Nonlinear Hearing Aids Research Articles

Investigation of hearing aid fitting according to the national acoustic laboratories’ prescription for non-linear hearing aids and the desired sensation level methods in Japanese speakers: a crossover-controlled trial

ObjectiveSome studies have directly compared the National Acoustic Laboratories’ prescription for non-linear hearing aids (HAs) version 2 (NAL-NL2) and Desired Sensation Level for non-linear HAs version 5 (DSLv5), although none were performed in Japan. As the Japanese language is a tonal language that has different linguistic characteristics than those of the studied languages, we compared the outcomes of the NAL-NL2 and DSLv5 in hearing-impaired Japanese participants. MethodsA crossover-controlled trial was conducted on 18 first-time HA users with bilateral moderate sensorineural hearing loss. Participants wore HAs adjusted with each prescriptive method for four weeks. The prescriptions were assessed using speech discrimination testing and the abbreviated profile of hearing aid benefit (APHAB). Consequently, participants were asked to select their preferred prescription and determine which was better for “listening to a conversation” and when “noisy.” ResultsThe mean DSLv5 real ear insertion gain for an input level of 65 dB sound pressure level (SPL) was higher than that of the NAL-NL2 at 250 and 500 Hz. The average speech discrimination score was 78 ± 14% at a 65-dB SPL and 75 ± 17% at an 80-dB SPL for the NAL-NL2, and 79 ± 11% at a 65-dB SPL and 77 ± 17% at an 80-dB SPL for the DSLv5. These differences were not significant. No significant differences were observed in APHAB subscale scores between the two prescription methods. Ultimately, 11 (61%) and 7 (39%) participants preferred the NAL-NL2 and DSLv5, respectively, with no significant differences. ConclusionAlthough the gain of the NAL-NL2 is smaller than that of the DSLv5, both had the same hearing effect. Therefore, the NAL-NL2 may be more useful than the DSLv5 in Japanese.

Amplification Strategies to Reduce Tinnitus: A Paired Comparison Method.

Background : The study investigates the best amplification strategy that provides tinnitus relief in a quiet environment, for individuals with sensorineural hearing loss with bothersome tinnitus.Methods: The repeated measures research design was utilized. Twenty participants (age range 25 years to 65 years; mean: 48.28 years) with bilateral symmetrical sloping sensorineural hearing loss with bothersome unilateral tinnitus were recruited. They were sub-grouped into low- and high-pitched tinnitus groups. A preference score was obtained for each of the strategies in hearing aid fitting, using the paired comparison method. The 4 strategies used were the desired sensation level (input/output) and the National Acoustic Laboratories’ nonlinear fitting method (version 1), at each of the low (30 dB SPL) and high (50 dB SPL) compression thresholds. Besides, the severity of tinnitus was assessed using the tinnitus severity index before and after 1 month of using the hearing aid in the best-selected strategy. Results: A repeated-measure ANOVA revealed no significant effect of the group on the preference score but was significant for strategies on relief from tinnitus. The desired sensation level (input/output) at a low compression threshold was the best strategy for alleviating tinnitus. Thirty-five percent of the study participants preferred the desired sensation level (input/output) strategy at low and high compression threshold, respectively. The remaining 25% preferred the National Acoustic Laboratories’ nonlinear hearing aid (version 1) at low compression threshold, and 5% selected the same device at high compression threshold. Furthermore, a significant association was observed in the severity of tinnitus before and after the hearing aid fitting set at the preferred program. Conclusion: The desired sensation level (input/output) method at the low compression threshold is the best program to alleviate bothersome tinnitus.

Comparison of Relative Loudness Judgment in Children using Listening Devices with Typically Developing Children.

