Patient experiences with multiband full dynamic range compression.

This investigation compared performance for 18 experienced hearing aid patients with a multiband full dynamic range compression hearing device and their previously worn linear or automatic gain control hearing aids. Performance was evaluated using a variety of clinical tests. These included functional gain and dynamic range measurements, speech recognition, and real ear measurements. Patients rated their performance with the multiband compression device and their previously worn aids on a rating scale pertaining to a variety of real life listening situations. Statistical analysis of data derived from test results shows significantly improved performance on all measures using the multiband compression aid over their conventional aids. Patients rated their performance higher with the compression instrument than with the conventional aids. Differences in performance on clinical tests and subjective patient responses appear to be related to the different signal processing schemes used in the two groups of devices.     

Compression-dependent differences in hearing aid gain between speech and nonspeech input signals

OBJECTIVE: A primary purpose of fitting hearing aids is to improve the audibility of speech; however, hearing aid gain is typically measured by using standardized nonspeech signals, e.g., swept pure tones, speech-weighted broadband noise, or modulated noise. When compression hearing aids are tested with these nonspeech input signals, the measured gain can be substantially different than if a real speech input signal were used. The purpose of this study was to systematically evaluate the effects of release time, compression ratio, and number of compression channels, as well as interactions of these parameters, on the gain difference between several common nonspeech hearing aid test signals and speech. It was hypothesized that the difference in hearing aid gain between static nonspeech signals and speech would increase as release time, compression ratio, and number of channels increased. DESIGN: Speech and several common nonspeech hearing aid test signals, matched at overall root-mean-square levels corresponding to average (65 dB SPL) and loud (80 dB SPL) conversational speech, were input into a master hearing aid circuit, and the gain of the circuit was measured in one-third octave bands. The hearing aid was programmed as a moderate-gain (23 dB) wide dynamic range compression instrument with a compression threshold of 50 dB SPL. The release time, compression ratio, and number of compression channels of the circuit were systematically adjusted by programming software. The one-third octave band gain differences between the nonspeech signals and speech were measured for all combinations of the compression settings. Multiple regression analysis was used to evaluate the effects of each compression parameter, and interactions of the parameters, on the gain difference between each nonspeech signal and speech. RESULTS: One-third octave band gain differences between nonspeech and speech signals (calculated as nonspeech signal minus speech signal) ranged from -3.1 to 10.4 dB, depending on frequency, nonspeech test signal, and input signal level. In most cases, the compression parameters accounted for more than 70% of the variance in gain differences between the speech and nonspeech signals. At an input level of 65 dB, increases in the release time and compression ratio led to an increase in the gain difference between most nonspeech signals and speech at most frequencies. Increases in the number of channels caused an increase in the gain difference when the spectra of the nonspeech signals differed from the speech spectrum. The effects of release time and number of channels increased as the compression ratio increased. At an 80 dB input level, increasing the compression ratio led to a decrease in the gain difference between the nonspeech signals and speech. Release time and number of channels had little to no effect at the higher input level. CONCLUSIONS: The compression parameters of release time, compression ratio, and number of compression channels explain most of the variance in differences in hearing aid gain between nonspeech and speech signals. It may be cumbersome, however, to quantitatively define this relationship for all hearing aid circuits. It is therefore recommended that hearing aid "use" gain or output be measured with a real speech signal. If a nonspeech signal must be used, then it should have spectral and temporal properties that are similar to speech.     

Effect of multichannel digital signal processing on loudness comfort, sentence recognition, and sound quality

This study evaluated the effect of increasing the number of processing channels from 32- to 64-signal processing channels on subjects' loudness comfort and satisfaction, sentence recognition, and sound quality of his or her own voice. Ten experienced hearing aid users with mild-to-moderate sensorineural hearing loss wore behind-the-ear (BTE) hearing aids with Adaptive Dynamic Range Optimization (ADRO) signal processing for a period of six weeks in the 32-channel and 64-channel conditions. Results revealed no significant differences in loudness comfort or satisfaction for the majority of sound samples as measured by the Subjective Loudness Test and Environmental Sounds Questionnaire. No significant differences in sentence recognition between the two processing conditions were found as measured by the Hearing In Noise Test (HINT). Additionally, no subjective differences in sound quality of subjects' own voice were determined by the Listening Tasks Questionnaire.     

