluations for all patients with a history of ototoxic antibiotic exposure. Conclusion Increased efforts for implementation of an ototoxicity management program in the CF care team model will improve identification of ototoxicity signs and symptoms, allow for timely therapeutic follow-up, and provide the clinician and patient an opportunity to make an informed decision about potential treatment modifications to minimize adverse events. Supplemental Material https://doi.org/10.23641/asha.16624366.

Functional Impacts of Aminoglycoside Treatment on Speech Perception and Extended High-Frequency Hearing Loss in a Pediatric Cystic Fibrosis Cohort

Purpose The purpose of this study is to better understand the prevalence of ototoxicity-related hearing loss and its functional impact on communication in a pediatric and young adult cohort with cystic fibrosis (CF) and individuals without CF (controls). Method We did an observational, cross-sectional investigation of hearing function in children, teens, and young adults with CF (n = 57, M = 15.0 years) who received intravenous aminoglycoside antibiotics and age- and gender-matched controls (n = 61, M = 14.6 years). Participants completed standard and extended high-frequency audiometry, middle ear measures, speech perception tests, and a hearing and balance questionnaire. Results Individuals with CF were 3-4 times more likely to report issues with hearing, balance, and tinnitus and performed significantly poorer on speech perception tasks compared to controls. A higher prevalence of hearing loss was observed in individuals with CF (57%) compared to controls (37%). CF and control groups had similar proportions of slight and mild hearing losses; however, individuals with CF were 7.6 times more likely to have moderate and greater degrees of hearing loss. Older participants displayed higher average extended high-frequency thresholds, with no effect of age on average standard frequency thresholds. Although middle ear dysfunction has not previously been reported to be more prevalent in CF, this study showed that 16% had conductive or mixed hearing loss and higher rates of previous otitis media and pressure equalization tube surgeries compared to controls. Conclusions Individuals with CF have a higher prevalence of conductive, mixed, and sensorineural hearing loss; poorer speech-in-noise performance; and higher rates of multiple symptoms associated with otologic disorders (tinnitus, hearing difficulty, dizziness, imbalance, and otitis media) compared to controls. Accordingly, children with CF should be asked about these symptoms and receive baseline hearing assessment(s) prior to treatment with potentially ototoxic medications and at regular intervals thereafter in order to provide otologic and audiologic treatment for hearing- and ear-related problems to improve communication functioning.

Audibility and Spectral-Ripple Discrimination Thresholds as Predictors of Word Recognition with Nonlinear Frequency Compression

BACKGROUND

Nonlinear frequency compression (NFC) lowers high-frequency sounds to a lower frequency and is used to improve high-frequency audibility. However, the efficacy of NFC varies widely-while some individuals benefit from NFC, many do not. Spectral resolution is one factor that might explain individual benefit from NFC. Because individuals with better spectral resolution understand more speech than those with poorer spectral resolution, it was hypothesized that individual benefit from NFC could be predicted from the change in spectral resolution measured with NFC relative to a condition without NFC.

PURPOSE

This study aimed to determine the impact of NFC on access to spectral information and whether these changes predict individual benefit from NFC for adults with sensorineural hearing loss (SNHL).

RESEARCH DESIGN

Present study is a quasi-experimental cohort study. Participants used a pair of hearing aids set to the Desired Sensation Level algorithm (DSL m[i/o]).

STUDY SAMPLE

Participants were 19 adults with SNHL, recruited from the Boys Town National Research Hospital Participant Registry.

DATA COLLECTION AND ANALYSIS

Participants were seated in a sound-attenuating booth and then percent-correct recognition of words, and spectral-ripple discrimination thresholds were measured for two different conditions, with and without NFC. Because audibility is known to influence spectral-ripple thresholds and benefit from NFC, audibility was quantified using the aided speech intelligibility index (SII). Linear mixed models were generated to predict word recognition using the aided SII and spectral-ripple discrimination thresholds.

RESULTS

While NFC did not influence percent-correct word recognition, participants with higher (better) aided SII and spectral-ripple discrimination thresholds understood more words than those with either a lower aided SII or spectral-ripple discrimination threshold. Benefit from NFC was not predictable from a participant's aided SII or spectral-ripple discrimination threshold.

CONCLUSION

We have extended previous work on the effect of audibility on benefit from NFC to include a measure of spectral resolution, the spectral-ripple discrimination threshold. Clinically, these results suggest that patients with better audibility and spectral resolution will understand speech better than those with poorer audibility or spectral resolution; however, these results are inconsistent with the notion that individual benefit from NFC is predictable from aided audibility or spectral resolution.

Effects of Adaptive Non-linear Frequency Compression in Hearing Aids on Mandarin Speech and Sound-Quality Perception

Objective

This study was aimed at examining the effects of an adaptive non-linear frequency compression algorithm implemented in hearing aids (i.e., SoundRecover2, or SR2) at different parameter settings and auditory acclimatization on speech and sound-quality perception in native Mandarin-speaking adult listeners with sensorineural hearing loss.