Introduction Loudness perception is considered important for the perception of emotions, relative distance and stress patterns. However, certain digital hearing devices worn by those with hearing impairment may affect their loudness perception. This could happen in devices that have compression circuits to make loud sounds soft and soft sounds loud. These devices could hamper children from gaining knowledge about loudness of acoustical signals. Objective To compare relative loudness judgment of children using listening devices with age-matched typically developing children. Methods The relative loudness judgment of sounds created by day-to-day objects were evaluated on 60 children (20 normal-hearing, 20 hearing aid users, & 20 cochlear implant users), utilizing a standard group comparison design. Using a two-alternate forced-choice technique, the children were required to select picturized sound sources that were louder. Results The majority of the participants obtained good scores and poorer scores were mainly obtained by children using cochlear implants. The cochlear implant users obtained significantly lower scores than the normal-hearing participants. However, the scores were not significantly different between the normal-hearing children and the hearing aid users as well as between the two groups with hearing impairment. Conclusion Thus, despite loudness being altered by listening devices, children using non-linear hearing aids or cochlear implants are able to develop relative loudness judgment for acoustic stimuli. However, loudness growth for electrical stimuli needs to be studied.

Limitations of the Envelope Difference Index as a Metric for Nonlinear Distortion in Hearing Aids.

The envelope difference index (EDI) compares the envelopes of two signals. It has been used to measure nonlinear distortion in hearing aids, but it also responds to linear processing. This article compares linear and nonlinear processing effects on the EDI. The EDI for spectral tilt and peak clipping distortion is computed to illustrate the effects of linear and nonlinear signal modifications. The EDI for wide dynamic-range compression is then compared with that obtained for linear amplification for a set of standard audiograms to show the expected range of EDI values for linear and nonlinear hearing aid processing. The EDI for hearing aid amplification and compression is also compared with a measure of time-frequency envelope modulation distortion for the same conditions. The EDI is shown to be as sensitive to linear amplification as it is to nonlinear processing. The EDI values for spectral tilt can exceed those for peak clipping, and the EDI values for linear amplification exceed those for wide dynamic-range compression for four of the nine audiograms considered. The agreement of the EDI with a nonlinear envelope distortion measure is shown to depend on the long-term spectra of the signals being compared when computing the EDI. The accuracy of the EDI as an indicator of nonlinear distortion for sentence materials can be improved by equalizing the long-term spectrum of the processed signal to match that of the unprocessed input. However, the EDI does not have a clear interpretation because of the confound between linear and nonlinear processing effects and the lack of an auditory model in calculating the signal differences.

Hearing Aid Self-Adjustment: Effects of Formal Speech-Perception Test and Noise.

While listening to recorded sentences with a sound-field level of 65 dB SPL, 24 adults with hearing-aid experience used the “Goldilocks” explore-and-select procedure to adjust level and spectrum of amplified speech to preference. All participants started adjustment from the same generic response. Amplification was provided by a custom-built Master Hearing Aid with online processing of microphone input. Primary goals were to assess the effects of including a formal speech-perception test between repeated self-adjustments and of adding multitalker babble (signal-to-noise ratio +6 dB) during self-adjustment. The speech test did not affect group-mean self-adjusted output, which was close to the National Acoustics Laboratories’ prescription for Non-Linear hearing aids. Individuals, however, showed a wide range of deviations from this prescription. Extreme deviations at the first self-adjustment fell by a small but significant amount at the second. The multitalker babble had negligible effect on group-mean self-selected output but did have predictable effects on word recognition in sentences and on participants’ opinion regarding the most important subjective criterion guiding self-adjustment. Phoneme recognition in monosyllabic words was better with the generic starting response than without amplification and improved further after self-adjustment. The findings continue to support the efficacy of hearing aid self-fitting, at least for level and spectrum. They do not support the need for inclusion of a formal speech-perception test, but they do support the value of completing more than one self-adjustment. Group-mean data did not indicate a need for threshold-based prescription as a starting point for self-adjustment.

Which Patients With a Unilateral Hearing Aid for Symmetric Sensorineural Hearing Loss Have Auditory Deprivation?