Automatic regulation systems with relevance to hearing aids.

Compression amplification in hearing aids has gained much interest in the recent years. Other types of nonlinear signal processing in hearing aids are developing. The principles of nonlinear signal processing through automatic regulation, as opposed to instanteaneously acting nonlinear signal transfer, is described in general. In particular the properties and terminology of amplitude compression and limiting circuits in relation to hearing aids are discussed. Several examples are given of nonlinear regulation systems for hearing aids involving other features than amplitude compression.     

Performance with an adaptive frequency response hearing aid in a sample of elderly hearing-impaired listeners.

This study assessed the efficacy of an adaptive frequency response hearing aid (AFR) for improving speech perception ability in noise among a group of elderly hearing-impaired listeners. A speech recognition task, self-assessed speech intelligibility task, and qualitative judgment task were administered to examine subtle differences in the effects of the AFR "signal processing" versus linear amplification. Group scores showed statistically significant improvement with AFR processing on the speech recognition task involving high-predictability sentences, but not on any other measures. However, there was a trend toward improved scores with AFR processing for low-predictability sentences as well. These results suggest that AFR circuitry may be most useful for enhancing recognition of speech in high-cue contexts. Wide individual subject variability was observed on all measures. This demonstrates the importance of evaluating the effectiveness of noise reduction hearing aids on an individual basis and with more than one task.     

Cognitive function in relation to hearing aid use

Two experiments were conducted to investigate possible relationships between cognitive function and hearing aid use. In Experiment 1, 72 first-time hearing aid users were tested for speech recognition in noise (Hagerman sentence test) with and without hearing aids. Cognitive function was assessed by tests of working memory (reading span test) and verbal information-processing speed. The results indicate that, after controlling for age and hearing loss, significant correlations exist between the measures of cognitive performance and speech recognition in noise, both with and without hearing aids. High cognitive performance was associated with high performance in the speech recognition task. In Experiment 2, 17 first-time hearing aid users with either high or low working-memory capacity tested an experimental hearing aid which processed the sound differently depending on whether or not speech was detected. The results revealed that those with high working-memory capacity were better than those with low capacity at identifying and reporting the specific processing effects of the aid. This may have implications for how reported results should be interpreted in a research context, how a person's rehabilitation needs are formulated, and how hearing aid controls should be supervised. In conclusion, careful attention should be paid to the cognitive status of listeners, as it can have a significant influence on their ability to utilize their hearing aids.     

Impact of compression and hearing aid style on directional hearing aid benefit and performance.

OBJECTIVE: To evaluate the impact of low-threshold compression and hearing aid style (in-the-ear [ITE] versus behind-the-ear [BTE]) on the directional benefit and performance of commercially available directional hearing aids. DESIGN: Forty-seven adult listeners with mild-to-moderate sensorineural hearing loss were fit bilaterally with one BTE and four different ITE hearing aids. Speech recognition performance was measured through the Connected Speech Test (CST) and Hearing in Noise Test (HINT) for a simulated noisy restaurant environment. RESULTS: For both the HINT and CST, speech recognition performance was significantly greater for subjects fit with directional in comparison with omnidirectional microphone hearing aids. Performance was significantly poorer for the BTE instrument in comparison with the ITE hearing aids when using omnidirectional microphones. No differences were found for directional benefit between compression and linear fitting schemes. CONCLUSIONS: No systematic relationship was found between the relative directional benefit and hearing aid style; however, the speech recognition performance of the subjects was somewhat predictable based on Directivity Index measures of the individual hearing aid models. The fact that compression did not interact significantly with microphone type agrees well with previously reported electroacoustic data.     

