Hearing aids: expectations and satisfaction of people with an intellectual disability, a descriptive pilot study.

BACKGROUND: In spite of an increased risk of hearing impairment in persons with an intellectual disability (ID), rehabilitation with hearing aids often fails. We performed a descriptive pilot study with the following study questions: 1 Do comparable elements as in the general population contribute to expectations of and satisfaction with hearing aids in adults with mild or moderate IDs? 2 To what extent do adults with an ID depend on carers in use and maintenance of hearing aids? STUDY POPULATION: 16 adults with a mild or moderate ID and a recent diagnosis of hearing impairment. Method: information by means of specially designed booklets; semi-structured interviews prior to hearing aid fitting and 6 months afterwards. ANALYSIS: descriptive. RESULTS: In total, 14/16 participants were able to give reliable answers. Most were aware of their hearing loss and familiar with reasons for hearing aids. A minority expressed positive expectations. Some expressed explicit wishes on the looks of hearing aids. All satisfaction domains as described for the general population could be recognized. Most participants were partially or totally dependent on carers in use and maintenance of hearing aids. CONCLUSIONS: Adults with ID may have explicit ideas and wishes about hearing aids and, if specifically asked, are capable of expressing these. Given information should be checked and repeated. In satisfaction with hearing aids, comparable elements may play a role as in the general population: benefit, cosmetics, sound quality/acoustics, comfort/ease of use, and service delivery. These findings, however, are from a small-scale study. Additional research is necessary to find out whether they are applicable more generally.

Prevalence of visual and hearing impairment in a Dutch institutionalized population with intellectual disability.

A screening of hearing and visual function was performed using clinical assessment methods in a Dutch institutionalized population of 672 people with mild to profound intellectual disability (ID). Because the studied population was not comparable to the total Dutch population with ID, subgroups were distinguished according to level of ID, age younger and older than 50 years, and the presence or absence of Down's syndrome (DS). The prevalences of both hearing and visual impairment were considerably increased in all subgroups, as compared with the general population. In the least affected group, i.e. those < 50 years with a mild or moderate ID by other causes than DS, the prevalences of hearing and visual impairment were 21% and 4%, respectively (as opposed to 2-7% and 0.2-1.9% in the general Dutch population <50 years, respectively). The prevalence of hearing impairment showed a sharp and highly significant increase in individuals with DS and subjects > or = 50 years. To a lesser extent, young adults with severe or profound ID had an increased risk of hearing impairment. Visual impairment and blindness were specifically highly prevalent in people with severe or profound ID (51% < 50 years of age). Down's syndrome and an age > or = 50 years were also significant risk factors for visual impairment. There was an alarmingly high prevalence of combined sensory impairment, especially in those with severe or profound ID (20%). Although hearing impairment had been diagnosed prior to this screen in 138 people and visual impairment in 65 individuals, a first diagnosis of hearing impairment was made in 128 subjects and of visual impairment in 90 cases. This highlights the tendency for sensory impairments to go unnoticed in people with ID, which is not restricted to those with severe or profound ID. Therefore, the present authors stress the importance of regular screening as outlined in the existing IASSID international consensus statement.

ICRA noises: artificial noise signals with speech-like spectral and temporal properties for hearing instrument assessment. International Collegium for Rehabilitative Audiology.

Current standards involving technical specification of hearing aids provide limited possibilities for assessing the influence of the spectral and temporal characteristics of the input signal, and these characteristics have a significant effect on the output signal of many recent types of hearing aids. This is particularly true of digital hearing instruments, which typically include non-linear amplification in multiple channels. Furthermore, these instruments often incorporate additional non-linear functions such as "noise reduction" and "feedback cancellation". The output signal produced by a non-linear hearing instrument relates to the characteristics of the input signal in a complex manner. Therefore, the choice of input signal significantly influences the outcome of any acoustic or psychophysical assessment of a non-linear hearing instrument. For this reason, the International Collegium for Rehabilitative Audiology (ICRA) has introduced a collection of noise signals that can be used for hearing aid testing (including real-ear measurements) and psychophysical evaluation. This paper describes the design criteria, the realisation process, and the final selection of nine test signals on a CD. Also, the spectral and temporal characteristics of these signals are documented. The ICRA noises provide a well-specified set of speech-like noises with spectra shaped according to gender and vocal effort, and with different amounts of speech modulation simulating one or more speakers. These noises can be applied as well-specified background noise in psychophysical experiments. They can also serve as test signals for the evaluation of digital hearing aids with noise reduction. It is demonstrated that the ICRA noises show the effectiveness of the noise reduction schemes. Based on these initial measurements, some initial steps are proposed to develop a standard method of technical specification of noise reduction based on the modulation characteristics. For this purpose, the sensitivity of different noise reduction schemes is compared by measurements with ICRA noises with a varying ratio between unmodulated and modulated test signals: a modulated-unmodulated ratio. It can be anticipated that this information is important to understand the differences between the different implementations of noise reduction schemes in different hearing aid models and makes.

Effects of single-channel phonemic compression schemes on the understanding of speech by hearing-impaired listeners.