ObjectivesThe aim of study is to find conditions that aggravate auditory deprivation in patients with symmetric hearing loss after unilateral digital, non-linear hearing aid (HA).MethodsIn the retrospective case-comparison study, we assessed 47 patients with symmetric sensorineural hearing loss (SNHL), wearing unilateral conventional HAs. Audiological outcomes were assessed >1 year after HA fitting (mean duration, 31.0 months). Pure-tone audiometry in HA-aided and HA-unaided conditions was performed over time. Word recognition score (WRS) was evaluated at the most comfortable listening level.ResultsThe initial pure tone average of four frequency thresholds at 500, 1,000, 2,000, and 4,000 Hz (PTA4) did not show a difference of >5 dB HL between HA-aided and HA-unaided ears. WRS progressively decreased for both HA-aided and HA-unaided ears although the extent of decrease was significantly greater for HA-unaided (7.6%) than for HA-aided ears (5.1%, P<0.05). Notably, auditory deprivation in HA-unaided ears was significantly greater in patients with an initial PTA4 ≥53 dB HL (P<0.001).ConclusionBilateral HAs are strongly recommended, particularly for patients with moderate to severe SNHL to prevent auditory deprivation in the contralateral ear.

Benefits of Non-Linear Frequency Compression Hearing Aids

Benefits of Non-Linear Frequency Compression Hearing Aids

Preferred Compression Threshold and Release Time in Quiet and Noisy Conditions for Elderly Korean Hearing Aid Users.

Background and ObjectivesListeners with sensorineural hearing loss want to compensate for their narrow dynamic range from appropriate compression functions of hearing aids. The present study aimed to determine which compression threshold and release time of nonlinear hearing aids might affect speech recognition and speech quality judgments.Subjects and MethodsTen elderly listeners with symmetrical moderate-to-severe sensorineural hearing loss participated in the study. To compare two compression threshold (31 dB SPL vs. 61 dB SPL) and two release time (50 ms vs. 500 ms) conditions, subjects’ speech recognition was measured using the Korean version of the Hearing in Noise Test in both quiet and noisy situations. All subjects were also asked to rate the degree of speech quality in terms of loudness, sharpness, clarity, and background noise immediately after completing the speech recognition test.ResultsAlthough no significant difference emerged in speech recognition thresholds between the two compression thresholds in the quiet situation, the compression threshold of 31 dB SPL showed a lower (or better) signal-to-noise ratio of speech recognition compared to that of 61 dB SPL. The release times of 50 and 500 ms did not statistically differ in both quiet and noisy situations. Subjective categories were found to be louder and clearer in the 50 ms release time for quiet and noisy, respectively.ConclusionsWe expect that these patterns of current results will apply for better-fitting protocol of elderly Korean hearing aid users.

Repeated Measurement of Absolute and Relative Judgments of Loudness: Clinical Relevance for Prescriptive Fitting of Aided Target Gains for soft, Comfortable, and Loud, But Ok Sound Levels.

This study was undertaken with the purpose of streamlining clinical measures of loudness growth to facilitate and enhance prescriptive fitting of nonlinear hearing aids. Repeated measures of loudness at 500 and 3,000 Hz were obtained bilaterally at monthly intervals over a 6-month period from three groups of young adult listeners. All volunteers had normal audiometric hearing sensitivity and middle ear function, and all denied problems related to sound tolerance. Group 1 performed judgments of soft and loud, but OK for presentation of ascending sound levels. We defined these judgments operationally as absolute judgments of loudness. Group 2 initially performed loudness judgments across a continuum of seven loudness categories ranging from judgments of very soft to uncomfortably loud for presentation of ascending sound levels per the Contour Test of Loudness; we defined these judgments as relative judgments of loudness. In the same session, they then performed the absolute judgments for soft and loud, but OK sound levels. Group 3 performed the same set of loudness judgments as did group 2, but the task order was reversed such that they performed the absolute judgments initially within each test session followed by the relative judgments. The key findings from this study were as follows: (1) Within group, the absolute and relative tasks yielded clinically similar judgments for soft and for loud, but OK sound levels. These judgments were largely independent of task order, ear, frequency, or trial order within a given session. (2) Loudness judgments increased, on average, by ∼3 dB between the first and last test session, which is consistent with the commonly reported acclimatization effect reported for incremental changes in loudness discomfort levels as a consequence of chronic bilateral hearing aid use. (3) Measured and predicted comfortable judgments of loudness were in good agreement for the individual listener and for groups of listeners. These comfortable judgments bisect the measured levels judged for soft and for loud, but OK sounds. (4) Loudness judgments within the same loudness category varied across listeners within group by as much as 50 to 60 dB. Such large variation in judgments of loudness is problematic, especially because hearing-impaired listeners are known to exhibit similarly large ranges of intersubject response variation and, yet, poplar prescriptive fitting strategies continue to use average rather than individual loudness data to fit nonlinear hearing aids. The primary conclusions drawn from these findings are that reliable absolute judgments of soft and loud, but OK are clinically practical and economical to measure and, from these judgments, good estimates of comfortable loudness can also be predicted for individuals or for groups of listeners. Such loudness data, as measured as described in this report, offer promise for streamlining and enhancing prescriptive fitting of nonlinear hearing aids to target gain settings for soft (audible), comfortable, and loud, but OK (tolerable) sound inputs for the individual listener.

