Detecting the recruitment phenomenon in adults using 80-Hz auditory steady-state response.

OBJECTIVES: The ASSR is used widely as an objective measurement of hearing in clinical settings because of its high frequency specificity. The recruitment phenomenon is generally detected using subjective evaluations which require direct communication with the patient. If the recruitment phenomenon can be detected with ASSR, it would facilitate diagnosis in patients with developmental disorders and infants. SUBJECTS AND METHODS: We examined 2 groups of subjects: 10 subjects with unilateral hearing impairment in whom the recruitment phenomenon was detected by the alternate binaural loudness balance test and 12 normal subjects. We compared the relationships between the ASSR response and the stimulus sound pressure level in the 2 groups using the 80-Hz ASSR. RESULTS: The amplitude of ASSR was significantly higher in the impaired ear in hearing-impaired subjects compared to a normal ear in normal subjects. The latency of ASSR was significantly shorter in the impaired ear in hearing-impaired subjects than in the normal ear in the normal subjects. CONCLUSION: This study showed that the recruitment phenomenon caused the higher amplitude and the shorter latency observed in hearing-impaired subjects in the 80-Hz auditory steady-state response (ASSR) in comparison with normal subjects.

Using beamforming and binaural synthesis for the psychoacoustical evaluation of target sources in noise.

The potential of spherical-harmonics beamforming (SHB) techniques for the auralization of target sound sources in a background noise was investigated and contrasted with traditional head-related transfer function (HRTF)-based binaural synthesis. A scaling of SHB was theoretically derived to estimate the free-field pressure at the center of a spherical microphone array and verified by comparing simulated frequency response functions with directly measured ones. The results show that there is good agreement in the frequency range of interest. A listening experiment was conducted to evaluate the auralization method subjectively. A set of ten environmental and product sounds were processed for headphone presentation in three different ways: (1) binaural synthesis using dummy head measurements, (2) the same with background noise, and (3) SHB of the noisy condition in combination with binaural synthesis. Two levels of background noise (62, 72 dB SPL) were used and two independent groups of subjects (N=14) evaluated either the loudness or annoyance of the processed sounds. The results indicate that SHB almost entirely restored the loudness (or annoyance) of the target sounds to unmasked levels, even when presented with background noise, and thus may be a useful tool to psychoacoustically analyze composite sources.

Detection of the uncomfortable loudness level by electroencephalographic data: a novelty detection approach using habituation correlates.

The objective fitting of hearing aids and cochlear implants in uncooperative patients still remains a challenge. Especially in determining the threshold of uncomfortable loudness which cannot be predicted from the auditory threshold. In this study, we propose a single sweeps processing method which employs a hybrid approach of adaptive frame decomposition adaptation by a tight wavelet frame and the gaussian novelty detection for the detection of large-scale electroencephalographic responses correlates of habituation in late auditory evoked potentials. For this, habituation is discerns as a novel event. It is concluded that the new approach provides a fast and reliable method in the discrimination of uncomfortable loudness level from comfortable loudness level. It can be further use in more clinically oriented studies related to an objective frequency specific fitting of hearing aids or cochlear implants.

Recruitment en la presbiacusia / Recruitment in presbycusis

La presbiacusia se caracteriza por una hipoacusia neurosensorial, sobre todo de los agudos, simétrica y progresiva, y una mala inteligibilidad. El recruitment, típico de las hipoacusias cocleares estaría presente en los casos de presbiacusia sensorial que cursan primariamente con cocleopatía. Analizamos en 241 pacientes presbiacúsicos varias variables y las posibles interrelaciones con el recruitment

Presbycusis is characterised by a sensori neural hearing loss mainly in high frequencies, symmetrical and progressive and poor understanding. Recuritment, typical in cochlear hearing loss, would be present in cases of sensorial presbycusis which runs mainly in cochlear pathologies. We analyse variables and their possible interrelations with recruitment in 241 presbycusic patients

[Recruitment detection--a comparison of category loudness scaling and classical supra-threshold audiometry]. / Rekruitmentnachweis-Kategorial-Lautheitsskalierung und klassische überschwellige Audiometrie im Vergleich.