Design

Data consisted of participants’ unaided and aided hearing thresholds, Mandarin consonant and vowel recognition in quiet, and sentence recognition in noise, as well as sound-quality ratings through five sessions in a 12-week period with three SR2 settings (i.e., SR2 off, SR2 default, and SR2 strong).

Study Sample

Twenty-nine native Mandarin-speaking adults aged 37–76 years old with symmetric sloping moderate-to-profound sensorineural hearing loss were recruited. They were all fitted bilaterally with Phonak Naida V90-SP BTE hearing aids with hard ear-molds.

Results

The participants demonstrated a significant improvement of aided hearing in detecting high frequency sounds at 8 kHz. For consonant recognition and overall sound-quality rating, the participants performed significantly better with the SR2 default setting than the other two settings. No significant differences were found in vowel and sentence recognition among the three SR2 settings. Test session was a significant factor that contributed to the participants’ performance in all speech and sound-quality perception tests. Specifically, the participants benefited from a longer duration of hearing aid use.

Conclusion

Findings from this study suggested possible perceptual benefit from the adaptive non-linear frequency compression algorithm for native Mandarin-speaking adults with moderate-to-profound hearing loss. Periods of acclimatization should be taken for better performance in novel technologies in hearing aids.

The Influence of Non-Linear Frequency Compression on the Perception of Speech and Music in Patients with High Frequency Hearing Loss

Background and Objectives

Non-linear frequency compression (NLFC) technology compresses and shifts higher frequencies into a lower frequency area that has better residual hearing. Because consonants are uttered in the high-frequency area, NLFC could provide better speech understanding. The aim of this study was to investigate the clinical effectiveness of NLFC technology on the perception of speech and music in patients with high-frequency hearing loss.

Subjects and Methods

Twelve participants with high-frequency hearing loss were tested in a counter-balanced order, and had two weeks of daily experience with NLFC set on/off prior to testing. Performance was repeatedly evaluated with consonant tests in quiet and noise environments, speech perception in noise, music perception and acceptableness of sound quality rating tasks. Additionally, two questionnaires (the Abbreviated Profile of Hearing Aid Benefit and the Korean version of the International Outcome Inventory-Hearing Aids) were administered.

Results

Consonant and speech perception improved with hearing aids (NLFC on/off conditions), but there was no significant difference between NLFC on and off states. Music perception performances revealed no notable difference among unaided and NLFC on and off states. The benefits and satisfaction ratings between NLFC on and off conditions were also not significantly different, based on questionnaires, however great individual variability preferences were noted.

Conclusions

Speech perception as well as music perception both in quiet and noise environments was similar between NLFC on and off states, indicating that real world benefits from NLFC technology may be limited in Korean adult hearing aid users.

Extended high frequency hearing and speech perception implications in adults and children

Extended high frequencies (EHF), above 8 kHz, represent a region of the human hearing spectrum that is generally ignored by clinicians and researchers alike. This article is a compilation of contributions that, together, make the case for an essential role of EHF in both normal hearing and auditory dysfunction. We start with the fundamentals of biological and acoustic determinism - humans have EHF hearing for a purpose, for example, the detection of prey, predators, and mates. EHF hearing may also provide a boost to speech perception in challenging conditions and its loss, conversely, might help explain difficulty with the same task. However, it could be that EHF are a marker for damage in the conventional frequency region that is more related to speech perception difficulties. Measurement of EHF hearing in concert with otoacoustic emissions could provide an early warning of age-related hearing loss. In early life, when EHF hearing sensitivity is optimal, we can use it for enhanced phonetic identification during language learning, but we are also susceptible to diseases that can prematurely damage it. EHF audiometry techniques and standardization are reviewed, providing evidence that they are reliable to measure and provide important information for early detection, monitoring and possible prevention of hearing loss in populations at-risk. To better understand the full contribution of EHF to human hearing, clinicians and researchers can contribute by including its measurement, along with measures of speech in noise and self-report of hearing difficulties and tinnitus in clinical evaluations and studies.

Frequency-lowering processing to improve speech-in-noise intelligibility in patients with age-related hearing loss

OBJECTIVE

Modern hearing aids use various signal-processing strategies to improve speech intelligibility. In this manuscript, we studied the linear frequency transposition (LFT), a frequency-lowering algorithm, in patients with age-related hearing loss. Frequency-lowering algorithms transpose high-frequency sounds to a lower-frequency band. The study aimed to assess whether LFT could be used as a tool to improve speech intelligibility in patients with a better high-frequency preservation.

METHODS

The study population consisted of 77 patients (age average 74.8 ± 12.4) wearing hearing aids with an open or tulip coupling system with age-related hearing loss. The unaided air conduction pure tone average (PTA) at 500, 1000, 2000 Hz was 43.5 ± 14.3 dB; the unaided word recognition score (WRS) average was 53.7 ± 12.5%. We compared WRS in all patients with the hearing aid turned on, in "quiet" and using a "pink" and "babble" masking noise. Three hearing aid settings were tested in each acoustic conditions: no transposition (NT), high transposition (HT), and low transposition (LT). "High" and "low" refer to the "start frequency"; all sounds above the start frequency are transposed in a lower-frequency band. When the start frequency was suggested by the fitting software, we called the condition "high transposition"; when the start frequency was set at the lowest possible value provided by the fitting software, we called the condition "low transposition". The quality of the voice was also assessed asking the patient to give a score from 1 to 10, where 10 was the maximum listening comfort [quality of voice score (QVS)].