Theoretical Issues of Validity in the Measurement of Aided Speech Reception Threshold in Noise for Comparing Nonlinear Hearing Aid Systems.

Adaptive Speech Reception Threshold in noise (SRTn) measurements are often used to make comparisons between alternative hearing aid (HA) systems. Such measurements usually do not constrain the signal-to-noise ratio (SNR) at which testing takes place. Meanwhile, HA systems increasingly include nonlinear features that operate differently in different SNRs, and listeners differ in their inherent SNR requirements. To show that SRTn measurements, as commonly used in comparisons of alternative HA systems, suffer from threats to their validity, to illustrate these threats with examples of potentially invalid conclusions in the research literature, and to propose ways to tackle these threats. An examination of the nature of SRTn measurements in the context of test theory, modern nonlinear HAs, and listener diversity. Examples from the audiological research literature were used to estimate typical interparticipant variation in SRTn and to illustrate cases where validity may have been compromised. There can be no doubt that SRTn measurements, when used to compare nonlinear HA systems, in principle, suffer from threats to their internal and external/ecological validity. Interactions between HA nonlinearities and SNR, and interparticipant differences in inherent SNR requirements, can act to generate misleading results. In addition, SRTn may lie at an SNR outside the range for which the HA system is designed or expected to operate in. Although the extent of invalid conclusions in the literature is difficult to evaluate, examples of studies were nevertheless identified where the risk of each form of invalidity is significant. Reliable data on ecological SNRs is becoming available, so that ecological validity can be assessed. Methodological developments that can reduce the risk of invalid conclusions include variations on the SRTn measurement procedure itself, manipulations of stimulus or scoring conditions to place SRTn in an ecologically relevant range, and design and analysis approaches that take account of interparticipant differences.

Stability of Audiometric Thresholds for Children with Hearing Aids Applying the American Academy of Audiology Pediatric Amplification Guideline: Implications for Safety.

