New perspectives on assessing amplification effects

Clinicians have long been aware of the range of performance variability with hearing aids. Despite improvements in technology, there remain many instances of well-selected and appropriately fitted hearing aids whereby the user reports minimal improvement in speech understanding. This review presents a multistage framework for understanding how a hearing aid affects performance. Six stages are considered: (1) acoustic content of the signal, (2) modification of the signal by the hearing aid, (3) interaction between sound at the output of the hearing aid and the listener's ear, (4) integrity of the auditory system, (5) coding of available acoustic cues by the listener's auditory system, and (6) correct identification of the speech sound. Within this framework, this review describes methodology and research on 2 new assessment techniques: acoustic analysis of speech measured at the output of the hearing aid and auditory evoked potentials recorded while the listener wears hearing aids. Acoustic analysis topics include the relationship between conventional probe microphone tests and probe microphone measurements using speech, appropriate procedures for such tests, and assessment of signal-processing effects on speech acoustics and recognition. Auditory evoked potential topics include an overview of physiologic measures of speech processing and the effect of hearing loss and hearing aids on cortical auditory evoked potential measurements in response to speech. Finally, the clinical utility of these procedures is discussed.     

Effect of homolateral and contralateral routing of signals through body-worn hearing aids on the localization ability of hearing-impaired people

This investigation compared the localization abilities in the horizontal plane of 22 hearing-impaired adults (9 with symmetrical conductive and 13 with symmetrical sensorineural hearing impairment) whilst listening to speech through body-worn hearing aids in two different ways: (a) hearing-aid microphone placed on the same side as the stimulated ear (homolateral routing of signals); (b) hearing aid microphone placed on the opposite side to the stimulated ear (contralateral routing of signals). It was found that the localization performances of all the subjects, especially when using binaural hearing aids, under homolateral routing of signals, were far superior to their respective localization performances achieved with contralateral routing of signals.     

The robustness of hearing aid microphone preferences in everyday listening environments

Automatic directionality algorithms currently implemented in hearing aids assume that hearing-impaired persons with similar hearing losses will prefer the same microphone processing mode in a specific everyday listening environment. The purpose of this study was to evaluate the robustness of microphone preferences in everyday listening. Two hearing-impaired persons made microphone preference judgments (omnidirectional preferred, directional preferred, no preference) in a variety of everyday listening situations. Simultaneously, these acoustic environments were recorded through the omnidirectional and directional microphone processing modes. The acoustic recordings were later presented in a laboratory setting for microphone preferences to the original two listeners and other listeners who differed in hearing ability and experience with directional microphone processing. The original two listeners were able to replicate their live microphone preferences in the laboratory with a high degree of accuracy. This suggests that the basis of the original live microphone preferences were largely represented in the acoustic recordings. Other hearing-impaired and normal-hearing participants who listened to the environmental recordings also accurately replicated the original live omnidirectional preferences; however, directional preferences were not as robust across the listeners. When the laboratory rating did not replicate the live directional microphone preference, listeners almost always expressed no preference for either microphone mode. Hence, a preference for omnidirectional processing was rarely expressed by any of the participants to recorded sites where directional processing had been preferred as a live judgment and vice versa. These results are interpreted to provide little basis for customizing automatic directionality algorithms for individual patients. The implications of these findings for hearing aid design are discussed.     

An objective measure for selecting microphone modes in OMNI/DIR hearing aid circuits

OBJECTIVES: Studies have shown that listener preferences for omnidirectional (OMNI) or directional (DIR) processing in hearing aids depend largely on the characteristics of the listening environment, including the relative locations of the listener, signal sources, and noise sources; and whether reverberation is present. Many modern hearing aids incorporate algorithms to switch automatically between microphone modes based on an analysis of the acoustic environment. Little work has been done, however, to evaluate these devices with respect to user preferences, or to compare the outputs of different signal processing algorithms directly to make informed choices between the different microphone modes. This study describes a strategy for automatically switching between DIR and OMNI microphone modes based on a direct comparison between acoustic speech signals processed by DIR and OMNI algorithms in the same listening environment. In addition, data are shown regarding how a decision to choose one microphone mode over another might change as a function of speech to noise ratio (SNR) and spatial orientation of the listener. DESIGN: Speech and noise signals were presented at a variety of SNR's and in different spatial orientations relative to a listener's head. Monaural recordings, made in both OMNI and DIR microphone processing modes, were analyzed using a model of auditory processing that highlights the spectral and temporal dynamics of speech. Differences between OMNI and DIR processing were expressed in terms of a modified spectrotemporal modulation index (mSTMI) developed specifically for this hearing aid application. Differences in mSTMI values were compared with intelligibility measures and user preference judgments made under the same listening conditions. RESULTS: A comparison between the results of the mSTMI analyses and behavioral data (intelligibility and preference judgments) showed excellent agreement, especially in stationary noise backgrounds. In addition, the mSTMI was found to be sensitive to changes in SNR as well as spatial orientation of the listener relative to signal and noise sources. Subsequent mSTMI analyses on hearing aid recordings obtained from real-life environments with more than one talker and modulated noise backgrounds also showed promise for predicting the preferred microphone setting in varied and complex listening environments.     