RESULTS

Collected data were compared for each condition (NT, HT, LT, in quiet, pink noise and babble noise) and no statistically significant differences were found in WRS and QVS (quiet WRS p = 0.07, pink noise WRS p = 0.18, babble noise WRS p = 0.11, QVS p = 0.91). We selected 33 patients with a better WRS in babble noise using transposition (high and low). In this group, the age was significantly lower than patients who did not use transposition (p = 0.01).

CONCLUSION

Linear frequency transposition is not useful to improve speech-in-noise intelligibility in patients with age-related hearing loss. Despite that no statistically significant differences were found, younger people could get advantages from the LFT when babble noise disturbs the listening of speech. The use of FL algorithm as a way to improve speech intelligibility in noisy environments should be always considered.

A double-blind, randomized controlled trial exploring the efficacy of frequency lowering hearing aids in patients with high-frequency hearing loss

OBJECTIVE

Whether linear frequency transposition (LFT) assists individuals with hearing difficulties has been studied for years, but no reliable comparison between LFT hearing aids (HAs) and conventional compression-type HAs has been conducted. Herein, we report on the first, relevant, double-blind, randomized controlled trial on this topic using a large sample size. We compared the efficacies of LFT HAs to those of compression-type HAs in patients with high-frequency hearing loss (HFHL); we also reviewed the literature.

METHODS

A total of 103 patients were randomized into three groups: conventional HAs featuring wide dynamic range compression (control group); HAs featuring LFT (LFT group); and HAs employing both LFT and wide dynamic range compression of high frequencies (combined group). Pure tone averages (PTAs), speech recognition thresholds (SRTs), word recognition scores (WRSs), and Abbreviated Profile of Hearing Aid Benefit (APHAB) inventories were assessed at the initial visit and after 3 months of HA use. Subject preferences in terms of continued use of their HAs were also evaluated.

RESULTS

The PTA, SRT, and WRS scores significantly improved in all three groups. No significant among-group differences were evident. The APHAB score significantly improved only in the control group; HA future-use preference was also highest in this group.

CONCLUSION

LFT did not provide an additional benefit for subjects with HFHL over conventional amplification and users preferred conventional HAs featuring wide dynamic range compression.

Effects of nonlinear frequency compression on Mandarin speech and sound-quality perception in hearing-aid users

Objective: The purpose of the present study was to examine the effects of NLFC fitting in hearing aids and auditory acclimatisation on speech perception and sound-quality rating in hearing-impaired, native Mandarin-speaking adult listeners.Design: Mandarin consonant, vowel and tone recognition were tested in quiet and sentence recognition in noise (speech-shaped noise at a +5 dB signal-to-noise ratio) with NLFC-on and NLFC-off. Sound-quality ratings were collected on a 0-10 scale at each test session. A generalised linear model and correlational analyses were performed.Study sample: Thirty native Mandarin-speaking adults with moderate-to-severe sensorineural hearing loss were recruited.Results: The hearing-impaired listeners showed significantly higher accuracy with NLFC-on than with NLFC-off for consonant and sentence recognition and the recognition performance improved with both NLFC-on and off as a function of increased length of use. The satisfaction score of sound-quality ratings for different types of sounds significantly increased with NLFC-on than with NLFC-off. The speech recognition results showed moderate to strong correlation with the unaided hearing thresholds.Conclusion: For native Mandarin-speaking listeners with hearing loss, the NLFC technology provided modest but significant improvement in Mandarin fricative and sentence recognition. Subjectively, the naturalness and overall preference of sound-quality satisfaction judgement also improved with NLFC.

Speech Perception and Sound-Quality Rating with an Adaptive Nonlinear Frequency Compression Algorithm in Mandarin-Speaking Hearing Aid Users

BACKGROUND

Mandarin Chinese has a rich repertoire of high-frequency speech sounds. This may pose a remarkable challenge to hearing-impaired listeners who speak Mandarin Chinese because of their high-frequency sloping hearing loss. An adaptive nonlinear frequency compression (adaptive NLFC) algorithm has been implemented in contemporary hearing aids to alleviate the problem.

PURPOSE

The present study examined the performance of speech perception and sound-quality rating in Mandarin-speaking hearing-impaired listeners using hearing aids fitted with adaptive NLFC (i.e., SoundRecover2 or SR2) at different parameter settings.

RESEARCH DESIGN

Hearing-impaired listeners' phoneme detection thresholds, speech reception thresholds, and sound-quality ratings were collected with various SR2 settings.