Children who wear hearing aids may be at risk for further damage to their hearing from overamplification. Previous research on amplification-induced hearing loss has included children using linear amplification or simulations of predicted threshold shifts based on nonlinear amplification formulae. A relationship between threshold shifts and the use of nonlinear hearing aids in children has not been empirically verified. The purpose of the study was to compare predicted threshold shifts from amplification to longitudinal behavioral thresholds in a large group of children who wear hearing aids to determine the likelihood of amplification-induced hearing loss. An accelerated longitudinal design was used to collect behavioral threshold and amplification data prospectively. Two-hundred and thirteen children with mild-to-profound hearing loss who wore hearing aids were included in the analysis. Behavioral audiometric thresholds, hearing aid outputs, and hearing aid use data were collected for each participant across four study visits. Individual ear- and frequency-specific safety limits were derived based on the Modified Power Law to determine the level at which increased amplification could result in permanent threshold shifts. Behavioral thresholds were used to estimate which children would be above the safety limit at 500, 1000, 2000, and 4000 Hz using thresholds in dB HL and then in dB SPL in the ear canal. Changes in thresholds across visits were compared for children who were above and below the safety limits. Behavioral thresholds decreased across study visits for all children, regardless of whether their amplification was above the safety limits. The magnitude of threshold change across time corresponded with changes in ear canal acoustics as measured by the real-ear-to-coupler difference. Predictions of threshold changes due to amplification for children with hearing loss did not correspond with observed changes in threshold over across 2-4 yr of monitoring amplification. Use of dB HL thresholds and predictions of hearing aid output to set the safety limit resulted in a larger number of children being classified as above the safety limit than when safety limits were based on dB SPL thresholds and measured hearing aid output. Children above the safety limit for the dB SPL criteria tended to be fit above prescriptive targets. Additional research should seek to explain how the Modified Power Law predictions of threshold shift overestimated risk for children who wear hearing aids.

Evaluation of non-linear frequency compression hearing aids using speech P1-cortical auditory evoked potential

Objective: To investigate the potential effects of frequency lowering technology on outcome measures of hearing aid efficacy. The detection of mid- and high-frequency syllables in children with sensorineural hearing loss (SNHL) fitted with non-linear frequency compression (NLFC) hearing aids was studied using speech P1 cortical auditory evoked potentials (CAEP). Study design: Thirty Arabic speaking children with bilateral high frequency SNH and with a history of regular binaural hearing aid use were included. All children were fitted with binaural Phonak Naida III UP with a NLFC feature. Verification of NLFC was achieved through aided sound field testing and aided speech P1-CAEP recordings. Aided P1-CAEPs were elicited using synthetic speech stimuli ‘da’ and ‘ga’. Fifteen age-matched normal hearing children served as a control group to provide a reference of typically maturing CAEPs without the influence of hearing impairment. Results: NLFC improved aided thresholds in the mid and high frequencies. No statistically significant difference existed between the control and study group in their CAEP responses to the ‘ga’ stimulus in both NLFC-disabled/enabled conditions. The ‘da’ stimulus elicited P1-CAEP in only 27% of the study group with the NLFC disabled condition; this increased to 83% with activation of NLFC. The P1-CAEP latency of the study group was prolonged compared to children of the control group for both stimuli. The presence of P1-CAEP to both ‘ga’ and ‘da’ stimuli was significantly negatively correlated with the age of the child, duration of hearing loss, and duration of hearing aid use. Conclusion: The NLFC significantly improved the audibility of high frequency sounds for children with severe high frequency SNHL. Speech P1-CAEP can be used as an objective validation tool in children to evaluate the benefit from NLFC especially when behavioural aided thresholds are difficult to obtain.

Comparing NAL-NL1 and DSL v5 in Hearing Aids Fit to Children with Severe or Profound Hearing Loss: Goodness of Fit-to-Targets, Impacts on Predicted Loudness and Speech Intelligibility.

