Hyperacusis: case studies and evaluation of electronic loudness suppression devices as a treatment approach.

Hyperacusis, as defined here, is a relatively rare condition in which the patient, with or without hearing loss, experiences severe loudness discomfort to everyday environmental sound levels. The case studies of 14 patients with severe hyperacusis are described; all wore passive attenuators (earplugs and/or earmuffs) in an attempt to alleviate their discomfort, frequently producing communication difficulties. These subjects were fitted binaurally with experimental electronic loudness suppression devices housed in in-the-ear casings. The devices supplied low-level amplification followed by an extreme form of amplitude compression for moderate or high-level inputs in an attempt to reduce loudness discomfort without reducing audibility. Many of the subjects were found to function with a wider dynamic range with the active devices compared with passive attenuators or the unoccluded ear, and most reported that they benefited from the devices in at least some listening situations.

Field trial evaluations of a switched directional/omnidirectional in-the-ear hearing instrument.

The use of directional microphones is one of the few methods available for hearing aids to increase the signal-to-noise ratio. The smaller microphones available with today's technology have increased the viability of their application for in-the-ear (ITE) hearing aids. This study evaluated an ITE hearing aid containing two nondirectional microphones that provides wearer-selectable omnidirectional/directional operating modes. Ten sensorineural hearing-impaired patients were fitted binaurally. During the first trial period, the low-frequency gain decrease produced by the directional mode was not compensated for. The frequency responses were matched during the second trial period. For both trial periods, Hearing in Noise Test results using two uncorrelated noise sources indicated significant speech recognition improvements for the directional mode relative to the omnidirectional mode. Responses on Abbreviated Profile of Hearing Aid Benefit questionnaires, paired-comparison judgments, and interview data revealed that most subjects preferred the directional mode in noisier environments, but many also preferred the omnidirectional mode in quiet listening.

The role of consonant-vowel amplitude ratio in the recognition of voiceless stop consonants by listeners with hearing impairment.

Several authors have evaluated consonant-to-vowel ratio (CVR) enhancement as a means to improve speech recognition in listeners with hearing impairment, with the intention of incorporating this approach into emerging amplification technology. Unfortunately, most previous studies have enhanced CVRs by increasing consonant energy, thus possibly confounding CVR effects with consonant audibility. In this study, we held consonant audibility constant by reducing vowel transition and steady-state energy rather than increasing consonant energy. Performance-by-intensity (PI) functions were obtained for recognition of voiceless stop consonants (/p/, /t/, /k/) presented in isolation (burst and aspiration digitally separated from the vowel) and for consonant-vowel syllables, with readdition of the vowel /a/. There were three CVR conditions: normal CVR, vowel reduction by 6 dB, and vowel reduction by 12 dB. Testing was conducted in broadband noise fixed at 70 dB SPL and at 85 dB SPL. Six adults with sensorineural hearing impairment and 2 adults with normal hearing served as listeners. Results indicated that CVR enhancement did not improve identification performance when consonant audibility was held constant, except at the higher noise level for one listener with hearing impairment. The re-addition of the vowel energy to the isolated consonant did, however, produce large and significant improvements in phoneme identification.

Differences in performance between Oticon MultiFocus Compact and ReSound BT2-E hearing aids.

Differences in performance were evaluated between binaural fittings of the Oticon MultiFocus (MF) and ReSound BT2-E on 25 hearing-impaired subjects across two sites. Subjects were initially fit using each manufacturer's algorithm and adjustments were made at 1 week based on subjects' responses to diary questions. Performance was assessed after a 4- to 6-week trial period with each hearing aid set using the Speech Perception in Noise (SPIN) test administered at 50, 65, and 80 dB SPL, the Abbreviated Profile of Hearing Aid Benefit (APHAB) questionnaire, loudness judgments of female connected discourse at 65 and 80 dB SPL, and an overall preference selection. The MF yielded significantly better SPIN scores at 50 and 65 dB SPL, while the BT2-E yielded a significantly better score at 80 dB SPL. No statistically significant differences were found in the APHAB benefit scores between the hearing aid sets, but both sets were significantly better than the subjects' own hearing aids on three of the four subscales. The MF produced slightly higher mean loudness judgments at both input levels than the BT2-E. Finally, 12 subjects preferred the BT2-E, 10 subjects preferred the MF, and three subjects stated no preference. The results are discussed in terms of audiogram effects on preference and effects of differences in signal processing approaches between the devices.

Effect of low-frequency gain reduction on speech recognition and its relation to upward spread of masking.