The effect of digital processing on speech intelligibility was studied in hearing-impaired listeners with moderate to severe high-frequency losses. The amount of smoothed phonemic compression in a high-frequency channel was varied using wide-band control. Two alternative systems were tested to compensate for upward spread of masking (USOM) and to reduce modulations in the high-frequency channel effectively. Consonant-vowel-consonant tests were conducted in a group of 14 subjects using eight different speech-processing settings. Speech intelligibility improved significantly with compression, mainly due to positive effects on the initial-consonant score. Surprisingly, listeners with a smaller residual dynamic range tended to profit less from compression. Compensation for USOM gave an additional improvement of vowel intelligibility. In background noise, consistently negative effects of speech processing were found. The combined use of phonemic compression and USOM compensation is promising in conditions without background noise.

Effectiveness of a single and a repeated screen for hearing loss in the elderly.

The aim of this study was to assess the value of repeated audiometric screens offered to elderly in general practice. In 1991, an audiometric screen was performed on 660 participants, aged 60 years and over, enlisted in one general practice near Rotterdam, the Netherlands. We repeated the audiometric screen 5 years later in 80.2% (405/505) of the eligible participants of the first screen. After the first screen, 24.3% of those who were hearing impaired had discussed this with their general practitioner, 21.5% were referred to a specialist in otolaryngology and 12.1% had been prescribed a hearing aid. The effect of the repeated screen was lower as only 7.3% of the hearing impaired participants received a hearing aid. Efforts to screen on hearing loss will be fruitless and can best be avoided by general practitioners unless strategies are developed to increase the use of hearing aids after a positive screening result.

Evaluation of spectral enhancement in hearing aids, combined with phonemic compression.

In this study, the separate and combined effects on speech perception of compensation of the reduced dynamic range by compression and compensation of the reduced frequency resolution by spectral enhancement is investigated. The study has been designed to compare the effects of signal processing on monosyllabic consonant-vowel-consonant words for hearing-impaired listeners in conditions of quiet, fluctuating noise, and continuous noise. Speech perception of spectrally enhanced speech was compared with unprocessed speech. In addition, a comparison was made between combinations of spectrally enhanced speech and two types of phonemic compression. In the past, the definition "syllabic compressor" is often used to indicate fast compressors. However, the time constants of the fast compressors used in this study are so short that syllabic has become an inappropriate term. Moreover, intelligibility tests were performed in which scores were acquired of monosyllabic words, and their constituent "phonemic" parts. Therefore, the definitions "phoneme" and phonemic will be used throughout this paper. In one condition, spectral enhancement produced significant improvements for vowel perception. But, this was counteracted by deterioration of the consonant scores for all but one subject. In general, the best overall scores for consonant-vowel-consonant words were obtained in the unprocessed condition. After the spectral enhancement, a single-channel phonemic compressor added no improvement. There are indications that a multichannel phonemic compressor and spectral enhancement have opposite effects, because the scores for this combination are, in general, the lowest.

Clinical evaluation of a full-digital in-the-ear hearing instrument.

In this study we measured the efficacy of a digital hearing aid with compression and noise reduction in a well-controlled clinical field trial in two independent centres. The experiments focused on a number of aspects of the application of the digital hearing aids. The study combines a field test of 2x4 weeks with laboratory experiments. We used objective measurements (speech perception tests in background noise, loudness scaling) and subjective assessments (questionnaires). The measurements were performed before and after the field test. The questionnaires were collected after each field test. The results of the digital hearing aids were compared to the results of similar tests with newly fitted analogue reference aids. The study involved 27 sensorineural hearing-impaired subjects, wearing new hearing aids. They comprised a representative sample of in-the-ear users. We used a crossover design in which the subjects used successively digital hearing aids and analogue reference aids in a randomized order. On average, the subjective data are more positive than the objective data. In the end, 20 out of 27 subjects had an overall preference for the digital hearing aid. The financial implications were not taken into consideration. However, objective data do not support this strong subjective preference. A reason could be that the method of analysis (short sentences in a short-duration background noise) is not suited for the digital hearing aid; the testing procedure does not allow the noise-reduction algorithm to adapt to the background noise. There was a striking difference between the results for the two centres. This difference can, to at least a certain extent, be attributed to the timing of speech relative to the background noise in the objective tests. This illustrates that the test conditions are critical in modern non-linear signal-processing hearing aids with long time constants. New evaluation techniques should be developed for this new generation of active non-linear hearing aids.

Design of two syllabic nonlinear multichannel signal processors and the results of speech tests in noise.