An important goal of providing amplification to children with hearing loss is to ensure that hearing aids are adjusted to match targets of prescriptive procedures as closely as possible. The Desired Sensation Level (DSL) v5 and the National Acoustic Laboratories' prescription for nonlinear hearing aids, version 1 (NAL-NL1) procedures are widely used in fitting hearing aids to children. Little is known about hearing aid fitting outcomes for children with severe or profound hearing loss. The purpose of this study was to investigate the prescribed and measured gain of hearing aids fit according to the NAL-NL1 and the DSL v5 procedure for children with moderately severe to profound hearing loss; and to examine the impact of choice of prescription on predicted speech intelligibility and loudness. Participants were fit with Phonak Naida V SP hearing aids according to the NAL-NL1 and DSL v5 procedures. The Speech Intelligibility Index (SII) and estimated loudness were calculated using published models. The sample consisted of 16 children (30 ears) aged between 7 and 17 yr old. The measured hearing aid gains were compared with the prescribed gains at 50 (low), 65 (medium), and 80 dB SPL (high) input levels. The goodness of fit-to-targets was quantified by calculating the average root-mean-square (RMS) error of the measured gain compared with prescriptive gain targets for 0.5, 1, 2, and 4 kHz. The significance of difference between prescriptions for hearing aid gains, SII, and loudness was examined by performing analyses of variance. Correlation analyses were used to examine the relationship between measures. The DSL v5 prescribed significantly higher overall gain than the NAL-NL1 procedure for the same audiograms. For low and medium input levels, the hearing aids of all children fit with NAL-NL1 were within 5 dB RMS of prescribed targets, but 33% (10 ears) deviated from the DSL v5 targets by more than 5 dB RMS on average. For high input level, the hearing aid fittings of 60% and 43% of ears deviated by more than 5 dB RMS from targets of NAL-NL1 and DSL v5, respectively. Greater deviations from targets were associated with more severe hearing loss. On average, the SII was higher for DSL v5 than for NAL-NL1 at low input level. No significant difference in SII was found between prescriptions at medium or high input level, despite greater loudness for DSL v5 than for NAL-NL1. Although targets between 0.25 and 2 kHz were well matched for both prescriptions in commercial hearing aids, gain targets at 4 kHz were matched for NAL-NL1 only. Although the two prescriptions differ markedly in estimated loudness, they resulted in comparable predicted speech intelligibility for medium and high input levels.

Changes of Dynamic Range, Signal-to-Noise Ratio, and Consonant-to-Vowel Ratio by Electroacoustic Adjustment and Fitting in Non-linear Hearing Aids

Although there have been tremendous development of hearing aid technology, it is important to understand features of non-linear hearing aid technology and to adjust various electroacoustic parameters when fitting hearing aids. The author described changes of dynamic range, signal-to-noise ratio and consonant-to-vowel ratio by adjustment of compression ratio (CR), compression threshold (CT), attack time (AT) and release time (RT) in non-linear hearing aids using Korean sentence waveforms. In addition, the author suggested effective methods to determine CR, CT, AT and RT in non-linear hearing aid fitting for children and adults with hearing loss. Further, to maximize communication abilities of hearing-impaired, especially Korean children and adults with hearing loss, future researches are needed regarding to understanding of Korean language, Korean version of hearing aid fitting fomulae, and aural rehabilitation programs.

Benefit from non-linear frequency compression hearing aids in a clinical setting: The effects of duration of experience and severity of high-frequency hearing loss

Objectives: To determine whether non-linear frequency compression (NLFC) is effective for hearing-impaired adults in a clinical setting. To determine whether benefit from NLFC is related to duration of NLFC experience or severity of high-frequency hearing loss. Design: Participants were fitted with Phonak frequency compression hearing aids as part of their standard clinical care, using the manufacturer's default fitting settings. Participants had been using NLFC for between 1 and 121 weeks at the time of testing. Speech recognition thresholds in noise and consonant recognition in quiet were measured with and without NLFC enabled. Study sample: Forty-six experienced adult hearing-aid users. Results: Consonant recognition in quiet, but not speech recognition in noise was significantly better with NLFC enabled. There was no significant correlation between duration of frequency compression experience and benefit. Benefit for consonant recognition was negatively correlated with mean audiometric thresholds from 2–6 kHz. Conclusions: NLFC was beneficial for consonant recognition but not speech recognition in noise. There was no evidence to support the idea that a long period of acclimatization is necessary to gain full benefit. The relation between benefit and high-frequency thresholds might be explained by the poor audibility of compressed information for some listeners with severe loss.

