B. Z. Rappaport

A system for evaluating auditory function from 8000–20 000 Hz

A system for the measurement of auditory function from 8000--20 000 Hz is described. This system introduces advances in: (a) maximum power output, (b) signal fidelity, and (c) transducer characteristics. Two case studies are presented to illustrate the clinical information gained from the measurement of high-frequency auditory sensitivity, which is not readily apparent in conventional threshold assessment.

The effects of noise upon human hearing sensitivity from 8000 to 20 000 Hz

High-frequency (8 to 20 kHz) hearing sensitivity was compared in thirty-six, 20 to 29-year-old military veterans with histories of steady-state or impulsive noise exposure. Threshold shifts were prominent for the steady-state noise subjects from 13 to 20 kHz. Mean thresholds from 8 through 12 kHz were maximally 20 dB poorer than a sample of young adult normals. Audiometric configurations for this group were generally smooth and symmetrical above 8000 Hz. For the impulsive noise group, substantial shifts in sensitivity were seen from 2 to 20 kHz and the high-frequency audiometric configurations were often jagged and/or asymmetrical. The variability of subjects in this group was greater than that seen in the steady-state noise exposed sample. Several case studies are presented to illustrate these characteristics. Measurement of auditory sensitivity from 8 to 20 kHz extends the mapping of basal cochlear function, providing information which often is not predictable from conventional audiometric measurement. This additional information provides for more comprehensive inter- and intra-subject comparison of the degree and extent of threshold changes present.

Detection of aminoglycoside ototoxicity by high-frequency auditory evaluation: selected case studies.

A practical monitoring procedure utilizing frequencies higher than those tested by conventional audiometry for the detection of ototoxicity has the potential for preventing or minimizing irreversible communication deficits in patients receiving aminoglycoside antibiotic therapy. If ototoxicity produced by these drugs could be detected before it progresses to involve the frequencies essential for communication, it might be possible to lower the dose or to change to another antibiotic to prevent a permanently handicapping hearing impairment. From a total of 77 patients monitored by serial audiograms, three case studies illustrate the various types of auditory sensitivity changes observed with high-frequency audiometry. Ototoxicity was generally detected by high-frequency auditory testing before it could be detected by conventional audiometric procedures. These cases demonstrate the utility of monitoring audition at frequencies higher than those tested conventionally in patients receiving aminoglycoside antibiotics.

Age categorization of high-frequency auditory threshold data.

This article presents high-frequency (8- to 20-kHz) auditory threshold measurements for 157 subjects with normal conventional hearing, ranging in age from 6-30 years. Normative descriptive data are provided in five semidecade age categories. Intra-age category mean and variance values for threshold sensitivity and interaural threshold differences are included. Generally, the data are consistent with the expectation of a gradual diminution of high-frequency sensitivity through the adolescent and early adult years. Several unresolved issues related to high-frequency normative data and clinical applicability of high-frequency threshold measurements are discussed.

A multi-center, double blind clinical trial comparing benefit from three commonly used hearing aid circuits.

Objective Although numerous studies have demonstrated that hearing aids provide significant benefit, carefully controlled, multi-center clinical trials have not been conducted. A multi-center clinical trial was conducted to compare the efficacy of three commonly used hearing aid circuits: peak clipping, compression limiting, and wide dynamic range compression. Design Patients (N = 360) with bilateral, sensorineural hearing loss were studied using a double blind, three-period, three-treatment crossover design. The patients were fit with each of three programmable hearing aid circuits. Outcome tests were administered in the unaided condition at baseline and then after 3 mo usage of each circuit, the tests were administered in both aided and unaided conditions. The outcome test battery included tests of speech recognition, sound quality and subjective scales of hearing aid benefit, including patients’ overall rank-order rating of the three circuits. Results Each hearing aid circuit improved speech recognition markedly, with greater improvement observed for soft and conversationally loud speech in both quiet and noisy listening conditions. In addition, a significant reduction in the problems encountered in communication was observed. Some tests suggested that the two compression hearing aids provided a better listening experience than the peak clipping hearing aid. In the rank-order ratings, patients preferred the compression limiting hearing aid more frequently than the other two hearing aids. Conclusions The three hearing aid circuits studied provide significant benefit both in quiet and in noisy listening situations. The two compression hearing aids appear to provide superior benefits compared to the linear circuit, although the differences between the hearing aids were smaller than the differences between unaided and aided conditions.

An investigation of the validity of high‐frequency audition

In this investigation, a masking experiment was utilized to explore the validity of high-frequency audition. Threshold shifts produced by a narrow-band noise with sharp filter slopes and variable center frequency were determined for pure-tone stimuli from 8000 to 14 000 Hz. Subjects were young adults with normal hearing from 250 through 8000 Hz, and with high-frequency thresholds comparable to those obtained in a previously conducted normative survey. After pure-tone thresholds were obtained for each test frequency, a narrow-band masker was presented ipsilateral to the pure-tone stimulus with center frequency equal to the pure tone. The masker was adjusted to an intensity level necessary to shift the pure-tone threshold approximately 17 dB. The center frequency of the masker was then decreased in discrete steps with the pure-tone threshold re-established at each step. The experimental results, as demonstrated by release-from-masking functions, are consistent with the expectation of increased masker effectiveness as the center frequency of the masker approximates the test frequency. The findings of this investigation suggest that responses to high-frequency auditory stimulation are the result of high-frequency perception, and not the perception of some lower frequency distortion process.

A Prospective Study of High-Frequency Auditory Function in Patients Receiving Oral Neomycin

Orally administered, neomycin is reported to cause ototoxicity rarely. Most reports on hearing loss due to oral neomycin have been case studies. One prospective study of a pediatric sample demonstrated a significant loss of hearing in the frequency range of 2 to 8 kHz in 9 of 17 children. To our knowledge there are no published prospective studies on this type with adult samples and therefore little is known of the true incidence or nature of ototoxicity from oral neomycin. This prospective study presents the results of long-term use of oral neomycin in 30 adult subjects. Hearing sensitivity was serially monitored in the frequency range 250-20,000 Hz. Two of the 30 subjects subsequently revealed ototoxicity. Thus the results of this investigation suggest that clinical use of oral neomycin implies relatively little risk of ototoxicity.

Effects of steady-state noise upon human hearing sensitivity from 8000 to 20 000 Hz

Young adults with steady-state noise exposure histories were evaluated with a high frequency (8--20 kHz) test system. High frequency hearing threshold shifts were most prominent from 12-20 kHz and were often highly individual-specific. Good standard range (.25-8 kHz) sensitivity does not assure good hearing above this region. Mild through severe threshold changes may be present. High frequency testing expands monitoring audiometry and has potential special application to hearing conservation programs.

Investigation of interaural attenuation factors for frequencies above 8000 Hz

Interaural attenuation values for frequencies from 8000 to 20 000 Hz were obtained from subjects with profound unilateral hearing loss. The values presented are specific to the Koss HV/1A earphone and cushion which is used as a transducer in our high‐frequency testing system. Data are provided regarding the influence of nontest ears at frequencies above 8000 Hz in cases where ear asymmetry exists.