STUDY SAMPLE

The participants included 15 Mandarin-speaking adults aged 32 to 84 years old who had symmetric sloping severe-to-profound sensorineural hearing loss.

INTERVENTION

The participants were fitted bilaterally with Phonak Naida V90-SP hearing aids.

DATA COLLECTION AND ANALYSIS

The outcome measures included phoneme detection threshold using the Mandarin Phonak Phoneme Perception test, speech reception threshold using the Mandarin hearing in noise test (M-HINT), and sound-quality ratings on human speech in quiet and noise, bird chirps, and music in quiet. For each test, five experimental settings were applied and compared: SR2-off, SR2-weak, SR2-default, SR2-strong 1, and SR2-strong 2.

RESULTS

The results showed that listeners performed significantly better with SR2-strong 1 and SR2-strong 2 settings than with SR2-off or SR2-weak settings for speech reception threshold and phoneme detection threshold. However, no significant improvement was observed in sound-quality ratings among different settings.

CONCLUSIONS

These preliminary findings suggested that the adaptive NLFC algorithm provides perceptual benefit to Mandarin-speaking people with severe-to-profound hearing loss.

Comparison of Frequency Transposition and Frequency Compression for People With Extensive Dead Regions in the Cochlea

The objective was to determine the effects of two frequency-lowering algorithms (frequency transposition, FT, and frequency compression, FC) on audibility, speech identification, and subjective benefit, for people with high-frequency hearing loss and extensive dead regions (DRs) in the cochlea. A single-blind randomized crossover design was used. FT and FC were compared with each other and with a control condition (denoted ‘Control’) without frequency lowering, using hearing aids that were otherwise identical. Data were collected after at least 6 weeks of experience with a condition. Outcome measures were audibility, scores for consonant identification, scores for word-final /s, z/ detection (S test), sentence-in-noise intelligibility, and a questionnaire assessing self-perceived benefit (Spatial and Qualities of Hearing Scale). Ten adults with steeply sloping high-frequency hearing loss and extensive DRs were tested. FT and FC improved the audibility of some high-frequency sounds for 7 and 9 participants out of 10, respectively. At the group level, performance for FT and FC did not differ significantly from that for Control for any of the outcome measures. However, the pattern of consonant confusions varied across conditions. Bayesian analysis of the confusion matrices revealed a trend for FT to lead to more consistent error patterns than FC and Control. Thus, FT may have the potential to give greater benefit than Control or FC following extended experience or training.

The S-SH Confusion Test and the Effects of Frequency Lowering

Purpose Frequency lowering in hearing aids can cause listeners to perceive [s] as [ʃ]. The S-SH Confusion Test, which consists of 66 minimal word pairs spoken by 6 female talkers, was designed to help clinicians and researchers document these negative side effects. This study's purpose was to use this new test to evaluate the hypothesis that these confusions will increase to the extent that low frequencies are altered. Method Twenty-one listeners with normal hearing were each tested on 7 conditions. Three were control conditions that were low-pass filtered at 3.3, 5.0, and 9.1 kHz. Four conditions were processed with nonlinear frequency compression (NFC): 2 had a 3.3-kHz maximum audible output frequency (MAOF), with a start frequency (SF) of 1.6 or 2.2 kHz; 2 had a 5.0-kHz MAOF, with an SF of 1.6 or 4.0 kHz. Listeners' responses were analyzed using concepts from signal detection theory. Response times were also collected as a measure of cognitive processing. Results Overall, [s] for [ʃ] confusions were minimal. As predicted, [ʃ] for [s] confusions increased for NFC conditions with a lower versus higher MAOF and with a lower versus higher SF. Response times for trials with correct [s] responses were shortest for the 9.1-kHz control and increased for the 5.0- and 3.3-kHz controls. NFC response times were also significantly longer as MAOF and SF decreased. The NFC condition with the highest MAOF and SF had statistically shorter response times than its control condition, indicating that, under some circumstances, NFC may ease cognitive processing. Conclusions Large differences in the S-SH Confusion Test across frequency-lowering conditions show that it can be used to document a major negative side effect associated with frequency lowering. Smaller but significant differences in response times for correct [s] trials indicate that NFC can help or hinder cognitive processing, depending on its settings.

Speech Perception in Noise and Listening Effort of Older Adults With Nonlinear Frequency Compression Hearing Aids

OBJECTIVES

The purpose of this laboratory-based study was to compare the efficacy of two hearing aid fittings with and without nonlinear frequency compression, implemented within commercially available hearing aids. Previous research regarding the utility of nonlinear frequency compression has revealed conflicting results for speech recognition, marked by high individual variability. Individual differences in auditory function and cognitive abilities, specifically hearing loss slope and working memory, may contribute to aided performance. The first aim of the study was to determine the effect of nonlinear frequency compression on aided speech recognition in noise and listening effort using a dual-task test paradigm. The hypothesis, based on the Ease of Language Understanding model, was that nonlinear frequency compression would improve speech recognition in noise and decrease listening effort. The second aim of the study was to determine if listener variables of hearing loss slope, working memory capacity, and age would predict performance with nonlinear frequency compression.