BACKGROUND: The assessment and localization of hearing impairments require reliable and valid recruitment indicators. Although many diagnostic tests are available, which of these tests are most important is still the subject of controversy. METHOD: To compare the efficacy of various diagnostic audiometric tests, 51 subjects with monaural sensorineural hearing loss were submitted to the following tests at 500 and 2000 Hz: category loudness scaling of narrowband noise bursts, alternate binaural loudness balance (ABLB), intensity difference limen test, SISI test, fixed frequency Békésy audiometry, and contralateral determination of the acoustic reflex threshold for pure tones. RESULTS: Using the findings of the ABLB test as reference, the results of the present study revealed that category loudness scaling and acoustic reflex audiometry are reliable quantitative recruitment indicators. This holds for the intensity difference limen test to a lesser extend as well. However, the recruitment selectivity of the SISI test and Békésy audiometry turned out to be considerably poorer. CONCLUSIONS: Category loudness scaling has proven to be a valuable element in the conventional recruitment test battery particularly for patients with symmetrical hearing loss. Therefore, category loudness scaling, ABLB test (when feasible), acoustic reflex measurement, and to a lesser extend the intensity difference limen test should be given the highest priority when selecting appropriate diagnostic audiometric tests. The efficacy of the SISI test and Békésy audiometry should be comprehensively reevaluated on the basis of expanded data. Until such material is available and a final judgement of the clinical value is possible, both these tests should be used and interpreted carefully.

[Loudness scaling. A procedure for quantitative recruitment detection]. / Lautheitsskalierung. Ein Verfahren zum quantitativen Recruitmentnachweis.

Direct loudness scaling has been known as an audiological tool for about four decades. Although numerous publications have shown its clinical importance, loudness scaling has not been used in audiology and hearing aid fitting until now. This might be due to the lack of audiometers equipped with loudness scaling devices as well as missing evidence for its clinical applicability. In this study normal data for a single-step direct scaling procedure were established and loudness determinations of 105 patients with sensorineural hearing losses collected. The results show that normal level loudness functions exhibit very similar shapes for narrow band stimulation in the frequency range of 500 to 4000 Hz. However, loudness scaling is affected by the gender of the subjects: females scale systematically louder than do males. In hearing-impaired subjects the slopes of the level loudness functions tend to decrease with increasing hearing loss, indicating negative recruitment. This holds particularly true in the high-frequency range, e.g. at 4000 Hz. Our long-term experience with single-step direct loudness scaling has proven its clinical feasibility in typical patients of an audiology unit. Loudness scaling will prove useful for the localization of hearing impairments, as it can be employed as a quantitative indicator of recruitment without any restrictive preconditions. In addition, it allows the evaluation of hearing aids and cochlear implants by frequency-specific gain measurement.

Use of alprazolam for relief of tinnitus. A double-blind study.

OBJECTIVE: To systematically test the effectiveness of alprazolam as a pharmacological agent for patients with tinnitus. DESIGN: Prospective, placebo-controlled, double-blind study. PATIENTS: Forty adult patients with constant tinnitus who had experienced their tinnitus for a minimum of 1 year and who resided in the Portland, Ore, metropolitan area. Twenty patients were randomly assigned to the experimental group and 20 to the control group. RESULTS: Seventeen of 20 patients in the experimental (alprazolam) group and 19 of the 20 in the placebo (lactose) group completed the study. Of the 17 patients receiving alprazolam, 13 (76%) had a reduction in the loudness of their tinnitus when measurements were made using a tinnitus synthesizer and a visual analog scale. Only one of the 19 who received the placebo showed any improvement in the loudness of their tinnitus. No changes were observed in the audiometric data or in tinnitus masking levels for either group. Individuals differed in the dosages required to achieve benefit from the alprazolam, and the side effects were minimal for this 12-week study. CONCLUSIONS: Alprazolam is a drug that will provide therapeutic relief for some patients with tinnitus. Regulation of the prescribed dosage of alprazolam is important since individuals differ considerably in sensitivity to this medication.