Clinical evaluation of a programmable three-channel automatic gain control amplification system

This paper reports on the clinical evaluation of a commercially available head-worn programmable 3-channel automatic gain control (AGC) hearing instrument (Siemens, Triton 3000). A preliminary fitting procedure is developed for the 3-channel AGC amplification system, which is compared by 26 experienced hearing instrument wearers with their own single-channel AGC instruments. The benefits of both amplification systems are assessed by speech audiometry at different signal-to-noise ratios utilizing German rhyme test speech material. In addition, subjective judgements concerning sound quality, speech intelligibility and comparison with the subject's own instrument are evaluated. The results indicate that the multichannel compression instrument is superior to single-channel aids in competitive speech situations. If the 3-channel AGC instrument is used as an automatic noise reduction system in patients requiring a certain amount of low-frequency gain, a markedly better speech recognition can be achieved compared to the subject's personal aids.     

Recognition of speech in noise with new hearing instrument compression release settings requires explicit cognitive storage and processing capacity

Evidence suggests that cognitive capacity predicts the ability to benefit from specific compression release settings in non-linear digital hearing instruments. Previous studies have investigated the predictive value of various cognitive tests in relation to aided speech recognition in noise using compression release settings that have been experienced for a certain period. However, the predictive value of cognitive tests with new settings, to which the user has not had the opportunity to become accustomed, has not been studied. In the present study, we compare the predictive values of two cognitive tests, reading span and letter monitoring, in relation to aided speech recognition in noise for 32 habitual hearing instrument users using new compression release settings. We found that reading span was a strong predictor of speech recognition in noise with new compression release settings. This result generalizes previous findings for experienced test settings to new test settings, for both speech recognition in noise tests used in the present study, Hagerman sentences and HINT. Letter monitoring, on the other hand, was not found to be a strong predictor of speech recognition in noise with new compression release settings.     

Effects of noise and reverberation on speech recognition with variants of a multichannel adaptive dynamic range compression scheme

Abstract

Objective: Adaptive compression methods in hearing aids have been developed to maximise audibility while preserving temporal envelope modulations. Increasing the number of channels may improve listening comfort for loud sounds. However, the effects of this on speech recognition in different environmental conditions are unknown. This study evaluated the effects of different channel architectures and adaptive compression properties on speech recognition in noise and reverberation.

Design: Sentences were mixed with steady or modulated noise at three signal-to-noise ratios (SNRs). These were processed with and without reverberation and amplified with four proprietary adaptive compression methods or linear amplification.

Study sample: 36 listeners with mild to moderately-severe hearing loss.

Results: Adaptive compression improved speech recognition over linear amplification to a small extent, with no significant differences among methods using 4 or 24 channels or a combination thereof. These effects remained across the different background noise and reverberation conditions.

Conclusions: Increasing the number of channels does not negatively affect speech recognition in noise and reverberation when adaptive compression is used. If future research shows that increasing the number of channels improves listening comfort for loud sounds, these results indicate that adaptive compression methods with as many as 24 channels are viable options for hearing aids.     

Quantifying the effect of compression hearing aid release time on speech acoustics and intelligibility.

Compression hearing aids have the inherent, and often adjustable, feature of release time from compression. Research to date does not provide a consensus on how to choose or set release time. The current study had 2 purposes: (a) a comprehensive evaluation of the acoustic effects of release time for a single-channel compression system in quiet and (b) an evaluation of the relation between the acoustic changes and speech recognition. The release times under study were 12, 100, and 800 ms. All of the stimuli were VC syllables from the Nonsense Syllable Task spoken by a female talker. The stimuli were processed through a hearing aid simulator at 3 input levels. Two acoustic measures were made on individual syllables: the envelope-difference index and CV ratio. These measurements allowed for quantification of the short-term amplitude characteristics of the speech signal and the changes to these amplitude characteristics caused by compression. The acoustic analyses revealed statistically significant effects among the 3 release times. The size of the effect was dependent on characteristics of the phoneme. Twelve listeners with moderate sensorineural hearing loss were tested for their speech recognition for the same stimuli. Although release time for this single-channel, 3:1 compression ratio system did not directly predict overall intelligibility for these nonsense syllables in quiet, the acoustic measurements reflecting the changes due to release time were significant predictors of phoneme recognition. Increased temporal-envelope distortion was predictive of reduced recognition for some individual phonemes, which is consistent with previous research on the importance of relative amplitude as a cue to syllable recognition for some phonemes.     