DESIGN

A total of 17 adults (age, 57-85 years) with symmetrical sensorineural hearing loss were tested in the sound field using hearing aids fit to target (NAL-NL2). Participants were recruited with a range of hearing loss severities and slopes. A within-subjects, single-blinded design was used to compare performance with and without nonlinear frequency compression. Speech recognition in noise and listening effort were measured by adapting the Revised Speech in Noise Test into a dual-task paradigm. Participants were required trial-by-trial to repeat the last word of each sentence presented in speech babble and then recall the sentence-ending words after every block of six sentences. Half of the sentences were rich in context for the recognition of the final word of each sentence, and half were neutral in context. Extrinsic factors of sentence context and nonlinear frequency compression were manipulated, and intrinsic factors of hearing loss slope, working memory capacity, and age were measured to determine which participant factors were associated with benefit from nonlinear frequency compression.

RESULTS

On average, speech recognition in noise performance significantly improved with the use of nonlinear frequency compression. Individuals with steeply sloping hearing loss received more recognition benefit. Recall performance also significantly improved at the group level, with nonlinear frequency compression revealing reduced listening effort. The older participants within the study cohort received less recall benefit than the younger participants. The benefits of nonlinear frequency compression for speech recognition and listening effort did not correlate with each other, suggesting separable sources of benefit for these outcome measures.

CONCLUSIONS

Improvements of speech recognition in noise and reduced listening effort indicate that adult hearing aid users can receive benefit from nonlinear frequency compression in a noisy environment, with the amount of benefit varying across individuals and across outcome measures. Evidence supports individualized selection of nonlinear frequency compression, with results suggesting benefits in speech recognition for individuals with steeply sloping hearing losses and in listening effort for younger individuals. Future research is indicated with a larger data set on the dual-task paradigm as a potential cognitive outcome measure.

The Use of Frequency Lowering Technology in the Treatment of Severe-to-Profound Hearing Loss: A Review of the Literature and Candidacy Considerations for Clinical Application

This article provides a review of the current literature on the topic of frequency lowering hearing aid technology specific to the treatment of severe and profound levels of hearing impairment in child and adult listeners. Factors to consider when assessing listener candidacy for frequency lowering technology are discussed. These include factors related to audiometric assessment, the listener, the type of hearing aid technology, and the verification and validation procedures that can assist in determining candidacy for frequency lowering technology. An individualized candidacy assessment including the use of real-ear verification measures and carefully chosen validation tools are recommended for listeners requiring greater audibility of high-frequency sounds, when compared with amplification via conventional hearing aid technology.

Listener Performance with a Novel Hearing Aid Frequency Lowering Technique

BACKGROUND

Sloping hearing loss imposes limits on audibility for high-frequency sounds in many hearing aid users. Signal processing algorithms that shift high-frequency sounds to lower frequencies have been introduced in hearing aids to address this challenge by improving audibility of high-frequency sounds.

PURPOSE

This study examined speech perception performance, listening effort, and subjective sound quality ratings with conventional hearing aid processing and a new frequency-lowering signal processing strategy called frequency composition (FC) in adults and children.

RESEARCH DESIGN

Participants wore the study hearing aids in two signal processing conditions (conventional processing versus FC) at an initial laboratory visit and subsequently at home during two approximately six-week long trials, with the order of conditions counterbalanced across individuals in a double-blind paradigm.

STUDY SAMPLE

Children (N = 12, 7 females, mean age in years = 12.0, SD = 3.0) and adults (N = 12, 6 females, mean age in years = 56.2, SD = 17.6) with bilateral sensorineural hearing loss who were full-time hearing aid users.

DATA COLLECTION AND ANALYSES

Individual performance with each type of processing was assessed using speech perception tasks, a measure of listening effort, and subjective sound quality surveys at an initial visit. At the conclusion of each subsequent at-home trial, participants were retested in the laboratory. Linear mixed effects analyses were completed for each outcome measure with signal processing condition, age group, visit (prehome versus posthome trial), and measures of aided audibility as predictors.

RESULTS

Overall, there were few significant differences in speech perception, listening effort, or subjective sound quality between FC and conventional processing, effects of listener age, or longitudinal changes in performance. Listeners preferred FC to conventional processing on one of six subjective sound quality metrics. Better speech perception performance was consistently related to higher aided audibility.

CONCLUSIONS

These results indicate that when high-frequency speech sounds are made audible with conventional processing, speech recognition ability and listening effort are similar between conventional processing and FC. Despite the lack of benefit to speech perception, some listeners still preferred FC, suggesting that qualitative measures should be considered when evaluating candidacy for this signal processing strategy.

Listening Effort and Speech Recognition with Frequency Compression Amplification for Children and Adults with Hearing Loss

BACKGROUND

Nonlinear frequency compression (NFC) can improve the audibility of high-frequency sounds by lowering them to a frequency where audibility is better; however, this lowering results in spectral distortion. Consequently, performance is a combination of the effects of increased access to high-frequency sounds and the detrimental effects of spectral distortion. Previous work has demonstrated positive benefits of NFC on speech recognition when NFC is set to improve audibility while minimizing distortion. However, the extent to which NFC impacts listening effort is not well understood, especially for children with sensorineural hearing loss (SNHL).