Acclimatization to Hearing Aids

Evidence for a clinically significant effect of acclimatization to hearing aids is mixed. The aim of this study was to test for auditory acclimatization effects in new unilateral and bilateral adult hearing aid users. Hypotheses were i) there would be improvements in aided speech recognition in new hearing aid users, compared with unaided listening and with a control group of experienced hearing aid users, and ii) improvements would correlate with severity of hearing loss, hearing aid use, and cognitive capacity. Speech recognition in noise was measured for a 65 and a 75 dB SPL target with the Four Alternative Auditory Feature test. Speech recognition in noise was measured within 1 week of fitting and retested at 12 weeks postfitting in new hearing aid users (16 unilateral and 16 bilateral fit). A control group of experienced hearing aid users (n = 17) was tested over a similar time scale. Cognitive capacity (reaction time and working memory) was measured, and self-reported change in performance was assessed using the Speech, Spatial and Qualities of Hearing Scale. Hearing aid use was assessed via data logging at the completion of the study. Mean improvements in speech recognition of up to 4% were observed across conditions and across groups consistent with a general practice effect. On average there was no evidence of auditory acclimatization in the new hearing aid user groups in terms of improvement in aided listening conditions above that observed in unaided recognition or in the control group. There was no correlation between change in aided speech recognition and severity of hearing loss, hearing aid use, or cognitive capacity. New users reported significant improvement over time in aided performance on a self-report questionnaire compared with the control group. On average, there was no improvement over time in new users' aided speech recognition relative to unaided recognition or to the control group. This does not support a robust acclimatization effect with nonlinear hearing aids. Test-retest variability may obscure small average acclimatization effects; variability was not accounted for by individual differences in severity of hearing loss, hearing aid use, or cognitive capacity. New users' subjective report of increased benefit over time may be reflective of other aspects of adjustment to hearing aid use not examined in this study.

Hearing-aid safety: A comparison of estimated threshold shifts for gains recommended by NAL-NL2 and DSL m[i/o] prescriptions for children

Objective: To investigate the predicted threshold shift associated with the use of nonlinear hearing aids fitted to the NAL-NL2 or the DSL m[i/o] prescription for children with the same audiograms. For medium and high input levels, we asked: (1) How does predicted asymptotic threshold shifts (ATS) differ according to the choice of prescription? (2) How does predicted ATS vary with hearing level for gains prescribed by the two prescriptions? Design: A mathematical model consisting of the modified power law combined with equations for predicting temporary threshold shift (Macrae, 1994b) was used to predict ATS. Study sample: Predicted threshold shift were determined for 57 audiograms at medium and high input levels. Results: For the 57 audiograms, DSL m[i/o] gains for high input levels were associated with increased risk relative to NAL-NL2. The variation of ATS with hearing level suggests that NAL-NL2 gains became unsafe when hearing loss > 90 dB HL. The gains prescribed by DSL m[i/o] became unsafe when hearing loss > 80 dB HL at a medium input level, and > 70 dB HL at a high input level. Conclusion: There is a risk of damage to hearing for children using nonlinear amplification. Vigilant checking for threshold shift is recommended.

Prescriptive Amplification Recommendations for Hearing Losses with a Conductive Component and Their Impact on the Required Maximum Power Output: An Update with Accompanying Clinical Explanation