OBJECTIVE: Multichannel syllabic compressors have not yet shown clear advantages for speech perception. New multichannel syllabic nonlinear processors are designed and evaluated in this study to test whether they enhance speech perception scores. DESIGN: Nonsense consonant-vowel-consonant words have been processed in real time with two syllabic nonlinear methods in nine different frequency channels: 1) 30 dB of speech information is mapped into the residual dynamic range (DR) of the subjects with hearing impairment using either compression or expansion; 2) speech levels above the rms level are compressed with a ratio of 3:1, and input levels below the rms level are mapped into the reduced DR of the subjects. The overall frequency spectrum of speech is tilted with more high-frequency output for this condition. The two syllabic nonlinear processors were compared with two linear reference systems (one of them with the same spectral tilt as the second nonlinear condition) for seven hearing-impaired subjects. RESULTS: On average, the syllabic nonlinear processors show scores similar to one of the linear systems. The linear reference with tilt has, on average, 3% higher scores, mainly due to improved vowel identification. CONCLUSIONS: No negative effects were shown on average for the syllabic nonlinear processors, but no positive effects were demonstrated either. Tilting of the overall speech spectrum was advantageous.

Audiological results of the bone-anchored hearing aid HC200: multicenter results.

Sixty-two patients with conductive or mixed hearing loss (average bone conduction threshold at 0.5, 1, and 2 kHz ranged from 1 to 44 dB hearing level) were fitted with a bone-anchored hearing aid (BAHA type HC200). Previously, 52 of them had used a conventional bone conduction hearing aid (CBHA) and 10 of them an air conduction hearing aid (ACHA). Audiological tests were conducted to compare the patients' performance with the BAHA to that with their previous conventional hearing aid. In the speech recognition in quiet test, only 5 patients in the CBHA group improved significantly: the majority had 100% scores with both hearing aids. In the speech recognition in noise test, 28 patients improved significantly. The mean improvement in the signal to noise ratio (S/N) in the CBHA group was -2.3 +/- 2.4 dB. That none of the patients in the CBHA group performed worse with the BAHA led us to the conclusion that the BAHA is superior to the CBHA. None of the patients in the ACHA group achieved a better speech recognition in quiet score using the BAHA. On average, there was no significant improvement in the S/N ratio in the ACHA group, although in 6 patients the S/N ratio improved significantly, and in 1 patient it worsened significantly. From the whole group, the performance of only 2 patients, both in the ACHA group, was significantly worse with the BAHA on one of the speech recognition tests.

The effects of syllabic compression and frequency shaping on speech intelligibility in hearing impaired people.

The effect of syllabic compression on speech intelligibility is rarely positive and in those cases that positive effects have been found, the same positive results could in general be obtained by frequency shaping of the frequency response curve. We programmed a syllabic compressor on a digital processor; the compressor differed from a conventional syllabic compressor by incorporating a delay in the signal path to suppress overshoots and thus minimize transient distortion. Furthermore, the time constants were short: attack time of 5 msec and release time of 15 msec. The compressor was only active in the high-frequency band. An essentially linear signal was added to deliver the low-frequency speech components. The processing resulted in a frequency response that mirrored the hearing loss near threshold and became much flatter for higher level input signals. Speech intelligibility scores for nonsense consonant-vowel-consonant words embedded in carrier phrases were determined for hearing-impaired persons with sloping audiograms and discrimination losses for speech. Results showed little additional effect of frequency shaping to the existing improved speech score for compressed speech. Optimum results were found for a compression ratio 2 with lower speech scores for linear amplification and for compression ratio 8. We next determined the effect of providing high-frequency emphasis to the speech signal and/or to the compression control signal to compensate for the upward spread of masking. The frequency response at the root-mean-square level was adjusted according to the half-gain rule. The positive effects of moderate compression could be found again; the high-frequency emphasis, however, was positive for the vowels but made consonant recognition poorer.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of input-output configuration in syllabic compression on speech perception.

Speech perception was tested through a broad-band syllabic compressor with four different static input-output configurations. All other parameters of the compressor were held constant. The compressor was implemented digitally and incorporated a delay to reduce overshoot. We studied four different input-output configurations, including a linear reference condition. Normal-hearing and hearing-impaired subjects participated in the experiments testing perception of meaningful sentences as well as nonsense CVCs in carrier phrases. The speech materials were presented in quiet and in noise. The results from the CVCs were analyzed quantitatively in terms of scores and qualitatively in terms of phoneme confusions. Differences in speech perception due to the different input-output configurations were small. The input-output configuration with the highest amplification of low amplitude sounds yielded the best results. Detailed analysis of the results included a correlational analysis with a number of auditory functions characterizing the ears tested. The pure-tone audiogram provided parameters of auditory sensitivity: average audiometric loss and audiometric slope. Psychophysical tests provided parameters of temporal resolution and frequency selectivity: the temporal resolution factor, temporal gap detection, and auditory filter shape. The correlational analysis showed that the subjects with better temporal acuity obtained better results.

Spatial and temporal summation in the human dark-adapted retina.

A coherent set of absolute-threshold data is presented for circular flashes with a diameter of 5-343 min of arc, a flash duration of 32-1000 msec, and at eccentricities between 7 and 50 deg in the temporal retina. A reduction in the flash interval from 4 to 1 sec causes a threshold elevation for eccentricities exceeding 15 deg for all other stimulus parameters. It is shown that local adaptation affects the measurements significantly, especially when long-lasting stimuli and large eccentricities exist. The results can be described with the help of a quanta-coincidence model if adaptational properties are included.