PURPOSE

To examine the impact of NFC on recognition and listening effort for speech in adults and children with SNHL.

RESEARCH DESIGN

Within-subject, quasi-experimental study. Participants listened to amplified nonsense words that were (1) frequency-lowered using NFC, (2) low-pass filtered at 5 kHz to simulate the restricted bandwidth (RBW) of conventional hearing aid processing, or (3) low-pass filtered at 10 kHz to simulate extended bandwidth (EBW) amplification.

STUDY SAMPLE

Fourteen children (8-16 yr) and 14 adults (19-65 yr) with mild-to-severe SNHL.

INTERVENTION

Participants listened to speech processed by a hearing aid simulator that amplified input signals to fit a prescriptive target fitting procedure.

DATA COLLECTION AND ANALYSIS

Participants were blinded to the type of processing. Participants' responses to each nonsense word were analyzed for accuracy and verbal-response time (VRT; listening effort). A multivariate analysis of variance and linear mixed model were used to determine the effect of hearing-aid signal processing on nonsense word recognition and VRT.

RESULTS

Both children and adults identified the nonsense words and initial consonants better with EBW and NFC than with RBW. The type of processing did not affect the identification of the vowels or final consonants. There was no effect of age on recognition of the nonsense words, initial consonants, medial vowels, or final consonants. VRT did not change significantly with the type of processing or age.

CONCLUSION

Both adults and children demonstrated improved speech recognition with access to the high-frequency sounds in speech. Listening effort as measured by VRT was not affected by access to high-frequency sounds.

Effects of nonlinear frequency compression on the acoustic properties and recognition of speech sounds in Mandarin Chinese

The present study examined the change in spectral properties of Mandarin vowels and fricatives caused by nonlinear frequency compression (NLFC) used in hearing instruments and how these changes affect the perception of speech sounds in normal-hearing listeners. Speech materials, including a list of Mandarin monosyllables in the form of /dV/ (12 vowels) and /Ca/ (five fricatives), were recorded from 20 normal-hearing, native Mandarin-speaking adults (ten males and ten females). NLFC was based on Phonak SoundRecover algorithms. The speech materials were processed with six different NLFC parameter settings. Detailed acoustic analysis revealed that the high front vowel /i/ and certain compound vowels containing /i/ demonstrated positional deviation in certain processed conditions in comparison to the unprocessed condition. All five fricatives showed acoustic changes in spectral features in all processed conditions. Fourteen Mandarin-speaking, normal-hearing adult listeners performed phoneme recognition with the six NLFC processing conditions. When the cut-off frequency was set relatively low, recognition of /s/ was detrimentally affected, whereas none of the NLFC processing configurations affected the other phonemes. The discrepancy between the considerable acoustic changes and the negligible adverse effects on perceptual outcomes is partially accounted for by the phonology system and phonotactic constraints in Mandarin.

Acoustic and perceptual effects of amplitude and frequency compression on high-frequency speech

This study investigated how six different amplification methods influence acoustic properties, and subsequently perception, of high-frequency cues in fricatives that have been processed with conventional full bandwidth amplification or nonlinear frequency compression (NFC)-12 conditions total. Amplification methods included linear gain, fast/slow-acting wide dynamic range compression crossed with fixed/individualized compression parameters, and a method with adaptive time constants. Twenty-one hearing-impaired listeners identified seven fricatives in nonsense syllables produced by female talkers. For NFC stimuli, frequency-compressed filters that precisely aligned 1/3-octave bands between input and output were used to quantify effective compression ratio, audibility, and temporal envelope modulation relative to the input. Results indicated significant relationships between these acoustic properties, each of which contributed significantly to fricative recognition across the entire corpus of stimuli. Recognition was significantly better for NFC stimuli compared with full bandwidth stimuli, regardless of the amplification method, which had complementary effects on audibility and envelope modulation. Furthermore, while there were significant differences in recognition across the amplification methods, they were not consistent across phonemes. Therefore, neither recognition nor acoustic data overwhelmingly suggest that one amplification method should be used over another for transmission of high-frequency cues in isolated syllables. Longer duration stimuli and more realistic listening conditions should be examined.

Languages in Drier Climates Use Fewer Vowels

This study offers evidence for an environmental effect on languages while relying on continuous linguistic and continuous ecological variables. Evidence is presented for a positive association between the typical ambient humidity of a language’s native locale and that language’s degree of reliance on vowels. The vowel-usage rates of over 4000 language varieties were obtained, and several methods were employed to test whether these usage rates are associated with ambient humidity. The results of these methods are generally consistent with the notion that reduced ambient humidity eventually yields a reduced reliance of languages on vowels, when compared to consonants. The analysis controls simultaneously for linguistic phylogeny and contact between languages. The results dovetail with previous work, based on binned data, suggesting that consonantal phonemes are more common in some ecologies. In addition to being based on continuous data and a larger data sample, however, these findings are tied to experimental research suggesting that dry air affects the behavior of the larynx by yielding increased phonatory effort. The results of this study are also consistent with previous work suggesting an interaction of aridity and tonality. The data presented here suggest that languages may evolve, like the communication systems of other species, in ways that are influenced subtly by ecological factors. It is stressed that more work is required, however, to explore this association and to establish a causal relationship between ambient air characteristics and the development of languages.