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.     

Expectations about hearing aids and their relationship to fitting outcome

Clinicians are often concerned that unrealistic prefitting expectations can have a negative impact on fitting success for new, hearing aid wearers. To investigate this concern and to explore the potential value of measuring expectations, we developed the Expected Consequences of Hearing aid Ownership (ECHO) questionnaire as a companion to the Satisfaction with Amplification in Daily Life questionnaire. Four experiments were conducted to (1) determine realistic expectations for hearing aids, (2) evaluate expectations of new users, (3) measure reliability of prefitting expectations, and (4) assess relationships between prefitting expectations and postfitting satisfaction. Novice hearing aid users were found to have stable prefitting expectations about hearing aids, and these expectations were unrealistically high for the typical individual. There were many different expectation patterns across subjects. Of the four subscales of the ECHO, only one was predictive of the corresponding satisfaction data. Potential clinical applications are described.     

Effect of hearing aids on hearing disability and quality of life in the elderly

The aim of this study was to assess the effects of fitting a hearing aid by measuring the benefits derived from hearing aid use. Besides audiologic tests, a short version of the Hearing Handicap Inventory for the Elderly, and the EuroQol questionnaire were used in a prospective study. Ninety-eight first-time hearing aid users were interviewed prior to, and six months after, the fitting of their first hearing aids. The total HHIE-S score changed from 28.7 before, to 12.7 six months after, hearing aid fitting. Altogether 40%-60% of the users reported fewer social or emotional problems. There was a statistically significant positive change in the EQ-VAS score. According to the HHIE-S, hearing aids clearly alleviated hearing disability. The EQ-5D questionnaire was not sensitive enough for measuring the health-related quality of life of subjects with hearing impairment.     

Use and benefit of hearing aids in the tenth decade--and beyond

The purpose of this study was to evaluate the use and benefit of hearing aids in 185 hearing-disabled subjects born before 1900, consecutively fitted with a hearing aid during the first 6 months of 1989. Information from 138 (75%) subjects, 117 females and 21 males with a median age of 93 years (range 90-107), was obtained from a questionnaire, which was mailed 4-6 months after the fitting procedure. The questionnaire included questions concerning use of the hearing aid(s), self-reported benefit, handling problems, overall satisfaction/dissatisfaction, social and domiciliary situation and self-reported visual capacity. Among these elderly subjects 75% had previously been provided with hearing aids, while 25% were first-time users. The results demonstrate that 76% use the hearing aid(s) at home and in small groups, and that 51% use the hearing aid(s) each day; however, 35% did not respond to this question. 64% expressed general satisfaction with their aid(s). Despite instruction and counselling, handling problems were frequently present. In those previously fitted with hearing aids a higher rate of time-related use and satisfaction was present, and handling problems were less frequent than in the first-time applicants. It is concluded that elderly hearing-impaired subjects in the tenth decade use and benefit from hearing aids; however, more problems concerning use and benefit of hearing aids are present in this age group than in the younger age groups.     

New hearing aid users' perception of the "hearing aid effect"

The negative attitude elicited by the presence of a hearing aid has been termed the "hearing aid effect." The purpose of this study was to examine the negative reactions associated with hearing aids among new hearing aid users themselves and their perception of the hearing aid effect in their immediate environment. This was accomplished through a questionnaire completed just prior to hearing aid fitting and again 6 months after initial use of amplification. The responses to the questionnaires were compared between individuals who had chosen either in the ear or behind the ear type hearing aids, and between those using either monaural or binaural instruments. The effect of age on the data was also examined. The results indicated that the hearing aid effect was not expected or perceived very widely among these subjects, as only about 10% of them reported sensing negative attitudes to the use of hearing aids. Positive responses to the benefits of hearing aid use from other people often fell short of expectations.     