Speech recognition was measured in listeners with normal hearing and in listeners with sensorineural hearing loss under conditions that simulated hearing aid processing in a low-pass and speech-shaped background noise. Differing amounts of low-frequency gain reduction were applied during a high-frequency monosyllable test and a sentence level test to simulate the frequency responses of some commercial hearing aids. The results showed an improvement in speech recognition with low-frequency gain reduction in the low-pass noise, but not in the speech-shaped background noise. Masking patterns also were obtained with the two background noises at 70 and 80 dB SPL to compare with the speech results. There was no correlation observed between the masking results and the improvement in speech recognition with low-frequency gain reduction.

Consonant recognition performance of hearing-impaired listeners using one linear and three nonlinear hearing aids.

Consonant recognition performance was examined in 18 subjects listening in quiet and speech noise with linear and nonlinear hearing aids. Subjects were divided into three groups by audiometric configuration: flat, moderately sloping, and sharply sloping. Nonlinear amplification schemes included adaptive high-pass filtering (Argosy's Manhattan II, experimentally modified; MANe), MANe circuitry followed by expansion (EXP), and infinite amplitude clipping (IAC). Consonant-to-vowel ratios (CVRs) were calculated for syllables processed through each hearing aid. Performance with the IAC was significantly poorer than with the other amplifiers across audiograms in noise. Intersubject variability in performance was high, even within audiogram groups. High-frequency phonemes were more often audible with the EXP than with the other hearing aids for subjects with moderately and severely sloping audiograms. Output CVRs increased for some phonemes with a nonlinear hearing aid versus linear, but recognition of individual phonemes did not correlate significantly with CVR.

Concurrently recorded auditory event-related potentials and behavioral responses to dichotic CV stimuli.

Auditory event-related potentials (AERPs) were recorded concurrently with behavioral responses to dichotic CVs in 16 young, normal, right-handed, female subjects. The results showed the expected behavioral right-ear advantage and an N105-P184 complex of significantly greater amplitude over the left temporal region than over the right. In another normal individual showing a consistent behavioral left-ear advantage, we found differences in AERP amplitude and morphology favoring right-hemispheric lateralization for speech.

Achieving prescribed gain/frequency responses with advances in hearing aid technology.

Technological limitations have restricted the capability of older generation in-the-ear (ITE) hearing aids to closely match prescribed real ear gain/frequency responses. Newer technology, widely available in currently marketed ITE hearing aids, has considerably improved this capability. Data for 60 ears are presented comparing the real ear insertion gain (REIG) actually achieved to the target REIG, using ITE hearing aids having: 1) older generation narrow-band receivers, and amplifiers with single-pole-filter low frequency tone control and a class A amplifier output stage (n = 30), and 2) newer generation amplifiers with a two- or four-pole-filter low frequency tone control, and wide band receivers, containing a class D amplifier output stage (n = 30). With the newer technology ITE hearing aids, the means and ranges of deviation from target gain were reduced. Capability for achieving prescription REIG with ITE hearing aids can be further improved with multichannel amplifiers. Examples of the latter are shown for several difficult-to-fit audiograms.

Ability to achieve gain/frequency response and SSPL-90 under three prescription formulas with in-the-ear hearing aids.

Custom in-the-ear (ITE) hearing aids (standard linear amplifiers with single-pole-filter low-frequency tone control and a class A amplifier output stage) were fit to 90 ears using the revised National Acoustics Laboratories' formula (NAL-R), and to 20 ears each using Prescription of Gain/Output II (POGO II) and Memphis State University (MSU) formulas. Both real-ear insertion gain and 2-cc coupler gain were evaluated. Examination of differences between prescribed gain and that actually achieved in the fittings revealed that too much gain was often given in the low- and mid-frequency range and insufficient gain in the high frequencies. There was little difference among the formulas in the degree of deviation from target. For some fittings, the deviation resulted in poorer predicted speech recognition scores (modified Speech Transmission Index). For the POGO II and MSU methods, underfitting of prescribed SSPL-90 values was far more common than overfitting.

Comparison of Etymotic insert and TDH supra-aural earphones in auditory brainstem response measurement.

There are few systematic comparisons of Etymotic ER-3A insert earphones versus supra-aural earphones in auditory brainstem response (ABR) measurement. We compared ER-3A insert earphones and two types of supra-aural earphones (TDH-39P and TDH-49P) in a group of normal hearing adults. Acoustic analyses revealed spectral and temporal differences among earphones. Behavioral and ABR thresholds to click stimuli were slightly elevated with the ER-3A compared to the TDH earphones. The ER-3A earphones produced a latency delay, relative to the TDH earphones, that varied from about 0.8 to 1.0 msec, and increased at lower stimulus intensity levels. In addition, ABR wave I amplitude was significantly reduced with the ER-3A earphone. Based on these data, we recommend collection of normative data with the ER-3A earphones prior to their use in ABR measurement.

A review of current "noise reduction" hearing aids: rationale, assumptions, and efficacy.