Auditory perceptual efficacy of nonlinear frequency compression used in hearing aids: A review

Many patients with sensorineural hearing loss have a precipitous high-frequency loss with relatively good thresholds in the low frequencies. This present paper briefly introduces and compares the basic principles of four types of frequency lowering algorithms with emphasis on nonlinear frequency compression (NLFC). A review of the effects of the NLFC algorithm on speech and music perception and sound quality appraisal is then provided. For vowel perception, it seems that the benefits provided by NLFC are limited, which are probably related to the parameter settings of the compression. For consonant perception, several studies have shown that NLFC provides improved perception of high-frequency consonants such as /s/ and /z/. However, a few other studies have demonstrated negative results in consonant perception. In terms of sentence recognition, persistent use of NLFC might provide improved performance. Compared to the conventional processing, NLFC does not alter the speech sound quality appraisal and music perception as long as the compression setting is not too aggressive. In the subsequent section, the relevant factors with regard to NLFC settings, time-course of acclimatization, listener characteristics, and perceptual tasks are discussed. Although the literature shows mixed results on the perceptual efficacy of NLFC, this technique improved certain aspects of speech understanding in certain hearing-impaired listeners. Little research is available on speech perception outcomes in languages other than English. More clinical data are needed to verify the perceptual efficacy of NLFC in patients with precipitous high-frequency hearing loss. Such knowledge will help guide clinical rehabilitation of those patients.

Quality ratings of frequency-compressed speech by participants with extensive high-frequency dead regions in the cochlea

OBJECTIVE

The objective was to assess the degradation of speech sound quality produced by frequency compression for listeners with extensive high-frequency dead regions (DRs).

DESIGN

Quality ratings were obtained using values of the starting frequency (Sf) of the frequency compression both below and above the estimated edge frequency, fe, of each DR. Thus, the value of Sf often fell below the lowest value currently used in clinical practice. Several compression ratios were used for each value of Sf. Stimuli were sentences processed via a prototype hearing aid based on Phonak Exélia Art P.

STUDY SAMPLE

Five participants (eight ears) with extensive high-frequency DRs were tested.

RESULTS

Reductions of sound-quality produced by frequency compression were small to moderate. Ratings decreased significantly with decreasing Sf and increasing CR. The mean ratings were lowest for the lowest Sf and highest CR. Ratings varied across participants, with one participant rating frequency compression lower than no frequency compression even when Sf was above fe.

CONCLUSIONS

Frequency compression degraded sound quality somewhat for this small group of participants with extensive high-frequency DRs. The degradation was greater for lower values of Sf relative to fe, and for greater values of CR. Results varied across participants.

Evaluation of a Frequency-Lowering Algorithm for Adults With High-Frequency Hearing Loss

The objective was to determine the effects of a frequency-lowering algorithm (frequency composition, Fcomp) on consonant identification, word-final /s, z/ detection, the intelligibility of sentences in noise, and subjective benefit, for people with high-frequency hearing loss, including people with dead regions (DRs) in the cochlea. A single-blind randomized crossover design was used. Performance with Bernafon Acriva 9 hearing aids was compared with Fcomp off and Fcomp on. Participants wore the hearing aids in each condition in a counterbalanced order. Data were collected after at least 8 weeks of experience with a condition. Outcome measures were audibility, scores from the speech perception tests, and scores from a questionnaire comparing self-perceived hearing ability with Fcomp off and Fcomp on. Ten adults with mild to severe high-frequency hearing loss (seven with extensive DRs, one with patchy or restricted DRs, and two with no DR) were tested. Fcomp improved the audibility of high-frequency sounds for 6 out of 10 participants. There was no overall effect of Fcomp on consonant identification, but the pattern of consonant confusions varied across conditions and participants. For word-final /s, z/ detection, performance was significantly better with Fcomp on than with Fcomp off. Questionnaire scores showed no differences between conditions. In summary, Fcomp improved word-final /s, z/ detection. No benefit was found for the other measures.

The effects of frequency lowering on speech perception in noise with adult hearing-aid users

OBJECTIVE

Frequency lowering (FL) strategies move high frequency sound into a lower frequency range. This study determined if speech perception differences are observed between some of the different frequency lowering strategies that are available.

DESIGN

A cross-sectional, repeated-measures design was used to compare three hearing aids that used wide-dynamic range compression (WDRC) and either non-linear frequency compression (NFC), linear frequency transposition (LFT), or frequency translation (FT). The hearing aids were matched to prescriptive real ear targets for WDRC. The settings for each FL strategy were adjusted to provide audibility for a 6300 Hz filtered speech signal. Sentence recognition in noise, subjective measures of sound quality, and a modified version of the speech intelligibility index (SII) were measured.