A Comparative Study Of Physical Characteristics Of Hearing Aids On Microphone And Telecoil Inputs

The variations of sensitivity and frequency response of telecoil input on 32 commercially available body-type and behind-the-ear hearing aids were investigated. The differences in response between the microphone and the telecoil input were also examined. Findings indicate that (1) given aids have different sensitivity and frequency response for telecoil vs. microphone operation, (2) the telecoil, in general, provides a better low-frequency response than the microphone input, and (3) aids with similar responses on acoustic input may produce different responses on magnetic input. These findings further emphasize the importance of knowing the performance characteristics of the hearing aid operating on its telecoil input in order to avoid inappropriate hearing aid selection.     

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.     

Advantages of directional hearing aid microphones related to room acoustics.

In this study, two types of hearing aids were used. Both aids had the same frequency characteristics for frontal sound, but one employed an omnidirectional microphone and the other a directional microphone. The frequency characteristics of both hearing aids were measured for five azimuths on KEMAR and in situ in 12 normal-hearing subjects. For these subjects we also determined the speech reception threshold (SRT) with background noise in two rooms with different reverberation times. The direction of the speech stimuli was always frontal; the direction of the noise was varied. Additionally, directional hearing was measured with short noise bursts from eight loudspeakers surrounding the subject. In the less reverberant room, sounds coming from behind were less amplified by the hearing aid with the directional microphone than by the one with the omnidirectional microphone. In this room the monaural SRT values were largely determined by the level of the background noise. For the directional hearing aids there was an extra binaural advantage which depended on the direction of the background noise. Only for low-frequency noise bursts was directional hearing better with directional hearing aids. In the more reverberant room, no distinct differences between the frequency characteristics of the two hearing aid types were measured. However, a systematic difference between monaural SRT values measured through the two hearing aids was found. This difference was independent of noise azimuth. In conclusion, hearing aid(s) with a directional microphone showed no disadvantages and clear advantages under specific conditions.     

Audiometric earphone discomfort level and hearing aid saturation sound pressure level for a 90 decibel input signal (SSPL90) as measured in the human ear canal

The acoustical problems involved in matching the saturation sound pressure level for a 90 dB input signal (SSPL90) of a hearing aid to individual discomfort level were investigated. The real ear SPL (RE/SSPL90) produced by a supra-aural earphone used when measuring uncomfortable loudness (UCL), and RE/SSPL90 produced by three different hearing aids at 90 dB SPL input, were measured for nine subjects, using a miniature microphone technique, and compared to the corresponding coupler levels used when matching hearing aid maximum output to UCL. It was found that a hearing aid often gives about 5 dB, and sometimes 10 dB, higher RE/SPLs than the earphone, if the hearing aid output levels, as measured in a 2-cc coupler (IEC126), are equal to the earphone output levels as measured in a 6-cc coupler (NBS9A). It is recommended that a safety margin of at least 5 dB be used in the preliminary fitting when matching hearing aid SSPL90 to the patient's UCL, converted to dB SPL.     

宁夏地区助听器康复救助项目受助者适配效果分析

目的调查分析宁夏地区136例听障患者发放助听器后的配戴效果,了解使用助听器情况及影响因素,为听障患者助听器验配及项目执行提供参考依据。方法通过询问病史,进行耳内镜检查、纯音听力测试,了解患者听力损失程度及听阈曲线类型,为患者进行助听器验配,采用助听器效果国际性调查问卷(the international outcome inwentory for hearing aids,IOI-HA)通过面对面问答或电话随访的方式进行助听器效果评价,比较不同配戴时间、听力损失程度、听阈曲线类型助听器IOI-HA的得分。结果118例(86.76%)助听器使用者认为配戴助听器后对生活有中等程度以上的帮助;130例(95.6%)助听器使用者认为使用助听器后生活满意度有中等及以上提高;每天使用时间及参与社会活动时仍存在的困难不同年龄段之间的平均得分不同,且差异具有统计学意义(P<0.05),随着年龄的增加,以上两个项目的平均得分逐渐减少;不同文化程度、听力损失程度、听阈曲线图类型的听力障碍患者配戴助听器使用效果组间差异无统计学意义。结论助听器使用者对配发的助听器总体较为满意,使用情况良好;助听器使用时,还要大力提倡坚持配戴、及早干预;加强对助听器配戴者回访的管理,对于助听器使用中的不足与问题应及时调试。     