Speech recognition ability in noise and its relationship to perceived hearing aid benefit

Hearing-impaired listeners with similar hearing losses may differ widely in their ability to understand speech in noise. Such individual susceptibility to noise may explain why patients obtain varying degrees of benefit from hearing aids. The chief purpose of this study was to determine if adaptive measures of unaided speech recognition in noise were related to hearing aid benefit. Additionally, the relationship between perceived hearing handicap and benefit from amplification was explored. Before being fit with hearing aids, 47 new hearing aid users completed a self-assessment measure of hearing handicap Then, unaided speech recognition ability was measured in quiet and in noise. Three months later, subjects completed a hearing aid benefit questionnaire. A weak relationship was observed between perceived hearing handicap and hearing aid benefit. There were no significant relationships between speech-in-noise measures and hearing aid benefit, suggesting that speech recognition ability in noise is not a major determinant of the benefit derived from amplification.     

Comparison of hearing aids over the 20th century

OBJECTIVE: To measure hearing aid performance using circuitry representative of the major eras of technological advancement during the 20th century. DESIGN: Twenty subjects with audiometric profiles consistent with hearing aid candidacy were fit with each of seven hearing aids. No directional microphones were used and binaural benefit was not assessed. Each hearing aid was fit to the strategy or fitting scheme of the era, or that which was intended by the presenting manufacturer. Electroacoustic and/or real ear measures of gain, output, bandwidth, and distortion were obtained. Objective outcome measures assessing speech perception in backgrounds of noise were obtained. Subjective outcome measures of sound quality and ease of listening were obtained in the laboratory and in real life settings. RESULTS: Electroacoustic and real ear measures indicate that gain and bandwidth have increased, and output and distortion have decreased with current electronic aids. Speech perception ability across the different outcome measures showed significantly poorer performance with the body and linear hearing aids when input levels were high; when input levels were low, outcome measures with hearing aids using a dynamic range compression were not negatively affected. At the most adverse signal to noise ratios, none of the hearing aids was shown to be superior. Measured bandwidth did not correlate highly with speech perception ability for any of the objective outcome measures used. For the subjective measures of sound quality done in a blinded manner, no significant differences were found across different listening situations for current hearing aids. CONCLUSIONS: The two most important factors for aided speech perception appear to be the audibility and distortion of the signal. No current compression scheme proved superior with the outcome measures used in this investigation.     