Amplification technology has changed considerably in the last decade, particularly with the introduction of more advanced adaptive signal processing approaches and digital/hybrid hearing aids. Because difficulty understanding speech in the presence of background noise is the most common complaint of hearing-impaired patients, an increasing number of these new products are being marketed as "noise reduction" hearing aids. There reamin, however, many unanswered questions regarding patient candidacy for these instruments, and the relative benefit that can be expected from the new technology. This article discusses issues and assumptions underlying noise reduction strategies, reviews categories of hearing aids on the market that are meant to alleviate listening difficulty in noise, and outlines future needs in research and development in this area.

Effects of relative starting phase and frequency separation of two-tone stimuli on the brain-stem auditory-evoked response.

Brain-stem auditory-evoked responses (BAERs) were obtained in six normal-hearing adults using single-tone and two-tone stimuli arithmetically centered around 4000 Hz. Two-tone stimuli varied in frequency separation from 200 to 3200 Hz, and started in-phase (homophasic) or 180 deg out-of-phase (antiphasic) with each other. Responses to each of the single-tone components of the two-tone stimuli were elicited and then summed for comparison with responses to the two-tone stimuli. Results indicated no significant difference in wave V latency between homophasic or antiphasic two-tone conditions, and summed single-tone conditions. Under the homophasic condition, the mean latency for the widest frequency separation of the tones was significantly longer than those for narrower separations. A significant difference in wave V amplitude between two-tone phase conditions was found for frequency separations of 200, 400, and 3200 Hz only. Summed single-tone BAERs demonstrated a significantly larger wave V amplitude than responses from either two-tone phase condition at all frequency separations.

Rapid threshold estimation using the "chained-stimuli" technique for auditory brain stem response measurement.

The "chained-stimuli" technique for rapid auditory brain stem response (ABR) threshold estimation involves lengthening the averaging time window and presenting a series ("chain") of click stimuli. Each stimulus chain contains, in addition to a silent interval, click stimuli of 10, 20, 30, 40, 50, 60, and 70 dB nHL that are separated by 10 msec intervals. Using this method, the single averaged response to the chained-stimulus contains up to seven individual ABRs. The responses elicited by each level of click stimulus within the chain can be analyzed separately. In this study, chained-stimuli ABR threshold estimations for normal hearers were essentially equivalent to those obtained using an automated conventional ABR method. The data for a seven point latency-intensity function using the chained-stimuli technique were obtained in a mean time of only 8 min per ear.

Interaural attenuation using etymotic ER-3A insert earphones in auditory brain stem response testing.

Click interaural attenuation (IA) was measured behaviorally and with the auditory brain stem response (ABR) in two unilaterally deaf adults with Etymotic ER-3A insert earphones, and TDH-39P and TDH-49P supraaural earphones. Stimulus crossover for each set of earphones was also determined with pure-tone audiometry. Pure-tone results agreed with previous research, showing that the ER-3A provided substantially greater IA than the supraaural earphones, particularly for low frequencies. For click stimuli, behavioral and ABR results revealed only modest, if any, improvement in IA with the ER-3A relative to the supraaural earphones. The results of this study suggest that while the ER-3A earphones provide a clear IA advantage for behavioral pure-tone audiometry, they do not eliminate the need for contralateral masking of click stimuli in ABR testing.

Variability of most comfortable and uncomfortable loudness levels to speech stimuli in the hearing impaired.

Methods for determining hearing aid settings often incorporate measurements of most comfortable loudness (MCL) and uncomfortable loudness (UCL) levels. This study examined the variability of loudness measures and their correlation to threshold data, using speech stimuli presented to hearing-impaired subjects. MCLs, UCLs, speech reception, and speech detection thresholds were obtained from 50 subjects having sensorineural impairments. The stimuli were CID W-2 spondees spoken by three female clinicians. Three MCLs and UCLs were obtained within each session, using ascending runs and a closed-set response list. Fifteen subjects were retested twice over intervals ranging from a week to several months. Between-session variability for the loudness measurements was less than or equal to 10 dB across sessions and speakers for the majority of subjects, with a tendency for the MCL and UCL to increase slightly over time. Significant variability was attributed to the use of live-voice presentation by different clinicians. High positive correlation was found between threshold and loudness data for subjects with relatively flat audiometric configurations but not for subjects demonstrating sharply sloping hearing losses.

The 40-Hz event-related potential as a measure of auditory sensitivity in normals.

Estimates of behavioral threshold using the 40-Hz Event-Related Potential (ERP) were obtained on sixteen normal subjects at frequencies of 500, 1000, 2000, and 4000 Hz, and compared with behavioral thresholds for the same stimuli. The mean differences were within 10 dB at the three lowest frequencies. The mean difference at 4000 Hz was 16 dB. Peak amplitude of the response did not vary significantly either with signal amplitude or test frequency, but the latency of the response varied significantly with frequency. Factors which may affect the reliability and validity of the 40-Hz ERP are discussed.