Directivity quantification in hearing aids: fitting and measurement effects

OBJECTIVE: To evaluate the impact of venting, microphone port orientation, and compression on the electroacoustically measured directivity of directional and omnidirectional behind-the-ear hearing aids. In addition, the average directivity provided across three brands of directional and omnidirectional behind-the-ear hearing aids was compared with that provided by the open ear. DESIGN: Three groups of hearing aids (four instruments in each group) representing three commercial models (a total of 12) were selected for electroacoustic evaluation of directivity. Polar directivity patterns were measured and directivity index was calculated across four different venting configurations, and for five different microphone port angles. All measurements were made for instruments in directional and omnidirectional modes. Single source traditional, and two-source modified front-to-back ratios were also measured with the hearing aids in linear and compression modes. RESULTS: The directivity provided by the open (Knowles Electronics Manikin for Acoustic Research) ear was superior to that of the omnidirectional hearing aids in this study. Although the directivity measured for directional hearing aids was significantly better than that of omnidirectional models, significant variability was measured both within and across the tested models both on average and at specific test frequencies. Both venting and microphone port orientation affected the measured directivity. Although compression reduced the magnitude of traditionally measured front-to-back ratios, no difference from linear amplification was noted using a modified methodology. CONCLUSIONS: The variation in the measured directivity both within and across the directional microphone hearing aid brands suggests that manufacturer's specification of directivity may not provide an accurate index of the actual performance of all individual instruments. The significant impact of venting and microphone port orientation on directivity indicate that these variables must be addressed when fitting directional hearing aids on hearing-impaired listeners. Modified front-to-back ratio results suggest that compression does not affect the directivity of hearing aids, if it is assumed that the signal of interest from one azimuth, and the competing signal from a different azimuth, occur at the same time.     

Clinical evaluation of a two-channel amplitude compression hearing aid

Twelve experienced hearing aid users with mild to moderate hearing loss used two new, commercially available behind-the-ear amplitude compression hearing aids for 1 month each. One aid was a single-channel device; the other was a two-channel aid. All subjects had used other compression aids for at least 1 year. Performance in real-life situations with the personal aid and the two trial aids was evaluated by the Hearing Performance Inventory (HPI). Another questionnaire probed subjective preference for the three aids and willingness to purchase each of the trial aids. The major HPI finding was an equal performance superiority for the two trial aids over the personal aid for half the subjects. The preference/purchase questionnaire results indicated that the two-channel aid had some sound quality advantages, but was unacceptable physically. The single-channel trial was clearly preferred over the personal and two-channel device.     

Effect of signal-to-noise ratio on directional microphone benefit and preference

This study examined speech intelligibility and preferences for omnidirectional and directional microphone hearing aid processing across a range of signal-to-noise ratios (SNRs). A primary motivation for the study was to determine whether SNR might be used to represent distance between talker and listener in automatic directionality algorithms based on scene analysis. Participants were current hearing aid users who either had experience with omnidirectional microphone hearing aids only or with manually switchable omnidirectional/directional hearing aids. Using IEEE/Harvard sentences from a front loudspeaker and speech-shaped noise from three loudspeakers located behind and to the sides of the listener, the directional advantage (DA) was obtained at 11 SNRs ranging from -15 dB to +15 dB in 3 dB steps. Preferences for the two microphone modes at each of the 11 SNRs were also obtained using concatenated IEEE sentences presented in the speech-shaped noise. Results revealed that a DA was observed across a broad range of SNRs, although directional processing provided the greatest benefit within a narrower range of SNRs. Mean data suggested that microphone preferences were determined largely by the DA, such that the greater the benefit to speech intelligibility provided by the directional microphones, the more likely the listeners were to prefer that processing mode. However, inspection of the individual data revealed that highly predictive relationships did not exist for most individual participants. Few preferences for omnidirectional processing were observed. Overall, the results did not support the use of SNR to estimate the effects of distance between talker and listener in automatic directionality algorithms.     

Open fitting: performance verification of receiver in the ear and receiver in the aid

ObjectiveTo verify the receiver in the ear and receiver in the aid adaptations by measuring in situ the speech perception and users’ level of satisfaction.MethodsThe study was approved by the research ethics committee (Process: 027/2011). Twenty subjects older than 18 years with audiological diagnosis of mild and moderate bilateral descending sensorineural hearing loss were evaluated. The subjects were divided into two groups, where G1 (group 1) was fitted with open-fit hearing aids with the built-in receiver unit (receiver in the ear) and G2 (group 2) was fitted with open-fit hearing aids with RITE. A probe microphone measurement was performed to check the gain and output provided by the amplification and for assessment of speech perception with Hearing in Noise Test with and without hearing aids. After a period of six weeks of use without interruption, the subjects returned for follow-up and answered the Satisfaction with Amplification in Daily Life questionnaire, and were again subjected to Hearing in Noise Test.ResultsBoth groups presented better test results for speech recognition in the presence of noise.ConclusionGroups 1 and 2 were satisfied with the use of hearing aids and improved speech recognition in silent and noisy situations with hearing aids.