Hearing aid users benefit from induction loop when using digital cellular phones

OBJECTIVE: Hearing aid users have recently been reported to experience problems with electromagnetic interference when using digital cellular phones. This study was undertaken to investigate the possible benefit of an induction loop system developed for use with some cellular phone models, and also to compare the possible benefit in two languages (Finnish and American English) as well as the benefit with two hearing aid technologies (analog versus digital). DESIGN: The study was performed in controlled laboratory conditions at two tertiary care hearing health care centers, one in Oulu, Finland and the other in Dallas, in the United States. The subjects were experienced users of behind-the-ear hearing aids and served as their own controls in three different listening conditions. Thirty-two eligible subjects (20 in Oulu and 12 in Dallas) participated in three test conditions: 1. call with a landline phone, 2. call with a digital cellular phone alone and 3. call with a digital cellular phone coupled to an induction loop. RESULTS: Sentence recognition scores and subjective judgments using a visual analog scale revealed the poorest results with the digital cellular phone alone. When the induction loop was used with the digital cellular phones, sentence recognition scores and the visual analog scale scores were comparable to the scores obtained with a landline phone. The mean sentence recognition score for analog hearing aids was 62.4% (95% confidence interval 50.2 to 74.6) with the landline phone, 12.6% (-1.6 to 26.9) with the digital cellular phone alone, and 63.3% (44.2 to 82.3) when using the digital cellular phone with the induction loop. For digital hearing aids, the sentence recognition scores were 62.4% (51.9 to 72.9), 37.4% (18.0 to 56.8) and 57.6% (39.0 to 76.2), respectively. There was no significant difference in performance between the two centers. However, when using the digital cellular phone alone, there was no drop in the sentence recognition scores with the few (N = 5) digital hearing aids in Dallas. The subjects ranked the digital cellular phone alone as the poorest test condition and the digital cellular phone with an induction loop as the best. CONCLUSIONS: Induction loops appear to offer one possible solution for the incompatibility problem between hearing aids and digital cellular phones. However, the generalizability of the results must be viewed cautiously, because testing included only one induction loop and two digital cellular phone models.     

Zur Indikationserweiterung des „cochlear-implant”Freiburger Ergebnisse bei Patienten mit Resthörigkeit

The usual indication for a cochlear implant (CI) is acquired deafness in patients for whom conventional hearing aids are of no benefit. The question is whether CI is superior to the best conventional hearing aids for patients with some residual hearing, but who achieve only minimal speech recognition (< 30% in the Freiburg monosyllable word test at 70 dB (I) SPL) with optimal hearing aids. We report our experience with five patients with residual hearing who underwent cochlear implantation (Nucleus Mini 22 and 24) on the worse side. The patients were examined preoperatively and at 1, 6 and 12 months following activation of the implant. The Freiburg monosyllabic word test, the G?ttingen sentence test and consonant recognition were used to assess postoperative results. All patients benefitted from CI when test scores were compared with preoperative ones. All patients achieved a score in the Freiburg monosyllabic word test of more than 60% at 70 dB (I) SPL 12 months post switch-on. Four patients achieved a score of more than 85% in the G?ttingen sentence test. These results and the progress made in cochlear implant technology are an impetus to continue discussions of various considerations of criteria for cochlear implants and possibly extend these for patients with severe hearing impairment.     

Clinical design and evaluation of the prototype of a new digital audioprosthesis for profound hearing loss: speech recognition aspects.

The design and implementation of the prototype of a digital hearing aid and its computerized fitting interface, followed by a basic preliminary clinical evaluation concerning speech recognition aspects, is reported. The final device is particularly destined to those patients suffering sensorineural hearing losses with recruitment and problems for speech recognition. The prototype is based on the digital signal processor TMS320C30. The host is a personal computer. The primary concept of the processing strategy is the 'integral treatment of acoustic information' within the remaining auditory field of the patient leading to minimum modification of the signal profile. The processing stages include linear amplification, specially designed AD conversion, real fast Fourier transform, 128 multiband single treatment (compression threshold and magnitude of compression), inverse fast Fourier transform, and DA conversion. Compression parameters and pure-tone audiometry data are entered by the computerized fitting interface which also provides real time information of input and output spectral profile. The preliminary clinical evaluation here reported corresponds to a series of 13 patients and it is focused on speech recognition performances. Ten patients had sensorineural hearing loss. Three subjects served as controls. All subjects were studied by an extensive audiological protocol. In 6 patients the prototype improved the maximum intelligibility with respect to unaided hearing reaching levels in the range of 90-100%. In 4 patients using conventional hearing aids, the prototype improved the maximum intelligibility with respect to the previous aided hearing. Values reached the same range as in the former 6 patients. Straightening of the speech audiometry curves was observed in those patients with recruitment. Two controls with previously normal speech recognition showed no worsening and others with conductive deafness reported additional improvement of the responses in noisy conditions with respect to the audioprosthesis in use.