Loudness discomfort levels in children.

Loudness discomfort levels (LDLs) traditionally have been used to set the saturation sound pressure level (SSPL) or maximum output of a hearing aid. Many procedures have been used to obtain LDLs for adults; however, no systematic study has been conducted to determine if LDLs could be obtained reliably for children. In the present study, LDLs were measured on 20 hearing-impaired children aged 7 to 14 years using a modification of a procedure described by Hawkins, Walden, Montgomery, and Prosek (Ear Hear 1987; 8: 162-169). Test-retest reliability measures were obtained for 8 of the 20 children, and this modified procedure was found to provide reasonably reliable results. Data from the group of 20 children also were compared with similar data obtained from 20 hearing-impaired adults. These results revealed no systematic differences in LDLs between the two groups, suggesting no a priori reason to limit the maximum output of a hearing aid for a child in this age range below the levels that are appropriate for adults. Poor correlation between LDLs and hearing levels for both age groups indicate a need for determining LDLs on an individual basis whenever possible.

The loudness of tinnitus.

Although tinnitus causes considerable suffering to many patients, its loudness is small in most cases. Traditionally the loudness is measured with a binaural loudness balance procedure. It is stated that when there is recruitment in the ear to which the test tone is presented, the intensity of the test tone is smaller than its loudness. Therefore in the case of recruitment in the ear to which the test tone is presented, the loudness of tinnitus will be underestimated. In this study the loudness in a group with recruitment in the ear to which the test tone was presented was compared with the loudness in a group with a normal ear to which the test tone was presented. The present results show that although recruitment does have a certain effect, it is very small.

Responses elicited from medial superior olivary neurons by stimuli associated with binaural masking and unmasking.

The responses of binaural neurons of the medial superior olive were measured as a function of interaural temporal differences for tones and as a function of signal-to-noise ratio under homophasic and antiphasic masking conditions. The degree of neural response synchrony to the frequency of the signal was related to the degree of behavioral detectability of the signal in the homophasic, but not the antiphasic masking condition. For the antiphasic condition, a decrease in discharge rate resulted from the addition of the signal to the noise, similar to the decrease which occurred when interaural temporal differences were introduced in the tonal stimuli. The results are compatible with a model in which interaural temporal-difference information arriving over monaural afferents in the form of synchronized impulses is mapped into a place code by a neural coincidence-detection device. Several differences were noted between the responses to tones found in the present experiment and those reported by others. These differences were attributed mainly to differences among the experimental procedures in use among the various reporting laboratories.

[Shunt evoked potentials. Objective significance for hearing aids]. / Potentiels évoqués dérivés. Intérêt pour l'audioprothèse objective.

A method first described in 1978, and improved since that date, is a reliable mean of assessing gain in hearing from prosthetic aids by the use of brain stem early auditory evoked potentials. The type of signal used with the prosthesis must be the click and click type with a high-pass filter, and the principle of shunt potentials must be applied.

Aging and auditory site of lesion.

The purpose of this study was to examine and quantify the functional auditory problems of presbycusis through a battery of recently developed diagnostic tests and to evaluate the usefulness of these tests with an elderly population. Diagnostic measures used were impedence measures, speech discrimination tests, synthetic sentence identification, compressed speech, two measures of tone decay, the short increment sensitivity index, a digit span test, and auditory brain stem response audiometry. Significant differences were found between scores for elderly subjects and those of young subjects who had similar audiograms. Use of the Metz test as an objective measure of recruitment yielded results suggesting a higher incidence of recruitment than evidenced by previous studies using loudness balancing procedures. The Olsen-Noffsinger procedure of quantifying tone decay revealed a greater difference between age groups than did the Suprathreshold Adaptation Test. Synthetic sentence identification revealed the most consistent age effect among the tests of central auditory function. Auditory brain stem response audiometry revealed several examples of abnormally long interpeak latencies. It is concluded that there is both behavioral and electrophysiological evidence of central and peripheral auditory disorder frequently accompanying senescence.