Hearing aid prescriptive recommendations for hearing losses having a conductive component have received less clinical and research interest than for losses of a sensorineural nature; as a result, much variation remains among current prescriptive methods in their recommendations for conductive and mixed hearing losses (Johnson and Dillon, 2011). The primary intent of this brief clinical note is to demonstrate differences between two algebraically equivalent expressions of hearing loss, which have been approaches used historically to generate a prescription for hearing losses with a conductive component. When air and bone conduction thresholds are entered into hearing aid prescriptions designed for nonlinear hearing aids, it was hypothesized that that two expressions would not yield equivalent amounts of prescribed insertion gain and output. These differences are examined for their impact on the maximum power output (MPO) requirements of the hearing aid. Subsequently, the MPO capabilities of two common behind-the-ear (BTE) receiver placement alternatives, receiver-in-aid (RIA) and receiver-in-canal (RIC), are examined. The two expressions of hearing losses examined were the 25% ABG + AC approach and the 75% ABG + BC approach, where ABG refers to air-bone gap, AC refers to air-conduction threshold, and BC refers to bone-conduction threshold. Example hearing loss cases with a conductive component are sampled for calculations. The MPO capabilities of the BTE receiver placements in commercially-available products were obtained from hearing aids on the U.S. federal purchasing contract. Prescribed gain and the required MPO differs markedly between the two approaches. The 75% ABG + BC approach prescribes a compression ratio that is reflective of the amount of sensorineural hearing loss. Not all hearing aids will have the MPO capabilities to support the output requirements for fitting hearing losses with a large conductive component particularly when combined with significant sensorineural hearing loss. Generally, current RIA BTE products have greater output capabilities than RIC BTE products. The 75% ABG + BC approach is more appropriate than the 25% ABG + AC approach because the latter approach inappropriately uses AC thresholds as the basis for determining the compression ratio. That is, for hearing losses with a conductive component, the AC thresholds are not a measure of sensorineural hearing loss and cannot serve as the basis for determining the amount of desired compression. The Australian National Acoustic Laboratories has been using the 75% ABG + BC approach in lieu of the 25% ABG + AC approach since its release of the National Acoustic Laboratories--Non-linear 1 (NAL-NL1) prescriptive method in 1999. Future research may examine whether individuals with conductive hearing loss benefit or prefer more than 75% restoration of the conductive component provided adequate MPO capabilities to support such restoration.

Initial Development of a Temporal-Envelope-Preserving Nonlinear Hearing Aid Prescription Using a Genetic Algorithm

Most hearing aid prescriptions focus on the optimization of a metric derived from the long-term average spectrum of speech, and do not consider how the prescribed values might distort the temporal envelope shape. A growing body of evidence suggests that such distortions can lead to systematic errors in speech perception, and therefore hearing aid prescriptions might benefit by including preservation of the temporal envelope shape in their rationale. To begin to explore this possibility, we designed a genetic algorithm (GA) to find the multiband compression settings that preserve the shape of the original temporal envelope while placing that envelope in the listener's audiometric dynamic range. The resulting prescription had a low compression threshold, short attack and release times, and a combination of compression ratio and gain that placed the output signal within the listener's audiometric dynamic range. Initial behavioral tests of individuals with impaired hearing revealed no difference in speech-in-noise perception between the GA and the NAL-NL2 prescription. However, gap detection performance was superior with the GA in comparison to NAL-NL2. Overall, this work is a proof of concept that consideration of temporal envelope distortions can be incorporated into hearing aid prescriptions.

Comparison of three fitting rationales in adults in an artificial intelligence parallel processing hearing aid

EnAbstract Introduction Hearing rehabilitation using nonlinear hearing aid (HA) fitting formulae provides hearing-impaired individuals with the audibility, comfort, and speech intelligibility for a better life. Objective To compare three nonlinear HA fitting formulae in adults in a Channel Free artificial intelligence parallel processing HA. Materials and methods The study included 19 adults with bilateral moderate to severe sensorineural hearing loss, monaurally fitted with nonlinear HA. Comparisons were made on the basis of aided speech intelligibility in quiet and in noise, aided sound field thresholds, and functional performance in real life using APHAB, COSI, and GHABP questionnaires. Results The three formulae have significantly improved speech discrimination in adults, with no significant difference among the formulae for speech intelligibility in quiet or in noise, with no sex or HA experience differences. The three formulae have significantly improved functional performance in real-life speech communication, with the NAL-NL1-based formula showing the greatest degree of benefit and improvement in listening needs, followed by NAL-NL1 and then DSL [I/O]. However, amplification with the three formulae increased aversiveness to environmental sounds. Participants reported significant benefits using NAL and NAL-NL1-based formulae. Experienced HA users, using the NAL-NL1-based formula, showed significantly less difficulty in listening quality in large spaces and greater capacity to recognize speech within competitive noise and better tolerance to environmental sounds than nonexperienced users. The SPIN test correlated well with real-life speech communication. Conclusion The three fitting rationales have equally improved intelligibility, with variable degrees of improvement in real-life speech communication with preferences for NAL-NL1 and the manufacture-specific NAL-NL1-based formula.