STUDY SAMPLE

Ten adults between the ages of 63 to 82 years with bilateral, high frequency hearing loss.

RESULTS

LFT and FT led to poorer sentence recognition compared to WDRC for most individuals. No difference in sentence recognition occurred with and without NFC. The quality questionnaire and SII showed few differences between conditions.

CONCLUSION

Under similar fitting and testing conditions of this study, FL techniques may not provide speech understanding benefit in certain background noise situations.

Nonlinear frequency compression: Influence of start frequency and input bandwidth on consonant and vowel recognition

By varying parameters that control nonlinear frequency compression (NFC), this study examined how different ways of compressing inaudible mid- and/or high-frequency information at lower frequencies influences perception of consonants and vowels. Twenty-eight listeners with mild to moderately severe hearing loss identified consonants and vowels from nonsense syllables in noise following amplification via a hearing aid simulator. Low-pass filtering and the selection of NFC parameters fixed the output bandwidth at a frequency representing a moderately severe (3.3 kHz, group MS) or a mild-to-moderate (5.0 kHz, group MM) high-frequency loss. For each group (n = 14), effects of six combinations of NFC start frequency (SF) and input bandwidth [by varying the compression ratio (CR)] were examined. For both groups, the 1.6 kHz SF significantly reduced vowel and consonant recognition, especially as CR increased; whereas, recognition was generally unaffected if SF increased at the expense of a higher CR. Vowel recognition detriments for group MS were moderately correlated with the size of the second formant frequency shift following NFC. For both groups, significant improvement (33%-50%) with NFC was confined to final /s/ and /z/ and to some VCV tokens, perhaps because of listeners' limited exposure to each setting. No set of parameters simultaneously maximized recognition across all tokens.

Harmonic Frequency Lowering: Effects on the Perception of Music Detail and Sound Quality

A novel algorithm for frequency lowering in music was developed and experimentally tested in hearing-impaired listeners. Harmonic frequency lowering (HFL) combines frequency transposition and frequency compression to preserve the harmonic content of music stimuli. Listeners were asked to make judgments regarding detail and sound quality in music stimuli. Stimuli were presented under different signal processing conditions: original, low-pass filtered, HFL, and nonlinear frequency compressed. Results showed that participants reported perceiving the most detail in the HFL condition. In addition, there was no difference in sound quality across conditions.

Neural-scaled entropy predicts the effects of nonlinear frequency compression on speech perception

The Neural-Scaled Entropy (NSE) model quantifies information in the speech signal that has been altered beyond simple gain adjustments by sensorineural hearing loss (SNHL) and various signal processing. An extension of Cochlear-Scaled Entropy (CSE) [Stilp, Kiefte, Alexander, and Kluender (2010). J. Acoust. Soc. Am. 128(4), 2112-2126], NSE quantifies information as the change in 1-ms neural firing patterns across frequency. To evaluate the model, data from a study that examined nonlinear frequency compression (NFC) in listeners with SNHL were used because NFC can recode the same input information in multiple ways in the output, resulting in different outcomes for different speech classes. Overall, predictions were more accurate for NSE than CSE. The NSE model accurately described the observed degradation in recognition, and lack thereof, for consonants in a vowel-consonant-vowel context that had been processed in different ways by NFC. While NSE accurately predicted recognition of vowel stimuli processed with NFC, it underestimated them relative to a low-pass control condition without NFC. In addition, without modifications, it could not predict the observed improvement in recognition for word final /s/ and /z/. Findings suggest that model modifications that include information from slower modulations might improve predictions across a wider variety of conditions.

Working memory and intelligibility of hearing-aid processed speech

Previous work suggested that individuals with low working memory capacity may be at a disadvantage in adverse listening environments, including situations with background noise or substantial modification of the acoustic signal. This study explored the relationship between patient factors (including working memory capacity) and intelligibility and quality of modified speech for older individuals with sensorineural hearing loss. The modification was created using a combination of hearing aid processing [wide-dynamic range compression (WDRC) and frequency compression (FC)] applied to sentences in multitalker babble. The extent of signal modification was quantified via an envelope fidelity index. We also explored the contribution of components of working memory by including measures of processing speed and executive function. We hypothesized that listeners with low working memory capacity would perform more poorly than those with high working memory capacity across all situations, and would also be differentially affected by high amounts of signal modification. Results showed a significant effect of working memory capacity for speech intelligibility, and an interaction between working memory, amount of hearing loss and signal modification. Signal modification was the major predictor of quality ratings. These data add to the literature on hearing-aid processing and working memory by suggesting that the working memory-intelligibility effects may be related to aggregate signal fidelity, rather than to the specific signal manipulation. They also suggest that for individuals with low working memory capacity, sensorineural loss may be most appropriately addressed with WDRC and/or FC parameters that maintain the fidelity of the signal envelope.